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Why do I need a white stripe in the scanner. The principle of operation of the automatic scanner calibration system

The design of absolutely any device, especially if it (the device) includes both electronic and mechanical elements, may seem to an uninformed person a storehouse of secrets and mysteries, which, oh, how difficult it is to figure it out on your own. Flatbed scanners are just such an option. At first glance, the scanner device does not seem particularly complicated: a body with a few connectors and a couple of buttons, a removable tablet cover, and a glass on which originals are placed for scanning. But here's how the "economy" works, and what the numbers of its specification mean - this, as they say, is a completely different song. To learn how to navigate the numerous models of scanners on the computer market today, you need to imagine the real value of the characteristics indicated by the manufacturers. But to make this article more informative, we will analyze the design of the scanner, as they say, in the literal sense of the word, "we will analyze it."
Let's start, perhaps, with the most important element of any scanner - a photosensitive matrix, which is, as it were, its "eyes".

Matrix

Yes. It is the matrix that is the most important part of any scanner. The matrix transforms changes in the color and brightness of the received light flux into analog electrical signals that will be understood only by its only electronic friend - an analog-to-digital converter (ADC). From this point of view, the ADC can be compared to a guide-interpreter, her constant companion. Only he, like no one else, understands the matrix, because no processors or controllers will parse its analog signals without preliminary interpretation by the converter. Only he is able to provide work for all his digital colleagues who perceive only one language - the language of zeros and ones. On the other hand, you can take any processor, converter or amplifier, illuminate them with the brightest light source and wait for any reaction for so long until you get bored. The result is known in advance - it will be zero, because no other electronic components of the scanner are sensitive to it. If you like, they are all blind from birth. Another thing is the matrix. The luminous flux, falling on its surface, literally "knocks out" electrons from its sensitive cells. And the brighter the light, the more electrons will be in the storage of the matrix, the greater will be their strength when they rush to the exit in a continuous stream. However, the strength of the electron current is so incommensurably small that even the most sensitive ADC is unlikely to "hear" them. That is why, at the exit from the matrix, an amplifier awaits them, which is comparable to a huge mouthpiece, which, figuratively speaking, turns even a mosquito squeak into a howl of a loud siren. An amplified signal (still analog) will "weigh" the transducer, and assign each electron a digital value, according to its current strength. And then ... Further, the electrons will be digital information, the processing of which will be handled by other specialists. The work on recreating the image no longer requires the assistance of the matrix.
But let's leave the general discussion. Let's look at the practical side of things. Most modern scanners for home and office are based on two types of matrices: CCD (Charge Coupled Device) or CIS (Contact Image Sensor). This fact raises two questions in the minds of users: what is the difference and which is better? If the difference is noticeable even to the naked eye - the body of a CIS scanner is flat compared to a similar CCD device (its height is usually about 40-50 mm), then answering the second question is much more difficult. The answer here needs to be argued in order to avoid an avalanche of generated questions like "how is it better?", "Why is it better?".
First, let's look at the main advantages and disadvantages of these two classes of scanners. For convenience, I reduced them to a small table:

The CCD scanner has a greater depth of field than its CIS counterpart. This is achieved through the use of a lens and a system of mirrors in its design.

In the figure, for ease of perception, only one mirror is drawn,
while a typical scanner has at least three or four

CCD scanners are much more common than CIS scanners. This can be explained by the fact that in most cases scanners are purchased not only for digitizing sheet text documents but also for scanning photographs and color images. In this regard, the user wants to get a scan with the most accurate and reliable color reproduction, and in terms of light sensitivity, a CCD scanner transmits color shades, highlights, and halftones much more strictly than a CIS scanner. I note that the error in the spread of the levels of color shades distinguished by standard CCD scanners is about ± 20%, while for CIS devices this error is already ± 40%.

Schematic representation of a CIS sensor

The CIS-matrix consists of an LED strip that illuminates the surface of the scanned original, self-focusing microlenses and the sensors themselves. The sensor design is very compact, so a scanner that uses a contact sensor will always be much thinner than its CCD counterpart. In addition, such devices are famous for their low power consumption; they are practically insensitive to mechanical influences. However, CIS scanners are somewhat limited in their use: devices, as a rule, are not adapted to work with slide modules and automatic document feeders.
Due to the peculiarities of the technology, the CIS-matrix has a relatively small depth of field. For comparison, CCD scanners have a depth of field of ±30 mm, while CIS scanners have a depth of field of ±3 mm. In other words, putting a thick book on the tablet of such a scanner, you will get a scan with a blurred stripe in the middle, i.e. where the original is not in contact with the glass. With a CCD device, the whole picture will be sharp, since its design has a system of mirrors and a focusing lens. In turn, it is the rather bulky optical system that does not allow the CCD scanner to reach the same compact dimensions as the CIS counterpart. However, on the other hand, it is the optics that provide the obvious gain in quality. I note that the requirements for optics are very high, so the rumors that some models of scanners use, de, "plastic mirrors" are greatly exaggerated, if not "fictional". ;)
In terms of resolution, CIS scanners are also not a competitor to CCDs. Already, some models of CCD scanners for home and office have an optical resolution of about 3200 dpi, while CIS devices have a limited optical resolution, if I'm not mistaken, so far 1200 dpi. But, in general, it is not worth throwing CIS technology off the shields. All technologies are developing rapidly. Scanners with a CIS matrix have found their application where it is required to digitize not books, but sheet originals. The fact that these scanners are completely USB-powered and do not need an additional power source, came in handy for owners of portable computers. They can digitize the original and translate it into a text file anywhere, without being tied to proximity electrical networks, which allows you to close your eyes to a number of shortcomings of the contact sensor. Actually, therefore, you can answer the question "which scanner is better" based on your specific requests.

The most important element of the scanner is the CCD matrix

In the photo above, you see a CCD that appears to be a "big chip" with a glass window. It is here that the light reflected from the original is focused. The matrix does not stop working all the time while the carriage with the scanning carriage, driven by a stepper motor, travels from the beginning of the tablet to its end. I note that the total distance of the carriage movement in the "Y" direction is called the sampling frequency or the mechanical resolution of the scanner (we will talk about this a little later). In one step, the matrix completely captures horizontal line tablet, which is called a raster line. After the time sufficient to process one such line, the carriage of the scanning unit moves a small step, and it is the turn to scan the next line, and so on.

Side view of the CCD-matrix

In the side view, you can see two ordinary screws that play a "delicate" role." printed circuit board in the top view), so that the reflected light from the mirrors falling on it would fall evenly over its entire surface. By the way, if one of the elements of the optical system is skewed, the image recreated by the computer will turn out to be "striped".

Enlarged image of part of the CCD sensor (Macro
taken with Canon EOS D60 digital camera)

The enlarged photo of the CCD-matrix clearly shows that the CCD-matrix is equipped with its own RGB filter. It is he who represents the main element of the color separation system, which many people talk about, but few people know how it actually works. Typically, many reviewers limit themselves to the standard wording: "a standard flatbed scanner uses a light source, a color separation system, and a charge-coupled device (CCD) to collect optical information about the object being scanned." In fact, light can be divided into its color components and then focused on the matrix filters. An equally important element of the color separation system is the scanner lens.

The scanner lens is actually not as big as it looks on
Photo

Frame

The body of the scanner must be sufficiently rigid to avoid possible distortions of the structure. Of course, it is best if the base of the scanner is a metal chassis. However, the bodies of most home and office scanners manufactured today are made entirely of plastic to keep costs down. In this case, the necessary structural strength is provided by stiffeners, which can be compared with the ribs and spars of an aircraft.

Location of the main functional units of the scanner

An important element of the housing is a transport lock, the presence of which is designed to protect the scanning carriage from damage during the transportation of the scanner. It must be remembered that before turning on any scanner equipped with such a latch, you need to unlock it. Otherwise, the mechanisms of the machine may be damaged. In principle, manufacturers focus buyers' attention on this small nuance with bright stickers with appropriate warnings.
Some people think that the body cannot affect the quality of the scan in any way. However, this is not the case. The fact is that the optical system of the scanner does not tolerate dust, so the body of the device must be sealed, without any cracks (even technological ones). More than once I came across models that did not meet such requirements. If you are going to buy a scanner, then I would recommend paying attention to this.
Also, when buying a scanner, pay attention to the possibility of detaching the tablet cover. This feature of the machine is especially useful when scanning originals such as thick books or magazines.
The edges of the flatbed should have a gentle slope - this makes it easier to quickly remove the original from the glass. In addition, there should not be any gap between the glass and the tablet that would prevent the original from being removed. Also pay attention to the presence of markings around the perimeter of the tablet.

Control block

All scanners are controlled from a personal computer to which they are connected, and the necessary settings before scanning are set in the user window of the control program. For this reason, scanners for home and office do not necessarily have their own control unit. However, many manufacturers go to meet the most unprepared users, and install (usually on the front panel) a few "quick scan" buttons.

Quick scan buttons - an element you can do without

In the photo above, you can see that each button corresponds to a specific icon. Typical quick start functions usually involve starting a standard scan operation, outputting to a printer, and then sending it by e-mail, fax, etc. It is clear that specific parameters of the scan quality are set for one or another button. However, pressing one or another button first leads to the launch on the computer of the application (if there are several) that is responsible for the called operation. I note that not all SOHO scanners are equipped with their own control unit, and professional devices lack such elements even more so.
Some manufacturers "sin" by excluding from the scanner driver a number of settings that, in their opinion, most ordinary users do not use. So, for example, Hewlett-Packard SOHO scanners lack the ability to change gamma correction, load ICC profiles, and much more. But it is Hewlett-Packard, like no one else, who likes to "pamper" users with a number of quick scan buttons.

About light sources

Absolutely every scanner uses its own illuminator. This is the name of a small and powerful module, the task of which is to turn on and off the scanner lamp (or whatever replaces this lamp). In CIS scanners, an LED bar is used as light sources, due to which this class of devices consumes so little energy.
In CCD scanners, originals are normally illuminated by Fluorescent Lamp with a cold cathode. Its light is thousands of times brighter than LEDs. But in order to cause the glow of the gas inside the lamp, you need to apply a very high voltage to its input. It is produced by a separate unit called an inverter.

The high voltage module is required to power the lamp

The inverter increases the voltage from five volts to several kilovolts, and also converts D.C. into a variable.

In general, there are three main types of lamps used in scanners:

xenon gas discharge lamp (Xenon Gas Discharge);
fluorescent lamp with a hot cathode (Hot Cathode Fluorescent);
cold cathode fluorescent lamp (Cold Cathode Fluorescent)

However, scanners for home and office use only cold cathode lamps for a number of reasons.

Cold cathode lamp

The scanner lamp is mounted on the plastic chassis of the scanning carriage directly above the reflector. The reflector itself has the form of a reflector (an effective "collector" and reflector of light) in the form of a magnifying mirror. The light from it is amplified to brightly illuminate the object on the tablet. Reflected from the original on the glass, the light passes through the slit of the chassis (I highlighted its outline in blue in the photo) and is received by the first, longest mirror of the optical system.
Among obvious benefits cold cathode lamps can be noted for a long service life, which is 5,000 - 10,000 hours. For this reason, by the way, some scanners do not turn off the lamp after the scan is completed. In addition, the lamps do not require any additional cooling and are very cheap to manufacture. Of the shortcomings, I note a very slow inclusion. Typical lamp warm-up time is 30 seconds to several minutes.
The lamp has an important effect on the scan result. Even with a slight difference in the characteristics of the light source, the light flux reflected from the original incident on the receiving matrix also changes. This is partly why you need such a long warm-up time of the lamp before scanning. I note that some drivers allow you to reduce the warm-up time if the quality of digitization is not so important (for example, when scanning text information). I will add, in order to somehow compensate for the loss of lamp characteristics (and this inevitably happens during long-term operation of the device), scanners automatically perform a self-calibration procedure using a black-and-white target located inside the case.

The photograph clearly shows how, under the influence of light over
time, the housing plastic and the calibration target tarnish

The scanner under study is no exception. The photo above clearly shows the color target, according to which the scanner adjusts the colors before scanning, compensating for the "aging" of the lamp. Here you can also see that with the passage of time, not only the internal plastic, permanently illuminated by the lamp, but also the calibration target itself fades. This, in turn, leads to color fade and increased color distortion.

A cold cathode lamp is somewhat similar to a fluorescent lamp.
light ... only a small

If desired, from an inverter and a cold cathode lamp, you can
build a table lamp

In the photo you see the misuse of the scanner lamp. ;) The inverter module was connected to a standard computer power supply, for which wires with an adapter were soldered to its board. In principle, if any holder is adapted here, then a pretty good and bright table lamp will come out.

ADC operation

Who helps the scanner processor "find a common language" with the matrix? Of course, an analog-to-digital converter that converts analog signals into digital form. This interesting process can be represented as follows. First, the ADC sort of "weighs" the input voltage, like a store clerk picking up a set of standard weights of the same weight as the product. Then, when the voltage is measured, the ADC presents the data to its "boss", that is, the processor, but in the form of numbers. And as a result, everyone is happy.
You can imagine yourself as a processor and ask what happens at the output of the ADC when the input voltage changes? Let's give, for example, 4 Volts to the input of the converter, then 9 Volts. The following variations of numbers will appear at its output: first 00000100, then 00001001. In binary code, these are numbers 4 and 9. The number of zeros and ones with which the ADC expresses the measured value is its bit depth, which is measured in bits. A setting such as converter capacity is extremely important for the scanner, because it characterizes the accuracy of the measurement of the input signal.
Today, on store shelves, you can see inexpensive scanners that use converters with a bit depth from 24 to 48 bits. Theoretically, it is always better to choose a scanner that has more bit depth. In this case, one subtlety should be taken into account: sometimes manufacturers write "48 bit" in large letters on the boxes, and somewhere in the corner they specify in small print: "software 48 bit, hardware 36 bit". This means that a large beautiful figure has nothing to do with the accuracy of the ADC installed in the scanner, and the real bit depth in this case is 36 bits. That is what you should be aiming for. It should be recognized that in home practice, the differences between the results of 36-bit and 42-bit scanners are almost imperceptible (the human eye is able to distinguish about 24 bits of color shades, i.e. about 16.7 million). In our case, the bit depth of the converter and the color depth are one and the same. After all, the converter calculates nothing more than the colors of the dots that make up the image. The greater the bit depth of the converter, the more reliably the scanner can convey the color of each point of the image. Accordingly, the more the image will resemble the original.

CPU

Modern scanners are equipped with specialized processors. The tasks of such a processor include coordinating the actions of all circuits and nodes, as well as generating image data for transmission to a personal computer. In some scanner models, the processor is also assigned the functions of an interface controller.
The list of program instructions for the processor is stored on the chip permanent memory. Data is written to this chip by the scanner manufacturer at the production stage. The contents of the chip are called "firmware" or "firmware". Some professional scanners have the ability to upgrade, but low-cost home and office models usually don't.
In addition to a permanent memory chip, scanners also use RAM, which plays the role of a buffer (its typical values are 1 or 2 MB). Scanned information is sent here, which is almost immediately transferred to a PC. After sending the contents from memory to a personal computer, the processor resets the buffer to form a new message. I note that the instructions for the processor are also entered in the cells random access memory, but already the processor itself (for this it is equipped with several kilobytes of its own "RAM"). The organization of its memory is built on the principle of a pipeline, i.e. after executing the first instruction in the queue, the second one takes its place, and the last one - new instruction.
The amount of scanner RAM was previously indicated by manufacturers in the technical specifications of scanners. However, since this parameter practically does not affect the performance of the device; in modern scanners it is often silent. It is also silent if a particular scanner uses a certain area of the computer's RAM, which is implemented by the driver.

interface controller

The interface controller is responsible for the exchange of information and commands between the scanner and the computer. As I noted above, this microcircuit may be absent if the processor has an integrated controller module. In the era of "kopeck pieces" and "three pieces" scanners were produced with SCSI, IEEE1284 (LPT) and even RS-232 interfaces. Today's range of SOHO scanners is limited to USB, FireWire and SCSI interfaces. At one time, there were rumors about the appearance of Bluetooth scanners, but so far things have not gone further than rumors. It is quite obvious that the same different controllers are installed in devices with different interfaces. They are not compatible with each other, because they "speak different languages."

In our case, the interface board combines SCSI and USB ports, as well as
has two slots for connecting additional modules

SCSI (Small Computer Systems Interface)

SCSI scanners were the most common a few years ago. It must be admitted that the era of SCSI scanners is coming (or has already come) to an end. The main reason is the emergence of high-speed USB and FireWire interfaces, which do not require any special delicacy when connecting, or additional adapters. Among the advantages of the SCSI interface are its high throughput, as well as the ability to connect up to seven different devices to one bus. Of the main disadvantages of SCSI is the high cost of organizing an interface and the need to use an additional controller.

USB (Universal Serial Bus)

The USB interface has become the most widely used due to its integration into all modern motherboards as the main connector for peripherals. Today, the vast majority of home scanners come with a USB interface. In addition, a group of CIS scanners receives the necessary power from the USB port, which attracts owners of portable computers. Agree, you cannot realize such quality by means of SCSI.

FireWire (IEEE1394)

When choosing a connection type, at least for me, the FireWire interface is more preferable. FireWire is a high-speed serial I/O interface that differs from USB in that it does not require a host controller to provide a connection. The organization of its work is carried out according to the peer-to-peer scheme. Actually due to this, a lower (in comparison with USB) CPU load is achieved.
Peripheral devices with a new modification of this interface, FireWire 800 (IEEE1394b), will soon see the light of day. That's when it will become the fastest among the peripheral standards that have ever been developed.

broaching mechanism

The main moving module of the scanner is its scanning carriage. It includes an optical unit, with a system of lenses and mirrors, a photosensitive matrix, a cold cathode lamp (if it is a CCD scanner) and an inverter board. To the scanning carriage is rigidly fixed toothed lingering belt, which sets in motion the stepper motor of the device.

Location of the belt attachment to the scanning carriage

Elements of the broaching mechanism

A special tension spring, which is put directly on it, is responsible for the tight contact of the belt with the gears. The carriage with the scanning carriage moves along the guide sled, along the body of the device (see photo).

Engine

stepper motor

The Step Motor can turn the spindle in both directions in very small increments. Because of this feature, it is always possible to move the scanner carriage a strictly defined distance. Such an engine is in every flatbed scanner. It rotates the gearbox (the gears you see in the photo) and drives the carriage, which contains the optical unit, lamp, and matrix. A special microcircuit, the motor controller, is responsible for choosing the direction and speed of rotation. The accuracy of carriage movement is called mechanical resolution in the "Y" direction (Y-direction).

The optical resolution of the scanner is the X direction, and its
mechanical resolution - Y direction

In general, optical resolution is determined by the number of matrix line elements divided by the width of the working area. Mechanical - the number of steps of the scanning carriage in the direction of movement Y. In the specifications for scanners, you can find designations such as "600x1200". Here the second digit is the mechanical resolution, while the first characterizes the optical resolution of the scanner. There is also an interpolated resolution, which is sometimes several orders of magnitude greater than the optical resolution, but does not depend on the physical equipment of the device. I would call it "zoom resolution". Interpolation functions (enlargement of the original image) are performed by software scanner. The value of the interpolation values indicated by the manufacturers is doubtful - any image can be enlarged with the same success using Photoshop.

Engine internals

Reducer

The motor core is connected from the outside by a gear train, which is a simple gearbox. Its large gear extends the strap to which the scanning carriage is attached.

Power Supply

Scanner power supply

Home or office scanners do not consume too much power from the network, so SOHO devices cannot be found in power supplies powerful elements. The internal power supply of the device considered in this article produces voltages of 24 Volts / 0.69 A, 12 Volts / 0.15 A and 5 Volts / 1 A. for a light source - a lamp with a cold cathode, a high voltage of several kilovolts is required, a separate unit, which I talked about a little higher, is responsible for its power supply.

Additional devices

For many flatbed scanners related accessories are available, in most cases purchased separately. Of these, we can note the automatic document feeder and the adapter for scanning transparent originals (slide adapter).

The scanner with automatic document feeder is a bulky
construction

The Automatic Paper Feeder is required when you have to scan many standard size print sheets. Making sure your scanner can connect the ADF is easy enough. To do this, you can simply look at the connection panel and make sure there is an ADF (Automatic Document Feeder) socket. Note that the automatic document feeder is always "linked" to specific model scanner, or to a series of models. There is no universal feeder! The reason is that this device controlled from the scanner interface board. It is clear that the feeder cannot work without communication with the scanner, so when buying, be careful and make sure that your scanner supports the specific ADF.

View of the transparent window of the automatic document feeder from the other
side glass

The automatic feeder works as follows. After the auto-calibration and readiness phase, the scanner positions the carriage in front of the transparent ADF window. Then, sheet originals are taken one by one from its input tray, and when passing through the designated window, they are digitized.
The slide adapter is an accessory designed to digitize transparent originals (films, slides, and negatives). There are two types of such adapters: passive, which uses the scanner's lamp, and active, which shines through a transparent original with its own lamp.
The Active Slide Adapter has its own light source that shines through the transparent original. Some models of such slide adapters have a movable carriage with a light source, which is driven by a motor and a pulling mechanism. The light source moves along the guide, according to the positioning of the scanner carriage. The scanner's own lamp turns off. Today, scanner models for home and office without moving parts in the slide adapter module are more common. A typical example is the recently tested EPSON Perfection 3200 Photo by our test lab. Its light source is built into the scanner cover and occupies its entire useful surface. To match the adapter with the scanner, a wire with a connector comes out of the cover, which connects to a special socket on the back of the device (it is denoted by the abbreviation XPA). The adapter lamp is activated automatically when the original type is changed in the control program, which is additionally indicated by the indicator in the scanner cover. Transparency originals are installed in the included templates that support: 12-frame 35mm film strip, four 35mm framed slides, 120/220 (6 x 9 cm) / 4 x 5" transparencies. Well, the templates themselves are placed on the scanner glass. During scanning, a stream of light passes through a transparent original, and when it enters the scanner's optical system, it is processed in the same way (as an opaque original). It is clear that such scanner properties as optical resolution and depth of light do not change when using a slide adapter, which cannot be said about the range of optical densities. This scanner parameter directly depends on the brightness of the light source and the exposure time. You can imagine it like this: the darker the original, the less light it transmits, the longer it takes for the CCD-matrix drives to collect the required amount of charge. The darkest of the transparent originals are x-ray films (up to 3.6D). To get a high-quality scan from them, you need a bright light source. However, the range of reproducible optical densities of the scanner is by no means determined only by the brightness of the lamp. It mainly depends on the bit depth (or accuracy) of the analog-to-digital converter, the quality of the optical system and the capabilities of the photosensitive matrix.
The passive slide module is simpler than the active one. This adapter uses the lamp of the scanner itself as a light source. The intensity of the light flux in this case is significantly lower than in the case of an active adapter. Accordingly, the quality of scanned images is also lower, which is quite acceptable, for example, for the Web. Passive slide adapters are also inexpensive.

Conclusion

In general, one can talk about a scanner as a complex electronic device for quite a long time, but it is still impossible to convey all the interesting nuances within the framework of one article. Today we found out the following: for what reasons CCD scanners digitize originals much better than devices with a contact sensor; why the bit depth of the converter is important, and how the optical resolution differs from the mechanical one; what are the light sources and how they affect the quality of the scan; how the electronic and mechanical parts of the scanner interact, and why slide adapters are not suitable for all devices. In general, I tried to tell about the features of modern SOHO scanners in the most accessible form, and I would be interested to know your opinion about this article.

Any multifunction device (MFP) consists of a printer and a scanner. And if it is described in a very comprehensive and detailed way, then there are practically no articles on repairing an MFP scanner. This article is devoted to the repair of MFP scanners, their diagnostics, compatibility and replacement.

Scanners in the MFP consist of a control board, a motor and a scanner unit, guides with a damper and cables. In some cases, the engine is located in the scanner unit.

The main feature of scanner repair multifunction devices is that the scanner blocks have different designs, characteristics and interfaces. For example, you cannot change the scanner unit from a higher resolution device to a lower resolution device, although the design and connectors are the same. This unit will not be recognized by the MFP.

Lamps used to be used as backlight, now LED strips.

The scanner unit has a single design that combines illumination, optics and photosensitive matrix and electronics board. Usually the scanner unit can only be replaced as a whole. Sometimes you can rearrange the elements in a collapsible block, for example, a lamp. In lamp scanners, the most common cause of failure is lamp burnout or a decrease in its luminosity. In this case, the MFP does not enter the operating mode. An example of such MFPs is the HP LaserJet 3330. Separate backlights for scanners can be difficult, if not impossible, to find. Replacing the scanner unit costs 2500-3000 rubles, if you can find a suitable one.

In modern devices, the scanner unit is made on the basis of an LED bar and lasts much longer. Troubleshooting - The MFP is not ready.
In some cheap scanners, gear axles made of plastic break. Diagnosis: crackle from the scanner. Repair of such a malfunction costs 1500 rubles.

If the MFP scanner engine burns out, you can replace it if you find a suitable one from a donor, or order a new one. Scanner Motor Symptoms - The scanner unit does not move when the power is turned on. The repair price is 2-3 thousand rubles.

When it turned out that the cause of the error was the scanner glass, which had minor defects near the white initial strip. The refraction of light on small glass defects can lead to failures of the scanning unit.

You can buy a scanning unit (1500 rubles), an engine (1000 rubles), a cable (500 rubles) from us.

AT MFP Samsung SCX-4521 scanner cable is often faulty, read about
In scanners with an automatic document feeder, the paper sensor and feed roller fail. The price of repairing the scanner in this case is about 1500 tr. If the document feeder does not respond to the position of the paper sensor, then the formatter is faulty - the main board of the MFP.

Matrix

The CCD scanner has a greater depth of field than its CIS counterpart. This is achieved through the use of a lens and a system of mirrors in its design.

In the figure, for ease of perception, only one mirror is drawn,
while a typical scanner has at least three or four

CCD scanners are much more common than CIS scanners. This can be explained by the fact that in most cases scanners are purchased not only for digitizing sheet text documents, but also for scanning photographs and color images. In this regard, the user wants to get a scan with the most accurate and reliable color reproduction, and in terms of light sensitivity, a CCD scanner transmits color shades, highlights, and halftones much more strictly than a CIS scanner. I note that the error in the spread of the levels of color shades distinguished by standard CCD scanners is about ± 20%, while for CIS devices this error is already ± 40%.

Schematic representation of a CIS sensor

The CIS-matrix consists of an LED strip that illuminates the surface of the scanned original, self-focusing microlenses and the sensors themselves. The sensor design is very compact, so a scanner that uses a contact sensor will always be much thinner than its CCD counterpart. In addition, such devices are famous for their low power consumption; they are practically insensitive to mechanical influences. However, CIS scanners are somewhat limited in their use: devices, as a rule, are not adapted to work with slide modules and automatic document feeders.
Due to the peculiarities of the technology, the CIS-matrix has a relatively small depth of field. For comparison, CCD scanners have a depth of field of ±30 mm, while CIS scanners have a depth of field of ±3 mm. In other words, putting a thick book on the tablet of such a scanner, you will get a scan with a blurred stripe in the middle, i.e. where the original is not in contact with the glass. With a CCD device, the whole picture will be sharp, since its design has a system of mirrors and a focusing lens. In turn, it is the rather bulky optical system that does not allow the CCD scanner to reach the same compact dimensions as the CIS counterpart. However, on the other hand, it is the optics that provide the obvious gain in quality. I note that the requirements for optics are very high, so the rumors that some models of scanners use, de, "plastic mirrors" are greatly exaggerated, if not "fictional". ;)
In terms of resolution, CIS scanners are also not a competitor to CCDs. Already, some models of CCD scanners for home and office have an optical resolution of about 3200 dpi, while CIS devices have a limited optical resolution, if I'm not mistaken, so far 1200 dpi. But, in general, it is not worth throwing CIS technology off the shields. All technologies are developing rapidly. Scanners with a CIS matrix have found their application where it is required to digitize not books, but sheet originals. The fact that these scanners are completely USB-powered and do not need an additional power source, came in handy for owners of portable computers. They can digitize the original and translate it into a text file anywhere, without being tied to the proximity of electrical networks, which allows them to close their eyes to a number of shortcomings of the contact sensor. Actually, therefore, you can answer the question "which scanner is better" based on your specific requests.

The most important element of the scanner is the CCD matrix

In the photo above, you see a CCD that appears to be a "big chip" with a glass window. It is here that the light reflected from the original is focused. The matrix does not stop working all the time while the carriage with the scanning carriage, driven by a stepper motor, travels from the beginning of the tablet to its end. I note that the total distance of the carriage movement in the "Y" direction is called the sampling frequency or the mechanical resolution of the scanner (we will talk about this a little later). In one step, the matrix completely captures the horizontal line of the tablet, which is called the raster line. After the time sufficient to process one such line, the carriage of the scanning unit moves a small step, and it is the turn to scan the next line, and so on.

Side view of the CCD-matrix

In the side view, you can see two ordinary screws that play a "delicate" role. "With their help, at the stage of assembling the scanner, the matrix was precisely adjusted (also note the U-shaped slots in the printed circuit board in the top view) so that the reflected incident on it the light from the mirrors would fall evenly over its entire surface.By the way, if one of the elements of the optical system is skewed, the image recreated by the computer will turn out to be "striped".

Enlarged image of part of the CCD sensor (Macro
taken with Canon EOS D60 digital camera)

The scanner lens is actually not as big as it looks on
Photo

Frame

Location of the main functional units of the scanner

Control block

Quick scan buttons - an element you can do without

About light sources

Absolutely every scanner uses its own illuminator. This is the name of a small and powerful module, the task of which is to turn on and off the scanner lamp (or whatever replaces this lamp). In CIS scanners, an LED bar is used as light sources, due to which this class of devices consumes so little energy.
In CCD scanners, originals are normally illuminated by a cold cathode fluorescent lamp. Its light is thousands of times brighter than LEDs. But in order to cause the glow of the gas inside the lamp, you need to apply a very high voltage to its input. It is produced by a separate unit called an inverter.

The high voltage module is required to power the lamp

The inverter increases the voltage from five volts to several kilovolts, and also converts direct current into alternating current.

In general, there are three main types of lamps used in scanners:

xenon gas discharge lamp (Xenon Gas Discharge);
fluorescent lamp with a hot cathode (Hot Cathode Fluorescent);
cold cathode fluorescent lamp (Cold Cathode Fluorescent)

However, scanners for home and office use only cold cathode lamps for a number of reasons.

Cold cathode lamp

The scanner lamp is mounted on the plastic chassis of the scanning carriage directly above the reflector. The reflector itself has the form of a reflector (an effective "collector" and reflector of light) in the form of a magnifying mirror. The light from it is amplified to brightly illuminate the object on the tablet. Reflected from the original on the glass, the light passes through the slit of the chassis (I highlighted its outline in blue in the photo) and is received by the first, longest mirror of the optical system.
Among the obvious advantages of a cold cathode lamp, one can note a long service life, which is 5,000 to 10,000 hours. For this reason, by the way, some scanners do not turn off the lamp after the scan is completed. In addition, the lamps do not require any additional cooling and are very cheap to manufacture. Of the shortcomings, I note a very slow inclusion. Typical lamp warm-up time is 30 seconds to several minutes.
The lamp has an important effect on the scan result. Even with a slight difference in the characteristics of the light source, the light flux reflected from the original incident on the receiving matrix also changes. This is partly why you need such a long warm-up time of the lamp before scanning. I note that some drivers allow you to reduce the warm-up time if the quality of digitization is not so important (for example, when scanning text information). I will add, in order to somehow compensate for the loss of lamp characteristics (and this inevitably happens during long-term operation of the device), scanners automatically perform a self-calibration procedure using a black-and-white target located inside the case.

The photograph clearly shows how, under the influence of light over
time, the housing plastic and the calibration target tarnish

A cold cathode lamp is somewhat similar to a fluorescent lamp.
light ... only a small

If desired, from an inverter and a cold cathode lamp, you can
build a table lamp

ADC operation

CPU

Modern scanners are equipped with specialized processors. The tasks of such a processor include coordinating the actions of all circuits and nodes, as well as generating image data for transmission to a personal computer. In some scanner models, the processor is also assigned the functions of an interface controller.
The list of program instructions for the processor is stored in a permanent memory chip. Data is written to this chip by the scanner manufacturer at the production stage. The contents of the chip are called "firmware" or "firmware". Some professional scanners have the ability to upgrade, but low-cost home and office models usually don't.
In addition to a permanent memory chip, scanners also use RAM, which plays the role of a buffer (its typical values are 1 or 2 MB). Scanned information is sent here, which is almost immediately transferred to a PC. After sending the contents from memory to a personal computer, the processor resets the buffer to form a new message. I note that the instructions for the processor are also entered into the RAM cells, but already the processor itself (for this, it is equipped with several kilobytes of its own "RAM"). The organization of its memory is built on the principle of a pipeline, i.e. after the execution of the first instruction in the queue, the second one takes its place, and the last one is replaced by a new instruction.
The amount of scanner RAM was previously indicated by manufacturers in the technical specifications of scanners. However, since this parameter practically does not affect the performance of the device; in modern scanners it is often silent. It is also silent if a particular scanner uses a certain area of the computer's RAM, which is implemented by the driver.

interface controller

In our case, the interface board combines SCSI and USB ports, as well as
has two slots for connecting additional modules

SCSI (Small Computer Systems Interface)

SCSI scanners were the most common a few years ago. It must be admitted that the era of SCSI scanners is coming (or has already come) to an end. The main reason is the emergence of high-speed USB and FireWire interfaces, which do not require any special delicacy when connecting, or additional adapters. Among the advantages of the SCSI interface are its high throughput, as well as the ability to connect up to seven different devices to one bus. Of the main disadvantages of SCSI is the high cost of organizing an interface and the need to use an additional controller.

USB (Universal Serial Bus)

The USB interface has become the most widely used due to its integration into all modern motherboards as the main connector for peripheral devices. Today, the vast majority of home scanners come with a USB interface. In addition, a group of CIS scanners receives the necessary power from the USB port, which attracts owners of portable computers. Agree, you cannot realize such quality by means of SCSI.

FireWire (IEEE1394)

When choosing a connection type, at least for me, the FireWire interface is more preferable. FireWire is a high-speed serial I/O interface that differs from USB in that it does not require a host controller to provide a connection. The organization of its work is carried out according to the peer-to-peer scheme. Actually due to this, a lower (in comparison with USB) CPU load is achieved.
Peripheral devices with a new modification of this interface, FireWire 800 (IEEE1394b), will soon see the light of day. That's when it will become the fastest among the peripheral standards that have ever been developed.

broaching mechanism

Location of the belt attachment to the scanning carriage

Elements of the broaching mechanism

Engine

stepper motor

The optical resolution of the scanner is the X direction, and its
mechanical resolution - Y direction

In general, optical resolution is determined by the number of matrix line elements divided by the width of the working area. Mechanical - the number of steps of the scanning carriage in the direction of movement Y. In the specifications for scanners, you can find designations such as "600x1200". Here the second digit is the mechanical resolution, while the first characterizes the optical resolution of the scanner. There is also an interpolated resolution, which is sometimes several orders of magnitude greater than the optical resolution, but does not depend on the physical equipment of the device. I would call it "zoom resolution". Interpolation functions (enlargement of the original image) are performed by the scanner software. The value of the interpolation values indicated by the manufacturers is doubtful - any image can be enlarged with the same success using Photoshop.

Engine internals

Reducer

The motor core is connected from the outside by a gear train, which is a simple gearbox. Its large gear extends the strap to which the scanning carriage is attached.

Power Supply

Scanner power supply

Home or office scanners do not consume too much power from the network, so there are no powerful elements in the power supplies of SOHO devices. The internal power supply of the device considered in this article produces voltages of 24 Volts / 0.69 A, 12 Volts / 0.15 A and 5 Volts / 1 A. for a light source - a lamp with a cold cathode, a high voltage of several kilovolts is required, a separate unit, which I talked about a little higher, is responsible for its power supply.

Additional devices

Many flatbed scanners come with accompanying accessories, in most cases purchased separately. Of these, we can note the automatic document feeder and the adapter for scanning transparent originals (slide adapter).

The scanner with automatic document feeder is a bulky
construction

The Automatic Paper Feeder is required when you have to scan many standard size print sheets. Making sure your scanner can connect the ADF is easy enough. To do this, you can simply look at the connection panel and make sure there is an ADF (Automatic Document Feeder) socket. It should be noted that the automatic document feeder is always "tied" to a specific scanner model, or to a series of models. There is no universal feeder! The reason is that this machine is controlled by the scanner interface board. It is clear that the feeder cannot work without communication with the scanner, so when buying, be careful and make sure that your scanner supports the specific ADF.

View of the transparent window of the automatic document feeder from the other
side glass

Conclusion

I will digress a little, the glasses are clear for what, but I will explain the purpose of the respirator a little. The fact is that Dremel works with rotation up to 33 thousand revolutions per minute and the dust from working with it is quite fine. And in order not to inhale it is not clear what the dust consists of, you need a respirator

I guessed everything well workplace and having made two pieces of plastic the same, we proceed to cut a hole for the power connector with a knife and a pencil.
Enough scribbled in pencil upper part power connector, and attaching to the right place on the plastic - we get an approximate stencil for cutting.
Having cut out, we apply both plastics to the circuit, inserting the power connector in advance. Next, we look at how the main fastening screw passes through the entire structure, we outline the hole first on one side, and, having inserted it into the already drilled hole, we outline and make the second hole.
Next, take the second plate, where the nut will be. We thread and tighten the screw with the nut on it. Then, with a little effort, using a hot soldering iron, we press the nut into the plastic until it stops protruding. Cool and unscrew the screw.
We take both covers of our box and from the inside we make small belts about a millimeter by a millimeter, stiffening ribs will be inserted there, which are also decorative plugs covering the edges of the power circuit.
By and large, almost everything is ready, it remains only to make the mounts for the lamp itself.

To do this, we take the same white plastic and cut out two small rectangles, make holes with drills, first small, then larger, but the holes should not be exactly in the center. then the mounts will not allow the lamp to turn, they need to be made with a slight downward shift. Next, we twist with screws and stick double-sided tape on the outer base of the resulting mounting planes.

We insert the lamp connector into its power supply circuit, and the circuit into our self-made box and slowly twist it, but not completely.
Now let's start making the side walls. To do this, we outline the place of cutting in the already prepared "blank gasket" and cut out the wall in advance of a slightly larger size. We put it on the box and see how it fits. When you like the size, you can make a second wall.
Having attached the finished first wall as a template, we adjust the second in size.
When everything is ready and all the burrs are removed, we proceed to the assembly.
We take the power circuit, cut off the connector for external connection power supply and solder our connector for the power supply to it. We reassemble the entire box, having previously isolated all the bare contacts and cleaned all traces of fuss. We twist, and at the end, we insert stiffeners, after which we twist to such a state that the box does not fall apart. If not everything is holding well, you can glue the stiffening ribs along the edges with additional superglue so that it does not fall apart, neither from a fall, nor from hands.

Not everything turned out well for me, namely: the screw was outside the cover, so that it had to be cut down.

Then, on the side of the nut, we glue four small pieces of double-sided tape, so that later it can be quickly and easily removed. I also did not find a switch button, it will be soldered to the bp cord. later.

If someone does not want to mess around like that (I just had to understand the work of Dremel with different materials), he can find any suitable box and fix the scheme in it.

Who wants to have a backlight in the case, I can advise you to connect to any 12v line with the right resistance.

You can also try to use the lamp without its reflector (besides, it is not quite a reflector, but rather an absorber, because it is not specular, but white-black). But for this you need to be extremely attentive to the ends of the lamp, since the wires soldered into the glass are thick enough and can be broken off, or the glass may crack in these places. There are rubberized special holders on the edges of the lamp, I would recommend equipping some of my own fasteners on them. The lamp worked for about 40 minutes with my b.p. practically did not heat up, neither the reflector, nor the rubber bands on the sides of it. If the voltage supplied to the lamp is more than 9V, then the lamp will most likely overheat, and possibly fail. If you decide to use it without a reflector, although it will illuminate everything around, it will also shine into the eyes, which somehow did not seem enough to me.

I also want to warn you about the transformer in the lamp power circuit. I don’t know what current it gives out and what it is, but if you bring a finger, or another part of the body, close to its contacts, an electric arc occurs, which, for example, burned out a pattern on my finger. In this case, the distance to the contacts can be up to two millimeters.
The current, of course, will not kill, but you can get a small burn.

I apologize for the quality of the pictures and video, but what was at hand))

In the sequel, I will describe how to use the hard drive motor to use it as a fan.
Assembling a homemade liquid cooling system using your own example.
Also a homemade basket for five hard drives from org. glass.

From kind people, I got into my hands such a fairly old scanner, Mustek 6000p, a device from the times of Windows 95 and large white plastic cases. As a rarity, it is not of great value, but it is a pity to throw it away without looking inside).

Actually, all its electronic contents, the body goes to the trash.

The illuminator from the scanning carriage is a conventional cold cathode fluorescent lamp (CCFL), similar to those used in LCD backlighting.

Carriage payment. On the left side we see a high-voltage inverter, it's time to try to light the lamp.

In the left corner is the integral stabilizer 7812, designated as Q8, it is easy to understand from which tracks the inverter receives power. At its input, when the scanner is turned on, there is about 14 volts, but the lamp does not light up, how to start it? There are not so many tracks leading to the board with the inverter from the connector that connects the carriage board to the main board, so let's assume that the key that starts the lamp is assembled on transistor Q5.

We close the resistor R3 connected to the base of the transistor with tweezers to + power, and ... let there be light!

Having figured out what's what, cut off all unnecessary, solder the jumper resistor between R3 and the power supply ...

... and pins for the printer's native power connector.

We get such a neat inverter board, we check again.

Of course, this is not enough to illuminate the workplace, but you can make a backlight in some drawer like a lamp in a refrigerator. As a body donor, an equally elderly mouse, the same age as the scanner, was a good fit. The switch will be a reed switch with normally closed contacts.

Assembled. It is a pity that the buttons do not carry any functional load =)

We fix the lamp and the body with double-sided tape. There is a magnet on the door hard drive on the same tape. Not very aesthetically pleasing, but it does the job.

More than enough to light up a small space

An attentive reader will notice that in the photo of the board in the mouse case there is already a jumper instead of a stabilizer - it is no longer needed, the inverter is powered by a home server, which is located on the same cabinet.

In contact with

Classmates

Which scanners are better - CCD or CMOS? In this review, we will try to answer this question by comparing the two technologies in several ways.

Charge coupled linear device or CCD- it's analog integrated circuit, which consists of light-sensitive photodiodes capable of converting light energy into charge. Invented in 1969 by Willard Boyle and George Smith, the technology has become widely used thanks to Sony, which has established the production of CCDs for its cameras.

CMOS stands for "complementary metal-oxide-semiconductor structure" and is a photosensitive matrix consisting of a set of photodetectors. The technology originated in the 60s of the twentieth century, but gained popularity only in the early 1990s. The fact is that until that time the gap in the main parameters with CCDs was so great that CMOS-based matrices did not receive noticeable development.

Use in scanners

The process of image processing in a CMOS sensor begins with the hit of light rays, which are reflected from the original, onto the surface of the scanning matrix. Further, during the exposure, the charge is accumulated on the LEDs and the subsequent reading of the obtained parameters. This occurs in an arbitrary form and depends on the moment the photon hits the reader.

By mixing red, green and blue, you can get any other color. One feature of CMOS sensors is that each pixel registers only one of these colors. And in order to get the rest, they use the so-called Bayer filter.

An important component of the operation of CMOS-based matrices is the use of a Bayer filter in the imaging process. The filter is used as a barrier in front of the matrix and passes only one color: green, red or blue. The final image is obtained by complex arithmetic averaging of information obtained from four (2 times more green pixels, therefore not three, but four) adjacent sensors of different colors.

In contrast, line-sensor-based CCD scanners capture red, green, and blue lines completely, one after the other. The image is then projected onto a linear CCD sensor. The ruler moves and alternately captures the red, green and blue elements. The computer then arranges the lines in the correct order and generates an RGB image. The formation of an electronic image in full resolution occurs without a Bayer filter.

The factor of using the Bayer filter directly affects the contrast and resolution of the scanned document. Under the same conditions of using CCD and CMOS, the dynamic range of the latter is often significantly inferior, since 2/3 of the color information is cut off by the filter.

Each subpixel in CMOS is represented by a normal pixel, although it captures only one channel out of three. In a CCD system, each pixel takes on all colors.

Resolution is the defining parameter for all digital images. Due to the "line by line" processing of elements, a linear CCD sensor is able to form the maximum number of pixels on each of the lines.

On the other hand, the matrix "removes" the image in one go and is clearly limited in the number of dots per inch. The missing components are calculated by the processor based on data from neighboring pixels as a result of interpolation, which is not an increase in resolution, but only the assignment of ordinary color values of nearby pixels. Therefore, the resolution of linear sensors, especially when scanning along the "narrow" side of the original, will be higher.

The most affordable planetary scanner with a three-line CCD in Russia is ELAR PlanScan A2V. Its price starts at 1.2 million rubles. An A2+ format scanner similar in characteristics based on a 70 MP CMOS matrix - Book2net Kiosk starts from 2.5 million rubles.

As opposed to quality, matrices win in scanning speed, which, together with pixel processing, is 1-2 seconds, against about 4-6 seconds of scanning with a CCD line.

Digitization processes

The specifics of working with stapled originals involves the use of the V-shaped mode of the scanner cradle when the document is scanned with incomplete disclosure. Such a digitization process involves transferring the resulting image to a two-dimensional plane, or in other words, image alignment. In this regard, the matrix is inferior to linear sensors. This is due to the fact that the entire image is taken, which entails the need to focus on the total scan area, causing geometric distortion at the edges of electronic images and the need for alignment from V-mode using the perspective compensation algorithm. Therefore, often CMOS scanners do not have V-mode or, in some models, are implemented using two cameras for each half of the cradle.

In contrast to CMOS, a linear sensor forms an image gradually. Additionally, linear CCD scanners are equipped with "tracking" laser focusing systems, which allows you to continuously focus on the extreme points of the document, despite height differences from the edge of the page to the spine, thereby providing the processor with accurate information for calculating compensation for geometric distortions when scanning in a V-shaped mode. Therefore, page alignment for "linear" scanners is more consistent.

Scanning a Book in V-Mode and Straightening

In the scanning department of the RSL, priority is given to scanners based on CCD sensors. The main fleet of equipment consists of ELAR PlanScan A2V planetary scanners, the scanning system of which includes 3 CCD arrays of 7500 pixels each.

Separately, it is worth considering the tasks of large-format scanning. Planetary scanners based on CMOS matrices from A1 format and larger are also mainly equipped with two cameras at once. This was done to improve the resolution of large originals, but this approach involves a number of compromises. The first of these is the need to programmatically stitch two halves of the original, which, even with the use of advanced algorithms, leads to a violation of the integrity of the image, especially when high-quality digitizing illustrations or text spreads.

Second, but no less significant - reliability and service. Since both chambers work alternately, the risk of breakage of one of the elements is exactly doubled, and maintenance costs also increase. Do not forget that the failure of any of the cameras completely stops the scanner from working.

The cost of manufacturing CMOS sensors increases with increasing sensor resolution. If an 18 megapixel matrix is cheaper than almost any CCD line, then a 70 megapixel matrix is already significantly more expensive. Therefore, planetary scanners with an optical resolution of 300 dpi or more based on CMOS matrices are more expensive than similar scanners based on linear CCD sensors.

Linear CCD technology is widely used in high-quality scanning systems that produce detailed images up to 2A0 without the use of software stitching. Such scanners can generate large-format images without geometric distortion and loss of resolution. Depending on the model, the scanning system during the digitization process either moves itself or is driven directly by the scanning surface, which passes under the static block of the scanning system. Serial CCD-based planetary scanners are capable of achieving significant resolutions - up to 600 dpi in A0+ format (with an original size of 914 mm x 1524 mm).

Along with this, a single scanning element reduces the number of nodes and Supplies in the scanning system, which improves overall design reliability and reduces service costs.

A common problem with CMOS sensors is overheating. Since the matrix in the scanner is constantly in working condition, often during long-term operation, the electronics heat up and lead to overheating of the pixel structure, which increases the digital “noise” of scan images. Linear CCD sensors, on the contrary, turn on only during scanning, so this problem is excluded on linear sensors.

Benchmarking

For a visual demonstration of the operation of scanning systems, we conducted a series of tests on key parameters. The German Microbox Book2net Kiosk based on a 70 MP CMOS matrix and the domestic ELAR PlanScan A2V with a three-line CCD sensor were chosen as the test subjects.

1. Color rendition

Scan color targets under the same ambient light conditions and resolution settings. Test digitization involves turning off all processing functions.

Both images of the test object are professional standards, but the result of the CCD sensor is color accurate with a large number of distinguishable tones. This factor does not play a leading role when scanning text originals, but will be very significant for working with illustrations.

2. Light uniformity

The operation of CMOS-based scanner illuminators is not related to the technological implementation of the scanning system - as a rule, these are always independently fixed lamps. As a result, the system is highly sensitive to external factors, and the power of the light flux forced to scatter over the entire scanning area is not enough to evenly distribute light on the document. Therefore, one of the main features of CMOS scanners is the shading of the edges in the image. Which is clearly visible on the test sample.

The scanner based on the CCD sensor shows a more even distribution of the light flux. The synchronous LED lighting, which passes along the original gradually, provides a greater uniformity of illumination of the document.

3. Resolution

For visual control and evaluation of optical resolution, it is recommended to use the TO-2 test object (GOST 13.1.701-95), which is scanned in turn on each device at an angle of 45 degrees. The test object contains a set of perpendicularly located groups of pairs of lines with different frequencies. For evaluation, it is necessary to select a group whose elements are distinguishable and readable. A value of 9.0 is commensurate with a resolution of 600 dpi

According to the results of testing on objects obtained with a CMOS sensor, lines up to the mark of 6.3 are clearly read and differ up to a value of 7.1. Indicators 9.0 are indistinguishable. What, in spite of a large number of megapixels in the matrix (70 megapixels), does not correspond to the optical resolution indicators declared by the manufacturer, namely, it does not provide 600 dpi on an A2 image.

On the test object of a scanner with a linear CCD, the mark 8.0 is well read and the lines are distinguished up to a value of 9.0, which fully corresponds to the optical resolution of 600 dpi in A2 format.

Scanning systems based on contact image sensors CIS (Contact Image Sensor) have become extremely popular among manufacturers of scanners, copiers, multifunctional office devices (MFPs), faxes. And therefore, when repairing and diagnosing all these devices, it often becomes necessary to make sure that the scanning line, which is sometimes also called the scanning head, is in good condition. The author proposes to get acquainted with one of the options for diagnosing this most important part of scanning devices.

LIDE (Light Indirect Exposure) technology, developed by CANON, is one of the varieties of contact image sensors (CDI), which received the name CIS in the literature. In contact image sensors, a line of photodetectors is used to read the line, which, most often, are phototransistors. The number of photodetectors corresponds to the number of points in the scanned line, i.e. each photodetector perceives one point (one pixel) of the scanned image. Each photodetector has its own focusing lens, which makes it possible to collect and focus on the surface of the photodetector the light flux reflected from one pixel of the original image. The general principle of scanning an image using CIS is demonstrated in Fig. one.

Rice. 1. The principle of scanning an image using CIS

As can be seen from the figure, the line of light-sensitive sensors occupies the entire width of the scanned line, and at the same time fits as tightly as possible to the scanner glass. Since scanning is carried out at a scale of 1:1, there is no need for a complex optical system, which is the main advantage of CIS technology.

The main feature of LIDE technology is the original design of the scanning lamp. In general, as such, there are no lamps. Instead of a lamp, three LEDs are used, placed on the side of the scanning head, and a plastic light guide of a special shape (Fig. 2). This light guide ensures that the light flux emitted by the LED is distributed over the entire length of the line and redirected to the scanned image.

Rice. 2. Design of the light guide of the scanning head

The internal arrangement of the LIDE scanning bar is shown in fig. 3. Thus, the scanning head has three LED "lamps" with different color glow, and these lamps must have independent control (Fig. 4).

Rice. 3. Internal structure of the LIDE scanning bar

Rice. 4. LED lamp control circuit

When scanning color images, the original must be alternately illuminated with three different colors of light: red (R), green (G), and blue (B). During scanning in full color mode, these "lamps" switch at a high enough frequency, resulting in the illusion that the document is being scanned with white light, which, in fact, is not true.

The development of cooperation in the office equipment and peripherals industry has led to the fact that the same LIDE head can be used in the most various devices different manufacturers. So, for example, in scanning devices entry level CANON's CIS head marked CLG-60216G (Fig. 5) has become very widespread. This LIDE module can be found in CANON and BENQ scanners, in CANON MFPs and copiers, in MFPs manufactured by Samsung, Xerox and HP. Such a massive use of this LIDE head has positive aspects, because service specialists have the opportunity to replace compatible modules from seemingly completely different and incompatible devices. So, for example, the author of this article successfully replaced the CIS module in the Samsung SCX-4100 device, and the module being replaced was taken from the BenQ 5250C scanner.

Rice. 5. CANON CIS head marked CLG-60216G

So, if enough scanning device malfunctions occur, you can observe a situation where the scanning lamps do not turn on, and the scanner does not enter the ready mode, but goes into a fatal error state. There can be several reasons for this behavior of the scanner:

Malfunction of the LIDE module;

Malfunction of the control microprocessor;

Malfunction of the motor that moves the LIDE carriage;

Malfunction of the sensor of the initial position of the scanning carriage (if any).

Thus, a specialist who diagnoses such a device needs to determine whether the LIDE head is working, or if there is a problem in another node.

How to check the LIDE-head serviceability, consider the example of the above-mentioned and widely used CANON CLG-60216G head.

Full check To maintain a LIDE head is quite laborious and requires, at a minimum, such equipment as an oscilloscope, multimeter, laboratory power supply and generator. The author proposes to consider a simplified version of the diagnostics of the CIS head, which consists in checking only its backlight module. Such diagnostics will make sure that all three lamps of the LIDE module are working.

The module under consideration has a 12-pin connector, which is used to connect it to the scanner's main board via a flat cable (see Fig. 5). The pin assignment of this connector is shown in the table, and the location of pin 1 is shown in fig. 6. Based on the information provided, the method for checking the lamps of the LIDE module suggests itself.

Rice. 6. 12-pin connector of the CLG-60216G module

To turn on each lamp, you only need to apply the appropriate voltage to it. Therefore, for diagnostics, only one device is required - an adjustable power source capable of generating constant pressure in the range of 0...3.5 V.

The module testing procedure is as follows:

1. Turn on the power supply and set its output voltage to about 3.3 V.

2. "Plus" of the power supply is applied to pin 8 (VLED).

3. "Minus" of the power supply is applied to pin 11 (RLED). As a result, the red LED "lamp" should light up. Changing the value of the supply voltage should lead to a change in the brightness of the lamp.

4. Next, the "minus" of the power supply is applied to pin 10 (GLED). As a result, the green "lamp" should light up. Its brightness should change in proportion to the change in the voltage value on pin 8 (VLED).

5. Similarly, a blue lamp, applying to pin 9 (BLED) "minus" of the power source.

Thus, having checked all three light sources, we can say with confidence that the LIDE head backlight module is in full working order. The general scheme of the diagnostic stand for testing the CIS module is shown in fig. 7.

Rice. 7. Scheme of a diagnostic stand for testing the CIS module

When carrying out this testing procedure, you may encounter an interesting feature. The fact is that the red LED is the brightest and lights up even when a voltage of 2.5 V is applied to it, while the green and blue LEDs light up when the voltage on them is more than 3 V.

Sometimes there are LIDE heads with a 16-pin connector, but everything said above is absolutely true for them. The fact is that in a 16-pin connector there are four recent contact are not used, and the purpose of the first 12 contacts is exactly the same as that described in the table.

Table. Assignment of the connector pins on the CLG-60216G module

contact no.	Designation	Description
		Data transmission line read by photodetectors

		"Earth" for photodetectors
		Photodetector supply voltage
		Reference voltage for photodetectors
		The starting pulse determines the moments of reading information by photodetectors
		Clock frequency for transmitting data read by photodetectors
		Supply voltage for LED lamps
		Blue control signal led lamp(active low)
		Green LED Lamp Control Signal (Active Low)
		Red LED Lamp Control Signal (Active Low)

Of course, this technique is not complete and does not allow to check the operability of photodetectors, but, nevertheless, it is very descriptive and informative, allowing you to make sure that the LIDE head is operable "in principle". This diagnostic method is convenient to use in a situation where there are suspicions about the serviceability of the control controller and the connecting cable of the scanner. The malfunction of these elements, as well as the LIDE head, manifests itself in the absence of the glow of the scanning lamps, as well as in the beating of the scanning carriage against the edge of the copier at the initialization stage when the scanner/MFP/copier is turned on.

In conclusion, I would like to draw attention to the fact that you can check the LEDs of the LIDE module with the most common tester in the "diode test" mode. To do this, you should "ring out" the diodes between the contacts VLED and RLED, GLED, BLED. When testing, it is necessary to change the polarity of connecting the probes of the device in order to ensure the open and closed state of the tested LEDs of the module. In this case, the glow of the "lamps" will not be intense (perhaps the lamps will not light up at all), and it will be impossible to control them. But, nevertheless, it is quite possible to get an answer to the question about the health of the LEDs.

We continue a series of publications of "general educational" articles on the principles of operation of various components of printers and MFPs. This article will focus on the automatic scanner calibration system.

The main element of scanners of modern MFPs is a scanning ruler CCD (Couple Charge Device, Charge Coupled Device, CCD). Accordingly, it is precisely the principles of operation of charge-coupled devices that it is desirable to know in order to understand where the “legs” of problems arising in scanners “grow from”.

Note that at present, the “contact image sensor” (Contact Image Sensor, CIS ), which is based on the same principle of charge bonding. Roughly speaking, CIS is a module that combines: a CCD scanning ruler with a length equal to the size of the scanned image; a line of short throw lenses that replaces a system of mirrors and lenses; and an exposure lamp, which is often a line of LEDs.

The theory of operation of charge-coupled devices is well described in an article on the StartCopy.net website, so we will not repeat it here, but we recommend reading it.

The main theses arising from the theory:

At the current stage of technology development, the scanning ruler in any scanner has differences in the sensitivity of individual pixels. It's unavoidable.

If you do not take any measures to correct differences in pixel sensitivity, then the scanned image will necessarily be "striped". Therefore, the automatic calibration system is used in all scanners. The most common terms to refer to this system are − AGC (Auto Gain Control, Automatic Level Control) and Shading Correction(Shadow correction).

The presence of an automatic calibration system, in addition to solving the main problem of correcting different pixel sensitivities, also solves other problems:

You do not need to control the brightness of the exposure lamp. Within a certain range, the system can compensate for excessive or insufficient lamp light. Accordingly, the lamp control circuit is simplified, and such a concept as “adjusting the brightness of the exposure lamp”, which was one of the key ones in analog machines, becomes unnecessary and is replaced by digital processing of the scanner output signal.
It is not necessary to have a lamp with uniform brightness along its entire length. The system can compensate for brightness differences in the same way as pixel sensitivity differences. This allows the LED strip to be used as a lamp.
The system can compensate for lamp aging, and even dust on mirrors. Up to a certain limit, of course.

Everything seems to be beautiful and magical, but there is a “weak link” - for the correct operation of the scanner’s automatic calibration system, reference white bar with the same whiteness along its entire length. And in real operating conditions, this band becomes dirty in places and loses its whiteness. This leads to the fact that for the pixels of the CCD line, on which a completely non-white part of the calibration strip is projected, the system sets an excessive correction - the image is brightened.

Practical aspects related to the scanner:

If you clean the scanner's optics, don't forget to clean the white calibration strip as well. It plays a very important role in the performance of the calibration system.

Typical position of the white bar

Despite the fact that the automatic calibration system is able to compensate for the contamination of mirrors and lenses, they also need to be thoroughly cleaned :). At a minimum, so that the correction values do not go beyond the range in which the system works correctly. In most cases, a dry, lint-free cloth is sufficient for cleaning mirrors and lenses. If the dirt is not wiped off with a dry cloth, then it is better to refrain from using "vigorous chemistry" and first try "soft" optics cleaners like "ScreenClene" from Katun.

Stripes of a lightened image on copies, parallel to the movement of the scanner carriage, with normal prints in printer mode, almost unambiguously indicate that the white calibration strip has ceased to be white in places. Clean it and all other optics.

Entirely faint copy with normal printouts in printer mode can have several causes:

The white strip in the scanner is no longer white along its entire length.
Contamination of the optics has caused the increased correction values set by the calibration system to become inaccurate, i.e. overcompensation has occurred.
Someone screwed up the user and / or service settings for the brightness of the image.
“The designer was overlooked”, i.e. The machine's firmware has an inaccurate scanned image processing algorithm that brightens the printout. Unfortunately, such cases are not uncommon.

The treatment for such pallor is simple and trivial - check the machine settings, clean the white stripe, clean all mirrors and lenses, including those that are not easy to reach.

Sometimes the contamination of the optics and the white band leads to the fact that the machine, being unable to set adequate correction values, generates a scanner error (AGC error, exposure lamp error, “scanner warm-up”, etc.). When these errors appear, do not rush to immediately change the CCD module, as often required by the service manual. The already mentioned thorough cleaning of everything and everything in the scanner saves from these errors quite often, although, of course, not always.

Some machines have the ability to adjust the position of the scanner carriage under the white bar during auto-calibration. This adjustment is useful when there is permanent damage or soiling on the strip that does not cover the full width of the strip.

And the last thing - the screws that secure the CCD ruler, the lens and some other parts of the scanning module are almost always painted over with paint. This was not done because of an excess of paint in production :) which means that you do not need to unscrew these screws, even if you really want to. The probability that the module will work normally after unscrewing/tightening the screws is very low.

20.08.2021

Internet

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