Methods, robots, and computer program products for braking control of at least one servo motor

Abstract

This invention relates to a method for braking control of at least one servo motor (M, M1-M6) using a frequency converter (1), the frequency converter comprising: a rectifier circuit (3) connectable to an AC voltage network (2); a DC voltage intermediate circuit (4) powered by the AC voltage network (2) when connected, the DC voltage intermediate circuit having an intermediate circuit capacitor (5) and a braking resistor (6) that can be switched on and off by a braking chopper (S7) of the DC voltage intermediate circuit (4); and at least one inverter circuit (7) powered by the DC voltage intermediate circuit (4), the inverter circuit having operable power semiconductor switches (S1-S6). The invention also relates to a correspondingly designed robot (8) and an associated computer program product.

Description

Technical Field

[0001] This invention relates to a method for braking control of at least one servo motor using a frequency converter, the frequency converter comprising: a rectifier circuit connectable to an AC voltage network; a DC voltage intermediate circuit powered by the AC voltage network when connected, the DC voltage intermediate circuit having an intermediate circuit capacitor and a braking resistor switchable by a braking chopper via the DC voltage intermediate circuit; and at least one inverter circuit powered by the DC voltage intermediate circuit, the inverter circuit having a controllable power semiconductor switch. The invention also relates to a robot of a corresponding design and a related computer program product. Background Technology

[0002] Patent document EP2224586A1 discloses a method for controlling a motor-driven industrial robot. The industrial robot includes at least one drive motor powered by a power supply circuit connectable to a mains voltage. This power supply circuit includes at least one rectifier circuit connectable to the mains voltage, an intermediate circuit having at least one intermediate circuit capacitor, and a bridge switching device connected to the drive motor on its output side. This bridge switching device provides AC or DC power to the drive motor, wherein the power supply circuit for the drive motor is controlled by a control device for accelerating and braking the drive motor. The method therein for electrically braking the drive motor includes the steps of disconnecting the intermediate circuit from the mains and adjusting the intermediate circuit voltage to a predetermined value greater than zero, wherein the intermediate circuit capacitor is fed during the generator operation of the drive motor.

[0003] Patent document DE102007059492B4 discloses an industrial robot having a robot arm with multiple axes and at least one electric actuator having a three-phase AC motor and power electronics for controlling the three-phase AC motor. The power electronics have a three-phase inverter for driving the three-phase AC motor and an intermediate circuit having an intermediate circuit capacitor connected upstream of the three-phase inverter. The intermediate circuit has a first braking resistor and a first switch. The electric actuator is designed to move the associated axes. The industrial robot is designed to briefly close the three-phase AC motor under emergency braking by means of two independent current paths and close the first switch during emergency braking, connecting the braking resistor in parallel with the intermediate circuit capacitor so that one of the two current paths for emergency braking extends through the first braking resistor. Summary of the Invention

[0004] The purpose of this invention is to provide a method for braking control of at least one servo motor, which is particularly effective and safe.

[0005] The objective of this invention is achieved by a method for braking control of at least one servo motor using a frequency converter, the frequency converter comprising: a rectifier circuit connectable to an AC voltage network; a DC voltage intermediate circuit powered by the AC voltage network when connected, the DC voltage intermediate circuit having an intermediate circuit capacitor and a braking resistor switchable and disconnectable by a braking chopper of the DC voltage intermediate circuit; and at least one inverter circuit powered by the DC voltage intermediate circuit, the inverter circuit having a controllable power semiconductor switch, the method comprising the following steps:

[0006] - Separate the DC voltage intermediate circuit from the AC voltage network.

[0007] - During regenerative braking operation, the servo motor is braked by controlling the power semiconductor switches in the inverter circuit to reduce the servo motor's speed.

[0008] - The braking chopper is controlled so that the braking resistor is turned on when the maximum intermediate circuit voltage forms the braking chopper's on-threshold, and turned off when the minimum intermediate circuit voltage forms the braking chopper's off-threshold.

[0009] - During the generator braking operation of the servo motor, the on and / or off thresholds are dynamically changed according to the instantaneous speed of the servo motor.

[0010] The method according to the invention can, in principle, be performed when manipulating a single servo motor. However, the method according to the invention can be performed, in particular, when manipulating at least two servo motors. In a specific embodiment that manipulates the actuators of a robotic arm, the method according to the invention can be performed, for example, when controlling six or seven servo motors that form the actuators of the robotic arm.

[0011] According to the present invention, braking control refers to braking one or more servo motors not by mechanical brakes, (electro)mechanical brakes, or short-circuit brakes during the execution of the method, but only during the power generation operation of the active control inverter circuit of one or more servo motors. Therefore, in such active control power generation operation of one or more servo motors, electrical energy is supplied to a DC voltage intermediate circuit or exchanged through the inverter circuit, thereby allowing corresponding AC current to be introduced into the windings of one or more servo motors by controlling the on and off of the power semiconductor switches of the inverter circuit. This generates a magnetic field that produces a braking mechanical force on the shaft of one or more servo motors. Braking means reducing the rotational speed of the corresponding servo motor shaft. It is not necessary to brake until the corresponding servo motor shaft comes to a complete stop. Instead, braking can be performed only from a higher first rotational speed to a lower second rotational speed, which is less than the first rotational speed.

[0012] When braking two or more servo motors according to one method of the present invention, it is not necessary to brake all servo motors simultaneously. Instead, braking can be selectively applied to a first subgroup of a subset of servo motors at any given time, while a second subgroup of another subset of servo motors remains stably undriven at a constant speed, i.e., idling, or even being accelerated. In a special state, only a single servo motor can be subjected to regenerative braking, while other servo motors cannot be subjected to regenerative braking. In a special state, regenerative braking can be applied to all servo motors simultaneously.

[0013] The at least one servo motor is electrically controlled by a frequency converter according to the invention for its position (motor position, i.e., the instantaneous angular position of the motor shaft), speed, acceleration, and / or its braking characteristics (negative acceleration). In the case of two or more servo motors, the frequency converter has a number of inverter circuits corresponding to the number of servo motors. These inverter circuits are connected to a common DC voltage intermediate circuit. When the frequency converter is connected to an AC voltage network, this common DC voltage intermediate circuit is powered from the same AC voltage network through a common rectifier circuit. However, during the braking control method according to the invention, the frequency converter, particularly the common rectifier circuit, is temporarily disconnected from the AC voltage network. This means that, in the case of two or more servo motors, when no servo motor is being braked, the frequency converter will reconnect to the AC voltage network.

[0014] An AC voltage network provides electrical energy from an energy supplier's power grid. This is typically a low-voltage grid. A low-voltage grid can be, in particular, a three-phase AC voltage network. The three-phase AC voltage network provides a sinusoidal AC voltage. This sinusoidal AC voltage can, in particular, have an effective value at which, for example, 230 volts exist between the live wire (Auβenleiter) and the neutral wire (Neutralleiter) of the three-phase AC voltage network, and for example, 400 volts exist between every two of the three live wires. The grid frequency can, for example, be 50 Hz or 60 Hz. The three-phase AC voltage network can, in particular, be constructed as a TN system, which includes three live wires (L1, L2, L3), one neutral wire (N), and one ground wire (PE).

[0015] The rectifier circuit of a frequency converter can be, for example, a three-phase rectifier. A three-phase rectifier can be implemented in the configuration of an uncontrolled three-phase AC bridge.

[0016] When the inverter is connected to an AC voltage network, the AC voltage network supplies power to the DC voltage intermediate circuit. When the DC voltage intermediate circuit is disconnected from the AC voltage network, as is the case during operation of the method according to the invention, the DC voltage intermediate circuit is powered only by power from the inverter circuit, which can provide power during the power generation operation of at least one servo motor.

[0017] During the operation of the method according to the invention, electrical energy can also be output from the intermediate circuit capacitor, and more precisely, either to the inverter circuit or to the braking resistor.

[0018] The braking resistor is configured such that, when connected to the DC voltage intermediate circuit, it extracts electrical energy from the DC voltage intermediate circuit and converts it into heat. When disconnected from the DC voltage intermediate circuit, the braking resistor has no electrical effect on the DC voltage intermediate circuit; that is, the DC voltage intermediate circuit remains unaffected by the braking resistor when it is disconnected.

[0019] A braking chopper is a controllable switch that connects and / or disconnects a braking resistor from a DC voltage intermediate circuit via the braking chopper. In this respect, the braking chopper can operate in a pulse-width controlled manner.

[0020] The inverter circuit, powered by a DC voltage intermediate circuit, includes power semiconductor switches, which can be electronically controlled, for example, by an associated drive circuit. The inverter circuit can be a three-phase inverter and, for example, configured as a two-stage inverter (U-converter) or a pulse inverter. In the inverter circuit, the power semiconductor switches deliver electrical energy to the servo motor when the current and voltage have the same sign. Therefore, electrical energy flows from the DC voltage intermediate circuit and into the servo motor. According to the invention, during power generation operation, the unloaded diodes associated with the power semiconductor switches do not discharge electrical energy so as to feed the generated energy back from one or more servo motors to the DC voltage intermediate circuit, i.e., the intermediate circuit capacitor; however, the power semiconductor switches remain active and are correspondingly controlled by the drive circuit associated with the power semiconductor switches to draw electrical energy from the servo motors and feed it back to the DC voltage intermediate circuit, i.e., the intermediate circuit capacitor.

[0021] In the method according to the invention, the DC voltage intermediate circuit is first separated from the AC voltage network. This is at least advantageous, or even absolutely necessary, for certain safety requirements that must be met, for example, in the event of an emergency shutdown of the corresponding machine driven by the at least one servo motor.

[0022] Therefore, in industrial robots, for example, if a Category 0 emergency stop occurs (e.g., according to standard EN60204), it is stipulated that the power supply should be interrupted immediately, especially in cases of mechanical disconnection, i.e., when decoupling in the drivetrain and / or mechanical braking cannot be achieved independently.

[0023] On the other hand, machines, such as exemplary industrial robots, can have system states in which the controlled speed of a servo motor is reduced, particularly to a stationary state at zero speed, much faster than by simple mechanical braking, in which the servo motor stops in a manner where its speed is not regulated.

[0024] Therefore, in the method according to the invention, braking of at least one servo motor is achieved by actively manipulating the power semiconductor switches of the inverter circuit during regenerative braking operation, so as to controllably reduce the speed of the servo motor. However, since the inverter is isolated from the AC voltage network in the case discussed, the invention ensures that sufficient electrical energy is maintained in the DC voltage intermediate circuit for operating the inverter circuit, while simultaneously reducing the energy in the DC voltage intermediate circuit to a minimum possible value, thereby at least largely or even completely preventing undesirable, potentially defective restarts of at least one servo motor. Thus, the function of Safe Torque Off (STO) can also be achieved in this way.

[0025] According to the present invention, this is achieved by manipulating a braking chopper such that the braking resistor is switched on at the maximum intermediate circuit voltage that forms the switching threshold of the braking chopper, and switched off at the minimum intermediate circuit voltage that forms the switching threshold of the braking chopper. Simultaneously, the switching threshold and / or the switching threshold are dynamically changed according to the instantaneous rotational speed of the servo motor during its generator braking operation. By dynamically changing the switching threshold and / or the switching threshold, the amount of electrical energy stored in the DC voltage intermediate circuit can be dynamically matched to the instantaneously required conditions, more specifically, with respect to two target variables: sufficiently high energy to supply power to the inverter circuit, enabling the servo motor to generate electricity, i.e., be braked; and as low as possible energy to obtain sufficient energy from the system, thereby reliably preventing possible, dangerous, and accidental servo motor restarts.

[0026] Compared to existing technologies where the intermediate circuit voltage applied to the intermediate circuit capacitor can only be adjusted to a predetermined target value, according to the present invention, such target value is not fixed, but is dynamically changed during the power generation operation of at least one servo motor by altering the on and / or off thresholds of the braking chopper.

[0027] In one particular implementation, during the generator braking operation of the servo motor, the on threshold and / or off threshold are dynamically changed according to the instantaneous speed of the servo motor, so that the intermediate circuit voltage continuously decreases as the speed of the servo motor decreases.

[0028] In the case of more than one servo motor, the intermediate circuit voltage can continuously decrease as the rotational speed of the servo motor that instantaneously induces the highest voltage during power generation decreases. During the execution of the method according to the invention, i.e., during the braking process, the servo motor used as a reference can, if necessary, change according to the continuously decreasing intermediate circuit voltage as its rotational speed decreases. That is, if the servo motor on which the intermediate circuit voltage is currently decreasing has stopped, or its instantaneous rotational speed has decreased to the point where another servo motor has a higher rotational speed, causing the intermediate circuit voltage to induce a larger voltage, then it can be said that the other servo motor is switched on to adjust the intermediate circuit voltage, thus making that other servo motor a new dominant variable for adjusting the intermediate circuit voltage.

[0029]

[0030] The rotational speed of a servo motor can be determined based on the instantaneous rotational speed measured by a motor position sensor. Therefore, the instantaneous rotational speed can be calculated based on the angular positions of the servo motor shaft detected at two different time points.

[0031] As an alternative to measuring servo motor speed using a motor position sensor, or as a supplement to this method, the servo motor speed can be determined based on the measured instantaneous motor voltage present in the servo motor. This can be used, for example, to provide redundant, and particularly diverse, analysis. To this end, the instantaneous speed of the servo motor can be read from a configuration-dependent, fixed characteristic curve of the servo motor with respect to the measured instantaneous motor voltage.

[0032] The reduction in intermediate circuit voltage can be particularly proportional to the reduction in servo motor speed. The reduction in intermediate circuit voltage can also be particularly synchronized with the reduction in servo motor speed.

[0033] As the servo motor's rotational speed decreases, the kinetic energy of the motion system coupled to it decreases, such as the drive mechanism connected to the servo motor's motor shaft, the limbs of the robot arm, and / or the distal teilkettes of the limbs and joints of the robot arm. As a result, due to the reduced kinetic energy, braking the coupled motion system requires less braking energy to bring it to a stop while it is still moving slowly. Ideally, at the point in time when the motion system coupled to the servo motor is at rest, the electrical energy in the intermediate circuit is completely or at least largely removed. This leads to another advantage: since there is no sufficient electrical energy in the intermediate circuit to start the servo motor, an undesirable restart, i.e., one that could be caused by a malfunction, is no longer possible.

[0034] In a particular extension scheme, the on and / or off thresholds can be changed according to the instantaneous rotational speed of the servo motor during the generator braking operation of the servo motor. This change in the on and / or off thresholds is based on the instantaneous rotational speed of the servo motor measured by a motor position sensor or on the measured instantaneous motor voltage present in the servo motor.

[0035] That is, in the first embodiment variant, the on and / or off thresholds can be changed based on the instantaneous rotational speed of the servo motor measured by a motor position sensor. The motor position sensor is used to detect the instantaneous angular position of the motor shaft of the servo motor. The motor position sensor is also called a rotary encoder. Based on the angular positions of the motor shaft detected at any two different time points, the rotational speed and / or rotational acceleration of the servo motor shaft can be derived and determined. For example, a coordinate resolver, an incremental encoder, and an absolute sensor can all be used as the motor position sensor.

[0036] However, in the second embodiment variant, the change of the on-threshold and / or off-threshold can also be based on the measured instantaneous motor voltage of the servo motor. It is well known that in a servo motor, the motor voltage, i.e., the voltage in the windings, is proportional to the rotational speed of the motor shaft. In this regard, the motor voltage of the servo motor can be directly measured electrically from the circuit connected to the inverter circuit of the inverter according to the invention. As a result, no separate sensor component is required in this second embodiment variant.

[0037] During the regenerative braking operation of the servo motor, the turn-on threshold and / or turn-off threshold can be reduced to a predetermined minimum threshold based on the instantaneous speed of the servo motor, and in particular, the turn-off threshold can be reduced to a minimum threshold lower than the grid voltage of the AC voltage network.

[0038] In simple terms, the turn-on and turn-off thresholds define a two-point regulator with hysteresis. When the turn-on threshold is exceeded, the braking chopper connects the braking resistor to the DC intermediate circuit from a lower voltage, causing electrical energy to be converted into heat in the braking resistor and the intermediate circuit voltage to drop. However, as the voltage drops from a higher voltage, the voltage in the DC intermediate circuit must continue to decrease beyond the turn-on threshold until it falls below the turn-off threshold. In this respect, the turn-off threshold is always lower than the turn-on threshold, specifically lower than the voltage difference that determines the hysteresis. When it falls below the turn-off threshold, the braking chopper disconnects the braking resistor from the DC intermediate circuit again from a higher voltage, allowing the intermediate circuit voltage to rise again.

[0039] By lowering the minimum threshold to a voltage value below the grid voltage of the AC voltage network, the intermediate circuit voltage can be reduced to the maximum extent, which allows for maximum power generation, thereby enabling one or more servo motors to be braked with maximum generated energy.

[0040] Therefore, the minimum threshold can be lowered to zero. However, depending on the operating type, the inverter circuit's driver, i.e., the inverter circuit's power semiconductor switch, can also be powered by electrical energy from the DC voltage intermediate circuit of the inverter. In this case, lowering the minimum threshold to zero volts is inappropriate.

[0041] Therefore, in one particular implementation, during the regenerative braking operation of the servo motor, the on-threshold and / or off-threshold can be adjusted based on the instantaneous speed of the servo motor, decreasing only to a minimum threshold such that a minimum voltage is applied in the DC voltage intermediate circuit, at which the regenerative braking operation of the servo motor can still be ensured by manipulating the power semiconductor switches of the inverter circuit. This minimum threshold can, for example, be located between zero and the mains voltage of the AC voltage network.

[0042] In order to control at least two servo motors simultaneously, the frequency converter may have a number of inverter circuits corresponding to the number of servo motors. These inverter circuits are connected to a common DC voltage intermediate circuit of the frequency converter, wherein, during the regenerative braking operation of one or more of the at least two servo motors, the turn-on threshold and / or turn-off threshold are dynamically changed according to the instantaneous speed of the servo motor that instantaneously senses the highest intermediate circuit voltage.

[0043] In the application of the exemplary robotic arm, the robotic arm can have multiple joints and multiple segments, which can be adjusted relative to each other through the movement of the joints of the robotic arm. Here, each joint can be equipped with its own servo motor. Each of the multiple servo motors is configured to adjust the joint of the robotic arm corresponding to it, more precisely, to adjust it through automatic control of the servo motor. For this purpose, the robotic arm can have a control device designed to automatically control the servo motors of the robotic arm so as to automatically adjust the segments of the robotic arm relative to each other through the driven joint movements.

[0044] Each joint, and therefore each servo motor associated with a corresponding joint, moves a motion system, which is correspondingly formed by a distal-side motion subsystem positioned upstream of the servo motors in the robot arm's kinematic chain. Therefore, servo motors positioned closer to the servo motors in the kinematic chain (the servo motors of the robot arm's base axis) typically must be braked with higher kinetic energy than servo motors positioned further to the servo motors positioned further to the servo motors of the robot arm's hand axes. However, at any given time, another servo motor can be loaded with the instantaneously highest braking load, depending on the posture of the robot arm's joints. Thus, for example, it might be possible that the base joint, which is precisely moving upwards against gravity, should be braked, and the braking force is therefore primarily provided by gravity, and the associated servo motor does not bear a particularly high electrical braking load. On the other hand, the lighter hand joints of the robot arm can move precisely in the direction of gravity, so that during braking, the servo motors must first overcome the acting gravitational acceleration, and thus the servo motors associated with the lighter hand joint bear a particularly high electrical braking load.

[0045] Therefore, during the execution of the method according to the invention, that is, during the braking process, the servo motor used as a reference can, if necessary, vary according to the intermediate circuit voltage, which continuously decreases as its rotational speed decreases. That is, if the servo motor on which the intermediate circuit voltage is currently decreasing has stopped, or its instantaneous rotational speed has decreased to a level where another servo motor has a higher rotational speed, causing a larger voltage to be induced in the intermediate circuit voltage, then it can be said that the other servo motor is switched on to adjust the intermediate circuit voltage, thus making that other servo motor a new dominant variable for adjusting the intermediate circuit voltage.

[0046] In all embodiments of the present invention, by making the intermediate circuit capacitor powered only by the energy generated by at least one servo motor from the inverter circuit, the electrical energy in the DC voltage intermediate circuit can be increased during the generator braking operation of the servo motor, during the dynamic change of the turn-on threshold and / or turn-off threshold, and when the braking chopper of the DC voltage intermediate circuit has disconnected the braking resistor.

[0047] The at least one servo motor may be, in particular, a permanent magnet excited synchronous motor.

[0048] The object of the invention is also achieved by a robot having a robotic arm with a plurality of joints and a plurality of limbs that can be adjusted relative to each other by movement of the joints of the robotic arm, wherein at least one joint is associated with a servo motor configured to adjust the at least one joint, more precisely by automatic manipulation of the servo motor; and the robot having a control device designed to automatically manipulate at least one servo motor of the robotic arm to automatically adjust the limbs of the robotic arm relative to each other by driven joint movement, wherein the control device is configured and designed to perform the method according to the described embodiments.

[0049] The control device can be configured as part of a robot controller. Alternatively, however, the control device can also be configured as a separate control unit that interacts with the robot controller, for example, via a communication connection. Specifically, the control device is configured to operate a frequency converter including a rectifier circuit connectable to an AC voltage network, a DC voltage intermediate circuit powered by the AC voltage network when connected, the DC voltage intermediate circuit having an intermediate circuit capacitor, a braking resistor that can be switched on and off by a braking chopper of the DC voltage intermediate circuit, and at least one inverter circuit powered by the DC voltage intermediate circuit, the inverter circuit having operable power semiconductor switches.

[0050] The object of the present invention is also achieved by a computer program product having a machine-readable carrier on which program code is stored, the program code being readable by a control device of a robot according to the present invention, and when the program code is executed by the control device, the control device is configured and / or designed to perform the method according to any of the described embodiments.

[0051] Computer program products can be, for example, CDs, DVDs, or USB flash drives (USB sticks). However, computer program products can also be control cards with integrated microprocessors. Computer program products can also be available for download, which can be offered and sold via the Internet or another network.

[0052] Therefore, a machine-readable medium can be a CD, DVD, or microprocessor storing program code. A machine-readable medium can also be a hard disk or SSD drive containing program code, for example, downloaded via download, particularly in the form of data packets.

[0053] Program code can be represented by edited programs and / or data stored on a machine-readable medium.

[0054] By reading edited programs and / or data, the read control device is constructed and / or designed to perform the method according to the invention.

[0055] The method according to the invention is executed when the control device actually executes the program code, i.e., the edited program, and / or actually processes the data accordingly. Attached Figure Description

[0056] Specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Specific features of these exemplary embodiments may be considered individually or in other combinations as needed to represent the general features of the invention, regardless of where they are specifically mentioned herein. Wherein:

[0057] Figure 1 A flowchart of the method according to the present invention is shown.

[0058] Figure 2 A side view of an exemplary industrial robot is shown, comprising a robot arm with articulated limbs, joints, and servo motors, and a robot controller designed to perform the method according to the present invention.

[0059] Figure 3 A schematic diagram of an exemplary frequency converter with a servo motor is shown, and

[0060] Figure 4The schematic diagram shows a circuit diagram of an exemplary variant of a frequency converter, which has two or more servo motors connected to a common DC voltage intermediate circuit. Detailed Implementation

[0061] Figure 1 A schematic illustration shows the method for using a frequency converter 1 (according to the present invention) Figure 3 , Figure 4 A flowchart of the basic method for braking control of at least one servo motor M.

[0062] like Figure 3 and Figure 4 As shown, the inverter 1 may have: a rectifier circuit 3 capable of being connected to an AC voltage network 2; a DC voltage intermediate circuit 4 powered by the AC voltage network 2 when connected to the AC voltage network 2, the DC voltage intermediate circuit having an intermediate circuit capacitor 5 and a braking resistor 6 that can be switched on and off by a braking chopper S7 of the DC voltage intermediate circuit 4; and at least one inverter circuit 7 powered by the DC voltage intermediate circuit 4, the inverter circuit having controllable power semiconductor switches S1 to S6.

[0063] like Figure 1 As shown, the method according to the present invention includes the following steps:

[0064] In the first step V1, the DC voltage intermediate circuit 4 is separated from the AC voltage network 2.

[0065] In the next second step V2, the servo motor M is braked by manipulating the power semiconductor switches S1-S6 of the inverter circuit 7 during generator braking operation, so as to reduce the speed of the servo motor M.

[0066] In the third step V3, the braking chopper S7 is manipulated such that the braking resistor 6 is turned on at the maximum intermediate circuit voltage that forms the turn-on threshold of the braking chopper S7, and turned off at the minimum intermediate circuit voltage that forms the turn-off threshold of the braking chopper S7. In step V4, the turn-on threshold and / or turn-off threshold are dynamically changed according to the instantaneous speed of the servo motor M during the generator braking operation of the servo motor M.

[0067] Figure 2 An industrial robot 8 is shown, which has a robot arm 9 and a robot controller 10. In this embodiment, the robot arm 9 includes a plurality of sequentially arranged limbs G1 to G7 that are rotatably interconnected by means of joints L1 to L6.

[0068] The industrial robot 8 has a robot controller 10 configured to execute a robot program and cause the limbs G1-G7 and joints L1-L6 of the robot arm 9 to move automatically. One of the limbs G1-G7 forms the end effector (G7) of the robot arm 9, which has a tool flange 11.

[0069] The robot controller 10 of the industrial robot 8 is constructed or designed to execute a robot program by which the joints L1 to L6 of the robot arm 9 can be automatically adjusted or rotated according to the robot program, either automatically or manually. For this purpose, the robot controller 10 is connected to controllable electric actuators, namely servo motors M1 to M6, which are designed to adjust the individual joints L1 to L6 of the robot arm 9.

[0070] In this embodiment, segments G1 to G7 include a robot base 13 and a turntable 14, which is rotatably mounted relative to the robot base 13 about a vertically extending axis A1. Other segments of the robot arm 9 include a rocker arm 15, a cantilever 16, and preferably a multi-axis robot hand 17, which has a fastening device configured as a tool flange 11 for securing tools. The rocker arm 15 is pivotally mounted on the turntable 14 at its lower end, i.e., at its joint L2 (also referred to as the rocker arm bearing head), about a preferably horizontal axis of rotation A2.

[0071] At the upper end of the rocker arm 15, on the first joint L3 of the rocker arm 15, a cantilever 16 is pivotally mounted about a similarly preferably horizontal axis A3. This cantilever carries a robot hand 17 at its end, which has preferably three rotation axes A4, A5, and A6. Joints L1 to L6 can be programmed and driven by electric servo motors M1 to M6, respectively, via the robot controller 10. For this purpose, as... Figure 3 and Figure 4 As shown, servo motors M1 to M6 are assigned to the frequency converter 1 according to the present invention.

[0072] like Figure 3 and Figure 4 As shown, inverter 1 can be connected to AC voltage network 2. AC voltage network 2 can be, for example, a 50 Hz three-phase AC voltage network. It can be configured, in particular, as a TN system.

[0073] If inverter 1 is connected to AC voltage network 2, its rectifier circuit 3 can convert the AC voltage supplied by AC voltage network 2 into a corresponding DC voltage. The DC voltage is then supplied to DC voltage intermediate circuit 4. DC voltage intermediate circuit 4 is equipped with intermediate circuit capacitor 5 and braking resistor 6, which can be switched on and off by braking chopper S7 of DC voltage intermediate circuit 4.

[0074] At least one inverter circuit 7 powered by the DC voltage intermediate circuit 4 is connected to the DC voltage intermediate circuit 4, which has controllable power semiconductor switches S1 to S6.

[0075] exist Figure 3 In the illustrated embodiment, only one inverter circuit 7 is connected to the DC voltage intermediate circuit 4. This single inverter circuit 7 is connected to the DC voltage intermediate circuit 4 according to... Figure 3 The only servo motor M is powered.

[0076] exist Figure 4 In the illustrated embodiment, multiple inverter circuits 7 are connected to the DC voltage intermediate circuit 4. These multiple inverter circuits 7 respectively supply power to the DC voltage intermediate circuit 4 according to... Figure 4 It is powered by one of the multiple servo motors M1 to M6. Figure 4 Only two inverter circuits 7 and two servo motors M1 and M2 are shown for illustrative purposes. The dashed arrows and markings M3, M4 indicate multiple other servo motors M3, M4, etc., as well as other inverter circuits 7, all of which are connected to a common DC voltage intermediate circuit 4.

[0077] exist Figure 2 In the case of the exemplary industrial robot 8 shown, for example, a total of six inverter circuits 7 can be set for the six servo motors M1 to M6 of the six joints L1 to L6 of the robot arm 9.

Claims

1. A method for braking control of at least one servo motor (M, M1-M6) via a frequency converter (1), the frequency converter comprising: A rectifier circuit (3) capable of being connected to an AC voltage network (2); a DC voltage intermediate circuit (4) powered by the AC voltage network (2) when connected to the AC voltage network (2), the DC voltage intermediate circuit having an intermediate circuit capacitor (5) and a braking resistor (6), the braking resistor being able to be switched on and off by a braking chopper (S7) of the DC voltage intermediate circuit (4); and at least one inverter circuit (7) powered by the DC voltage intermediate circuit (4), the inverter circuit having controllable power semiconductor switches (S1-S6), the method comprising the following steps: - Separate the DC voltage intermediate circuit (4) from the AC voltage network (2). - During generator braking operation, the servo motors (M, M1-M6) are braked by manipulating the power semiconductor switches (S1-S6) of the inverter circuit (7) to reduce the speed of the servo motors (M, M1-M6). - Manipulate the braking chopper (S7) such that the braking resistor (6) is turned on when the maximum intermediate circuit voltage forms the on-threshold of the braking chopper (S7), and turned off when the minimum intermediate circuit voltage forms the off-threshold of the braking chopper (S7), wherein, - During the generator braking operation of the servo motors (M, M1-M6), the on threshold and / or the off threshold are dynamically changed according to the instantaneous rotational speed of the servo motors (M, M1-M6).

2. The method according to claim 1, characterized in that, During the generator braking operation of the servo motors (M, M1-M6), the on threshold and / or the off threshold are dynamically changed according to the instantaneous rotational speed of the servo motors (M, M1-M6), so that the intermediate circuit voltage decreases continuously as the rotational speed of the servo motors (M, M1-M6) decreases.

3. The method according to claim 2, characterized in that, The reduction in the intermediate circuit voltage is proportional to the reduction in the rotational speed of the servo motors (M, M1-M6).

4. The method according to any one of claims 1 to 3, characterized in that, The on-threshold and / or the off-threshold change according to the instantaneous rotational speed of the servo motors (M, M1-M6) during the generator braking operation of the servo motors (M, M1-M6), wherein the change of the on-threshold and / or the off-threshold is based on the instantaneous rotational speed of the servo motors (M, M1-M6) measured by means of a motor position sensor or based on the measured instantaneous motor voltage of the servo motors (M, M1-M6) present in the servo motors (M, M1-M6).

5. The method according to any one of claims 1 to 3, characterized in that, During the generator braking operation of the servo motors (M, M1-M6), the turn-on threshold and / or the turn-off threshold are reduced to a predetermined minimum threshold based on the instantaneous rotational speed of the servo motors (M, M1-M6).

6. The method according to claim 5, characterized in that, The shutdown threshold is lowered to a minimum threshold below the grid voltage of the AC voltage network (2).

7. The method according to any one of claims 1 to 3, characterized in that, During the regenerative braking operation of the servo motors (M, M1-M6), the turn-on threshold and / or the turn-off threshold are reduced to a minimum threshold based on the instantaneous rotational speed of the servo motors (M, M1-M6): at this minimum threshold, a minimum voltage is applied in the DC voltage intermediate circuit (4), and the regenerative braking operation of the servo motors (M, M1-M6) can still be ensured by manipulating the power semiconductor switches (S1-S6) of the inverter circuit (7) even at this minimum voltage.

8. The method according to any one of claims 1 to 3, characterized in that, In order to simultaneously control at least two servo motors (M, M1-M6), the inverter (1) has a number of inverter circuits (7) corresponding to the number of servo motors (M, M1-M6), the inverter circuits being connected to a common DC voltage intermediate circuit (4) of the inverter (1), wherein, during the regenerative braking operation of one or more of the at least two servo motors (M, M1-M6), the turn-on threshold and / or the turn-off threshold are dynamically changed according to the instantaneous speed of the servo motor (M, M1-M6) that instantaneously senses the highest intermediate circuit voltage.

9. The method according to any one of claims 1 to 3, characterized in that, By supplying the intermediate circuit capacitor (5) with energy generated by only one servo motor (M, M1-M6) from the inverter circuit (7), during the generator braking operation of the servo motor (M, M1-M6), during the dynamic change of the on threshold and / or the off threshold, and in the state where the braking chopper (S7) has disconnected the braking resistor (6), the electrical energy in the DC voltage intermediate circuit (4) is increased.

10. A robot having a robotic arm (9) having a plurality of joints (L1-L6) and a plurality of limbs (G1-G7) adjustable relative to each other by movement of the joints (L1-L6) of the robotic arm (9), wherein at least one joint (L1-L6) is associated with a servo motor (M, M1-M6) configured to adjust the at least one joint (L1-L6), more specifically by automatic manipulation of the servo motor (M, M1-M6), and the robot having a control device (10) designed to automatically manipulate at least one servo motor (M, M1-M6) of the robotic arm (9) to automatically adjust the limbs (G1-G7) of the robotic arm (9) relative to each other by movement of the driven joints (L1-L6), wherein the control device (10) is configured and designed to perform the method according to any one of claims 1 to 9.

11. A computer program product having a machine-readable carrier on which program code is stored, the program code being readable by a control device (10) of a robot (9) according to claim 10, and the control device being configured and / or designed to perform the method of any one of claims 1 to 9 when the program code is executed by the control device (10).

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