JPH04312378A - Detecting system for load torque of motor controller - Google Patents

Abstract

PURPOSE:To calculate a load torque accurately from a load current applied to a motor. CONSTITUTION:A speed detector 3 which generates a speed feedback, a current detector 4 which detects a current applied to a motor 2 and a subtractor 6 which subtracts acceleration according to the output of a differentiator 5 which generates an acceleration by differentiating the speed feedback signal and the current detection signal are provided.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device, and more particularly to a method for detecting load torque of a spindle motor or servo motor that drives a machine tool.

0002

2. Description of the Related Art Machine tools are equipped with a servo motor that drives the table thereof and a spindle motor that drives the cutter and workpiece. A machining center is an example of a machine tool. A machining center processes a workpiece by cutting it with a blade attached to the tip of its spindle. When the blade wears, the cutting torque fluctuates, which appears as a fluctuation in the load torque. Monitoring the motor load torque is essential in order to manage wear and replacement timing of these blades.

FIG. 3 is a block diagram of a conventional motor control device of this type. The speed controller 1 includes a current detector 4
The speed feedback signal from the speed detector 3 forms a speed loop.

The motor 2 is driven by the output current from the speed controller 1. The speed detector 3 is directly connected to the motor 2 and directly detects the speed of the motor 2. The current detector 4 detects the current flowing through the motor 2, and is a current proportional to torque, that is, a torque current detector. In the case of an AC motor, it represents the torque current obtained by converting the current into a DC value using vector control or the like.

[0005] Now, when a speed command is given to the speed controller 1, current flows to the motor 2 and the motor 2 starts rotating. At this time, the torque current of the motor is detected by the current detector 4 and fed back to the speed controller 1, and at the same time,
Used for load torque monitoring.

[0006] Let us now consider the equation of motion of the motor.

[0007]

[Equation 1] T = J・dω/dt+TL Where, T is the torque generated by the motor, ω is the angular acceleration of the motor, J is the sum of the inertia moments of the motor and the load, TL is the load torque

[Formula 2] I=T/KT where I is the torque current and KT is the torque constant.Equation 1 shows that the sum of the acceleration component and the load torque component is the motor torque. Equation 2 shows that motor torque and torque current are proportional.

As shown by Equations 1 and 2, the torque current of the motor and the output torque are in a proportional relationship, so load torque has been monitored by monitoring the torque current of the motor.

[0009]

[Problems to be Solved by the Invention] However, since the conventional motor control device described above uses the torque current of the motor as it is to monitor load torque, the load caused by the acceleration when the motor accelerates or decelerates. The drawback is that current is added and correct load torque cannot be detected.

The present invention has been made in view of the above-mentioned conventional circumstances, and therefore, an object of the present invention is to provide a novel load torque for a motor control device that makes it possible to eliminate the above-mentioned drawbacks inherent in the conventional technology. The objective is to provide a detection method.

[0011]

[Means for Solving the Problems] In order to achieve the above object, a load torque detection method for a motor control device according to the present invention includes a speed detector that generates speed feedback, and a current detector that detects the current flowing through the motor. A motor control device comprising: a differentiating means for generating acceleration from a speed detector; and a subtracting means for calculating a difference between a signal from the current detector and an output generated from the differentiating means. configured.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

Referring to FIG. 1, parts equivalent to those in FIG. 3 are designated by the same reference numerals. Regarding the parts of FIG. 1 that are different from FIG. 3, the embodiment of the present invention shown in FIG. 1 includes a differentiator 5 that differentiates the output from the speed detector 3 of FIG. Output of differentiator 5 and current detector 4
A subtracter 6 is provided for determining the difference between the outputs of .

FIG. 2 shows an operation timing chart of this embodiment. When a speed command is input as shown in FIG. 2, current flows from the speed controller 1 to the motor 2, causing the motor 2 to rotate. The speed detector 3 outputs a signal a following the speed command. Upon receiving the signal a, the differentiator 5 outputs the differentiation result as a signal b. Signal b is a differential of velocity and represents acceleration. Signal b is input to subtracter 6.

On the other hand, the motor current signal c from the current detector 4 is input to the subtracter 6, and the difference between the signals b and c is the signal d.
is output as

Now, assuming that an intermittent load torque is applied to the motor 2, an intermittent current and a current due to acceleration during acceleration/deceleration are added to the motor 2, as shown in signal c. Current flows. However, this current includes a current caused by acceleration. Therefore, by subtracting signal b, which is the acceleration component, only the load torque is output as signal d.

[0018]

[Effects of the Invention] As explained above, according to the present invention,
By subtracting the acceleration component generated during acceleration and deceleration of the motor from the torque current, it is possible to calculate the pure load torque that the motor is applying to the load.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing one embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of an embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

1...Speed controller 2...Motor 3...Speed detector 4...Current detector 5...Differentiator 6...Subtractor

Claims (1)

[Claims] 1. A motor control device comprising: a speed detector that generates speed feedback; and a current detector that detects a current flowing through the motor; A load torque detection method for a motor control device, comprising a subtraction stage for calculating a difference between a signal from a current detector and an output generated from the differentiating means.