Method and system for stopping of axes of an industrial robot

Abstract

The invention relates to a method or a system for the dependable stopping of axes of an industrial robot. The industrial robot comprises a control device (501, 502), power electronics (201, 202, 203) and a DC source (300), as well as at least one axis (700), which is assigned to an electric motor (100) and to a mechanical brake (600). In order to stop the axis a direct current is supplied by the DC source in at least one motor phase of the motor, which generates a braking torque.

Claims

1. A method for stopping movement of axes of an industrial robot, wherein the industrial robot comprises at least one control device, power electronics, a DC source and at least one axis which is assigned to an electric motor that is equipped with a mechanical brake, and wherein the control device is configured to actuate the electric motor via the power electronics using control signals (.sub.ref), the method including the steps of: a) sending a signal from the control device to the mechanical brake to stop movement of the robot in the at least one axis; b) sending a signal to activate a short-circuit braking of the motor assigned to the at least one axis, whereby the motor phases are short-circuited to generate a braking torque that depends on a rotational speed of the electric motor at the time when the motor phases are short circuited; c) after activating the short-circuit braking of the motor, sending a signal to the DC source to activate a direct current braking of the motor before the mechanical brake takes effect; and d) in response to the signal of step c), supplying a direct current from the DC source in at least one motor phase of the motor assigned to the at least one axis to generate a braking torque that is independent of the rotational speed of the motor.

2. The method according to claim 1, wherein the power electronics comprise a rectifier, an intermediate circuit and an inverter and are supplied with operating power by a main power source, wherein the signals in steps a) through c) activate a stop such that the motor is disconnected from the operating power.

3. The method according to claim 2, wherein the disconnection of the operating power disconnects the power electronics from the main power source, disconnects the intermediate circuit from the rectifier and disconnects the power electronics from the motor.

4. The method according to claim 1, wherein step c) of the method is activated as a function of motor parameters, and wherein step c) occurs only when the motor rotational speed has fallen below a value of 1000 rpm.

5. A system for controlling an industrial robot, in particular for stopping movement of axes of the industrial robot, wherein the industrial robot has: at least one axis which is assigned to an electric motor that is equipped with a mechanical brake; a control device; and power electronics, wherein: the control device is configured to actuate the motor via the power electronics using control signals and to send signals to stop movement of the at least one axis, the signals to stop movement of the at least one axis bring about the activation of the mechanical brake and an electrical braking of the motor assigned to the at least one axis, the system additionally comprises a DC source for the electrical braking, the DC source being connected to the motor so as to supply direct current in at least one motor phase of the motor assigned to the at least one axis in order to generate a braking torque that is independent of the rotational speed of the motor, and the control device is configured to bring about the electrical braking of the motor before the intervention of the mechanical brake.

6. The system according to claim 5, wherein the DC source is autonomous from the power electronics.

7. The system according to claim 5, wherein the DC source is configured as an intermediate circuit of the power electronics comprising a capacitor for supplying the direct current to the at least one motor phase independent of operating power supplied to the power electronics by a main power source, and to the electric motor by the power electronics.

8. The system according to claim 5, wherein the DC source is a regulated DC source, and wherein the regulated DC source is configured to generate a regulated direct current that does not exceed a pre-determined maximum value and is kept constant over the period of time in which the direct current is supplied in the at least one motor phase.

9. The system according to claim 5, wherein: the control device comprises at least a first control system and a second control system, and wherein the first control system actuates the electric motor via the power electronics using the control signals, which power electronics receive operating power from a main power source and generate, dependent on the control signals, an alternating current voltage with variable frequency and amplitude for the supply and control of the at least one motor, and the second control system sends the signals to stop movement of the at least one axis when pre-determined limits are exceeded, causing the operating power to be disconnected from the power electronics.

10. The method according to claim 4, wherein step c) occurs only when the motor rotational speed has fallen below 100 rpm.

11. The method according to claim 4, wherein step c) occurs only when the motor rotational speed has fallen below 10 rpm.

12. The method according to claim 1, wherein the DC source is autonomous from the power electronics.

13. The method according to claim 1, wherein the DC source is configured as an intermediate circuit of the power electronics comprising a capacitor for supplying the direct current to the at least one motor phase independent of operating power supplied to the electric motor by the power electronics.

14. The method according to claim 1, wherein the DC source is a regulated DC source, and wherein the regulated DC source is configured to generate a regulated direct current that does not exceed a pre-determined maximum value and is kept constant over the period of time in which the direct current is supplied in the at least one motor phase.

15. The method according to claim 1, wherein: the control device comprises at least a first control system and a second control system, and wherein the first control system actuates the electric motor via the power electronics using the control signals, which power electronics receive operating power from a main power source and generate, dependent on the control signals, an alternating current voltage with variable frequency and amplitude for the supply and control of the at least one motor, and the second control system sends the signals to stop movement of the at least one axis when pre-determined limits are exceeded, causing operating power to be disconnected from the power electronics.

16. The method according to claim 1, wherein the braking torque that is independent of the rotational speed of the motor corresponds to a holding torque of the motor.

17. The system according to claim 5, wherein the braking torque corresponds to a holding torque of the motor.

Description

4. DESCRIPTION OF PREFERRED EMBODIMENTS

(1) Preferred embodiments of the invention are explained in greater detail below with reference to the accompanying figures, in which:

(2) FIG. 1 shows an industrial robot, which has six axes A1-A6;

(3) FIG. 2 shows a schematic signal and power flowchart of the system for controlling an industrial robot;

(4) FIG. 3 shows a signal and power flowchart of the system for controlling an industrial robot according to a first embodiment of the invention; and

(5) FIG. 4 shows a signal and power flowchart of the system for controlling an industrial robot according to a second embodiment of the invention.

(6) FIG. 1 depicts an industrial robot 1, which has a manipulator 2, which stands on a robot base 3, such that it can rotate about an axis A1, designed as a vertical axis. The manipulator 2 has a total of six rotational axes A1-A6, which are driven by electric motors 102, 104, 105, 106. Because of the perspective of the drawing, the electric motors of the axes A1 and A3 are not visible.

(7) FIG. 2 shows a schematic signal and power flowchart of the system for controlling an industrial robot. In FIG. 2, signal paths are represented by dashed lines and energy paths by a solid line when these are electrical energy paths, and by a double line when these are kinetic energy paths.

(8) A signal for executing a target movement of an axis 700 is delivered to the control device 500, for example, by a control program in the form of a motor angle , a motor rotational speed ;{dot over ( )} and/or a motor acceleration ;. This control device converts the signal for the power electronics 200. The power electronics generates, according to the signal, a three-phase alternating current voltage with variable frequency and amplitude or an alternating current for actuation of the motor 100, which drives an axis 700 via the motor shaft. The movements of the motor , ;{dot over ( )}, ; are monitored by a sensor system 800, and thus the actual values of the movement are determined. The control circuit is closed by the feedback of the actual values.

(9) FIG. 3 shows a signal and power flowchart of the system for controlling an industrial robot according to a first embodiment of the invention. The system comprises an industrial robot which has at least one axis 700, an electric motor 100 with associated power electronics and a control device. The axis 700 is assigned the motor 100, which is actuated by the power electronics. The motor 100 is equipped with a mechanical brake 600. The power electronics comprise a rectifier 201, an intermediate circuit 202 and an inverter 203, and are supplied with power by a main power source 400. A DC source 300 is connected to the motor 100 such that direct current can be supplied in at least one of the motor phases, in order to generate a braking torque. The motor is monitored by means of the sensor system 800, which sends relevant motor parameters, such as the rotational speed, torque and the like, to the control device.

(10) The control device is, in the embodiment of the invention depicted, in two parts and comprises a non-secure control system (first control system) 501 and a secure control system (second control system) 502. Both the first control system 501 and the second control system 502 comprise both software and hardware components and can be redundant systems.

(11) The first control system 501 is configured to actuate the motor via the power electronics using control signals .sub.ref and to monitor the sensor system 800 of the axis/axes, so that a regulation of the axes in the closed control circuit is possible. The second control system 502 monitors, amongst other things, the sensor system 800 and compares the measured values with permissible limits in order to detect control errors. If the second control system 502 detects, e.g., a control error, a signal to stop the axis is sent.

(12) In the case of a stop of category 0 (emergency stop) or of category 1, the second control system sends a signal to stop the axis S.sub.Bm to the mechanical brake and preferably simultaneously sends a signal to stop the axis S.sub.BDC to the DC source. In addition, a signal to disconnect the operating power is sent, preferably by the secure control system. The disconnection preferably occurs by addressing appropriate switches, which are designed, for example, as power transistors such as bipolar transistors or IGBTs. In the embodiment of FIG. 3, the disconnection of the operating power from the motor can, by way of example, be realized using three different methods; namely by disconnecting all of the power electronics from the main power source 400 (signal S.sub.E1), or by disconnecting the intermediate circuit 201 from the rectifier 202 (signal S.sub.E2) or by a disconnection of the power electronics from the motor (signal S.sub.E3). In practice, one of the three methods will suffice, and preferably that method is the disconnection of the power electronics from the motor (signal S.sub.E3). The different switch assemblies can, however, also be combined.

(13) In response to the signal to stop the axis S.sub.BDC, a direct current is supplied in at least one motor phase of the motor, in order to generate a braking torque. In one embodiment of the invention, the regulated DC source 300 is part of the power electronics and is configured to be supplied by the rectifier 201, but preferably by an intermediate circuit 202 of the power electronics. In a particularly preferred embodiment of the invention, the DC source 300 is supplied by an intermediate circuit capacitor, or it is the intermediate capacitor, so that the system can carry out, even after disconnection of the power electronics from the main power source 400 (signal S.sub.E1), a direct current braking.

(14) Alternatively, the DC source 300 can also be a completely redundant DC source, and is preferably a regulated DC source. The regulated DC source is preferably configured to generate a regulated direct current, which direct current does not exceed a pre-determined maximum value, so as to avoid damage to the motor. Furthermore, the regulated DC source can be configured such that the direct current is kept constant over the period of time in which the direct current is supplied in the motor phase.

(15) In a preferred embodiment of the invention it is provided that, in addition to the DC braking according to the invention, a short-circuit braking is realized. The short-circuit braking of the motor precedes the direct current braking (i.e. the sending of the signal to stop the axis to the DC source S.sub.BDC). For this purpose, the control device sends a signal to activate a short-circuit braking, which short-circuits the motor phases. The short circuit generates a braking torque dependent on the motor rotational speed. The motor phases can be short-circuited, for example, by means of a braking resistor. In this regard, reference is made, by way of example, to the document WO 2009/074 396 A1 mentioned at the outset. The short-circuit braking can be activated by the secure control system and by the first control system. In particular at high motor rotational speeds, the short-circuit braking generates a high braking torque. At low motor rotational speeds the achievable braking torque drops significantly, so that the direct current braking is then used.

(16) In another embodiment of the invention, the sending to the DC source S.sub.BDC of the signal to stop the axis is dependent on motor parameters, such as motor current or motor rotational speed or axis speed. Preferably, the signal destined for the DC source S.sub.BDC to stop the axis is only activated when the motor rotational speed has fallen below a value of 1000 rpm, preferably 100 rpm, and particularly preferably 10 rpm. As already mentioned, in the case of short-circuit braking, the braking torque decreases with the falling motor rotational speed. If the braking torque falls below a limit, then there is a changeover to the direct current braking according to the invention, which functions in a manner independent of the rotational speed.

(17) The present invention permits a very quick stopping of the motor and preferably stops the motor completely before the mechanical brake takes effect. In other words, the motor is electrically braked to a standstill, preferably during the activation delay of the mechanical brake, so that the mechanical brake serves purely as a holding brake. In this way, the mechanical loads to the axis are advantageously minimized.

(18) FIG. 4 shows a signal and energy flowchart according to a second embodiment of the invention. By contrast with the system shown in FIG. 3, the control device 500, which can comprise both a secure and a first control system, sends the signal to stop the axis S.sub.0. Additional control devices 503, 504, 505 receive the signal S.sub.0 and convert the signal to stop the axis into signals to disconnect the operating power S.sub.E1, S.sub.E2, S.sub.E3 (in practice, the disconnection will usually only occur at one location), into signals to activate the direct current braking S.sub.BDC and into signals to activate the mechanical braking S.sub.Bm. The power shut-off device 503 generates the signals S.sub.E1, S.sub.E2, and/or S.sub.E3 and sends these to the corresponding switch in order to disconnect the operating power from the motor. The DC brake activation device 504 generates the signal to activate the direct current braking S.sub.BDC and sends this to the DC source 300, in order to activate the direct current braking. The mechanical brake activation device 505 generates a signal to activate the mechanical braking S.sub.Bm and sends this to the mechanical brake 600. The control devices 503, 504, 505 can convert the signal S.sub.0 with a time delay, in order to thus achieve a desired chronological signal sequence. Not depicted is a device for activating a short-circuit braking. This can, however, be implemented in a similar manner to that already described.

(19) It should be noted that the invention claimed herein is not limited to the described embodiments, but may be otherwise variously embodied within the scope of the claims listed infra.

5. REFERENCE NUMERAL LIST

(20) 1: Industrial robot 2: Manipulator 3: Robot base 10: Link 11: Joint 100: Electric motor 102: Motor assigned to the axis A2 104: Motor assigned to the axis A4 105: Motor assigned to the axis A5 106: Motor assigned to the axis A6 200 Power electronics 201: Rectifier 202: Intermediate circuit 203: Inverter 300: DC source 400: Main power source 500 Control device 501: First control system 502: Second control system 503: Power shut-off device (second control system) 504: DC brake activation device (second control system) 505: Mechanical brake activation device (second control system) 600: Mechanical brake 700: Axis 800: Sensor system A1-A6: Axes of the industrial robot S.sub.E1, S.sub.E2, S.sub.E3: Signal to disconnect the operating power S.sub.BDC: Signal to activate a direct current braking S.sub.Bm: Signal to activate a mechanical braking .sub.0: Signal to stop the axis v.sub.M: Speed of the motor (actual value) .sub.ref: Control signal ,;{dot over ( )}, ;: Motor angle, motor rotational speed, motor acceleration (nominal values)