A stepper motor adaptive pressing force control device and a control method thereof

Abstract

The present application relates to motor control and precise pressing test technical field, especially to a kind of stepper motor adaptive pressing force control device and control method thereof.The device includes stepper motor, transmission mechanism, force sensor, replaceable pressing head and controller, and the pressing head end surface material is excellent glue, conductive foam or touch pen head.The method includes: pre-pressing stage is automatically identified according to the force-displacement curve feature pressing head material;According to the identification result, load corresponding FOC current loop parameters, pressing force PID parameters and deformation compensation function;When formal pressing, adopt outer ring pressing force PID and inner ring FOC current loop cascade control, real-time monitoring compression, using the compensation function matched with material to revise torque command, eliminate the non-linear error of force transmission caused by pressing head deformation.The present application realizes the adaptive identification of pressing head material and the accurate control of pressing force, and the pressing force precision is high, head replacement does not need manual debugging, and is suitable for key test, touch screen click and other scenes.

Description

Technical Field

[0001] This invention relates to the field of motor control and precision pressing test technology, and in particular to a stepper motor adaptive pressing pressure control device and its control method. Background Technology

[0002] Stepper motors are widely used in pressing scenarios such as button testing and haptic feedback testing due to their low cost and high positioning accuracy. Traditional stepper motors use pulse / direction open-loop control, which has problems such as large vibration at low speeds, high noise, rapid torque decay at high speeds, and easy step loss, which seriously affect the accuracy and stability of pressing force control.

[0003] In existing technologies, some pressing devices use servo motors in conjunction with force sensors to achieve closed-loop force control, but servo systems are costly and bulky. Furthermore, the material of the pressing head directly affects the force transmission characteristics: rigid contacts cannot simulate the smoothness of real finger pressure, while elastic pressing heads (such as urethane, conductive foam, and stylus tips) undergo non-linear deformation during pressing, leading to a deviation between the force sensor reading and the actual applied force. The deformation characteristics of different materials vary significantly, requiring readjustment of control parameters after replacing the pressing head, and lacking adaptive capability.

[0004] Currently, FOC control of stepper motors is mainly applied to speed and position control, lacking closed-loop control of pressing force, and does not consider the nonlinear effects caused by the deformation of pressing heads made of different materials, making it impossible to achieve parameter adaptation after pressing head replacement. Summary of the Invention

[0005] The purpose of this invention is to provide a stepper motor adaptive pressing pressure control device to solve the following problems in existing stepper motor pressing devices: 1. Traditional open-loop control leads to large low-speed vibration and low pressing pressure control accuracy; 2. Different materials of pressing heads (urethane, conductive foam, stylus tip) have significantly different deformation characteristics, resulting in nonlinear force transmission and requiring manual readjustment of parameters after replacement; 3. Lack of real-time compensation for pressing head deformation leads to large pressing pressure control errors.

[0006] The technical solution of this invention is implemented as follows: On one hand, this application provides a stepper motor adaptive pressing pressure control device, including a stepper motor, a transmission mechanism connected to the output end of the stepper motor, an upper slider connected to the transmission mechanism, a lower slider connected to the bottom of the upper slider, and a pressing head disposed at the bottom of the lower slider. The connection between the upper slider and the lower slider is provided with a force sensor, the upper slider and the lower slider are disposed on the same vertical guide rail, and the top of the stepper motor is provided with a controller.

[0007] Optionally, the stepper motor is a two-phase hybrid stepper motor with a step angle of 1.8° and a rated current of 0.5A. It adopts a fixed-shaft lead screw motor structure to convert rotary motion into linear motion. Optionally, the controller uses an STM32G431 microcontroller, which integrates an FOC control algorithm, an angle detection and processing unit, a pressure detection unit, a pressure PID adjustment module, and a material recognition module. It also integrates a dual H-bridge power stage and its drive and current sampling circuits to directly output PWM signals to drive the stepper motor.

[0008] Optionally, the force sensor is an S-type tension / compression sensor with a range of 0-1kg and an accuracy of 0.1%FS, used to detect the pressing force between the pressing head and the object being tested in real time.

[0009] Optionally, a sensor baffle is provided on the side wall of the upper slider, and a photoelectric sensor is provided on the back of the vertical guide rail. The sensor baffle and the photoelectric sensor form an origin detection component for detecting the origin position of the motor and returning to the origin. When the upper slider moves to the origin position, the sensor baffle inserts into the U-shaped groove of the photoelectric sensor and blocks its light path. The photoelectric sensor outputs a level transition signal to the controller. The controller confirms the mechanical origin position of the motor based on the signal. After power-on or receiving a zero-return command, the controller controls the motor to drive the upper slider to move towards the photoelectric sensor. When the sensor baffle blocks the light path, the controller receives a trigger signal and controls the motor to stop, completing the origin return.

[0010] Optionally, the top of the upper slider is connected to a transmission mechanism for connecting the rotating shaft of the stepper motor, and the bottom is used to fix the S-shaped force sensor and move up and down along the vertical guide rail; The lower slider is mounted on a vertical guide rail, and a pressing head is provided at the bottom of the lower slider. The top of the lower slider is connected to the bottom of an S-shaped force sensor via a height-equalizing screw.

[0011] Optionally, the pressing head can be replaced with different end faces of different materials according to testing requirements. The different end faces of different materials include urethane, conductive foam or stylus tip.

[0012] On the other hand, embodiments of this application provide a control method for a stepper motor adaptive pressing pressure control device, the method comprising: Pre-compression stage: Control the stepper motor to drive the pressing head movement, and identify the pressing head material based on the force-displacement curve characteristics; Parameter loading: Based on the identified material, load the corresponding FOC current loop parameters, pressure PID parameters, and deformation compensation function; Formal pressing: The outer loop pressing force PID and the inner loop FOC current loop are cascaded control. The outer loop calculates the target torque based on the error between the target pressing force and the force feedback value, and the inner loop FOC controls the stepper motor to output the torque. Deformation compensation: The compression amount of the press head is monitored in real time, and the target torque is corrected using the compensation function to compensate for the nonlinear error in force transmission caused by the deformation of the press head.

[0013] Optionally, the pressing head is made of urethane, conductive foam, or a stylus tip; The compensation function is a linear function for urethane, a piecewise linear function for conductive foam, and an exponential function for the stylus tip.

[0014] Optionally, during the pre-compression stage, the stepper motor is controlled to press down at 0.2~1 mm / s, and when the detected pressure value is greater than or equal to the contact force threshold, the current position is recorded as the zero point of compression, and the force-displacement curve is recorded. The average slope K of the elastic deformation stage and / or whether the curve has a compaction inflection point are extracted based on the force-displacement curve. If the average slope K is greater than the preset threshold, the material of the pressing head is determined to be urethane, and a linear compensation function is applied. If the average slope K is less than or equal to the preset threshold, and the force-displacement curve has a compaction inflection point, then the pressing head material is determined to be conductive foam, and a piecewise linear compensation function is applied. If the average slope K is less than or equal to the preset threshold and the force-displacement curve does not have a compaction inflection point, then the pressure head material is determined to be a touch pen tip, and an exponential compensation function is applied. During the parameter loading stage, based on the identified material type, the corresponding control parameters are loaded from the preset parameter group. The control parameters include FOC current loop bandwidth, torque limit value, pressure PID controller parameters and deformation compensation function parameters. The pressure PID controller parameters are the proportional coefficient, integral coefficient, integral separation threshold and output limit value of the pressure PID controller. During the formal pressing phase, a cascade control structure of outer loop pressing force PID and inner loop FOC current loop is adopted. The outer loop calculates the target torque command based on the error between the target pressing force and the feedback value from the force sensor using PID, and performs integral separation and output limiting based on the material parameters. The inner loop receives the target torque command from the FOC current loop, decomposes the quadrature axis component Iq and the direct axis component Id through Clark transformation and Park transformation, controls Id=0, adjusts Iq to track the target torque, and generates an SVPWM signal to drive the stepper motor. During the deformation compensation stage, the compression amount Δx of the pressing head is monitored in real time, and the target torque command is corrected according to the compensation function corresponding to the current material. For urethane adhesive, a linear compensation function is used: ΔT = a·Δx; For conductive foam, a piecewise linear compensation function is used to distinguish between the initial segment and the compacted segment; For the stylus tip (silicone), an exponential compensation function is used: ΔT = b·(e^{c·Δx} - 1); The compensated torque command is sent into the FOC current loop; Once the force sensor reading enters the target pressing pressure range and remains stable for a time T, the current torque output is maintained until a withdrawal command is received.

[0015] The beneficial effects of this invention are: High-precision pressing force control: FOC control eliminates low-speed vibration and noise from the stepper motor, and combined with a pressing force closed loop, achieves high-precision pressing force control. Furthermore, through low-friction transmission design and precision lubrication measures, the interference of friction on force control accuracy is effectively suppressed.

[0016] Material self-adaptation: Automatically identifies three common press head materials: urethane, conductive foam, and stylus tip, eliminating the need for manual parameter adjustment when changing heads.

[0017] Precise Deformation Compensation: A dedicated compensation model is established for the nonlinear deformation characteristics of press heads made of different materials, which greatly improves the accuracy of actual pressing force.

[0018] Wide applicability: It can be applied to scenarios such as smart glasses button testing, mobile phone button testing, touch screen click testing, and medical device button fatigue testing. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a stepper motor adaptive pressing pressure control device. Figure 2 This is a schematic diagram of the control method for an adaptive pressing control device for a stepper motor.

[0021] Icon labels: 1-Stepper motor; 2-Transmission mechanism; 3-Controller; 4-Pressing head; 5-Force sensor; 6-Sensor baffle; 7-Photoelectric sensor; 8-Lower slider; 9-Upper slider. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0024] Example 1: like Figure 1 As shown, this embodiment provides a stepper motor adaptive pressing pressure control device, including a stepper motor 1, a transmission mechanism 2 connected to the output end of the stepper motor 1, an upper slider 9 connected to the transmission mechanism 2, a lower slider 8 connected to the bottom of the upper slider 9, and a pressing head 4 disposed at the bottom of the lower slider 8. The pressing head 4 can be replaced with different material end faces according to testing requirements. The different material end faces include urethane, conductive foam, or stylus tip. The connection part between the upper slider 9 and the lower slider 8 is provided with a force sensor 5. The upper slider 9 and the lower slider 8 are disposed on the same vertical guide rail. The top of the stepper motor 1 is provided with a controller 3. The stepper motor 1 is a two-phase hybrid stepper motor with a step angle of 1.8° and a rated current of 0.5A. It adopts a fixed-shaft lead screw motor structure to convert rotary motion into linear motion. The transmission mechanism 2 includes a lead screw and a precision linear guide rail, which realizes the conversion of the motor's rotational motion into linear pressing motion, and ensures smooth motion and reduces lateral force interference. At the same time, by selecting low-friction guide rails and precision lubrication, the influence of sliding friction on the force detection accuracy is reduced.

[0025] The controller 3 uses an STM32G431 microcontroller, which integrates an FOC control algorithm, an angle detection and processing unit for magnetic encoder signal processing to obtain rotor angle, a pressure detection unit for force sensor signal acquisition, filtering, calibration and contact detection, a pressure PID adjustment module and a material identification module, and integrates a dual H-bridge power stage and its drive and current sampling circuits to directly output PWM signals to drive the stepper motor. The force sensor 5 is an S-type tension / compression sensor with a range of 0-1kg and an accuracy of 0.1%FS. It is used to detect the pressing force between the pressing head and the object being tested in real time. The top of the upper slider 9 is connected to the transmission mechanism 2 for connecting the rotating shaft of the stepper motor, and the bottom is used to fix the S-type force sensor 5 and move up and down along the vertical guide rail. The lower slider 8 is located on the vertical guide rail. The bottom of the lower slider 8 is provided with a pressing head 4, and the top of the lower slider 8 is connected to the bottom of the S-type force sensor 5 through a height-equalizing screw.

[0026] Secondly, a sensor baffle 6 is provided on the side wall of the upper slider 9, and a photoelectric sensor 7 is provided on the back of the vertical guide rail. The sensor baffle 6 and the photoelectric sensor 7 form an origin detection assembly for detecting the origin position of the motor and returning to the origin. When the upper slider 9 moves to the origin position, the sensor baffle 6 inserts into the U-shaped groove of the photoelectric sensor 7 and blocks its light path. The photoelectric sensor 7 outputs a level transition signal to the controller 3. The controller 3 confirms the mechanical origin position of the motor 1 based on this signal. After power-on or receiving a zero-return command, the controller 3 controls the motor 1 to drive the upper slider 9 to move towards the photoelectric sensor 7. When the sensor baffle 6 blocks the light path, the controller 3 receives a trigger signal and controls the motor 1 to stop, completing the origin return.

[0027] Example 2: This embodiment, based on Embodiment 1, provides a control method for a stepper motor adaptive pressing pressure control device, the method comprising: Pre-compression stage: Control the stepper motor to drive the pressing head movement, and identify the pressing head material based on the force-displacement curve characteristics; Parameter loading: Based on the identified material, load the corresponding FOC current loop parameters, pressure PID parameters, and deformation compensation function; Formal pressing: The outer loop pressing force PID and the inner loop FOC current loop are cascaded control. The outer loop calculates the target torque based on the error between the target pressing force and the force feedback value, and the inner loop FOC controls the stepper motor to output the torque. Deformation compensation: The compression amount of the press head is monitored in real time, and the target torque is corrected using the compensation function to compensate for the nonlinear error in force transmission caused by the deformation of the press head.

[0028] The pressing head is made of urethane, conductive foam, or a stylus tip; the compensation function is a linear function for urethane, a piecewise linear function for conductive foam, and an exponential function for the stylus tip.

[0029] Example 3: like Figure 2 As shown, this embodiment is based on Embodiment 2 and is used to further illustrate the specific implementation of the above control method: During the pre-compression stage, the stepper motor is controlled to press down at 0.2~1 mm / s. When the detected pressure value is greater than or equal to the contact force threshold, the current position is recorded as the zero point of compression, and the force-displacement curve is recorded. The average slope K of the elastic deformation stage and / or whether the curve has a compaction inflection point are extracted based on the force-displacement curve. If the average slope K is greater than the preset threshold, the material of the pressing head is determined to be urethane, and a linear compensation function is applied. If the average slope K is less than or equal to the preset threshold, and the force-displacement curve has a compaction inflection point, then the pressing head material is determined to be conductive foam, and a piecewise linear compensation function is applied. If the average slope K is less than or equal to the preset threshold and the force-displacement curve does not have a compaction inflection point, then the pressure head material is determined to be a touch pen tip, and an exponential compensation function is applied. During the parameter loading stage, based on the identified material type, the corresponding control parameters are loaded from the preset parameter group. The control parameters include FOC current loop bandwidth, torque limit value, pressure PID controller parameters and deformation compensation function parameters. The pressure PID controller parameters are the proportional coefficient, integral coefficient, integral separation threshold and output limit value of the pressure PID controller. During the formal pressing phase, a cascade control structure of outer loop pressing force PID and inner loop FOC current loop is adopted. The outer loop calculates the target torque command based on the error between the target pressing force and the feedback value from the force sensor using PID, and performs integral separation and output limiting based on the material parameters. The inner loop receives the target torque command from the FOC current loop, decomposes the quadrature axis component Iq and the direct axis component Id through Clark transformation and Park transformation, controls Id=0, adjusts Iq to track the target torque, and generates an SVPWM signal to drive the stepper motor. During the deformation compensation stage, the compression amount Δx of the pressing head is monitored in real time, and the target torque command is corrected according to the compensation function corresponding to the current material. For urethane adhesive, a linear compensation function is used: ΔT = a·Δx; For conductive foam, a piecewise linear compensation function is used to distinguish between the initial segment and the compacted segment; For the stylus tip (silicone), an exponential compensation function is used: ΔT = b·(e^{c·Δx} - 1); The compensated torque command is sent into the FOC current loop; Once the force sensor reading enters the target pressing pressure range and remains stable for a time T, the current torque output is maintained until a withdrawal command is received.

[0030] The stepper motor adaptive pressing pressure control device and control method based on this embodiment have the following beneficial effects: High-precision pressing force control: FOC control eliminates low-speed vibration and noise from the stepper motor, and combined with a pressing force closed loop, achieves high-precision pressing force control. Furthermore, through low-friction transmission design and precision lubrication measures, the interference of friction on force control accuracy is effectively suppressed.

[0031] Material self-adaptation: Automatically identifies three common press head materials: urethane, conductive foam, and stylus tip, eliminating the need for manual parameter adjustment when changing heads.

[0032] Precise Deformation Compensation: A dedicated compensation model is established for the nonlinear deformation characteristics of press heads made of different materials, which greatly improves the accuracy of actual pressing force.

[0033] Wide applicability: It can be applied to scenarios such as smart glasses button testing, mobile phone button testing, touch screen click testing, and medical device button fatigue testing.

[0034] Example 4: like Figure 2 As shown, the controller controls the stepper motor to press down at 0.5 mm / s, sampling the force sensor at 1 kHz. When the force value first exceeds 0.05 N, contact is determined, the current position is recorded as the zero point of compression, and force-displacement data is recorded. From the zero point, the compression continues to 1.5 mm, and the average slope K of the elastic segment with good linearity in the force-displacement curve (such as 0.2~0.8 mm after the zero point) is extracted. Based on this, the material type is identified (K>5 N / mm and no inflection point: urethane; K≤5 N / mm and inflection point: conductive foam; K≤5 N / mm and no inflection point, exponential increase: stylus tip). Based on the identification results, the corresponding FOC current loop parameters, pressing pressure PID parameters, and deformation compensation function are loaded. During actual pressing, the outer loop pressing pressure PID calculates the target torque based on the force error, calculates the compression amount Δx based on the motor position and the zero point, and corrects the torque using the compensation function. The inner loop FOC controls the stepper motor to output torque. When the force error is less than the allowable deviation and stabilizes for a preset time, the force output is maintained until a withdrawal command is received.

[0035] Material identification (urethane press head): The pre-compression speed was 0.5 mm / s, the stroke was 1.5 mm, and the force-displacement data were recorded. A linear fit was performed on the 0.2~0.8 mm segment, and the average slope of the elastic segment was calculated to be K = 12.3 N / mm. Since K is greater than the preset threshold (5 N / mm in this embodiment), and the curve has no obvious compaction inflection point, it is determined to be urethane adhesive.

[0036] Parameter loading: Utility rubber parameter set: FOC current loop bandwidth 2000 rad / s; torque limit 0.3 Nm; pressure PID: Kp=0.8, Ki=0.2; integral separation off; output limit ±0.1 mm; linear compensation coefficient a = 0.05 N·m / mm (i.e. ΔT= a·Δx).

[0037] Force control and compensation: The target force is 5N. The outer loop uses a pressure-based PID controller to calculate the target torque every 1ms. Simultaneously, it calculates the current compression amount Δx based on the stepper motor angle and lead screw lead, and calculates the torque correction using ΔT = a·Δx. These values ​​are then summed and fed into the FOC inner loop. By implementing force-based closed-loop control using these parameters, high-precision pressure-based control can be achieved. Material identification (conductive foam press head): The conductive foam has a density of 120 kg / m³ and a thickness of 5 mm. The pre-compression speed is 0.5 mm / s, the stroke is 1.5 mm, and force-displacement data are recorded. The average slope of the elastic segment is calculated to be K = 2.8 N / mm, which is less than the preset threshold (5 N / mm). Further inspection of the curve shape reveals a clear compaction inflection point (the slope changes from gentle to steep) at a displacement of approximately 0.8 mm, confirming it as conductive foam.

[0038] Parameter loading: Conductive foam parameter set: FOC bandwidth 800 rad / s; torque limit 0.15 Nm; pressure PID: Kp=0.3, Ki=0.08; integral separation threshold 0.2N; output limit ±0.3 mm; piecewise linear compensation function (coefficients are all in N·m / mm): When Δx<1 mm, ΔT =0.02 N·m / mm·Δx; When Δx ≥ 1 mm, ΔT =0.05 N·m / mm·Δx + 0.03 N·m.

[0039] Force control and compensation: By implementing closed-loop force control using the above parameters and compensation function, the steady-state pressing force error is significantly reduced, meeting the requirements for precision pressing tests.

[0040] Material recognition (touch pen tip / press head): The stylus tip is made of silicone, hemispherical, with a hardness of 20 Shore A. The pre-compression speed is 0.5 mm / s, the stroke is 1.5 mm, and force-displacement data is recorded. The average slope of the elastic segment is calculated to be K = 2.0 N / mm, which is less than the preset threshold. The curve exhibits a smooth exponential increase characteristic, with no compaction inflection point (the second derivative is always positive and gradually increases), based on which it is determined to be a stylus tip.

[0041] Parameter loading: Stylus tip parameter set: FOC bandwidth 1200 rad / s; torque limit 0.2 Nm; pressure PID: Kp=0.5, Ki=0.12; exponential compensation function: ΔT =0.1 N·m·(e^{0.8·Δx} - 1), where 0.8 is a dimensionless coefficient.

[0042] Force control and compensation: Force closed-loop control using the above parameters and compensation function can achieve good force tracking effect, and the control accuracy meets the application requirements. Comparison of effects: Under the same test conditions (target force 5N, pressing speed 0.5mm / s), the force error is large without compensation, but the force error is significantly reduced after compensation. Without material recognition, replacing the pressing head requires manual readjustment of parameters, which takes a long time. This solution automatically recognizes and loads parameters, which takes very little time.

[0043] The stepper motor adaptive pressing pressure control device and its control method described in this embodiment can be integrated into scenarios such as button feel testers, automatic touch screen clicking devices, AI smart glasses button testing, and medical device button life testing machines. This invention can adapt to different pressing head materials, achieving precise and stable pressing pressure control. Head replacement requires no manual adjustment, significantly improving testing efficiency. With its low-cost solution of a stepper motor and FOC (Focused Controlled Press) system, it has high industrial practical value and economic efficiency.

[0044] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A stepper motor adaptive pressing pressure control device, characterized in that, It includes a stepper motor (1), a transmission mechanism (2) connected to the output end of the stepper motor (1), an upper slider (9) connected to the transmission mechanism (2), a lower slider (8) connected to the bottom of the upper slider (9), and a pressing head (4) provided at the bottom of the lower slider (8). The connection between the upper slider (9) and the lower slider (8) is provided with a force sensor (5). The upper slider (9) and the lower slider (8) are provided on the same vertical guide rail. The top of the stepper motor (1) is provided with a controller (3).

2. The stepper motor adaptive pressing pressure control device according to claim 1, characterized in that, The stepper motor (1) is a two-phase hybrid stepper motor with a step angle of 1.8° and a rated current of 0.5A. It adopts a fixed-shaft screw motor structure to convert rotary motion into linear motion.

3. The stepper motor adaptive pressing pressure control device according to claim 1, characterized in that, The controller (3) adopts an STM32G431 microcontroller, which integrates an FOC control algorithm, an angle detection and processing unit, a pressure detection unit, a pressure PID adjustment module and a material identification module, and integrates a dual H-bridge power stage and its drive and current sampling circuits to directly output PWM signals to drive the stepper motor.

4. The stepper motor adaptive pressing pressure control device according to claim 1, characterized in that, The force sensor (5) is an S-type tension and compression sensor with a range of 0-1kg and an accuracy of 0.1%FS. It is used to detect the pressing force between the pressing head and the object being tested in real time.

5. The stepper motor adaptive pressing pressure control device according to claim 1, characterized in that, The upper slider (9) is provided with a sensor baffle (6) on its side wall, and a photoelectric sensor (7) is provided on the back of the vertical guide rail. The sensor baffle (6) and the photoelectric sensor (7) form an origin detection component for detecting the origin position of the motor and returning to the origin. The implementation method is as follows: the sensor baffle (6) moves synchronously with the upper slider (9). When the upper slider (9) moves to the origin position, the sensor baffle (6) blocks the detection light path of the photoelectric sensor (7). After receiving the blocking signal, the controller (3) confirms that the motor (1) is at the origin position and completes the origin return.

6. The stepper motor adaptive pressing pressure control device according to claim 4, characterized in that, The top of the upper slider (9) is connected to the transmission mechanism (2) for connecting the rotating shaft of the stepper motor, and the bottom is used to fix the S-shaped force sensor (5) and move up and down along the vertical guide rail; The lower slider (8) is mounted on a vertical guide rail. The bottom of the lower slider (8) is provided with a pressing head (4). The top of the lower slider (8) is connected to the bottom of the S-shaped force sensor (5) through a height-equalizing screw.

7. The stepper motor adaptive pressing pressure control device according to claim 1, characterized in that, The pressing head (4) can be replaced with different material end faces according to the test requirements. The different material end faces include urethane, conductive foam or stylus tip.

8. A control method for a stepper motor adaptive pressing pressure control device according to any one of claims 1-7, characterized in that, The method includes: Pre-compression stage: Control the stepper motor to drive the pressing head movement, and identify the pressing head material based on the force-displacement curve characteristics; Parameter loading: Based on the identified material, load the corresponding FOC current loop parameters, pressure PID parameters, and deformation compensation function; Formal pressing: The outer loop pressing force PID and the inner loop FOC current loop are cascaded control. The outer loop calculates the target torque based on the error between the target pressing force and the force feedback value, and the inner loop FOC controls the stepper motor to output the torque. Deformation compensation: The compression amount of the press head is monitored in real time, and the target torque is corrected using the compensation function to compensate for the nonlinear error in force transmission caused by the deformation of the press head.

9. The control method according to claim 8, characterized in that, The pressing head is made of urethane, conductive foam, or a stylus tip. The compensation function is a linear function for urethane, a piecewise linear function for conductive foam, and an exponential function for the stylus tip.

10. The control method according to claim 7, characterized in that, During the pre-compression stage, the stepper motor is controlled to press down at 0.2~1mm / s. When the detected pressure value is greater than or equal to the contact force threshold, the current position is recorded as the zero point of compression, and the force-displacement curve is recorded. The average slope K of the elastic deformation stage and / or whether the curve has a compaction inflection point are extracted based on the force-displacement curve. If the average slope K is greater than the preset threshold, the material of the pressing head is determined to be urethane, and a linear compensation function is applied. If the average slope K is less than or equal to the preset threshold, and the force-displacement curve has a compaction inflection point, then the pressing head material is determined to be conductive foam, and a piecewise linear compensation function is applied. If the average slope K is less than or equal to the preset threshold and the force-displacement curve does not have a compaction inflection point, then the pressure head material is determined to be a touch pen tip, and an exponential compensation function is applied. During the parameter loading stage, based on the identified material type, the corresponding control parameters are loaded from the preset parameter group. The control parameters include FOC current loop bandwidth, torque limit value, pressure PID controller parameters and deformation compensation function parameters. The pressure PID controller parameters are the proportional coefficient, integral coefficient, integral separation threshold and output limit value of the pressure PID controller. During the formal pressing phase, a cascade control structure of outer loop pressing force PID and inner loop FOC current loop is adopted. The outer loop calculates the target torque command based on the error between the target pressing force and the feedback value from the force sensor using PID, and performs integral separation and output limiting based on the material parameters. The inner loop receives the target torque command from the FOC current loop, decomposes the quadrature axis component Iq and the direct axis component Id through Clark transformation and Park transformation, controls Id=0, adjusts Iq to track the target torque, and generates an SVPWM signal to drive the stepper motor. During the deformation compensation stage, the compression amount Δx of the pressing head is monitored in real time, and the target torque command is corrected according to the compensation function corresponding to the current material. For urethane adhesive, a linear compensation function is used: ΔT = a·Δx; For conductive foam, a piecewise linear compensation function is used to distinguish between the initial segment and the compacted segment; For the stylus tip (silicone), an exponential compensation function is used: ΔT = b·(e^{c·Δx} - 1); The compensated torque command is sent into the FOC current loop; Once the force sensor reading enters the target pressing pressure range and remains stable for a time T, the current torque output is maintained until a withdrawal command is received.

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