JP2003087517A - Image reader, its control method, control program and storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader that has high productivity and can be made compact, and to provide its control method, a control program and a storage medium. SOLUTION: A movable image sensor for reading an original is moved to a home position (S302), if a read image at the home position is entirely a white image (S304), an image is read while moving the image sensor (S306 to S308), and a position obtained by moving the image sensor from a position where the entire black image is read by a prescribed distance (e) is defined as a new home position (S311).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus having movable image reading means, a control method therefor, a control program, and a storage medium.

[0002]

2. Description of the Related Art Conventionally, an image reading apparatus having a movable image reading unit has a sensor for detecting a home position of the image reading unit so that the image reading unit can be surely moved to the home position for each reading operation. Was moving.

[0003]

However, by having the home position sensor, the productivity of the device is improved,
There was a problem that it was difficult to make it compact.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a highly productive and compact image reading apparatus, a control method thereof, a control program, and a control program. To provide a storage medium.

[0005]

In order to achieve the above object, the apparatus according to the present invention provides a movable image reading unit for reading a document and a moving distance from a reference position to measure the image. Position detection means for detecting the position of the reading means, and image reading while moving the image reading means, based on the image reading position at the time when the prepared position detection image is read, the reference position is determined. And a reference position updating unit for updating.

The reference position updating means further includes a judging means for judging whether or not the position detecting means is normal, and the reference position updating means detects the position if the position detecting means is normal by the judging means. It is characterized in that the image reading means is moved to the reference position by means.

The reference position updating means further includes a judging means for judging whether or not the position detecting means is normal, and the reference position updating means detects the position when the position detecting means is normal by the judging means. After moving the image reading means to the reference position by means, the image reading means is moved from the reference position to read the position detection image.

The reference position updating means further comprises a judging means for judging whether or not the position detecting means is normal, and the reference position updating means reads the image when the position detecting means has an abnormality by the judging means. The means is moved to a movement limit position, and the image reading means is moved to read the position detection image based on the distance from the movement limit position.

When the image reading position is not within the predetermined distance range from the reference position, the reference position updating means moves the image reading means to the movement limit position, and based on the distance from the movement limit position, It is characterized in that the image reading means is moved to read the image for position detection.

When the reference position is updated a predetermined number of times based on the distance from the movement limit position, but the image reading position is not within a predetermined distance range from the reference position, an error notification is given. And

When the reference position is updated a predetermined number of times based on the distance from the movement limit position, but the image reading position is not within the predetermined distance range from the reference position, the distance from the movement limit position is detected. The error notification is performed after updating the reference position based on the above.

When the reference position is updated a predetermined number of times based on the distance from the movement limit position, but the image reading position is not within the predetermined distance range from the reference position, the distance from the movement limit position is detected. The moving operation of the image reading means is ended after the reference position is updated based on the above.

The reference position updating means moves the image reading means to the movement limit position and sets a position a predetermined distance from the movement limit position as a new reference position.

The position detecting image is a black band-shaped image.

The reference position updating means determines that the position detection image has been read when a predetermined percentage or more of the pixels read by the image reading means are black. To do.

A reference position image is prepared at a position facing the image reading means at the reference position, and the image read by the image reading means at the reference position is
Further comprising a reference position image determining means for determining whether or not the reference position image is recognized, the reference position updating means,
When the reference position image determination means determines that the reference position image is not recognized, the image reading means is moved to the movement limit position, and the position detection is performed based on the distance from the movement limit position. It is characterized in that the image reading means is moved to read an image.

The reference position image is a white image.

The reference position image determining means may recognize the reference position image when white pixels appearing at a predetermined ratio or more in the image read at the reference position.

After the reading operation by the image reading means is interrupted, the reference position updating means updates the reference position.

After the reading operation by the image reading means is completed, the reference position updating means updates the reference position.

The reference position updating means updates the reference position when the power source of the image reading device is turned on.

An image reading apparatus having movable image reading means for reading a document, the position detecting means for detecting the position of the image reading means by measuring a moving distance from a reference position, and Abnormality detection means for detecting the presence or absence of abnormality in the position detection means, and reference position update for updating the reference position based on the movement limit position of the image reading means when the abnormality detection means detects the abnormality. And means.

In order to achieve the above object, the method according to the present invention is a method for controlling an image reading apparatus having a movable image reading means for reading an original, which is to measure a moving distance from a reference position. By the position detection step of detecting the position of the image reading means, the image reading is performed while moving the image reading means, and based on the image reading position at the time when the prepared position detection image is read, A reference position updating step of updating the reference position.

A method of controlling an image reading apparatus having movable image reading means for reading an original, the position detecting step of detecting the position of the image reading means by measuring a moving distance from a reference position. And an abnormality detection step of detecting whether or not there is an abnormality in position detection in the position detection step, and if an abnormality is detected in the abnormality detection step,
A reference position updating step of updating the reference position based on the movement limit position of the image reading means.

In order to achieve the above object, a program according to the present invention is a control program for an image reading apparatus having a movable image reading means for reading a document and a processor. A position detection step of detecting the position of the image reading means by measuring the moving distance of the image reading means, the image reading is performed while moving the image reading means, and the prepared position detection image is read at the time of reading. And a reference position updating step of updating the reference position based on the image reading position. A control program for an image reading apparatus having a movable image reading unit for reading a document and a processor, wherein the processor detects the position of the image reading unit by measuring a moving distance from a reference position. Position detection step, an abnormality detection step of detecting the presence or absence of abnormality in position detection in the position detection step, and when an abnormality is detected in the abnormality detection step, based on the movement limit position of the image reading means. And a reference position updating step of updating the reference position.

In order to achieve the above object, a storage medium according to the present invention is characterized by storing the above control program.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the relative arrangement of the constituent elements, the display screen, and the like described in this embodiment are not intended to limit the scope of the present invention to them unless otherwise specified.

(Embodiment) First, as an embodiment of an image reading apparatus according to the present invention, an M which has a scanning function, a printing function, and a FAX transmission / reception function together.
The FP (Multi Function Peripheral) will be described.

FIG. 1 is a block diagram showing the circuit configuration of the MFP according to the present embodiment.

The CPU 101 is a system control unit of the MFP and controls the entire MFP.

The ROM 102 stores the system control program of the MFP. The CPU 101
Executes various operations related to the MFP based on the control program stored in the ROM 102. Such a control program of the CPU 101 is not limited to the one stored in the ROM 102, but may be a floppy (registered trademark).
It may be stored in an external storage medium such as a disk or a CD-ROM, and this is read by a dedicated reading device into the RAM (for example, SRAM 104) of the MFP, and the CPU 101 decodes and executes it. Good.

The printer 103 is for printing the input image data on recording paper.

The SRAM 104 mainly stores the registration data of the MFP and the like, and the DRAM 105 mainly stores the image data.

The PC I / F 106 is the MFP and the PC 10.
PC 107 is an interface for connecting to
Is a host computer capable of changing various setting data of the MFP and requesting activation of various operations via this.

The image processor 108 performs various image processing on the image data input by the image sensor 109. The image sensor 109 is an image reading unit such as a contact-type reading sensor for reading an image on a document.

The operation panel 110 has a display 111 for displaying the state of the device, etc., and inputs an operation instruction from an operator, registers various data, and displays the display 111.
It is for confirming the state of the device through.

The NCU 112 controls a public line network, and the modem 113 modulates and demodulates a digital signal and an analog signal.

FIG. 2 is a diagram showing the positional relationship between the image reading range and the home position of the sensor on the document table of this MFP.

The home position of the image sensor is set near the end of the document table, and the document table near the home position facing the image sensor is colored white by a predetermined width a as shown in the figure. There is.

On the other hand, a black band-shaped image having a predetermined width b is prepared in advance at a position separated from the home position of the image sensor in the sub-scanning direction by a predetermined distance.

Such a white portion a (for example, 10 m
An image composed of two colors, m) and a black portion b (for example, 5 mm) is called a position mark. The position e (for example, 3 mm) to the left of the color boundary position of the position mark is the home position of the image sensor, and the position further left (d, for example, 2 mm) is the left end movement limit position of the image sensor. Has been done. Further, the original readable range is c (eg, 350) from the right end of the black portion of the position mark.
mm), and the image sensor can be further moved rightward by f (for example, 2 mm). This position is the right end movement limit position of the image sensor. Then, g (d + e + b + c +) from the left end movement limit position to the right end movement limit position
f In this example, 362 mm is the movable range of the image sensor.

In the present embodiment, the device is constructed with the above-mentioned positional relationship, but it is needless to say that the positional relationship of each part can be changed according to the shape, size, etc. of the device.

FIG. 3 is a flowchart showing the home position detecting process of the image sensor when the power is turned on.

First, as a premise of this processing, in order to detect the home position of the image sensor, the reading mode of the apparatus is set to the monochrome binarization mode, and a predetermined resolution (for example, 8) is set in the main scanning direction of the image sensor. Pixels /
mm) to read the image.

Then, in S301, the sum of the position counter stored in the SRAM backup memory is checked. This confirms whether the value of the position counter is normal. Here, when it is determined that the position counter is normal, the process proceeds to S302, and the image sensor is moved to a position considered to be a home position (a position where the counter value is 0) based on the position counter.

The position counter is a counter that counts the number of steps of the reading motor driven to move the image sensor when the home position of the image sensor is zero. The right direction is a positive number and the left direction is a negative number, and each time the reading motor is driven, the value stored in the backup area on the SRAM is counted up or down. Therefore, when this value is other than 0, it is possible to know that the image sensor is at a position other than the home position, and also the position from the home position. However, when the reading motor runs idle due to a hardware problem, the actual position of the image sensor deviates from the value of the position counter, and thus the position counter alone cannot return to the home position. That is, the position where the value of the position counter becomes 0 (reference position) deviates from the actual home position.
In this case, it is necessary to perform the operation of returning the reference position to the actual home position. Therefore, the following S303 to S3
In the processing of 11, the boundary of the black and white reference plate is searched and the reference position is updated.

According to the position counter, the position of the image sensor can be easily grasped and the processing time can be shortened.

A plurality of motor drive patterns (for example, 1-2 phase
(When reading in monochrome) and microstep (when reading in color) 150dpi drive, 300dpi drive, 600dpi drive, 1200d
If there is a pi drive, etc., the position counter indicates the number of steps when driving with the smallest step (for example, microsteps during color reading (6 divisions: 3600 dpi).
It can be calculated with the numerical value of (drive). That is, in this example, during monochrome driving, the motor is incremented or decremented by 3 each time the motor is driven one step, and during color driving, the motor is incremented or decremented by 1 each time the motor is driven one step. For example, if the image sensor is stopped at a position 30.0 mm to the right from the home position, the value of the position counter at that time is (30.0 × 3600 ÷ 25.4 ÷
3) × 3 = 4251.

After moving the image sensor, the following processing is performed in order to confirm whether the position is really the home position.

If the image sensor is truly located at the home position, all white data should be obtainable when the image data is obtained at that position. Because, as shown in Figure 2, the position of the home position is
This is because the color of the position mark is white. Therefore, S30
3, the image data of one line is acquired, and S304
Check if the data is all white data. If it is determined that the line is the all-white line, the process returns from S305 to S303, the image data of one line is acquired again for reconfirmation, and it is checked whether it is the all-white data. Here, if it is possible to reconfirm that the data is all-white data, the process proceeds from S305 to S306 to search for the color boundary of the position mark.

First, in S306, one line of image data is acquired at that position, and in S307, it is checked whether it is all black data. If it is not all black data,
In step S308, n (for example, 0.02 mm) is moved to the right, one line of image data is acquired again, and it is checked whether the data is all black data. This is done until all black data is found in S307, or the moving distance is b in S309.
Repeat until + e (for example, 8 mm). This is because there is a possibility that the image sensor itself is in an abnormal state when there is no change in the acquired image data even after the position at the right end of the black portion of the position mark, that is, the position b + e (eg, 8 mm) from the home position. . When all black data is found, the process proceeds from S307 to S310, moves from that position to the left by e (for example, 3 mm), and the position counter is initialized to 0 in S311 to finish.

If the position counter is judged to be abnormal, cannot be judged to be all-white data, or all-black data is not found during the above-mentioned processing, the process proceeds to S312 and the following processing is performed.

First, in S312, S313 and S314.
Check whether the home position check has already been performed twice. That is, the number of movements to the left end movement limit position is counted, and it is checked whether the count value is 1 or less. If it is 1 or less, the process proceeds to S313, and the image sensor is reliably moved to the left end movement limit position. That is, for example, to the left g or more (for example, 364 m
m) Move. This moving distance is a margin (for example, 2 mm) in consideration of the case where there is play in the mechanical structure.
Is included. Next, in S314, the left end movement limit position is moved to the right by d (for example, 2 mm). If the image sensor moves normally, this position becomes the home position.

Here, in order to surely move the image sensor to the right end movement limit position, g (eg, 364 m) to the right.
m) It may be moved and then moved to the home position to the right by f + c + b + e (for example, 360 mm). In this case, since the distance from the home position is shorter from the left end movement limit position than from the right end movement limit position, moving to the left end movement limit position shortens the processing time as a whole. However, even if it is moved to the right end movement limit position, there is no problem if it is surely moved.

Next, whether or not this position is really the home position is repeated by the same processing as the processing from S303. Here, if it is not judged again as all-white data or if all-black data is not found, it is checked whether the home position check has already been performed twice.

If the home position check has already been performed twice in S312 (when the number of times of movement to the left end movement limit position in S313 is 2), in order to reliably move the image sensor to the left end movement limit position, , S31
The position is provisionally set to the home position by moving leftward by 5 or more (for example, 364 mm) at 5 and then moving rightward by d (for example, 2 mm) at S316. In this case as well, the process of moving to the right end movement limit position may be performed as described above. When the position is temporarily moved to the home position, the process proceeds to S317, and the position counter is initialized to 0.
However, in this case, there is a possibility that the image sensor is not moving properly due to a failure of the motor etc. while moving.
Since it is not clear if this is really the home position, an error notification is given in S318 and the process ends.

In this embodiment, the number of times the home position is detected is two. However, it goes without saying that another number may be adopted depending on the configuration of the apparatus.

FIG. 4 is a flowchart showing the home position detecting process of the image sensor after the reading is completed and after the interruption.

After the reading is completed, the home position detecting operation flow of the image sensor after the interruption does not check whether the position counter is normal at the start of the process.
All other processing is the same as the home position detection operation flow at power-on shown in FIG. Therefore, the boxes having the same processing contents are given the same reference numerals and the description thereof will be omitted.

FIG. 5 is a diagram showing a method of determining all white data during the home position detection process of the image sensor.

For example, when the image sensor of this apparatus has an A4 width (216 mm) in the main scanning direction, a maximum of 21 lines per line is obtained in the monochrome binarization mode and a resolution of 8 pixels / mm.
It is possible to obtain 6 bytes of data. However, the data on both ends may be incorrect due to the structure of the device and the influence of light. Therefore, the 8-byte data at both ends is ignored, and the central part 200
Byte data is converted to white data (0x
00). In S502, this 20
If 90% or more of the 0-byte data is white data, the flow advances to S503 to determine that it is all-white data.
If it is less than 90%, the process proceeds to S504, and it is determined that it is not all white data. Although the judgment conditions are made stricter by judging every byte (every 8 pixels) in this way, the processing time can be shortened. In the present embodiment, the numerical values as described above are given, but the present invention is not limited to this, and it goes without saying that various combinations can be made in consideration of the width of the image sensor, the structure of the device, and the like. Yes.

FIG. 6 is a diagram showing a method of determining all black data during the home position detection process of the image sensor.

For example, when the image sensor of this device has an A4 width (216 mm) in the main scanning direction, a maximum of 21 lines per line is obtained in the monochrome binarization mode and a resolution of 8 pixels / mm.
It is possible to obtain 6 bytes of data. However, the data on both ends may be incorrect due to the structure of the device and the influence of light. Therefore, the 8-byte data at both ends is ignored, and the central 200-byte data is black data for each byte (8 pixels) in S601.
It is determined whether it is (0xFF). In S602, if 50% or more of the 200 bytes is black data, the process proceeds to S603, and it is determined to be all black data. If it is less than 50%, the process proceeds to S604 and it is not all black data. to decide. When detecting the white part, the surface is read, whereas in this case the boundary line from white to black is detected, so when reading the center of the line exactly or when reading slightly obliquely due to the mechanical structure It is a numerical value considering. Although the judgment conditions are made stricter by judging every byte (every 8 pixels) in this way, the processing time can be shortened. In the present embodiment, the numerical values as described above are given, but the present invention is not limited to this, and it goes without saying that various combinations can be made in consideration of the width of the image sensor, the structure of the device, and the like. Yes.

Even when the present invention is applied to a system composed of a plurality of devices (for example, host computer, interface device, reader, printer, etc.), a device composed of one device (for example, a copying machine, a facsimile). Device).

Further, an object of the present invention is to supply a storage medium (or recording medium) recording a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to supply a computer of the system or apparatus ( Alternatively, by the CPU or MPU) reading and executing the program code stored in the storage medium,
It goes without saying that it will be achieved. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.
Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also based on the instruction of the program code,
An operating system (OS) running on the computer does some or all of the actual processing,
It goes without saying that the processing includes the case where the functions of the above-described embodiments are realized.

Further, after the program code read from the storage medium is written in the memory provided in the function expansion card inserted in the computer or the function expansion unit connected to the computer, based on the instruction of the program code, , The CPU provided in the function expansion card or the function expansion unit performs some or all of the actual processing,
It goes without saying that the processing includes the case where the functions of the above-described embodiments are realized.

When the present invention is applied to the above storage medium, the storage medium stores the program code corresponding to the above-described flowchart (shown in FIG. 3 and / or FIG. 4).

[0068]

As described above, according to the present invention,
It is possible to provide an image reading apparatus that has high productivity and can be made compact, a control method therefor, a control program, and a storage medium.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an MFP as an embodiment of the present invention.

FIG. 2 is a diagram showing a positional relationship between an image reading range of an MFP and a home position of a sensor as an embodiment of the present invention.

FIG. 3 is a diagram illustrating an MFP according to an embodiment of the present invention.
It is a flow chart which shows home position detection processing of an image sensor at the time of power supply starting.

FIG. 4 is a block diagram of an MFP according to an embodiment of the present invention.
6 is a flowchart showing a home position detection process of the image sensor after the reading is completed and after the interruption.

FIG. 5 is a diagram showing an MFP according to an embodiment of the present invention.
It is a flow chart which shows judgment processing whether it is all-white data.

FIG. 6 is a diagram illustrating an MFP according to an embodiment of the present invention,
It is a flow chart which shows judgment processing whether it is all black data.

Continued front page    (72) Inventor Makoto Satake             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Naomi Nakamura             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Takashi Imai             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Toshiaki Saito             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H027 DA23 DA32 DA41 DB01 DE02                       DE07 DE09 EC07 EC09 EC10                       EC12 ED04 EE02 EE04 EE05                       EE07 EE08 HA02 HA04 HA20                       HB05 HB07 HB16 HB17 ZA07                 5B047 AA01 AB01 BA02 BB02 BC16                       CA12 CB07 CB09 DC01                 5C072 AA01 BA01 MB04 MB08 RA07                       UA14

Claims (23)

[Claims] 1. A movable image reading unit for reading a document, a position detecting unit for detecting a position of the image reading unit by measuring a moving distance from a reference position, and a moving unit for moving the image reading unit. And an image reading device, and a reference position updating unit that updates the reference position based on the image reading position at the time when the prepared position detection image is read. . 2. A determination means for determining whether or not the position detection means is normal, wherein the reference position update means, when the position detection means is determined to be normal by the determination means, The image reading apparatus according to claim 1, wherein the image reading unit is moved to the reference position by a position detection unit. 3. A determination means for determining whether or not the position detection means is normal, wherein the reference position updating means determines the position detection means when the position detection means is normal. 2. The image according to claim 1, wherein after moving the image reading means to the reference position by the position detection means, the image reading means is moved from the reference position to read the position detection image. Reader. 4. A determination means for determining whether or not the position detection means is normal, wherein the reference position update means is configured to detect the abnormalities in the position detection means by the determination means. The image reading means is moved to a movement limit position, and the image reading means is moved so as to read the position detection image based on a distance from the movement limit position. The image reading apparatus described in 1. 5. When the image reading position is not within a predetermined distance range from the reference position, the reference position updating means moves the image reading means to a movement limit position, and based on the distance from the movement limit position. The image reading device according to claim 1, 2, 3 or 4, wherein the image reading means is moved to read the position detection image. 6. When the image reading position is not within a predetermined distance range from the reference position even though the reference position is updated a predetermined number of times based on the distance from the movement limit position, an error notification is issued. The image reading device according to claim 5. 7. If the reference position is updated a predetermined number of times based on the distance from the movement limit position, but the image reading position is not within a predetermined distance range from the reference position, the movement limit position is changed. The image reading apparatus according to claim 5, wherein the error notification is performed after the reference position is updated based on the distance. 8. When the image reading position is not within a predetermined distance range from the reference position, even though the reference position is updated a predetermined number of times based on the distance from the movement limit position, 8. The image reading apparatus according to claim 4, wherein the moving operation of the image reading unit is terminated after the reference position is updated based on the distance. 9. The reference position updating means moves the image reading means to the movement limit position and sets a position a predetermined distance from the movement limit position as the new reference position. 9. The image reading device according to any one of 8 to 8. 10. The image reading apparatus according to claim 1, wherein the position detection image is a black band-shaped image. 11. The reference position updating means determines that the position detection image has been read when a predetermined proportion or more of the pixels read by the image reading means are black. The image reading apparatus according to claim 10, which is characterized in that. 12. A reference position image is prepared at a position facing the image reading means at the reference position, and whether the image read by the image reading means at the reference position is recognized as the reference position image. Further comprising a reference position image determining means for determining whether or not the reference position updating means determines the image reading means when the reference position image determining means determines that the reference position image is not recognized. 12. The image reading unit is moved to read the position detection image based on a distance from the movement limit position and the movement limit position, and the image reading unit is moved. Image reading device. 13. The image reading apparatus according to claim 12, wherein the reference position image is a white image. 14. The reference position image determining means recognizes the reference position image when white pixels appearing at a predetermined ratio or more in the image read at the reference position. The image reading apparatus described in 1. 15. The image reading apparatus according to claim 1, wherein the reference position updating unit updates the reference position after the reading operation by the image reading unit is interrupted. 16. The image reading apparatus according to claim 1, wherein the reference position updating means updates the reference position after the reading operation by the image reading means is completed. 17. The image reading apparatus according to claim 1, wherein the reference position updating unit updates the reference position when the power source of the image reading apparatus is turned on. 18. An image reading apparatus having movable image reading means for reading an original, comprising position detecting means for detecting a position of the image reading means by measuring a moving distance from a reference position. An abnormality detection unit that detects the presence or absence of an abnormality in the position detection unit, and a reference that updates the reference position based on the movement limit position of the image reading unit when the abnormality detection unit detects an abnormality. An image reading apparatus comprising: a position updating unit. 19. A control method of an image reading apparatus having movable image reading means for reading an original, which position detects the position of the image reading means by measuring a moving distance from a reference position. A detecting step, an image reading is performed while moving the image reading means, and a reference position updating step of updating the reference position based on the image reading position at the time when the prepared position detection image is read, A method for controlling an image reading apparatus, comprising: 20. A method of controlling an image reading apparatus having a movable image reading unit for reading a document, the position detecting a position of the image reading unit by measuring a moving distance from a reference position. A detection step, an abnormality detection step of detecting the presence or absence of abnormality in position detection in the position detection step, and when an abnormality is detected in the abnormality detection step, based on the movement limit position of the image reading means, A reference position updating step of updating the reference position, and a control method of the image reading apparatus. 21. A control program for an image reading apparatus having a movable image reading unit for reading a document and a processor, wherein the image reading is performed by the processor measuring a moving distance from a reference position. Position detection step of detecting the position of the means, image reading is performed while moving the image reading means, and the reference position is updated based on the image reading position at the time when the prepared position detection image is read. A control program for executing a reference position updating step of: 22. A control program for an image reading apparatus having a movable image reading means for reading a document and a processor, wherein the image reading is performed by the processor measuring a moving distance from a reference position. A position detection step of detecting the position of the means, an abnormality detection step of detecting the presence or absence of an abnormality in the position detection in the position detection step, and a movement of the image reading means when an abnormality is detected in the abnormality detection step. A reference program updating step of updating the reference position based on a limit position, and a control program. 23. A storage medium having the control program according to claim 21 or 22 stored therein.