JPH09261996A - Image reading apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress resonance of optical parts to improve quality of the image obtained by providing a control means for changing the number of divisions of microsteps so that the drive frequency of a stepping motor does not match the resonance frequency of optical members and a motor drive means. SOLUTION: A drive and energizing circuit of a stepping motor 9 is provided with a constant current motor drive element 11 comprising a chopping circuit to determine a drive current and a CPU 12 for sending thereto an activation pattern and a current setting signal. Moreover, the number of divisions is changed so that the drive pulse frequency of the stepping motor 9 does not match the resonance frequency of the optical members. Thereby, since resonance of optical member is not generated, influence of vibration on the image read by the apparatus can be reduced and image quality can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device for driving an optical traveling body by a stepping motor.

[0002]

2. Description of the Related Art (1) In an image reading device that reads an image by driving an optical scanning device with a stepping motor, torque fluctuations occur at every driving pulse of the stepping motor, and this vibration affects the optical scanning device. This will affect the quality of the read image.

In order to avoid this, in the conventional image reading apparatus, the driving method of the stepping motor is set to 1-2 phase excitation or microstepping to increase the frequency of the driving pulse and reduce the driving step per pulse. We have reduced the torque fluctuations and the torque fluctuations generated by the motor. For this reason, as the drive method of the motor, a method in which the frequency of the drive pulse is highest within the range permitted by hardware and software is selected.

(2) Further, in the image reading apparatus of the above system, when the rotation speed of the motor changes due to zooming or the like, due to hardware or software restrictions, the drive step is more finely divided at low speed rotation. At high speed, the drive step angle may be rougher than at low speed.

Generally, in an image reading apparatus, an operation called homing for moving the optical scanning apparatus to a home position is performed when the power is turned on. However, at the time of this operation, the operation is performed at a low speed, and for the purpose of noise reduction, it is further divided. In many cases, the motor is rotated at a reduced drive step angle.

[0006]

In the above method (1), the vibration from the motor is reduced by reducing the driving step of the motor. However, in this method, the image reading with variable reading speed is performed. In the case of the device, since the frequency of the drive pulse of the motor changes, at a certain reading speed, the resonance frequency of the mirror or the like used in the optical scanning device may match the drive pulse frequency of the motor. Even if the vibration is small, a phenomenon occurs in which the quality of the read image is not so improved despite the fact that the resonance of the mirror is added to the vibration and the vibration level from the motor alone is reduced.

In the case of (1), a part of the motor stop position at the subdivided drive step angle has a portion that does not coincide with the motor stop position at the coarse drive step angle.
If it is driven by a subdivided driving method and stopped at this non-matching point, the next coarse driving method will start the driving, the moment it moves from the non-matching point to the matching point, and the driving is started. .

By moving from this stop position to the excitation point,
A predetermined position shift determined by the homing operation occurs. This shift may occur each time the excitation is switched.

The present invention has been made in view of such a background, and improves the quality of a read image by suppressing the resonance of an optical component such as a mirror, and also performs optical scanning even when the excitation method is switched. An object of the present invention is to provide an image reading apparatus in which the initial position of the apparatus does not shift.

[0010]

In order to achieve this object, a first aspect of the present invention is an image reading apparatus for reading an original image while driving an optical scanning device by a stepping motor, wherein the driving frequency of the stepping motor is an optical member. Is provided with a control means and a motor drive means for changing the number of divisions of the microstep so as not to match the resonance frequency.

A second aspect of the invention is an image reading apparatus in which an optical scanning device is driven by a stepping motor to change the number of divisions of microsteps according to the driving speed. It is characterized in that it is provided with a control means and a motor drive means for performing the microstep drive with the smallest division number among the microsteps used.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 is a front sectional view of the image reading device, FIG. 2 is a perspective view showing a drive system of the image reading device, and FIG. 3 is a control block diagram of a stepping motor.

As shown in FIGS. 1 and 2, this image reading apparatus has a contact glass 2 on which a document to be read is placed, a light source 3 for illuminating the document surface, and a first light source for reflecting the reflected light from the document. Mirror 4, second mirror 3 and 5, which guide the light reflected by the first mirror 4, first traveling body 7 that holds the light source 3 and the first mirror 4, second and third mirrors 5 and 6 The second traveling body 8, the stepping motor 9 for driving the first and second traveling bodies 7, 8 and the belt 10 for transmitting the driving force of the stepping motor 9 to the first and second traveling bodies 7, 8. .

Further, as shown in FIG. 3, the driving and exciting circuit of the stepping motor 9 has a constant current motor driving element 11 internally provided with a chopping circuit for determining the driving current of the motor 9, and a constant current motor driving element 11. And a CPU 12 for generating an excitation pattern and a current setting signal.

The constant current motor drive element 11 is provided with an analog port for inputting a current setting signal, and a CPU
The drive current to the motor 9 is changed in proportion to the analog value output from the 12 D / A converter.

Further, the constant current motor drive element 11 is provided with a terminal for inputting an excitation pattern, and the CPU 12
The motor 9 is rotated by drawing a current from each phase of the motor 9 according to the excitation pattern output by the motor.

FIG. 4 is an output waveform diagram of the CPU 12 during W1-2 phase excitation. The excitation pattern shown in FIG. 9A and the current setting signal shown in FIG. 7B are input from the CPU 12 to the constant current motor drive element 11. Next, the operation of the first embodiment will be described with reference to FIGS.

By way of example, one of the optical components of an optical scanning device
When the resonance frequency of one mirror is 6.4 KHz, if the driving step of the driving two-phase stepping motor 9 is divided into ⅛ of the basic step for driving (2 W
(1-2 phase excitation), when the rotation speed of the motor 9 is 4 rps,
The drive pulse frequency to the motor 9 becomes 6.4 KHz.
At this time, the vibration generated by the motor 9 at each driving step reaches the mirror through the driving belt and causes the mirror to resonate.

In order to reduce this, it is necessary to change the drive frequency of the motor 9, but normally, the frequency of the drive pulse and the subdivision of the drive step are hard as described above.
Since there is an upper limit due to a soft constraint, it is often difficult to increase the frequency of the driving pulse by adopting a driving method with a larger division number than 4W1-2 phase.

Therefore, in the first embodiment, the driving step of the two-phase stepping motor is reduced to 1 / th of the basic step.
Change to 6 and drive pulse frequency at 4 rps to 4.8K
Change to Hz. Since the driving step of the motor 9 becomes coarse, the vibration generated by the motor 9 for each driving step increases, but since the resonance of the mirror does not occur, the influence of the vibration on the image read by the entire apparatus should be small. It is possible to improve the image quality.

The same control is performed for the resonance frequency of the optical components other than the mirror, and the motor 9 is driven in the drive steps that are as finely divided as possible in the drive frequency range other than the resonance frequency of the optical components. And improve the image quality.

Next, the operation of the second embodiment will be described with reference to FIGS. Here, FIG. 5 is an explanatory diagram showing a vector locus. The image reading device includes a home position sensor (see FIG. 1) that determines the initial position of the optical scanning device.
Is schematically shown by reference numeral 13 in FIG.
When the power is turned on, the optical scanning device is driven at a low speed, the driving of the motor 9 is stopped when the home position sensor 13 is turned on, and the position is used as the initial position and used as the origin of the subsequent reading operation.

For example, as a driving method of the motor 9, 1-
When using from 2-phase excitation to 2W1-2-phase excitation, 1-
In the two-phase excitation, there are twice as many stop positions as in the basic step, and in the 2W1-2-phase excitation, there are eight stop positions as compared with the basic step.

Therefore, the homing operation is performed by 2W1-2 phase excitation, and when stopped, the motor 9 is moved to the "3" position in FIG.
Then, when the driving is started by the 1-2 phase excitation next, the motor 9 is instantaneously moved to the position "1" or "5" in FIG. 5, and the normal rotation of the motor 9 is started from there. Therefore, a maximum deviation of 1/4 of the basic step occurs,
This shift may occur each time the excitation method is switched from the subdivided one to the coarse one. As described above, when this deviation is accumulated, the stop position of the motor 9 deviates from the initial position, the home position sensor 13 does not turn on at a predetermined timing, and an error occurs.

In the control method of the present embodiment, by driving and stopping by the excitation method of the coarsest number of divisions, which uses part or all of the homing operation for determining the initial position, the excitation method is common to all excitation methods. The initial position is determined by the motor stop position of.

As an example, in the case where 1-2 phase excitation to 2W1-2 phase excitation are used as the driving method, the homing operation is performed by the driving method 1-2 phase excitation having the coarsest driving step. At this time, the motor 9 is set to “1”, “5”,
It is excited at the position "9" and stops at any of the positions "1", "5", and "9" even after the homing operation is completed.

The motor drive after the homing operation is an integral multiple (2W1-2) of the number of pulses required to move the motor 9 from the origin to the origin when driven by the excitation method.
An integer multiple of 8 pulses for phase excitation, 4 for W1-2 phase excitation
(Integral multiple of pulse, 1-2 multiple excitation in pulse multiple of 2)
The motor 9 can always be stopped at any one of the stop positions "1", "5", and "9" common to all the excitation methods by being driven by. Therefore, even if the excitation method is switched, the initial position is not displaced.

In addition to the above, a part of the homing operation is driven by the 1-2 phase excitation, and thereafter, the excitation method having a smaller driving step is switched to.
It is also possible to manage the number of pulses so that the motor 9 is stopped at any of the "1", "5", and "9" positions.

[0029]

According to the invention described in claim 1, in the rotation range in which the frequency of the drive pulse to the motor matches or approximates the resonance frequency of the optical member, the drive system of the motor is changed to drive the motor. Since the resonance of the optical member is suppressed by changing the pulse frequency, the quality of the read image information can be improved.

According to the second aspect of the present invention, part or all of the homing operation is performed by the driving method having the largest driving step among the excitation methods used for driving the motor.
By determining the initial position of the optical scanning device at the stop position common to all excitation methods, it is possible to prevent the initial position from shifting even if the excitation method is switched.

[Brief description of drawings]

FIG. 1 is a front sectional view of an image reading apparatus.

FIG. 2 is a perspective view showing a drive system of the image reading apparatus.

FIG. 3 is a control block diagram of a stepping motor.

FIG. 4 is an output waveform diagram of the CPU during W1-2 phase excitation.

FIG. 5 is an explanatory diagram showing a vector locus.

[Explanation of symbols]

 3 Light source (optical member) 4, 5, 6 Mirror (optical member) 7, 8 Traveling body (optical scanning device) 9 Stepping motor 11 Constant current motor drive element (motor drive means) 12 CPU (control means)

Claims (2)

[Claims] 1. An image reading device for reading an original image while driving an optical scanning device by a stepping motor, and a control means for changing a division number of microsteps so that a driving frequency of the stepping motor does not match a resonance frequency of an optical member. An image reading apparatus comprising a motor drive means. 2. An image reading device in which an optical scanning device is driven by a stepping motor and the number of divisions of microsteps is changed according to a driving speed, in a homing operation at power-on among microsteps used at image reading. An image reading apparatus comprising a control unit and a motor driving unit for performing microstep driving with the smallest number of divisions.