A method and system for hybrid force-position servo- stepper closed loop control

Abstract

The application relates to a force-position hybrid servo stepping closed-loop control method and system, and the method comprises the following steps: obtaining a position deviation and a speed deviation according to an actual angle position and an actual speed of a stepping motor rotor end, constructing a system error dynamics equation of the stepping motor, constructing a proportional differential auxiliary variable based on the position deviation and the speed deviation and a approaching equation for guaranteeing that the proportional differential auxiliary variable converges to 0 in a limited time; combining the system error dynamics equation, the proportional differential auxiliary variable and the approaching equation to construct a force-position hybrid controller, obtaining a system control input through the force-position hybrid controller, obtaining two-phase reference currents based on the system control input, and realizing driving control of the stepping motor by adopting a hardware current closed loop. Compared with the prior art, the application can improve the position control precision of the stepping motor when the system has interference and uncertainty, and realizes hybrid control of torque and position.

Description

Technical Field

[0001] This invention relates to the field of stepper motor control technology, and in particular to a force-position hybrid servo stepper closed-loop control method and system. Background Technology

[0002] Stepper motors are widely used in many different industrial fields due to their high positioning accuracy, simple control methods, reliable operation, and low cost. Typically, the precise positioning accuracy and stable force control performance of stepper motors are required in many applications. To improve the control performance of stepper motors, existing methods can be divided into the following three categories:

[0003] 1. Improving positional accuracy by using stepper motor microstepping drive methods, such as the stepper motor microstepping control circuit disclosed in utility model application CN207588746U and the document "Design of Two-Phase Hybrid Stepper Motor Microstepping Driver" (Hao Xinwei et al., Electronic World, 2019, (02)). This type of method achieves this by generating precise phase currents through the stepper motor driver. Its initial purpose is to reduce the low-frequency vibration and noise of the stepper motor and make the movement smoother. Therefore, it works well when operating at low-frequency cycles. However, at higher speeds, this type of method is prone to step loss and pulse loss, which reduces positional accuracy.

[0004] 2. Improving position tracking accuracy by constructing a closed-loop controller, such as the stepper motor closed-loop control system disclosed in utility model application CN 204886773U and the literature "Research and Application of Stepper Motor Closed-Loop Control System" (Xia Siquan et al., Mechanical and Electrical Engineering, 2017, 34(12)). In industrial applications, this type of method often uses a PI correction unit for the design of the closed-loop controller, which is suitable for linear time-invariant systems. However, the stepper motor is a multivariable strongly coupled nonlinear system, and the traditional control method is difficult to adapt to various disturbances under complex working conditions, resulting in a decrease in position tracking accuracy. In addition, in the closed-loop control framework of the stepper system, a dual closed-loop control strategy is often used. In this way, since the position loop response speed is slower than the speed loop, the dynamic response speed of the position servo will be reduced.

[0005] 3. Improving the torque holding performance of stepper motors through constant current driving, such as the stepper motor drive circuit and stepper motor driver disclosed in utility model application CN216134441U and the literature "Design of Constant Current Drive Circuit for Stepper Motor" (Zhang Chao et al., Computer Measurement & Control, 2019, 27(05)). This control method uses a pre-given sinusoidal current as a reference value and generates a PWM signal by comparing it with the winding coil current to control the on / off state of the H-bridge, thereby achieving torque holding. This method can effectively improve voltage utilization, has high position accuracy and fast response speed, and can significantly reduce low-frequency vibration of the motor. However, the torque magnitude of this method cannot be self-adjusted. The current magnitude at any given time is only related to the reference current of the sinusoidal ammeter at that time and is independent of the position state. In actual industrial applications where force control requirements are high, this can easily cause system damage. Furthermore, due to the lack of a position closed loop, the problem of step loss also exists.

[0006] Therefore, how to improve the position control accuracy of stepper motors and achieve torque / position hybrid control when there are disturbances and uncertainties in the system has become an important issue for high-performance servo stepper motors in industrial applications. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of the existing technology, such as vibration, step loss and uncontrollable torque of stepper motors in industrial applications, and to provide a force-position hybrid servo stepper closed-loop control method and system.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] A force-position hybrid servo stepper closed-loop control method includes the following steps: obtaining position deviation and speed deviation based on the actual angular position and actual speed of the stepper motor rotor end, constructing the system error dynamic equation of the stepper motor, constructing a proportional-derivative auxiliary variable based on the position deviation and speed deviation, and a convergence equation that ensures that the proportional-derivative auxiliary variable converges to 0 in a finite time.

[0010] A force-position hybrid controller is constructed by combining the system error dynamic equation, proportional-differential auxiliary variables and the approaching equation. The system control input is obtained through this force-position hybrid controller. Based on the system control input, the phase current is distributed to obtain the two-phase reference current, and the stepper motor drive control is realized by hardware current closed loop.

[0011] Furthermore, the system error dynamic equation The calculation expression is:

[0012] :

[0013] In the formula, For positional deviation, For speed deviation, For a given speed, For actual speed, The coefficient of viscous friction is... For rotational inertia, For system control input, The torque constant of the motor. This is system interference;

[0014] The proportional-differential auxiliary variable The calculation expression is:

[0015]

[0016] In the formula, It is a proportionality coefficient, and ;

[0017] The approaching equation The calculation expression is:

[0018]

[0019] In the formula, , For time-varying gain parameters;

[0020] The expression for obtaining the system control input is:

[0021] .

[0022] Furthermore, the time-varying gain parameter and The conditions to be met are:

[0023]

[0024] In the formula, , , , and All parameters are adjustable. , , , , >0.

[0025] Furthermore, the system control input is also configured with a variable limiting parameter. The final system input is obtained based on the variable limiting parameter, and the phase current is distributed based on the final system input to obtain the two-phase reference current.

[0026] Furthermore, the final system input calculation expression is:

[0027]

[0028] In the formula, For the final system input, For system control input, These are variable constraint parameters.

[0029] Furthermore, the calculation expression for the two-phase reference current is as follows:

[0030]

[0031] In the formula, , These are the currents of the motor's A and B phase windings, respectively. The torque constant of the motor. The number of rotor teeth. This represents the actual angle and position.

[0032] Furthermore, performing a Park transformation on the two-phase reference currents yields: , = This enables torque control of the stepper motor.

[0033] Furthermore, a hardware current closed-loop control is used to implement the stepper motor control, specifically as follows:

[0034] The two-phase reference current signal is converted into an analog signal by a DAC. After being compared with the feedback sampled current by a voltage comparator, the output is used to generate an H-bridge PWM switching signal to drive the stepper motor to operate in closed loop.

[0035] This invention also provides a control system based on the force-position hybrid servo stepper closed-loop control method described above, comprising a force-position hybrid controller, an angle sensor, a current closed-loop drive circuit, a sampling circuit, and a stepper motor. The angle sensor is installed at the rotor end of the stepper motor for acquiring the actual angular position. and actual speed ;

[0036] The force-position hybrid controller is used to obtain position deviation and speed deviation based on the actual angular position and actual speed of the stepper motor rotor end, construct the system error dynamic equation of the stepper motor, construct proportional-derivative auxiliary variables and a reaching equation that ensures that the proportional-derivative auxiliary variables converge to 0 in a finite time based on the position deviation and speed deviation; combine the system error dynamic equation, proportional-derivative auxiliary variables and reaching equation to construct the force-position hybrid controller, obtain the system control input through the force-position hybrid controller, and obtain the two-phase reference current by performing phase current distribution based on the system control input;

[0037] The sampling circuit is used to acquire the actual current of the two phases, and the current closed-loop drive circuit is used to compare the reference current of the two phases with the actual current of the two phases, so as to realize the drive control of the stepper motor through the hardware current closed loop.

[0038] Furthermore, when the torque limit is not reached, the system input... Under the influence of the position deviation and velocity deviation, respectively satisfy the following conditions: , .

[0039] Compared with the prior art, the present invention has the following advantages:

[0040] (1) The force-position hybrid servo stepper closed-loop control method designed in this invention can ensure the closed-loop operation of the motor system, realize precise control of position and torque, effectively improve the positioning accuracy of the stepper motor and reduce vibration and noise, and ensure the smooth operation of the motor.

[0041] (2) The force-position hybrid servo stepping closed-loop control method designed in this invention has the advantages of faster dynamic response speed and stronger anti-interference ability compared with the existing cascade PI closed-loop controller.

[0042] (3) The force-position hybrid servo stepping closed-loop control method designed in this invention can realize the vector control of current, thereby achieving the desired torque output control by constraining the system input. Attached Figure Description

[0043] Figure 1 This is a system block diagram of a force-position hybrid servo stepping closed-loop control system provided in an embodiment of the present invention;

[0044] Figure 2 This is a hardware current closed-loop schematic diagram provided in an embodiment of the present invention;

[0045] Figure 3 This is an experimental comparison diagram of the position tracking curves of the present invention and a cascaded PI controller provided in an embodiment of the present invention;

[0046] Figure 4 This is an experimental comparison diagram of the speed curves of the present invention and a cascaded PI controller provided in an embodiment of the present invention;

[0047] Figure 5 This is an experimental comparison diagram of the current curves of the present invention and the cascade PI controller provided in an embodiment of the present invention;

[0048] Figure 6 This is a diagram showing the control curves of different torque outputs during position tracking, provided in an embodiment of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0050] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0051] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0052] Example 1

[0053] To address the problems of vibration, step loss, and uncontrollable torque in stepper motors used in industrial applications, this invention proposes a force-position hybrid servo stepper motor closed-loop control method. First, based on the position and velocity deviation states, a system error dynamic equation is constructed. Second, proportional-derivative state auxiliary variables are designed, and combined with the finite-time approach equation, a force-position hybrid controller is constructed. Finally, the phase current of the controller input signal is distributed to obtain two-phase reference currents, and a hardware current closed-loop is used to realize the drive control of the stepper motor. The overall block diagram is shown below. Figure 1 As shown, the hardware current closed-loop process is as follows: Figure 2 As shown.

[0054] The specific process of this method includes: obtaining the position deviation and speed deviation based on the actual angular position and actual speed of the stepper motor rotor end, constructing the system error dynamic equation of the stepper motor, constructing a proportional differential auxiliary variable based on the position deviation and speed deviation, and a reaching equation that ensures that the proportional differential auxiliary variable converges to 0 in a finite time.

[0055] A force-position hybrid controller is constructed by combining the system error dynamic equation, proportional-differential auxiliary variables and the approaching equation. The system control input is obtained through this force-position hybrid controller. Based on the system control input, the phase current is distributed to obtain the two-phase reference current, and the stepper motor drive control is realized by hardware current closed loop.

[0056] In a preferred embodiment, the system control input is also provided with a variable limiting parameter. The final system input is obtained based on the variable limiting parameter, and the phase current is distributed based on the final system input to obtain the two-phase reference current.

[0057] The final calculation expression for the system input is:

[0058]

[0059] In the formula, For the final system input, For system control input, These are variable constraint parameters.

[0060] like Figure 1 As shown, this embodiment also provides a control system based on the above-described force-position hybrid servo stepper closed-loop control method, including a force-position hybrid controller, an angle sensor, a current closed-loop drive circuit, a sampling circuit, and a stepper motor; the stepper motor, angle sensor, force-position hybrid controller, current closed-loop drive circuit, and stepper motor are connected in sequence to form a loop circuit, and the sampling circuit is connected to the current closed-loop drive circuit.

[0061] An angle sensor is installed at the rotor end of the stepper motor to collect the actual angular position. and actual speed ;

[0062] The force-position hybrid controller is used to obtain position deviation and speed deviation based on the actual angular position and actual speed of the stepper motor rotor end, construct the system error dynamic equation of the stepper motor, construct proportional-derivative auxiliary variables and a reaching equation that ensures that the proportional-derivative auxiliary variables converge to 0 in a finite time based on the position deviation and speed deviation; combine the system error dynamic equation, proportional-derivative auxiliary variables and reaching equation to construct the force-position hybrid controller, obtain the system control input through the force-position hybrid controller, and obtain the two-phase reference current by performing phase current distribution based on the system control input;

[0063] The sampling circuit is used to obtain the actual current of the two phases, and the current closed-loop drive circuit is used to realize the drive control of the stepper motor based on the two-phase reference current and the two-phase actual current.

[0064] The specific implementation process of this embodiment is described below:

[0065] In this example, the electrical parameters of the two-phase hybrid stepper motor selected here are shown in Table 1:

[0066] Table 1 Electrical parameters of stepper motor

[0067]

[0068] The specific steps are as follows:

[0069] Step 1): Obtain the actual angular position by installing a magnetic encoder at the rotor end of the stepper motor. and actual speed and with a given position The positional deviation was obtained by comparison. , with a given speed The speed deviation was obtained by comparison. ;

[0070] Step 2): Based on the motion characteristics of the stepper motor, establish the mechanical dynamics equations of the stepper motor. :

[0071] : ,

[0072] in, The number of rotor teeth. The torque constant of the motor. The coefficient of viscous friction is... For rotational inertia, , These are the currents of the motor's A and B phase windings, respectively. For load torque disturbance;

[0073] Step 3): Set system control input System interference The state variables in step 1) and Substitute into the dynamic equation of step 2) From this, we can obtain the system error dynamic equation. :

[0074] : ;

[0075] Step 4): Design proportional-differential auxiliary variables ,in c It is a proportionality coefficient, and And combined with the error dynamics equation obtained in step 3), ,right Differentiating the equation yields the equation :

[0076] : ;

[0077] Step 5): Design a method to ensure the auxiliary variable Approaching equations that converge to 0 in finite time :

[0078] : ,

[0079] in, , For time-varying gain parameters, the equations are... and By combining the two systems, the system control input is obtained. :

[0080] : ;

[0081] Step 6): Input system control data. Set a variable limit parameter The final system input is:

[0082] ;

[0083] Step 7): Based on the system input in Step 6) Establish a current distribution scheme for phase A and phase B windings. :

[0084] : ;

[0085] Step 8): Current distribution scheme The currents of phases A and B are obtained by using a hardware-based current closed-loop method, i.e., the reference current... and The signal is converted to an analog signal by a DAC, compared with the feedback sampled current by a voltage comparator, and then the output is used to generate an H-bridge PWM switching signal to drive the stepper motor in closed-loop operation. The schematic diagram is shown below. Figure 2 As shown.

[0086] The time-varying gain parameter in step 5) above , satisfy:

[0087] ,

[0088] The value of this time-varying gain parameter can be changed in real time according to the value of the auxiliary variable, which can effectively reduce controller vibration and improve controller performance.

[0089] The method proposed in this embodiment, when the torque limit is not reached, inputs the following into the system: Under the influence of the position deviation and velocity deviation, respectively satisfy the following conditions: , Meanwhile, the current distribution scheme By performing the park transformation, we can obtain: , = Thus, the current distribution scheme is obtained. Under its influence, the torque of the stepper motor can be controlled; and by adjusting... The value can be adjusted to control the output torque.

[0090] Finally, by comparing the two-phase hybrid stepper motor used in this example with a traditional position and speed dual closed-loop cascade PI controller, the effectiveness of this solution is verified.

[0091] The cascade PI closed-loop controller is designed as follows:

[0092] 1) Position loop P controller ;

[0093] 2) Speed ​​loop PI controller ;

[0094] The control parameters for this invention are set as shown in Table 2:

[0095] Table 2 Force-position hybrid controller parameters

[0096]

[0097] The parameters for the cascade PI controller are shown in Table 3:

[0098] Table 3 Parameters of Cascade PI Controller

[0099]

[0100] Experiment 1: The desired turning angle is 500°, and a disturbance torque of 0.1 N·m (37% of the rated torque) is applied at 1 s.

[0101] Experiment 2: The desired rotation angle is 360°, and the maximum torque is limited to 0.1 N·m during the rotation. The torque is then changed to 0.2 N·m after 2 seconds.

[0102] Figures 3-5 The diagram shows a comparison of the position, velocity, and current of the force-position hybrid controller proposed in this invention and the traditional PI cascade controller under Experiment 1. The experimental results demonstrate that, compared to the traditional cascade PI controller, this invention achieves a faster dynamic response and stronger anti-interference performance.

[0103] Figure 6 The experiment demonstrates the control effect of the force-position hybrid controller proposed in this invention under different torque constraints in Experiment 2. The experimental results show that this invention can achieve position control while maintaining good control over different torques.

[0104] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A force-position hybrid servo stepping closed-loop control method, characterized in that, Includes the following steps: Based on the actual angular position and actual speed of the stepper motor rotor end, the position deviation and speed deviation are obtained, and the system error dynamic equation of the stepper motor is constructed. Based on the position deviation and speed deviation, a proportional differential auxiliary variable and a reaching equation that ensures that the proportional differential auxiliary variable converges to 0 in a finite time are constructed. A force-position hybrid controller is constructed by combining the system error dynamic equation, proportional-differential auxiliary variables and approaching equation. The system control input is obtained through this force-position hybrid controller. Based on the system control input, the phase current is distributed to obtain the two-phase reference current, and the stepper motor drive control is realized by hardware current closed loop. The system error dynamics equation The calculation expression is: ： In the formula, For positional deviation, For speed deviation, For a given speed, For actual speed, The coefficient of viscous friction is... For rotational inertia, For system control input, The torque constant of the motor. This is system interference; The proportional-differential auxiliary variable The calculation expression is: In the formula, It is a proportionality coefficient, and ; The approaching equation The calculation expression is: In the formula, , For time-varying gain parameters; The expression for obtaining the system control input is: The time-varying gain parameter and The conditions to be met are: In the formula, , , , and All parameters are adjustable. , , , , >0; The system control input is also set with a variable limit parameter. The final system input is obtained according to the variable limit parameter. The phase current is distributed according to the final system input to obtain the two-phase reference current. The final system input calculation expression is: In the formula, For the final system input, For system control input, These are variable constraint parameters; The calculation expression for the two-phase reference current is: In the formula, , These are the currents of the motor's A and B phase windings, respectively. The torque constant of the motor. The number of rotor teeth. This refers to the actual angle and position. By performing a Park transformation on the two-phase reference currents, we can obtain: , = This enables torque control of the stepper motor; The stepper motor is controlled using a hardware current closed-loop system, specifically as follows: The two-phase reference current signal is converted into an analog signal by a DAC. After being compared with the feedback sampled current by a voltage comparator, the output is used to generate an H-bridge PWM switching signal to drive the stepper motor to operate in closed loop.

2. A control system based on the force-position hybrid servo stepping closed-loop control method described in claim 1, characterized in that, It includes a force-position hybrid controller, an angle sensor, a current closed-loop drive circuit, a sampling circuit, and a stepper motor. The angle sensor is installed at the rotor end of the stepper motor to collect the actual angular position. and actual speed ; The force-position hybrid controller is used to obtain position deviation and speed deviation based on the actual angular position and actual speed of the stepper motor rotor end, construct the system error dynamic equation of the stepper motor, construct proportional-derivative auxiliary variables and a reaching equation that ensures that the proportional-derivative auxiliary variables converge to 0 in a finite time based on the position deviation and speed deviation; combine the system error dynamic equation, proportional-derivative auxiliary variables and reaching equation to construct the force-position hybrid controller, obtain the system control input through the force-position hybrid controller, and obtain the two-phase reference current by performing phase current distribution based on the system control input; The sampling circuit is used to acquire the actual current of the two phases, and the current closed-loop drive circuit is used to compare the reference current of the two phases with the actual current of the two phases, so as to realize the drive control of the stepper motor through the hardware current closed loop.

3. The control system according to claim 2, characterized in that, When the torque limit is not reached, the system input Under the influence of the position deviation and velocity deviation, respectively satisfy the following conditions: , .

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