JP2003087521A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a carriage from vibrating during its reciprocal movement and to accelerate its read speed. SOLUTION: The image reader for reading an image of an original reflected through an optical system is provided with the carriage that supports the optical system and is subjected to reciprocal movement with driving of a motor 1, and a control part 3 for controlling acceleration, uniform motion and deceleration of carriage reciprocal movement and current application to the motor 1, sets second current application given to the motor 1 at the reciprocal movement so as to be larger than a first current applied to the motor 1 at carriage reciprocal movement with the control part 3, and also sets a switching time point between the first current application and the second current application between a deceleration end time point of the carriage reciprocal movement and an acceleration start time point of the reciprocal movement.

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 which scans and reads a reflection image of a document set at a reading position as the carriage moves.

[0002]

2. Description of the Related Art An image reading apparatus such as a copying machine or a scanner includes a platen glass on which a document to be read is placed, a carriage which reciprocates with a mirror below the platen glass, and a carriage. And a reading unit such as a solid-state image sensor that reads an image of a document reflected by a mirror and converts the image into an electric signal as the image is moved.

In order to read an image of a document with such an image reading apparatus, the carriage is driven by a stepping motor to reciprocate while the document is placed on the platen glass. The document is scanned by the forward movement of the carriage back and forth, and the image reflected by the mirror is read by the reading means. After the reading is completed, the carriage is moved back to the start position in preparation for the next reading.

Here, a stepping motor is used as a drive source for moving the carriage.
By using the stepping motor, it is possible to accurately control the reciprocating movement of the carriage. That is, the carriage moves at a low speed on the outward path for reading the original image, and moves at a high speed on the return path after the reading. As a result, high-definition reading and reduction in continuous reading time can be achieved.

The moving speed of the carriage is controlled by the amount of current applied to the stepping motor. As described above, since the carriage moves at a low speed on the outward path and moves at a high speed on the return path, different currents are applied to the stepping motor on the outward path and the return path. Therefore, in the stepping motor control for moving the carriage, the point is the current amount and the current switching in the forward and return paths.

As a control of such a stepping motor, in Japanese Patent No. 2831716, switching of the current is set between the acceleration end time of the forward movement and the start time of the backward movement to avoid step-out during the backward movement. The image shift is prevented. Further, in Japanese Patent Laid-Open No. 7-199370,
From the viewpoint of preventing image shift due to vibration during current switching, current switching is set after the end of forward travel acceleration. Further, in Japanese Patent Laid-Open No. 11-187696,
The electric power at the time of deceleration of the forward movement and the electric power at the time of the backward movement are made to be the same so as to speed up the backward movement.

[0007]

However, when the current switching is performed at the end of forward travel acceleration, the image quality is affected by the vibration generated at the time of switching. Further, when switching is performed at the end of the backward movement deceleration, the vibration generated at the time of deceleration has an influence. Further, the current switching in the constant speed region requires an attenuation section for preventing image blurring, and an attenuation distance is required for that, and the movable range of the carriage must be increased.

[0008]

The present invention has been made to solve the above problems. That is, the present invention is an image reading apparatus that reads an image of a document reflected through an optical system, and includes a carriage that carries the optical system and is reciprocally moved by driving a motor, and acceleration and reciprocal speed of reciprocal movement of the carriage. , Control means for controlling deceleration and controlling current application to the motor are provided, and by the control means,
The second current application applied to the motor during the forward operation is set to be larger than the first current applied to the motor during the forward operation of the carriage, and the switching time point between the first current application and the second current application is set to the return path of the carriage. It is set between the end point of deceleration of the operation and the start point of acceleration of the forward path operation.

According to the present invention as described above, the current is not switched immediately after the deceleration of the forward movement of the carriage or immediately before the start of acceleration, so that it is less likely to be affected by the vibration of the carriage. Further, since the current switching is not performed after the outward travel acceleration is completed, it is possible to suppress the influence of the vibration due to the switching on the image.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating this embodiment. That is, the block diagram shown in FIG. 1 shows a drive configuration of the carriage applied to the image reading apparatus.
A driver 2 for driving the motor 2 and a controller 3 for controlling the driver 2 and the motor 1 are provided.

The carriage of the image reading apparatus carries an optical system such as a mirror and reciprocates according to the reading operation of the original image. A motor 1 such as a stepping motor is applied as a drive source for this reciprocating movement.

Further, the driver 2 has a reciprocating movement selection signal (CW / CCW) from the control section $, a clock Clock,
Upon receiving the voltage Vref, a signal for driving is given to the motor 1. The control unit 3 outputs various signals to the driver 2 in order to drive the motor 1 and control acceleration, constant velocity, and deceleration in the reciprocating movement of the carriage.

The control unit 3 includes transistors Tr1 and Tr1.
Vref given to driver 2 by switching 2
Adjust. The amount of current given to the motor 1 changes depending on the magnitude of this Vref.

In the present embodiment, in such motor control of the carriage, the second current applied to the motor 1 during the forward movement is set to be larger than the first current applied to the motor 1 during the forward movement of the carriage, and It is characterized in that the switching time point between the first current application and the second current application is set between the deceleration end time of the carriage return movement and the acceleration start time of the forward movement.

FIG. 2 is a diagram showing the excitation profile of the carriage and the motor applied current in the image reading apparatus of this embodiment. That is, point a of the excitation profile
The first set current I ₁ is applied to the motor up to the point b, and the carriage is moved forward.

Next, b, which is the start point of deceleration of the carriage
A second set current I ₂ is applied from the point. The second applied current is from the deceleration start point b in the forward movement of the carriage to the backward movement acceleration, constant speed, and deceleration, and is the deceleration end point c.
It is applied up to the point d between the point and the point e which is the start point of the next forward movement. That is, the time point of switching from the _second set current I ₂ to the first set current I ₁ is set between the end point of deceleration of the backward movement and the start point of acceleration of the next forward movement.

With such a switching timing, it becomes possible to suppress the vibration due to the change in the moving direction of the carriage.

Further, as the d point which becomes the switching timing, each time interval between the c point and the e point is set to 2T or more. Here, T is the cycle of the natural frequency of the system of the carriage moving mechanism. In this way, the vibration of the carriage can be damped by setting the carriage movement stop time before and after the switching timing to 2T or more.

That is, by opening at least 2T from the point c to the point d, it is possible to damp vibration generated by deceleration of the backward movement and to avoid step-out in the acceleration region of the subsequent forward movement. Further, by opening 2T or more from the point d to the point e, it is possible to damp the vibration of the carriage generated by the current switching and avoid the step-out in the acceleration region of the subsequent outward movement.

The distance from the point c to the point d and the distance from the point d to the point e should be shorter than 8T. Even if these intervals are 8T or more, a large damping effect cannot be obtained, so
By making it shorter than 8T, it becomes unnecessary to lengthen the scanning time unnecessarily.

Further, switching from the point f, which is the deceleration start time of the next forward movement of the carriage, to the second set current again,
After deceleration of the forward movement, acceleration of the backward movement, constant speed, and deceleration, switching is performed at point h. This switching is performed at point h, which is a time interval of 2T or more from point g, which is the end point of deceleration of the backward movement.

After the point h at which the series of carriage movements is completed, the third set current I ₃ lower than usual is applied. This makes it possible to reduce the power consumption when the carriage is on standby.

To switch the current to the motor as described above, the transistor Tr1,
This is performed by driving Tr2 and switching the current supplied from the driver 2 to the motor 1. That is, when applying the _first set current I ₁ , Tr2 is set to ON and Tr1 is set to OFF, and when applying the _second set current I ₂ , both Tr1 and Tr2 are set to OFF, When applying the third set current I ₃ , both Tr1 and Tr2 are set to ON. As a result, a voltage based on the resistors R0 to R3 is applied to Vref of the driver 2, and a current corresponding to the voltage of Vref is applied to the motor 1.

The moving speed of the carriage is the clock C.
When the carriage is stopped by controlling the lock cycle by changing it, the clock Clock may not be applied.

By switching the current applied to the motor 1 in this manner, vibration of carriage movement can be suppressed,
It is possible to improve the read image quality by avoiding step-out.

Further, in this embodiment, the control unit 3 causes
The acceleration profile of the carriage is controlled such that the first time from the stopped state to the maximum acceleration and the second time from the maximum acceleration to the end of the acceleration are each equal to or longer than the cycle of the natural frequency of the carriage. By adopting such an acceleration profile, it is possible to suppress the occurrence of vibration at the time of accelerating the outward movement, avoid the risk of step-out, and improve the read image quality.

FIG. 3 is a diagram for explaining the details of the excitation profile and the applied current at the time of switching the current in this embodiment. Looking at the excitation profile in detail, from the point b, which is the deceleration start point of the forward movement of the carriage, to the c point, which is the deceleration end point of the backward movement, the first set current I
The second set current I ₂ is higher than ₁ and the degree of deceleration from the constant speed movement on the outward path is small, so that it is less likely to be affected by vibration.

On the other hand, from the point c, which is the end point of deceleration of the return movement, to the point e, which is the start of the next forward movement, the vibration is easily affected. Therefore, in the present embodiment, the current switching point is set to the point d between the points c and e, and a time period of 2T or more is provided between the points c and d so that the points d and e A time of 2T or more is provided between the point and the point.

That is, immediately after the point c, vibration occurs due to deceleration during the backward movement, but the set current value remains high and is sufficiently damped by the time point d. Further, although vibration occurs immediately after the point d due to current switching, it is sufficiently damped by the point e when the set current value is low, and it is possible to prevent the forward acceleration operation from being adversely affected.

As a result, the vibration in the section from the point c to the point e can be damped and step out can be prevented. Furthermore, from point c to e
Since the vibration in the section up to the point can be damped, the first set current I ₁ in the forward movement can be set low, and the power consumption can be reduced.

Next, the flow of control in the control unit during the scanning operation will be described. FIG. 4 is a flowchart explaining the operation in the case of one-time scanning. First, step S10
In step 1, it is determined whether or not scan (forward movement) acceleration is started, and when acceleration is started, the current supplied to the motor is set to the first set current I ₁ .

If acceleration is not started, or if the first
After the set current I ₁ is set to, the process proceeds to step S102, and it is determined whether or not the scan deceleration is started. When the scan deceleration is started, the current supplied to the motor is set to the second set current I ₂ .

If deceleration is not started, or if the second
After setting the set current I ₂ of step S103 to step S103, it is determined whether or not a predetermined time has elapsed from the end of the return (return trip). After a lapse of a predetermined time from the end of the return, the current given to the motor is set to the third set current I ₃ . Otherwise, the process returns to step S102.

Next, the control flow in the case of multiple scans will be described with reference to the flow charts of FIGS. First, in step S201, it is determined whether or not the scan (forward movement) acceleration is started, and when the acceleration is started, the current supplied to the motor is set to the first set current I ₁ .

If acceleration is not started, or if the first
After the set current I ₁ is set to, the process proceeds to step S202, and it is determined whether or not the scan deceleration is started. When the scan deceleration is started, the current supplied to the motor is set to the second set current I ₂ .

If the deceleration is not started, or if the second
After the setting current I ₂ is set to, the process proceeds to step S203, and it is determined whether or not it is the last scan. If it is not the final scan, the process proceeds to step S204, and it is determined whether or not a predetermined time has elapsed from the end of the return (return movement). After a lapse of a predetermined time from the end of the return, the current given to the motor is set to the first set current I ₁ . Otherwise, the process returns to step S202.

If it is determined in step S203 that the scan is the last scan, the flow advances to step S205 in FIG. 6 to determine whether or not the scan deceleration is started. When the scan deceleration is started, the current given to the motor is set to the second set current I
_Set to ₂ .

If deceleration is not started, or if the second
After setting the set current I ₂ at step S206, the process proceeds to step S206, and it is determined whether a predetermined time has elapsed from the end of the return (return trip). After a lapse of a predetermined time from the end of the return, the current given to the motor is set to the third set current I ₃ , and the process is finished. Otherwise, the process returns to step S205.

By such processing of the control unit, it is possible to realize the current control for suppressing the vibration of the carriage and reducing the power consumption.

[0040]

As described above, the present invention has the following effects. That is, the vibration of the carriage can be suppressed by controlling the current value switching to the motor that drives the carriage, and it becomes possible to prevent high-definition image reading, and particularly to prevent image quality deterioration at the leading edge of the reading.
Further, since the vibration of the carriage can be suppressed at the timing of switching the current, it is not necessary to supply an unnecessary current to the motor, and the power consumption can be reduced. Moreover, by suppressing the vibration of the carriage, unnecessary waiting time of the carriage can be reduced, and the reading speed can be increased.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating an embodiment.

FIG. 2 is a diagram showing an excitation profile of a carriage and a motor applied current.

FIG. 3 is a diagram illustrating details of an excitation profile and an applied current.

FIG. 4 is a flowchart illustrating an operation in the case of a single scan.

FIG. 5 is a flowchart (No. 1) illustrating control in the case of multiple scans.

FIG. 6 is a flowchart (part 2) explaining control in the case of multiple scans.

[Explanation of symbols]

1 ... Motor, 2 ... Driver, 3 ... Control unit

Claims (5)

[Claims] 1. An image reading apparatus for reading an image of a document reflected through an optical system, comprising: a carriage that carries the optical system and is reciprocally moved by driving a motor; acceleration of reciprocating operation of the carriage; A control means for controlling deceleration and applying a current to the motor, wherein the control means supplies a first current to the motor during a forward movement of the carriage to a motor during a forward movement. The second current application is set to be large, and the switching time point between the first current application and the second current application is set between the deceleration end time of the backward movement operation of the carriage and the acceleration start time of the forward movement operation. An image reading device characterized by the above. 2. The carriage is configured such that a time from a deceleration end time of a backward movement operation of the carriage to the switching time point and a time from the switching time point to an acceleration start time of a forward movement operation of the carriage are both included in the carriage. The image reading apparatus according to claim 1, wherein the period is set to be twice or more the cycle of the natural frequency of. 3. The carriage is configured such that the time from the deceleration end time of the backward movement operation of the carriage to the switching time point and the time from the switching time point to the acceleration start time of the forward movement operation of the carriage are both the carriage. The image reading apparatus according to claim 1, wherein the period is set to be less than 8 times the cycle of the natural frequency of the. 4. The control means, when the carriage reciprocates continuously, the control means applies a current to the motor after the final return path operation is lower than the first current. The image reading apparatus according to claim 1, wherein the third current is set. 5. The carriage has a first time period from when the acceleration profile of the carriage reaches a maximum acceleration to a maximum acceleration, and a second time period from the maximum acceleration until the acceleration is terminated, respectively. The image reading apparatus according to claim 1, wherein the image reading apparatus is controlled to have a period equal to or longer than a cycle of the natural frequency of the above.