JPH04261385A - Servo motor controller provided with anti-drift rotation function - Google Patents

Abstract

PURPOSE:To prevent drift rotation by interrupting a speed feedback loop during halt of motor and controlling power conversion so that the field produced by an armature winding is fixed. CONSTITUTION:A PWM three-phase inverter comprises a current amplifier 4 for producing a variable frequency AC power supply from a DC power supply and feeding AC power to an AC synchronous servo motor 5. When a motor 5 is controlled through a speed regulator 1 and based on an external speed command Vs so that the actual speed Vi thereof matches with the speed command, a switch 10 is turned from side A to side B based on a latch signal 71a upon lowering of the rotational speed of the motor 5 below a predetermined level and a pole signal 6a is latched by means of the latch circuit 9. Consequently, a speed control loop is opened and a current command circuit 8a provides a command to a current control minor loop through the switch 10 so that a fixed phase current is fed to the motor thus fixing the rotor position and bringing the speed to zero. According to the invention, rotation due to drift of IC in the control circuit can be prevented.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides
The present invention relates to a servo motor control device having a drift rotation prevention function that generates stopping torque without causing rotation due to drift. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

0002

2. Description of the Related Art FIG. 4 shows a block diagram of a conventional servo motor control circuit related to the present invention. In the figure, 5 is a synchronous three-phase AC servo motor, and 6 is an encoder attached to this servo motor 5. This encoder 6 controls the speed and magnetic pole position of the rotor of the motor 5, as shown in FIG. A three-phase signal 6a (hereinafter referred to as a magnetic pole signal) is output so that it can be detected. 7 is a speed detection circuit that detects the speed Vi of the motor 5 from the magnetic pole signal 6a. In this example, the servo motor 5 is made up of six so-called PWM-controlled switching power transistors connected in a three-phase bridge, and receives a variable frequency rectangular wave with a width of 120° (electrical angle) from a DC power supply (not shown). It is assumed that it is driven by an inverter device (not shown) that converts and outputs three-phase alternating current, and this inverter device performs variable frequency control by a speed control circuit having a current control circuit as a minor loop. That is, the speed regulator 1 inputs the deviation between the given speed command Vs and the actual speed Vi of the servo motor 5 detected from the encoder 6 attached to the servo motor 5 via the speed detection circuit 7, and calculates this deviation. A signal 1a that makes the deviation zero is given to the current command circuit 2. Each of the following means 2, 3, 4, and 11 corresponds to one phase of the servo motor 5. The current command circuit 2 receives the magnetic pole signal 6a from the encoder 6 and the adjustment output signal 1a from the speed regulator 1, and outputs a current command circuit output 2a as shown in FIG. 2, which will be described later. Next, the current regulator 3 inputs the deviation between the current command circuit output 2a and the current detection signal 11a of the detector 11 of the input current to the servo motor 5,
A signal 3a that makes this deviation zero is applied to a current amplifier 4, and a drive current is supplied to the servo motor 5 via the current amplifier 4. Here, the current amplifier 4 corresponds to a part of a three-phase bridge connection of PWM-controlled switching power transistors in the inverter device (that is, a part that drives one phase of the armature winding of the servo motor 5).

By the way, when the control function as shown in FIG. 4 is configured with an analog IC (for example, an operational amplifier),
Since the output voltage cannot be set to 0∇ due to the drift of C itself, drift occurs in the speed detection circuit 7 and speed regulator 1, and even if the speed command Vs is set to zero, the motor rotation speed must always be strictly controlled. It is impossible to reduce it to zero. Therefore, as a control method to strictly bring the servo motor to zero speed,
A method is used in which a position control loop is further added to the circuit shown in Figure 4, and the motor is stopped using the adjustment function of this position control loop, or a method is used in which a mechanical brake mechanism is added to the motor shaft to stop the motor. .

0004

However, the method of adding a position control loop and the method of adding a mechanical brake mechanism described above have the disadvantage that they increase the cost and complicate the control device. SUMMARY OF THE INVENTION An object of the present invention is to provide a servo motor control device with a drift rotation prevention function that can solve the above problem.

[0005]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the servo motor control device of claim 1 ``creates variable frequency AC power from a DC power source and supplies it to a synchronous AC servo motor (such as 5). It is equipped with a power conversion means (current amplifier 4, etc.), and is configured to adjust the actual speed (Vi, etc.) of the motor to match the speed command (speed regulator 1, etc.) based on the speed command (Vs, etc.) from the outside. (via) a control device for controlling the power conversion means, wherein the power conversion means is controlled so as to interrupt the speed feedback loop and fix the magnetic field created by the armature winding of the motor while the motor is stopped; shall be equipped with means for preventing drift rotation,

[0006] In the servo motor control device according to claim 2, in the servo motor control device according to claim 1, ``the drift rotation prevention means controls the AC power supply in the power conversion means based on the interruption of the speed feedback loop. ``equipped with means for outputting the DC power only between two predetermined terminals among the output terminals of the

The servo motor control device according to claim 3 is the servo motor control device according to claim 2, further comprising: an encoder for detecting the speed and magnetic pole position of the rotor of the motor, and outputting the DC power source. The means includes connecting the predetermined two terminals to terminals of an armature winding of the motor that are proximate to the magnetic pole position of the rotor at the time when the speed feedback loop is cut off and that form a magnetic pole that attracts the magnetic pole. means (latch circuit 9, current command circuit 8, etc.)
shall be equipped with the following:

[0008] In the servo motor control device according to claim 4, in the servo motor control device according to any one of claims 1 to 3, ``the drift rotation prevention means detects that the speed of the motor has become below a predetermined value. It is provided with means (speed detection circuit 71, switch 10, etc.) for determining the speed and shutting off the speed feedback loop.

[0009]

[Function] When the motor rotation speed falls below a certain rotation speed, the speed detection circuit 7 and speed regulator 1 are affected by drift.
Furthermore, the motor rotation speed is brought to zero by flowing a direct current between two terminals determined by the motor rotor position among the three alternating current input terminals of the motor three-phase armature winding. That is, a synchronous AC servo motor is a synchronous motor that has a permanent magnet rotor inside. The operating principle of a normal AC servo is shown in FIG. That is, a magnetic field of the armature 22 is created in a direction perpendicular to the magnetic field of the permanent magnet (rotor) 21 (at a position of 90°), and the rotor 21 is rotated by the attraction and repulsion of the mutual magnetic forces. In the case of FIG. 5, the rotation is counterclockwise. When the speed drops below a certain number of revolutions, the rotation of the rotating magnetic field created by the current in the armature 22 is stopped as shown in Figure 3, and as a result, the magnetic field of the armature and the magnetic field of the rotor 21 are Rotation due to drift is prevented by opposing and fixing with a 180° shift.

0010

[Embodiment] Next, an embodiment of the present invention will be explained using FIGS. 1 to 3. FIG. 1 shows a control block diagram when the present invention is added to the control circuit of FIG. 4. In other words, in Figure 1, Figure 4
A current command circuit 8, a latch circuit 9, and a switch 10 consisting of an analog switch are added, and a speed detection circuit 7 is added.
It has been replaced with 1. Note that this current command circuit 8 is also for one phase corresponding to the same circuit 2. The speed detection circuit 71 inputs the magnetic pole signal 6a from the encoder, outputs the actual value Vi of the speed of the servo motor 5, and also outputs a latch signal 71a when this speed Vi becomes less than a predetermined value. . This latch signal 71a is applied to latch circuit 9 and switch 10. The latch circuit 9 always uses the magnetic pole signal 6
a is given as is to the current command circuit 2 and the same circuit 8, but when the latch signal 71a is input, the output value of the magnetic pole signal 6a at that time is latched and held.

FIG. 2 shows an example of the waveforms of the magnetic pole signal (output signal of the encoder 6) 6a in FIG. 1 and the output values 2a, 8a of the current command circuits 2, 8 when the latch circuit 9 is not latched. That is, the magnetic pole signal 6a consists of a three-phase signal in which high level and 0 level are repeated at 180° (electrical angle), and the current command circuit outputs 2a and 8a are 30° and 120°.
, 30 degrees (each electrical angle) in the order of 0 level, High level, and 0 level as a half wave, and this half wave waveform consists of an AC waveform that repeats forward and reverse inversion, and the current command circuit output 8a is the same. It is in phase delayed by 60° with respect to output 2a.

In FIG. 1, when the speed of the motor falls below a predetermined value, the switch 10 is turned on based on the latch signal 71a.
The magnetic pole signal 6a is switched from the side to the B side, and the latch circuit 9 latches the magnetic pole signal 6a. This opens the speed control loop, and the current command circuit output 8a, which is fixed based on the latch, is given as a command value to the current control minor loop via the switch 10. This causes a fixed phase current (direct current) to flow through the motor, fixing the rotor position and reducing the speed to zero. As shown in FIG. 2, the output 8a of the current command circuit 8 is always delayed by 60 degrees in phase compared to the output 2a of the current command circuit 2, so simply switching the switch 10 to the B side shown in FIG. This enables the shortest fixed stop of the rotor magnetic poles shown in FIG. Here, the reason why the phase switching from the current command circuit 2a to 8a is set to 60° instead of 90° is because the three-phase drive waveform of the servo motor 5 is 1
This is because it is a rectangular wave with a width of 20° (electrical angle), so it can only be controlled every 60°.

[0013]

According to the present invention, a PWM three-phase inverter is provided as a power conversion means for generating variable frequency AC power from a DC power source and supplying it to the synchronous AC servo motor 5.
In a control device that controls the power conversion means via a speed regulator 1 so that the actual speed Vi of the motor matches the speed command based on a speed command Vs from the outside, while the motor is stopped, the A current command circuit 8, a latch circuit 9, a switch 10, and a speed detection circuit as a drift rotation prevention means for controlling the power conversion means to interrupt the speed feedback loop and fix the magnetic field created by the armature winding of the motor. 71 etc., the IC in the control circuit can be used without using a position control loop or brake.
This makes it possible to prevent rotation due to drift.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a motor control circuit as an embodiment of the present invention.

[Figure 2] Waveform diagram for explaining the operation of Figure 1

[Figure 3] Illustration of the principle of the present invention

[Figure 4] Conventional circuit diagram corresponding to Figure 1

[Figure 5] Explanatory diagram of motor drive principle

[Explanation of symbols]

1 Speed regulator 2 Current command circuit 2a Current command circuit output 3 Current regulator 4 Current amplifier 5 Servo motor 6 Encoder 6a Encoder output signal (magnetic pole signal) 71
Speed detection circuit 71a Latch signal 8 Current command circuit 8a Current command circuit output 9 Latch circuit 10 Switch 11 Current detector

Claims (4)

[Claims] 1. A power conversion means for generating variable frequency AC power from a DC power source and supplying it to a synchronous AC servo motor, wherein the actual speed of the motor matches the speed command based on an external speed command. In the control device for controlling the power conversion means, the power conversion means is controlled so as to interrupt the speed feedback loop and fix the magnetic field created by the armature winding of the motor while the motor is stopped. A servo motor control device with a drift rotation prevention function, characterized by being equipped with a drift rotation prevention means. 2. The servo motor control device according to claim 1, wherein the drift rotation prevention means controls two predetermined output terminals of the AC power supply in the power conversion means based on the interruption of the speed feedback loop. A servo motor control device with a drift rotation prevention function, comprising means for outputting the DC power only between terminals. 3. The servo motor control device according to claim 2, further comprising an encoder for detecting the speed and magnetic pole position of the rotor of the motor, and wherein the means for outputting the DC power is configured to detect the speed and magnetic pole position of the rotor of the motor. It is characterized by comprising means for making the terminal correspond to a terminal of an armature winding of the motor that is closest to the position of the magnetic pole of the rotor at the time of cutting off the speed feedback loop and that creates a magnetic pole that attracts the magnetic pole. A servo motor control device with a drift rotation prevention function. 4. The servo motor control device according to claim 1, wherein the drift rotation prevention means comprises:
A servo motor control device with a drift rotation prevention function, comprising means for determining that the speed of the motor has become less than a predetermined value and interrupting the speed feedback loop.