JP3820945B2 - Image reading device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus that scans and reads a reflection image of a document set at a reading position as a carriage moves.
[0002]
[Prior art]
An image reading apparatus such as a copying machine or a scanner is configured with a platen glass for placing a document to be read, a carriage that reciprocates while holding a mirror under the platen glass, and a mirror as the carriage moves. And a reading unit such as a solid-state imaging device that reads the image of the reflected original and converts it into an electrical signal.
[0003]
In order to read an image of a document with such an image reading apparatus, the carriage is driven by a stepping motor and reciprocated with the document placed on the platen glass. The document is scanned by the forward movement of the reciprocating movement of the carriage, and the image reflected by the mirror is read by the reading means. After the reading is completed, the carriage is moved backward to return to the start position in preparation for the next reading.
[0004]
Here, a stepping motor is used as a drive source for moving the carriage. By using the stepping motor, the reciprocation of the carriage can be accurately controlled. That is, the carriage moves at a low speed on the forward path for reading the document image, and moves at a high speed on the return path after the reading. Thereby, high-definition reading and continuous reading time can be shortened.
[0005]
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 forward path and moves at a high speed on the return path, different currents are applied to the stepping motor between the forward path and the return path. Therefore, in the stepping motor control for moving the carriage, the current amount and the current switching in the forward path and the return path are the points.
[0006]
As a control of such a stepping motor, in Japanese Patent No. 2831716, the current switching is set between the acceleration end time of the forward movement and the start time of the backward movement to avoid the step-out during the backward movement and to prevent the image shift. To prevent this. In Japanese Patent Laid-Open No. 7-199370, current switching is set after the end of forward movement acceleration from the viewpoint of preventing image shift due to vibration during current switching. In Japanese Patent Application Laid-Open No. 11-187696, the power during the forward movement deceleration is the same as that during the backward movement, so that the speed of the backward movement is increased.
[0007]
[Problems to be solved by the invention]
However, when the current is switched at the end of the forward movement acceleration, the image quality is affected by the vibration generated at the time of switching. In addition, when switching at the end of the backward movement deceleration, vibrations generated during deceleration are affected. Furthermore, current switching in the constant speed region requires an attenuation section for preventing image blurring, and accordingly, an attenuation distance is required, and the movable range of the carriage needs to be increased.
[0008]
[Means for Solving the Problems]
The present invention has been made to solve such problems. That is, the present invention is an image reading apparatus that reads an image of a document reflected through an optical system, and carries the optical system and reciprocates by driving a motor, acceleration of reciprocation of the carriage, constant speed, Control means for controlling deceleration and current application to the motor, and the control means causes the second current application to be applied to the motor during the backward operation to be larger than the first current applied to the motor during the forward operation of the carriage. In addition, the time point for switching between the first current application and the second current application is set between the end of deceleration of the carriage return path operation and the start of acceleration of the forward path operation , and the carriage is continuously reciprocated. In the case of the movement, the current application to the motor after the last return path operation is completed is set to a third current lower than the first current .
[0009]
In the present invention, the current is not switched immediately after the end of the forward movement of the carriage, or immediately before the start of acceleration, so that it is less susceptible to carriage vibration. In addition, since the current switching is not performed after the forward movement acceleration is finished, the influence of the vibration on the image due to the switching can be suppressed.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described 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 carriage drive configuration applied in the image reading apparatus. The motor 1 is a carriage drive source, the driver 2 for driving the motor 1, the driver 2 and And a control unit 3 for controlling the motor 1.
[0011]
The carriage of the image reading apparatus carries an optical system such as a mirror, and reciprocates according to the reading operation of the document image. A motor 1 such as a stepping motor is applied as a driving source for this reciprocation.
[0012]
In addition, the driver 2 receives a reciprocating movement selection signal (CW / CCW), a clock Clock, and a voltage Vref from the control unit $, and gives a driving signal to the motor 1. The control unit 3 outputs various signals to the driver 2 in order to control the acceleration, constant speed, and deceleration in the reciprocating operation of the carriage by driving the motor 1.
[0013]
The control unit 3 adjusts Vref applied to the driver 2 by switching the transistors Tr1 and Tr2. The amount of current applied to the motor 1 varies depending on the magnitude of Vref.
[0014]
In this embodiment, in such motor control of the carriage, the second current applied to the motor 1 during the forward operation is set larger than the first current applied to the motor 1 during the forward operation of the carriage, and the first current is set. It is characterized in that the switching time point between the application and the second current application is set between the deceleration end time of the carriage return path operation and the acceleration start time of the forward path operation.
[0015]
FIG. 2 is a diagram illustrating a carriage excitation profile and a motor applied current in the image reading apparatus of the present embodiment. That is, the first set current I ₁ is applied to the motor from the points a to b of the excitation profile, and the carriage is moved in the forward direction.
[0016]
Next, the second set current I ₂ is applied from the point b which is the deceleration start time of the carriage. The second applied current is from the deceleration start point b in the forward movement of the carriage through the acceleration, constant speed, and deceleration of the backward movement, and from the point c that is the end point of deceleration to the point e that is the start point of the next forward movement. To point d. That is, the switching time point from the _second set current I ₂ to the first set current I ₁ is set between the deceleration end time of the backward movement and the acceleration start time of the next forward movement.
[0017]
With such switching timing, it is possible to suppress vibration due to the change in the moving direction of the carriage.
[0018]
In addition, the time interval between the point c and the point e is set to 2T or more as the point d serving as the switching timing. Here, T is the period of the natural frequency of the system of the carriage movement mechanism. As described above, by setting the carriage movement stop time before and after the switching timing to 2T or more, the vibration of the carriage can be attenuated.
[0019]
That is, by opening more than 2T from the point c to the point d, it is possible to attenuate the vibration generated by the deceleration of the backward movement and avoid the step-out in the acceleration area of the subsequent forward movement. Further, by opening 2T or more from the point d to the point e, it is possible to attenuate the carriage vibration generated by the current switching and avoid the step-out in the acceleration region of the subsequent forward movement.
[0020]
Note that the interval from the point c to the point d and the interval from the point d to the point e are shorter than 8T. Since a large attenuation effect cannot be obtained even if these intervals are set to 8T or more, the scan time does not need to be unnecessarily increased by making it shorter than 8T.
[0021]
In addition, the second set current is switched again from the point f which is the deceleration start point of the next forward movement of the carriage, and the switching is performed at the point h through the deceleration, the constant speed and the deceleration of the backward movement from the deceleration of the forward movement. This switching is performed at a point h that is at least 2T apart from the point g, which is the time point when deceleration of the backward movement is completed.
[0022]
Then, after the point h at which the series of carriage movements is completed, the third set current I ₃ lower than usual is applied. As a result, the power consumption during carriage standby can be reduced.
[0023]
Such switching of the current to the motor is performed by driving the transistors Tr1 and Tr2 according to an instruction from the control unit 3 shown in FIG. That is, when applying the _first set current I1, Tr2 is set to ON and Tr1 is set to OFF, and when applying the _second set current I2, both Tr1 and Tr2 are set to OFF, When the third set current I ₃ is applied, both Tr1 and Tr2 are set to ON. As a result, voltages based on the respective resistors R0 to R3 are applied to Vref of the driver 2, and a current corresponding to the voltage of Vref is applied to the motor 1.
[0024]
The carriage moving speed is controlled by changing the cycle of the clock clock, and when the carriage is stopped, the clock clock is not applied.
[0025]
By switching the current applied to the motor 1 in this way, it is possible to suppress the vibration of the carriage movement and to avoid the step-out and improve the reading image quality.
[0026]
In the present embodiment, the control unit 3 sets the first acceleration time of the carriage from the stop state to the maximum acceleration and the second time from the maximum acceleration to the end of acceleration, respectively. Control is performed so that it is equal to or greater than the natural frequency period. By adopting such an acceleration profile, it is possible to suppress the occurrence of vibration during acceleration of the forward movement, avoid the risk of step-out, and improve the reading image quality.
[0027]
FIG. 3 is a diagram for explaining the details of the excitation profile and the applied current at the time of current switching according to the present embodiment. Looking at the excitation profile in detail, the second set current that is higher than the _first set current I ₁ from the point b that is the deceleration start point of the forward movement of the carriage to the point c that is the deceleration end point of the return path movement. In addition to being I ₂ , the degree of deceleration from the constant speed movement in the forward path is also small, so that it is less susceptible to vibration.
[0028]
On the other hand, it is easy to be affected by vibration between the point c which is the time point when deceleration of the backward movement is completed and the point e which is the start of the next forward movement. Therefore, in the present embodiment, the current switching point is set to the point d which is between the points c and e, and a time of 2T or more is provided between the points c and d, and the points d and e A time of 2T or more is provided between the points.
[0029]
That is, immediately after the point c, vibration occurs due to deceleration at the time of reverse movement, but the set current value remains high and is sufficiently attenuated until reaching the point d. Further, although vibration occurs due to current switching immediately after the point d, the vibration is sufficiently attenuated to the point e when the set current value is low, and it is possible to prevent the forward acceleration operation from being adversely affected.
[0030]
Thereby, the vibration of the area from c point to e point can be attenuated, and step-out can be prevented. Further, since the vibration in the section from the point c to the point e can be attenuated, the first set current I ₁ in the forward movement can be set low, and the power consumption can be reduced.
[0031]
Next, a control flow in the control unit during the scan operation will be described. FIG. 4 is a flowchart for explaining the operation in the case of one-time scanning. First, the scan in step S101 (forward movement) to determine acceleration start or not, in the case of the acceleration start to the current applied to the motor in the first set current I _1.
[0032]
If the acceleration is not started, or after the first set current I ₁ is set, the process proceeds to step S102 to determine whether or not the scan deceleration is started. The current applied to the motor to the second set current I ₂ in the case of starting the scan deceleration.
[0033]
When the instruction is not to start decelerating, or is after the second set current I ₂ proceeds to step S103, the return is determined whether elapsed (backward movement) predetermined from the end time. After a predetermined time has elapsed from the end of the return, the current applied to the motor is set to the third set current I ₃ . Otherwise, the process returns to step S102.
[0034]
Next, the flow of control in the case of multiple scans will be described with reference to the flowcharts of FIGS. First, the scan in step S201 (forward movement) to determine acceleration start or not, in the case of the acceleration start to the current applied to the motor in the first set current I _1.
[0035]
If the acceleration is not started, or after the first set current I ₁ is set, the process proceeds to step S202 to determine whether or not the scan deceleration is started. The current applied to the motor to the second set current I ₂ in the case of starting the scan deceleration.
[0036]
If the deceleration is not started, or after the second set current I ₂ is set, the process proceeds to step S203, and it is determined whether or not it is the last scan. If it is not the last scan, the process proceeds to step S204, and it is determined whether or not a predetermined time has elapsed since the end of the return (return trip). After a predetermined time has elapsed from the end of the return, the current applied to the motor is set to the first set current I ₁ . Otherwise, the process returns to step S202.
[0037]
If it is determined in step S203 that the scan is the last scan, the process proceeds to step S205 in FIG. 6 to determine whether or not scan deceleration is started. The current applied to the motor to the second set current I ₂ in the case of starting the scan deceleration.
[0038]
Further, when deceleration is not started, or after the second set current I ₂ is set, the process proceeds to step S206, and it is determined whether or not a predetermined time has elapsed since the end of return (return movement). After a predetermined time has elapsed from the end of the return, the current applied to the motor is set to the third set current I ₃ and the process is terminated. Otherwise, the process returns to step S205.
[0039]
By such processing of the control unit, it is possible to realize current control that can suppress vibration of the carriage and reduce power consumption.
[0040]
【The invention's effect】
As described above, the present invention has the following effects. In other words, the vibration of the carriage can be suppressed by the current value switching control to the motor that drives the carriage, and it becomes possible to prevent high-definition image reading, particularly deterioration in image quality at the reading tip. In addition, since the vibration of the carriage can be suppressed at the current switching timing, it is not necessary to supply an unnecessary current to the motor, and the power consumption can be reduced. In addition, by suppressing carriage vibration, unnecessary waiting time of the carriage can be reduced, and reading speed can be increased.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an embodiment.
FIG. 2 is a diagram illustrating a carriage excitation profile 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 for explaining the operation in the case of one-time scanning.
FIG. 5 is a flowchart (No. 1) for explaining control in the case of multiple scans.
FIG. 6 is a flowchart (part 2) for explaining the control in the case of multiple scans.
[Explanation of symbols]
1 ... Motor, 2 ... Driver, 3 ... Control part

Claims (1)

In an image reading apparatus that reads an image of a document reflected through an optical system,
A carriage carrying the optical system and reciprocatingly driven by a motor;
Control means for controlling acceleration, constant speed, deceleration of the reciprocating operation of the carriage and controlling current application to the motor;
The control means sets the second current application to be applied to the motor during the backward operation to be larger than the first current applied to the motor during the forward operation of the carriage, and also applies the first current application and the second current. The switching time with application is set between the deceleration end time of the return path operation of the carriage and the acceleration start time of the forward path operation,
Further, when the carriage is continuously reciprocated, the current application to the motor after completion of the final return path operation is set to a third current lower than the first current. apparatus.

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