KR20120044913A - Stepping motor driving apparatus - Google Patents

Abstract

PURPOSE: A driving apparatus for a stepping motor is provided to simplify the structure of a controlling system by eliminating a processing or memorizing unit memorizing preceding instruction current values. CONSTITUTION: A current detecting part detects current values through the coil(4, 5) of a bipolar type two phased stepping motor(1). A controlling part feed-back-controls the current through the coil based on the deviation of an instruction current value based on an operational instruction and a detected current value from the current detecting part. The controlling part calculates the integrated value of the current deviation and determines current values for the coil. The controlling part resets the integrated value of the current deviation under the plus/minus polarity conversion state of the instruction current value. After the resetting, the controlling part keeps integrating the current deviation.

Description

Stepping motor driving device {STEPPING MOTOR DRIVING APPARATUS}

The present invention relates to a drive device for a stepping motor.

As a general stepping motor, a two-phase stepping motor is known which is driven by exciting two coils at different excitation timings.

In the conventional bipolar two-phase stepping motor 1, the drive device 100 (FIG. 10) which switches and drives the constant area of an energization direction with respect to each of the two coils is provided for each coil.

The drive device 100 includes a CPU 101 for outputting a current value command that is an operation command of the stepping motor 110, a D / A converter 102 for outputting a command current value according to the current value command, and a command. A current deviation generator 103 for outputting a deviation by the difference in the current value flowing through the stepping motor's coil with respect to the current value, a triangular wave generator circuit 104 for outputting a regular sawtooth triangle wave, and a comparison value PWM generation circuit 105 for generating a PWM signal that is a continuous signal of ON-OFF according to the comparison of the signal and the triangle wave signal, and the forward and backward directions of the current flowing through each of the two coils of the stepping motor 110 A bridge circuit 106 for switching is provided, and a current detector 107 for detecting current flowing through each coil.

By the above configuration, the drive device 100 has performed so-called proportional control (P control) on the stepping motor 110 (see Patent Document 1, for example).

Japanese Patent Publication No. 2009-095148

However, the proportional control (P control) performed in the conventional drive device of the bipolar type two-phase stepping motor has drawbacks such as the fact that a normal deviation occurs in the output or the noise is easily affected.

As a countermeasure, there is a method using proportional + integral control (PI control). However, in the control of a bipolar two-phase stepping motor, it is necessary to periodically switch the +/- polarity of the current flowing through each coil, When the current at the high speed of rotation is switched to one of +/-, there is a problem that the current following is delayed by the integrated value of the current deviation accumulated until then.

Referring to FIG. 11, in the integral control, the influence of the normal deviation and the noise can be reduced by reflecting the integrated value Iei of the current deviation in the current value flowing through the coil. However, since the integrated value Iei of the current deviation is still positive at the time when the command current value Ir is changed from positive to negative (point C1 in the figure), a negative current value (current in the reverse direction) must be flowed into the coil. In addition, the component of the integral control reflects the integrated value (Iei) to correct the positive, thereby reducing the followability.

The same phenomenon also occurred at the point in time when the command current value Ir was changed from negative to positive (point C2 in the figure).

In addition, there is a method using proportional + integral control + derivative control (PID control), but there is a problem in that the control system becomes complicated and control diverges depending on gain setting. In addition, since the integral control is also included in the case of PID control, the problem of the followability cannot be solved fundamentally.

An object of the present invention is to improve the followability without complicating a control system for a drive device of a bipolar type two-phase stepping motor.

Invention of Claim 1 is a current-detection part which detects the electric current value which flows through a coil of a bipolar type two-phase stepping motor, and the command current value and the said electric current with respect to the said coil based on the operation command with respect to the said bipolar type two-phase stepping motor. And a control unit for performing feedback control of the current flowing through the coil based on the current deviation between the detection current values of the detection unit, wherein the control unit obtains an integrated value of the current deviation and applies the integrated value to the value of the current deviation. The current value to be passed to the coil is determined, and when the +/- polarity of the command current value is switched, integration is continued after resetting the integrated value of the current deviation.

The invention described in claim 2 has the same configuration as the invention described in claim 1, and the controller controls switching of +/- polarity of the command current value from a multiplication value of the command current value and the integrated value of the current deviation. It is characterized by determining.

The invention described in claim 3 has the same configuration as the invention described in claim 1 or 2, and the controller is configured by a DSP (Digital Signal Processor).

The invention according to claim 1 performs a process of detecting the switching and resetting the value of the current deviation integrated value when the polarity of the command current value is periodically switched. Therefore, immediately after the polarity of the command current value is switched. In addition, the influence of the drop of the followability of the current flowing through the coil is eliminated as the polarity of the current deviation integrated value does not match the command current value. Therefore, it is possible to improve the followability in feedback control without complicating the control system such as performing differential control.

In the invention according to claim 2, since the switching of the polarity of the command current value +/- is determined from the multiplication value of the command current value and the integrated value of the current deviation, for example, the previous command current value is stored, Compared with the case of determining the switching of the polarity by contrast with the command current value, the control system can be simplified by eliminating the need for a process for storing the immediately preceding command current value or a storage means.

The invention according to claim 3 uses a DSP suitable for periodic and continuous processing as the controller, whereby the processing can be speeded up, and the followability can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which shows the structure of the bipolar type two-phase stepping motor with which the drive device of the stepping motor which concerns on this invention is connected.
2 is a block diagram showing the configuration of a drive device for a stepping motor.
3 is a circuit diagram of a bridge circuit.
4 is a functional block diagram of a DSP.
FIG. 5 is a line diagram showing the change of the command current value Ir, the detected current value Id, the current deviation Ie, and the current deviation integrated value Iei with the horizontal axis as time and the vertical axis as current values. FIG. (A) is a line diagram showing the change of the command integrated value Ir and the detected current value Id from the CPU with the horizontal axis as the time and the vertical axis as the current value, and FIG. It is a line drawing which shows the change of the current deviation Ie and the current deviation integrated value Iei, with a vertical axis as a current value.
Fig. 6 is a flowchart showing the energization control of the coil of the stepping motor by the DSP.
Fig. 7 shows the detected current value Id and the current deviation integrated value Iei when control is performed to reset the command current value Ir and the current deviation integrated value Iei according to the time elapsed at the time of low speed driving of the motor. Is a line diagram showing a change in the detected current value Idm when control is performed without reset.
Fig. 8 shows the detected current value Id and the current deviation integrated value Iei when control is performed to reset the command current value Ir and the current deviation integrated value Iei according to the time lapse of the motor during medium speed driving. Is a line diagram showing a change in the detected current value Idm when control is performed without reset.
Fig. 9 shows the detected current value Id and the current deviation integrated value Iei when the control for resetting the command current value Ir and the current deviation integrated value Iei according to the elapse of time at high speed of the motor is performed. Is a line diagram showing a change in the detected current value Idm when control is performed without reset.
10 is a block diagram showing an example of a configuration of a drive device of a conventional bipolar type two-phase stepping motor.
Fig. 11 shows the change of the command current value Ir, the current value Id actually flowing through the coil, their current deviation Ie, and the integrated value Iei of the current deviation, with time on the horizontal axis and time on the vertical axis. It is a line drawing to show.

(Overall Configuration of Embodiments of the Invention)

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail based on FIG.

The driving device 7 of the stepping motor 1 according to the embodiment of the present invention is provided for each of the coils 4 and 5 of the A and B phases of the stepping motor 1, and each of the driving devices 7 The stepping motor 1 is connected to a CPU 8 that outputs a current value command determined in accordance with the intended operation.

(Stepping motor)

The stepping motor 1 includes a cylindrical rotor 2 provided so as to rotate integrally with the rotation shaft of the stepping motor 1, a cylindrical stator 3 provided around the rotor 2, And the cores 3a and 3b protruding from the inner circumferential portion of the stator 3 in a direction proximate to the rotor 2 and wound around the core portions 3a and 3b provided for the current control by the drive device 7 described later. And coils 4 and 5 which are excited by each other and change / hold the rotation angle of the rotor 2. In addition, although each coil 4, 5 is shown in brief, in practice, it consists of a plurality of coils, which are alternately arranged at uniform intervals in series around the rotor 2.

The rotor 2 is a magnetic body such as a permanent magnet and is supported to be rotated by being connected to a rotating shaft of a stepping motor 1 (not shown). The stator 3 is a cylindrical magnetic material (for example, iron) provided around the rotor 2, and core portions 3a to 3b protruding in the direction proximate to the rotor 2 at its inner circumference are formed. It is installed.

The coils 4 and 5 are windings wound around the cores 3a and 3b. The coils 4 and 5 are excited by a drive device 7 to be described later and function as an electromagnet. At this time, the coils 4 and 5 are shifted in phase by the CPU 8 through the respective drive devices 7, and current control is performed in which current values change periodically. Further, by slightly changing the current ratios of the two coils 4 and 5, the rotational driving of the stepping motor 1 is performed by the microstep which can obtain a finer step angle.

(Stepping motor drive device)

Next, the drive device 7 of the stepping motor will be described in detail.

The drive device 7 of the stepping motor controls the drive / stop and the rotation angle of the stepping motor 1. As shown in FIG. 1, the driving device 7 of the stepping motor is installed in each of the coils 4 and 5 of the stepping motor 1 to control the current flowing through the coils 4 and 5.

In the following description, the drive device 7 connected to the coil 4 will be described, and the description of the drive device 7 of the coil 5 having the same structure will be omitted.

As shown in FIG. 2, the drive device 7 of the stepping motor includes a current detection unit 11 for detecting a current value flowing through the coil 4 of the stepping motor 1, and a predetermined direction with respect to the coil 4. In the positive direction) and in the opposite direction, the bridge circuit 20 for switching the connection so that energization is performed, and the current according to the command current value from the CPU 8 through the bridge circuit 20 is applied to the coil 4. DSP (Digital Signal Processor; 30) as a control unit which performs feedback control of the current flowing through the coil 4 based on the current deviation between the command current value and the detected current value of the current detection unit 11, do.

(Drive device: current detector)

The current detector 11 is a shunt resistor connected in series with the coil 4, and can obtain a detection signal corresponding to the current value flowing through the coil 4.

(Drive device: bridge circuit)

As shown in FIG. 3, the bridge circuit 20 constitutes an H bridge circuit formed by the FETs 21 to 24 and the diodes 25 to 28, and supplies the coil 4 to the power supply device through the bridge circuit 20. (6).

In addition, the power supply 6 is shared by the coils 4 and 5. That is, the bridge circuits 20 of the two drive units 7 are connected to one power supply unit 6 so that current flows in the coils 4 and 5.

The FETs 21 to 24 are so-called three-terminal field effect transistors in which one electrode of the FETs 21 and 22 is one end of the coil 4 and one electrode of the FETs 23 and 24 is the coil 4. It is connected to the other end of. In addition, the other electrode of the FETs 21 and 23 is connected to the power supply device 6, and the other electrode of the FETs 22 and 24 is connected to the earth 9.

The gates of the FETs 21 to 24 are connected to the DSP 30, and when a voltage is applied to the gate by the DSP 30, the currents according to the value of the voltage are supplied from the power supply device 6 to the coil 4. It functions as a "switching element" which flows into the. In addition, the FETs 21 to 24 can conduct electricity in both directions.

Then, the DSP 30 simultaneously turns on the FETs 21 and 24, turns off the FETs 22 and 23 simultaneously, turns off the FETs 21 and 24 simultaneously, and turns off the FETs 22 and 24. Switch to connected state by turning on 23) at the same time. In the former connected state, current flows to the coil 4 in the right direction in FIG. 3 (solid line arrow in FIG. 3), and in the latter connected state, the coil 4 in the left side in FIG. 3. Current flows in the direction (dotted arrow in FIG. 3).

The diodes 25 to 28 are connected in parallel with each of the FETs 21 to 24. In addition, the anode (anode) of each diode 25-28 is connected to the earth 9 side, and the cathode (cathode) is connected to the power supply device 6 side. That is, when a current in the opposite direction to the direction of the current by the power supply device 6 flows without the current from the power supply device 6 flowing to the diodes 25 to 28, the current in the opposite direction is the diode ( 25-28). As a result, the current in the opposite direction flows to the FETs 21 to 24, thereby preventing the FETs 21 to 24 from being damaged. In other words, the diodes 25 to 28 function as protection circuits of the FETs 21 to 24.

(Drive device: DSP)

In FIG. 4, the DSP 30 mainly determines the detection current value Id of the current detection unit 11 with respect to the command current value Ir based on the coil 4 of the stepping motor 1 from the CPU 8. A comparator 31 for obtaining the deviation Ie, a proportional processor 32 for multiplying the deviation Ie by a proportional gain Kp, an integral processor 33 for integrating based on the deviation Ie, and Function as a PWM signal generation unit 36 for generating a PWM signal to the bridge circuit 20 so that a predetermined current is supplied to the coil 4 based on the processing results of the proportional processing unit 32 and the integration processing unit 33. It is configured to realize.

In addition, the continuous series of processes in the units 31, 32, 33, and 36 are repeatedly executed at regular intervals.

In FIG. 5, the line diagram of the upper end A shows the change of the command current value Ir and the detected current value Id from the CPU with the horizontal axis as time and the vertical axis as current value. The line diagram shows the change of the current deviation Ie and the current deviation integrated value Iei with the horizontal axis as the time and the vertical axis as the current value.

The coil 4 and the coil 5 are energized so that the change of the periodic current value which becomes a sine wave with a phase difference of (pi) / 2 is repeated. Then, the CPU 8 performs a microstep drive by performing a numerical output of the command current, which makes a step change, to plot the sinusoidal waveform.

The comparator 31 calculates the current deviation Ie by subtracting the command current value Ir from the CPU 8 and the detected current value Id from the current detector 11.

Ir-Id = Ie

Then, the calculated current deviation Ie is output to the proportional processing unit 32 and the integration processing unit 33.

The proportional processor 32 multiplies the current deviation Ie input from the comparator 31 by a predetermined proportional gain Kp and outputs the predetermined proportional gain Kp to the PWM signal generator 36.

The integration processor 33 resets the integration section 34 for integrating each current deviation Ie input from the comparator 31 and the current deviation integration value Iei that the integration section 34 integrates. The determination part 35 which determines the is provided. In addition, the DSP 30 has a built-in memory, and the current deviation integrated value Iei is stored and stored in the memory.

In the integration control by the feedback which has been conventionally performed, integration of the current deviation Ie has been continuously performed from the drive of the stepping motor 1 to the stop. As a result, like the bipolar two-phase stepping motor 1, when the polarity of the command current value Ir is periodically switched, the current accumulated up to that time immediately after switching of the polarity of the command current value Ir is A discrepancy between the deviation integration value Iei and the polarity has occurred, and as the integral control component acts to prevent following the command current value Ir, a problem has arisen that the followability of the energization of the coil is lowered.

Thus, the determination unit 35 of the integration processing unit 33 reads the command current value Ir from the CPU 8 to determine whether or not the polarity thereof has been switched with respect to the immediately preceding command current value. Specifically, it is determined by whether or not the multiplication value obtained by multiplying the command current value Ir by the current deviation integration value Iei becomes a negative polarity. In other words, when the polarity of the command current value Ir does not change, the polarity of the current deviation integrated value Iei up to that point is the same, so multiplying it becomes positive, and the polarity of the command current value Ir is switched. Since the multiplication value does not coincide with the current deviation integrated value Iei immediately after the conversion, the multiplication value is always negative, so that the switching of the polarity of the command current value Ir can be detected.

When the determination unit 35 determines that the polarity of the command current value Ir is not immediately changed, the integral signal is multiplied by the current deviation integrated value Iei in the same manner as in the conventional control to generate a PWM signal generation unit. Output to (36). When it is determined immediately after the polarity of the command current value Ir is switched, the determination unit 35 outputs the current deviation integrated value Iei to 0 to the PWM signal generation unit 36.

That is, as shown in FIG. 5, at the points P1 to P3 where the polarity of the command current value Ir is switched, the current deviation integration value Iei is reset to 0, and after that, the integration is newly performed. do.

The PWM signal generator 36 adds Kp × Ie, which is the output of the proportional processor 32, and Ki × Iei, which is the output of the integration processor 33, (Iei = 0 when reset) to add the sum value Ret. Calculate.

Ret = Kp × Ie + Ki × Iei

The PWM signal, which is a repetitive signal of ON and OFF, is generated in a duty cycle according to the numerical value of the total value Ret and output to the bridge circuit. The duty ratio is set to increase proportionally according to the value of Ret. That is, if the value of Ret is positive and the absolute value is large, the duty ratio is determined so that the ratio of ON is 0.5 or more and closer to 1.0 according to the absolute value.If the value of Ret is negative and the absolute value is large, the ratio of OFF is 0.5 or more. The duty ratio is set to be closer to 1.0 depending on the absolute value.

In addition, the duty ratios of the sum value Ret and the PWM signal may be prepared in the DSP 30 in a table in which a correspondence relationship is determined, and the process of specifying the duty ratio according to the sum value Ret is performed with reference to this. It's okay.

Thereby, a predetermined electric current flows in the forward or reverse direction with respect to the coil 4, and it is correct | amended so that an electricity supply may follow a command current value.

That is, the DSP 30 (control unit) obtains the integrated value Iei (current deviation integrated value Iei) of the current deviation, and applies the coil 4 to the coil 4 based on the integrated value Iei and the current deviation Ie. The current value to be passed is determined, and when the +/- polarity of the command current value Ir is switched, the integrated value of the current deviation is reset (Iei = 0), and then integration is continued.

(Control of Stepping Motor by Driving Device)

Regarding the control of the stepping motor 1 by the drive device 7, the energization control of the coil 4 of the stepping motor 1 by the DSP 30 (control unit) will be described based on the flowchart of FIG. 6. Do it.

First, when driving of the stepping motor 1 is started, the value of the current deviation integrated value Iei is reset ([Iei = 0]: step S1).

Then, the DSP 30 reads the command current value Ir from the CPU 8, and at the same time reads the detected current value Id from the current detector 11 (step S3), and the comparator 31 reads the command current. The current deviation Ie is calculated by subtracting the detection current value Id from the value Ir ([Ir-Id = Ie]: step S5).

Next, in the integration section 34 of the integration processing section 33, the current deviation Ie is added to the value of the current deviation integration value Iei in the memory (step S7).

Further, the determination unit 35 multiplies the command current value Ir by the current deviation integrated value Iei, and determines whether the multiplication value is less than zero (minus) ([Ir × Iei <0]: Step S9).

At this time, if Ir x Iei <0 (step S9: YES), immediately after the polarity of the command current value Ir is switched, the current deviation integrated value Iei is in a state in which the polarity is not yet switched. A process of resetting the current deviation integrated value Iei within is performed ([Iei = 0]: step S11).

On the other hand, if Ir x Iei? 0 (step S9: NO), the proportional processing unit 32 multiplies the current deviation Ie by the proportional gain Kp, and the integration processing unit 33 increases the current deviation integrated value Iei. The integral gain Ki is multiplied to calculate the total value Ret of these values ([Ret = Kp × Ie + ki × Iei]: step S13).

The PWM signal generation unit 36 then specifies the duty ratio based on the total value Ret, and outputs the PWM signal accordingly to the bridge circuit 20 (step S15).

The bridge circuit 20 alternately turns ON the FETs 21 and 24 and the ON of the FETs 22 and 23 according to the PWM signal, and flows a constant current to the coils 4 so that the current depends on the duty ratio. Energize.

After that, the process returns to the process of step S3 to read the next command current value Ir and the detected current value Id. Incidentally, the processes from steps S3 to S17 are repeatedly executed at regular intervals during the driving of the stepping motor 1.

In the above flowchart, only the current control of one coil 4 in the stepping motor 1 is shown, but the phase of the command current value Ir is delayed by? / 2 for the other coil 5 as well. In the state, the same current control as described above is performed.

(Effect of Control by Driving Device of Stepping Motor)

The current control by the drive device 7 of the stepping motor is characterized by resetting the current deviation integrated value Iei by detecting switching of the polarity of the command current value Ir.

This effect will be described based on FIGS. 7 to 9.

The decrease in the followability with respect to the command current value due to the delay in switching the polarity of the current deviation integrated value Iei from the command current value Ir becomes more pronounced as the driving of the stepping motor 1 becomes faster.

In the low-speed drive of the stepping motor 1 shown in FIG. 7, the difference is small in the detection current value Id by the drive device 7 and the detection current value Idm by the conventional PI control. In the medium speed drive shown, the detection current value Id by the drive device 7 follows the value closer to the command current value Ir than the detection current value Idm by the conventional PI control. At the time of high speed driving in FIG. 9, the detection current value Id by the drive device 7 is closer to the command current value Ir than the detection current value Idm by the conventional PI control, and also the command current value. It can be seen that following the phase close to (Ir) can be followed.

In this way, the drive device 7 of the bipolar type two-phase stepping motor 1 performs a process of resetting the value of the current deviation integrated value Iei when detecting the change of the polarity of the command current value Ir. It is possible to perform feedback control on the current flowing through the coil of the stepping motor 1 with a high tracking property without adding a control system of differential control. In particular, the following delay can be suppressed at the high speed of the motor.

(Etc)

In addition, the driving device 7 of the stepping motor exemplifies a case in which the command current value Ir of the CPU 8 performs the output according to the microstep. In this case, the same current control is also effective.

In addition, although the DSP 30 is used in the drive device 7, a CPU, a microcomputer using a sequencer, and an analog circuit which can read out current may be used instead.

1: Bipolar Type 2 Phase Stepping Motor
4,5: coil
6: power supply
7: driving device
9: Earth
11: current detector
20: bridge circuit
30: DSP (control unit)
31: comparison unit
32: proportional processing unit
33: integral processing unit
34: totalizer
35: judgment unit
36: PWM signal generator
Id: Detection current value
Ie: current deviation
Iei: Current deviation integration value
Ir: Command current value

Claims (3)

A current detector for detecting a current value flowing through a coil of a bipolar type two-phase stepping motor;
And a control unit configured to perform feedback control of the current flowing through the coil based on a current deviation between the command current value for the coil and the detected current value of the current detection unit based on the operation command for the bipolar type two-phase stepping motor. ,
The control unit obtains an integrated value of the current deviation, determines the current value to be passed to the coil based on the integrated value and the value of the current deviation,
And when the +/- polarity of the command current value is switched, the integration is continued after the integration value of the current deviation is reset. The method of claim 1,
And the control unit determines the switching of the +/- polarity of the command current value from the multiplication of the command current value and the integrated value of the current deviation. 3. The method according to claim 1 or 2,
The control unit is a driving device of a bipolar type two-phase stepping motor, characterized in that consisting of a DSP (Digital Signal Processor).

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