JP2005117833A - Stepping motor drive and control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor drive and control circuit wherein a reference voltage generating portion is inexpensively constructed using a pulse width modulation circuit and a smoothing circuit without use of an expensive D/A conversion circuit. <P>SOLUTION: The reference voltage generation circuit portion comprises the pulse width modulation circuit that outputs voltage pulses with the duty ratio varied; the smoothing circuit that smoothes the voltage pulses outputted from the pulse width modulation circuit and outputs them as reference voltage; an A/D conversion circuit that takes in the reference voltage outputted from the smoothing circuit, converts it into a digital signal, and outputs a feedback control signal; and a control processing means for which a reference voltage to be taken as a control objective is preset, and which outputs the feedback signal from the A/D conversion circuit and controls the pulse width modulation circuit by feedback so that its output is matched with the value of control objective. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a stepping motor drive circuit that controls torque according to a load by controlling a winding current of a stepping motor while referring to a reference voltage, and more particularly, a configuration of a reference voltage generation circuit unit that generates the reference voltage It is about.

In printers and facsimile machines, the torque required for the stepping motor that drives the transport mechanism changes according to the amount and quality of the recording paper transported. In order to cope with this situation, these stepping motor drive circuits adjust the reference voltage that defines the torque of the motor by changing it in multiple steps, thereby preventing the motor from stepping out and achieving optimum conveyance accuracy, power saving, Low noise is realized.
Conventionally, as such a motor drive circuit, a digital reference value from a CPU is converted into an analog reference voltage by a D / A converter to generate the reference voltage. However, the expensive D / A converter is continuously occupied only for this purpose, and there is a problem in cost.
Further, as a technique for controlling the torque of a stepping motor, the following patent document compares a detection voltage corresponding to a winding current with a reference voltage Vref by a constant current chopper drive circuit, and based on the comparison result, a pulse The width control unit has been proposed to adjust the winding current, but the reference voltage has a configuration using a D / A converter and a voltage dividing resistor circuit, and no special contrivance has been made.
JP-A-5-344792

  The present invention provides a relatively inexpensive and simple motor drive circuit that can replace a conventional stepping motor drive circuit based on a reference voltage generation method using a D / A converter, which is a cause of high costs. With the goal.

  In order to solve the above objects and problems, a stepping motor drive for controlling the torque of a motor by controlling a winding current with reference to a reference voltage output from a reference voltage generation circuit unit according to claim 1 of the present invention. In the circuit, the reference voltage generation circuit unit outputs a pulse width modulation circuit that outputs a voltage pulse with a variable duty ratio, and a smoothing that smoothes the voltage pulse output from the pulse width modulation circuit and outputs the pulse as a reference voltage. A circuit, an A / D conversion circuit that takes in the reference voltage output from the smoothing circuit, converts it into a digital signal and outputs a feedback control signal, and a reference voltage to be a control target are set in advance. The feedback signal from the A / D converter circuit is compared with the control target value, and the feedback control is performed so that the pulse width modulation circuit matches the control target value. Control process and means are configured to.

Furthermore, in the stepping motor drive circuit according to claim 2, the smoothing circuit and the A / D conversion circuit are connected by an analog switch, and the analog switch is a reference voltage adjustment signal generated at a predetermined timing. When the signal is received, the pulse width modulation circuit is feedback-corrected.
According to a third aspect of the present invention, in the first aspect, the smoothing circuit is formed of a low-pass filter circuit including a resistor and a capacitor, and a buffer circuit.

  In the stepping motor drive circuit proposed in claims 1 to 3 of the present invention, a reference circuit is obtained by configuring a feedback circuit including a pulse width modulation circuit, a smoothing circuit, and an A / D conversion circuit. That is, as compared with a motor drive control circuit using a conventional D / A converter, an expensive D / A converter is not required, so that it can be configured at a lower cost.

  In addition, since the reference voltage error caused by voltage pulse duty and frequency variations in the pulse width modulation circuit, offset of the smoothing circuit, etc. can be corrected by feedback control, the stepping motor rotates properly in the device. The apparatus does not cause problems such as step-out. Such correction using feedback control is particularly effective when capacitors with large variations are used in the smoothing circuit.

  Also, the control processing means can set a plurality of control targets accordingly, and the reference voltage output according to the set control target value can be corrected by feedback control, so that a plurality of types of reference voltages for multi-stage torque control Can be generated without variation.

  Further, according to the second aspect of the present invention, by controlling the analog switch, the feedback correction can be executed immediately after the stepping motor drive circuit is turned on or at a predetermined cycle after the power is turned on. The / D conversion circuit can be effectively used for other processing.

  The stepping motor drive circuit according to the present invention is mainly used for drive control of a stepping motor that operates a mechanism such as a printer or a facsimile machine. Of course, the scope of the present invention is not limited by the application.

  Embodiments of the present invention will be described below.

An embodiment of a stepping motor driving circuit according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a stepping motor drive circuit 1A according to an embodiment and a stepping motor 2 that is driven and controlled by the stepping motor drive circuit 1A.
The stepping motor drive circuit 1 refers to the reference voltage Vref output from the reference voltage generation circuit unit 12, controls the winding current, and generates the motor drive circuit unit 11 for torque control of the motor and the reference voltage Vref. And a reference voltage generation circuit unit 12.

  The reference voltage generation circuit unit 12 includes a pulse width modulation circuit (hereinafter referred to as a PWM circuit) 12a that outputs a voltage pulse with a variable duty ratio, a smoothing circuit 12b that smoothes the voltage pulse and outputs it as a reference voltage Vref, An A / D conversion circuit 12c that takes in the reference voltage Vref output from the smoothing circuit 12b, converts it into a digital signal and outputs a feedback control signal, and a reference voltage Vref to be a control target are set in advance. A control processing means (hereinafter referred to as CPU) 12d that compares the feedback signal from the / D conversion circuit 12c with the control target value to control the PWM circuit 12a so as to match the control target value, and a reference output from the smoothing circuit 12b In order to capture the voltage Vf as a feedback signal into the A / D conversion circuit 12c, a signal processing unit (not shown) is used as a reference. Receiving a voltage adjustment signal, and a closed analog switch SW.

  The CPU 12d controls the PWM circuit 12a according to software stored in a memory (not shown). A digital value for the reference voltage Vref output from the A / D conversion circuit 12c is set in advance and held in the memory. The reference voltage Vref is lowered if the digital value is larger than the target value, and the reference voltage Vref is raised if the digital value for the reference voltage Vref is smaller than the target value. As described above, the PWM circuit 12a is feedback-controlled. As a result, errors in the reference voltage Vref caused by variations in duty and frequency of voltage pulses in the PWM circuit 12a, offsets in the smoothing circuit 12b, and the like are corrected.

  FIG. 2 is a waveform diagram for explaining voltage pulses generated by the PWM circuit. The horizontal axis indicates time, and the vertical axis indicates the voltage amplitude of the voltage pulse. Here, the waveform of the graph of (a) is a waveform of a voltage pulse corresponding to the high voltage reference voltage Vref, and the waveform of the graph of (b) is a waveform of the voltage pulse corresponding to the low voltage reference voltage Vref. It is. This voltage pulse is smoothed by the smoothing circuit 12b, and the voltage is averaged by the duty ratio.

  FIG. 3 is a block diagram showing the configuration of the smoothing circuit. In the figure, the resistor R and the capacitor C form a low-pass filter F, and the voltage pulse is smoothed by the low-pass filter F as described above. For this purpose, the time constant of the low-pass filter F is used. Rather, the period of the voltage pulse needs to be sufficiently small. The output of the low-pass filter F is converted to a low impedance by the buffer circuit B to be a reference voltage Vref, which is sent to the motor drive circuit unit 11 and the A / D conversion circuit 12c3. The buffer circuit B may be formed of, for example, an operational amplifier or the like, and may be configured to perform operational amplification as necessary.

Further, in the stepping motor drive circuit 1A according to the present invention, the PWM circuit 12a is controlled by software processing by the CPU 12d to generate voltage pulses with a predetermined duty ratio, so that only a different reference voltage Vref can be obtained by changing the software. Can be easily generated. Thereby, the torque of the stepping motor 2 that is driven and controlled can be made variable. Moreover, since it is not necessary to provide an expensive D / A converter, it is advantageous in terms of cost.
Next, another embodiment of the stepping motor driving circuit according to the present invention will be described with reference to FIG. The stepping motor drive circuit 1B has substantially the same configuration as the above-described stepping motor drive circuit 1A, but is provided with a time measuring timer 14.

  Therefore, the same components as those in the stepping motor drive circuit 1A are denoted by the same reference numerals, and the description thereof is omitted. The timekeeping timer 14 measures a predetermined time, for example, one day, and notifies the elapsed time by inputting an interrupt signal to the CPU 12d every time that time elapses. Upon receiving this notification, the CPU 12d feedback-corrects the PWM circuit 12a based on the digital value converted from the reference voltage Vref by the A / D conversion circuit 12c as described above. That is, feedback corresponding to the reference voltage Vre is input to the CPU 12d at this timing, and the control content to the PWM circuit 12a is corrected and updated.

  If the stepping motor drive circuit 1B is configured in this manner, the A / D conversion circuit 12c can be used effectively for other processing except for the time for performing this correction. That is, if such correction by feedback control is performed only once a day, the A / D conversion circuit 12c is practically always used for other processing such as image processing of a printer device or a facsimile device. Is available. Of course, in that case, it is necessary to switch from the reference voltage Vref to another voltage by an analog switch or the like provided at the input terminal portion of the A / D conversion circuit 12c and to input the voltage to the A / D conversion circuit 12c.

  Further, the stepping motor drive circuit 1 according to the present invention is required because a different reference voltage Vref can be generated if a control target value corresponding to a reference voltage necessary for torque control is set in the control means in advance. It is also possible to drive and control a plurality of motors having different torques. Such an embodiment is described with reference to FIG. The stepping motor drive circuit 1C includes a plurality of motor drive circuit units 11X to 11Y, but the other components are common to the stepping motor drive circuit 1A. Omitted.

  Here, since the motor drive circuit unit 11X controls the driving of the stepping motor 2X that requires high torque, three different types of reference voltages Vref1-2 are required for this purpose, and the motor drive circuit unit 11Y has a low torque. Therefore, only one reference voltage Vref3 is required for this purpose.

  In this case, if the CPU 12d controls driving of the stepping motor 2X with appropriate software, the CPU 12d controls the reference voltage generation circuit unit 12 to cause the PWM circuit 12a to have a duty ratio corresponding to any one of the reference voltages Vref1-2. If the stepping motor 2Y is driven and controlled, the PWM circuit 12a is similarly made to generate a voltage pulse having a duty ratio corresponding to the reference voltage Vref3. As a result, any of the reference voltages Vref1 to Vref3 can be generated. Of course, in such a configuration, the stepping motor 2X and the stepping motor 2Y cannot be simultaneously driven and controlled.

  Since the stepping motor drive circuit according to the present invention can variably control the torque of the stepping motor in multiple stages, it can be used for a device such as a printing device, a facsimile machine, etc., that operates a load changing mechanism by a motor.

It is a block diagram which shows one Example of the stepping motor drive circuit by this invention. 2 is a diagram illustrating a modulated waveform of a voltage pulse. It is a block diagram which shows the structure of a reference voltage generation circuit part. It is a block diagram which shows another Example by this invention. It is a block diagram which shows another Example by this invention.

Explanation of symbols

1A, 1B, 1C... Stepping motor drive circuit 11... Motor drive circuit unit 12... Reference voltage generation circuit unit 12a .. Pulse width modulation circuit 12b .. Smoothing circuit 12c. 12d. Control processing means (CPU)
14 ... Timekeeping timer 2 ... Stepping motor SW ... Analog switch

Claims (3)

In the stepping motor drive circuit that controls the winding current with reference to the reference voltage output from the reference voltage generation circuit unit and controls the torque of the motor,
The reference voltage generation circuit section is
A pulse width modulation circuit that outputs a voltage pulse with a variable duty ratio; and
A smoothing circuit for smoothing the voltage pulse output from the pulse width modulation circuit and outputting it as a reference voltage;
An A / D conversion circuit that takes in the reference voltage output from the smoothing circuit, converts the reference voltage into a digital signal, and outputs a feedback signal;
A reference voltage to be a control target is set in advance, the feedback signal from the A / D conversion circuit is compared with a control target value, and the pulse width modulation circuit is feedback-controlled so as to match the control target value. A stepping motor drive circuit comprising a control processing means. In claim 1,
The smoothing circuit and the A / D conversion circuit are connected by an analog switch,
A stepping motor drive circuit in which the analog switch is configured to feedback-correct the pulse width modulation circuit by closing when receiving a reference voltage adjustment signal generated at a predetermined timing. In claim 1,
The smoothing circuit is a stepping motor drive circuit formed by a low-pass filter circuit composed of a resistor and a capacitor and a buffer circuit.

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