JP2003264993A - Motor control device and image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor control device that reduces vibration and noise of a stepping motor by applying an input current having an optimum waveform corresponding to a drive condition, and to provide an image reader using the device. <P>SOLUTION: The motor control device comprises constant current drive means (63, 84, and 85) that apply input currents having certain magnitudes to phases of the stepping motor 61 by chopping control; a damped waveform switching means (64) that switches low-speed attenuation and high-speed attenuation at prescribed timing during the attenuations corresponding to set voltages when the input current is damped by the chopping control; and predetermined voltage apply means (81, 82, 83 and 86) that apply the predetermined voltages to the damped waveform switching means. A set voltage corresponding to the drive condition of the stepping motor 61 is applied to the damped waveform switching means. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device and an image reading device.

[0002]

2. Description of the Related Art Since stepping motors have excellent rotational positioning accuracy, they have been widely used as a drive source for industrial equipment in recent years, and drive for moving scanning lines even in image reading devices such as image scanners and electronic copying devices. Many are used as motors for automobiles.

FIG. 2 is a schematic diagram showing an example of a stepping motor. Stepping motor 61 in the illustrated example
Is a two-phase stepping motor of A phase and B phase. When a predetermined input current is applied to the A phase and the B phase of the stepping motor 61, the rotor 611 rotates in the designated direction by the designated number of drive microsteps.

FIG. 3 shows A in microstep driving.
It is a figure which shows the waveform of the input current to a phase. The waveform of the input current is controlled by a sine wave voltage and step pulses input at predetermined intervals. The magnitude of the input current shifts from the previous step to the next step at the timing when the input step pulse rises. As shown in the figure, the waveform of the input current changes stepwise into a shape approximated by a sine wave, while the magnitude of the input current during one step is PWM (Puls
e Width Modulation) Constantly maintained by chopping control. The PWM chopping control turns on / off the input current switch according to the rising or falling timing of a pulse (hereinafter, that pulse is referred to as a “PWM pulse”) different from the step pulse for controlling the waveform of the input current. This is an operation in which the magnitude of the input current is kept constant by repeating the OFF state. When the switch is turned off in the PWM chopping control, the input current gradually attenuates. At this time, as a damping method, there are a low-speed attenuation that attenuates the input current at a low speed and a high-speed attenuation that attenuates at a high speed.

FIG. 4 (a) is a diagram showing the waveform of the input current and the PWM pulse due to the slow decay during one step, and FIG. 4 (b) is the waveform of the input current and the PWM pulse due to the fast decay during one step. It is a figure showing. As shown,
In the case of slow decay, the input current decays more slowly than in fast decay. Such decay rate is controlled by switching the current path during decay.

FIG. 5A is a circuit diagram showing the current path of the input current applied to the coil C of the A phase at the time of slow decay.
The circuit is formed as a bridge circuit by a power supply voltage V, a coil C, a plurality of transistors, a plurality of diodes D, a sense voltage converter SVC, and the like. When the switch is turned on, the transistors Q1 and Q4 are turned on, the transistors Q2 and Q3 are turned off, and the input current flows through the path 4 and is applied to the A-phase coil C. When the input current after switching off is attenuated at a low speed, the transistor Q1 is turned off, that is, only the transistor Q4 is turned on. When only the transistor Q4 is turned on, the current generated by the back electromotive force flows through the path 5 and the input current decays slowly. FIG. 5B is a circuit diagram showing a current path during high-speed decay. When the input current after switching off is rapidly attenuated, the transistors Q1 and Q4 are turned off, that is, all the transistors are turned off. When all the transistors are turned off, the current generated by the counter electromotive force flows through the path 6 and the input current to the A phase decays quickly.

When slow decay is used, the waveform when the input current decays from the upper step to the lower step (hereinafter,
The change in "attenuation waveform") becomes gradual, and the waveform of the input current can be approximated to a sine wave. However,
In the case of low-speed attenuation, if the step pulse input interval is short, there is a problem that the next step pulse is input before it is attenuated to the lower step and the attenuation cannot be done in time. If the attenuation of the input current is not in time, the balance of the magnetic force generated by each phase of the stepping motor will be lost, and the rotation of the stepping motor will not be smooth, and vibration and noise will occur. Therefore, complex attenuation is used in which high-speed attenuation and low-speed attenuation are switched at a specific timing during the attenuation. According to the composite attenuation, the attenuation waveform can be approximated to the optimum waveform by performing high-speed attenuation until a certain point after the switch is turned off and switching to low-speed attenuation after that.

[0008]

In the conventional composite attenuation, the switching timing is fixed because the time ratio of the low speed attenuation and the high speed attenuation during the switch-off time is determined according to a preset constant voltage. Has been done. Therefore, when the decay waveform of the input current is fixed and the input interval of the step pulse changes, it is not always possible to apply the input current having the optimum waveform in all the input intervals.

FIG. 6 is a diagram schematically showing an attenuation waveform when the input current falls from the upper step to the lower step for a plurality of step pulse input intervals. The solid line in the figure represents the waveform of the input current. In addition, T1 and T2 in the figure represent the difference between the input intervals of the step pulses. Further, in FIG. 6, the change in the waveform when the size is continuously maintained by the PWM chopping control during one step is omitted. FIG. 6B shows an optimum attenuation waveform in which the timing when the next step pulse rises coincides with the timing when the magnitude of the input current decreases to the lower step. When the decay waveform of the input current is fixed, when the input interval of the step pulse is long as shown in FIG. 6 (a), the magnitude of the input current falls to a lower step before the next step pulse rises. On the other hand, when the step pulse input interval is short, as shown in FIG. 6C, the next step pulse rises before the magnitude of the input current falls to the lower step. If the decay waveform of the input current is fixed in this way, the waveform is not optimal depending on the input interval of the step pulse, and the timing at which the magnitude of the input current drops to the lower step deviates from the design timing. It will be.

For example, when the scanning line of the image reading apparatus is moved by the stepping motor, the step pulse input interval is changed according to the sub-scanning resolution to change the rotation speed of the stepping motor. Does not have an optimal waveform. When the waveform of the input current is not optimum, noise is generated due to the vibration of the stepping motor, and the position of the scanning line is displaced due to the vibration, so that the image cannot be read accurately.

The present invention has been made in view of the above problems, and its object is to provide a motor control device for applying an input current having an optimum waveform according to a driving condition to reduce vibration and noise of a stepping motor. An object is to provide an image reading device using the same.

[0012]

A motor control device according to the present invention comprises constant current drive means for applying a constant magnitude input current to each phase of a stepping motor by chopping control, and damping of the input current by chopping control. In this case, a damping waveform switching means for switching the low speed damping and the fast damping at a predetermined timing in the middle of damping according to the set voltage, and a set voltage applying means for applying a set voltage according to the driving condition of the stepping motor to the decay waveform switching means. And are provided. According to such a motor control device, when the input current is attenuated by the chopping control, it is possible to switch between low-speed attenuation that attenuates the input current at a low speed and high-speed attenuation that attenuates the input current at a predetermined timing during the attenuation according to the set voltage. By changing the set voltage according to the driving condition of the stepping motor, the waveform of the input current applied to the stepping motor can be made an optimum waveform according to the driving condition of the stepping motor. This can reduce the vibration and noise of the stepping motor.

The image reading apparatus according to the present invention is
A linear image sensor that outputs an electrical signal that correlates with the density of an optical image, an optical system that forms an optical image on a scanning line on the linear image sensor, a stepping motor that moves the scanning line, and a stepping motor are controlled. The motor control device according to claim 1 is provided. According to such an image reading apparatus, vibration and noise of the stepping motor can be reduced by applying a set voltage for applying an input current having an optimum waveform for each sub-scanning resolution, and the position of the scanning line can be reduced. The image can be read accurately without shifting.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 7 is a schematic diagram showing an image scanner 1 as an image reading device according to an embodiment of the present invention. The image scanner 1 is a so-called flat bed type including a document table 11. In the following description, the configuration will be described by taking the A phase as an example, but it is assumed that the B phase has the same configuration and the same control is performed with a 1/4 cycle difference from the A phase.

The document table 11 is formed of a transparent plate such as a generally rectangular glass plate, and a document M such as a photograph or a document is placed on the plate surface 12 thereof. The carriage 40 is accommodated in the main body so as to be capable of reciprocating in parallel with the plate surface 12 of the document table 11. The carriage 40 includes the optical system 20 and the linear image sensor 3.
0 is mounted and slidably locked to a guide shaft or the like parallel to the plate surface 12 of the document table 11. The longitudinal axis of the guide shaft extends in the X direction of FIG. 7, and the carriage 40 is pulled by, for example, the belt 65 to move the optical system 20 and the linear image sensor 30 to the X direction of FIG.
Carry in the direction.

The optical system 20 comprises a light source 21, a mirror 22 and a lens 23. The light source 21 is composed of a tube lighting device such as a fluorescent tube lamp, and is mounted on the carriage 40 with its longitudinal axis extending parallel to the longitudinal axis of the linear image sensor 30. The mirror 22 and the lens 23 form an optical path for forming an optical image on the scanning line on the linear image sensor 30 as shown by a broken line in FIG.

The linear image sensor 30 is mounted on the carriage 40 in a posture in which a plurality of light receiving elements such as photodiodes are arranged linearly in the direction perpendicular to the paper surface of FIG. The linear image sensor 30 scans the optical image on the scanning line formed by the optical system 20, and outputs an electric signal that correlates with the density of the optical image. The linear image sensor 30 accumulates electric charges obtained by photoelectrically converting light in a predetermined wavelength region such as visible light, infrared light, and ultraviolet light for a certain period of time, and outputs an electric signal according to the amount of light received by each light receiving element to a CCD. (Charge C
Oupled Device), MOS transistor Transistor, etc. are used for output.

FIG. 1 is a block diagram showing an image scanner 1. The main scanning drive unit 50 is mounted on a substrate fixed to the carriage 40. The main scanning drive unit 50 is a drive circuit that outputs a drive pulse necessary for driving the linear image sensor 30 to the linear image sensor 30. The main scanning drive section 50 is composed of, for example, a synchronization signal generator, a driving timing generator, and the like.

The sub-scanning drive unit 60 is composed of a belt 65 locked to the carriage 40, a stepping motor 61 for rotating the belt 65, a motor drive unit 62, a gear train, and the like, and is housed in the main body. When the sub-scanning drive unit 60 pulls the carriage 40 with the belt 65, the scanning line extending in the direction perpendicular to the paper surface of FIG. 7 moves in the X direction perpendicular thereto, so that a two-dimensional image can be scanned.

The motor drive unit 62 is a motor current control unit 6
3 and a decay mode control unit 64. The motor current controller 63 is a circuit that drives the stepping motor 61 in micro steps. The motor current controller 63 has the same structure as the conventional circuit shown in FIG. A sine wave voltage is applied from the D / A converter 85 to the motor current control unit 63. When the step pulse is input from the pulse generator 84, the motor current control unit 63 sets the magnitude of the input current applied to each phase of the stepping motor 61 according to the magnitude of the sine wave voltage when the step pulse rises. Change. As a result, the step shifts from the previous step to the next step, and the input current is gradually changed into a shape approximated by a sine wave. Motor current controller 63
During one step, PWM chopping control is performed based on a PWM pulse output from a PWM pulse generator (not shown), and the magnitude of the input current is kept constant. When the input current is turned on / off by the PWM chopping control, for example, when the phase A is switched on, the transistors Q1 and Q4 are turned on and the transistors Q2 and Q3 are turned off. When the phase A is switched off and rapidly attenuated, the transistors Q1 and Q4 are turned off, that is, the transistors Q1, Q2, Q3 and Q4 are all turned off.

The constant current drive means described in the claims is a motor current control section 63, a pulse generator 84 and a D /
It corresponds to the A converter 85. Decay mode control unit 64
Is a circuit for switching between low speed attenuation and high speed attenuation at a predetermined timing during the attenuation when the switch is turned off and the input current is attenuated during the PWM chopping control.
The decay mode control unit 64 can turn on the transistor Q4 of the motor current control unit 63 in the case of the A phase, for example. When the switch is turned off by the motor current control unit 63, the decay mode control unit 64 sets D
The transistor Q4 is turned on at a timing corresponding to the set voltage applied from the A / A converter 86 to switch the current path and switch from high-speed attenuation to low-speed attenuation.

The decay waveform switching means described in the claims corresponds to the decay mode control section 64. An AFE (Analog Front End) unit 71 performs analog signal processing such as amplification and noise reduction processing on the analog output signal output from the linear image sensor 30 and outputs the output signal.

The A / D converter 72 quantizes the analog output signal output from the AFE unit 71 into a digital representation output signal having a predetermined bit length and outputs the quantized output signal. Signal processing unit 7
3 produces image data by performing processing such as gamma correction, defective pixel interpolation by a pixel interpolation method, white balance correction, and image signal sharpening on the output signal output from the AFE unit 71. The above-mentioned various processes performed by the signal processing unit 73 may be replaced with the processes by the computer program executed by the control unit 80.

The control unit 80 includes a CPU 81, a ROM 82,
A RAM 83, a pulse generator 84, a D / A converter 85, and a D / A converter 86 are provided and are connected to the main scanning drive unit 50, the sub-scanning drive unit 60, the signal processing unit 73, and the like. CPU
Reference numeral 81 executes a computer program stored in the ROM 82 to control each part of the image scanner 1, and determines the driving condition of the stepping motor 61 to control the waveform of the input current to the stepping motor 61 to be optimum. The ROM 82 is a memory that stores computer programs executed by the CPU 81, various data, and the like, and the RAM 83 is a memory that temporarily stores programs and various data.

The pulse generator 84 outputs a step pulse having an input interval corresponding to the pulse generation signal output from the CPU 81 to the motor current controller 63. D / A converter 8
Reference numeral 5 is a so-called sine wave inverter, which applies a sine wave voltage having a cycle corresponding to the waveform control signal output from the CPU 81 to the motor current control unit 63.

The D / A converter 86 is a circuit for converting the set voltage control signal output from the CPU 81 into a set voltage correlated with the set voltage control signal and applying the set voltage to the decay mode control section 64.

The set voltage applying means described in the claims corresponds to the CPU 81, the ROM 82, the RAM 83 and the D / A converter 86. The configuration of the image scanner 1 has been described above. Hereinafter, a process in which the CPU 81 determines the driving condition of the stepping motor 61 and controls so that the waveform of the input current to the stepping motor 61 is optimized will be described. In the following, the stepping motor 6
An example will be described in which 1 is always driven with the same number of microsteps.

The CPU 81 determines the driving condition of the stepping motor 61 according to the operating condition of the image scanner 1, and outputs a set voltage control signal corresponding to the determined driving condition D.
And outputs to the / A converter 86. For example, image scanner 1
When the image is read at a resolution close to the low resolution, the stepping motor 61 is rotated at a high speed by shortening the cycle of the waveform of the input current in order to move the scanning line at a high speed. Since the same microstep number is driven in a short cycle, the input interval of each step pulse becomes short, so that the "short input interval" is the stepping motor 61.
Driving conditions. The CPU 81 has a large time ratio of high-speed attenuation so that the attenuation is in time for a short input interval, and performs low-speed attenuation and high-speed attenuation at a timing corresponding to the time ratio at which the timing at which the input current is completely attenuated and the timing at which the next step pulse rises match. And outputs a set voltage control signal for switching to the D / A converter 86. Further, for example, in the case of reading a document with a resolution close to high resolution, the step pulse input interval is lengthened in order to drive the same number of microsteps in a long cycle. Therefore, the "long input interval" is the stepping motor 61.
Under the driving condition of, the CPU 81 has a large low-speed decay time ratio so that the magnitude of the input current does not fall to the lower step before the next step pulse rises in a long input interval, and the timing at which the input current decays completely The D / A converter 8 outputs the set voltage control signal for switching between the low speed decay and the high speed decay at the timing corresponding to the time ratio at which the step pulse rise timing coincides.
Output to 6. On the other hand, the CPU 81 outputs to the D / A converter 85 a waveform control signal for applying a sine wave voltage having a cycle corresponding to the rotation speed of the stepping motor 61 to the motor drive unit 62. The CPU 81 also outputs to the pulse generator 84 a pulse generation signal for generating step pulses with an input interval corresponding to the rotation speed of the stepping motor 61 and the number of microsteps.

In the above description, the number of driving microsteps is always the same. However, when the number of driving microsteps is switched according to the operating condition of the image scanner 1, the rotation speed of the stepping motor 61 and the number of driving microsteps after switching. The driving condition is determined according to the number of driving micro steps.

The process in which the CPU 81 determines the driving condition and controls so that the waveform of the input current to the stepping motor 61 is optimized has been described above. The operation of the image scanner 1 of this embodiment will be described below.

FIG. 8 is a flow chart showing the flow of processing for reading an original by the image scanner 1. After placing the original on the original table 11, the user designates the resolution and issues an instruction to read the original from an image processing apparatus such as a personal computer connected to the image scanner 1. In response to the command, the image scanner 1 operates as follows. (1) Based on the designated resolution, the driving condition of the stepping motor 61 and the optimum time ratio of the high speed damping and the low speed damping for the driving condition are determined (S200). (2) The light source 21 is turned on, the stepping motor 61 is driven under the determined driving condition, and the carriage 40 is moved to a predetermined reading position. The stepping motor 61
During driving, the attenuation of the input current is controlled by the composite attenuation based on the determined time ratio. As a result, an optical image on the scanning line of the document placed on the document table 11 is formed by the optical system 20 on the light receiving element of the linear image sensor 30.
(S205). (3) The main scanning drive unit 50 inputs a drive pulse such as a shift pulse to the linear image sensor 30 in a predetermined sequence. As a result, an amount of electric charge (signal electric charge) that is correlated with the density of the optical image is accumulated in the linear image sensor 30,
The accumulated charge is AFE as an electric signal by CCD or the like.
It is output to the unit 71. The AFE unit 71 performs a predetermined analog signal processing on the electric signal and outputs it to the A / D converter 72,
The A / D converter 72 performs quantization and outputs it to the signal processing unit 73 (S210). (4) The signal processing unit 73 subjects the output signal output from the A / D converter 72 to predetermined processing, and transfers the image data created as a result to the image processing apparatus (S215). (5) While driving the stepping motor under the determined driving condition, the above (2) to (4) are repeatedly executed until the reading is completed (S220).

As described above, the image data representing the optical density information of the optical image of the original is acquired by the image processing apparatus.
The effects of the motor control device of this embodiment will be described below.

The motor control device of the present embodiment has a D / A converter 86 for applying a set voltage to the decay mode control section 64.
And a CPU 81 for changing the set voltage applied to the decay mode control unit 64 by the D / A converter 86, a ROM
And a RAM 83. As a result, during damping, low-speed damping and high-speed damping can be switched at a timing according to the driving condition, and the input current applied to each phase of the stepping motor can have an optimum waveform for each driving condition. FIG. 9 is a diagram schematically showing a part of the input current waveform by the motor control device of this embodiment for a plurality of step pulse input intervals. As shown in the figure, according to the motor control device of the present embodiment, at any input interval, the timing when the step pulse rises and the timing when the magnitude of the input current falls to the lower step become the optimum waveform, and the stepping motor vibration or Noise is reduced.

Further, the image scanner 1 of this embodiment is
A set voltage to which an input current having a waveform optimal for each resolution is applied can be applied to the motor drive unit 62. For example, when an image is read at a resolution close to the high resolution, a set voltage control signal for increasing the low speed decay ratio is applied to the motor drive unit 62 so that the magnitude of the input current does not fall to the lower step before the step pulse rises. can do. In this way, the waveform of the input current can be optimized at any resolution, and therefore the image scanner 1 of the present embodiment can accurately read an image at any resolution.

Although the present embodiment has been described by taking the two-phase stepping motor as an example, the stepping motor may be a three-phase stepping motor or a five-phase stepping motor.

In the present embodiment, the flatbed type image scanner has been described as an example of the image reading apparatus. However, the present invention may be applied to a sheet feed type image scanner, or an electronic copying apparatus or a facsimile. The invention may be applied.

Further, in this embodiment, the magnitude of the input current is kept constant by the PWM chopping control, but when the magnitude of the input current reaches the set value, the switch is turned off, and when a predetermined time elapses. Alternatively, the size of the input current may be maintained constant by turning on the switch when the voltage has dropped to a predetermined level.

[Brief description of drawings]

FIG. 1 is a block diagram showing an image scanner as an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an example of a stepping motor.

FIG. 3 is a diagram showing an example of a waveform of an input current.

FIG. 4 (a) is a diagram showing a waveform of an input current due to slow decay, and FIG. 4 (b) is a diagram showing a waveform of an input current due to fast decay. FIG. 4C is a diagram showing the waveform of the input current due to the composite attenuation.

FIG. 5 (a) is a circuit diagram showing a current path during low-speed decay, and FIG. 5 (b) is a circuit diagram showing a current path during high-speed decay.

6 (a), (b) and (c) are diagrams schematically showing a part of a conventional input current waveform for a plurality of step pulse input intervals.

FIG. 7 is a schematic diagram showing an image scanner as an image reading apparatus according to an embodiment of the present invention.

FIG. 8 is a flowchart showing a flow of processing for reading an original by an image scanner as an image reading apparatus according to an embodiment of the present invention.

9 (a), (b) and (c) are diagrams schematically showing a part of an input current waveform by the motor control device of the present embodiment for a plurality of step pulse input intervals.

[Explanation of symbols]

1 image scanner 11 Platen 12 board 20 Optical system 21 light source 22 mirror 23 lenses 30 linear image sensor 40 carriage 50 Main scanning drive 60 Sub-scan drive unit 61 Stepping motor 62 Motor drive unit 63 Motor current controller 64 Decay mode controller 65 belt 71 AFE section 72 A / D converter 73 Signal processing unit 80 Control unit 611 rotor

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Claims (2)

[Claims] 1. A constant current drive means for applying a constant amount of input current to each phase of a stepping motor by chopping control, and a low-speed decay and a high-speed decay set voltage when the input current is attenuated by the chopping control. Damping voltage switching means for switching at a predetermined timing during damping according to, setting voltage applying means for applying a setting voltage according to the driving condition of the stepping motor to the damping waveform switching means,
A motor control device comprising: 2. A linear image sensor that outputs an electric signal that correlates with the density of an optical image, an optical system that forms an optical image on a scanning line on the linear image sensor, and a stepping motor that moves the scanning line. An image reading apparatus, comprising: the motor control apparatus according to claim 1, which controls the stepping motor.