JP2002031861A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image reader by which the vibration of a driving shaft due to the overshooting of a stepping motor can be suppressed. SOLUTION: When the driving of the stepping motor 8 is switched from a full step to a quadripartite step by a driving controlling plate 21 after passing specified time since the speed of respective carriages 1 and 2 reaches specified speed, a motor driving pulse number becomes four thousands and some hundreds, and a moving amount is set as 0.72/4=0.18 deg., and the vibration of the driving shaft 4 is reduced because the moving amount per one step is small, and the overshooting by the stepping motor 8 can be suppressed, so that speed fluctuation can be reduced. In the case that the respective carriages 1 and 2 are moved in the same distance, since the stepping motor 8 is moved in a short time rather by the full step, it is moved by the full step to the vicinity of a reading start position, and one reading time is made as short as possible, so that cpm improvement can be attained.

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, and more particularly to drive control of a stepping motor for driving a traveling body for optically scanning a document in the image reading apparatus.

[0002]

2. Description of the Related Art Conventionally, when an original is read by an image reading apparatus such as a scanner, a facsimile or a copying machine, a stepping motor is used as a driving device of a traveling body for optically scanning the original. In recent years, the vibration of the stepping motor is suppressed as much as possible, the scanning optical system (hereinafter referred to as a carriage) of the image reading apparatus is driven stably, and the number of copies per minute is cpm (copy per minute).
Various image reading apparatuses aiming at improvement of e) have been proposed.
By the way, Japanese Patent No. 2637455 discloses an image reading apparatus that switches the drive current of a stepping motor to a predetermined value when a predetermined speed is reached during the slow-up of the scanning optical system in order to suppress vibration.
Further, Japanese Patent No. 2752689 discloses a document scanning device that switches the driving current of the stepping motor in accordance with the magnification in the sub-scanning direction in order to prevent vibration and noise of the stepping motor. FIG. 7 shows a conventional slow-up control motor drive pulse (PP
FIG. 5 is a diagram showing S) and speed fluctuation. In the prior art of FIG. 7, the half step of the stepping motor is 0.36 °.
(Full step divided into two parts) drives the entire carriage from slow-up to slow-down.

[0003]

However, as shown in FIG. 7, the overshoot at the time of slowing up of the carriage has not yet stopped even at the image reading start position (the position indicated by the arrow in the figure), and an abnormal condition is found at the leading end of the image. This may cause an image to be generated. In addition, since the carriage rapidly slows down, overshooting of the stepping motor is generated as vibration coaxially. In particular,
On the reduction side of image reading, the reading speed by the carriage is fast, and the time from startup to the start of image reading is short,
In some cases, reading had to be started when a large vibration remained in the drive shaft.

Further, the drive time of the carriage can be reduced as much as possible by reducing the forward slow-up time, the slow-down time, and the return stop time. However, the return vibration of the carriage is reduced by shortening the stop time. If the forward slow-up is started before it can be accommodated, there is a possibility that the carriage may lose synchronism, and a certain stop period is required. This somewhat required stop period requires about 50 ms and cannot be shortened to less.

Accordingly, a first object of the present invention is to provide an image reading apparatus capable of suppressing vibration of a drive shaft due to overshoot of a stepping motor.
A second object of the present invention is to provide an image reading apparatus capable of shortening the driving time of a scanning optical system (carriage) and improving cpm.

[0006]

According to the first aspect of the present invention, there is provided a scanning means for reading a document on a document table by optical scanning, and a stepping motor for driving the scanning means to move in the sub-scanning direction of the document table. A slow-up drive unit capable of switching a moving amount per step of the stepping motor when the scanning unit drives the scanning unit to read the original on the platen by the stepping motor; The up drive means achieves the first and second objects by switching the amount of movement of the stepping motor per one step after a predetermined time has elapsed since the stepping motor started slowing up.

According to a second aspect of the present invention, in the first aspect of the invention, the predetermined time for switching the amount of movement of the stepping motor per one step is determined according to the timing at which the scanning means starts reading an original on an original platen. The first object is achieved by being configurable.

According to a third aspect of the present invention, in the first or second aspect of the present invention, when the reading of the original by the scanning unit is reduced, the slow-up driving unit includes:
The first object is achieved by switching a moving amount per step of the stepping motor at a driving speed of the stepping motor according to a predetermined reduction magnification.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the scanning means is driven by the stepping motor so as to finish reading the original. A slow-down driving means for switching a moving amount per one step of the stepping motor when the slowing-down is performed. By switching, the second object is achieved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to FIGS. FIG. 1 is a diagram illustrating a drive system of the image reading apparatus. The drive system of the image reading apparatus according to the present embodiment includes a first carriage 1,
A second carriage 2, a wire 3, a drive shaft 4, a wire pulley 5 integrated with the drive shaft 4, idle pulleys 6a to 6d,
A timing belt 7, a stepping motor 8, timing belt pulleys 9 and 10, a detection unit 11 and a home position sensor 12 are provided. The first carriage 1 and the second carriage 2 are traveling bodies that scan and read a document.

FIG. 2 is a diagram showing the configuration of the image reading apparatus. Contact glass (document table) 13, exposure lamp 1
4. First mirror 15, second mirror 16, third mirror 1
7, an imaging lens 18, a CCD (charge coupled device) 19, a drive control board 21 and a scanner control board 20.
The scanner control board 20 controls the image processing and the drive control board 21 of the stepping motor 8. The drive control plate 21 is a motor drive power supply (DC (direct current)) for the stepping motor 8.
24V) and a drive circuit for controlling the drive of the stepping motor 8.

Next, the operation of the drive system of the image reading apparatus will be described. The first carriage 1 includes an exposure lamp 1
4 and the first mirror 15 are integrated, and scans an original. The second carriage 2 integrates the second mirror 16 and the third mirror 17 and guides light from the first carriage 1 to the imaging lens 18. Power is transmitted to the first carriage 1 and the second carriage 2 via wires 3 stretched over two objects. The wire 3 is driven by a wire pulley 5 that is wound around and integrated with the driving coaxial 4. The wire pulley 5 is driven by a timing belt pulley 10 integrated with a shaft of a stepping motor 8 via a timing belt pulley 9 and a timing belt 7 which are coaxial.

When the power switch is turned on, the stepping motor 8 starts driving for homing, and the first carriage 1 and the second carriage 2 move in the direction of the arrow A in FIG. 1 (forward side). When the first carriage 1 and the second carriage 2 move by a predetermined distance, they start to reverse (return) in the direction of arrow B in FIG. Then, when the home position sensor 12 detects the detection unit 11 below the first carriage 1, the first carriage 1 and the second carriage 2 move by a predetermined pulse and stop. The first carriage 1 and the second carriage 2 wait at this position (hereinafter referred to as the home position HP position), and start a reading operation when a reading command is issued.

FIG. 3 is a block diagram showing a drive control plate for controlling the drive of the stepping motor. When a document is placed on the contact glass 13 and a start key (not shown) is pressed, a stepping motor drive clock is output from the scanner control board 20 to the drive control board 21 at a predetermined timing. At the same time when the stepping motor 8 starts driving, the first carriage 1 and the second carriage 2 start moving from the HP position in the direction of arrow A in FIG. 1 (forward side). The stepping motor 8 is driven by a drive control plate 21. The drive control plate 21 is driven by a stepper motor drive clock, forward / reverse rotation signal, and microstep drive from a scanner control plate 20 equipped with a host CPU (central processing unit). And a drive current switching signal are input. The drive control plate 21 controls the drive current flowing through each phase of the stepping motor 8 based on these signals.

The speed of the stepping motor 8 is determined by the driving clock frequency. The drive control plate 21 controls the phase switching timing of the stepping motor 8 according to the drive clock frequency. Thus, the speed of the stepping motor 8 becomes faster when the frequency is higher, and becomes slower when the frequency is lower, so that various kinds of slow-up control can be performed by controlling the drive clock frequency. Also,
The drive control plate 21 controls the stepping motor 8 by switching the drive current depending on the state of slow-up, slow-down, reading operation, return, standby, or the like, or switching the number of one-step divisions of the stepping motor 8. . Thus, the drive control is performed based on the speed pattern of the stepping motor 8.

Next, a description will be given of a drive pattern for improving the cpm (the number of copies that can be made per minute) and shortening the carriage drive time. FIG. 4 is a diagram illustrating a driving pattern of the carriage of the image reading apparatus. This figure shows a typical speed pattern used for traveling control as an example. The first carriage 1 and the second carriage 2 start running in the direction of arrow A (forward direction) in FIG. 1 by driving the stepping motor 8, and the original (not shown) placed on the contact glass 13 is exposed by the exposure lamp 14. Irradiate the reflected light and form an imaging lens 18 via a first mirror 15, a second mirror 16, and a third mirror 17.
Forms an image on the CCD 19 and reads the original. The read image data is transferred to the scanner control board 20, where image processing is performed.

When the reading of the original is completed, the first carriage 1 and the second carriage 2 move to the return step, and the stepping motor 8 starts to rotate in the reverse direction. Then, the first carriage 1 is moved at a high speed, and the second carriage 2 returns at a high speed at half the speed. When the home position sensor 12 detects the detecting unit 11 provided on the first carriage 1, the home position sensor 12 moves by a predetermined pulse and the stepping motor 8
Stop at the position. As shown in FIG. 4, during the period of running at a constant speed after the slow-up, that is, from the original reading start position to the end of the original reading in the drawing, the original is read from the leading end to the trailing end. During this time, the optical system (carriage) must be controlled so that the speed is most stable.

Here, the first embodiment will be described. FIG. 5 is a diagram illustrating motor drive pulses (PPS) and speed fluctuations of the stepping motor according to the present embodiment. In the figure, the upper part shows the speed fluctuation of the stepping motor 8,
The lower part shows a motor drive pulse (PPS). In the present embodiment, the drive control plate 21 has a full step of 0.72 ° of the stepping motor 8 at the time of slow-up.
Slow-up control is performed based on (movement amount per step). When each of the carriages 1 and 2 as the scanning optical system rises to a predetermined speed, the motor drive pulse is about 1000 PPS.
To reach. This motor drive pulse (PPS, pulse
“es per second, the number of drive pulses” is the number of pulses per unit time of an input signal for driving the stepping motor.

When a predetermined time has elapsed after the carriages 1 and 2 have reached the predetermined speed (approximately several tens of milliseconds), the drive control plate 21 switches the stepping motor 8 from full step to four division steps. About 400
It becomes 0 pulse, and the movement amount becomes 0.72 / 4 = 0.18 °. As a result, since the movement amount per step is small, the vibration of the drive shaft 4 is small, the overshoot by the stepping motor 8 can be suppressed, and the speed fluctuation can be reduced as shown in FIG. Further, when the carriages 1 and 2 move the same distance, the stepping motor 8 can move in a full step in a shorter time in a full step, so that the stepping motor 8 moves in a full step up to near a reading start position. The cpm can be improved by shortening the reading time as much as possible.

As described above, the distance movement to the same position in a short time can be shortened by switching the driving by the stepping motor 8 for slow-up and slow-down from half step to full step. Further, at a predetermined time from the start of the slow-up of the stepping motor 8, the movement amount per step is switched from full step to four divisions, so that vibration can be suppressed. Furthermore, since slow-up is performed in full steps, the time for slow-up is short and cpm can be improved. The vertical axis in the lower part of FIG. 5 indicates that the scale of the motor drive pulse in the case of the full step of the stepping motor 8 and the case of the four divided steps is 2 in order to make it easy to understand the switching of the movement amount per step of the stepping motor 8. Has become one.

Next, a second embodiment will be described. In the second embodiment, as an example, a case will be described in which the switching of the one-step movement amount by the drive control plate 21 is controlled to be switched 100 ms before the document reading start position. At the document reading start timing shown in FIG. 5, the one-step movement amount is switched in accordance with the leading edge of the transfer paper to be fed, the image movement, and the like. The plate 21 always has the image reading start timing of 100.
It can be controlled to switch the amount of one step before ms.

Therefore, the switching of the one-step moving amount is not performed after the original reading start timing, and the reading is not started before the vibration is attenuated, so that the speed fluctuation occurs during the image reading. And the occurrence of an abnormal image can be suppressed. As described above, since the time for switching the movement amount per step changes in conjunction with the start of document reading, even if the document reading start timing changes, the movement amount of one step is not switched during image reading. Therefore, occurrence of abnormal speed fluctuation can be suppressed.

Next, a third embodiment will be described.
FIG. 6 is a diagram showing a change in the motor drive pulse (PPS) during image reading magnification change. When the magnification is changed in the sub-scanning direction, the time from when the stepping motor 8 rises to a constant speed to the start of image reading greatly changes according to the magnification, so that the time from the constant speed to the image reading start timing is changed. Will also change. For example, if it is set in advance so that the movement amount of one step is switched from 100 ms before the start of image reading, it is possible to control all the slow-ups at a fixed inclination (the portion where the slow-up time has elapsed in the figure). In other words, the time from when the speed rises from a certain reduction magnification until reaching the reading start position is shortened, and reading may be started before the speed fluctuation attenuates. In order to prevent such a situation, the drive control plate 21 is preset to change the inclination of the motor drive step at the time of slow-up from a certain magnification.

In FIG. 6, as an example, from the reduction ratio of 60% or less, the slope of the slow-up is made steeper, so that the switching time is secured 100 ms before the start of the image reading. As described above, by setting the inclination of the motor drive step at the time of slow-up to be changed at the magnification, the time from the one-step switching timing to the reading start timing can be secured, so that the speed fluctuation at the time of reading can be reduced. Can be. In the present embodiment, the reduction ratio is set to 60% or less as an example. However, the present invention is not limited to this. In addition, as shown in FIG. 6, at the time of enlargement, the time until the start of image reading is delayed, so that there is no need for slow-up control.

Next, a fourth embodiment will be described.
Since the full step can be moved in a shorter time to move the same distance, the stepping motor 8 is slowed down by the full step at the same time as the reading is completed, so that the reading time of one reading is shortened as much as possible to improve the cpm. Can be planned. As described above, since the movement amount per step is switched from four divisions to full steps simultaneously with the start of the slowdown of the stepping motor 8, the cpm can be improved by shortening the slowdown time, and the drive time of the carriage can be reduced. It can be shortened. As described above, the first to fourth embodiments have been individually described. However, the embodiments can be combined.

[0026]

According to the first aspect of the invention, the slow-up drive means switches the movement amount per step of the stepping motor after a predetermined time has elapsed since the step-up of the stepping motor started, thereby suppressing vibration. Therefore, the slow-up time is short and the cpm can be improved.

According to the second aspect of the present invention, the predetermined time for switching the amount of movement of the stepping motor per step can be set in accordance with the timing at which the scanning means starts reading the document on the document table. Even if the value has changed, it is possible to prevent the occurrence of abnormal speed fluctuation without switching one step during image reading.

According to the third aspect of the present invention, when the reading of the original by the scanning means is reduced, the slow-up driving means includes:
Since the amount of movement per step of the stepping motor is switched at the driving speed of the stepping motor according to the predetermined reduction magnification, the time from the step switching timing to the reading start timing can be secured, and the speed fluctuation at the time of reading can be reduced. Can be.

According to the fourth aspect of the present invention, the slowdown driving means switches the moving amount per one step simultaneously with the start of the slowdown of the stepping motor, so that the cpm can be improved by shortening the slowdown time. In addition, it is possible to shorten the driving time of the carriage.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a driving system of an image reading apparatus.

FIG. 2 is a diagram illustrating a configuration of an image reading apparatus.

FIG. 3 is a block diagram showing a drive control plate for driving and controlling a stepping motor.

FIG. 4 is a diagram illustrating a driving pattern of a carriage of the image reading apparatus.

FIG. 5 is a diagram showing a motor drive pulse (PPS) and a speed fluctuation of the stepping motor according to the present embodiment.

FIG. 6 is a diagram illustrating a change in a motor drive pulse (PPS) during image reading magnification change.

FIG. 7 is a diagram showing a conventional slow-up control motor drive pulse (PPS) and a speed fluctuation of a stepping motor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st carriage 2 2nd carriage 3 Wire 4 Driving coaxial 5 Wire pulley 6a-d Idle pulley 7 Timing belt 8 Stepping motor 9, 10 Timing belt pulley 11 Detector 12 Home position sensor 13 Contact glass 14 Exposure lamp 15 First mirror 16 Second mirror 17 Third mirror 18 Imaging lens 19 CCD (charge imaging element) 20 Scanner control board 21 Drive control board

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04N 1/107

Claims (4)

[Claims] A scanning means for reading a document on the document table by optical scanning; a stepping motor for driving the scanning means to move in a sub-scanning direction of the document table; At the time of slow-up driving to read the original,
A slow-up drive unit capable of switching a moving amount per one step of the stepping motor, wherein the slow-up drive unit starts the stepping motor after a lapse of a predetermined time from the start of the slow-up. An image reading apparatus characterized by switching a moving amount per one step. 2. The apparatus according to claim 1, wherein the predetermined time for switching the amount of movement of the stepping motor per one step can be set in accordance with the timing at which the scanning means starts reading a document on a document table. Image reading device. 3. When the reading of the original by the scanning unit is reduced, the slow-up driving unit switches a moving amount per step of the stepping motor at a driving speed of the stepping motor according to a predetermined reduction magnification. The image reading device according to claim 1 or 2, wherein 4. A slowdown driving means for switching a moving amount per one step of the stepping motor when the scanning means is driven by the stepping motor so as to finish reading the document. 4. The image reading apparatus according to claim 1, wherein the down driving unit switches a moving amount per one step at the same time when the stepping motor starts to slow down. .