JP2007037301A - Robot control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stop a motor in a short period of time at the time of a system failure while preventing a failure of a short-circuit switch connected between DC power supply lines. <P>SOLUTION: A control circuit 24 opens relay contacts 2a (2R, 2S and 2T) and outputs OFF command signals to IGBTs Q1-Q3 and on-signals to IGBTs Q4-Q6, when detecting an error signal Fo from a drive circuit 23. Simultaneously, the on-command signal is outputted to a MOSFET Q7 of a regeneration circuit 11. Then, the on-command signal is outputted to the MOSFET Q8 when a DC voltage VDC detected by a voltage detection circuit 27 drops to a prescribed threshold voltage (60 V, for example) determined according to a withstand capacity of the MOSFET Q8 or lower. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a robot control apparatus including a motor drive circuit.

A motor provided in the robot, for example, a brushless motor, is driven by an inverter mounted on the robot controller. If a system abnormality occurs during motor driving, it is necessary to stop the motor immediately. Patent Document 1 discloses a synchronous motor control circuit for quickly performing an emergency stop of a synchronous motor. This synchronous motor control circuit turns off all the switching elements that constitute the inverter when the synchronous motor is urgently stopped, and turns on the switching elements connected between the DC power supply lines via a regenerative resistor. The regenerative power is controlled to be bypassed to the DC power line and consumed by the regenerative resistor.
JP 2001-204184 A

  The synchronous motor control circuit performs stop control using power consumption by a regenerative resistor, but has a drawback that it takes a relatively long time to stop. Therefore, in the robot controller, in order to stop the motor in a shorter time, all the switching elements on the upper arm side of the inverter are turned off and all the switching elements on the lower arm side are turned on to electrically connect the motor terminals. Means for short-circuiting are used.

  FIG. 4 shows the configuration of the motor drive circuit in this robot control apparatus. When the robot controller drives the motor, a DC voltage VDC is output from the three-phase AC power supply 1 to the DC power supply lines 4 and 5 through the contacts 2R, 2S and 2T of the power relay 2 and the converter 3, and the inverter An AC voltage is output from 6 to the motor 7. Between the DC power supply lines 4 and 5, a smoothing capacitor 8, a regenerative circuit 9 including a regenerative resistor 9 and a transistor 10 (indicated by a switch symbol), and a relay contact 12 that functions as a short-circuit switch are connected in parallel. The transistor 10 and the relay contact 12 are turned off in the motor driving state.

  On the other hand, when the robot control device detects a decrease in the driving voltage of the IGBTs Q4 to Q6 as a system abnormality and stops the motor 7 urgently, the control circuit 13 generates a system abnormality detection signal as shown in FIG. Accordingly, relay contacts 2R, 2S, and 2T are turned off, and an off command signal for IGBTs Q1 to Q3 and an on command signal for IGBTs Q4 to Q6 are output. Then, after the relay contacts 2R, 2S, and 2T are reliably turned off, the relay contact 12 is turned on. As a result, even when the driving voltages of the IGBTs Q4 to Q6 are lowered and the IGBTs Q4 to Q6 cannot be turned on, a short circuit is formed from the terminals of the motor 7 via the diodes D1 to D6 of the inverter 6 and the relay contacts 12 and more. The motor can be stopped in a short time.

  However, when the relay contact 12 is turned on in this robot control device, an excessive current flows through the relay contact 12 due to a short circuit of the capacitor 8, so that there is a problem that the contact portion is likely to be welded.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a robot control device capable of stopping a motor in a short time in the event of a system abnormality while preventing a failure of a short-circuit switch connected between DC power supply lines. There is to do.

  According to the first aspect of the present invention, when a system abnormality is detected, the voltage output by the converter is stopped and the first switch connected between the DC power supply lines via the regenerative resistor is closed. Thereby, a current flows from the capacitor connected between the DC power supply lines to the regenerative resistor, and the DC voltage decreases. At this time, for example, when the inverter is switched to a current return mode (a mode in which all the elements of the upper arm or the lower arm are turned on in a bridge configuration), a short-circuit current flows from the rotating motor via the internal elements of the inverter. A dynamic brake (short-circuit brake) acts on the motor.

  However, the inverter may not be switched to the current return mode due to the system abnormality. In this case, a short circuit path is not formed in the internal circuit of the inverter, a current path is formed from the motor through the freewheeling diode, the DC power supply line, the regenerative resistor, and the first switch in the inverter, and the motor has a regenerative brake. Works.

  When such a brake is applied, when the DC voltage drops below a predetermined threshold voltage determined according to the withstand capability of the second switch, the second switch directly connected between the DC power supply lines is Closed. In this case, if the above-described dynamic brake has already been applied, the operation continues. If the above-described regenerative brake is applied, a current short-circuit path is newly formed from the motor through the return diode in the inverter, the DC power supply line, and the second switch, and the dynamic brake acts on the motor.

  That is, according to this means, since the DC power source line is finally short-circuited via the second switch, the dynamic brake is activated even when the inverter cannot be switched to the current return mode due to a system abnormality. The motor can be stopped in a shorter time than when only the regenerative brake is used. Since the second switch is closed when the DC voltage drops below a predetermined threshold voltage, the short-circuit current or generated loss that flows through the second switch when it is closed is limited to less than the tolerance of the switch. Thus, the failure of the second switch due to excessive current or excessive loss can be reliably prevented.

  According to the means described in claim 2, the inverter is constituted by a switching element connected in a bridge, and an operation abnormality of the switching element is detected as a system abnormality. That is, when a system abnormality is detected, in many cases, the switching element cannot be normally turned on, and the current return mode is not formed in the inverter. Therefore, if the system abnormality detection method according to this means is used, the above-described short-circuit control in which the second switch is short-circuited to actuate the dynamic brake is particularly effective.

  According to the means described in claim 3, since the first and second switches are constituted by semiconductor elements, it is possible to reduce the size, improve the controllability, and improve the reliability.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.
FIG. 1 is an electrical configuration diagram of a motor drive circuit in a robot control apparatus, and the same reference numerals are given to the same portions as FIG. 4 showing the conventional configuration. Further, it is partially shown in more detail than FIG. A robot (not shown) is provided with a plurality of motors 7 for moving its movable part (joint), and the robot control device includes a motor drive circuit 21 for driving each motor 7. The motor 7 is a brushless motor, and a rotary encoder 22 is attached to detect the rotor position.

  A contact 2a (2R, 2S, 2T) of the power relay 2 is interposed between the three-phase 200V AC power supply 1 and the converter 3. These relay contacts 2a (2R, 2S, 2T) are closed by energizing the relay coil 2b. Converter 3 has a known circuit configuration in which diodes are connected in a three-phase bridge, and inverter 6 has a known circuit configuration in which IGBTs Q1 to Q6 and diodes D1 to D6 are connected in a three-phase bridge. Yes.

  The inverter 6 and its drive circuit 23 are integrally configured as an intelligent power module (IPM). The drive circuit 23 operates in response to the supply of drive power, and drives the IGBTs Q <b> 1 to Q <b> 6 on and off in accordance with an on / off command signal given from the control circuit 24. Further, when an arm short circuit occurs in the inverter 6, an overheat state occurs, or when the drive power supply voltage decreases, an error signal Fo (system abnormality detection signal) is output to the control circuit 24. .

  The regenerative circuit 11 connected between the DC power supply lines 4 and 5 is constituted by a series circuit of a regenerative resistor 9 and a MOSFET Q7 (equivalent to the transistor 10 shown in FIG. 4). Further, a MOSFET Q8 is connected between the DC power supply lines 4 and 5 in place of the relay contact 12 shown in FIG. These MOSFETs Q7 and Q8 correspond to a first switch and a second switch, respectively, in the present invention. The drive circuits 25 and 26 are configured to drive the MOSFETs Q7 and Q8 in accordance with on / off command signals given from the control circuit 24, respectively. Further, a voltage detection circuit 27 (corresponding to voltage detection means) for detecting the DC voltage VDC between the DC power supply lines 4 and 5 is provided.

  The control circuit 24 (corresponding to the control means) is a CPU, memory (RAM, ROM, electrically rewritable nonvolatile memory), I / O circuit, PWM signal generation circuit, timer circuit, A / D conversion circuit, display A device (LED, liquid crystal display panel, etc.) is provided. Specifically, a signal from the rotary encoder 22 is input to the I / O circuit, and the rotor position of the motor 7 is detected based on the signal. The PWM signal generation circuit generates an on / off command signal and outputs it to the drive circuit 23, and outputs a drive signal to the drive circuits 25 and 26 and the relay coil 2b via the I / O circuit. It is like that. Further, the DC voltage VDC is A / D converted and inputted by an A / D conversion circuit.

Next, the operation of the present embodiment will be described with reference to FIGS.
The control circuit 24 performs position feedback control or speed feedback control to perform follow-up control of the rotational position or rotational speed of the motor 7. If a system abnormality occurs during driving of the motor, it is necessary to stop the motor 7 immediately. In the present embodiment, an arm short circuit and an overheat state in the inverter 6 and a decrease in the drive power supply voltage in the drive circuit 23 are regarded as system abnormalities, and the control circuit 24 detects the system abnormality by the error signal Fo from the drive circuit 23. Can do.

  FIG. 2 is a flowchart showing the processing contents of the control circuit 24 when a system abnormality occurs, and FIG. 3 is a waveform diagram of each signal and DC voltage VDC when the system abnormality occurs. The waveforms shown in FIG. 3 are, in order from the top, error signal Fo, relay contact 2a (2R, 2S, 2T), upper arm side IGBTQ1-Q3 command signal, lower arm side IGBTQ4-Q6 command signal, MOSFET Q7 command signal, The command signal of the MOSFET Q8 and the DC voltage VDC.

  In step S1 shown in FIG. 2, the control circuit 24 determines whether or not a system abnormality has occurred, that is, whether or not the error signal Fo has become H level. Here, if it is determined that a system abnormality has occurred (YES), the process proceeds to step S2 to display an error on a display device (not shown), and the motor 7 is stopped for the user (operator) of the robot controller. Inform the cause. On the other hand, if it is determined that no system abnormality has occurred (NO), the determination process of step S1 is executed again. The error signal Fo may be input by interruption.

  When detecting a system abnormality, the control circuit 24 cuts off the energization to the relay coil 2b in step S3 and opens the relay contact 2a (2R, 2S, 2T). At the same time, an off command signal is output to the IGBTs Q1 to Q3 on the upper arm side of the inverter 6 and an on command signal is output to the IGBTs Q4 to Q6 on the lower arm side so that the inverter 6 enters the current return mode. To do. This current return mode is a mode in which the terminals of the respective phases of the motor 7 are short-circuited via the lower arm side elements (IGBTs Q4 to Q6 and diodes D4 to D6). However, since the error signal Fo is output from the drive circuit 23, there are many cases where the IGBTs Q4 to Q6 cannot actually be turned on due to overheating or a decrease in the drive power supply voltage. Further, the control circuit 24 proceeds to step S5 and outputs an ON command signal for the MOSFET Q7 of the regenerative circuit 11. It is desirable to execute the processes in steps S3 to S5 immediately after detecting a system abnormality (time t1 in FIG. 3).

  As a result of the above processing, when the inverter 6 shifts to the current return mode, a short-circuit current flows from the rotating motor 7 via the lower arm side element of the inverter 6, and a so-called dynamic brake (short-circuit brake) is supplied to the motor 7. ) Acts. On the other hand, as described above, when the IGBTs Q4 to Q6 cannot be turned on and cannot shift to the current return mode, the diodes D1 to D3, the DC power supply line 4, the regenerative resistor 9, the MOSFET Q7, the DC power supply line 5, A current flows through the diodes D4 to D6 of the inverter 6, and a so-called regenerative brake acts on the motor 7. FIG. 3 shows a case where the regenerative brake acts.

  When the MOSFET Q7 is turned on, a current flows from the capacitor 8 through the regenerative resistor 9 and the MOSFET Q7, and the DC voltage VDC between the DC power supply lines 4 and 5 gradually decreases as shown in FIG. In step S6, the control circuit 24 inputs the DC voltage VDC from the voltage detection circuit 27. In step S7, whether the DC voltage VDC has dropped to a predetermined threshold voltage determined according to the withstand capability of the MOSFET Q8, for example, 60 V or less. Judge whether or not. The withstand capability of the MOSFET Q8 includes the withstand capability of the current flowing through the MOSFET Q8, the withstand capability of the voltage, and the withstand capability of the collector loss. Steps S6 and S7 are repeated until the DC voltage VDC decreases to 60V or less. Then, when the DC voltage VDC decreases to 60 V or less, it is determined as “YES”, the process proceeds to step S8, and an ON command signal for the MOSFET Q8 is output (time t2 in FIG. 3).

  When the MOSFET Q8 is turned on, the DC power supply lines 4 and 5 are short-circuited. At this time, if the above-described dynamic brake is already operating, the operation continues. On the other hand, when the IGBTs Q4 to Q6 cannot be turned on and the above-described regenerative brake is operating, the regenerative current flowing from the motor 7 through the regenerative circuit 11 is replaced with the diodes D1 to D1 of the inverter 6 from the motor 7. A short-circuit current flows through D3, DC power supply line 4, MOSFET Q8, DC power supply line 5, and diodes D4 to D6 of inverter 6. Thereby, a dynamic brake acts on the motor 7 instead of the regenerative brake. Further, since the DC power supply lines 4 and 5 are short-circuited, the DC voltage VDC rapidly decreases.

  As described above, the motor drive circuit 21 of the present embodiment includes the regenerative circuit 11 and the short-circuit MOSFET Q8 in parallel between the DC power supply lines 4 and 5, and turns on the regenerative circuit 11 when a system abnormality is detected. The MOSFET Q8 is turned on. Therefore, even if the IGBTs Q4 to Q6 cannot be turned on due to a system abnormality relating to the inverter 6 or the drive circuit 23, a dynamic brake can be finally applied to the motor 7 by causing a short-circuit current to flow through the MOSFET Q8. The motor 7 can be stopped in a shorter time than when only the brake is used.

  The MOSFET Q8 is closed when the DC voltage VDC drops below a predetermined threshold voltage (60V) determined according to the withstand capability of the MOSFET Q8, so that the short-circuit current that flows through the MOSFET Q8 when it is closed, the applied voltage, and the collector The loss is limited to be equal to or less than the withstand capability of the MOSFET Q8, and the failure of the MOSFET Q8 can be prevented.

  In the present embodiment, the error signal Fo output from the drive circuit 23 is used as a system abnormality detection signal when an arm short circuit occurs, an overheated state, or when the drive power supply voltage decreases, so that the IGBTQ4 ~ In many cases, Q6 cannot be turned on. Therefore, the above-described two-stage brake control works particularly effectively.

  According to the present embodiment, unlike the conventional configuration, the second switch can be configured by a MOSFET which is a semiconductor element, so that downsizing, improvement in controllability, and improvement in reliability are achieved. Further, by using a semiconductor element, even when an impact is applied to the robot control device, the on / off state is not erroneously switched.

The present invention is not limited to the embodiment described above and shown in the drawings. For example, the present invention can be modified or expanded as follows.
The system abnormality is not limited to the abnormality of the inverter 6 and the drive circuit 23.
The first switch and the second switch are not necessarily semiconductor elements, and may be relay contacts or the like as in the conventional configuration. However, by adopting the semiconductor element, the above-described specific effect can be obtained. These switches are not limited to MOSFETs, but may be bipolar transistors, IGBTs, or the like.

1 is an electrical configuration diagram of a motor drive circuit provided in a robot control apparatus showing an embodiment of the present invention. Flow chart showing the processing contents of the control circuit when a system abnormality occurs Waveform diagram of each signal and DC voltage when system abnormality occurs 1 equivalent diagram showing the prior art 3 equivalent figure

Explanation of symbols

  In the drawings, 3 is a converter, 4 is a DC power supply line, 6 is an inverter, 7 is a motor, 9 is a regenerative resistor, 24 is a control circuit (control means), 27 is a voltage detection circuit (voltage detection means), Q1 to Q1. Q6 is an IGBT (switching element), Q7 is a MOSFET (first switch, semiconductor element), and Q8 is a MOSFET (second switch, semiconductor element).

Claims (3)

A converter that rectifies AC voltage and outputs DC voltage between DC power supply lines;
An inverter that inputs a DC voltage between the DC power lines and outputs an AC voltage to the motor;
A first switch connected between the DC power supply lines via a regenerative resistor;
A second switch directly connected between the DC power lines;
Voltage detecting means for detecting a DC voltage between the DC power supply lines;
When a system abnormality is detected, the voltage output of the converter is stopped and the first switch is closed, and then the DC voltage detected by the voltage detecting means is a predetermined value determined according to the withstand capability of the second switch. And a control means for controlling the second switch to close when the threshold voltage is lower than the threshold voltage. The inverter is composed of switching elements connected in a bridge,
The robot control apparatus according to claim 1, wherein the control unit detects an operation abnormality of the switching element as a system abnormality. 3. The robot control apparatus according to claim 1, wherein the first and second switches are constituted by semiconductor elements.

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