METHOD FOR CONTROLLING AT LEAST ONE SERVOMOTOR IN A BRAKING MANNER, ROBOT, AND COM- PUTER PROGRAM PRODUCT

Abstract

A method for controlling at least one servomotor in a braking manner with a frequency converter includes disconnecting a direct-voltage intermediate circuit from an electric alternating-voltage network, braking the servomotor by controlling semiconductor switches of an inverter circuit in a regenerative braking mode in order to reduce the speed of the servomotor, and controlling a brake chopper such that a brake resistor is switched on at a maximum intermediate-circuit voltage, which forms a switch-on threshold for the brake chopper, and is disconnected at a minimum intermediate-circuit voltage, which forms a switch-off threshold for the brake chopper. The switch-on threshold and/or the switch-off threshold are dynamically changed during regenerative braking of the servomotor as a function of the current speed of the servomotor.

Claims

1-10. (canceled)

11. A method for controlling at least one servomotor in a braking manner using a frequency converter which comprises a rectifier circuit connectable to an electric alternating-voltage network, a direct-voltage intermediate circuit, which is fed from the electric alternating-voltage network in the state connected to the electric alternating-voltage network and has an intermediate-circuit capacitor and has a brake resistor, which can be connected and disconnected via a brake chopper of the direct-voltage intermediate circuit, and at least one inverter circuit, which is fed from the direct-voltage intermediate circuit and has controllable semiconductor switches, the method comprising: disconnecting the direct-voltage intermediate circuit from the electric alternating-voltage network; braking the at least one servomotor by controlling the semiconductor switches of the inverter circuit in a regenerative braking mode in order to reduce the speed of the servomotor; controlling the brake chopper in such a way that the brake resistor is switched on at a maximum intermediate-circuit voltage, which forms a switch-on threshold for the brake chopper, and the brake resistor is disconnected at a minimum intermediate-circuit voltage, which forms a switch-off threshold for the brake chopper; and dynamically changing at least one of the switch-on threshold or the switch-off threshold during regenerative braking of the servomotor as a function of the current speed of the servomotor.

12. The method of claim 11, wherein dynamically changing at least one of the switch-on threshold or the switch-off threshold comprises changing the switch-on threshold and/or the switch-off threshold such that the intermediate-circuit voltage is continuously reduced as the speed of the servomotor decreases.

13. The method of claim 12, further comprising reducing the intermediate-circuit voltage in proportion to the decrease in the speed of the servomotor.

14. The method of claim 11, wherein dynamically changing at least one of the switch-on threshold or the switch-off threshold comprises changing the switch-on threshold and/or the switch-off threshold on the basis of a current speed of the servomotor measured by a motor position sensor or on the basis of the measured motor voltage of the servomotor currently prevailing in the servomotor.

15. The method of claim 11, wherein dynamically changing at least one of the switch-on threshold or the switch-off threshold comprises lowering the switch-on threshold and/or the switch-off threshold to a predetermined minimum threshold value.

16. The method of claim 15, wherein the switch-off threshold value is lowered to a minimum threshold value which is below the network voltage of the alternating-voltage network.

17. The method of claim 11, wherein dynamically changing at least one of the switch-on threshold or the switch-off threshold comprises lowering the switch-on threshold and/or the switch-off threshold only to a minimum threshold value at which a minimum voltage is present in the direct-voltage intermediate circuit at which regenerative braking of the servomotor is still ensured by controlling the semiconductor switches of the inverter circuit.

18. The method of claim 11, wherein: controlling at least one servomotor comprises controlling at least two servomotors simultaneously; the frequency converter comprises a number of inverter circuits corresponding to the number of simultaneously controlled servomotors; the inverter circuits are connected to the common direct-voltage intermediate circuit of the frequency converter; and dynamically changing at least one of the switch-on threshold or the switch-off threshold comprises dynamically changing the switch-on threshold and/or the switch-off threshold during regenerative braking of one or more of the at least two servomotors as a function of the current speed of the servomotor that is currently inducing the highest intermediate-circuit voltage.

19. The method of claim 11, further comprising: increasing the electrical energy in the direct-voltage intermediate circuit during the dynamic change in the switch-on threshold and/or the switch-off threshold in those states of the direct-voltage intermediate circuit in which the brake chopper has disconnected the brake resistor, by the intermediate-circuit capacitor being fed exclusively by the energy generated by the at least one servomotor from the inverter circuit.

20. A robot, comprising: a robot arm comprising a plurality of links connected by a plurality of respective joints for adjustment of the links relative to one another by movements of the joints; at least one servomotor assigned to a respective joint and designed to adjust the at least one joint, namely via automatic control of the servomotor; and a control device designed to automatically control the at least one servomotor in order to automatically adjust the links of the robot arm in relation to one another by moving the joints in a driven manner; wherein the control device is designed and configured to control the at least one servomotor according to the method of claim 11.

21. A computer program product for controlling at least one servomotor in a braking manner using a frequency converter which comprises a rectifier circuit connectable to an electric alternating-voltage network, a direct-voltage intermediate circuit, which is fed from the electric alternating-voltage network in the state connected to the electric alternating-voltage network and has an intermediate-circuit capacitor and has a brake resistor, which can be connected and disconnected via a brake chopper of the direct-voltage intermediate circuit, and at least one inverter circuit, which is fed from the direct-voltage intermediate circuit and has controllable semiconductor switches, the computer program product comprising a non-transient, machine-readable storage medium on which a program code is stored, the program code, when executed by a computer, causing the computer to: disconnect the direct-voltage intermediate circuit from the electric alternating-voltage network; brake the at least one servomotor by controlling the semiconductor switches of the inverter circuit in a regenerative braking mode in order to reduce the speed of the servomotor; control the brake chopper in such a way that the brake resistor is switched on at a maximum intermediate-circuit voltage, which forms a switch-on threshold for the brake chopper, and the brake resistor is disconnected at a minimum intermediate-circuit voltage, which forms a switch-off threshold for the brake chopper; and dynamically change at least one of the switch-on threshold or the switch-off threshold during regenerative braking of the servomotor as a function of the current speed of the servomotor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.

[0059] FIG. 1 is a flowchart of the inventive method,

[0060] FIG. 2 is a side view of an exemplary industrial robot, which comprises a robot arm with links, joints and servomotors, and which comprises a robot controller which is designed to carry out an inventive method,

[0061] FIG. 3 is a schematic representation of a circuit diagram of an exemplary frequency converter with a servomotor, and

[0062] FIG. 4 is a schematic representation of a circuit diagram of an exemplary modified frequency converter with two or more servomotors that are connected to a common direct-voltage intermediate circuit.

DETAILED DESCRIPTION

[0063] In FIG. 1, the sequence of the basic inventive method for controlling at least one servomotor M in a braking manner by means of a frequency converter 1 (FIG. 3, FIG. 4) is shown schematically.

[0064] As shown in FIGS. 3 and 4, the frequency converter 1 can comprise a rectifier circuit 3 connectable to an electric alternating-voltage network 2, a direct-voltage intermediate circuit 4, which is fed from the electric alternating-voltage network 2 in the state connected to the electric alternating-voltage network 2 and has an intermediate-circuit capacitor 5 and has a brake resistor 6, which can be connected and disconnected via a brake chopper S70 of the direct-voltage intermediate circuit 4, and at least one inverter circuit 7, which is fed from the direct-voltage intermediate circuit 4 and has controllable semiconductor switches S1 to S6.

[0065] The inventive method, as shown in FIG. 1, comprises the following steps:

[0066] In the first step VI, the direct-voltage intermediate circuit 4 is disconnected from the electric alternating-voltage network 2.

[0067] In a subsequent second step V2, the servomotor M is braked by controlling the semiconductor switches S1-S6 of the inverter circuit 7 in a regenerative braking mode in order to reduce the speed of the servomotor M.

[0068] In a third step V3, the brake chopper S7 is controlled in such a way that the brake resistor 6 is switched on at a maximum intermediate-circuit voltage, which forms a switch-on threshold for the brake chopper S7, and is disconnected at a minimum intermediate-circuit voltage, which forms a switch-off threshold for the brake chopper S7, wherein, according to step V4, the switch-on threshold and/or the switch-off threshold are dynamically changed during regenerative braking of the servomotor M as a function of the current speed of the servomotor M.

[0069] FIG. 2 is a depiction of an industrial robot 8 which comprises a robot arm 9 and a robot controller 10. In the case of the present exemplary embodiment, the robot arm 9 comprises a plurality of links G1 to G7 which are arranged one after the other and are rotatably connected to one another by means of joints L1 to L6.

[0070] The industrial robot 8 comprises the robot controller 10 which is designed to execute a robot program and to move the links G1-G7 and joints L1-L6 of the robot arm 9 automatically. One of the plurality of links G1-G7 forms an end link (G7) of the robot arm 9, which comprises a tool flange 11.

[0071] The robot controller 10 of the industrial robot 8 is designed or configured to execute a robot program, by means of which the links L1 to L6 of the robot arm 9 can be automated or automatically adjusted or rotated in a manual mode in accordance with the robot program. For this purpose, the robot controller 10 is connected to controllable electric drives, the servomotors M1 to M6, which are designed to adjust the respective joints L1 to L6 of the robot arm 9.

[0072] In the case of the present exemplary embodiment, the links G1 to G7 are a frame 13 and a carousel 14 which is rotatably mounted relative to the frame 13 about a vertically extending axis A1. Further elements of the robot arm 9 are a link arm 15, a boom arm 16 and a preferably multi-axis robot hand 17 with a fastening device designed as a tool flange 11 for fastening a tool. The link arm 15 is mounted at the lower end on the carousel 14, i.e., on the link L2 of the link arm 15, which can also be referred to as the pivot bearing head so as to be pivotable about a preferably horizontal axis of rotation A2.

[0073] At the upper end of the link arm 15, the boom arm 16 is again mounted on the first link L3 of the link arm 15 so as to be pivotable about a likewise preferably horizontal axis A3. At its end, the boom arm supports the robot hand 17 with its preferably three axes of rotation A4, A5, A6. The links L1 to L6 can each be driven by a robot controller 10 in a program-controlled manner by one of the electrical servomotors M1 to M6. For this purpose, an inventive frequency converter 1, as shown in FIGS. 3 and 4, is assigned to the servomotors M1 to M6.

[0074] The frequency converter 1, as shown in FIGS. 3 and 4, can be connected to an electric alternating-voltage network 2. The electric alternating-voltage network 2 can be a three-phase alternating-voltage network, for example of 50 Hertz. In particular, it can be configured as a TN system.

[0075] If the frequency converter 1 is connected to the alternating voltage network 2, its rectifier circuit 3 can convert the alternating voltage fed from the electric alternating-voltage network 2 into a corresponding direct voltage. The direct voltage is then fed to a direct-voltage intermediate circuit 4. The direct-voltage intermediate circuit 4 is provided with an intermediate-circuit capacitor 5 and with a brake resistor 6 which can be connected and disconnected via a brake chopper S7 of the direct-voltage intermediate circuit 4.

[0076] At least one inverter circuit 7 fed from the direct-voltage intermediate circuit 4 and having controllable semiconductor switches S1 to S6 is connected to the direct-voltage intermediate circuit 4.

[0077] In the case of the exemplary embodiment in FIG. 3, only a single inverter circuit 7 is connected to the direct-voltage intermediate circuit 4. This single inverter circuit 7 powers the single servomotor M shown in FIG. 3.

[0078] In the case of the exemplary embodiment in FIG. 4, a plurality of inverter circuits 7 are connected to the direct-voltage intermediate circuit 4. The plurality of inverter circuits 7 each supply one of a plurality of servomotors M1 to M6 according to FIG. 4. Only two inverter circuits 7 and two servomotors M1 and M2 are shown in full in FIG. 4 for the sake of illustration. The dashed arrows and the designations M3 and M4 indicate a number of further servomotors M3, M4, etc., and further inverter circuits 7, all of which are connected to the common direct-voltage intermediate circuit 4.

[0079] In the case of the exemplary industrial robot 8 shown in FIG. 2, for example, a total of six inverter circuits 7 can be provided for the six servomotors M1 to M6 of the six joints L1 to L6 of the robot arm 9.

[0080] While the present invention has been illustrated by a description of various embodiments, and while these embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such de-tail. The various features shown and described herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be