Robot joint motor four-quadrant operation cooperative control circuit and method

Abstract

The invention discloses a robot joint motor four-quadrant operation cooperative control circuit and a robot joint motor four-quadrant operation cooperative control method, in the cooperative control circuit, a bus positive electrode and a bus negative electrode of each motor controller are respectively connected together, and the working states of a plurality of joint motors are controlled through a relatively simple cooperative control logic; the electric energy generated by the joint motors in the II-quadrant generator state and the IV-quadrant generator state is directly supplied to other joint motors in the mechanical arm to be completely consumed, the risk of overvoltage of a bus of a motor controller can be avoided, and therefore four-quadrant operation of the robot joint motors is achieved. The defect that energy is completely wasted in a traditional energy consumption braking mode can be overcome, and the defect that hardware circuit cost and motor control algorithm complexity are greatly increased in an energy feedback mode can also be overcome. In addition, hardware circuits such as a robot main controller and a motor controller in the robot joint motor four-quadrant operation cooperative control circuit already exist in an original system, and the circuit does not increase the hardware cost of the control system.

Description

Technical Field

[0001] The present invention relates to the technical field of robot control, and particularly to a cooperative control circuit and method for four-quadrant operation of a robot joint motor. Background Art

[0002] With the rapid growth of the application of robots in various industries, people have increasingly paid attention to the research on the technology in the field of robot control, and the robot joint control, as the basic technology of the core component of the entire control system, has also become a research hotspot. As one of the important components of the robot joint control system, the design of the joint servo drive system directly affects the overall motion performance of the robot joint.

[0003] The robot joint motor is essentially a permanent magnet synchronous motor. As Figure 1 is a schematic diagram of the four-quadrant operation state of the permanent magnet synchronous motor. The abscissa is defined as the motor speed, and the ordinate is defined as the motor output torque. Figure 1 In the figure, the first quadrant is forward motoring operation, the second quadrant is reverse braking power generation operation, the third quadrant is reverse motoring operation, and the fourth quadrant is forward braking power generation operation. When the joint motor operates in the first and third quadrants, the motor works in the motor state, and the energy flows unidirectionally from the power grid to the motor; when the joint motor operates in the second and fourth quadrants, the joint motor works in the reverse braking power generation state, and the energy flows unidirectionally from the motor to the power grid. During the process of a robot grasping a heavy object and lifting it, the joint motor works in the motor state. However, when the robot grasps a heavy object and lowers it, the potential energy of the heavy object is converted into electrical energy, and the joint motor works in the reverse braking power generation state. The robot joint motor needs to frequently perform four-quadrant operation. Therefore, it becomes very important how the robot joint motor control system changes from driving in the first and third quadrants of the permanent magnet synchronous motor with unidirectional energy flow to a control system that can operate in the first, second, third, and fourth quadrants with bidirectional energy flow.

[0004] In order to enable the joint motor to have the four-quadrant operation function, the prior art usually adopts the energy consumption braking method to consume or the energy feedback method to absorb the electrical energy generated by the motor during the operation in the second and fourth quadrants. As Figure 2It is a circuit diagram of a commonly used dynamic braking method. A high-power braking resistor and a high-power switching tube are connected in parallel on the DC side of the motor, and the braking resistor consumes the electric energy generated by the motor operating in the second and fourth quadrants. Due to the simple and practical circuit structure, the dynamic braking method was adopted in the early control of robot joint motors. However, the energy consumed in the high-power braking resistor is completely wasted. To avoid the waste of electric energy, the energy feedback type four-quadrant operation method of the motor is used to feed the regenerative energy back to the power grid. Currently, in the market of the motor control field, there are already products that support the four-quadrant drive of the motor. It mainly separates the active inverter unit from the frequency converter and realizes the feedback of regenerative energy to the power grid as a peripheral device connected in parallel to the DC side of the frequency converter. However, the energy feedback method greatly increases the complexity of the motor control algorithm. In addition, both the dynamic braking method and the energy feedback method have obvious disadvantages: they require an increase in the hardware circuit cost of the control system. Summary of the Invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art, and in combination with the characteristics that there are multiple joint motors in the robot arm and often multiple joint motors work simultaneously, to provide a four-quadrant operation cooperative control circuit and method for robot joint motors. Through the cooperative control logic, some joint motors work in the first and third quadrants, while some other joint motors can work in the second and fourth quadrants, so that the electric energy generated by the joint motors operating as generators is completely consumed by other joint motors in the robotic arm, and the four-quadrant operation of the robot joint motors is realized without increasing the hardware cost of the control system.

[0006] To achieve the above object, the technical solution provided by the present invention is as follows:

[0007] A four-quadrant operation cooperative control circuit for robot joint motors, comprising a robot main controller, n motor controllers, and n joint motors participating in cooperative control;

[0008] Each motor controller includes a power amplification module, a positive bus, and a negative bus;

[0009] The positive buses of each motor controller are connected together;

[0010] The negative buses of each motor controller are connected together;

[0011] The three-phase windings of each joint motor are respectively connected to the power amplification module of the corresponding motor controller;

[0012] The robot main controller is respectively connected to each motor controller.

[0013] Furthermore, each motor controller also includes a motor control microprocessor and a base signal driving module;

[0014] The robot main controller is connected to the motor control microprocessor of each motor controller respectively;

[0015] In each motor controller, the motor control microprocessor generates multiple PWM signals, which are enhanced by the base signal driving module and then control the power amplifier module to drive the corresponding joint motor to operate.

[0016] Furthermore, the present invention also provides a robot joint motor four-quadrant operation coordinated control method, which is implemented by the above-mentioned robot joint motor four-quadrant operation coordinated control circuit, including:

[0017] S1, the robot main controller sends a run or stop command to each motor control microprocessor;

[0018] S2. Each motor control microprocessor that receives the operation instruction controls the operation of each joint motor, detects and calculates the instantaneous input power of each motor controller. When the instantaneous input power is a positive value, it indicates that the joint motor is in the motor operation state of quadrants I and III. When the instantaneous input power is a negative value, it indicates that the joint motor is in the generator operation state of quadrants II and IV. The instantaneous input power of the stopped joint motor is zero. All motor control microprocessors return the instantaneous input power information of each joint motor to the robot main controller.

[0019] S3, the robot main controller counts the number of joint motors with positive instantaneous input power as p, and calculates the sum of all positive instantaneous input powers as P in_pos , the number of joint motors with negative instantaneous input power is m, and the sum of all negative instantaneous input power is calculated as P in_neg , the number of joint motors that are stopped and on standby and have zero input power is z; the number of joint motors participating in cooperative control is n=p+m+z;

[0020] S4. The robot main controller performs logic analysis:

[0021] If m=0, it indicates that all joint motors are in the motor state or the shutdown standby state, and the process directly returns to step S1;

[0022] If P in_pos ≥P in_neg , indicating that the electric energy generated by the joint motor operating as a generator can be completely consumed by the joint motor operating as a motor, and there is no risk of overvoltage of the motor controller bus, and the process returns to step S1 to continue monitoring the instantaneous input power of each motor controller;

[0023] If P in_pos <P in_neg, indicating that the electric energy generated by the joint motor operating as a generator cannot be completely consumed by the joint motor operating as a motor, it is necessary to increase the input power of the joint motors in the motor state or standby state in the first and third quadrants, and proceed to step S5;

[0024] S5. Increase the input power by |P in_neg -P in_pos |, which is shared by the joint motors in the motor state or the stop state, and the robot main controller distributes the additional input power required for each motor as

[0025] S6. The robot main controller sends a command to the joint motor controllers operating in the first and third quadrants to enter the field weakening operation mode, and realizes the increase of the input power through field weakening operation to consume the input power P shared in step S5 in_inc ;

[0026] S7. The robot main controller sends a command to the motor controller in standby to enter the current locking mode, and consumes the input power P shared in step S5 by applying a constant current to the motor winding through the current locking mode in_inc ;

[0027] S8. The current round of coordinated control loop ends, and returns to step S1.

[0028] Further, in step S2, each motor control microprocessor that receives the operation command controls the operation of each joint motor, including the following steps:

[0029] S2.1. Real-time obtain the three-phase stator currents i U 、i V 、i W of the joint motor through the stator current detection module of the joint motor vector control system, and obtain the rotor angle θ of the current joint motor through the encoder;

[0030] S2.2. The three-phase currents are subjected to Clark transformation to obtain the current components i α 、i β in the stationary coordinate system;

[0031] S2.3. According to the rotor angle θ of the current motor, perform Park transformation on the current components i α 、i β in the stationary coordinate system to obtain the d-axis current i d and the q-axis current i q in the two-phase synchronous rotating coordinate system;

[0032] S2.4. According to the stator current i s, the given values of the PI regulators of the d-axis current loop and the q-axis current loop during the normal operation of the joint motor are calculated according to the maximum torque per ampere algorithm and the given values of the PI regulators of the q-axis current loop

[0033]

[0034] In the formula, Ψ f is the permanent magnet flux linkage, L d , L q are the d-axis and q-axis inductances of the motor respectively;

[0035] S2.5. Compare the d-axis current value i d in the two-phase synchronous rotating coordinate system with the given d-axis current value , and use the difference as the input of the PI regulator of the d-axis current loop. Compare the q-axis current value i q in the two-phase synchronous rotating coordinate system with the given q-axis current value , and use the difference as the input of the PI regulator of the q-axis current loop. After calculation by the current loop PI regulator, the output voltages V d , V q of the PI regulators of the d-axis and q-axis current loops are obtained respectively;

[0036] S2.6. According to the rotor angle θ of the motor, perform the inverse Park transformation on the output voltages V d , V q of the current loop PI regulator to obtain the voltage components V α , V β in the stationary coordinate system, and then form a three-phase PWM wave signal through the space pulse modulation module of the joint motor vector control system;

[0037] S2.7. The three-phase PWM wave signal controls the power amplification module to output three-phase voltages to drive the joint motor to operate.

[0038] Furthermore, in step S2, the instantaneous input power of each motor controller is detected and calculated, including:

[0039] First, detect the output voltage of the current regulator and the actual current feedback value, and then calculate the input power p em = u d i d + u q i q of each joint motor, where u em is the output voltage of the d-axis current regulator, u d is the output voltage of the q-axis current regulator, i q is the actual d-axis current feedback value, and i d is the actual q-axis current feedback value. qis the actual feedback value of the q-axis current; by obtaining the input power of each joint motor, the instantaneous input power of each motor controller can be obtained.

[0040] Further, in step S6, the robot main controller issues an instruction to the joint motor controllers of the motors operating in the first and third quadrants to enter the field-weakening operation mode. On the premise of keeping the rotational speed of the joint motor unchanged, the input power of the motor controller is increased by increasing the d-axis current, and the q-axis current is still determined by the output of the speed loop.

[0041] Further, the field-weakening control keeps the rotational speed of the joint motor tracking the given rotational speed, and increases the input power by increasing the d-axis current; the calculation formula for the d-axis current to achieve the field-weakening control is where I d is the d-axis current before the field-weakening control, and V d is the output voltage of the PI regulator of the d-axis current loop.

[0042] Further, when the motor controller in the standby state enters the current-locking mode, a constant current is generated in the three-phase windings of the joint motor, the rotational speed of the motor is set to zero, the rotor angle of the motor is fixed to the current rotor angle of the motor, and the given value of the PI regulator of the d-axis current loop and the given value of the PI regulator of the q-axis current loop are calculated according to the following formula:

[0043]

[0044] In the formula, V dc is the bus voltage, ξ is the voltage coefficient, and θ present is the current rotor angle.

[0045] Compared with the prior art, the principles and advantages of the present technical solution are as follows:

[0046] 1. Connect the positive and negative poles of the bus of each motor controller together, control the working states of multiple joint motors through a relatively simple cooperative control logic, and directly supply the electric energy generated by the joint motors in the generator state in the second and fourth quadrants to be completely consumed by other joint motors in the robotic arm, which can avoid the risk of overvoltage of the motor controller bus, thereby realizing the four-quadrant operation of the robot joint motor.

[0047] The present technical solution can overcome the disadvantage that the traditional energy consumption braking method completely wastes energy, and can also overcome the disadvantages that the energy feedback method greatly increases the hardware circuit cost and the complexity of the motor control algorithm.

[0048] 2. In the four - quadrant operation cooperative control circuit of the robot joint motor, the hardware circuits such as the robot main controller and the motor controller already exist in the original system, and the circuit described in this technical solution does not increase the hardware cost of the control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the services required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0050] Figure 1 It is a schematic diagram of the four - quadrant operation of a permanent magnet synchronous motor;

[0051] Figure 2 It is the main circuit diagram of the energy consumption braking method;

[0052] Figure 3 It is the circuit diagram of a four - quadrant operation cooperative control circuit for a robot joint motor according to the present invention;

[0053] Figure 4 It is the block diagram of the vector control system of the robot joint motor in the embodiment of the present invention;

[0054] Figure 5 It is the principle flowchart of a four - quadrant operation cooperative control method for a robot joint motor according to the present invention;

[0055] Figure 6 It is the robot arm adopted in the embodiment of the present invention;

[0056] Figure 7 It is the load torque curve of the third joint motor during the process of lowering the heavy object;

[0057] Figure 8 It is the speed curve of the third joint motor during the process of lowering the heavy object;

[0058] Figure 9 It is the U - phase current waveform of the third joint motor during the process of lowering the heavy object;

[0059] Figure 10 It is the output electromagnetic torque waveform of the third joint motor during the process of lowering the heavy object;

[0060] Figure 11 It is the U - phase current waveform of the second joint motor in the ordinary electric mode when the load torque is 1 Nm;

[0061] Figure 12 It is the input power of the two motors and the total input power of the second joint motor in the ordinary electric mode when the load torque is 1 Nm;

[0062] Figure 13 The U-phase current waveform of the second joint motor in the ordinary electric mode when the load torque is 0.1 Nm;

[0063] Figure 14 The input power of the two motors and the total input power of the second joint motor in the ordinary electric mode when the load torque is 0.1 Nm;

[0064] Figure 15 The U-phase current waveform of the second joint motor in the flux-weakening electric mode when the load torque is 0.1 Nm;

[0065] Figure 16 The input power of the two motors and the total input power of the second joint motor in the flux-weakening electric mode when the load torque is 0.1 Nm;

[0066] Figure 17 The three-phase current waveforms of the second joint motor in the current-locking mode;

[0067] Figure 18 The input power of the two motors and the total input power of the second joint motor in the current-locking mode. Specific embodiments

[0068] The present invention will be further described below in conjunction with specific embodiments:

[0069] As Figure 3 shown, a collaborative control circuit for the four-quadrant operation of a robot joint motor according to this embodiment further realizes the collaborative control of the motor during four-quadrant operation on the basis of the vector control system of the robot joint motor. It includes a robot main controller, n motor controllers, and n joint motors participating in collaborative control; each motor controller includes a power amplification module, a positive bus, and a negative bus; the positive buses of each motor controller are connected together; the negative buses of each motor controller are connected together; the three-phase windings of each joint motor are respectively connected to the power amplification module of the corresponding motor controller; the robot main controller is respectively connected to each motor controller.

[0070] Each motor controller also includes a motor control microprocessor and a base signal driving module; the robot main controller is respectively connected to the motor control microprocessors of each motor controller; in each motor controller, the motor control microprocessor generates multiple PWM signals, and after signal enhancement by the base signal driving module, it controls the power amplification module to work and drive the corresponding joint motor to operate.

[0071] As Figure 4As shown, the robot joint motor vector control system includes a stator current detection module, encoder-based rotor position angle detection and speed calculation, Clarke and PARK transformation, maximum torque current ratio control (MTPA), position regulator, speed regulator, dq axis current regulator, power real-time calculation module, PARK inverse transformation, space pulse modulation module (SVPWM calculation) and three-phase PWM inverter and other units.

[0072] like Figure 5 As shown, the principle of the four-quadrant coordinated control of the robot joint motor through the four-quadrant coordinated control circuit of the robot joint motor is as follows:

[0073] S1, the robot main controller sends a run or stop command to each motor control microprocessor;

[0074] S2. Each motor control microprocessor that receives the operation instruction controls the operation of each joint motor, detects and calculates the instantaneous input power of each motor controller. When the instantaneous input power is a positive value, it indicates that the joint motor is in the motor operation state of quadrants I and III. When the instantaneous input power is a negative value, it indicates that the joint motor is in the generator operation state of quadrants II and IV. The instantaneous input power of the stopped joint motor is zero. All motor control microprocessors return the instantaneous input power information of each joint motor to the robot main controller.

[0075] S3, the robot main controller counts the number of joint motors with positive instantaneous input power as p, and calculates the sum of all positive instantaneous input powers as P in_pos , the number of joint motors with negative instantaneous input power is m, and the sum of all negative instantaneous input power is calculated as P in_neg , the number of joint motors that are stopped and on standby and have zero input power is z; the number of joint motors participating in cooperative control is n=p+m+z;

[0076] S4. The robot main controller performs logic analysis:

[0077] If m=0, it indicates that all joint motors are in the motor state or the shutdown standby state, and the process directly returns to step S1;

[0078] If P in_pos ≥P in_neg , indicating that the electric energy generated by the joint motor operating as a generator can be completely consumed by the joint motor operating as a motor, and there is no risk of overvoltage of the motor controller bus, and the process returns to step S1 to continue monitoring the instantaneous input power of each motor controller;

[0079] If P in_pos <P in_neg, indicating that the electric energy generated by the joint motor operating as a generator cannot be completely consumed by the joint motor operating as a motor, it is necessary to increase the input power of the joint motors in the motor state or standby state in the I and III quadrants, and go to step S5;

[0080] S5. Increase the input power to |P in_neg -P in_pos |, which is shared by the joint motors in the motor state or the stop state, and the robot main controller distributes the input power that each motor needs to increase as

[0081] S6. The robot main controller issues an instruction to the joint motor controller operating in the motor state in the I and III quadrants to enter the field weakening operation mode, and realizes the increase of the input power through the field weakening operation, and consumes the input power P shared in step S5 in_inc ;

[0082] S7. The robot main controller issues an instruction to the motor controller in the standby state to enter the current locking mode, and consumes the input power P shared in step S5 by applying a constant current to the motor winding through the current locking mode in_inc ;

[0083] S8. The current round of cooperative control loop ends, and returns to step S1.

[0084] In the above step S2, each motor control microprocessor that receives the operation instruction controls the operation of each joint motor, including the following steps:

[0085] S2.1. Real-time obtain the three-phase stator currents i U 、i V 、i W of the joint motor through the stator current detection module of the joint motor vector control system, and obtain the rotor angle θ of the current joint motor through the encoder;

[0086] S2.2. The three-phase currents are subjected to Clark transformation to obtain the current components i α 、i β in the stationary coordinate system;

[0087] S2.3. According to the rotor angle θ of the current motor, perform Park transformation on the current components i α 、i β in the stationary coordinate system to obtain the d-axis current i d and the q-axis current i q in the two-phase synchronous rotating coordinate system;

[0088] S2.4. According to the stator current i s, the given values of the PI regulators of the d-axis current loop and the q-axis current loop during normal operation of the joint motor are calculated according to the maximum torque current ratio algorithm and the given values of the PI regulators of the q-axis current loop

[0089]

[0090] In the formula, ψ f is the permanent magnet flux linkage, and L d , L q are the d-axis and q-axis inductances of the motor respectively;

[0091] S2.5. Compare the d-axis current value i d in the two identical synchronous rotating coordinate systems with the given d-axis current value . The difference is used as the input of the PI regulator of the d-axis current loop. Compare the q-axis current value i q in the two identical synchronous rotating coordinate systems with the given q-axis current value . The difference is used as the input of the PI regulator of the q-axis current loop. After calculation by the current loop PI regulator, the output voltages V d , V q of the PI regulators of the d-axis and q-axis current loops are obtained respectively;

[0092] S2.6. According to the rotor angle θ of the motor, perform Park inverse transformation on the output voltages V d , V q of the current loop PI regulator to obtain the voltage components V ɑ , V β in the stationary coordinate system, and then form a three-phase PWM wave signal through the space pulse modulation module of the joint motor vector control system;

[0093] S2.7. The three-phase PWM wave signal controls the power amplification module to output three-phase voltages to drive the joint motor to operate.

[0094] In step S2 above, the instantaneous input power of each motor controller is detected and calculated, including:

[0095] First, detect the output voltage of the current regulator and the actual current feedback value, and then calculate the input power p em = u d i d + u q i q of each joint motor, where ud is the output voltage of the d-axis current regulator, u em is the output voltage of the q-axis current regulator, i q is the actual d-axis current feedback value, and i d is the actual q-axis current feedback value qis the actual feedback value of the q-axis current; by obtaining the input power of each joint motor, the instantaneous input power of each motor controller can be obtained.

[0096] In the above step S6, the robot main controller issues an instruction to the joint motor controllers of the motors operating in the I and III quadrants to enter the field-weakening operation mode. On the premise of keeping the rotation speed of the joint motor unchanged, the input power of the motor controller is increased by increasing the d-axis current, while the q-axis current is still determined by the output of the speed loop.

[0097] The field-weakening control keeps the rotation speed of the joint motor tracking the given speed, and increases the input power by increasing the d-axis current; the calculation formula for the d-axis current to achieve field-weakening control is where I d is the d-axis current before field-weakening control, and V d is the output voltage of the PI regulator of the d-axis current loop.

[0098] In the above step S7, when the motor controller in the standby state enters the current-locking mode, a constant current is generated in the three-phase windings of the joint motor, the rotation speed of the motor is set to zero, the rotor angle of the motor is fixed at the current rotor angle of the motor, and the given values of the PI regulator of the d-axis current loop and the given value of the PI regulator of the q-axis current loop are calculated according to the following formula:

[0099]

[0100] In the formula, V dc is the bus voltage, ξ is the voltage coefficient, and θ present is the current rotor angle.

[0101] To prove the effectiveness of the method described in the present invention, it is described in combination with the UR5 type robot arm:

[0102] The UR5 type robot arm includes 6 joint motors, namely: shoulder joint 1 motor (the 1st joint motor), shoulder joint 2 motor (the 2nd joint motor), elbow joint motor (the 3rd joint motor), wrist joint 1 motor (the 4th joint motor), wrist joint 2 motor (the 5th joint motor), and wrist joint 1 motor (the 6th joint motor).

[0103] In a specific embodiment of the present invention, the robot arm grabs a 10 Kg heavy object and places it on the ground from a position 0.85 m high. The reduction ratio of the harmonic reducer driven by the 3rd joint motor of the robot arm is 1:30. During the process of putting down the heavy object, the load torque curve of the 3rd joint motor is as Figure 7As shown, due to the action of the heavy object, the torque of the third joint motor becomes negative. The harmonic reducer has a damping effect on the torque of the heavy object. The load torque generated by the heavy object varies between -2.4 Nm and -1.8 Nm. During the process of lowering the heavy object, the third joint motor operates in the generator state, converting the potential energy of the heavy object into electrical energy.

[0104] In a specific embodiment of the present invention, the positive busbars of the second and third joint motor controllers are connected, and the negative busbars of the second and third joint motor controllers are connected to implement coordinated control of the second and third joint motors. A simulation model of the coordinated operation of the second joint motor and the third joint motor is established through MATLAB software, and the sum of the input powers of the two motors is calculated to determine whether the electrical energy generated by the third joint motor can be completely consumed by the second joint motor through different operating modes, thereby verifying the effectiveness of the coordinated control method proposed by the present invention.

[0105] Assume that the parameters of the second joint motor, the third joint motor and their controllers are the same: the rated voltage of the motor is 310 V DC, the rated power is 300 W, the number of pole pairs p n = 3, the stator resistance R = 0.62 Ω, the stator direct-axis inductance L d = 4.3 mH, the stator quadrature-axis inductance L q = 6.2 mH, the permanent magnet flux linkage ψ f = 0.125 Wb, the rotor moment of inertia J = 0.001 K g m 2 , and the maximum limit value of the motor phase current is 15 A.

[0106] During the process of lowering the heavy object, the third joint motor operates in the power generation mode, and the second joint motor operates in the ordinary electric mode:

[0107] As Figure 8 is the speed curve of the third joint motor during the process of lowering the heavy object. In the interval of 0 to 0.5 seconds, the motor accelerates from rest to 500 revolutions per minute (rpm). During the acceleration stage, the fluctuation amplitude of the simulated motor speed reaches 250 rpm. In actual operation, through the mechanical damper and the motor chattering suppression strategy, this speed fluctuation amplitude will be greatly reduced; in the interval of 0.5 to 1.8 seconds, the motor maintains a speed of 500 rpm; in the interval of 1.8 to 2.3 seconds, it decelerates from 500 rpm to 0.

[0108] As Figure 9 is the waveform of the U-phase current of the third joint motor during the process of lowering the heavy object. During the entire operation process, the current peak value is -12.0 A to 10.0 A, and the corresponding phase current amplitude of the motor during operation at 500 rpm is 8.0 A.

[0109] As Figure 10is the electromagnetic torque waveform output by the third joint motor during the process of lowering a heavy object. The dashed line in the figure is Figure 7 the corresponding load torque curve. During the motor starting interval from 0 to 0.5 seconds, the electromagnetic torque fluctuates. During the interval from 0.5 to 1.8 seconds, the electromagnetic torque gradually approaches the load torque. During the interval from 1.8 to 2.3 seconds, the negative value of the electromagnetic torque is smaller than the given load torque, causing the motor to decelerate.

[0110] As Figure 11 is the waveform of the U-phase current when the second joint motor works in the normal electric mode during the process of lowering a heavy object. Assuming the load torque is 1 Nm, the peak value of the motor phase current is ±12.0 A during the interval from 0 to 0.5 seconds, and the motor runs stably during the interval from 0.5 to 2.3 seconds, with the phase current stabilizing at ±4.5 A. In the normal electric mode, according to the maximum torque current ratio algorithm calculation formula of the vector control system, the given value of the PI regulator of the d-axis current loop is taken as a constant value and the given value of the PI regulator of the q-axis current loop is the output current i of the speed regulator s .

[0111] As Figure 12 is the waveform diagram of the input power of the two motors and the total input power when the load torque of the second joint motor is 1 Nm in the normal electric mode during the process of lowering a heavy object. The dashed line in the figure is the input power of the second joint motor, the dotted line is the input power of the third joint motor, and the thick solid line is the total input power of the two motors. During the interval from 0 to 0.5 seconds, the two motors accelerate from rest to the given speed. Most of the time in a cycle of the total input power represented by the thick solid line is positive, and only a very small part of the time is negative. Due to the filtering effect of the electrolytic capacitor, the negative value of the input power during this small part of the time will not cause overvoltage of the control system bus. During the interval from 0.5 to 1.8 seconds, the two motors approach the given speed. The input power of the second joint motor is always positive, the input power of the third joint motor is always negative, and the amplitude of the input power of the second joint motor (about 75 W) is greater than the amplitude of the output power of the third joint motor (about 40 W). The total input power of the system is always positive, indicating that the electrical energy consumed by the second joint motor is greater than the electrical energy generated by the third joint motor. The electrical energy generated by the third joint motor during the process of lowering a heavy object will not cause overvoltage of the control system bus.

[0112] During the process of lowering a heavy object, the third joint motor works in the power generation mode, and the second joint motor works in the field-weakening electric mode:

[0113] In some occasions, in addition to the rotation of the third joint motor, although the other joint motors of the robot arm are rotating but the load is very light, the field-weakening electric mode needs to be adopted. As Figure 13This is the U-phase current waveform of the second joint motor in the light-load ordinary electric mode during the process of lowering a heavy object. Assuming the load torque is 0.1 Nm, the peak value of the motor phase current is ±12.0 A in the interval of 0 to 0.5 seconds. The motor operates stably in the interval of 0.5 to 2.3 seconds. Since it is a light load, the peak value of the phase current is only ±0.5 A. In the light-load ordinary electric mode, the given value of the PI regulator of the d-axis current loop is taken as a constant value The given value of the PI regulator of the q-axis current loop is the output current i of the speed regulator s 。

[0114] Such as Figure 14 This is the waveform diagram of the input power of the two motors and the total input power when the second joint motor has a load torque of 0.1 Nm in the ordinary electric mode during the process of lowering a heavy object. The dotted line in the figure is the input power of the second joint motor, the dotted line is the input power of the third joint motor, and the thick solid line is the total input power of the two motors. In the interval of 0 to 0.5 seconds, the two motors accelerate from rest to the given speed. The waveform diagrams of the input power of the two motors and the total input power are close to Figure 12 the waveform. Most of the time in one cycle of the total input power is positive, and only a very small part of the time is negative. Due to the filtering effect of the electrolytic capacitor, the negative value of the input power will not cause overvoltage of the control system bus. In the interval of 0.5 to 1.8 seconds, the two motors approach the given speed. The input power of the second joint motor is always positive, and the input power of the third joint motor is always negative. However, due to the light load and the amplitude of the input power of the second joint motor (about 10 W) being less than the amplitude of the output power of the third joint motor (about 40 W), the total input power of the system is always negative, indicating that the second joint motor far cannot consume the electrical energy generated by the third joint motor.

[0115] From Figure 14 it can be seen that if no measures are taken, the electrical energy generated by the third joint motor during the process of lowering a heavy object will cause overvoltage of the control system bus. The present invention precisely realizes an increase in the input power of the second joint motor through the flux-weakening electric mode.

[0116] Such as Figure 15 This is the U-phase current waveform of the second joint motor in the flux-weakening electric mode during the process of lowering a heavy object. Assuming the load torque is 0.1 Nm, the peak value of the motor phase current is ±15.5 A in the interval of 0 to 0.5 seconds. The motor operates stably in the interval of 0.5 to 2.3 seconds. The given value of the PI regulator of the d-axis current loop is taken as a constant value The given value of the PI regulator of the q-axis current loop takes the output current i of the speed regulator s , and since the peak value of the phase current during flux-weakening operation reaches ±10.0 A, the input power of the second joint motor is thus greatly increased.

[0117] Such as Figure 16Waveform diagrams of the input power of the two motors and the total input power in the field-weakening motoring mode with the load torque of the second joint motor being 0.1 Nm during the process of lowering a heavy object. In the figure, the dashed line represents the input power of the second joint motor, the dotted line represents the input power of the third joint motor, and the thick solid line represents the total input power of the two motors. In the interval from 0 to 0.5 s, the two motors accelerate from rest to the given speed, and the waveform diagrams of the input power of the two motors and the total input power are similar to those of Figure 14 The total input power is positive for most of a cycle and only negative for a very short time. Due to the filtering effect of the electrolytic capacitor, the negative input power will not cause overvoltage on the control system bus. In the interval from 0.5 to 1.8 s, the two motors approach the given speed. Since the second joint motor operates in the field-weakening mode, its input power is always positive (about 100 W), and the input power of the third joint motor is always negative. However, due to the light load and the fact that the amplitude of the input power of the second joint motor is greater than that of the third joint motor (about 40 W), the total input power of the system is always positive, indicating that the electrical energy consumed by the second joint motor is greater than the electrical energy generated by the third joint motor. The electrical energy generated by the third joint motor during the process of lowering the heavy object will not cause overvoltage on the control system bus.

[0118] During the process of lowering a heavy object, the third joint motor operates in the generating mode, and the second joint motor operates in the current-locking mode:

[0119] In some cases, in addition to the rotation of the third joint motor, the other joint motors of the robot arm do not rotate. In this case, the current-locking mode needs to be adopted. For example, Figure 17 is the three-phase current waveform in the current-locking mode of the second joint motor during the process of lowering a heavy object. The given value of the PI regulator of the d-axis current loop is taken as a constant value The given value of the PI regulator of the q-axis current loop is 0, and the three-phase current waveforms are all constant values. Among them, the amplitude of the U-phase current is 0, the amplitude of the V-phase current is -7.5 A, and the amplitude of the W-phase current is +7.5 A.

[0120] For example, Figure 18 is the waveform diagram of the input power of the two motors and the total input power in the current-locking mode of the second joint motor during the process of lowering a heavy object. In the figure, the dashed line represents the input power of the second joint motor, the dotted line represents the input power of the third joint motor, and the thick solid line represents the total input power of the two motors. In the interval from 0 to 0.5 s, the two motors accelerate from rest to the given speed, and the waveform diagrams of the input power of the two motors and the total input power are similar to those of Figure 16The waveform is close, and the total input power is positive for most of a cycle and only negative for a very short time. Due to the filtering effect of the electrolytic capacitor, the negative input power will not cause overvoltage on the control system bus. In the interval of 0.5 to 1.8 seconds, the two motors approach the given speed. Since the input power of the second joint motor is always positive (about 100 W) and the input power of the third joint motor is always negative (amplitude about 40 W) in the current locking mode, the total input power of the system is always positive, indicating that the electrical energy consumed by the second joint motor is greater than the electrical energy generated by the third joint motor. The electrical energy generated by the third joint motor during the process of lowering the heavy object will not cause overvoltage on the control system bus.

[0121] Through the above three working modes, it can be proved that the collaborative control method proposed by the present invention is effective.

[0122] The above-mentioned embodiments are only the preferred embodiments of the present invention and do not limit the scope of implementation of the present invention. Therefore, all changes made according to the shape and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A four-quadrant operation collaborative control circuit for a robot joint motor, characterized in that It includes a robot main controller, n motor controllers, and n joint motors participating in cooperative control; Each motor controller includes a power amplification module, a bus positive terminal, and a bus negative terminal; The bus positive terminals of each motor controller are connected together; The bus negative terminals of each motor controller are connected together; The three-phase windings of each joint motor are respectively connected to the power amplification module of the corresponding motor controller; The robot main controller is respectively connected to each motor controller.

2. The collaborative control circuit for the four-quadrant operation of a robot joint motor according to claim 1, characterized in that Each motor controller also includes a motor control microprocessor and a base signal drive module; The robot main controller is respectively connected to the motor control microprocessors of each motor controller; In each motor controller, the motor control microprocessor generates multiple PWM signals. After signal enhancement by the base signal drive module, it controls the power amplification module to work and drives the corresponding joint motor to run.

3. A cooperative control method for the four-quadrant operation of a robot joint motor, characterized in that, It is implemented by using the four-quadrant operation cooperative control circuit of the robot joint motor described in claim 2, including: S1. The robot main controller issues an operation or stop command to each motor control microprocessor; S2. Each motor control microprocessor that receives the operation command controls each joint motor to run, detects and calculates the instantaneous input power of each motor controller. When the instantaneous input power is positive, it indicates that the joint motor is in the motor operation state in the first and third quadrants. When the instantaneous input power is negative, it indicates that the joint motor is in the generator operation state in the second and fourth quadrants; the instantaneous input power of the stopped joint motor is zero; all motor control microprocessors return the instantaneous input power information of each joint motor to the robot main controller; S3, the robot main controller counts the number of joint motors with positive instantaneous input power as p, and calculates the sum of all positive instantaneous input powers as P in_pos , the number of joint motors with negative instantaneous input power is m, and the sum of all negative instantaneous input power is calculated as P in_neg , the number of joint motors that are stopped and on standby and have zero input power is z; the number of joint motors participating in cooperative control is n=p+m+z; S4. The robot main controller performs logical analysis: If m = 0, it indicates that all joint motors are in the motor state or in the stop standby state, and directly returns to step S1; If P in_pos ≥ P in_neg , it indicates that the electric energy generated by the joint motor operating as a generator can be completely consumed by the joint motor operating as a motor, and there is no risk of overvoltage on the bus of the motor controller. Return to step S1 and continue to monitor the instantaneous input power of each motor controller; If P in_pos <P in_neg , it indicates that the electric energy generated by the joint motor operating as a generator cannot be completely consumed by the joint motor operating as a motor. It is necessary to increase the input power of the joint motors in the motor state in the first and third quadrants or in the standby state, and then go to step S5; S5. Increase the input power by |P in_neg -P in_pos |, which is shared by the joint motors in the motor state or the stopped state. The main controller of the robot distributes the additional input power required for each motor as S6. The robot main controller sends instructions to the joint motor controllers of the motors operating in the first and third quadrants to enter the field-weakening operation mode, and increases the input power through field-weakening operation to consume the input power P allocated in step S5. in_inc ; S7. The robot main controller issues an instruction to the motor controller on standby for shutdown to enter the current locking mode, and a constant current is applied to the motor winding through the current locking mode to consume the input power P allocated in step S5. in_inc ; S8. This round of cooperative control cycle ends, and returns to step S1.

4. A collaborative control method for the four-quadrant operation of a robot joint motor according to claim 3, characterized in that In step S2, each motor control microprocessor that receives the operation command controls the operation of each joint motor, including the following steps: S2.

1. Obtain the three-phase stator currents \(i_{a}\), \(i_{b}\), \(i_{c}\) of the joint motor in real time through the stator current detection module of the joint motor vector control system, and obtain the rotor angle \(\theta\) of the current joint motor through the encoder; U \(_{a}\) V \(_{b}\) W \(_{c}\) S2.

2. The three-phase currents are transformed by the Clark transformation to obtain the current components \(i_{\alpha}\) and \(i_{\beta}\) in the stationary coordinate system. α _{\alpha} β ; S2.

3. According to the rotor angle θ of the current motor, perform Park transformation on the current components i α and i β to obtain the d-axis current i d and the q-axis current i q in the two-phase synchronous rotating coordinate system; S2.

4. Calculate the stator current \(i\) obtained from the speed loop PI regulator s , and calculate the given values of the PI regulators for the d-axis current loop and the q-axis current loop during normal operation of the joint motor according to the maximum torque current ratio algorithm and the given values of the PI regulators for the q-axis current loop : where ψ f is the permanent magnet flux linkage, and L d , L q are the d-axis and q-axis inductances of the motor, respectively; S2.

5. Compare the d-axis current value \(i_d\) in the two identical synchronous rotating coordinate systems with the given d-axis current value d and use their difference as the input of the PI regulator for the d-axis current loop. Compare the q-axis current value \(i_q\) in the two identical synchronous rotating coordinate systems with the given q-axis current value and use their difference as the input of the PI regulator for the q-axis current loop. After calculation by the PI regulators of the current loops, the output voltages \(V_d\) q and \(V_q\) of the PI regulators for the d-axis and q-axis current loops are obtained respectively; d q ​ S2.

6. According to the rotor angle θ of the motor, perform an inverse Park transformation on the output voltages V d and V q to obtain the voltage components V α and V β in the stationary coordinate system, and then form a three-phase PWM wave signal through the space pulse modulation module of the joint motor vector control system; S2.

7. The three-phase PWM wave signal controls the power amplification module to output three-phase voltage to drive the joint motor to run.

5. A collaborative control method for four-quadrant operation of a robot joint motor according to claim 3 or 4, characterized in that In step S2, detecting and calculating the instantaneous input power of each motor controller includes: First, detect the output voltage of the current regulator and the actual current feedback value, and then calculate according to the formula p em = u d i d + u q i q to calculate the input power p em of each joint motor, where u d is the output voltage of the d-axis current regulator, u q is the output voltage of the q-axis current regulator, i d is the actual d-axis current feedback value, and i q is the actual q-axis current feedback value; by obtaining the input power of each joint motor, the instantaneous input power of each motor controller can be obtained.

6. The collaborative control method for the four-quadrant operation of a robot joint motor according to claim 3, characterized in that, In step S6, the robot main controller issues a command to the joint motor controller in the motor operation state in the first and third quadrants to enter the field-weakening operation mode. On the premise of keeping the rotation speed of the joint motor unchanged, the input power of the motor controller is increased by increasing the d-axis current, and the q-axis current is still determined by the output of the speed loop.

7. A cooperative control method for four-quadrant operation of a robot joint motor according to claim 6, characterized in that, The flux-weakening control maintains the rotational speed of the joint motor to track the given speed, and increases the d-axis current to increase the input power. The calculation formula for the d-axis current to achieve the flux-weakening control is where I d is the d-axis current before the flux-weakening control, and V d is the output voltage of the PI regulator of the d-axis current loop.

8. A cooperative control method for four-quadrant operation of a robot joint motor according to claim 3, characterized in that, When the motor controller in standby mode enters the current-locking mode, a constant current is generated in the three-phase windings of the joint motor, the rotation speed of the motor is set to zero, the rotor angle of the motor is fixed at the current rotor angle of the motor, and the given values of the PI regulators of the d-axis current loop and the q-axis current loop during the operation of the joint motor current-locking mode and the given values of the PI regulators of the q-axis current loop are calculated according to the following formula: Wherein, V dc is the bus voltage, ξ is the voltage coefficient, and θ present is the current rotor angle.

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