Closed loop stepper motor system with linear encoder and method of controlling the same

Abstract

The application relates to a closed-loop stepping module system with a linear encoder and a control method thereof, which comprises a motor driver and a motor controller, a motor mounting support and a base, and a stepping motor, a screw rod, a nut, a guide rail and a load sliding block which are respectively mounted on the motor mounting support and the base. The motor controller is connected with the stepping motor through the motor driver. The stepping motor is in transmission connection with the nut through the screw rod. The nut drives the load sliding block to move on the guide rail. The system further comprises a linear encoder magnetic strip and a linear encoder module. The linear encoder magnetic strip is mounted on the inner side wall of the shell of the motor mounting support and the base. The linear encoder module is oppositely arranged with the linear encoder magnetic strip and is connected with the nut. Compared with the prior art, the application has the advantages of greatly improving the motion precision of the linear stepping module.

Description

Technical Field

[0001] This invention relates to a closed-loop stepper module system and its control method, and more particularly to a closed-loop stepper module system with a linear encoder and its control method. Background Technology

[0002] Stepping motors, due to their good low-speed motion response characteristics, are often connected with linear transmission mechanisms, guide rails, etc., and are widely used in various machines and equipment as linear motion actuators. They convert control signals into linear motion, thereby controlling the actuator to move a given distance and generating thrust that can effectively drive the load.

[0003] However, this commonly used integration method and mechanism design have significant drawbacks: Firstly, because stepper motors are usually controlled in an open-loop manner, it is difficult to detect problems such as step loss, overshoot, and stall during operation, and the dynamic response capability of the open-loop method is also very low. Secondly, because the entire module system contains transmission mechanisms such as lead screws, nuts, and guide rails, these transmission mechanisms inevitably have varying degrees of backlash and cumulative linear motion errors, resulting in low overall linear motion accuracy of the system. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art by providing a closed-loop stepper module system with a linear encoder and its control method. This method can effectively overcome the above-mentioned shortcomings and has significant improvements in accuracy, stability and system dynamic response.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A closed-loop stepper module system with a linear encoder includes a motor driver and a motor controller, a motor mounting bracket and a base, and a stepper motor, a lead screw, a nut, a guide rail, and a load slider respectively mounted on the motor mounting bracket and the base. The motor controller is connected to the stepper motor through the motor driver, and the stepper motor is driven by the lead screw and the nut. The nut drives the load slider to move on the guide rail. The system also includes a linear encoder magnetic strip and a linear encoder module. The linear encoder magnetic strip is mounted on the inner side wall of the housing of the motor mounting bracket and the base, and the linear encoder module is arranged opposite to the linear encoder magnetic strip and connected to the nut.

[0007] Preferably, the inner wall of the outer shell of the motor mounting bracket and base is provided with a groove for mounting the magnetic strip of the linear encoder.

[0008] Preferably, the distance between the center of the linear encoder magnetic strip positioned by the groove and the center of the encoder module is less than 0.3 mm.

[0009] Preferably, the system further includes an encoder mounting block, in which the linear encoder module is embedded, and the encoder mounting block is connected to the encoder by screws and nuts.

[0010] Preferably, the lead screw is a trapezoidal lead screw or a ball screw; the nut is a trapezoidal nut or a ball nut.

[0011] Preferably, the linear encoder module uses a magnetic linear sensor chip, which is internally composed of a Hall element array.

[0012] Preferably, the mounting base for the linear encoder magnetic strip is made of aluminum or other non-magnetic materials; the mounting base for the linear encoder module is made of aluminum or other non-magnetic materials.

[0013] Preferably, the gap between the linear encoder magnetic strip and the linear encoder module varies from 0.02 to 0.2 mm, the flatness of the mounting base of the linear encoder magnetic strip is less than 0.15, and the gap tolerance between the linear encoder magnetic strip and the linear encoder module is less than + / - 0.1 mm.

[0014] A control method for a closed-loop stepper module system with a linear encoder is provided. In this method, during the linear motion of the system, the linear encoder module senses the magnetic field signal of the linear encoder strip, thereby feeding back real-time position information to the motor controller or motor driver. The motor controller or motor driver forms a closed-loop control based on the position signal fed back by the linear encoder module, wherein the closed-loop control range includes a speed loop and a position loop.

[0015] Preferably, the closed-loop control algorithm adopts a PD or PID control algorithm, and dead zone control is added to the PD or PID control algorithm. The dead zone parameter is obtained by measuring in the early stage to obtain the dead zone parameter that best matches the system.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. This invention significantly improves the motion accuracy of linear stepper modules, increasing the repeatability of positioning accuracy from about 0.1mm to within 0.01mm, raising the accuracy of applications by an order of magnitude, and bringing tremendous value to fields such as consumer electronics and automation.

[0018] 2. This invention enables users to know the operating status of the linear motion module in real time during the system's movement, thereby avoiding problems such as step loss, overshoot, and stall during the movement of the mechanism.

[0019] 3. This invention enables users to use control strategies such as PD or PID to control the speed or position of the linear module, thereby achieving higher dynamic response, greater stability, and avoiding system errors.

[0020] 4. This invention incorporates a dead-zone control algorithm into PD control, and the dead-zone parameter can be obtained through prior measurement to best match the system's dead-zone parameter. This allows for further elimination of nonlinearity caused by backlash in the screw drive system and the resulting transient overshoot and overspeed issues during system startup and shutdown during subsequent control. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the internal structure of the present invention;

[0022] Figure 2 This is a side view of the structure of the present invention;

[0023] Figure 3 This is a flowchart of the PI control process of the present invention;

[0024] Figure 4 This is a flowchart of the PID control process of the present invention. Detailed Implementation

[0025] 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, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0026] like Figure 1 As shown, a closed-loop stepper module system with a linear encoder includes a motor driver 9 and a motor controller 10, a motor mounting bracket and base 4, and a stepper motor 1, a lead screw 2, a nut 3, a guide rail 5, and a load slider 6 respectively mounted on the motor mounting bracket and base 4. The motor controller 10 is connected to the stepper motor 1 through the motor driver 9. The stepper motor 1 is driven by the lead screw 2 and the nut 3. The nut 3 drives the load slider 6 to move on the guide rail 5. The system also includes a linear encoder magnetic strip 7 and a linear encoder module 8. The linear encoder magnetic strip 7 is mounted on the inner side wall of the housing of the motor mounting bracket and base 4. The linear encoder module 8 is arranged opposite to the linear encoder magnetic strip 7 and connected to the nut 3.

[0027] The motor driver 9 and motor controller 10 can be a single unit or two separate parts. The inner wall of the motor mounting bracket and base 4 has grooves 11 for mounting the linear encoder magnetic strip 7. The center of the groove 11 is less than 0.3mm from the center of the encoder module 8, and the groove 11 helps determine the relative position of the linear encoder magnetic strip 7. The linear encoder module 8 can slide linearly along the load slider 6 on the guide rail 5 inside the linear module.

[0028] like Figure 2 As shown, the system also includes an encoder mounting block 12, in which the linear encoder module 8 is embedded. The encoder mounting block 12 is connected to the nut 3 by two screws.

[0029] The lead screw 2 is a trapezoidal lead screw or a ball screw; the nut 3 is a trapezoidal nut or a ball nut.

[0030] The linear encoder module 8 uses a magnetic linear sensor chip, which is internally composed of a Hall element array.

[0031] The mounting base of the linear encoder magnetic strip 7 is made of aluminum or other non-magnetic materials; the mounting base of the linear encoder module 8 is made of aluminum or other non-magnetic materials.

[0032] The linear encoder magnetic strip is installed on the inner wall of the outer casing inside the module. The linear encoder module is installed at the opposite position of the magnetic strip, and the mechanical structure ensures that the gap between the linear encoder magnetic strip 7 and the linear encoder module 8 varies from 0.02 to 0.2 mm throughout the entire linear stroke. The flatness of the mounting base of the linear encoder magnetic strip 7 is less than 0.15, and the gap tolerance between the linear encoder magnetic strip 7 and the linear encoder module 8 is less than + / - 0.1 mm.

[0033] The working principle of this invention is as follows: During system operation, the controller generates a control signal, which is sent to the drive circuit to drive the stepper motor to rotate. The stepper motor, driven by the driver according to the controller signal, rotates at a predetermined speed and angle, simultaneously rotating the lead screw at a predetermined angle. This, in turn, drives the nut to move linearly a specified distance at a given speed via the transmission pair. The system's functional objective is for the nut to drive the load to perform actual motion according to the customer-defined trajectory. Ultimately, the system's performance depends on the dynamic characteristics and accuracy of the linear motion. During the linear motion, the linear encoder module 8 senses the magnetic field signal of the linear encoder strip 7, thereby feeding back real-time position information to the motor controller 10 or the motor driver 9. The motor controller 10 or motor driver 9 forms a closed-loop control based on the position signal fed back by the linear encoder module 8. This closed-loop control includes both a speed loop and a position loop, achieving high control accuracy and performance.

[0034] The PD closed-loop control algorithm of this invention is as follows: Figure 3 , Figure 4 This is another preferred embodiment of the PID control algorithm.

[0035] By combining this closed-loop control algorithm with the aforementioned closed-loop stepper linear module system, the PD algorithm can be used to control a nonlinear ball screw system with backlash. The dead zone linear error value is set according to the traditional backlash of the ball screw and nut system. If the ball screw and nut backlash is α, then the range of the dead zone value β is: β < 0.5 * α.

[0036] Dead-zone filter setting range (assuming the input signal to the dead-zone filter is Sin and the output signal is Sout):

[0037]

[0038] Therefore, this invention incorporates a dead-zone control algorithm into PD control, and the dead-zone parameter can be obtained through prior measurement to best match the system's dead-zone parameter. This allows for further elimination of nonlinearity caused by backlash in the screw drive system and the resulting transient overshoot and overspeed response problems during system startup and shutdown during subsequent control.

[0039] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A closed-loop stepper module system with a linear encoder, comprising a motor driver (9) and a motor controller (10), a motor mounting bracket and a base (4), and a stepper motor (1), a lead screw (2), a nut (3), a guide rail (5), and a load slider (6) respectively mounted on the motor mounting bracket and the base (4), wherein the motor controller (10) is connected to the stepper motor (1) through the motor driver (9), the stepper motor (1) is connected to the nut (3) through the lead screw (2), and the nut (3) drives the load slider (6) to move on the guide rail (5), characterized in that, The system also includes a linear encoder magnetic strip (7) and a linear encoder module (8). The linear encoder magnetic strip (7) is installed on the inner wall of the housing of the motor mounting bracket and base (4). The linear encoder module (8) is arranged opposite to the linear encoder magnetic strip (7) and connected to the nut (3). The inner wall of the outer shell of the motor mounting bracket and base (4) is provided with a groove (11) for mounting the linear encoder magnetic strip (7). The system also includes an encoder mounting block (12), in which the linear encoder module (8) is embedded, and the encoder mounting block (12) is connected to the nut (3) by screws; The closed-loop control algorithm of the system adopts PD or PID control algorithm, and dead zone control is added to the PD or PID control algorithm. The dead zone parameter is obtained by prior measurement to obtain the dead zone parameter that best matches the system. The gap between the linear encoder magnetic strip (7) and the linear encoder module (8) varies from 0.02 to 0.2 mm, and the gap tolerance between the linear encoder magnetic strip (7) and the linear encoder module (8) is less than + / - 0.1 mm.

2. A closed-loop stepper module system with a linear encoder according to claim 1, characterized in that, The center of the linear encoder magnetic strip (7) positioned by the groove (11) is less than 0.3 mm away from the center of the encoder module (8).

3. A closed-loop stepper module system with a linear encoder according to claim 1, characterized in that, The lead screw (2) is a trapezoidal lead screw or a ball screw; the nut (3) is a trapezoidal nut or a ball nut.

4. A closed-loop stepper module system with a linear encoder according to claim 1, characterized in that, The linear encoder module (8) uses a magnetic linear sensor chip, which is internally composed of a Hall element array.

5. A closed-loop stepper module system with a linear encoder according to claim 1, characterized in that, The mounting base of the linear encoder magnetic strip (7) is made of aluminum or other non-magnetic materials; the mounting base of the linear encoder module (8) is made of aluminum or other non-magnetic materials.

6. A control method for a closed-loop stepper module system with a linear encoder as described in claim 1, characterized in that, In the process of linear motion of the system, the linear encoder module (8) senses the magnetic field signal of the linear encoder strip (7) and feeds back the real-time position information to the motor controller (10) or the motor driver (9). The motor controller (10) or the motor driver (9) forms a closed-loop control based on the position signal fed back by the linear encoder module (8), wherein the closed-loop control range includes the speed loop and the position loop.

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