JP4229097B2 - Load protection device with failure detection function - Google Patents

Description

  The present invention provides a fault detection function provided on the DC output side of a DC power supply circuit comprising a rectifier for AC power rectification and a smoothing capacitor, and shorting the output side of the DC power supply circuit to guarantee the operation of the robot when an overcurrent occurs. The present invention relates to a load protection device.

  Conventionally, for example, a robot controller that operates a robot is supplied with a DC output (DC power supply) of a DC power supply circuit including a rectifier for AC power rectification and a smoothing capacitor. A load protection device is provided on the output side of the DC power supply circuit, and when an overcurrent occurs when the robot controller is energized, the output side of the DC power supply circuit is short-circuited to operate the robot as a load. I guarantee it.

  FIG. 6 shows a conventional load protection device 2 used for the robot controller 1. This load protection device 2 connects a protective switch 4 comprising a mechanical three-contact relay switch between a positive power line 3a and a negative power line 3b of the DC power circuit 3 that converts the AC power into DC. When an overcurrent detecting means (not shown) detects an overcurrent, the protective switch 4 is turned on (closed between the contacts ca) via the relay drive circuit 5 and the output side of the DC power supply circuit 3 is short-circuited. The robot 6 is protected.

  Furthermore, this conventional load protection device 2 has a function of detecting its own failure. This is because, as shown in FIG. 6, a detection power supply is connected to the fixed contact b on the normally open side of the protection switch 4. The configuration is such that Vd is applied through a resistor 7, and the failure of the protection switch 4 is detected by determining the potential of the fixed contact b by the failure detection circuit 8. In other words, the failure detection circuit 8 detects the “L” level during normal operation, and becomes “H” level during failure (welding between the contacts ca).

In addition, although there exists a structure shown by patent document 1 as what aims at the short circuit protection of the semiconductor device for electric power, this does not have the function to detect a self-failure, and is not directly related to this invention.
Patent Registration No. 2777307

  However, the load protection device 2 with the failure detection function configured as shown in FIG. 6 has a problem that the failure mode that can be detected is only a short failure (contact welding), so that it cannot cope with detection of a plurality of failure modes. In order to solve this problem, the inventor considers using a semiconductor switch as a protective switch. However, there is a possibility that only one semiconductor switch may be damaged by a large current at the time of a short circuit.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to detect a plurality of failure modes by using a semiconductor switch and to provide a load protection device with a failure detection function that does not damage the semiconductor switch. To provide.

  In order to achieve the above object, the invention of claim 1 is characterized in that a first semiconductor switch connected between a plus side power line and a minus side power line of the DC power circuit, a plus side power line of the DC power circuit, A series circuit connected between the negative power supply line and connecting a resistor and a second semiconductor switch, and protection control means for turning on the first semiconductor switch after turning on the second semiconductor switch when an overcurrent occurs As a load protection device, a semiconductor switch capable of detecting a plurality of failure modes is used for overcurrent protection, but the semiconductor switch is not damaged during the protection operation. That is, when an overcurrent occurs, the protection control means first turns on the second semiconductor switch in series with the resistor, so that no overcurrent flows instantaneously in the second semiconductor, and this second semiconductor The switch is not damaged, and the charging voltage of the smoothing capacitor is discharged. Next, the protection control means turns on the first semiconductor switch, thereby instantaneously shorting the DC output side of the DC power supply circuit. To do. At this time, since the voltage across the terminals of the smoothing capacitor is lowered, the first semiconductor switch is not damaged.

  For detecting the failure of the first and second semiconductor switches, the failure detection means charges the smoothing capacitor of the DC power supply circuit with a predetermined voltage, and after executing the charge control. A second semiconductor switch on command output control for outputting an on command to the second semiconductor switch; and a first semiconductor switch on command output control for outputting an on command to the first semiconductor switch thereafter. And detecting the presence or absence of a short circuit failure and an open failure of the first and second semiconductor switches according to the change in the detection voltage by the voltage detection means for detecting the voltage between the terminals of the smoothing capacitor during these controls, It is possible to satisfactorily detect a short circuit failure and an open failure of the first and second semiconductor switches which are a plurality of failure modes. The ability.

  In this case, the failure detection means detects the presence or absence of a short failure and an open failure in the first and second semiconductors, and in addition, according to a change in the detection voltage by the voltage detection means during the charge control. The presence or absence of a half-short fault having a resistance component in the first and second semiconductor switches may be detected (invention of claim 2). In this way, it is possible to satisfactorily detect a half-short failure of the first and second semiconductor switches which are different failure modes.

  The charge control in the failure detection means may be performed by turning on an AC power supply switch provided on the input side of the DC power supply circuit (invention of claim 3). As a result, the AC power source, which is the input power source for the load, can be converted into a direct current by the rectifier of the DC power source circuit and charged to the smoothing capacitor, and it is not necessary to prepare a separate power source for inspection, thereby simplifying the configuration. it can.

  Further, the failure detection means detects a short-circuit failure of the second semiconductor switch based on a degree of increase in detection voltage by the voltage detection means being smaller than normal during the charge control, and detects the detection voltage during the charge control. A short failure of the first semiconductor switch is detected based on the fact that the voltage does not rise, and an open fault of the second semiconductor switch is detected based on the fact that the detected voltage does not decrease during the second semiconductor switch-on command output control. And detecting an open failure of the first semiconductor switch based on the degree of decrease in the detected voltage being smaller than the degree of decrease in the detected voltage during normal operation during the first semiconductor switch-on command output control. (Invention of claim 4). In this way, it is possible to accurately detect a short circuit failure and an open failure of the first and second semiconductor switches.

  In addition, the failure detection means may detect the second semiconductor switch based on the fact that the degree of increase in the detection voltage by the voltage detection means during the charge control is smaller than the degree of increase in the detection voltage when the second semiconductor switch is short-circuited. A half short-circuit failure of the first semiconductor switch based on the fact that the degree of increase in the detection voltage during the charge control is smaller than the degree of increase in the detection voltage during the half-short failure of the second semiconductor switch. It is good also as a structure which detects a failure (invention of Claim 5). In this way, it is possible to accurately detect a half-short failure of the first and second semiconductor switches.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a power supply circuit 12 of a robot controller 11 that controls a robot 10 as a load. The power supply circuit 12 includes a DC power supply circuit 14 that rectifies and smoothes, for example, a three-phase AC power supply (AC power) 13. The DC power supply circuit 14 includes a rectifier 15 including, for example, a three-phase diode full-wave rectifier, and a smoothing capacitor 16.

  The three-phase AC power supply 13 is connected to the input side of the rectifier 15 via a circuit switch 17 as a switch for turning on AC power. The smoothing capacitor 16 is connected between the output terminals of the rectifier 15. Is connected. The robot controller 11 is connected between a positive power line 14a and a negative power line 14b which are output power lines of the DC power circuit 14. The circuit switch 17 is turned on and off by a control unit 22 described later.

  A load protection device 18 is provided on the output side of the DC power supply circuit 14. The load protection device 18 includes a first FET 19 that is a first semiconductor switch, a second FET 20 that is a second semiconductor switch, a resistor 21, and a control unit 22. The first FET 19 is connected between the positive power line 14 a and the negative power line 14 b of the DC power circuit 14. The resistor 21 and the second FET 20 constitute a series circuit 23, and the series circuit 23 is connected between the plus side power supply line 14a and the minus side power supply line 14b. The control unit 22 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an FET drive circuit, a voltage detection circuit (voltage detection means) that detects a voltage Vk between terminals of the smoothing capacitor 16, and the like. It is configured and serves as protection control means and failure detection means. A display device 24 and a buzzer 25 as notification means are connected to the control unit 22. Although not shown, the load protection device 18 is provided with an overcurrent detection circuit as overcurrent detection means. The overcurrent detection circuit may use the voltage detection circuit described above.

  As shown in FIG. 2, a robot controller 11 is connected to the robot 10, and a teach pendant 26 is connected to the robot controller 11. The power supply circuit 12 of the robot controller 11 supplies power to a drive control circuit that drives and controls a servo motor that operates each arm of the robot 10 (not shown).

  The protection control means in the control unit 22 detects the overcurrent when an overcurrent is generated when power is supplied to the robot 10 when the circuit switch 17 is turned on. First, an on command is sent to the gate of the second FET 20. Is output, the second FET 20 is turned on, and the resistor 21 is discharged. When the voltage detection circuit detects that the voltage is lower than a predetermined voltage (lower than the allowable maximum voltage of the first FET 19), the first FET 19 is discharged. An ON command is output to the gate of the FET 19 and is turned ON to short-circuit the output side of the DC power supply circuit 14, thereby guaranteeing the operation of the robot 10 as a load. In this case, since no overcurrent flows through the first and second FETs 19 and 20, the FETs 19 and 20 are not damaged. That is, if the first FET 19 is provided without the series circuit 23 of the second FET 20 and the resistor 21 and only the first FET 19 is turned on when an overcurrent is detected, this may be damaged. In the example, the first FET 20 discharges first to reduce the overcurrent (the second FET 20 does not break the second FET 20 because the current is consumed by the resistor 19), and then the first FET 20 Since the FET 19 is turned on, both the FETs 19 and 20 are not damaged.

  Here, the control contents as the failure detection means in the control unit 22 will be described with reference to the flowchart of FIG. This flowchart is automatically started periodically when the operation of the robot 10 is stopped. It may be started by operating a start switch (not shown).

  An outline of the flowchart of the control contents of the failure detection will be described. In this flowchart, basically, as shown in FIG. 4A, the circuit switch 17 is turned on for a predetermined time TA and the second time after the predetermined time TB has elapsed. The TC ON command Son2 is output for a predetermined time to the gate of the FET 20, and then the ON command Son1 is output to the gate of the first FET 19 for a predetermined time TD while the ON command Son2 is output. During this on / off control, the degree of change in the detected voltage is detected to detect a short circuit failure, an open failure, and a half short circuit failure of the first and second FETs 19 and 20. Here, when the first and second FETs 19 and 20 have no failure (normal), the detection voltage changes, and when the first and second FETs 19 and 20 have a short failure, an open failure, and a half-short failure. A change in the detection voltage will be described in advance.

  (1) When there is no failure (normal) in the first and second FETs 19 and 20, the detection voltage changes as shown by a solid line in FIG. That is, when the circuit switch 17 is turned on, since the first and second FETs 19 and 20 are normally turned off, the output voltage of the rectifier 15 is normally charged in the smoothing capacitor 16. Even when the circuit switch 17 is turned off, the charged voltage does not drop. When the ON command Son2 is output to the second FET 20 after a predetermined time TB has elapsed, the second FET 20 is normally turned on, and the capacitor charge is discharged with a time constant determined by the smoothing capacitor 16 and the resistor 21. The detection voltage decreases. When a predetermined time TC elapses and the on command Son1 is output to the first FET 19, the FET 19 is normally turned on and the charge of the smoothing capacitor 16 is rapidly discharged.

(2) When the second FET 20 has an open failure, the detection voltage does not decrease the charge voltage of the smoothing capacitor 16 as indicated by the broken line in FIG.
(3) When the second FET 20 has a short circuit failure, as shown in FIG. 4B, the change (increase) in the charge voltage when the circuit switch 17 is turned on is smaller than that in the normal state. . Considering this, the control unit 22 is set with a change degree determination value K1.

(4) When the second FET 20 has a half-short fault (short fault with a resistance value), as shown by a dotted line in FIG. And smaller than when the second FET 20 is short-circuited. Considering this, the control unit 22 is set with a determination value K2 (K2 <K1).
(5) When the first FET 19 has an open failure, the first FET 19 does not turn on even when the on command Son1 is given, as indicated by the dotted line in FIG. The degree of change (decrease) is smaller than the time. Considering this, the control unit 22 is set with a determination value K3 of the degree of change.

(6) When the first FET 19 has a short-circuit failure, the smoothing capacitor 16 is not charged as indicated by the dotted line in FIG. Not).
(7) When the first FET 10 has a half short-circuit failure, as shown by a dotted line in FIG. 5C, the change (increase) in the charge voltage is the detection voltage when the first FET 19 has a short failure. It is larger than the degree of increase and smaller than the degree of increase in the detection voltage when the second FET 20 is half short-circuited (smaller than when the second FET 20 is half-short-out failed in FIG. 4C). Considering this, the control unit 22 is set with a change degree determination value K4 (K4 <K2).

  Now, the flowchart of FIG. 1 will be specifically described. From the state in which the circuit switch 17 is turned off, the control unit 22 first detects the voltage across the smoothing capacitor 16 in step S1. In step S2, the circuit switch 17 is turned on, and the smoothing capacitor 16 is charged with a predetermined voltage for testing, in this case, the DC voltage of the rectifier 15 (charge control). In step S3, detection of the change in the detected voltage is started. That is, every very short time, the previous value is subtracted from the current value of the detected voltage, and the degree of change is detected by the magnitude of the difference. In step S4, it is determined whether or not the second FET 20 has a short fault. That is, it is determined whether the degree of change (increase) in the detected voltage is less than the determination value K1 and equal to or greater than K2 (less than normal).

If it is determined that the second FET 20 is short-circuited ("YES"), the process proceeds to step S18 to execute a failure-corresponding process. In the failure handling process, for example, the circuit switch 17 is turned off, and the fact that the second FET 20 is short-circuited is displayed on the display device 24 and notified by the buzzer 25.
If it is determined in step S4 that there is no short-circuit failure in the second FET 20 ("NO"), it is determined in step S5 whether there is a half-short failure in the second FET 20. That is, it is determined whether or not the degree of change (increase) in the detected voltage is less than the determination value K2 (less than the increase in case of a short failure). If it is less than the determination value K2, the failure handling process in step S18 described above is executed, the circuit switch 17 is turned off, and the second FET 20 is displayed and notified that it is a half-short failure.

  If it is determined in step S5 that there is no half-short failure of the second FET 20, it is determined in step S6 whether there is a short failure of the first FET 19. That is, it is determined whether the detection voltage does not increase. If the detection voltage does not increase, it is determined that there is a short-circuit failure in the first FET 19. In step S18, the circuit switch 17 is similarly turned off and the first FET 19 is displayed and notified of a short circuit failure.

  If it is determined in step S6 that there is no short-circuit failure in the first FET 19, it is determined in step S7 whether there is a half-short failure in the first FET 19. That is, the first FET 19 has a half-short fault because the degree of increase in the detected voltage is smaller than the determination value K4 and larger than the degree of increase zero (the degree of increase is zero when the first FET 19 is short-circuited). to decide. In this case, in the same manner as described above, in step S18, display and notification of the presence of a half short-circuit failure of the FET 19 are provided.

  If it is determined in step S7 that the first FET 19 is not short-circuited, the process proceeds to step S8. If it is determined that the predetermined time TA has elapsed, the circuit switch 17 is turned off in step S9. . If it is determined in step S10 that the predetermined time TB has elapsed, an on command Son2 is output to the second FET 20 (on command output control) in step S11. In the next step S12, it is determined whether or not there is an open failure of the second FET 20. That is, it is determined that there is an open failure of the second FET 20 when the detection voltage does not decrease. If it is determined that there is an open failure, the circuit switch 17 is turned off in step S18 as described above, and an open failure of the second FET 20 is displayed and notified.

If it is determined in step S12 that there is no open failure of the second FET 20, and it is determined in step S13 that the predetermined time TC has elapsed, an ON command Son1 for the first FET 19 is output (ON command output control). In step S15, it is determined whether or not there is an open failure of the first FET 19. That is, it is determined that there is an open failure of the first FET 19 when the degree of decrease in the detected voltage is smaller than the determination value K3 (the degree of decrease in the detected voltage is smaller than the degree of decrease in the detected voltage at normal time). Then, the process goes to step S18 to turn off the circuit switch 17 and to display and notify that the first FET 19 has an open failure.
When it is determined in step S15 that the first FET 19 has no open failure, the output of the ON commands Son1 and Son2 to the first and second FETs 19 and 20 is stopped when the predetermined time TD has elapsed (step S16). To do.

  As described above, according to the present embodiment, the first FET 19 is connected between the plus-side power supply line 14 a and the minus-side power supply line 14 b of the DC power supply circuit 14, and the resistor 21 and the second semiconductor switch 20 are connected. Since the series circuit 23 is connected and the control unit 22 turns on the first FET 19 after turning on the second FET 20 when an overcurrent occurs, a plurality of failure modes can be detected as a load protection device. Even though overcurrent protection is achieved using a simple FET (semiconductor switch), there is no possibility that these FETs 19 and 20 are damaged during the protection operation.

  For detecting the failure of the first and second FETs 19 and 20, the control unit 22 performs charge control for charging the smoothing capacitor 16 of the DC power supply circuit 14 with a predetermined voltage, and execution of this charge control. Thereafter, a second FET on command output control for outputting an on command Son2 to the second FET 20, and a first FET on command output control for outputting an on command Son1 to the first FET 19 thereafter. Since the presence or absence of short-circuit failure and open failure of the first and second FETs 19 and 20 is detected according to the change in the detection voltage during these controls, the first and second FETs 19 that are a plurality of failure modes, It is possible to detect 20 short faults and open faults satisfactorily.

In this case, according to the present embodiment, in addition to detecting the presence or absence of a short-circuit failure and an open failure of the first and second FETs 19 and 20, the first and second FETs 19 and 20 are detected according to a change in the detection voltage during the charge control. In addition, since the presence or absence of a half-short fault in the second FETs 19 and 20 is detected, it is possible to detect a half-short fault that is a different failure mode.
Further, since the charge control is performed by turning on the circuit switch 17 that is a switch for turning on the AC power supply 13 provided on the input side of the DC power supply circuit 14, the AC power supply that is the input power supply for the load is used. 13 can be converted to a direct current by the rectifier 15 of the direct current power supply circuit 14 and charged to the smoothing capacitor 16, so that it is not necessary to prepare a separate power supply for inspection, and the configuration can be simplified.

  Further, the control unit 22 detects a short-circuit failure of the second FET 20 based on the degree of increase in the detection voltage during the charge control being smaller than normal, and based on the detection voltage not increasing during the charge control. A short failure of the first FET 10 is detected, and an open failure of the second FET 20 is detected based on the fact that the detection voltage does not decrease during the second FET 20 on command output control, and the first FET 19 is turned on. Since the open failure of the first FET 19 is detected based on the degree of decrease in the detected voltage being smaller than the degree of change in the detected voltage at the time of command output control, the first and second FETs 19 and 20 are detected. It is possible to accurately detect a short-circuit failure and an open failure.

Further, the control unit 22 detects a half short-circuit failure of the second FET 20 based on the increase in the detection voltage during the charge control being smaller than the detection voltage increase at the time of the short failure of the second FET 20, Based on the increase in the detection voltage during the charge control being greater than the detection voltage increase during the short failure of the first FET 19 and smaller than the detection voltage increase during the half short failure of the second FET 20. Since the configuration is such that a short-circuit failure of one FET 19 is detected, a short-circuit failure and an open failure of the first and second FETs 19 and 20 can be accurately detected.
In the above embodiment, the FET is used as the semiconductor switch. However, another semiconductor switch such as an IGBT may be used as the semiconductor switch. Further, the AC power supply 13 may be a single phase instead of three phases. The load may be other than the robot controller.

Electrical circuit diagram showing one embodiment of the present invention Schematic configuration diagram of the robot Flow chart showing the control contents of the control unit Diagram for explaining failure mode (1) Diagram for explaining the failure mode (2) 1 equivalent diagram showing a conventional example

Explanation of symbols

  In the drawings, 10 is a robot, 11 is a robot controller, 12 is a power supply circuit, 14 is a DC power supply circuit, 15 is a rectifier, 16 is a smoothing capacitor, 17 is a circuit switch (switch), 18 is a load protection device, and 19 is a first 1 FET (first semiconductor switch), 20 a second FET (semiconductor switch), 21 a resistor, 22 a control unit (protection control means, voltage detection means, failure detection means), and 23 a series circuit .

Claims (5)

A load protection device with a failure detection function that is provided on the DC output side of a DC power supply circuit comprising a rectifier for AC power rectification and a smoothing capacitor, and protects the load by short-circuiting the output side of the DC power supply circuit when an overcurrent occurs. And
A first semiconductor switch connected between a positive power line and a negative power line of the DC power circuit;
A series circuit connected between a positive power line and a negative power line of the DC power circuit and connecting a resistor and a second semiconductor switch;
Protection control means for turning on the first semiconductor switch after turning on the second semiconductor switch when an overcurrent occurs;
Voltage detecting means for detecting a voltage between terminals of the smoothing capacitor;
Charge control for charging the smoothing capacitor of the DC power supply circuit with a predetermined voltage; and second semiconductor switch on command output control for outputting an on command to the second semiconductor switch after the charge control is executed. Thereafter, a first semiconductor switch on command output control for outputting an on command to the first semiconductor switch is performed, and the first and second semiconductor switches are controlled according to changes in the detected voltage by the voltage detecting means during these controls. 2. A load protection device with a failure detection function, comprising: failure detection means for detecting the presence or absence of a short-circuit failure and an open failure of the semiconductor switch. In the load protection device with a failure detection function according to claim 1,
The failure detection means detects the presence or absence of short-circuit failure and open failure of the first and second semiconductors, and also detects the first and second according to the change in the detection voltage by the voltage detection means during the charge control. A load protection device with a fault detection function for detecting the presence or absence of a half-short fault having a resistance component in a semiconductor switch. In the load protection device with a failure detection function according to claim 1 or 2,
The load control device with a failure detection function, wherein the charge control in the failure detection means is performed by turning on an AC power supply switch provided on an input side of the DC power supply circuit. In the load protection device with a failure detection function according to any one of claims 1 to 3,
The failure detection means detects a short-circuit failure of the second semiconductor switch based on the degree of increase in the detection voltage by the voltage detection means being smaller than normal during the charge control, and the detection voltage increases during the charge control. A short failure of the first semiconductor switch is detected based on the failure of the first semiconductor switch, and an open failure of the second semiconductor switch is detected based on the fact that the detected voltage does not decrease during the second semiconductor switch-on command output control. The open failure of the first semiconductor switch is detected based on the degree of decrease in the detected voltage being smaller than the degree of decrease in the detected voltage during normal operation during the first semiconductor switch-on command output control. Load protection device with failure detection function. In the load protection device with a failure detection function according to claim 2,
The failure detection means is based on the fact that the degree of increase in the detection voltage by the voltage detection means during the charge control is smaller than the degree of increase in the detection voltage at the time of short-circuit failure of the second semiconductor switch. A short-circuit failure is detected, and the first semiconductor switch has a half-short failure based on the fact that the degree of increase in the detection voltage during the charge control is smaller than the degree of increase in the detection voltage at the time of the half-short-circuit failure of the second semiconductor switch. A load protection device with a failure detection function characterized by detecting.

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