JPH04372521A - Method of protecting temperature of servo motor - Google Patents

Abstract

PURPOSE:To detect overload quickly and protect a motor by setting a plurality of overload reference values in accord with the stoppage positions during the stoppage of a servo motor, and setting one overload reference value during rotation, and sampling it in specified cycles, and detecting the sum total of the quantity of overload. CONSTITUTION:By the command of the CPU 1 of a robot controller 20, a shaft controller (six-axis control) 4 rotates and steps the servo motor 6 coupled to a robot mechanism 8. The allowable current value of the motor during rotation is set in RAM 3 in advance. Moreover, during the stepping, a plurality of allowable current values corresponding to the stoppage position are set in RAM 3 in advance. The stoppage position is encoded 10 and input into a shaft controller 4. The load is sampled in specified cycles with the program of ROM 2 to seek the sum total of the quantity of overload, and when it exceeds the allowable value, the motor 6 is stopped with a brake 7. Hereby, the overload in accord with operating condition is detected quickly and surely, and reliability improves.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to industrial robots, NC
This article relates to a method for protecting the temperature of AC servo motors used in machine tools, etc., when the motor is running and when it is stopped.

0002

[Prior Art] Generally, in AC type servo motors used in industrial robots, NC machine tools, etc., when the motor is overloaded, temperature or temperature substitute characteristics are detected to prevent motor burnout. If the temperature exceeds a certain level, the power is turned off. Conventionally, as shown in FIG. 6, the servo control section 62 is driven by a control signal from the operation control section 61,
A motor drive signal is applied to the servo motor 63 from 2, a temperature sensor 64 and a position/speed sensor 65 are attached to the motor 63, and the servo motor 63 is protected by the outputs of the temperature sensor 64 and position/speed sensor 65. For example, find an approximate equation that matches the overload characteristics of the motor at point A [represented in FIG. 3, which will be described later] of the approximate equation for overload tolerance at stop, such as the X curve shown in Figure 5. The value of the approximation formula and the overload amount summed at each sampling time are compared and calculated according to the operation flow shown in FIG. The sum of overload currents ΣI of the protected servo motors 63 of each axis being driven
2 OL is calculated (step 72), and the calculated total load current ΣI2 OL and the previously registered X curve (
Compare with the overload amount OL in Fig. 3) (step 73), Σ
There is an arithmetic detection protection means [referred to as conventional example (2)] which turns off the power to the servo motor when I2 OL≧OL, and returns to step 72 if not. moreover,
As a conventional example (2), there is a temperature detection device for an AC servo motor and a heating protection device using the same, disclosed in Japanese Patent Application Laid-Open No. 62-239822. This conventional example ■ includes means for detecting the stop state of an AC servo motor, means for detecting the magnitude of the primary current,
This invention uses temperature information output means for an AC servo motor from each output from the means for detecting the magnitude of the primary voltage, and more specifically, outputs a signal corresponding to the maximum value of the primary phase current. This invention uses the temperature detection means of an AC servo motor based on the magnitude of the voltage applied to the primary winding through which the maximum phase current flows, and also detects the output of the voltage detection means when the AC servo motor is in a stopped state. This invention uses a temperature information output means for an AC servo motor that outputs a signal obtained by dividing the voltage by the current detection means, and when the AC servo motor is in a stopped state, the output of the voltage detection means is greater than a certain value, and the current detection Temperature information output means for an AC servo motor that outputs a signal indicating that the output of the means is smaller than a certain value, and furthermore, a speed detection means when the AC servo motor is energized, and a magnitude of the primary phase current. and voltage detection means that outputs a signal according to the magnitude of the primary voltage, and temperature information output means for the AC servo motor, and controls power to the AC servo motor based on the information from the voltage detection means. This is a motor overheat protection device.

0003

[Problem to be Solved by the Invention] However, in FIG. 3, the horizontal axis represents time T, and the vertical axis represents current I,
When considering the V and W phase currents IU, IV, and IW,
Generally, when the servo motor is in the servo lock state, Figure 3
As shown in the figure, the currents IU, IV, and Iw flowing through each phase differ depending on the stop position A or B. therefore,
For example, when stopping at point A in Figure 3, in order to produce the same torque as when rotating, the U-phase current IU must be

It is necessary to flow [Equation 1], and the loss will be twice as high. As a result, there is a risk that the U-phase winding will overheat and burn out. By the way, if it stops at point A, the current flowing through each phase is

[
Equation 2] V-phase current IV = -0.5Im, W-phase current IW = -0
．． 5Im, and when it stops at point B, the current flowing through each phase is U
Phase current IU = 0.866 Im, V phase current IV =
0, W phase current IW=-0.866Im. In other words, since the current flowing through each phase differs depending on the motor's stopping position, in order to prevent the motor from overheating no matter where it is stopped or in the servo-locked state, in conventional example Therefore, the operating temperature of the temperature sensor is lowered, and in conventional example (2), the overload capacity is the smallest among the overload approximations at stop shown in Fig. 5, that is, Fig. 3
In the example, the approximation formula In this situation, it will be used to a lesser extent than its actual capacity. Furthermore, in conventional example ■, when the servo motor is in the servo lock state, the reactance of the primary winding becomes zero, so the voltage and current of the target part are detected, and then the resistance of the resistor part through which the current flows is detected. Because the method detects the temperature of the winding by deriving the value using Ohm's law, the circuit configuration is complicated, and there is a time loss in calculating and making decisions. The problem was a lack of quick response. Therefore, an object of the present invention is to provide a temperature protection method for a servo motor that can immediately exhibit 100% of the motor's overload performance under all operating conditions, ie, during rotation and zero speed.

0004

[Means for solving the problem] Here, in order to solve the above problem, an overload tolerance approximation formula suitable for each stop position and rotation of the motor shown in FIG. , select from the rotation information and set as the reference value. By the way, in Fig. 5, the horizontal axis shows the overload amount, and the vertical axis shows the allowable energization time, the curve The load tolerance approximation equation, curve Z, is the overload tolerance approximation equation during stoppage of the present invention. Therefore, when an overload occurs, the product sum of the overloads is compared with the reference value mentioned above, and the servo power is turned on and off to ensure that the motor performs at 100% and provides overload protection. This is also done immediately. That is, the present invention relates to a multiphase AC servo motor of synchronous machine type or induction machine type, and separates the reference value for overload protection of the motor during stop and rotation, and when the motor is stopped, the rotation during one rotation of the motor is A plurality of first reference values held and prepared in advance corresponding to the position are set, and one of the plurality of first reference values corresponding to this stop position is set based on a signal indicating zero speed and a signal of the stop position. The motor is prevented from overheating by comparing the overload amount summed up at each sampling time with the reference value of 1, and a second reference value that is set corresponding to the rotation and a certain sampling time. This is a temperature protection method for a servo motor, characterized in that heating of the motor is prevented by comparing overload amounts summed up for each time.

[0005]

[Operation] According to the present invention configured as described above, the motor overload tolerance approximation formula is set as a reference value according to the operating state of the motor. The motor's performance against overload can be demonstrated over the entire operating range, and overload protection can also be provided immediately.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. Note that the same or equivalent members will be described using the same reference numerals. FIG. 1 is a block diagram showing the main parts of a control mechanism of an industrial robot according to an embodiment of the present invention. In FIG. 1, 20 is a robot control device (C
8 is the robot mechanism section (ONTROLLOR), and 8 is the robot mechanism section (R
), and a servo motor (M) 6, a brake (B) 7, and an encoder (D) 10 are attached to each axis. The robot control device 20 includes a central processing unit (hereinafter referred to as C).
The CPU 1 has a memory 2 consisting of ROM, a memory 3 consisting of RAM, and an axis control unit (AXIS
) 4 [in this embodiment, 6-axis control is performed], an input/output interface (INT) 9, etc. are connected by a data bus 12. A servo amplifier (AMP) 5 for each axis of the robot is connected to the axis control unit 4, and an output from the amplifier 5 is applied to each axis. Each phase current of the servo motor 6 driving each axis is indirectly detected from the output command value to the output of the amplifier 5, and the signal indicating zero speed is detected from the presence or absence of a movement command, and the servo motor 6 The reference value for the stop position is also derived from the step number, which is the output command value.

Next, the operation of the present invention will be explained with reference to the flowchart shown in FIG. Turn on the robot power and start the servo motor 6.
When the power supply [hereinafter simply referred to as "servo power supply"] is turned on (step 100), the movement command of each axis motor is checked (step 110). If there is a movement command (YE
S), the overload tolerance approximation formula OLr to be held in advance is set in memory 2 as a reference value (step 120).
), the overload tolerance approximation formula OLr at this time is the curve of the rotating overload tolerance approximate formula Z in FIG. After that, the square of the overload current is the sum ΣI2 at each sampling time.
OLR is performed (step 130) and compared with the reference value OLr (curve Z) (step 140). If the total amount ΣI2 OLR is larger than the reference value (YE
S), ΣI2 OLR ≧OLr, the servo power is turned off (step 190) and the motor is stopped. If the total amount ΣI2 OLR is smaller than the reference value (NO),
If ΣI2 OLR <OLr, the process returns to step 110 and this calculation operation is repeated. Furthermore, if there is no movement command in step 110 of checking the presence or absence of a movement command (NO), this servo motor moves a certain distance for each command pulse, so the stop position is the position of the origin pulse in terms of the U phase in Fig. 3. A point at a position moved from point B, that is, a point at a position moved by a pulse amount of, for example, points S1 to Sn in FIG. 4 is determined. The range S1, S2, S3,..., Sn is held in advance based on the pulse amount and is set to a certain width in this way.
Since we know that S1, S2, S3,..., Sn
Overload tolerance approximation formula OLS1 held in advance corresponding to
However, the vertical axis represents the allowable energization time Ta, and the horizontal axis represents the overload amount O.
The reference value is set from the stop overload tolerance approximation Y in FIG. 5 in which L is taken (step 160). Here, Figure 4 (
a) is the U-phase induced voltage waveform, whose peak value E is expressed by time on the horizontal axis, and the step range is divided from S1 to S7,
Furthermore, it is newly divided from S1 in the same way, as shown in Figure 4(b).
indicates that the step range S1,..., S5...S1 corresponding to the pulse number SN at that time is repeated, and the servo motor 6 has stopped at ST. To explain further, the allowable energization time is determined by the characteristics of the motor, so for example, if line 51 is drawn, the intersection with the curve of the overload allowable approximation formulas X and Y at stop is S4 in FIG. 4 and S3 (S5).
becomes. The intersection point with curve C shown by a dotted line between curves X and Y can be assumed to be S2 (S6), and the intersection point with curve D shown by a dotted line between curves Z and Y can be assumed to be S1 (S7). In other words, a curve C shown by a dotted line between curves X and Y,
Intersections subdivided by D...G, etc. are assumed. This can be done in as much detail as you like depending on the accuracy of the information on the motor's stop position. A plurality of these intersection points are set and will be referred to as the first reference value. Also, in the rotational overload tolerance approximation formula Z when the motor is rotating, the intersection 5z with the line 51 will be referred to as the second reference value. In this way,
Due to the characteristics of the motor, when stopping, S1, S2, and S
3 and the overload tolerance at stop are determined from the three-phase waveform in Figure 3,
These are uniquely determined from the conditions for equally dividing the 1/2 cycle in FIG. 4, and are preset and stored in the memory 2. In this way, in step 150 where the stop position of the servo motor 6 is determined, if the stop position is found to be, for example, the position S1, OLS1 of the curve of the overload tolerance approximation formula Y at the time of stop corresponding to the position S1 is Memory (ROM)
)2 and set on the CPU (step 1
60), the total amount of overload current ΣI2 OLS1 of each axis servo motor for each sampling time is calculated in step 170, and the total amount of overload current ΣI2 OLS1 is calculated in step 180.
OLS of the curve of OLS1 and overload tolerance approximation formula Y at stop
ΣI2 OLS1
≧OLS1, the process goes to step 190, the servo motor stops, and ΣI2 when the total amount of overload current is smaller than the reference value. will be repeated.

[0008]

As described above, according to the present invention, the motor overload tolerance approximation formula is set as a reference value depending on the operating state of the motor. In addition, the overload protection can be performed quickly, responsively, and accurately, and the reliability of the overload protection of the servo motor is significantly improved.

[Brief explanation of drawings]

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

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

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

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

FIG. 5 is a diagram showing an overload tolerance approximation formula according to an embodiment of the present invention.

FIG. 6 is a diagram illustrating a conventional protection method for incorporating a temperature sensor into a servo motor.

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

[Explanation of symbols]

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

Claims (1)

[Claims] Claim 1: Relating to a synchronous machine type or induction machine type polyphase AC servo motor, the reference value for overload protection of the motor is divided into periods of stop and rotation, and when the motor is stopped, the rotational position during one rotation of the motor is provided. A plurality of first reference values held and prepared in advance corresponding to the stop position are set, and based on the zero speed signal and the stop position signal, one of the plurality of first reference values corresponding to this stop position is set. The reference value of the motor is compared with the overload amount summed for each sampling time to prevent the motor from overheating. A temperature protection method for a servo motor, characterized in that overheating of the motor is prevented by comparing the amount of overload that is summed up at each time.