JP3033856B2 - Servo motor temperature protection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an industrial robot, NC
The present invention relates to a method for protecting the temperature of an AC servomotor used in a machine tool or the like when the motor is operating or stopped.

[0002]

2. Description of the Related Art Generally, in an AC servomotor used for an industrial robot, an NC machine tool, etc., when the motor is overloaded, a temperature or a temperature substitution characteristic is detected to prevent the motor from burning. When the temperature reaches a certain level, the power supply is stopped. Conventionally, as these protection methods, as shown in FIG. 6, a servo control unit 62 is driven by a control signal from an operation control unit 61, and a motor drive signal is applied from the servo control unit 62 to the servo motor 63, and A means for attaching a temperature sensor 64 and a position / speed sensor 65 to protect the servomotor 63 by the outputs of the temperature sensor 64 and the position / speed sensor 65 (referred to as a conventional example), as shown in FIG. A of stop overload allowable approximation formula
An approximate expression that matches the overload characteristic of the motor at the time of [shown in FIG. 3 to be described later] is obtained, and the value of the approximate expression and the overload amount summed up at every certain sampling time are compared with the operation flow shown in FIG. In other words, turn on the power of the servo motor 63 to start the servo motor 63 (step
71), and it calculates the total sum .SIGMA.I ² OL overload current of the servo motor 63 to be protected of each axis is driven (step 72), is previously registered sum .SIGMA.I ² OL of the calculated load current X Compare with the overload amount OL of the curve (FIG. 3) (step 73).
, ΔI ² OL ≧ OL, there is a calculation detection protection means [conventional example] that turns off the power supply of the servo motor, and otherwise returns to step 72 again. further,
As a conventional example, there is JP-A-62-239822, a temperature detecting device for an AC servomotor, and a heating protection device using the same. In this conventional example, AC servomotor stop state detecting means, means for detecting the magnitude of the primary current, means for detecting the magnitude of the primary voltage, and temperature information output means for the AC servomotor from respective outputs from the means for detecting the magnitude of the primary voltage. More specifically, the AC servo motor outputs a signal corresponding to the maximum value of the primary phase current and determines the magnitude of the voltage applied to the primary winding through which the maximum value phase current flows. In addition, the invention is a temperature information output means of an AC servomotor which outputs a signal of a value obtained by dividing the output of the voltage detection means by the current detection means when the AC servomotor is stopped. Yes, an AC server that outputs a signal indicating that the output of the voltage detecting means is larger than a certain value and the output of the current detecting means is smaller than the certain value when the AC servomotor is stopped. Motor temperature information output means, and furthermore, speed detection means when the AC servomotor is energized, means for detecting the magnitude of the primary phase current, and output of a signal corresponding to the magnitude of the primary voltage A temperature protection output device for the AC servomotor, comprising: a temperature information output device for the AC servomotor; and a power control device for the AC servomotor based on information from the voltage detection device.

[0003]

However, the time T is plotted on the horizontal axis and the current I is plotted on the vertical axis in FIG.
When considering the currents IU, IV, IW of the V and W phases, generally, when the servomotor is in the servo locked state, the currents IU, IV flowing in each phase at the stop position A or B as shown in FIG. , Iw are different. Therefore, for example, in FIG.
When the motor stops at a point, the U-phase current IU is required to produce the same torque as during rotation.

(Equation 1) And the loss is doubled. As a result, there is a danger that the U-phase winding will overheat and burn out. By the way, when stopped at point A, the current flowing in each phase is

(Equation 2) V-phase current IV = -0.5 Im, W-phase current IW = -0.5 Im, and when stopped at point B, the current flowing in each phase is U-phase current IU = 0.86.
6 Im, V-phase current IV = 0, W-phase current IW = -0.866 Im
It is. That is, since the current of each phase that flows differs depending on the stop position of the motor, in order to prevent the motor from overheating regardless of the position where the motor is stopped or in the servo lock state, in the conventional example, the position of the sensor and the time constant need to be considered. The operating temperature of the temperature sensor is lowered, and in the prior art, the overload tolerance is the smallest of the overload approximation formulas at stop shown in FIG. 5, that is, the approximation in the case of stopping at the point A in the example of FIG. Equation X will be set in all operating states,
As a result, in both the conventional example and the overloaded state, in most operating states of the motor, a range smaller than the actual performance is used. Further, in the conventional example, first, when the servo motor is in the servo locked state, the reactance of the primary winding becomes zero, so that the voltage and current of the target portion are detected, and then the resistance value of the resistance portion through which the current flows is detected. Means is derived by Ohm's law to detect the temperature of the windings, so the circuit configuration is complicated, and there is a time loss in performing calculations and judgments. There was a lack of sex. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for protecting a servo motor temperature, which exhibits 100% of the overload performance of the motor in all operating states, that is, at zero speed during rotation.

[0004]

Here, in order to solve the above-mentioned problems, an overload allowable approximation formula corresponding to each stop position and rotation of the motor shown in FIG. 5 is obtained. , Selected from information at the time of rotation and set as a reference value. FIG. 5 shows the overload amount on the horizontal axis and the allowable energizing time on the vertical axis. Curve X is a conventional approximation formula for overload at stop (an example of the stop position A in FIG. 3), and curve Y is overload during rotation. The load allowable approximation formula, curve Z, is the stop overload allowable approximation formula of the present invention. For this reason, if an overload occurs with the previous reference value, the sum of the overloads is compared, and the servo power is turned on and off to achieve 100% motor performance and overload protection. Is also immediate. That is, the present invention provides a synchronous or induction type polyphase AC servo.
In the temperature protection method when the motor is stopped,
The previously held and prepared complex corresponding to the stop position during
Set several reference values, signal zero speed and stop
According to the position signal, a plurality of
Is summed up with one reference value of every sampling time
It is characterized by comparing the overload amount and preventing the motor from heating.
This is a servo motor temperature protection method.

[0005]

According to the present invention having the above-described structure, the approximate expression of the allowable overload of the motor is set as a reference value in accordance with the operation state of the motor. The motor can exhibit the performance against the overload in the entire operation range, and the overload protection is also responsive.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. The same or corresponding members are denoted by the same reference numerals. FIG. 1 is a block diagram showing a main part of a control mechanism of an industrial robot according to one embodiment of the present invention. In FIG. 1, reference numeral 20 denotes a robot controller (CONTR
OLLOR), 8 is a robot mechanism (R), and each axis has a servo motor (M) 6, a brake (B) 7, and an encoder (D) 1
0 is attached. The robot controller 20 has a central processing unit (hereinafter referred to as a CPU) 1. The CPU 1 has a memory 2 composed of a ROM 2, a memory composed of a RAM 3, and an axis control unit (AXIS) 4 [in this embodiment, six-axis control is performed. Yes, input / output interface (INT) 9 and the like are connected by data bus 12. The axis control section 4 is connected to a servo amplifier (AMP) 5 for each axis of the robot, and the output of the amplifier 5 is applied to each axis. Each phase current of the servo motor 6 for driving each axis is indirectly detected from an output command value to the output of the amplifier 5, and a signal indicating zero speed is detected from the presence or absence of a movement command. The stop position also derives a reference value from the number of steps which is the output command value.

Next, the operation of the present invention will be described with reference to the flowchart of FIG. Turn on the robot power, and
Turn on the power supply [hereinafter referred to simply as “servo power supply”] (Step 100). The movement command of each axis motor is checked.
(Step 110). If there is a movement command (YES), the overload allowable approximate expression OLr to be held in advance is set in the memory 2 as a reference value (step 120). 6 is a curve of a time overload allowable approximate expression Z. Thereafter, at every certain sampling time, the square of the overload current is summed up ΣI ² OLR (step 130),
It is compared with a reference value OLr (curve Z) (step 140).
If the total amount ΣI ² OLR is larger than the reference value (YES), ΣI
^{2 If} OLR ≧ OLr, the servo power is turned off (step 190), and the motor is stopped. If the total amount ΣI ² OLR is smaller than the reference value (NO), step 11 is performed when ΣI ² OLR <OLr.
Returning to 0, this operation is repeated. If there is no movement command in the step 110 for checking the presence or absence of the movement command (NO), the servomotor moves a fixed distance for each command pulse. The point at the position moved from the point B, that is, FIG.
Then, for example, a point at a position moved by the pulse amount of points S1 to Sn is obtained. Since the range S1, S2, S3,..., Sn set with a certain width is known in advance from the pulse amount, it is held in advance corresponding to the S1, S2, S3,. The overload allowable approximation formula OLS1 is represented by the allowable energizing time T on the vertical axis.
is set as a reference value from the overload allowable approximate expression Y of FIG.
160). Here, FIG. 4 (a) is a U-phase induced voltage waveform, in which the peak value E is represented by time on the horizontal axis, and the step range is from S1 to S1.
7 and then newly from S1
FIG. 4 (b) repeats the step ranges S1,..., S5... S1 corresponding to the pulse number SN at that time, and indicates that the servo motor 6 has stopped at ST. More specifically, the allowable energizing time is determined by the characteristics of the motor.
Then, the intersection with the curves of the overload allowable approximate expressions X and Y at stop is S4 in FIG. 4 and S3 (S5). The intersection of the curve C indicated by a dotted line between the curves X and Y is S2
(S6), and the intersection of the curve D indicated by a dotted line between the curves Z and Y can be assumed to be S1 (S7). That is, an intersection point which is subdivided by a curve C, D... G represented by a dotted line between the curves X and Y is assumed. This can be made as fine as possible from the accuracy of the information on the motor stop position. A plurality of these intersections are set and are referred to as a first reference value. In addition, the overload allowable approximate expression Z at the time of rotation of the motor
However, the intersection 5z with the line 51 will be referred to as a second reference value. In this way, from the characteristics of the motor, S1, S2 and S3 at stop and the overload allowance at stop are sequentially determined from the three-phase waveform of FIG. Is determined and stored in the memory 2 in advance. Thus, the servo motor 6
If the stop position is found to be, for example, the position of S1 in step 150 where the stop position of S1 is determined, the OLS1 of the curve of the overload allowable approximate expression Y corresponding to the position of S1 is accessed from the memory (ROM) 2. is set to CPU Te (step 160), total amount .SIGMA.I ² OLS1 overload current of each axis servo motors at each sampling time is calculated in step 170, total amount .SIGMA.I ² of overload current at step 180 OLS1
Is compared with the over load point S1 of OLS1 curves stop overload acceptable approximation formula Y, leads to step 190 when the .SIGMA.I ² OLS1 ≧ OLS1, the servo motor stops, total amount of overload current If ΣI ² OLS1 <OLS1 when the value is smaller than the reference value, the process returns to step 110 and repeats the comparison operation.
Thereafter, the above flow is repeated.

[0008]

As described above, according to the present invention, the overload allowable approximation formula of the motor is set as the reference value according to the operation state of the motor, so that the performance with respect to the overload of the motor is set within the entire operation range. And the overload protection is quickly and responsively and accurately performed, and the reliability of the servomotor for overload protection is significantly improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a circuit configuration of an industrial robot embodying the present invention.

FIG. 2 is a flowchart showing the operation of one embodiment of the present invention.

FIG. 3 is an explanatory diagram showing that current of each phase differs depending on a stop position of a servomotor in one embodiment of the present invention.

FIG. 4 is an explanatory diagram for obtaining a motor stop position from an encoder pulse amount according to one embodiment of the present invention.

FIG. 5 is a diagram showing an overload allowable approximate expression according to one embodiment of the present invention.

FIG. 6 is a diagram showing a protection method in which a conventional temperature sensor is incorporated in a servomotor.

FIG. 7 is an operation flowchart of the conventional temperature protection method of FIG. 6;

[Explanation of symbols]

 1 CPU 2 Memory (ROM) 3 Memory (RAM) 4 Axis control unit 5 Servo amplifier 6 Servo motor 7 Brake 8 Robot mechanism unit 9 Input / output interface 10 Encoder 12 Data bus 20 Robot controller

Claims (1)

(57) [Claims] 1. Synchronous or induction type polyphase AC servo
In the temperature protection method at the time of stopping the motor, hold and prepare in advance corresponding to the stop position during one rotation of the motor.
Set multiple reference values, and if it is zero speed
Corresponding to the stop position from the stop signal and the stop position signal.
For one reference value among a plurality and for a certain sampling time
To prevent motor heating by comparing the total overload
And a temperature protection method for the servo motor.