JPH08275589A - Drive circuit for stepping motor - Google Patents

Abstract

PURPOSE: To obtain a drive circuit for a stepping motor in which the drive torque is prevented from lowering while suppressing vibration. CONSTITUTION: The drive circuit for a stepping motor M comprising free-wheel diodes DA,... connected in parallel with the exciting coil LA,... of respective phases of the stepping motor in the direction reverse to the drive current flow from exciting circuits IA,... is provided with a brake switch 2 in series with the free-wheel diodes DA,.... When the output demand is severe, the brake switch 2 is not turned ON and under a condition where vibration may take place, the brake switch 2 is turned ON by means of a CPU 10 at the end of the exciting step.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step motor drive circuit, and more particularly, to a step motor drive circuit that enables both reduction of vibration of the step motor and securing of drive torque.

[0002]

2. Description of the Related Art Conventionally, stepping motors have been used for various purposes, but stepping vibrations may occur depending on operating conditions. This is because, due to the characteristics of the step motor, the holding torque generated in the vicinity of the stable point that self-holds the position acts as a rotating spring element, while the rotor has a finite moment of inertia. In particular, step vibration is likely to occur under a condition where the load of the step motor is light, and this vibration may cause problems such as noise generation and bearing wear.

Therefore, a free wheel diode is provided in the drive circuit to reduce the step vibration. An example of such a circuit is shown in FIG. In this circuit, a known excitation circuit 101a is connected in series to an excitation coil La of a step motor M and a free wheel diode Da is connected in parallel, and the excitation circuit 101a is connected to the CPU1.
Excitation coil L from power supply VIG according to the command signal from 00
The current is applied to a. Here, the free wheel diode Da is connected such that the cathode thereof is on the side of the exciting circuit 101a. Then, such a circuit is provided for each phase of the step motor M, and the CPU 100 drives the step motor M by sequentially energizing the exciting coils (La, Lb ...) Of each phase via the exciting circuits (101a, 101b ...). Is configured to.

In this circuit, when a command signal is input from the CPU 100 to the exciting circuit 101a of a certain phase (a phase), a current flows through the exciting coil La, and the step motor M is driven by the magnetic action of the rotor and the stator. To be done.
At this time, no current flows because the free wheel diode Da is in the opposite direction.

Here, the step motor M cannot be stopped immediately because of the moment of inertia of the rotor even if it rotates to a stable point which is a target angle. For this reason, the rotor continues to rotate and passes through the stable point, so that a stepping vibration occurs due to the holding torque. Due to this oscillating motion, another phase (for example, b
An induced voltage is generated by the field magnetic field in the (phase) exciting coil Lb, so that an annular current flows through the ground in a loop formed by the exciting coil Lb and the free wheel diode Db. This is because the free wheel diode Db is in the forward direction with respect to this annular current. This current is the exciting coil L
Since the magnetic field generated in b is in the direction that hinders the rotation of the rotor, the vibration is quickly damped. Thus, the step vibration is suppressed.

FIG. 6 shows the effect of vibration suppression by the free wheel diode. In FIG. 6, the vertical axis represents the rotor rotation angle, and the horizontal axis represents time. Here, the curve p (solid line) is the target angle in the energization step. The curve q (broken line) is the actual angle of the rotor in the case of the drive circuit without the free wheel diode, and a remarkable step vibration occurs. The actual angle when a free wheel diode is used is curve r (dashed line) and curve q
It can be understood that the rising is gentle and the step vibration is almost eliminated as compared with.

Incidentally, as a conventional technique in which a drive wheel of an electric motor is provided with a free wheel diode, there is disclosed in JP-A-60-2.
Some of them are disclosed in Japanese Patent Application Laid-Open No. 0702, Japanese Patent Laid-Open No. 56-91693, etc., but the free wheel diode in them recirculates current fluctuations during switching operations such as chopper control in motors other than step motors. Yes, it has a different taste.

[0008]

However, the above-mentioned conventional step motor drive circuit has the following problems. That is, in the drive circuit shown in FIG. 11, since the free wheel diode is always connected, the annular current between the exciting coil and the free wheel diode flows in all non-energized phases during rotation of the rotor. Therefore, in the non-energized phase excitation coil, magnetic flux that hinders the rotation of the rotor is constantly generated, and the driving torque of the step motor is reduced. Therefore, the original performance of the step motor cannot be utilized, such that step-out tends to occur especially under heavy load.

When the stepping motor is driven to the next step, the energization of the phase (a phase) which has been energized until then is cut off, but the self-inductance of the exciting coil La causes the occurrence. Power is exciting coil La
An annular current is caused to flow in and the free wheel diode Da. This current causes the magnetic flux generated in the exciting coil La to enter the other phase and interfere with the original magnetic flux of that phase, which also reduces the driving torque of the step motor.

The influence of the magnetic flux after the power supply is cut off is particularly remarkable when, for example, a four-phase step motor is driven by two-phase excitation, not only the torque is reduced but also the high-speed response is deteriorated. In the case of this drive system, when the energization of a certain phase is cut off, the energization of the opposite phase is started immediately after that,
This is because the magnetic flux after interruption cuts into the opposite phase almost as it is.

This will be described with reference to FIG. The upper part of FIG. 12 shows the current flowing through the a-phase exciting coil La.
The curve d during the a-phase excitation period is the original drive current supplied from the excitation circuit 101a. The reason why the curve d rises gently is because of a delay due to the inductive reactance of the exciting coil La.

However, even when the excitation of the a-phase is completed and the opposing phase (hereinafter referred to as the "a-1 phase") is entered, the current indicated by the curve s flows through the exciting coil La. This is due to the self-inductance of the coil. Further, the subsequent curve t is an induced current generated in the exciting coil La when the rotor is actually driven. And the curve u is
This is an induced current generated by the step vibration of the rotor and is small because the step vibration itself is suppressed. The currents of these curves s, t, and u are all annular currents that flow in the loop of the exciting coil La and the free wheel diode Da.

Next, the influence of the currents of the curves s, t and u on the a-1 phase will be described. The curve v (solid line) in the lower part of FIG. 12 is the original drive current of the a-1 phase supplied from the excitation circuit,
It corresponds to the upper curve d. At this time, a magnetic flux proportional to the curve v is generated in the a-1 phase exciting coil, but not only that, but a magnetic flux due to the current of the a phase exciting coil curves s, t, u enters the a-1 phase. Since these magnetic fluxes are in opposite directions, they cancel each other out, so that the net magnetic flux in the a-1 phase eventually becomes a curve w (dashed line), the driving force is greatly reduced and the torque is reduced.

In the curve w, almost no magnetic flux is generated at the beginning of the a-1 phase excitation period. This is because the a-phase curve s has a particularly large influence. This means that the torque shortage is significant at the beginning of the driving step, and the poor high speed responsiveness is due to this. This is the curve q in FIG.
It appears that the rising of the curve r is gentle compared with. When the step motor is driven at a relatively high pulse rate, this poor high speed response becomes a serious problem.

The present invention has been made in order to solve such a problem, and not only suppress the occurrence of step vibration but also prevent the driving torque from being lowered and bring out the original performance of the step motor. It is an object of the present invention to provide a drive circuit for a step motor capable of achieving the above. It is also an object of the present invention to prevent deterioration of high-speed response, which is likely to cause a problem in such a stepper motor drive circuit. It is also an object to stop the rotor early after the driving of the step motor is completed. Further, according to the present invention, the step motor is optimized under various conditions by suppressing the vibration in the light load condition where the influence of the step vibration is large and not suppressing the vibration in the heavy load condition in which a sufficient torque is required. It is an object of the present invention to provide a drive circuit for a step motor that can be driven at any speed.

[0016]

In order to achieve this object, a step motor drive circuit according to the present invention comprises a motor terminal, a drive means for intermittently supplying a drive current to the motor terminal, and the drive means. A step-motor drive circuit including, for each phase of a step motor, a free wheel diode having one end connected between the motor terminal and the motor terminal in a direction opposite to the drive current, the free wheel diode being Switching means provided in series and switch switching means for controlling switching of the switching means are provided.

The switch switching means turns off the switching means when the drive current starts to be supplied to the motor terminals by the driving means, and then delays the switching means by delaying a predetermined time. It is desirable to include means. Further, the switch switching means in this case includes stop control means for turning off the switching means after a predetermined time has elapsed when the drive current has been supplied to the last motor terminal by the driving means. Is desirable. Further, the switch switching means may include prohibition control means for prohibiting turn-on of the switching means when the load of the step motor is larger than a predetermined amount.

[0018]

In the step motor drive circuit of the present invention having the above-described structure, the drive means for each phase is sequentially interrupted according to the excitation system such as one-phase excitation and two-phase excitation, so that the motor terminals for each phase are sequentially obtained. A drive current is supplied to the excitation coil through the drive coil to drive the step motor. Since the free wheel diode of each phase is in the opposite direction to the drive current,
No drive current flows through the freewheel diode.

When the switching means is turned on by the control signal of the switch switching means,
A ring including the exciting coil and the free wheel diode is formed via the motor terminal and the ground. In this state, an annular current flows forward in the free wheel diode due to the induced electromotive force generated in the exciting coil due to the movement of the step motor. The magnetic action of this current hinders the rotation of the step motor and suppresses vibration. On the other hand, when the switching means is turned off by the switch switching means, the ring between the exciting coil and the free wheel diode becomes non-conductive. In this state, even if the step motor moves, the induced current does not flow in the exciting coil. Therefore, the magnetic action of the current does not cause the rotation resistance of the step motor,
Driving torque is secured.

When the switch changeover means includes the delay control means, the switching means is turned off when the drive means starts supplying the drive current to the motor terminals, and the phase other than the excited phase is excited. Induction current is prevented from flowing in the coil. As a result, the rotation resistance immediately after the start of driving is prevented, the driving torque is secured, and the high speed response is prevented from being degraded. Then, the switching means is turned on with a delay of a predetermined time. This suppresses vibration after the step motor has moved to the target angle.

Further, in the case where the switch switching means includes the stop control means, even if the step motor rotates to the final target position and the supply of the final drive current to the motor terminals is completed, it continues for a predetermined time. As a result, the switching means is brought into conduction, whereby the vibration of the step motor is damped at an early stage, and the step motor is stopped at the stable point. Further, when the switch switching means includes the prohibition control means, the switching means is not turned on when the load of the step motor is larger than a predetermined amount, and the torque shortage is prevented.

[0022]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 illustrates a circuit configuration for driving the step motor M. This drive circuit is used, for example, as a drive circuit for a step motor that adjusts the damping force of a shock absorber for an electronically controlled suspension of an automobile. In the figure, a step motor M which is a four-phase step motor
Has exciting coils LA, LB, LA-1 and LB-1 for each phase, and motor terminals TA and TB of the drive circuit, respectively.
It is connected to TA-1 and TB-1. In the step motor M, the A phase and the A-1 phase, and the B phase and the B-1 phase are opposite to each other.

This drive circuit is basically provided with exciting circuits IA, IB, IA-1, IB-1 for each phase of the step motor M, and from the power source VIG (12V) to the motor terminals TA, TB, T.
This is to switch the conduction to the A-1 and TB-1 terminals. Then, the excitation circuits IA, IB, IA-1, IB-1
A control device (CPU) 10 for inputting a control signal is provided. The excitation circuits IA, IB, IA-1 and IB-1 normally have the power supply VIG and the motor terminals TA, TB, TA-1 and TB.
-The terminal PA is disconnected from the terminal -1, and the terminal PA of the CPU 10
It is configured to be conductive when it receives a control signal from PB, PA-1, PB-1.

Free-wheel diodes DA, DB, DA-1, DB are provided between the excitation circuit of each phase and the motor terminal.
The cathode of -1 is connected, those anodes are concentrated, and it is grounded via the brake switch 2. The free wheel diodes DA, DB, DA-1, DB-1 are connected to the motor terminals TA, TB, TA-1, TB-1 from the power source VIG when the exciting circuits IA, IB, IA-1, IB-1 are turned on. The direction is opposite to the current flowing to the terminal.

The brake switch 2 is for switching connection / disconnection between the free wheel diodes DA, DB, DA-1, DB-1 and ground, and the CPU 10 has a terminal PD for outputting a control signal for this purpose. I have it. The brake switch 2 includes transistors Q1 and Q2 and a resistor R1.
, R2, R3, R4. The base electrode of the transistor Q1 is connected to the CPU1 via the resistor R1.
0, the emitter pole is connected to the 5V power supply, and the collector pole is connected to the base pole of the transistor Q2 via the resistor R3. The emitter pole of the transistor Q2 is connected to the anode concentrated terminals of the free wheel diodes DA, DB, DA-1, and DB-1, and the collector pole is grounded. Resistors R2 and R4 are provided between the bases and emitters of the transistors Q1 and Q2, respectively.

In such a brake switch 2, the transistor Q2 has free wheel diodes DA, DB, DA-.
1. It has a role of a switching element for switching connection / disconnection between DB-1 and ground. When the transistor Q2 is turned on, a free loop diode DA, etc., a motor terminal TA, etc., an exciting coil LA, etc. of the step motor M, and a closed loop returning to the brake switch 2 via the ground are formed for each phase, and the exciting coil LA, etc. The step motor M is configured to be braked by the action of the magnetic flux generated at.

The reason why the transistor Q1 is not directly turned on / off by the output signal of the CPU 10 but the transistor Q1 is interposed is to prevent malfunction of the circuit. That is, due to the structure of the CPU 10, each terminal output is composed of a CMOS, and a parasitic diode exists between each MOS so that the terminal voltage is clamped within a certain range. On the other hand, when the transistor Q2 is off, its emitter potential drops to about -20V. Therefore, in the configuration without the transistor Q1, the forward N channel M
Since a current flows from the base diode of the transistor Q2 to the emitter electrode from the parasitic diode of the OSFET through R3, the transistor Q2 is turned on and the brake is applied.
This is to prevent this.

Next, the exciting circuit IA will be described with reference to FIG. The exciting circuits IB, IA-1, IB-1 are also equivalent to this. The exciting circuit IA is basically composed of a bipolar transistor Q3 and a MOS transistor Q4. The NPN transistor Q3 has a base pole connected to the CPU 10 via a resistor R5 and a collector pole connected to a resistor R7.
To the power supply VIG, and the emitter pole is grounded. The base electrode is also grounded via the resistor R6.

P-channel transistor Q4
The gate pole is the collector pole of the transistor Q3 via the resistor R8 and the diode D1 and the source pole is the power supply VIG.
Further, the drain electrode is connected to the free wheel diode DA and the motor terminal TA, respectively. A capacitor C and a reverse connection series body connecting the cathodes of a diode D2 and a zener diode ZD are respectively interposed between the gate electrode and the drain electrode.

In this circuit, when a control signal is applied from the CPU 10 to the base electrode of the transistor Q3, the transistor Q3 is turned on, so that the transistor Q4 is turned on.
The gate-source voltage VGS is raised, and when the threshold voltage VTH is exceeded, the transistor Q4 is turned on and the voltage application from the power source VIG to the motor terminal TA is started. Here, the capacitor C is for adjusting the switching time of the transistor Q4. Further, the diode D2 and the Zener diode ZD protect the transistor Q4 from the kick voltage generated by the energy remaining in the exciting coil LA after the transistor Q4 is turned off, and at the same time, turn off the current immediately to turn off the current to ensure high-speed response. It is an arc element.

The CPU 10 includes exciting circuits IA, IB, IA.
-1, IB-1 and the brake switch 2 to operate the step motor M, and the excitation circuit IA, I
Output terminals PA, P for controlling B, IA-1, IB-1
An output terminal PD for controlling B, PA-1, PB-1, and the brake switch 2 is provided. Further, it has a built-in memory that stores various programs for driving control of the circuit. Examples of such programs include a drive program for driving the step motor M via the excitation circuits IA, IB, IA-1, and IB-1, a braking program for operating the brake switch 2 at a predetermined timing, and There is a prohibition program for prohibiting the operation of the brake switch 2.

A sensor group 11 for detecting various states of the automobile is attached to the CPU 10. The sensor group 11 includes a vehicle height sensor, a power supply voltage sensor, and various other sensors for reflecting the damping force control.

Next, the operation of the stepper motor drive circuit having the above-described structure will be described. First, the normal operation of driving the step motor will be described. FIG. 3 shows a state when the A phase of the step motor M is excited. At this time, a control signal of active high is input from the PA terminal of the CPU 10 to the exciting circuit IA, and the exciting circuit IA becomes conductive. That is, the control signal of the CPU 10 is the resistance R of FIG.
It is applied via 5 to the base pole of transistor Q3, which turns on transistor Q3. As a result, the gate-source voltage VGS of the transistor Q4 is raised and exceeds its threshold voltage VTH. Therefore, the transistor Q4 is turned on and the power supply VIG and the motor terminal TA are brought into conduction.

Thus, as shown in FIG. 3, a current flows from the power source VIG to the exciting coil LA of the step motor M through the transistor Q4 of the exciting circuit IA and the motor terminal TA. Therefore, magnetic flux is generated in the A phase of the step motor M, and the step motor M is directed toward the target drive of the next step. At this time, since the free wheel diode DA is in the opposite direction to the current flowing through the exciting circuit IA, this current escapes to the ground via the brake switch 2 or the exciting coils (LB, LA- of other phases). 1, LB-
1) never invades. When the transistor Q4 is turned off, it is extinguished by the diode D2 and the zener diode ZD, and the exciting coil L
The current of A disappears rapidly.

Then, as shown in FIG. 4, the terminals PA, PB, PA-1 and PB-1 of the CPU 10 sequentially generate signals, so that the exciting circuit which is brought into the conductive state is sequentially changed, so that the step motor M of the step motor M is changed. It is driven. Although FIG. 4 shows the case of the one-phase excitation method, it goes without saying that the two-phase excitation method is also possible.

Next, the operation of the brake switch 2 will be described. In this embodiment, the PD terminal of the CPU 10 is PA,
After the output of each terminal of PB, PA-1, PB-1 turns on, it turns on with a delay of time e, and terminals PA, PB, PA-1, PB
It turns off when the output state of -1 advances to the next step. That is,
The brake switch 2 does not act at the beginning of each excitation step of driving the step motor M, but the brake switch 2 acts at the end of each exciting step. This state is shown in FIG.
The reason is that it is necessary to move the rotor to the target position quickly in the initial stage of the step, and when the brake switch 2 is operated, it is disadvantageous in terms of high-speed response and generated torque, while the rotor reaches the target position. This is because it is more advantageous to apply the brake switch 2 to suppress rotor vibration.

At the same time as the end of each excitation step, the PD
In principle, the output of the terminal is turned off, but only after the end of the final excitation step (B-phase excitation in FIG. 4), the on state is continued and is turned off after a delay of time f. This is because it is not necessary to consider the responsiveness of the next step when the rotor reaches the final target position and stops the operation. Therefore, it is better to continue the action of the brake switch 2 so that the brake switch 2 stops at the target position quickly. This is because it is advantageous in that

FIG. 5 shows a state in which a control signal is input from the PD terminal of the CPU 10 to the brake switch 2.
The active low control signal from the PD terminal is the resistor R1.
Is input to the base pole of the transistor Q1 via the transistor Q1, and the transistor Q1 is turned on. Therefore, from the 5V power source, through the transistor Q1 and the resistor R3, the transistor Q
A high signal is input to 2 and the transistor Q2 is turned on. At this time, focusing on the B phase, a closed loop is formed from the transistor Q2 of the brake switch 2 to the brake switch 2 via the free wheel diode DB, the motor terminal TB, the exciting coil LB of the step motor M, and the ground. In FIG. 5, only the B phase is shown, but the same applies to the other phases.

Therefore, an induced electromotive force is generated in the exciting coil LB due to the oscillating movement of the rotor of the step motor M, and an annular current flows in this closed loop in the direction indicated by the arrow. The direction of the induced electromotive force is the power source VIG described in FIG.
This is because the voltage is in the same direction as the voltage from, and the free wheel diode DB is in the forward direction with respect to this current.
For this reason, magnetic flux is generated in the exciting coil LB in the direction in which the movement of the rotor is stopped, and thus the step motor M is braked. At the end of each excitation step, the rotor has already reached the target position and is vibrating around it, so this vibration is suppressed by applying the brake.

On the other hand, at the beginning of each excitation step, P
The signal at the D terminal is off, and in the brake switch 2, both the transistors Q1 and Q2 are turned off. Therefore, a closed loop is not formed and the step motor M
Does not brake. The reason why the braking action is not applied in the initial stage of the step is to improve the high-speed response and generate the generated torque. Especially, in the phase that was energized in the previous step, the current from the power supply VIG was cut off,
Since an electromotive force is generated by the self-inductance of the exciting coil, if the brake switch 2 is turned on at this time, the generated torque is greatly reduced by the invasion of the magnetic flux into the opposite phase, and the high-speed response is significantly deteriorated. It is preventing it.

This effect will be described with reference to the graph of FIG.
The curve x (solid line) shows the actual angle of the rotor when driven according to this example. Brake switch 2
The same rise as in the case of driving with always off (curve q) is shown, and the same vibration suppressing effect as in the case of driving with brake switch 2 always on (curve r) is obtained. This means that the braking action is performed only on the vibration component of the rotor motion, so that if the annular current is regenerated to the power source, the vibration energy which was conventionally wasted can be effectively used.

FIG. 7 shows the relationship between the coil current and the effective magnetic flux. The upper part of FIG. 7 shows the current of the exciting coil LA. During the A-phase excitation period, a drive current having a predetermined waveform supplied from the excitation circuit IA flows (curve d). Since the brake switch 2 is turned off at the same time that the current from the exciting circuit IA is cut off after the end of the A-phase excitation period, no current flows at the beginning of the next-phase excitation period. Then, the current of the curve u slightly flows until the period g in which the brake switch 2 is turned on at the end of the next phase excitation period. This is an annular current generated by the step vibration of the rotor and is small because the step vibration is suppressed by the braking action of the brake switch 2.

The lower part of FIG. 7 shows the effective magnetic flux in the phase excited next to the A phase. A drive current having the same waveform as the curve d is supplied to this phase, and almost no disturbing current is generated in the phase A. Therefore, the magnetic flux proportional to the curve d is removed except for the portion of the curve y corresponding to the curve u. Has occurred, indicating that it is energy efficient.
As a result, the torque generated by the step motor M is gained. In particular, since the torque does not drop in the initial stage, the high speed response is excellent.

Here, if the delay time e until the brake switch 2 is turned on in each excitation step is too short, the torque is lowered, and if it is too long, the vibration is insufficiently suppressed, so that the rotor is excited. The brake switch 2 should be turned on shortly before the first stable point in the step is reached. The optimum delay time e is set by attaching an encoder to the step motor M so that the actual angle of the rotor can be detected, and by gradually changing the time e.
It is determined by driving. Since it is often impossible to attach an encoder in an actual automobile due to the structure of the suspension, measurement is performed using a test product, and the optimum value based on the result is stored in the internal memory of the CPU 10 to perform predictive control.

Next, an example of adjusting the damping force according to various states of the vehicle by the step motor drive circuit having the above-described structure and operation will be described. In an actual automobile, it may be better not to perform the brake switch control as described above depending on various situations of the vehicle. Therefore, for each excitation step, the routine shown in the flowchart of FIG. 8 is executed to determine whether to turn on the brake switch 2.

This flow is started when the step motor M needs to be rotated, that is, the damping force needs to be changed. It is necessary to change the damping force when a sudden change in vehicle height or vibration of the vehicle body is detected, when acceleration due to acceleration / deceleration or turning is detected, and the like. In the case of a vehicle model equipped with a suspension mode changeover switch, this also occurs when the switch operation is performed.

At the start of this flow, the brake switch 2 is off. First, in S1, the absolute value of the vehicle speed vertical movement is a predetermined value (for example, 0.5 m / sec).
It is determined whether or not The vehicle height vertical movement speed is a relative speed with respect to the wheels of the vehicle body, and is the speed of the expansion and contraction movement of the shock absorber. As shown in FIG. 9, this determination is made by a vehicle height sensor (mounted on the shock absorber).
The voltage signal from is time-differentiated and further absolute valued is compared with a preset value by a comparator.

If this is less than the predetermined value (S1:
Yes), and proceed to S5. That is, in this case, in the excitation step, the brake switch is turned on at the end of the step as described in the time chart of FIG. This is because in this case, the required rotation speed of the step motor M is low, so that the step vibration remarkably occurs unless the brake switch 2 is operated.

When the vehicle speed vertical movement speed exceeds the predetermined value in S1 (S1: No), the process proceeds to S2, and it is determined whether or not the power supply voltage is a predetermined value (for example, 11 V) or more. The drive power source of the step motor M is an in-vehicle battery,
The effective generated voltage may fluctuate and fall depending on the charging state and the usage of other electric devices, so that the damping force is adjusted normally even at a voltage that is somewhat lower than the voltage at full charge. is there. This determination is made by comparing the voltage value sampled from the power supply VIG with a preset voltage value by a comparator, as shown in FIG.

When the power supply voltage is equal to or higher than the predetermined value (S
2: Yes), and in S5, the brake switch 2 is turned on in the excitation step. This is because in this case, since the power supply voltage is high, the generated torque is strong, and the rotor reaches the stable point in a shorter time than the excitation step period. Therefore, unless the brake switch 2 is actuated thereafter, the step vibration remarkably occurs.

When the power supply voltage is less than the predetermined value in S2 (S2: No), the process proceeds to S3, and it is determined whether or not the load torque applied to the step motor M is in the same direction as the torque generated by the step motor M itself. To judge. Step motor M
The load torque applied to the shock absorber is the torque by which the flow of the working fluid associated with the expansion and contraction of the shock absorber tends to rotate the step motor M via the damping force adjusting valve. The load torque depends on whether the shock absorber extends or contracts. The direction is opposite. Therefore, although it is determined by the sign of the output signal of the vehicle height sensor, it is not always coincident with the direction of the generated torque because it is affected by external factors such as the road surface condition. The direction of the generated torque is determined by the driving direction of the CPU 10.

If these are compared and the directions are the same (S
3: Yes), the process proceeds to S5, and in the exciting step, the brake switch 2 is turned on. In this case, since the step motor M is assisted by the load torque, the rotor reaches the stable point in a shorter time than the excitation step period even if the power supply voltage is less than the predetermined value. Therefore, if the brake switch 2 is not actuated thereafter, the step vibration is remarkably generated.

When the load torque is in the opposite direction to the generated torque (S3: No), the process proceeds to S4, and it is determined whether or not the pulse rate for driving the step motor M is below a predetermined value (for example, 200 pulses / second). to decide. That is, it is determined whether or not the step motor M is driven slowly. This is because the pulse rate varies depending on the situation such that the damping force is slowly driven to avoid a sudden change in riding comfort, while the damping force is rapidly driven to prevent bottoming when the damping force is increased.

When the pulse rate is less than the predetermined value (S4: Yes), the process proceeds to S5, and the brake switch 2 is turned on in the exciting step. In this case, the period of the excitation step is long, so that step vibration is significantly generated unless the brake switch 2 is operated after the rotor reaches the stable point.

When the pulse rate exceeds the predetermined value (S4: No), the brake switch 2 is not turned on in the excitation step. That is, in this case, the vertical movement of the vehicle height is fast (S1: No), and the power supply voltage is low (S1: No).
2: No), the load torque and the generated torque are in opposite directions (S3: No), and the pulse rate is large (S4:
No), the burden on the step motor M is very large. Therefore, the rotor may not reach the stable point even at the end of the excitation step. Therefore, if the output of the step motor M is not ensured, there is a risk of step-out. On the other hand, there is not enough margin to generate step vibration, and it is not necessary to turn on the brake switch 2 either.

Then, in S6, it is determined whether or not the rotor has reached the final target position and the driving of the step motor M has been completed. If not finished yet (S6: No), S7
Switch the excitation phase to the next stage, turn off the brake switch 2 if the previous step was performed by turning on the brake switch 2, and perform a new excitation step S1.
Repeat the following operations. When it is determined in S6 that the driving of the step motor M is completed (S6: Yes), S
At 8, the brake switch 2 is turned on for the time f (see FIG. 4). This is because the step vibration is converged and the rotor is quickly stopped at the stable point. Then, when the brake switch 2 is turned off in S9, this flow ends.

As described in detail above, according to the present embodiment, the stepper motor drive circuit for adjusting the damping force of the shock absorber for the electronically controlled suspension of the automobile,
Free wheel diode DA, DB, DA-1, D of each phase
Since the brake switch 2 is provided in series with B-1 so that the braking action is performed only when necessary, the step vibration of the rotor can be effectively performed without impairing the torque generated by the step motor M and the high-speed response. Can be suppressed.

Particularly, since the brake switch 2 is turned off immediately after the switching of the excitation phase of the step motor M to prevent the braking action, the generated torque of the step motor M and the high-speed response are excellent. Each excitation circuit IA,
The provision of arc extinguishing elements in IB, IA-1, and IB-1 also promotes this effect. Since the brake switch 2 is turned on after a delay of a predetermined time from the switching of the excitation phase, the braking action is performed at the end of the excitation step where the step vibration mainly occurs, and the vibration is effectively reduced. Further, since the brake switch 2 is turned on for a predetermined time after the driving of the step motor M is finished, the step vibration is quickly converged and the rotor can be stopped.

Since the brake switch 2 has the two-stage structure of the transistors Q1 and Q2, no malfunction occurs due to the potential drop when the transistor is off. Further, since the braking action is performed only on the vibration component of the rotor motion, it is possible to effectively utilize the vibration energy by regenerating the annular current to the power source.

Further, depending on the condition of the vehicle, the speed of vertical movement of the vehicle is large, the power supply voltage is reduced, the load is in the opposite direction to the generated torque, and the pulse rate is large. Brake switch 2
Since it is not turned on, the drive torque can be secured and the original output of the step motor can be exhibited under the heavy load condition for the step motor M, while the brake switch 2 is activated under the light load condition. Vibration can be reduced.

Needless to say, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the spirit of the present invention. For example, the various numerical values shown in the above embodiments are merely examples, and the present invention is not limited thereto. The driven step motor may be of a type having a detent torque when not energized, or of a type having no detent torque. Further, the specific circuit configurations of the excitation circuit and the brake switch are not limited to those shown in the figure, and other configurations may be used as long as the same effects can be obtained. Furthermore, the present invention is not limited to adjusting the damping force of the shock absorber, and may be used for a step motor for other purposes.

[0062]

As is apparent from the above description, according to the present invention, the free wheel diode is provided with the switching means, so that the braking action is performed only when necessary and the generation of the step vibration is suppressed. In addition, it is possible to provide a step motor drive circuit capable of preventing the reduction of the drive torque and bringing out the original performance of the step motor. In particular, since the switching means is turned off at the initial stage of the excitation step, the high speed response of the step motor can be secured. Then, since the switching means is turned on for a predetermined time after the step motor drive is completed, the rotor can be stopped early.

Further, according to the present invention, the switching means is not turned on by the prohibition control means in a heavy load situation where sufficient torque is required while vibration is not a problem, and in a light load situation where the influence of step vibration is great. Since the vibration is suppressed by the switching means, the step motor drive circuit capable of optimally driving the step motor under various conditions is provided.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a step motor drive circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of an excitation circuit.

FIG. 3 is a diagram illustrating a state in which a step motor is driven by an exciting circuit.

FIG. 4 is a time chart showing the output of each terminal of the CPU.

FIG. 5 is a diagram illustrating an annular current generated by a brake switch.

FIG. 6 is a graph showing movement of a rotor in a step motor.

FIG. 7 is a graph showing a current and a magnetic flux flowing in an exciting coil of a step motor.

FIG. 8 is a flowchart showing on / off control of a brake switch.

FIG. 9 is a diagram illustrating detection of a vehicle height vertical movement speed.

FIG. 10 is a diagram illustrating detection of a power supply voltage.

FIG. 11 is a circuit diagram of a conventional step motor drive circuit.

FIG. 12 is a graph showing a current and a magnetic flux flowing in an exciting coil of a step motor when a conventional step motor drive circuit is used.

[Explanation of symbols]

 2 Brake switch 10 CPU DA, DB, DA-1, DB-1 Free wheel diode IA, IB, IA-1, IB-1 Excitation circuit TA, TB, TA-1, TB-1 Motor terminal M Step motor

Claims (4)

[Claims] 1. A motor terminal, drive means for intermittently supplying a drive current to the motor terminal, and one end connected between the drive means and the motor terminal in a direction opposite to the drive current. In a step motor drive circuit provided with each free wheel diode for each phase of a step motor, switching means provided in series with the free wheel diode and switch switching means for performing switching control of the switching means are provided. A step motor drive circuit characterized by the above. 2. The switch switching means turns off the switching means when supply of a drive current to the motor terminal by the drive means is started,
The step motor drive circuit according to claim 1, further comprising delay control means for turning on the switching means after a predetermined time delay. 3. The switch switching means includes stop control means for turning off the switching means after a lapse of a predetermined time when the supply of the drive current to the last motor terminal by the drive means is completed. The drive circuit for the step motor according to claim 2. 4. The switch switching means includes prohibition control means for prohibiting turn-on of the switching means when the load of the step motor is larger than a predetermined amount, according to any one of claims 1 to 3. The step circuit drive circuit described.