Electric cylinder servo control system and method

Abstract

An electric cylinder servo control system and method, including a position compensation controller, an adjustment module and an electric cylinder; each electric cylinder corresponds to an adjustment module, all adjustment module inputs are connected to the input of the position compensation controller, and the output of the position compensation controller is connected to the output of each adjustment module to form a plurality of closed adjustment loops; the present invention adopts Hall-based FOC control, and the position accuracy can be adjusted according to the number of motor pole pairs and the number of Hall plates. Hall has the advantages of easy installation, small structure size and low cost. And the driver can detect the rotor position without adding a decoding chip.

Description

Technical Field

[0001] The invention belongs to the technical field of electric cylinder adjustment, and in particular relates to an electric cylinder servo control system and method. Background Art

[0002] The electric cylinder is an electric linear actuation system that replaces the traditional hydraulic cylinder. It consists of a motor, a reduction mechanism, a screw and a housing. It converts the motor's rotary motion into linear motion. With its simple structure, maintenance-free and high precision, it has developed rapidly in the fields of industry and civil use.

[0003] The electric cylinder system not only needs to push a large load, but also often requires precise position control. The driver needs to have a servo function to accurately detect the position of the rotor, and then control it in the position loop to accurately control the rise and fall of the electric cylinder.

[0004] In scenarios where electric cylinder applications require dual-cylinder or multi-cylinder synchronization or proportional synchronization, encoders are required to monitor the rotor position in real time. And the drive system needs to work in the position loop. Encoders such as photoelectric, gear or rotary transformers are often difficult to use in practical applications due to cost and structural space limitations.

[0005] Most of the existing electric cylinders use stepper motors or DC brushed motors. When stepper motors are used as servo cylinder controls, they are prone to step loss and cannot guarantee long-term synchronous and reliable operation. In some applications, the complex structural processing adds position encoders with photoelectric encoders and rotary transformers, but this brings about complex structures and high costs. The driver must be equipped with a corresponding decoding chip, which is expensive and not suitable for large-scale promotion. Summary of the invention

[0006] The object of the present invention is to provide an electric cylinder servo control system and method to solve the above problems.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] An electric cylinder servo control system includes a position compensation controller, an adjustment module and an electric cylinder; each electric cylinder corresponds to an adjustment module, all adjustment module input ends are connected to the input end of the position compensation controller, and the output end of the position compensation controller is connected to the output end of each adjustment module to form a plurality of adjustment closed loops;

[0009] The regulating module comprises a position regulator, a limiting module and a speed regulator, and the position regulator, the limiting module and the speed regulator are connected in sequence.

[0010] Furthermore, the input of the position compensation controller is the position command and the position feedback of each electric cylinder, and the output is the speed feedforward of each electric cylinder. The speed feedforward fine-tunes the speed command of each electric cylinder respectively, and after fine-tuning, it is input to the electric cylinder through the speed regulator.

[0011] Furthermore, a PI regulator is provided in the position compensation controller, and the PI regulator is used to adjust the difference between the actual position value of the electric cylinder and the position command value to output a speed feedforward value.

[0012] Furthermore, the position command serves as the input of both the position regulator and the position compensation controller.

[0013] Furthermore, the speed command is a command input into the position regulator and output after being limited by the limiting module.

[0014] Furthermore, a plurality of Hall elements are provided on the electric cylinder for reading position feedback and speed feedback.

[0015] Furthermore, a method for controlling an electric cylinder servo includes the following steps:

[0016] Inputting position commands to the position regulator and the position compensation controller, respectively calculating the difference between the actual position value of the electric cylinder and the position command value;

[0017] Then the deviation of the difference is PI-adjusted, and the output adjustment feedforward amount is output after limiting;

[0018] The parameters and limit values ​​of the PI regulator are adjusted to achieve precise control of the electric cylinder position synchronization.

[0019] Furthermore, the expression of the position instruction is:

[0020]

[0021] t is the duration of a key operation, T0 is the time of the slow start and slow stop stages, T is the moment when the key is stopped, A is the maximum acceleration planned, and v is the speed of the motor in the constant speed section.

[0022] Furthermore, the parameters and the amplitude limit of the PI regulator are adjusted to meet the following conditions:

[0023] Δu=K P (y0-y1)+K I (∫y0-∫y1)

[0024] Where y0 is the target position, y1 is the initial position, Δu is the adjustment amount, K P and K I is the adjustment coefficient, K P and K ITogether they are called PI regulation.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] The present invention adopts FOC control based on Hall, and the position accuracy can be adjusted according to the number of motor pole pairs and the number of Hall plates. Hall has the advantages of easy installation, small structure size and low cost. And the driver can detect the rotor position without adding a decoding chip. The control method used by the present invention adopts FOC control of Hall at low speed, switches to positionless FOC control at high speed, collects Hall pulses in real time as the actual value of the position loop, compares it with the reference value of the actual position target, and the difference is input into the speed loop calculation after passing through the PID regulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a logic block diagram of the present invention;

[0028] Figure 2 It is a schematic diagram of the command position and actual position of the twin cylinders;

[0029] Figure 3 It is the logic block diagram of the position compensation controller;

[0030] Figure 4 It is a process without using S-curve acceleration and deceleration;

[0031] Figure 5 It is the process of accelerating and decelerating using an S curve. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the accompanying drawings:

[0033] An electric cylinder servo control system, characterized in that it comprises a position compensation controller, an adjustment module and an electric cylinder; each electric cylinder corresponds to an adjustment module, the input ends of all adjustment modules are connected to the input end of the position compensation controller, and the output end of the position compensation controller is connected to the output end of each adjustment module to form a plurality of adjustment closed loops;

[0034] The regulating module comprises a position regulator, a limiting module and a speed regulator, and the position regulator, the limiting module and the speed regulator are connected in sequence.

[0035] A servo control method for an electric cylinder comprises the following steps:

[0036] Inputting position commands to the position regulator and the position compensation controller, respectively calculating the difference between the actual position value of the electric cylinder and the position command value;

[0037] Then the deviation of the difference is adjusted by PI, and the output adjustment feedforward amount is output after limiting.

[0038] The adjustment amount is shown as follows:

[0039] Δu=K P (y0-y1)+K I (∫y0-∫y1)

[0040] Among them, y0 is the target position, y1 is the initial position. If the PI is too large, it will easily cause position overshoot, resulting in repeated position adjustment, which will cause the electric cylinder to oscillate repeatedly at the specified position and cannot be stabilized. If the PI is too small, the position adjustment speed will be too slow and it will not be able to reach the specified position within the specified time. In fact, it is necessary to select appropriate PI parameters through testing and adjust them to achieve precise control of the electric cylinder position synchronization.

[0041] Example:

[0042] Taking dual cylinder control as an example, the drive control of two-axis synchronous electric cylinders (cylinder A and cylinder B) shares a MCU. When receiving key operation instructions, A and B move according to the same stroke position instructions, such as electric lifting tables. Ideally, the stroke trajectory of A and B cylinders can be completely consistent with the stroke position instructions, or slightly lag behind the instructions, but the trajectories of A and B can be completely consistent, so that synchronization can be guaranteed.

[0043] However, due to the inevitable deviations in the mechanical structure manufacturing and assembly of A and B electric cylinders, as well as the differences in the servo motors used by A and B electric cylinders, the stroke positions of A and B are not completely consistent when they act according to the same instruction. The possible stroke position curves are as follows: Figure 1 As shown, the actual values ​​of A and B in the figure have a constant small deviation. In reality, this deviation may be a constantly changing value because the resistance they experience at different positions in the motion cannot remain completely unchanged.

[0044] Therefore, a high-precision position synchronization algorithm must be added to the FOC servo drive using Hall. Figure 2 shown. Figure 2 The position compensation controller in the figure is the key to the designed high-precision position synchronization method. Its input is the position command and the position feedback of A and B read out by the Hall elements on the motor. The output is the speed feedforward Fa and Fb of A and B. The two fine-tune the speed commands of A and B respectively, and finally achieve the purpose of consistent positions of the two.

[0045] Assuming the position command is P0, the position feedback of A is PA, and the position feedback of B is PB, the principle block diagram of the position compensation controller is as follows: Figure 3As shown in the figure, the principle is: calculate the differences EA and EB between the actual position values ​​of A and B and the position command values ​​respectively, then perform PI adjustment on the deviations of EA and EB, and output the adjustment feedforward amounts Fa and Fb after limiting. According to different actual application scenarios, the parameters and limit values ​​of the PI regulator should be reasonably designed to achieve precise control of the synchronization of the positions of A and B.

[0046] In addition, in the synchronous application of electric lifting cylinders, there must be an S-curve acceleration and deceleration process to protect the mechanical structure from reduced life due to hard movements, and to improve comfort during use so that the electric cylinder can start and stop smoothly.

[0047] Applications without adding S-curve acceleration and deceleration such as Figure 4 As shown: when the button is pressed, the travel command is Δ*t, Δ is the displacement increment per unit time, t is the continuous pressing time, and the travel command and time change in a linear relationship from the beginning. When Δ is large, this will cause abrupt actions when starting and stopping. The travel command is expressed as: P = Δ*t.

[0048] Add S-curve acceleration and deceleration applications such as Figure 5 As shown:

[0049] After the start button is pressed, the stroke command increases according to the maximum acceleration plan. After the stop button is pressed, the electric cylinder does not stop immediately. The stroke command stops according to the maximum negative acceleration plan. The time of the slow start and slow stop stages is equal and should not be too long to avoid a sense of lag in operation. The stroke command is expressed as:

[0050]

[0051] Among them, t is the duration of a key operation, T0 is the time of the slow start and slow stop stages, T is the moment when the key is stopped, A is the maximum acceleration planned, and v is the speed of the motor in the constant speed section.

[0052] The use of a position compensation controller with a high-precision position synchronization algorithm can achieve reliable position control accuracy requirements in a simple servo system using Hall.

Claims

1. A servo control method for an electric cylinder, characterized in that: Based on the electric cylinder servo control system, it includes a position compensation controller, an adjustment module and an electric cylinder; each electric cylinder corresponds to an adjustment module, the input ends of all adjustment modules are connected to the input ends of the position compensation controller, and the output ends of the position compensation controller are connected to the output ends of each adjustment module to form several closed adjustment loops; The regulating module comprises a position regulator, a limiter module and a speed regulator, and the position regulator, the limiter module and the speed regulator are connected in sequence; The input of the position compensation controller is the position command and the position feedback of each electric cylinder, and the output is the speed feedforward of each electric cylinder. The speed feedforward fine-tunes the speed command of each electric cylinder respectively, and after fine-tuning, it is input to the electric cylinder through the speed regulator; The position compensation controller is provided with a PI regulator, which is used to adjust the difference between the actual position value of the electric cylinder and the position command value to output the speed feedforward value; The position command is used as the input of the position regulator and the position compensation controller at the same time; The speed command is the position command input into the position regulator, and the command output after being limited by the limit module; The electric cylinder is equipped with several Hall elements for reading position feedback and speed feedback; The following steps are involved: Inputting position commands to the position regulator and the position compensation controller, respectively calculating the difference between the actual position value of the electric cylinder and the position command value; Then the deviation of the difference is PI-adjusted, and the output adjustment feedforward amount is output after limiting; The parameters and limit values ​​of the PI regulator are adjusted to achieve precise control of the electric cylinder position synchronization.

2. The electric cylinder servo control method according to claim 1, characterized in that: Expression for position instruction: t is the duration of a key operation, T0 is the time of the slow start and slow stop stages, T is the moment when the key is stopped, A is the maximum acceleration planned, and v is the speed of the motor in the constant speed section.

3. The electric cylinder servo control method according to claim 1, characterized in that: The parameters and limit values ​​of the PI regulator are adjusted to meet the following requirements: Δu=K P (y0-y1)+K I (∫y0-∫y1) Where y0 is the target position, y1 is the initial position, Δu is the adjustment amount, K P and K I is the adjustment coefficient, K P and K I Together they are called PI regulation.

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