JP7699488B2 - Robot controller and preventive maintenance method - Google Patents

Description

The present invention relates to a robot controller used to drive and control an industrial robot, and a preventive maintenance method for a line filter installed inside the robot controller.

The motors of each axis of the manipulator of an industrial robot are, for example, three-phase synchronous motors, 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 AC with variable frequency and variable current (or variable voltage) by switching DC power. Therefore, the robot controller used to drive and control the industrial robot receives 50 Hz or 60 Hz AC power from an external commercial power source, converts it to 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 of the servo amplifier is, for example, on the order of kHz, and accordingly, switching noise with frequency components of several kHz to several tens of kHz is generated. To prevent the switching noise from leaking out to the external power source or the noise on the external power source from adversely affecting the robot controller, a line filter is provided at the position where the AC power from the external power source is received in the robot controller.

Since the frequency of noise components is considered to be sufficiently higher than the power supply frequency, line filters are generally constructed by combining inductors that present high impedance to noise components to block the noise components, and capacitors that present low impedance to noise components to absorb the noise components. The capacitors provided in line filters are classified into inter-line capacitors (X capacitors) inserted between the power lines of each phase, and line-to-earth capacitors (Y capacitors) whose one end is connected to a ground point (mainly the 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 a zero-phase current occurs for some reason, the zero-phase current flows through the Y capacitor, and the Y capacitor may deteriorate or break down over time. In particular, when the zero-phase current flowing through the Y capacitor is large, the capacity of the Y capacitor decreases and the temperature rises, and in the worst case, the Y capacitor may burn out. Of the zero-phase currents, it is believed that noise components caused by switching in the servo amplifier, i.e. components with frequencies relatively higher than the power supply frequency components, have a greater effect on the Y capacitor.

Regarding the detection of zero-phase current, Patent Document 1 discloses detecting zero-phase current from a three-phase AC power supply cable via a zero-phase current transformer in order to detect leakage current. Patent Document 2 discloses that in a power conversion device having a filter provided at the input section of AC power, a converter that performs AC-DC conversion, a DC intermediate circuit including a capacitor, an inverter that performs DC-AC conversion, and a chopper that performs DC-DC conversion, the current flowing between the filter and the converter is detected for each phase of AC power to determine the zero-phase current, and balance control is performed in the converter or chopper depending on the magnitude of the zero-phase current.

JP 2008-164375 A JP 2018-03558 A

In robot controllers that perform AC-DC-AC power conversion, the zero-phase current flowing through the Y capacitor of the line filter installed at the input of external AC power can cause the Y capacitor to deteriorate over time, but traditionally there has been no monitoring of the zero-phase current, and therefore no attempt to predict the occurrence of a fault in the Y capacitor. As a preventive maintenance measure, the entire line filter is sometimes replaced every two to three years, but such replacements lead to increased costs.

The object of the present invention is to provide a robot controller that can predict deterioration of the Y capacitor in a line filter and perform preventive maintenance, and a preventive maintenance method for a line filter installed in the robot controller.

The robot controller of the present invention is a robot controller that drives and controls the motors of each axis of a manipulator, and includes a line filter that has at least a Y capacitor placed between a power line and a ground point and is provided at a receiving section for AC power from an external power source, a converter that is provided on the load side of the line filter and converts AC power to DC power, a servo amplifier that switches the DC power and supplies the AC power obtained by switching to the motor to servo-control the motor, a detection means that is provided on the power line between the line filter and the converter to detect 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 detection means exceeds a threshold value.

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 approximately equivalent to the value of the zero-phase current flowing through the Y capacitor of the line filter. Furthermore, 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, making it possible to replace the line filter before a failure occurs in the Y capacitor, and to perform preventive maintenance of the line filter.

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 . By determining the threshold value in this manner, it becomes possible to quickly detect the progress of deterioration in the Y capacitor.

In the robot controller of the present invention, the detection means is, for example, a current detector provided on the wiring for each phase in the power supply line between the line filter and the converter, and in this case, the sum of the detection outputs of the current detectors for each phase is calculated to obtain the zero-phase current. When a current detector is provided for each phase, it is possible to separate, for example, normal mode noise from common mode noise by calculation processing. The detection means may also be a clamp current transformer arranged to detect the sum of the currents of each phase in the power supply line between the line filter and the converter. When such a clamp current transformer is used, it is possible to immediately obtain the value of the zero-phase current without performing addition calculations, etc.

The zero-phase current flowing through the Y capacitor includes a component of the power supply frequency of the external power supply and a relatively high frequency component generated by switching in the servo amplifier. Since the zero-phase current of the relatively high frequency component contributes more to deterioration of the Y capacitor, the robot controller of the present invention may include a filter between the detection means and the control circuit for blocking the component of the power supply frequency of the external power supply, or the control circuit may output an alarm when it is detected that the frequency component of the zero-phase current exceeding the power supply frequency of the external power supply exceeds a threshold value. 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.

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 the motors of each axis of a manipulator, and that includes a line filter that includes at least a Y capacitor placed between a power line and a ground point and is provided at a receiving section for AC power from an external power source, a converter that is provided on the load side of the line filter and converts AC power to DC power, and a servo amplifier that switches the DC power and supplies the AC power obtained by switching to the motors of each axis of the manipulator to servo-control the motors, and detects the zero-phase current flowing through the power line between the line filter and the converter, and predicts the progress of deterioration in the Y capacitor based on the detected zero-phase current.

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 approximately equivalent to the value of the zero-phase current flowing through the Y capacitor of the line filter. Furthermore, 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 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. This makes it possible to prevent the occurrence of breakdowns and other problems associated with deterioration of the Y capacitor.

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 is equal to or greater than a threshold value. By outputting an alarm, it is possible to reliably know that it is time to replace the Y capacitor or the line filter. It is preferable that the threshold value is determined based on the allowable value of the zero-phase current in the Y capacitor. By determining the threshold value in this manner, it becomes possible to perform appropriate preventive maintenance in accordance with the deterioration of the Y capacitor.

The zero-phase current flowing through the Y capacitor contains a component at the power supply frequency of the external power supply and a relatively high frequency component caused by switching in the servo amplifier. Since the relatively high frequency component of the zero-phase current contributes more to deterioration of the Y capacitor, the progression of deterioration in the Y capacitor may be predicted based on the frequency component of the zero-phase current that exceeds the power supply frequency of the external power supply. By making a prediction using the relatively high frequency component of the zero-phase current, the effects caused by the external power supply can be eliminated, allowing for more appropriate preventive maintenance of the line filter.

According to the present invention, the degree of deterioration of the Y capacitor can be estimated by measuring the zero-phase current, so that the deterioration of the Y capacitor in the line filter can be predicted and preventive maintenance of the line filter can be performed.

FIG. 2 is an equivalent circuit diagram showing a zero-phase current flowing through a Y capacitor of a line filter. 1 is a block diagram showing a robot controller according to an embodiment of the present invention; FIG. 11 is a block diagram showing a robot controller according to another embodiment. FIG. 13 is a block diagram showing a robot controller according to yet another embodiment.

Next, an embodiment 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 explaining the zero-phase current flowing through the Y capacitor, and is an equivalent circuit diagram showing the section from the external AC power source to the manipulator with respect to the common mode component. FIG. 1 shows the path through which the zero-phase current of the high-frequency component generated by the switching operation in the servo amplifier flows.

The robot controller 10 is supplied with AC power from an external power source (primary power source) 50, which is a single-phase or three-phase AC power source, 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 the robot controller 10 performs AC-DC-AC power conversion. For this reason, the robot controller 10 is equipped with a line filter 20 provided at the receiving section of the AC power from the external power source 50, a converter (e.g., 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 receives DC power from the converter 30 and drives the motor of each axis of the manipulator. In the figure, resistance Rs is the equivalent internal resistance of the external power source 50.

The line filter 20 is represented as an equivalent circuit as a low-pass filter consisting of an inductor L1 and a capacitor C1, where the capacitor C1 is a Y-capacitor (line-to-earth capacitor) provided in the line filter 20. In the converter 30, for example, for smoothing, a capacitor C2 is provided with one end connected to the ground point. 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 is represented in the figure as an AC source 41 that switches the DC power to generate AC power. The switching frequency is, for example, several kHz to 10 kHz, and since switching generates pulses with steep rising and falling edges, the AC source 41 acts as a strong noise source. In the figure, a capacitor C3 is also depicted in the servo amplifier 40 with one end connected to the ground point, which is also a Y-capacitor.

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

The robot controller based on the present invention detects the zero-phase current flowing through the Y capacitor provided in the line filter, predicts the progress of deterioration of the Y capacitor based on the detection results, and outputs an alarm to prevent failures that may occur due to deterioration of the Y capacitor. Figure 2 shows the configuration of a robot controller according to one embodiment of the present invention.

The robot controller shown in FIG. 2 is supplied with three-phase AC power from an external power source, and similar to that shown in FIG. 1, includes a line filter 20 that receives three-phase AC power, a converter 30 consisting 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 arranged at the input of the common mode L11 on the external power source side, an X capacitor C12 arranged between the common mode coils L11 and L12, and a Y capacitor C13 provided between the neutral point and the ground point of the X capacitor C12. Furthermore, an inter-line 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 of the line filter 20 is the frame ground (FG), but this ground point is drawn out to the outside of the line filter 20 for protective grounding (PE).

The converter 30 and servo amplifier 40 are provided in the internal circuit block 11 of the robot controller. A main power circuit capacitor C10 is provided in the DC power wiring between the converter 30 and the servo amplifier 40. The internal circuit block 11 also includes 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. The control circuit 12 is composed of, for example, a microprocessor.

Between the line filter 20 and the converter 30, three wirings are provided for each phase as power supply lines to supply three-phase AC power. In the robot controller of this embodiment, a current detector 13 is provided for each of the three wirings. The detection output of each current detector 13 is input to the control circuit 12. Since it is three-phase AC power, if the balance between the phases is maintained, the sum of the instantaneous values of the current detection values of the three current detectors 13 is always 0. If there is a zero-phase current due to noise components 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 a value due to the zero-phase current. The magnitude of the zero-phase current changes due to changes in the wiring stray capacitance (capacitor C4 in FIG. 1) in the manipulator, but the zero-phase current also increases depending on 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 to predict the progress of deterioration of the Y capacitors C13 and C15. When the value of the zero-phase current exceeds the threshold, the control circuit 12 outputs an alarm and prompts the robot controller administrator to replace the line filter 20. This makes it possible to prevent failures in the Y capacitors C13 and C15 in the line filter 20. The threshold can be determined, for example, based on the allowable zero-phase current value in the Y capacitors C13 and C15.

Among the zero-phase currents, the zero-phase current of the power supply frequency component does not contribute much to the deterioration of the Y capacitor, but noise components generated by switching in the servo amplifier 40, for example, components with frequencies of several hundred Hz or more, may significantly deteriorate the Y capacitor when they flow as zero-phase current, and the zero-phase current of these high-frequency components becomes large when the deterioration of the Y capacitor progresses. Therefore, the control circuit 12 may extract 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 component exceeds a threshold value. Such frequency component extraction can be performed, for example, by removing low-frequency components such as the power supply frequency component in the control circuit 12 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.

In the robot controller of the present embodiment described above, a current detector 13 is provided on the wiring of each phase in the power line between the line filter 20 and the converter 30. The zero-phase current is calculated by calculating the sum of the instantaneous values of the detection outputs of these current detectors 13. Since the value of the zero-phase current calculated in this manner is approximately equivalent to the value of the zero-phase current flowing through the Y capacitors C13 and C15, the progress of deterioration in the Y capacitors C13 and C15 can be predicted from the value of the zero-phase current. Since the zero-phase current flowing through the Y capacitors C13 and C15 also flows through the X capacitors C12 and C14, the progress of deterioration in the X capacitors C12 and C14 can be predicted in the same way as the Y capacitors C13 and C15. In particular, by detecting that the zero-phase current value exceeds the threshold value, it is possible to know that the deterioration of the Y capacitors C13 and C15 is progressing and that it is time to replace the line filter 20. That is, in this embodiment, preventive maintenance of the line filter 20 can be performed without periodic replacement of the line filter 20, and the occurrence of failures in the Y capacitors C13 and C15 can be prevented. In addition, because the current detection value for each phase of the AC power is input to the control circuit 15, it is possible to determine the difference between the common node component and the normal mode component of the noise components generated by switching in the servo amplifier 40, and furthermore, based on the observation of the zero-phase current, it is possible to check for defects in the wiring on the external power supply side or inside the manipulator.

In the robot controller shown in FIG. 2, a current detector 13 is provided on 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 of detecting the zero-phase current is not limited to this. For example, the zero-phase current can also be detected using a clamp current transformer or a zero-phase current transformer. In the robot controller of another embodiment of the present invention shown in FIG. 3, the zero-phase current is detected using a clamp current transformer 16. 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 a central hole of the doughnut-shaped magnetic core (or iron core) that constitutes 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. In the robot controller shown in FIG. 3, in order to detect only the zero-phase current due to the noise components generated by switching in the servo amplifier 40, the control circuit 50 may use digital filter technology to obtain the value of the zero-phase current from which low-frequency components such as the power supply frequency components have been removed. 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.

The present invention has been described above assuming that three-phase AC power is supplied to the robot controller from an external power source, but the AC power supplied to the robot controller from the external power source does not necessarily have to be three-phase. In a robot controller that receives single-phase AC power from an external power source, the degree of deterioration of the Y capacitor of the line filter can be determined 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, and preventive maintenance of the line filter can be performed.

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 (10)

A robot controller that drives and controls the motors of each axis of a manipulator,
a line filter provided at a receiving portion of AC power from an external power source, the line filter including at least a Y capacitor disposed between a power source line and a ground point;
a converter provided on a load side of the line filter to convert the AC power into DC power;
a servo amplifier that switches the DC power and supplies AC power obtained by the switching to the motor to servo-control the motor;
a detection means for detecting a zero-phase current, the detection means being provided in a power supply line between the line filter and the converter;
a control circuit for outputting an alarm related to the Y capacitor when the zero-phase current detected by the detection means becomes equal to or greater than a threshold value;
having
The threshold value is determined based on an allowable value of a zero-phase current in the Y capacitor . A robot controller that drives and controls the motors of each axis of a manipulator,
a line filter provided at a receiving portion of AC power from an external power source, the line filter including at least a Y capacitor disposed between a power source line and a ground point;
a converter provided on a load side of the line filter to convert the AC power into DC power;
a servo amplifier that switches the DC power and supplies AC power obtained by the switching to the motor to servo-control the motor;
a detection means for detecting a zero-phase current, the detection means being provided in a power supply line between the line filter and the converter;
a control circuit for outputting an alarm related to the Y capacitor when the zero-phase current detected by the detection means becomes equal to or greater than a threshold value;
having
a filter between the detection means and the control circuit for blocking power supply frequency components of the external power supply ; A robot controller that drives and controls the motors of each axis of a manipulator,
a line filter provided at a receiving portion of AC power from an external power source, the line filter including at least a Y capacitor disposed between a power source line and a ground point;
a converter provided on a load side of the line filter to convert the AC power into DC power;
a servo amplifier that switches the DC power and supplies AC power obtained by the switching to the motor to servo-control the motor;
a detection means for detecting a zero-phase current, the detection means being provided in a power supply line between the line filter and the converter;
a control circuit for outputting an alarm related to the Y capacitor when the zero-phase current detected by the detection means becomes equal to or greater than a threshold value;
having
The robot controller outputs the alarm when the control circuit detects that a frequency component in the zero-phase current that exceeds a power supply frequency of the external power supply becomes equal to or greater than the threshold value. 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. the detection means is a current detector provided on wiring for each phase in a power supply line between the line filter and the converter,
5. The robot controller according to claim 1 , wherein a sum of detection outputs of the current detectors for each phase is calculated as the zero-phase current. 5. The robot controller according to claim 1, wherein the detection means is a clamp current transformer arranged to detect the sum of the currents of each phase in the power supply line between the line filter and the converter. A preventive maintenance method for a line filter in a robot controller which drives and controls a motor of each axis of a manipulator, the robot controller comprising: a line filter which includes at least a Y capacitor disposed between a power supply line and a ground point and is provided at a section which receives AC power from an external power supply; a converter which is provided at a load side of the line filter and converts the AC power into DC power; and a servo amplifier which switches the DC power and supplies the AC power obtained by the switching to the motor of each axis of the manipulator to servo-control the motor, the method comprising the steps of:
Detecting a zero-phase current flowing through a power supply line between the line filter and the converter;
A preventive maintenance method for predicting the progression of deterioration in the Y-capacitor based on the detected zero-phase current. The preventive maintenance method according to claim 7, which outputs an alarm related to the Y capacitor when it is detected that the zero-phase current is equal to or greater than a threshold value. The preventive maintenance method according to claim 8, wherein the threshold value is determined based on an allowable value of the zero-phase current in the Y capacitor. 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 frequency components in the zero-phase current that exceed the power supply frequency of the external power supply.

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