Robot Controller and Preventive Maintenance Method

Abstract

To preventatively maintain a robot controller by predicting the degradation of a Y-capacitor in a line filter.SOLUTION: Detection means for detecting the zero-phase current is provided in a power supply line between a line filter 20 and a converter 30, which is provided on the load side of the line filter 20 and converts AC power to DC power. An alarm related to a Y capacitor is output when it is detected that the zero-phase current detected by the detection means is above a threshold. The detection means is, for example, a current detector 13 provided in a wiring for each phase in a power supply line, and the sum of the detection outputs of the current detectors 13 for each phase is obtained to make a zero-phase current.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a robot controller used for driving and controlling an industrial robot, and a preventive maintenance method for a line filter provided inside the robot controller.

Background Art

[0002] Motors for each axis provided on a manipulator of an industrial robot are, for example, three-phase synchronous motors, etc., and are driven by servo control by feeding back the motor rotation position detected by an encoder connected to the motor. In servo control, a servo amplifier (or servo driver) is used to drive the motor. The servo amplifier generates three-phase alternating current with a variable frequency and variable current (or variable voltage) by switching direct current power. Therefore, a robot controller used for driving and controlling an industrial robot receives AC power of 50 Hz or 60 Hz from an external commercial power source, converts this into DC power by a rectifier circuit, and supplies it to the servo amplifier, and AC-DC-AC power conversion is performed inside the robot controller. The switching speed in the servo amplifier is, for example, on the order of kHz, and accordingly, switching noise having a frequency component from several kHz to several tens of kHz is generated. In order to prevent the switching noise from leaking to the external power supply side or the noise on the external power supply side from adversely affecting the robot controller, a line filter is provided at the position where the robot controller receives AC power from the external power supply.

[0003] Since it is considered that the frequency of the noise component is sufficiently higher than the power supply frequency, a line filter generally consists of a combination of an inductor that exhibits a high impedance to the noise component and blocks the noise component, and a capacitor that exhibits a low impedance to the noise component and absorbs the noise component. The capacitors provided in the line filter are classified into line-to-line capacitors (X capacitors) inserted between the power supply lines of each phase and line-to-earth capacitors (Y capacitors) with one end connected to the ground point (mainly frame ground). When the other end of the Y capacitor is connected to the neutral point between the phases of the power supply line, if the balance between the phases is maintained on the external power supply side and the noise is normal mode noise, no current should flow through the Y capacitor. However, if zero-phase current is generated for some reason, the zero-phase current will flow through the Y capacitor, so the Y capacitor may deteriorate or fail over time. Especially when the zero-phase current flowing through the Y capacitor is large, the capacitance of the Y capacitor may decrease and the temperature may rise, and in the worst case, the Y capacitor may burn out. Among the zero-phase currents, it is considered that the noise components caused by switching in the servo amplifier, that is, the components with a relatively higher frequency than the power supply frequency component, have a greater impact on the Y capacitor.

[0004] Regarding the detection of zero-phase current, Patent Document 1 discloses detecting the zero-phase current from the power supply cable of three-phase AC power through a zero-phase current transformer for detecting leakage current. Patent Document 2 also discloses that in a power conversion device having a filter provided at the input part of AC power, a converter for performing AC-DC conversion, a DC intermediate circuit including a capacitor, an inverter for performing DC-AC conversion, and a chopper for performing DC-DC conversion, detecting the current flowing between the filter and the converter for each phase of the AC power to obtain the zero-phase current, and performing balance control in the converter or the chopper according to the magnitude of the zero-phase current.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2008-164375 Patent Document 2 Japanese Patent Application Laid-Open No. 2018-03558 Summary of the Invention Problems to be Solved by the Invention

[0006] In a robot controller that performs AC-DC-AC power conversion, the zero-phase current flowing through the Y capacitor of the line filter provided in the input section of the external AC power may cause the Y capacitor to deteriorate over time. Conventionally, however, monitoring of the zero-phase current has not been performed, and therefore, the occurrence of a failure in the Y capacitor has not been predicted. As preventive maintenance, the line filter may be replaced every two to three years, but such replacement causes an increase in cost.

[0007] An object of the present invention is to provide a robot controller capable of predicting the deterioration of a Y capacitor in a line filter and performing preventive maintenance, and a preventive maintenance method for a line filter provided in the robot controller. Means for Solving the Problems

[0008] The robot controller of the present invention is a robot controller that drives and controls motors of respective axes of a manipulator, and includes at least a Y capacitor disposed between a power line and a ground point and provided in a receiving section of AC power from an external power source, a line filter, a converter provided on the load side of the line filter and converting AC power into DC power, a servo amplifier that switches DC power and supplies the AC power obtained by the switching to a motor to servo-control the motor, a detecting means provided on a power line between the line filter and the converter for detecting a zero-phase current, and a control circuit that outputs an alarm related to the Y capacitor when it is detected that the zero-phase current detected by the detecting means has become equal to or greater than a threshold value.

[0009] In a robot controller that performs AC-DC-AC conversion, the value of the zero-phase current flowing through the power line between the line filter and the converter is substantially equivalent to the value of the zero-phase current flowing through the Y capacitor of the line filter. Also, as the deterioration of the Y capacitor progresses, the zero-phase current flowing through the Y capacitor tends to increase. In the robot controller of the present invention, the zero-phase current flowing through the power line between the line filter and the converter is detected, and an alarm is output when the detected zero-phase current exceeds a threshold value. As a result, in the robot controller of the present invention, an alarm is output when the deterioration of the Y capacitor progresses, and it becomes possible to replace the line filter, etc. before a failure occurs in the Y capacitor, and it becomes possible to perform preventive maintenance of the line filter.

[0010] In the robot controller of the present invention, the threshold value is determined based on the allowable value of the zero-phase current in the Y capacitor It is. By determining the threshold value in this way, it becomes possible to quickly detect the progress of deterioration in the Y capacitor.

[0011] In the robot controller of the present invention, the detection means is, for example, a current detector provided in the wiring for each phase in the power line between the line filter and the converter. At this time, the sum of the detection outputs of the current detectors for each phase is obtained as the zero-phase current. When a current detector is provided for each phase, it also becomes possible to separate, for example, normal mode noise and common mode noise by arithmetic processing. Also, the detection means may be a clamp current transformer arranged to detect the sum of the currents of each phase in the power line between the line filter and the converter. When such a clamp current transformer is used, it becomes possible to immediately obtain the value of the zero-phase current without performing addition operations or the like.

[0012] The zero-phase current flowing through the Y capacitor includes a component of the power supply frequency of the external power supply and a component of a relatively high frequency generated by switching in the servo amplifier. Since the zero-phase current of the relatively high frequency component contributes more significantly to the deterioration of the Y capacitor, the robot controller of the present invention may be provided with a filter for blocking the component of the power supply frequency of the external power supply between the detection means and the control circuit, or alternatively, when it is detected that the frequency component exceeding the power supply frequency of the external power supply in the zero-phase current becomes equal to or greater than a threshold value, the control circuit may be configured to output an alarm. In these cases, it is not essential to determine the threshold value based on the allowable value of the zero-phase current in the Y capacitor.

[0013] The preventive maintenance method of the present invention is a preventive maintenance method for a line filter in a robot controller that drives and controls motors of each axis of a manipulator, comprising at least a Y capacitor disposed between a power supply line and a ground point, a line filter provided in a receiving section of AC power from an external power supply, a converter provided on the load side of the line filter for converting AC power into DC power, and a servo amplifier for switching DC power and supplying the AC power obtained by the switching to motors of each axis of the manipulator to servo-control the motors. The method includes detecting a zero-phase current flowing through a power supply line between the line filter and the converter, and predicting the progress of deterioration in the Y capacitor based on the detected zero-phase current.

[0014] In a robot controller that performs AC-DC-AC conversion, the value of the zero-phase current flowing through the power supply line between the line filter and the converter is substantially equivalent to the value of the zero-phase current flowing through the Y capacitor of the line filter. Also, as the deterioration of the Y capacitor progresses, the zero-phase current flowing through the Y capacitor tends to increase. Therefore, in the preventive maintenance method of the present invention, the zero-phase current flowing through the power supply line between the line filter and the converter is detected, and the deterioration of the Y capacitor is predicted based on the detected zero-phase current. Thereby, it is possible to prevent the occurrence of failures and the like associated with the deterioration of the Y capacitor.

[0015] In the preventive maintenance method of the present invention, it is preferable to output an alarm related to the Y capacitor when it is detected that the zero-phase current has become equal to or higher than the threshold value. By outputting the alarm, it is possible to surely know that the time has come to replace the Y capacitor or the line filter, etc. The threshold value is preferably determined based on the allowable value of the zero-phase current in the Y capacitor. By determining the threshold value in this way, it becomes possible to accurately perform preventive maintenance according to the deterioration in the Y capacitor.

[0016] The zero-phase current flowing through the Y capacitor includes a component of the power supply frequency of the external power supply and a component of a relatively high frequency generated by switching in the servo amplifier. Since the zero-phase current of the relatively high frequency component contributes more to the deterioration of the Y capacitor, the progress of the deterioration in the Y capacitor may be predicted based on the frequency component exceeding the power supply frequency of the external power supply in the zero-phase current. By performing the prediction using the relatively high frequency component in the zero-phase current, the influence caused by the external power supply can be excluded and more appropriate preventive maintenance of the line filter can be performed.

Effects of the Invention

[0017] According to the present invention, since the progress of the deterioration of the Y capacitor can be estimated by measuring the zero-phase current, it becomes possible to predict the deterioration of the Y capacitor in the line filter and perform preventive maintenance of the line filter.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Best Mode for Carrying Out the Invention

[0019] Next, embodiments of the present invention will be described with reference to the drawings. First, the zero-phase current flowing through the Y capacitor of the line filter in the robot controller will be described. FIG. 1 is a diagram for explaining the zero-phase current flowing through the Y capacitor, and is an equivalent circuit diagram showing a section from an external AC power supply to the manipulator with respect to the common-mode component. In FIG. 1, the path through which the zero-phase current of the high-frequency component generated by the switching operation in the servo amplifier flows is shown.

[0020] The robot controller 10 is supplied with AC power from an external power supply (primary power supply) 50 that is a single-phase or three-phase AC power supply, and drives and controls the motors of each axis of the manipulator 70. The motors of each axis of the manipulator 70 are, for example, three-phase motors, and in the robot controller 10, AC-DC-AC power conversion is performed. Therefore, the robot controller 10 includes a line filter 20 provided in the AC power receiving section from the external power supply 50, a converter (for example, a diode rectifier circuit) 30 that is connected to the secondary side (load side) of the line filter 20 and performs AC-DC conversion, and a servo amplifier 40 that is supplied with DC power from the converter 30 and drives the motor of each axis of the manipulator. In the figure, the resistance Rs is the equivalent internal resistance of the external power supply 50.

[0021] The line filter 20 is represented as a low-pass filter consisting of an inductor L1 and a capacitor C1 as an equivalent circuit, where the capacitor C1 is a Y capacitor (capacitor between line and ground) provided in the line filter 20. In the converter 30, for example, for smoothing, etc., a capacitor C2 with one end connected to the ground point is provided. The capacitor C2 is also a Y capacitor. The servo amplifier 40 is a circuit that performs DC-AC conversion by switching the supplied DC power, and in the figure, it is represented as an AC source 41 that switches DC power to generate AC power. The switching frequency is, for example, from several kHz to 10 kHz, and steep rising and falling pulses are generated by the switching, so the AC source 41 acts as a strong noise source. In the figure, a capacitor C3 with one end connected to the ground point is also drawn in the servo amplifier 40, and this is also a Y capacitor.

[0022] The three-phase motor driven by the servo amplifier 40 can be ignored as a common-mode component, but there is a capacitor C4, which is a wiring stray capacitance, between the power wiring leading to the three-phase motor and the ground point inside the manipulator 70. Therefore, as shown by the arrow in the figure, the noise generated by the AC source 41 flows to the ground point through the capacitors C1 to C3, which are Y capacitors, from one end of the AC source 41, and also flows to the ground point through the capacitor C4, which is a wiring stray capacitance, from the other end of the AC source 41. Eventually, the high-frequency noise components generated by the AC source 41 flow into the capacitors C1 to C3, which are Y capacitors. In particular, since the capacitor C1, which is a Y capacitor in the line filter 20, is provided within the AC section, the noise components from the AC source 41 flow as zero-phase current in the capacitor C1. The zero-phase current flowing through the capacitor C1 can cause deterioration of the capacitor C1. When the industrial robot becomes larger and the size of the manipulator 70 increases, the length of its internal wiring becomes longer, and accordingly, the capacitor C4, which is a wiring stray capacitance, also becomes larger, so the zero-phase current flowing through the capacitor C1, which is a Y capacitor, also becomes larger.

[0023] Therefore, in the robot controller based on the present invention, the zero-phase current flowing through the Y capacitor provided in the line filter is detected, the progress of deterioration of the Y capacitor is predicted according to the detection result, and an alarm is output, etc., to prevent in advance the failures that may occur due to the deterioration of the Y capacitor. FIG. 2 shows the configuration of a robot controller according to an embodiment of the present invention.

[0024] The robot controller shown in FIG. 2 is supplied with three-phase AC power from an external power source, and similar to the one shown in FIG. 1, it includes a line filter 20 that receives three-phase AC power, a converter 30 composed of a diode rectifier circuit, and a servo amplifier 40. The line filter 20 has two common-mode coils L11 and L12 connected in series, an X capacitor (inter-line capacitor) C11 is arranged at the input part of the common-mode L11 on the external power source side, an X capacitor C12 is also arranged between the common-mode coils L11 and L12, and a Y capacitor C13 is provided between the neutral point and the ground point of the X capacitor C12. Further, a line-interval resistor R11 and an X capacitor C14 are provided on the output side of the common-mode coil L12 on the load side, and a Y capacitor C15 is provided between the neutral point and the ground point of the X capacitor C14. The ground point in the line filter 20 is the frame ground (FG), and this ground point is drawn out to the outside of the line filter 20 for protective grounding (PE).

[0025] The converter 30 and the servo amplifier 40 are provided in the internal circuit block 11 of the robot controller. A main power supply circuit capacitor C10 is provided in the DC power wiring between the converter 30 and the servo amplifier 40. A control circuit 12 that controls the entire robot controller, and in particular controls the servo amplifier 40 to operate the manipulator based on commands, is also provided in the internal circuit block 11. The control circuit 12 is composed of, for example, a microprocessor or the like.

[0026] Between the line filter 20 and the converter 30, three wires for each phase are provided as power lines to supply three-phase AC power. In the robot controller of this embodiment, a current detector 13 is provided for each of these three wires. The detection output for each current detector 13 is input to the control circuit 12. Since it is three-phase AC power, if the balance between phases is maintained, the sum of the instantaneous values of the current detection values by the three current detectors 13 is always 0. If there is a zero-phase current due to a noise component generated by switching in the servo amplifier 40, the sum of the instantaneous values of the current detection values will not be 0, but will be the value due to that zero-phase current. Although the magnitude of the zero-phase current changes due to a change in the wiring stray capacitance (capacitor C4 in FIG. 1) in the manipulator, the zero-phase current also increases according to the degree of deterioration of the Y capacitors C13 and C15. Therefore, the control circuit 50 constantly monitors the zero-phase current by calculating the sum of the detection outputs from each current detector 12 and predicts the progress of the deterioration of the Y capacitors C13 and C15. Then, when the value of the zero-phase current exceeds the threshold, the control circuit 12 outputs an alarm, prompting the administrator of the robot controller to replace the line filter 20. Thereby, the occurrence of failures in the Y capacitors C13 and C15 in the line filter 20 can be prevented in advance. The threshold can be determined based on, for example, the allowable zero-phase current values in the Y capacitors C13 and C15.

[0027] Among the zero-phase currents, the contribution of the zero-phase current of the power supply frequency component to the deterioration of the Y capacitor is not large. However, noise components generated by switching in the servo amplifier 40, for example, components with frequencies of several hundred Hz or more, may cause significant deterioration of the Y capacitor when flowing as the zero-phase current. Moreover, the zero-phase current of these high-frequency components increases when the deterioration of the Y capacitor progresses. Therefore, the control circuit 12 may extract the frequency components in the zero-phase current that exceed the power supply frequency of the external power supply, and output an alarm when the value of the zero-phase current in the extracted frequency components exceeds the threshold. Such extraction of frequency components can be performed, for example, in the control circuit 12 by removing low-frequency components such as the power supply frequency component using digital filter technology. Alternatively, a high-pass filter configured to block the power supply frequency component may be provided between each current detector 13 and the input of the control circuit 50.

[0028] In the robot controller according to the present embodiment described above, a current detector 13 is provided in the wiring of each phase in the power line between the line filter 20 and the converter 30. The sum of the instantaneous values of the detection outputs of these current detectors 13 is obtained to obtain the zero-phase current. Since the value of the zero-phase current thus obtained is substantially equivalent to the value of the zero-phase current flowing through the Y capacitors C13 and C15, it is possible to predict the progress of deterioration in the Y capacitors C13 and C15 from the value of the zero-phase current. The zero-phase current flowing through the Y capacitors C13 and C15 also flows through the X capacitors C12 and C14. Therefore, similar to the Y capacitors C13 and C15, it is possible to predict the progress of deterioration in the X capacitors C12 and C14. In particular, by detecting that the zero-phase current value has exceeded the threshold value, it can be determined that the deterioration of the Y capacitors C13 and C15 has progressed and the time has come to replace the line filter 20. That is, in the present embodiment, preventive maintenance of the line filter 20 can be performed without periodically replacing the line filter 20, and the occurrence of failures in the Y capacitors C13 and C15 can be prevented. Further, since the current detection values for each phase of the AC power are input to the control circuit 15, it is possible to obtain the difference between the common-mode component and the normal-mode component of the noise component generated by the switching in the servo amplifier 40. Furthermore, based on the observation of the zero-phase current, it is also possible to confirm the defects in the wiring on the external power supply side or inside the manipulator.

[0029] In the robot controller shown in FIG. 2, a current detector 13 is provided in the wiring of each phase in the power line between the line filter 20 and the converter 30 to detect the zero-phase current, but the method for detecting the zero-phase current is not limited to this. For example, a clamp current transformer or a zero-phase current transformer can also be used to detect the zero-phase current. In the robot controller according to another embodiment of the present invention shown in FIG. 3, a clamp current transformer 16 is used to detect the zero-phase current. In the example shown in FIG. 3, the clamp current transformer 16 is configured as a zero-phase current transformer, and the wiring conductors of each phase are passed together through the central hole of the doughnut-shaped core (or iron core) constituting the clamp current transformer 16. The output current of the clamp current transformer 16 is proportional to the zero-phase current and is input to the control circuit 13. Also in the robot controller shown in FIG. 3, in order to detect only the zero-phase current due to the noise component generated by the switching in the servo amplifier 40, the value of the zero-phase current from which low-frequency components such as the power supply frequency component are removed using digital filter technology may be obtained in the control circuit 50. Alternatively, as shown in FIG. 4, a high-pass filter 17 may be provided between the clamp current transformer 16 and the input of the control circuit 50.

[0030] As described above, the present invention has been described assuming that three-phase AC power is supplied from an external power source to the robot controller. However, the AC power supplied from the external power source to the robot controller does not necessarily have to be three-phase. Even in a robot controller to which single-phase AC power is supplied from an external power source, by detecting the zero-phase current from the current flowing through the power line between the line filter and the converter in the same manner as described above, the degree of deterioration of the Y capacitor of the line filter can be known, and preventive maintenance of the line filter can be performed.

Explanation of Reference Numerals

[0031] 10... Robot controller; 11... Internal circuit block; 12... Control circuit; 13... Current detector; 16... Clamp current transformer; 17... High-pass filter; 20... Line filter; 30... Converter; 40... Servo amplifier; 41... AC source; 50... External power source; 70... Manipulator.

Claims

1. A robot controller for driving and controlling motors of respective axes of a manipulator, comprising: a line filter provided in a receiving section of AC power from an external power source, the line filter including at least a Y capacitor disposed between a power line and a ground point; a converter provided on a load side of the line filter for converting the AC power into DC power; a servo amplifier for switching the DC power and supplying the AC power obtained by the switching to the motor to servo-control the motor; detection means provided on a power line between the line filter and the converter for detecting a zero-phase current; a control circuit for outputting an alarm related to the Y capacitor when it is detected that the zero-phase current detected by the detection means becomes equal to or greater than a threshold value; and having a robot controller, wherein the threshold value is determined based on an allowable value of the zero-phase current in the Y capacitor.

2. A robot controller for driving and controlling motors of respective axes of a manipulator, comprising: a line filter provided in a receiving section of AC power from an external power source, the line filter including at least a Y capacitor disposed between a power line and a ground point; a converter provided on a load side of the line filter for converting the AC power into DC power; a servo amplifier for switching the DC power and supplying the AC power obtained by the switching to the motor to servo-control the motor; detection means provided on a power line between the line filter and the converter for detecting a zero-phase current; a control circuit for outputting an alarm related to the Y capacitor when it is detected that the zero-phase current detected by the detection means becomes equal to or greater than a threshold value; and having a robot controller, further comprising a filter for blocking a component of a power frequency of the external power source between the detection means and the control circuit.

3. A robot controller for driving and controlling motors of respective axes of a manipulator, comprising: a line filter provided in a receiving section of AC power from an external power source, the line filter including at least a Y capacitor disposed between a power line and a ground point; a converter provided on a load side of the line filter for converting the AC power into DC power; a servo amplifier for switching the DC power and supplying the AC power obtained by the switching to the motor to servo-control the motor; Detection means provided on a power line between the line filter and the converter for detecting a zero-phase current; A control circuit that outputs an alarm related to the Y capacitor when it detects that the zero-phase current detected by the detection means has reached or exceeded a threshold value; having; The control circuit is a robot controller that outputs the alarm when it detects that a frequency component exceeding the power supply frequency of the external power supply in the zero-phase current has reached or exceeded the threshold value.

4. The robot controller according to claim 2 or 3, wherein the threshold value is determined based on an allowable value of a zero-phase current in the Y capacitor.

5. The detection means is a current detector provided in wiring for each phase on a power line between the line filter and the converter, The robot controller according to any one of claims 1 to 4, wherein the sum of the detection outputs of the current detectors for each phase is obtained as the zero-phase current.

6. The detection means is a clamp current transformer arranged to detect the sum of the currents of each phase on a power line between the line filter and the converter, and the robot controller according to any one of claims 1 to 4.

7. A line filter provided at a receiving portion of AC power from an external power supply, including at least a Y capacitor disposed between a power line and a ground point, a converter provided on the load side of the line filter for converting the AC power into DC power, and a servo amplifier for switching the DC power and supplying the AC power obtained by the switching to motors of respective axes of a manipulator to servo-control the motors, and a preventive maintenance method for the line filter in the robot controller for driving and controlling the motors of the respective axes of the manipulator, detecting a zero-phase current flowing through a power line between the line filter and the converter, A preventive maintenance method for predicting the progress of deterioration in the Y capacitor based on the detected zero-phase current.

8. The preventive maintenance method according to claim 7, wherein an alarm related to the Y capacitor is output when it is detected that the zero-phase current has reached or exceeded a threshold value.

9. The preventive maintenance method according to claim 8, wherein the threshold value is determined based on an allowable value of a zero-phase current in the Y capacitor.

10. The preventive maintenance method according to any one of claims 7 to 9, which predicts the progress of deterioration in the Y capacitor based on a frequency component exceeding the power supply frequency of the external power supply in the zero-phase current.

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