JPH04351482A - Method and apparatus for controlling motor - Google Patents

Abstract

PURPOSE:To increase an output of a motor at the time of nonlocking by alleviating an overload judging condition during nonlocking as compared with that during locking. CONSTITUTION:Memory means 30 stores overload deciding conditions of locking and nonlocking states of a motor 10. For example, it is assumed as the condition at the time of locking that a maximum allowable current I1 continuously flows for a time t1. And, it is also assumed as the condition at the time of nonlocking that a maximum allowable current I2 continuously flows for a time t2, where I1<I2, t1<t2 are satisfied. Thus, the conditions I2, t2 at the time of the nonlocking are alleviated as compared with the conditions I1, t1 at the time of locking. Lock detecting means 32 decides whether a rotor 12 is locked or not. That is, if a current command (i) is a state of the current I1 during a period when the present position theta of the rotor 12 is continued for a predetermined time, the motor 10 is judged to be locked, a coil current is interrupted by current control means 22 to protect the motor 10. If it is judged to be non- locked, a phase controller 24 judges the load is an overload by using the conditions I2, t2 at the time of nonlocking from the means 30.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method and a control device for determining overload operation of a motor used in an industrial robot or the like.

0002

BACKGROUND OF THE INVENTION In industrial robots, a movable part may hit a stopper or the like at the limit of its operating range, or the movable part may hit a large obstacle and become locked. In motors used in this type of robot, such a locked state is detected and the motor current is cut off to protect the motor. Also, although the motor is not locked, the load may become abnormally large, resulting in an overload condition. When this condition occurs, the current is cut off to protect the motor.

Conventionally, this locked state and an overload due to an increase in resistance during an unlocked state were not distinguished, and a lock or an overload was determined based on, for example, a state in which the current exceeded a predetermined value for a certain period of time or more.

However, in actual motors, even if the same current is flowing, the amount of heat generated when the motor is locked is greater than when it is not locked, and it has been found that the time required for the motor to burn out is shorter when the motor is locked. Ta. This seems to be because in a completely locked state, current continues to flow only to a fixed coil, but as long as the operation continues, even under heavy load and low speed, the coils through which current flows will change in order.

Conventionally, the allowable overload current and overload duration time have been set based on the lock state, which is the most severe operating condition. For this reason, when the lock is unlocked, the motor is judged to be overloaded and stops operating, even though there is actually a surplus of load, making it impossible to get the maximum performance out of the motor. There was an inconvenience.

[0006]

[Object of the Invention] The present invention was made in view of the above circumstances, and it is possible to increase the motor output by increasing the overload time and current limit value of the motor, especially when the lock is not locked. The purpose of this invention is to provide a method for controlling a motor. Another object is to provide a control device that can be used directly for implementing this method.

[0007]

[Structure of the Invention] According to the present invention, this object is achieved by a motor control method characterized in that the conditions for determining overload during unlocking are made looser than the conditions for determining overload during locking. .

[0008]

[Embodiment] Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2
is a diagram showing an example of the operation, and FIG. 3 is an operation flowchart.

In FIG. 1, reference numeral 10 denotes a brushless servo motor, which has a permanent magnet rotor 12 and a three-phase field coil 14. The rotor 12 has an encoder 1
6 are connected, and this encoder 16 controls the rotor 12.
The rotation angle of is detected. The subtractor 18 is the command speed v0
The difference between the current speed v obtained from this encoder 16 (v
0 - v). The speed control amplifier 20 uses this difference (v
0-v) is sent to the current control means 22.

The current control means 22 includes a phase control circuit 24 and a transistor bridge circuit 26. The bridge circuit 26 has a plurality of switching transistors for selectively exciting the three coils 14, and the phase control circuit 24
selectively turns on and off the corresponding transistors based on the rotation angle θ of the rotor 12. Here, the rotation angle .theta. of the rotor 12 is determined by a current position counter 28 that counts the pulse output of the encoder 16.

Further, the phase control circuit 24 changes the firing phase of each transistor of the bridge circuit 26 based on the current command i, and changes the excitation current of the coil 14. As a result, the excitation current of the coil 14 is controlled so that the rotation speed v of the motor 10 matches the command speed v0.

Reference numeral 30 denotes a memory means, which stores conditions for determining overload of the motor 10. That is, the overload determination conditions for the locked state and unlocked state of the motor 10 are stored. For example, as shown in FIG. 2, it is assumed that the maximum allowable current I1 continues to flow for a time t1 as a locking condition. Further, as a condition for unlocking, the maximum allowable current I2 continues for a time t2. However, I1 <I
2, t1 < t2. In this way, the conditions I2 and t2 when not locked are more relaxed than the conditions I1 and t1 when locked.

The overload discrimination conditions for locking and unlocking are not only defined by the maximum allowable current and time, but also by the product of current and time when the current exceeds a certain level, that is, as shown in FIG.
It may also be defined by the area in .

The phase control circuit 24 normally sets the conditions (I2, t2) for the non-lock state one after another (FIG. 3, step 100).

Numeral 32 is a lock detection means that determines whether or not the rotor 12 is locked (step 102 in FIG. 3).
. That is, when the current position θ of the rotor 12 continues for a certain period of time (for example, 10 msec), if the current command i is at the maximum allowable current (I1) during this period, it is determined that the current position θ is locked. If it is determined that the lock is present, the overload determination condition (I1, t1
) (step 104), overload is determined (step 106), and when overload occurs, the coil current is cut off to protect the motor 10 (step 108). Further, when it is determined that the lock is not locked, the phase control circuit 24
An overload is determined using the unlock condition (I2, t2) (step 106). When an overload occurs, the coil current is cut off to protect the motor 10 (step 108).
).

[0016] If it is determined that there is no overload (step 1
06), it is determined whether the locked state is released (step 110). For example, if the encoder 16 outputs a predetermined pulse or more after locking is detected, or if the current command i
It is assumed that the lock is released because the value becomes less than the maximum allowable value (I1, I2), and the above operation is repeated.

The above embodiment is a brushless servo motor 1.
0, the present invention can be applied to other motors and those with various control methods, and the present invention includes these.

[0018]

Effects of the Invention As described above, the invention of claim 1 has relaxed overload determination conditions during unlocking compared to conditions during locking, so the motor output during unlocking can be increased and the motor - Maximize the performance of your computer.

According to the second aspect of the invention, there is obtained a control device that can be used directly for carrying out this method.

[Brief explanation of drawings]

FIG. 1: Block diagram of one embodiment of the present invention

[Figure 2] Diagram showing an example of its operation

[Figure 3] Operation flow chart

[Explanation of symbols]

10 Motor 22 Current control means 30 Memory means 32 Lock detection means

Claims (2)

[Claims] 1. A method for controlling a motor, characterized in that conditions for determining overload during unlocking are made more relaxed than conditions for determining overload during locking. 2. Lock detection means for detecting locking of the motor; condition memory means for separately storing overload determination conditions for locked and non-locked states; and memory means based on the output of the lock detection means. A control device for a motor, comprising: control means for controlling an excitation current of the motor using corresponding overload/overload determination conditions successively determined from the above.