JP2013099068A - Controller of stepping motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller of a stepping motor capable of controlling a stepping motor to free rotation state, by controlling a signal input to the PWM signal input section of a half-bridge drive circuit.SOLUTION: When a free signal is input from a microprocessor (CPU) 10 via a signal line 16 to a PWM signal generation circuit 11, the PWM signal generation circuit 11 outputs, for all phases, a control signal corresponding to the on-level of a PWM signal to the PWM signal input section of a half-bridge drive circuit 5. An upper stage FET 21 is thereby turned off and a lower stage FET 22 is turned on by maintaining the output of the control signal to discharge a bootstrap capacitor 53 and the upper stage FET is turned off, thus controlling the stepping motor M to free rotation state. Subsequently, before driving rotation, a control signal corresponding to the off level of the PWM signal is output for a predetermined time, thus performing charging.

Description

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

  Conventionally, stepping motors are known as electric motors that can accurately position the angle of a rotating shaft, and are often used in sewing machines. There are many types of stepping motors depending on their configurations, but a two-phase stepping motor that is driven by exciting two coils at different excitation timings is generally known.

For example, Patent Document 1 describes a conventional bipolar two-phase stepping motor control device. One example will be described with reference to FIG.
As shown in FIG. 5, a bridge circuit 2 that outputs a two-phase motor drive current is connected to a bipolar two-phase stepping motor M via a drive current output line 1. The bridge circuit 2 includes two phases of bridges in which an upper FET 21 and a lower FET 22 are connected in series. A half bridge drive circuit 5 that applies a reciprocal switching voltage is connected to the upper stage FET 21 and the lower stage FET 22 of the bridge circuit 2. 3 is a switching voltage input line to the upper stage FET 21, and 4 is a switching voltage input line to the lower stage FET 22. The half bridge drive circuit 5 operates based on a signal input from the integrating circuit 7. Reference numeral 6 denotes a signal line to the half bridge drive circuit 5. An operation / stop signal from the microprocessor (CPU) 10 is input to the integrating circuit 7 via the signal line 8, and a PWM signal from the PWM signal generation circuit 11 is input via the signal line 9. Further, a current value command signal based on an analog amount from the microprocessor (CPU) 10 is input to the PWM signal generation circuit 11 via the signal line 12.

  Based on the current value command signal from the PWM signal generation circuit 11, the PWM signal generation circuit 11 controls the duty ratio to generate a PWM signal and outputs it to the integration circuit 7. During the period when the operation signal from the microprocessor (CPU) 10 is input to the integrating circuit 7 via the signal line 8, the PWM signal is input to the half bridge drive circuit 5 as it is, and the half bridge drive circuit 5 A reciprocal switching operation is driven to the upper stage FET 21 and the lower stage FET 22 based on the input PWM signal, whereby a two-phase motor drive current is output from the bridge circuit 2 and the motor M is driven in accordance with the current value command signal. Works with values. At this time, the half bridge drive circuit 5 turns on the upper FET 21 when the PWM signal is turned on, turns off the lower FET 22, turns off the upper FET 21 when the PWM signal is turned off, and turns on the lower FET 22. A motor drive current is generated by the bridge circuit 2 connected to. The motor drive current value is detected by a current detector 13 attached to the drive current output line 1 and is input to the PWM signal generation circuit 11 via the signal line 14 and feedback controlled. In some cases, the microprocessor (CPU) 10 and the PWM signal generation circuit 11 shown in a broken line 15 in FIG. 5 are realized by one IC.

  During a period in which a stop signal from the microprocessor (CPU) 10 is input to the integrating circuit 7 via the signal line 8, an OFF signal is always input from the integrating circuit 7 to the half bridge drive circuit 5, and the upper FET 21 Is turned OFF, the lower FET 22 is turned ON, and the motor M stops.

JP 2009-095148 A

However, in the conventional stepping motor control apparatus described above, the motor M always performs a braking operation when the motor M is stopped. This is because the upper stage FET 21 is turned off and the lower stage FET 22 is turned on, so that all the windings of the motor M are connected to GND, and electromagnetic braking force is generated.
If the stepping motor is braked, it requires a large amount of force to be moved by a human hand, which hinders the motor from being moved by a human hand when necessary, such as when adjusting a machine equipped with a stepping motor. There is a problem.
To make the stepping motor rotation free, turn off the power of the stepping motor or stop the output, that is, a half bridge with a driver IC with a function to turn off both the upper and lower FETs There are methods such as using a drive circuit. In the former case, the circuit becomes complicated in order to free individual stepping separately. Therefore, both methods have a problem that the cost is increased due to hardware changes.

  The present invention has been made in view of the above problems in the prior art, and can control a stepping motor in a rotation-free state by controlling a signal input to a PWM signal input unit of a half-bridge drive circuit. It is an object of the present invention to provide a control device.

The invention according to claim 1 for solving the above-described problems includes a stepping motor,
A bridge circuit having upper and lower switching elements for generating a drive current for the stepping motor;
A bootstrap circuit for charging the switching drive power supply of the upper switching element and a PWM signal input unit, and reciprocally switching the upper and lower switching elements in accordance with the PWM signal input to the PWM signal input unit. Half-bridge drive circuit,
In a stepping motor control device for controlling the stepping motor by outputting a control signal to the PWM signal input unit for a stepping motor driving mechanism comprising:
Rotation drive control means for controlling the rotation of the stepping motor by outputting a PWM signal to the PWM signal input unit;
For all phases, by outputting a control signal corresponding to the ON level of the PWM signal to the PWM signal input unit, the upper switching element is turned ON, the lower switching element is turned OFF, and the ON signal is turned ON. By maintaining the output of the control signal corresponding to the level, the switching drive power supply is discharged to change the upper switching element from ON to OFF, and both the upper and lower switching elements are turned OFF and the stepping is performed. Rotation free control means for controlling the motor rotation to a free state;
Is a control device for a stepping motor.

  According to a second aspect of the present invention, when the rotation of the stepping motor is controlled by the rotation drive control means from the state where the rotation of the stepping motor is made free by the rotation free control means, the rotation drive control means is activated. Prior to this, for all phases, by outputting a control signal corresponding to the OFF level of the PWM signal to the PWM signal input unit, the lower switching element is turned ON, and the control corresponding to the OFF level of the PWM signal is performed. 2. The stepping motor control device according to claim 1, further comprising a return control unit configured to charge the switching drive power supply by maintaining a signal output and to control the upper switching element in a state in which the switching drive is possible. 3. is there.

When a bridge circuit for generating a driving current for a stepping motor is configured with an NMOS output (a circuit in which NchMOS is arranged in both upper and lower stages), a bootstrap circuit is generally used as a booster circuit for driving the upper NchMOS.
The bootstrap circuit connects one electrode of the switching drive power supply (capacitor) to the motor output. Therefore, the switching drive power source is charged during the ON period of the lower switching element (the upper switching element is OFF at this time). Further, the switching drive power supply is discharged during the ON period of the upper switching element (the lower switching element is OFF at this time), and further, charging and discharging are repeated during the motor rotation driving.
According to the present invention, for all phases, a control signal corresponding to the ON level of the PWM signal is output to the PWM signal input section of the half bridge drive circuit, so that the upper switching element is first turned ON and the lower switching element is turned ON. Set to OFF. Further, by maintaining the output of the control signal corresponding to the ON level, the switching drive power supply is discharged, and the upper switching element is lowered to a level at which the upper switching element cannot be driven ON, thereby changing the upper switching element from ON to OFF ( Turn off). As a result, both the upper and lower switching elements are turned off. When both the upper and lower switching elements are turned off, the winding of the stepping motor is disconnected from both the motor power supply and GND, and the rotation is free of electromagnetic load due to the winding against the rotation. It becomes.
As described above, according to the present invention, the stepping motor can be controlled in a rotation-free state by controlling the signal input to the PWM signal input unit of the half-bridge drive circuit. There is an effect that the function of controlling the stepping motor to a rotation-free state can be obtained without any change.

1 is a block circuit diagram illustrating a stepping motor driving mechanism and a control device thereof according to an embodiment of the present invention. It is a circuit diagram which shows the inside of the bridge circuit and half bridge drive circuit which comprise the stepping motor drive mechanism which concerns on one Embodiment of this invention. It is a flowchart which shows the control flow by the control apparatus of the stepping motor which concerns on one Embodiment of this invention. It is a signal waveform diagram which shows an example of the time change of the signal processed in the control apparatus of the stepping motor which concerns on one Embodiment of this invention. It is a block circuit diagram showing a stepping motor drive mechanism and its control device according to a conventional example.

  An embodiment of the present invention will be described below with reference to the drawings. The following is one embodiment of the present invention and does not limit the present invention.

  As shown in FIG. 1, the stepping motor driving mechanism according to the present embodiment includes a bipolar two-phase stepping motor M and a bridge circuit 2 that outputs a two-phase motor driving current, as in the conventional example shown in FIG. And a half bridge drive circuit 5 for applying a reciprocal switching voltage to the upper stage FET 21 and the lower stage FET 22 of the bridge circuit 2. Corresponding elements are denoted by the same reference numerals and description thereof is omitted. 1 is a drive current output line, 3 is a switching voltage input line to the upper stage FET 21, and 4 is a switching voltage input line to the lower stage FET 22. A signal line 6 to the half bridge drive circuit 5 is connected to the PWM signal input section of the half bridge drive circuit 5.

The bridge circuit 2 includes an upper FET 21 and a lower FET 22 as upper and lower switching elements that generate a drive current for the stepping motor M. In FIG. 2, only one phase is illustrated and simplified. Each of the upper stage FET 21 and the lower stage FET 22 is an N-channel MOSFET as shown in the figure, and a parallel diode is attached.
As shown in FIG. 2, the half bridge drive circuit 5 includes a half bridge driver IC 51, a bootstrap charging circuit 52, and a bootstrap capacitor 53. The bootstrap charging circuit 52 and the bootstrap capacitor 53 constitute a bootstrap circuit.
A bootstrap capacitor 53 serving as a switching drive power source for obtaining a switching voltage for turning on the upper stage FET 21 is connected to the drive current output line 1 and the half bridge driver IC 51.
The half bridge drive circuit 5 performs switching driving of the upper stage FET 21 and the lower stage FET 22 in a reciprocal manner in accordance with the PWM signal input to the PWM signal input unit.

The stepping motor control apparatus according to the present embodiment includes a microprocessor (CPU) 10, a PWM signal generation circuit 11, and a current detection unit 13, as in the conventional example shown in FIG. Corresponding elements are denoted by the same reference numerals and description thereof is omitted. Reference numeral 8 denotes a signal line for an operation / stop signal output from the microprocessor (CPU) 10, and this operation / stop signal is input to the PWM signal generation circuit 11. A current value command signal based on an analog amount from the microprocessor (CPU) 10 is input to the PWM signal generation circuit 11 via the signal line 12.
The configuration including the microprocessor (CPU) 10 and the PWM signal generation circuit 11 shown in a broken line 15 in FIG. 1 can be realized by one IC.

The above points are the same as in the prior art. However, in the present embodiment, unlike the above-described conventional example, the operation / free signal output from the microprocessor (CPU) 10 is input to the PWM signal generation circuit 11 via the signal line 16 and will be described below. The difference is that the motor M can be controlled in a rotation-free state.
1 includes a microprocessor (CPU) 10 and a PWM signal generation circuit 11 indicated by a broken line 15 and outputs a PWM signal to the PWM signal input unit to control the rotation of the stepping motor M as in the prior art. The rotation drive control means and the brake stop control means for controlling the brake to act on the rotation of the stepping motor M are configured, and unlike the prior art, the rotation free control for controlling the rotation of the stepping motor M to be free. And a return control means for controlling the upper switching element to a state in which switching driving is possible.

As shown in the flowchart of FIG. 3, the PWM signal generation circuit 11 includes an operation / stop signal (signal line 8), an operation / free signal (signal line 16), and a current value command signal (signal) that are input motor control signals. Process according to line 12).
When the motor control signal is input (step S1), the PWM signal generation circuit 11 determines whether there is a stop signal (step S2).
When there is a stop signal (Yes in step S2), the PWM signal generation circuit 11 executes stop control (control as brake stop control means) S3. In the stop control S3, the PWM signal generation circuit 11 outputs an OFF signal to the signal line 6 (for all phases). This corresponds to outputting a PWM signal that is OFF for all periods. Therefore, the OFF signal is always input to the half-bridge drive circuit 5, the upper FET 21 is turned OFF, the lower FET 22 is turned ON, the motor M is stopped, and the motor M is stopped when the motor M is stopped as in the above-described conventional example. Always operates as a brake.

If No in step S2, the PWM signal generation circuit 11 determines whether there is a free signal (step S4).
If there is a free signal (Yes in step S4), the PWM signal generation circuit 11 executes free control (control as rotation free control means) S5. In the free control S5, the PWM signal generation circuit 11 outputs an ON signal to the signal line 6. This corresponds to outputting a PWM signal that is ON for the entire period. This is performed for all phases. Immediately after the ON signal is input to the half-bridge drive circuit 5, the upper FET 21 is turned ON and the lower FET 22 is turned OFF (at this time, the motor M is connected to the motor power supply side). The motor M is braked). At the same time, the bootstrap capacitor 53 starts to be discharged. If the output of the ON signal is maintained for about several tens of milliseconds or more, the bootstrap capacitor 53 is discharged, and the upper FET 21 is stepped down to a level where it cannot be turned on. Then, since a turn-on voltage cannot be applied to the upper stage FET 21, the upper stage FET 21 changes from ON to OFF. As a result, both the upper stage FET 21 and the lower stage FET 22 are turned off. When both the upper stage FET 21 and the lower stage FET 22 are turned off, the stepping motor M is disconnected from both the motor power supply and the GND, and the rotation that does not apply an electromagnetic load to the rotation is made free.

In the case of No in step S4, the PWM signal generation circuit 11 outputs a PWM signal according to the current value command signal to the PWM signal input unit to control the rotation of the motor M. Prior to this, the PWM signal generation circuit 11 is input immediately before. It is determined whether or not there is a free signal in the motor control signal (step S6).
In the case of Yes in step S6, since the bootstrap capacitor 53 is discharged due to the execution of the free control S5, there is a possibility that the upper stage FET 21 cannot be switched and driven. A bootstrap charging control (control as a return control means) S7 for charging the bootstrap capacitor 53 to a sufficient voltage is executed. In the bootstrap charging control S <b> 7, the PWM signal generation circuit 11 outputs an OFF signal to the signal line 6. This corresponds to outputting a PWM signal that is OFF for all periods. This is performed for all phases, and when this OFF signal is input to the half-bridge drive circuit 5, the lower FET 22 is turned ON (at this time, the upper FET 21 is OFF, and the motor M is connected to the GND side to be connected to the motor M. Is the brake action). At the same time, charging of the bootstrap capacitor 53 is started. When the output of the OFF signal is maintained for about 10 microseconds or more, the bootstrap capacitor 53 is charged, and the upper FET 21 is boosted to a level at which the upper FET 21 can be sufficiently turned on. Thereby, the half bridge drive circuit 5 is returned to a state in which the switching drive of the upper stage FET 21 is possible.

  If NO in step S6, immediately after step S6 returns to the state in which the switching drive of the upper stage FET 21 can be switched by the bootstrap charging control S7, the PWM signal generation circuit 11 follows the current value command signal. The motor normal control (control as the rotation drive control means) S8 for controlling the rotation of the motor M by outputting the PWM signal to the PWM signal input unit is executed. Thus, the stepping motor is controlled to rotate and stop at a current value according to the current value command signal (stopping is when the current value related to the current value command signal is 0).

The control method by the stepping motor control apparatus of this embodiment is as described above. Various control operations according to this control method will be confirmed with reference to FIG.
FIG. 4A shows an example of a signal waveform of an operation / free signal for energizing the signal line 16. FIG. 4B is an example of a signal waveform of a current value command signal energized to the signal line 12. FIG. 4C is an example of a signal waveform of an operation / stop signal for energizing the signal line 8. FIG. 4 (d) shows the waveform of the PWM signal according to the motor control signal shown in FIGS. 4 (a), 4 (b) and 4 (c). The operation / free signal and the operation / stop signal are binary signals. Here, the HIGH signal is assigned to the operation signal, and the LOW signal is assigned to the free signal and the stop signal, respectively.

In the periods T1 to T3, since the signals in FIGS. 4A and 4C are both operation signals, the normal motor control S8 based on the PWM signal is executed as can be seen from the flowchart in FIG. . The case where the current value related to the current value command signal is large in the period T1, the case where the current value is 0 in the period T3, and the current value during the period T2 is shown.
In the period T1, since the current value is increased, the duty ratio of the PWM signal is increased. That is, the ON period is long. On the other hand, in the period T2, the duty ratio is smaller than that in the period T1, since the current value is lower than that in the period T1.
In the period T3, since the current value is 0, the entire period OFF signal (duty ratio is 0). As a result, all the upper stage FETs 21 are turned off and all the lower stage FETs 22 are turned on, so that the motor M is connected to GND and performs a braking operation.

  In the period T4, FIG. 4 (a) is a free signal, FIG. 4 (c) is an operation signal, and in FIG. 4 (b), the first half is a command signal with a current value of 0 and the second half is a large current value. As can be seen from the confirmation in accordance with the flowchart of FIG. 3, the free control S5 is executed. Therefore, in the period T4, the PWM signal in FIG. 4D is the ON signal for the entire period. As described above, the motor M changes to a rotation-free state.

  At the time of transition from the period T4 to the period T5, the free signal in FIG. 4A is changed to an operation signal. In this period T5, since there was a free signal in the immediately preceding motor control signal, the bootstrap charging control S7 is executed as can be seen by checking according to the flowchart of FIG. Therefore, in the period T5, the PWM signal in FIG. 4D is an OFF signal for the entire period.

The period T5 ends with a predetermined period. This period is set as a period during which the bootstrap capacitor 53 can be sufficiently charged.
When the period T5 ends and the next period T6 is reached, since the command signal having a large current value is still output, the motor normal control S8 by the PWM signal is executed as in the period T1.

  In the period T7, a stop signal is output as shown in FIG. When the stop signal is output, the stop control (S3 in the flowchart of FIG. 3) is forcibly executed regardless of the other motor control signals (FIGS. 4A and 4B). Is done. Therefore, even if the free signal and the stop signal are output at the same time, the stop control is executed. This corresponds to “Yes” in the decision branch step S2 in the flowchart of FIG.

According to the above embodiment,
Stepping motor M,
A bridge circuit 2 having upper and lower switching elements 21 and 22 for generating a drive current for the stepping motor M;
It has a bootstrap circuit (52, 53) for charging the switching drive power supply (capacitor 53) of the upper switching element 21 and a PWM signal input unit 6, and according to the PWM signal inputted to the PWM signal input unit 6, A half-bridge drive circuit 5 for driving the switching elements 21 and 22 in a reciprocal manner;
In the stepping motor control device for controlling the stepping motor M by outputting a control signal to the PWM signal input unit 6 for the stepping motor driving mechanism provided with
Rotation drive control means (CPU 10, PWM signal generation circuit 11) for controlling the rotation of the stepping motor M by outputting a PWM signal to the PWM signal input unit 6;
By outputting a control signal corresponding to the ON level of the PWM signal to the PWM signal input unit 6 for all phases, the upper switching element 21 is turned ON, the lower switching element 22 is turned OFF, and the ON level By maintaining the output of the control signal corresponding to the above, the switching drive power supply is discharged, the upper switching element 21 is changed from ON to OFF, and both the upper and lower switching elements 21 and 22 are turned OFF, so that the stepping motor And a rotation-free control means (10, 11) for controlling the rotation of M to a free state, so that the stepping motor is controlled by controlling the signal input to the PWM signal input section of the half-bridge drive circuit. M can be controlled in a rotation-free state.

  When the rotation of the stepping motor is controlled by the rotation drive control means (10, 11) from the state where the rotation of the stepping motor is made free by the rotation free control means (10, 11), the rotation drive control means is activated. Prior to this, by outputting a control signal corresponding to the OFF level of the PWM signal to the PWM signal input unit 6 for all phases, the lower switching element 22 is turned ON, and the control signal corresponding to the OFF level of the PWM signal is output. Since the switching drive power supply 53 is charged by maintaining the output, and the return control means (10, 11) for controlling the switching device 21 in the upper stage to be capable of switching driving is provided, the rotation of the stepping motor M is provided. From the state where the motor is free to the state where the rotation of the stepping motor M is controlled It can be changed to ease.

The configuration and control content of the embodiment of the present invention described above are only specific examples, and can be appropriately changed without departing from the gist of the present invention.
In the above embodiment, the central part of the control device has been described as being divided into two blocks of the microprocessor (CPU) 10 and the PWM signal generation circuit 11. However, the rotation described above is performed without regard to block division or block names. It is sufficient to configure the drive control means, the rotation free control means, and the return control means in the control device. If necessary, the brake stop control means is configured as in the prior art.

1 Drive current output line 2 Bridge circuit 21 Upper stage FET
22 Lower FET
5 Half-bridge drive circuit 51 Half-bridge driver IC
52 Bootstrap Charging Circuit 53 Bootstrap Capacitor 11 PWM Signal Generation Circuit M Two-Phase Stepping Motor S3 Stop Control (Stops in Brake Operation State)
S5 Free control (stop in rotation free state)
S7 Bootstrap charge control (return control)
S8 Motor normal control (rotational drive control by PWM signal)

Claims (2)

A stepping motor,
A bridge circuit having upper and lower switching elements for generating a drive current for the stepping motor;
A bootstrap circuit for charging the switching drive power supply of the upper switching element and a PWM signal input unit, and reciprocally switching the upper and lower switching elements in accordance with the PWM signal input to the PWM signal input unit. Half-bridge drive circuit,
In a stepping motor control device for controlling the stepping motor by outputting a control signal to the PWM signal input unit for a stepping motor driving mechanism comprising:
Rotation drive control means for controlling the rotation of the stepping motor by outputting a PWM signal to the PWM signal input unit;
For all phases, by outputting a control signal corresponding to the ON level of the PWM signal to the PWM signal input unit, the upper switching element is turned ON, the lower switching element is turned OFF, and the ON signal is turned ON. By maintaining the output of the control signal corresponding to the level, the switching drive power supply is discharged to change the upper switching element from ON to OFF, and both the upper and lower switching elements are turned OFF and the stepping is performed. Rotation free control means for controlling the motor rotation to a free state;
Stepping motor control device comprising:   From the state in which the rotation of the stepping motor is made free by the rotation free control means, in controlling the rotation of the stepping motor by the rotation drive control means, prior to the activation of the rotation drive control means, for all phases, By outputting a control signal corresponding to the OFF level of the PWM signal to the PWM signal input unit, the lower switching element is turned ON, and the output of the control signal corresponding to the OFF level of the PWM signal is maintained. 2. The stepping motor control device according to claim 1, further comprising a return control unit configured to charge the switching drive power supply so as to control the upper switching element so that the switching drive is possible.

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