Discharge circuit and method for motor drive power supply circuit, robot controller

Abstract

The present application provides a discharge circuit and a discharge method for a power supply circuit for driving a motor, and a robot controller, which are used for driving a motor of an industrial robot, can safely stop the robot at the time of power failure and the time of emergency stop, and can reduce the voltage on the secondary side of the power supply circuit to a safe voltage within a prescribed time. In the case where the voltage on the primary side of the power supply circuit (10) is lower than a power failure determination value, after the time required for the stop operation of the industrial robot (30), discharge control is performed to make current flow through a discharge resistor (18) that is provided in parallel with respect to the secondary side of the power supply circuit (10) and is used for consumption of regenerated energy.

Description

Technical Field

[0001] The present invention relates to a discharge circuit provided for a power supply circuit for a motor driving each axis of an industrial robot, a method for discharging the power supply circuit, and a robot controller having the power supply circuit and the discharge circuit. Background Technology

[0002] In devices that drive and control motors such as synchronous motors and induction motors via servo drives, the servo drive is supplied with DC power obtained by rectifying and smoothing AC power from an external power source such as a commercial AC power supply through a rectifier circuit. Here, the circuit including the rectifier circuit and a smoothing capacitor (capacitor) located at the output of the rectifier circuit is referred to as the power supply circuit. When controlling the motor to decelerate, regenerative current flows from the motor to the power supply circuit side via the servo drive. When the regenerative current flows to the power supply circuit side, the DC voltage on the secondary side (output side) of the power supply circuit rises, potentially exceeding the withstand voltage (i.e., the maximum permissible input power supply voltage) of the devices or components connected to the power supply circuit. Therefore, in devices using motors, a discharge resistor is generally provided on the secondary side of the power supply circuit. Once the power supply voltage exceeds a fixed value, the regenerative current flows through the discharge resistor, dissipating the regenerative energy. Patent Document 1 discloses a circuit that dissipates regenerative energy through the discharge resistor during emergency stops, thereby applying braking to the motor.

[0003] When the AC power supply to the primary side (input side) of the power supply circuit is cut off, or when the AC power supply fails, charge still accumulates in the smoothing capacitor of the power supply circuit, and DC voltage continues to be output. However, in this case, to ensure safety, the DC voltage on the secondary side of the power supply circuit needs to be reduced to a specified value within a specified time. Patent Document 2 discloses a control device that, when the AC power supply to the power supply circuit is cut off by a contactor, uses a discharge resistor for regenerative energy consumption to force the accumulated charge in the smoothing capacitor to discharge. Patent Document 3 discloses a control device that, when a power outage is detected in the AC power supply, uses a discharge resistor for regenerative energy consumption to force the accumulated charge in the smoothing capacitor to discharge. Patent Document 4 discloses a motor stop circuit that, when a power outage is detected, outputs a deceleration control command to the inverter driving the motor and a regenerative discharge command to a regenerative discharge circuit equipped with a discharge resistor.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 11-262283

[0007] Patent Document 2: Japanese Patent Application Publication No. 2004-249534

[0008] Patent Document 3: Japanese Patent Application Publication No. 9-121592

[0009] Patent Document 4: Japanese Patent Application Publication No. 10-243675 Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] In industrial robots, synchronous motors or induction motors are generally used to drive their axes. These motors are driven and controlled by servo drives with inverter functions. Since the motors in industrial robots also generate regenerative current during deceleration, a discharge resistor is connected in the power supply circuit to dissipate the regenerative energy, allowing the regenerative current to flow through the discharge resistor according to the voltage on the secondary side of the power supply circuit. Furthermore, in industrial robots, safety standards require that when the power supply from an external power source is cut off due to an emergency stop of the robot or a power outage, the voltage on the secondary side of the power supply circuit must be set to a specified voltage value (e.g., 43V) or lower within a specified time (e.g., one minute). Emergency stops of the robot are typically achieved by cutting off the AC power supply on the primary side of the power supply circuit using relays or contactors. The techniques described in Patent Documents 2-4 are also considered for setting the voltage on the secondary side of the power supply circuit to the specified value within a specified time. However, in the event of an emergency stop of the robot, it is necessary to safely stop each axis of the moving robot; therefore, it is sometimes necessary to supply power to the servo drives that control the motors during the stopping operation. For example, in the case of an emergency stop for a robot while one of its arms is rising, the speed of the rising arm needs to be reduced to zero by a predetermined deceleration. At this point, power is supplied to the motor to operate it. If the power supply to the motor is cut off during the control to decelerate and stop the robot, the robot may enter an uncontrolled so-called free state, potentially leading to a more dangerous situation. Therefore, when using the technology described in Patent Documents 2-4, there is a possibility that a safe stop for the robot cannot be achieved during a power outage or emergency stop.

[0012] The purpose of this invention is to provide a discharge circuit and a discharge method for the power supply circuit used in the drive of the motor of an industrial robot. This discharge circuit and method enable the robot to stop safely when the external power supply fails or during an emergency stop, and also enable the voltage on the secondary side of the power supply circuit to decrease to a safe voltage within a time specified by safety standards. Another purpose of this invention is to provide a robot controller equipped with such a discharge circuit and power supply circuit.

[0013] Technical solutions adopted to solve technical problems

[0014] The discharge circuit of the present invention is provided relative to a power supply circuit for driving a motor of an industrial robot, and discharges a capacitor provided in the power supply circuit. The discharge circuit includes: a first voltage detector that detects the voltage input to the primary side of the power supply circuit; a second voltage detector that detects the voltage on the secondary side of the power supply circuit; a discharge resistor that is connected in parallel with the power supply circuit on the secondary side of the power supply circuit; a switching element that turns on or off the current flowing through the discharge resistor; and a power control unit that performs discharge control to allow current to flow through the discharge resistor. The power control unit controls the switching element to perform discharge control when the voltage detected by the second voltage detector is higher than a regeneration determination value, and performs discharge control after the time required for the industrial robot to stop operating when the voltage on the primary side of the first voltage detector is lower than a power outage determination value.

[0015] In industrial robots, the power supply to the primary side of the power circuit is cut off by disconnecting mechanical contacts during an emergency stop. Therefore, when the external power supply fails or the robot stops urgently, the power supply to the primary side is cut off, causing the voltage on the primary side to fall below the power outage threshold. In the discharge circuit of this invention, when a discharge resistor that consumes regenerative energy generated in the motor is installed on the secondary side (output side) of the power circuit, this discharge resistor is also used to discharge the smoothing capacitor within the power circuit during external power outages or robot emergency stops. Then, when an external power outage or robot emergency stop is detected because the voltage on the primary side of the power circuit falls below the power outage threshold, the discharge resistor is discharged after the time required for the robot to stop. During the time required for the robot to stop, a residual voltage remains on the secondary side of the power circuit, allowing the robot to stop safely. Furthermore, the subsequent discharge through the discharge resistor can reduce the voltage on the secondary side of the power circuit to a safe level within a short time, such as within the time specified in safety standards.

[0016] In the discharge circuit of this invention, ideally, the time required for the industrial robot to stop is pre-stored as a value. The stored value can also be determined according to the type of industrial robot. Furthermore, since the maximum value of the safe stopping time for the robot is known in advance based on its structure or specifications, it is preferable to set the stopping time of the industrial robot as the value obtained by adding an appropriate margin to this maximum value. By pre-stored the stopping time of the industrial robot, the discharge operation can be performed more reliably when the robot needs to stop urgently or when there is an external power failure. When a main control unit is provided to control the motors of each axis of the robot, the power control unit can also notify the stopping time of the industrial robot from the main control unit. By managing the stopping time of the industrial robot at the main control unit level, it is possible to respond more flexibly to changes in robot models, etc.

[0017] In the discharge circuit of this invention, the power control unit may also notify the industrial robot that the stopping action has ended from the main control unit controlling the motor, and upon receiving this notification, determine that the time required for the industrial robot to stop has elapsed and execute discharge control. In this case, since discharge control is performed after confirming that the stopping action has actually ended, the robot can be stopped more reliably and safely.

[0018] The discharge method of the present invention discharges a capacitor installed in the power supply circuit for the motor driving an industrial robot. In the discharge method, when the voltage on the secondary side of the power supply circuit is higher than the regeneration determination value, discharge control is executed, and current flows through a discharge resistor installed in parallel with the secondary side of the power supply circuit. Even when the voltage on the primary side of the power supply circuit is lower than the power outage determination value, discharge control is executed after the time required for the industrial robot to stop operating.

[0019] In the discharge method of this invention, a discharge resistor that consumes the regenerative energy generated in the motor is provided on the secondary side of the power supply circuit. This discharge resistor is also used to discharge the smoothing capacitor within the power supply circuit, in cases of external power failure or emergency robot stoppage. Furthermore, in the event of an external power failure or emergency robot stoppage, the discharge resistor is discharged after the time required for the robot to stop. During the time required for the robot to stop, a residual voltage remains on the secondary side of the power supply circuit, allowing the robot to stop safely. Additionally, the voltage on the secondary side of the power supply circuit can be reduced to a safe level within a short time, for example, within the time specified in safety standards, by the subsequent discharge of the discharge resistor.

[0020] In the discharge method of this invention, discharge control can be performed based on a pre-stored value representing the time required for the stopping action of the industrial robot. By pre-stored the time required for the stopping action of the industrial robot, discharge can be performed more reliably during emergency stops of the robot or when there is a power outage. When a main control unit is provided that controls the motors of each axis of the robot, discharge control can also be performed based on the time required for the stopping action of the industrial robot as notified from the main control unit. By managing the time required for the stopping action of the industrial robot at the main control unit level, it is possible to respond more flexibly to changes in robot models, etc.

[0021] In the discharge method of the present invention, it is also possible to determine, upon receiving notification from the main control unit controlling the motor that the stopping action of the industrial robot has ended, that the time required for the stopping action of the industrial robot has elapsed and to execute discharge control. In this case, since discharge control is performed after confirming that the stopping action has actually ended, the robot can be stopped more reliably and safely.

[0022] The robot controller of the present invention controls an industrial robot with an electric motor on each axis. The robot controller includes: a power supply circuit having a rectifier circuit and a smoothing capacitor, which outputs direct current from the secondary side based on alternating current supplied to the primary side; a first voltage detector that detects the alternating current input to the primary side of the power supply circuit; a second voltage detector that detects the voltage on the secondary side of the power supply circuit; a discharge resistor connected in parallel with the power supply circuit on the secondary side; a switching element that connects or disconnects the current flowing through the discharge resistor; a servo controller supplied with the direct current output from the secondary side to drive and control the electric motor; a main control unit that controls the electric motor by outputting commands to the servo controller; and a power control unit that performs discharge control of the switching element to allow current to flow through the discharge resistor. The power control unit performs discharge control when the voltage detected by the second voltage detector is higher than a regeneration determination value, and performs discharge control after the time required for the industrial robot to stop when the voltage on the primary side in the first voltage detector is lower than a power outage determination value. The main control unit performs a process to decelerate and stop the industrial robot when the voltage on the primary side is lower than the power outage determination value.

[0023] In the robot controller of this invention, a discharge resistor that consumes the regenerative energy generated in the motor is provided on the secondary side of the power supply circuit. When the AC power supply to the power supply circuit is cut off due to external power failure or emergency robot stop, this discharge resistor is also used to discharge the smoothing capacitor within the power supply circuit. Then, when it is detected that the AC power supply has been cut off because the voltage on the primary side of the power supply circuit is lower than the power outage threshold, the power control unit discharges the discharge resistor after the time required for the robot to stop. During the time required for the robot to stop, a residual voltage remains on the secondary side of the power supply circuit, allowing the robot to stop safely during this period via deceleration and stop processing by the main control unit. Furthermore, the discharge resistor can then reduce the voltage on the secondary side of the power supply circuit to a safe level within a short time, for example, within the time specified by safety standards.

[0024] In the robot controller of this invention, ideally, the main control unit has a memory that stores the time required for the industrial robot to stop as a discharge delay time, and notifies the power control unit of the discharge delay time stored in the memory. The power control unit then performs discharge control based on the notified discharge delay time. Since the main control unit typically has a memory that stores various parameters required for robot control, the time required for the industrial robot to stop is also stored in this memory as a discharge delay time. Therefore, by notifying the power control unit of the discharge delay time each time the robot is connected to the robot controller, it is possible to handle any type of robot and flexibly respond to changes in robot model.

[0025] In the robot controller of this invention, when the process of decelerating and stopping the industrial robot is completed, the main control unit notifies the power control unit. Upon receiving the notification, the power control unit determines that the time required for the stopping action of the industrial robot has elapsed and executes discharge control. In this case, since discharge control is performed after confirming that the stopping action has actually ended, the robot can be stopped more reliably and safely.

[0026] In the robot controller of the present invention, it is ideal to insert an input relay between the external AC power supply and the primary side of the power circuit, which opens during an emergency stop of the industrial robot. Accordingly, the robot can be stopped more reliably and safely during an emergency stop, and the voltage on the secondary side of the power circuit can be reliably set to a safe voltage level for a specified time during an emergency stop.

[0027] Invention Effects

[0028] According to the present invention, the robot can be safely stopped when the external power supply fails or when the robot needs to stop urgently, and the voltage on the secondary side of the power supply circuit can be reduced to a safe voltage within a time specified by safety standards, etc. Attached Figure Description

[0029] Figure 1 This is a block diagram illustrating the structure of a robot controller according to an embodiment of the present invention.

[0030] Figure 2 It is a timing diagram illustrating the actions taken when an emergency stop command is input from an external source.

[0031] Explanation of reference numerals in the attached figures

[0032] 10…Power supply circuit; 11…Power receiving terminal; 12…Input relay; 13…AC voltage detector; 14…Full-wave rectifier circuit; 15…Smoothing capacitor; 16…DC voltage detector; 18…Discharge resistor; 19…Discharge transistor; 20…Servo driver; 21…Power control unit; 22…Main control unit; 30…Robot; 31…Motor. Detailed Implementation

[0033] Next, embodiments of the present invention will be described with reference to the accompanying drawings. The discharge circuit based on the present invention is preferably used in a robot controller for controlling an industrial robot. Figure 1 This is a block diagram illustrating the structure of a robot controller according to one embodiment of the present invention. Hereinafter, industrial robots will also be referred to simply as robots.

[0034] Figure 1 The robot controller shown is for controlling a robot 30, each axis equipped with a motor 31, and is connected to an external power source, such as a single-phase 200 / 230V, 50 / 60Hz commercial AC power supply. In the following description, it is assumed that the external power source is AC. The robot controller has a power receiving terminal 11 for receiving power from the external power source. The AC power received at the power receiving terminal 11 is supplied to the primary side of the power circuit 10 via an input relay 12. The input relay 12 has mechanical contacts that supply AC power from the external power source to the power circuit 10 or disconnect it. In particular, the input relay 12 is configured to immediately disconnect the AC power supply to the primary side of the power circuit 10 when an emergency stop command is input.

[0035] The power supply circuit 10 includes a full-wave rectifier circuit 14 that rectifies the AC power supplied to its primary side and a smoothing capacitor 15 disposed on the output side of the full-wave rectifier circuit 14. Smoothed DC power is output from the secondary side for driving the motors 31 of each axis of the robot 30. An AC voltage detector 13 for detecting the voltage of the input AC power is disposed on the primary side of the power supply circuit 10, and a DC voltage detector 16 for detecting the voltage of the output DC power is disposed on the secondary side of the power supply circuit 10. The AC voltage detector 13 and the DC voltage detector 16 correspond to the first voltage detector and the second voltage detector, respectively. The DC power output from the secondary side of the power supply circuit 10 is supplied to a servo driver 20 corresponding to each axis of the robot 30. As described below, the robot controller also includes a main control unit 22, which controls the servo drivers 20, driving and servo-controlling the motors 31 of the corresponding axes in the robot 30. The motors 31 are, for example, synchronous motors or induction motors, and generate electromotive force during deceleration. The servo driver 30 also has the function of outputting the regenerative current of the electromotive force generated in the motor 31 during deceleration to the power supply circuit 10 side.

[0036] When the regenerative current from the motor 31 flows to the power supply circuit 10, the voltage on the secondary side of the power supply circuit 10 rises. If this voltage rises excessively, it may exceed the maximum allowable input power supply voltage of devices or components connected to the power supply circuit 10, such as the servo driver 20, or it may exceed the withstand voltage of the smoothing capacitor 15 of the power supply circuit 10 itself. Therefore, a discharge resistor 18 is provided in parallel with the secondary side of the power supply circuit 10, and a switching element 19 is provided to turn the current flowing through the discharge resistor 18 on or off. In the illustrated example, an NPN bipolar transistor is used as the switching element 19. One end of the discharge resistor 18 is connected to a wire extending from the secondary side of the power supply circuit 10 on the positive (+) side, and the other end of the discharge resistor 18 is connected to the collector of the switching element 19, i.e., the transistor. The emitter of the transistor is connected to a wire extending from the secondary side of the power supply circuit 10 on the negative (-) side. Furthermore, in order to control the conduction of the switching element 19, a power control unit 21 for outputting signals is provided at the port of the switching element 19, i.e., the transistor.

[0037] Assuming the AC voltage supplied to the primary side of the power supply circuit 10 is 200V, a DC voltage of approximately 280V is output from the secondary side of the power supply circuit 10. When regenerative current flows from the motor 31, the voltage on the secondary side of the power supply circuit 10 rises, for example, and is expected to exceed 400V. Therefore, the power control unit 21 monitors the DC voltage on the secondary side of the power supply circuit 10 via the DC voltage detector 16 and outputs a signal to the switching element 19. When the DC voltage exceeds the regeneration determination value, the switching element 19 is turned on; when it falls below the regeneration determination value, the switching element 19 is turned off. By controlling the switching element 19 to be in the on state, regenerative current flows through the discharge resistor 18, regenerative energy is consumed, thereby reducing the voltage on the secondary side of the power supply circuit 10. The control of setting the switching element 19 to the on state and allowing current to flow through the discharge resistor 18 is called discharge control. In practice, the control of turning on and off the switching element 19 has a hysteresis characteristic. Once the voltage on the secondary side of the power supply circuit 10 exceeds, for example, 400V, the power control unit 21 turns on the switching element 19, consuming regenerative energy through the discharge resistor 18. When the voltage on the secondary side of the power supply circuit 10 drops below, for example, 380V due to the consumption of regenerative energy, the switching element 19 is turned off. Thus, even if regenerative current exists, the DC voltage on the secondary side of the power supply circuit 10 is maintained below 400V. The power control unit 21 is, for example, composed of a CPU (Central Processing Unit) or a microprocessor.

[0038] Furthermore, in the robot controller of this embodiment, the power control unit 21 also performs control when the external power supply fails or when the robot undergoes an emergency stop, so as to keep the voltage on the secondary side of the power circuit 10 within a specified safe level for a time specified by safety standards. For example, the safety standards specify that the voltage should be lower than 43V within one minute when the external power supply is cut off or an emergency stop occurs. The robot controller is equipped with an input relay 12. When an emergency stop command is input to the input relay 12, the input relay 12 immediately becomes open, and the voltage on the primary side of the power circuit 10 becomes 0V. Of course, when the external power supply fails, the voltage on the primary side of the power circuit 10 also becomes 0V. The AC voltage detector 13 constantly monitors the AC voltage on the primary side of the power circuit 10. When this voltage is lower than a specified power outage determination value, it can be determined that an emergency stop of the robot or an external power outage has occurred. When the AC voltage detected by the AC voltage detector 13 is lower than the power outage threshold, the power control unit 21 performs discharge control by turning on the switching element 19 after the time required for the robot 30 to stop, regardless of whether regenerative current is controlled to flow through the discharge resistor 18 to consume regenerative energy at that moment. If the time required for the robot 30 to stop is called the discharge delay time, the same control as before is implemented from the moment the AC voltage detected by the AC voltage detector 13 is lower than the power outage threshold until the discharge delay time has elapsed. This includes the consumption of regenerative energy. As a result, even if the AC power supply from the external power source is cut off after a power outage or emergency stop is detected until the discharge delay time has elapsed, a residual voltage sufficient to drive the motor 31 is generated on the secondary side of the power circuit 10 through the charge previously accumulated in the smoothing capacitor 15. Therefore, by using this residual voltage to perform an action to decelerate and stop the robot 30, the robot 30 can be safely stopped. Then, after the discharge delay time, the power control unit 21 connects a pair of wires extending from the secondary side of the power circuit 10 with a discharge resistor 10 by executing discharge control to turn on the switching element 19. As a result, the charge stored in the smoothing capacitor 15 is discharged through the discharge resistor 15, and the voltage on the secondary side of the power circuit 10 drops rapidly to 0V according to a time constant, which is the product of the capacitance value of the low-activity capacitor 15 and the resistance value of the resistor 18.

[0039] Here, the discharge delay time, which is the time required for the robot 30 to stop, will be explained. Assuming the robot 30 is in motion, consider the action of slowing down and safely stopping the robot 30 via an emergency stop command. The time required for a safe stop varies depending on the size of the robot 30 and the type of motion it is performing, but the maximum value required for slowing down and safely stopping can be determined in advance for each robot model and based on its structure or design. In this embodiment, the discharge delay time is defined as the value obtained by adding an appropriate safety margin to this maximum value. In cases where the robot controller can handle multiple robot models 30, it is preferable to determine the discharge delay time for each robot model 30. Larger robots require a longer time to slow down and safely stop the robot 30 in motion, up to a few seconds. On the other hand, in safety standards, during an emergency stop, the voltage on the output side of the power supply circuit 10 is required to drop below a so-called safe voltage after approximately one minute. Therefore, setting the discharge delay time and delaying the start time of the discharge of the smoothing capacitor 15 from the emergency stop timing by a few seconds to approximately ten seconds will not cause any safety issues.

[0040] The discharge delay time can be pre-stored in the power control unit 21. Alternatively, as described below, the discharge delay time can be stored on the main control unit 22 side, and when the robot 30 is connected to the robot controller, or when the robot controller is started, the main control unit 22 notifies the power control unit 21.

[0041] Next, the main control unit 22 in the robot controller of this embodiment will be described. When an action command is given to the robot 30 from the outside, in order for the robot 30 to act based on the action command, the main control unit 22 outputs a servo driver 20 for each axis to control the motor 31 of each axis. The main control unit 22 is composed of a CPU or a microprocessor. A non-volatile memory 23 storing various parameters required for the control of the robot 30 is connected to the main control unit 22. Alternatively, the non-volatile memory 23 may be provided inside the main control unit 23, in which case a flash memory built into the CPU or microprocessor may be used as the non-volatile memory 23. The main control unit is composed of the main control unit 22 and the non-volatile memory 23. The parameters stored in the non-volatile memory 23 may also include the discharge delay time for each model of the robot 23, in which case the discharge delay time used by the power control unit 21 is notified from the main control unit 22 to the power control unit 21. Alternatively, the regeneration determination value used for discharge control that consumes regeneration energy may also be stored in the non-volatile memory 23 and notified to the power control unit 21 from the main control unit 22.

[0042] Furthermore, when the AC voltage detected by the AC voltage detector 13 is lower than the power outage determination value, that is, when it is determined that the AC power supply to the primary side of the power supply circuit 10 has been cut off, the main control unit 22 executes a process to decelerate and stop the robot 30. Figure 1 In the process, the output of AC voltage detector 13 is also directly supplied to the main control unit 22, but the main control unit 22 can also notify the power control unit 21 that the AC voltage detected by AC voltage detector 13 is lower than the power outage judgment value.

[0043] Figure 2 This diagram illustrates the action of an emergency stop command input from an external source during normal robot operation in the robot controller of this embodiment. AC 200V is supplied to the primary side of the power supply circuit 10, resulting in a DC voltage of 280V for the power supply to the motor 31, i.e., the secondary side of the power supply circuit 10. In the diagram, an external emergency stop signifies a change from normal operation to emergency stop, meaning an emergency stop command is input to the robot controller. When an emergency stop command is input, the state of the contacts of the input relay 12 changes from closed (ON) to open (OFF), cutting off the AC power supply to the primary side of the power supply circuit 10. The AC voltage detector 13 detects that the AC power supply has been cut off. At this point, the switching element 19 connected to the discharge resistor 18 is in the off state, and the discharge resistor 18 does not perform a discharge operation.

[0044] When the AC voltage detector 13 detects that the AC power supply has been cut off, the main control unit 22 executes a process to decelerate and stop the robot 30 at that time. At this time, the power supply voltage of the motor 31 gradually decreases, but does not decrease indefinitely to the point of preventing the robot 30 from stopping safely. On the other hand, after a discharge delay time has elapsed since the AC voltage detector 13 detected that the AC power supply has been cut off, the power control unit 21 performs discharge control to turn on the switching element 19. The deceleration and stopping of the robot 30 is completed before the discharge delay time has elapsed, and the robot 30 is in a safe stopped state at the moment when the discharge resistor 18 begins to discharge. In the figure, A represents the margin between when the robot 30 has completely stopped and when the discharge resistor 18 begins to discharge. Once the discharge resistor 18 begins to discharge, the power supply voltage of the motor 31, i.e., the voltage on the secondary side of the power circuit 10, quickly becomes 0V.

[0045] As described above, in this embodiment, the time required for the robot 30 to stop is preset as a discharge delay time. After the discharge delay time has elapsed following the detection of the interruption of AC power to the primary side of the power circuit 10, the discharge resistor 18 is discharged. This allows the robot 30 to stop safely and meets safety standards related to the residual voltage on the secondary side of the power circuit 10. By storing the discharge delay time of each model of the robot 30 as a parameter in the non-volatile memory 23, it is possible to flexibly respond to changes in the model of the robot 30 connected to the robot controller.

[0046] In the above description, the time required for the robot 30 to stop is pre-stored, i.e., the discharge delay time. Based on the stored discharge delay time, the power control unit 21 discharges the discharge resistor 18 after the discharge delay time has elapsed following the detection of the interruption of AC power to the primary side of the power circuit 10. However, in this invention, it is possible to determine whether the time required for the robot 30 to stop has elapsed even without relying on the pre-set and stored discharge delay time. The main control unit 22 actually executes the process of decelerating and stopping the robot 20, and can know whether the robot 20 has completely stopped. Thus, it is also possible that when the process of decelerating and stopping the robot 30 ends, the main control unit 22 notifies the power control unit 21 of this intention, and upon receiving this notification, the power control unit 21 determines that the time required for the robot 30 to stop has elapsed and executes discharge control. In this configuration, discharge control is performed after confirming that the stopping action has actually ended, so the robot 30 can be stopped more reliably and safely.

Claims

1. A discharge circuit provided with respect to a power supply circuit provided for driving a motor of an industrial robot, to discharge a capacitor provided in the power supply circuit, the discharge circuit comprising: a first voltage detector that detects a voltage input to a primary side of the power supply circuit; a second voltage detector that detects a voltage of a secondary side of the power supply circuit; a discharge resistor provided in parallel with the power supply circuit at the secondary side of the power supply circuit; a switching element that turns on or off a current flowing through the discharge resistor; and a power supply control unit that performs discharge control of the switching element to cause a current to flow through the discharge resistor, when the voltage detected by the second voltage detector is higher than a regeneration determination value, and performs the discharge control after a time required for a stop operation of the industrial robot from a point in time at which the voltage of the primary side in the first voltage detector is lower than a power-off determination value, in a case where the voltage of the primary side is lower than the power-off determination value.

2. The discharge circuit according to claim 1, wherein the time required for the stop operation of the industrial robot is stored in advance.

3. The discharge circuit according to claim 1, wherein the power supply control unit is notified of the time required for the stop operation of the industrial robot from a main control unit that controls the motor.

4. The discharge circuit according to claim 1, wherein the power supply control unit is notified of an end of the stop operation of the industrial robot from a main control unit that controls the motor, and judges that the time required for the stop operation of the industrial robot has elapsed and performs the discharge control when the notification is made.

5. A discharge method of discharging a capacitor provided in a power supply circuit for driving a motor of an industrial robot, in the discharge method, when a voltage of a secondary side of the power supply circuit is higher than a regeneration determination value, discharge control is performed to cause a current to flow through a discharge resistor provided in parallel with the secondary side of the power supply circuit, the discharge control is performed after a time required for a stop operation of the industrial robot from a point in time at which a voltage of a primary side of the power supply circuit is lower than a power-off determination value, even in a case where the voltage of the primary side is lower than the power-off determination value, the time required for the stop operation of the industrial robot is a time required for the industrial robot to perform a deceleration and safe stop operation by a residual voltage generated by a charge accumulated in the capacitor in a control operation of an emergency stop instruction.

6. The discharge method according to claim 5, wherein the discharge control is performed based on a value stored in advance as the time required for the stop operation of the industrial robot. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 7. The discharging method according to claim 5, wherein the discharging control is executed based on a time required for a stop operation of the industrial robot notified from a main control unit that controls the motor.

8. The discharging method according to claim 5, wherein the discharging control is executed when a time required for a stop operation of the industrial robot has elapsed, which is judged from a notification of the stop operation of the industrial robot by a main control unit that controls the motor.

9. A robot controller that controls an industrial robot each axis of which is provided with a motor, the robot controller comprising: a power supply circuit that includes a rectification circuit and a smoothing capacitor, and that outputs a direct current from a secondary side based on an alternating current supplied to a primary side; a first voltage detector that detects an alternating voltage input to the primary side of the power supply circuit; a second voltage detector that detects a voltage of the secondary side of the power supply circuit; a discharging resistor that is provided in parallel with the power supply circuit at the secondary side; a switching element that turns on or off a current flowing through the discharging resistor; a servo controller that is supplied with the direct current output from the secondary side, and that drives and controls the motor; a main control unit that controls the motor by outputting an instruction to the servo controller; a power supply control unit that executes a discharging control that controls the switching element so that a current flows through the discharging resistor, the power supply control unit executing the discharging control when a voltage detected by the second voltage detector is higher than a regeneration determination value, and executing the discharging control after a time required for a stop operation of the industrial robot has elapsed from a point in time when the voltage of the primary side is lower than a power failure determination value in a case where the voltage of the primary side is lower than the power failure determination value in the first voltage detector, the main control unit executing a process of deceleration stop of the industrial robot in a case where the voltage of the primary side is lower than the power failure determination value, the time required for the stop operation of the industrial robot being a time required for the industrial robot to execute a deceleration and safe stop operation by an emergency stop instruction control operation using a residual voltage generated by a charge accumulated in the smoothing capacitor.

10. The robot controller according to claim 9, wherein the main control unit includes a memory that stores the time required for the stop operation of the industrial robot as a discharging delay time, and notifies the power supply control unit of the discharging delay time stored in the memory, the power supply control unit executing the discharging control based on the notified discharging delay time.

11. The robot controller according to claim 9, wherein the main control unit notifies the power supply control unit when the process of deceleration stop of the industrial robot ends, the power supply control unit judging that the time required for the stop operation of the industrial robot has elapsed and executing the discharging control when there is the notification. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 12. The robot controller according to any one of claims 9 to 11, wherein Further provided is an input relay interposed between an external alternating-current power supply and the primary side of the power supply circuit, the input relay being opened when the industrial robot is in an emergency stop.

Images