JPH07337094A - Stepping motor drive - Google Patents

Abstract

PURPOSE:To lessen the load on a microprocessor in speed control processing at the time of slow-up/slow-down of a stepping motor. CONSTITUTION:A speed command signal S* from a microprocessor 1 is converted through a D/A converter 2 into an analog signal (voltage level) which is then fed to a delay circuit 3 comprising an RC series circuit. The level of an output from the delay circuit 3 varies gradually depending on the speed command signal S* and thereby the frequency of an output pulse signal phi varies gradually. Consequently, the microprocessor 1 is simply required to output a speed target value in the form of a speed command signal S*.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepping motor driving device suitable for use in an image reading device, a printer and the like.

[0002]

2. Description of the Related Art In image reading devices, printers and the like, stepping motors are used to drive respective parts. As is well known, the rotation speed of the stepping motor is controlled by the frequency of the excitation pulse. For example, in the case of controlling the rotation of a stepping motor using a microprocessor, a digital speed command signal is output by this microprocessor, and the D / A
The speed command signal is converted into a voltage level by the converter. Then, the V / F (voltage / frequency) converter generates a pulse signal having a frequency corresponding to this voltage level, and an exciting pulse synchronized with this pulse signal is supplied to the stepping motor. In such a configuration, when the speed command signal output from the microprocessor is appropriately changed, the frequency of the excitation pulse is changed and the rotation speed of the stepping motor is changed.

However, when the rotation speed of the stepping motor is suddenly changed, its output torque becomes large and it becomes necessary to supply a large exciting current to the stepping motor. Since the exciting current of the stepping motor is generally set to a constant value, it is necessary to supply a large exciting current to the stepping motor even during constant speed operation, assuming that the rotation speed is changed rapidly. However, power will be wasted. Therefore, when changing the rotation speed of the stepping motor, the speed command signal is set to D / A so that the frequency of the excitation pulse is gradually increased (slow up) or gradually decreased (slow down).
It is common to feed the converter. As a result, the maximum required torque of the stepping motor becomes small, so that the exciting current can be suppressed to a low value.

[0004]

By the way, a microprocessor used in an image reading device, a printer or the like does not simply control a stepping motor.
The stepping motor is controlled while performing other various processes. If these various processes are performed in a time-division manner, the cycle for changing the speed command signal becomes long, and the speed command signal and the rotation speed are changed in a staircase waveform. An example of the output signal of the D / A converter and the output frequency of the V / F converter in this case is shown in FIGS. 5 (a) and 5 (b). Same figure
When the rotation speed of the stepping motor changes in a stepwise manner as shown in (b), vibration is generated from the stepping motor, which adversely affects the surroundings. That is, in the image reading device or the printer, the image reading accuracy and the printing accuracy are deteriorated.

If a considerable part of the processing capacity of the microprocessor can be spent on the motor control, the frequency of changing the speed command signal becomes high and the vibration can be suppressed to some extent. However, in such a case, there arises a problem that the load on the microprocessor increases. The present invention has been made in view of the above circumstances, and an object thereof is to provide a stepping motor drive device that smoothly controls the speed of a stepping motor without increasing the load of the speed control process.

[0006]

In order to solve the above problems, according to the present invention, speed command means for issuing a speed command according to the level of a first analog signal and gradually follow the first analog signal. The present invention is characterized by comprising delay means for outputting a second analog signal and pulse generating means for supplying a drive pulse having a frequency corresponding to the level of the second analog signal to the stepping motor.

[0007]

When the level of the first analog signal changes, the second analog signal gradually changes and changes, and the frequency of the drive pulse also changes gradually. Therefore, since it is not necessary to gradually change the first analog signal itself, the speed control process for setting the level of the first analog signal can be easily performed.

[0008]

EXAMPLES A. First embodiment A-1. Configuration of Embodiments A first embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a microprocessor,
A speed command signal S ^* for instructing the rotation speed of the stepping motor 7 is output. The speed command signal S ^* is converted into a voltage level by the D / A converter 2 and supplied to the delay circuit 3. Details of the delay circuit 3 are shown in FIG. In the figure, the voltage Vin output from the D / A converter 2 is applied to a series circuit including a resistor 32 and a capacitor 33 via a voltage follower circuit 31. The voltage at the connection point between the resistor 32 and the capacitor 33 is output as the voltage Vout via the voltage follower circuit 34.

Next, 4 is a V / F converter, and the frequency of the pulse signal φ ₁ output from the V / F converter is set to a value proportional to the voltage Vout. An excitation pattern generation circuit 5 outputs a multi-phase excitation pulse signal in synchronization with the pulse signal φ ₁ . Further, the excitation pattern generation circuit 5 can receive the command signal in the rotation direction from the microprocessor 1 and change the phase relationship of the multi-phase excitation pulse signal based on the command signal. A driver 6 amplifies the multi-phase excitation pulse signal and supplies it to the stepping motor 7, thereby driving the stepping motor 7.

A-2. Operation of Embodiment Next, the operation of this embodiment will be described. First, assuming that the speed command signal S ^* is changed from a state of “0” to a predetermined value at time t = 0 and then returned to “0” again at time t ₁ , the voltage output from the D / A converter 2 Vin changes as shown in FIG. In the delay circuit 3, the voltage Vin is set by the resistor 32 and the capacitor 33.
Is delayed and the result is output as the voltage Vout.
As a result, the waveform of the voltage Vout gradually follows the voltage Vin as shown in FIG. That is, the resistor 32
If the resistance value of R is "R", the capacitance of the capacitor 33 is "C", and the voltage Vin rises at time t = 0, the rising value of the voltage Vout is expressed by the following mathematical expression 1.

[0011]

## EQU1 ## Vout = Vin {1-exp (-t / RC)}

Details of the waveform of the rising portion of the voltage Vout are shown in FIG. 2 (b). Next, since the frequency of the pulse signal φ ₁ is proportional to the voltage Vout, it changes as shown in FIG. As is clear from comparison between FIG. 3 (c) and FIG. 5 (b), in the present embodiment, since the frequency of the pulse signal φ ₁ changes smoothly, the stepping motor 7 smoothly accelerates and decelerates, The vibration of the stepping motor 7 can be suppressed. Moreover, the microprocessor 1
Requires only a process of intermittently outputting the speed command signal S ^* , the load required for the process is extremely small.

B. Second Embodiment Next, a second embodiment of the present invention will be described. The configuration of the second embodiment is similar to that of the first embodiment, but the delay circuit 3 is constructed as shown in FIG. In the figure, a multistage variable resistor 35 is provided in place of the resistor 32. The multi-stage variable resistor 35 is configured so that its resistance value (R ₁ , R ₂ , ... R _n ) can be appropriately switched based on a time constant selection signal from the microprocessor 1.

In the above configuration, the microprocessor 1
When changing the speed command signal S ^* , outputs a time constant selection signal that decreases the resistance value of the multistage variable resistor 35 as the change width increases. Therefore, by appropriately setting the relationship between the change width and the resistance value, the rise time of the voltage Vout can be made substantially constant. An example thereof is shown in FIG.

C. Third embodiment C-1. Configuration Example Next, a third embodiment of the present invention will be described with reference to FIG. In the figure, a D / A converter 2, a delay circuit 3 and a V / F
The converter 4 has the same structure as that of the first embodiment, and the frequency of the pulse signal φ ₁ is set to a value according to the speed command signal S ^* . The microprocessor 1 receives the pulse signal φ ₁ as a synchronization signal and outputs the pulse signal φ ₂ by the processing described later.

Reference numeral 8 is a pulse selection circuit, which selects and outputs _{one of} the pulse signals φ ₁ and φ ₂ based on the pulse selection signal SEL output from the microprocessor 1.
The excitation pattern generation circuit 5, the driver 6 and the stepping motor 7 are also constructed in the same manner as in the first embodiment. That is, the excitation pattern generation circuit 5 outputs a multi-phase excitation pulse signal in synchronization with the pulse signal output from the pulse selection circuit 8, and drives the stepping motor 7 via the driver 6.

C-2. Operation of Embodiment Next, the operation of this embodiment will be described. First, when the microprocessor 1 changes the speed command signal S ^* , it immediately supplies the pulse selection circuit 8 with the pulse selection signal SEL for instructing the selection of the pulse signal φ ₁ . As a result, the pulse signal φ ₁ is supplied to the excitation pattern generation circuit 5 via the pulse selection circuit 8. Here, if the speed command signal S ^* rises from "0" to a predetermined value, the frequency of the pulse signal φ ₁ gradually increases, as in the case of the first embodiment.

Next, when the pulse signal phi ₁ after a predetermined time Ta has elapsed falls, together with the microprocessor 1 outputs a pulse signal phi _2, pulses a pulse selection signal SEL that directs the selection of the pulse signal phi ₂ It is supplied to the selection circuit 8. Here, the pulse signal φ ₂ is a signal that has a frequency corresponding to the speed command signal S ^* , and the phase of the pulse signal φ ₂ initially matches that of the pulse signal φ ₁ .

The time Ta is set to such a time that the frequency of the pulse signal φ ₁ is sufficiently stable. Time T
An example of setting a is shown in FIGS. In the illustrated example, after the time t ₁ , the pulse signal φ ₂ is supplied to the excitation pattern generation circuit 5 via the pulse selection circuit 8. Further, detailed input / output signal waveforms of the pulse selection circuit 8 before and after the time t ₁ are shown in FIGS. It has been enlarged).

Here, since the pulse signal φ ₂ can be easily synchronized with the internal clock of the microprocessor 1 (for example, the crystal oscillator), its frequency can be set precisely. On the other hand, since the pulse signal φ ₁ is output through the analog circuit such as the delay circuit 3, the pulse signal φ ₁ is easily affected by variations in the characteristics of components and temperature drift, and the frequency cannot be set precisely. Have difficulty. However, during slow-up and slow-down, control that is as precise as in the constant speed range is not required, so the problem of inferior frequency accuracy does not pose a problem.

As described above, according to this embodiment, the rotation speed of the stepping motor 7 at the time of constant speed operation can be set extremely accurately, and the speed command can be set similarly to the first and second embodiments. It is possible to reduce the load on the microprocessor 1 when switching the signal S ^* . In this embodiment, since the microprocessor 1 directly outputs the pulse signal φ ₂ , if the processing is executed by the timer interrupt processing, the microprocessor 1 will be frequently interrupted. However, since the processing required for outputting a pulse signal phi ₂ is the ultimately pulse signal phi ₂ level ( "1" or "0") to only be inverted every predetermined time T, the frequency of the interrupt However, even if the load increases, it is unlikely that the load on the microprocessor 1 becomes excessive.

D. Modifications The present invention is not limited to the above-described embodiments, but various modifications are possible. That is, in the present invention,
Since the purpose can be achieved if the second analog signal gradually follows the first analog signal, any manner may follow. For example, in each of the above embodiments, the waveform of the voltage Vout is configured to rise exponentially based on Equation 1, but each embodiment may be configured such that the voltage Vout rises linearly. .

[0023]

As described above, according to the stepping motor drive device of the present invention, the second analog signal is made to gradually follow the first analog signal, and the drive pulse is thrown by the second analog signal. Since the speed can be increased or decreased, the speed of the stepping motor can be smoothly controlled without increasing the load on the speed control processing.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a first embodiment of the present invention.

FIG. 2 (a) is a circuit diagram of a main part of the first embodiment, FIG.
(b) is the output characteristic diagram.

FIG. 3 is a waveform diagram of each part of FIG.

FIG. 4 (a) is a circuit diagram of a main part of the second embodiment, FIG.
(b) is the output characteristic diagram.

FIG. 5 is a waveform diagram of each part of a conventional stepping motor drive device.

FIG. 6 is a block diagram showing an overall configuration of a third embodiment of the present invention.

7 is a waveform diagram of each part of FIG.

[Explanation of symbols]

 1 Microprocessor (speed command means) 2 D / A converter (speed command means) 3 Delay circuit (delay means) 4 V / F converter (pulse generation means) 5 Excitation pattern generation circuit (pulse generation means) 6 Driver (pulse generation) Means) 7 stepping motor

Claims (1)

[Claims] 1. A speed command means for issuing a speed command according to the level of a first analog signal, a delay means for outputting a second analog signal that gradually follows the first analog signal, and a second analog signal. A stepping motor driving device, comprising: a pulse generating unit that supplies a driving pulse having a frequency corresponding to a signal level to the stepping motor.