Ultrasonic spot welding machine based on stepper motor drive with controllable position and pressure

Abstract

The present invention discloses an ultrasonic spot welder driven by a stepper motor and capable of controlling position and pressure. The welder comprises a mechanical device and a control unit. The mechanical device includes a stepper motor with an encoder, a base plate, a gear, a rack, a guide rail, a slider, and a pressure rod. The guide rails are provided with limit blocks at both ends. The control unit includes a microcontroller and a stepper motor microstepping drive module. During the control process, the microcontroller sends corresponding pulses to the stepper motor microstepping drive module. The stepper motor microstepping drive module controls the rotation of the stepper motor spindle based on the received pulses, thereby controlling the pressure rod through transmission. The spot welder of the present invention can simultaneously achieve automatic welding position detection and precise position and pressure control, and has the advantages of simple structure, low cost, no need for an air source, and low noise.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic spot welding machines, and in particular relates to an ultrasonic spot welding machine driven by a stepping motor and having controllable position and pressure. Background Art

[0002] Ultrasonic spot welding is widely used for welding thermoplastic materials. Compared with traditional processes (such as gluing, electric ironing or screw fastening), it has significant advantages such as high production efficiency, good welding quality, environmental protection and energy saving. Common ultrasonic spot welding machine pressure rods are controlled by cylinders. Cylinder control can achieve basic pressure control, but it has many disadvantages: in addition to the disadvantages of requiring an air source and high operating noise, the cylinder, especially a small-diameter cylinder, is affected by variables such as air source pressure, ambient temperature, and humidity, and its characteristics vary greatly. It is difficult to stably control pressure and processing time, which seriously affects the quality of spot welding. For example, the Chinese patent application with publication number CN112756767A provides an ultrasonic spot welding machine that uses a cylinder, a grating scale and a pressure sensor to achieve position control and pressure control. However, it is difficult to achieve fast and accurate position and pressure control by controlling the cylinder through a pressure regulating valve, and it is difficult to meet the requirements of high speed and low impact.

[0003] The stepper motor is a commonly used actuator in the industrial field. It directly controls the rotation angle of the motor through the input electric pulse signal and is widely used in open-loop position control systems. In order to improve the position control accuracy, a low-cost encoder can be installed to achieve closed-loop position control of the stepper motor. Replacing the cylinder used for controlling the pressure rod of the existing ultrasonic spot welding machine with a stepper motor can easily achieve position control of the pressure rod, but the pressure control problem of the pressure rod still needs to be solved. For example, the Chinese patent application with publication number CN115415660A provides a servo motor loaded ultrasonic spot welding machine, which uses a servo motor, a grating scale and a pressure sensor to achieve position control and pressure control, but the use of a servo motor, its driver and a pressure sensor greatly increases the cost of the equipment.

[0004] Therefore, achieving precise position and pressure control simultaneously with a stepper motor control system without increasing hardware costs is a key technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] In view of the above, the present invention provides an ultrasonic spot welding machine driven by a stepper motor with controllable position and pressure, which can simultaneously achieve precise position and pressure control, and has the advantages of simple structure, low cost, no need for gas source, and low noise.

[0006] An ultrasonic spot welding machine driven by a stepper motor and with controllable position and pressure, consists of two parts: a mechanical device and a control unit. The mechanical device includes a stepper motor with an encoder, a base plate, a gear, a rack, a guide rail, a slider, and a pressure rod. Limit blocks are provided at both ends of the guide rail. The stepper motor and the guide rail are mounted and fixed on the base plate. The gear is fixed on the main shaft of the stepper motor. The slider is set on the guide rail. A connecting plate is fixed on the slider. The pressure rod is mounted on the bottom of the connecting plate. The rack is mounted on the side of the connecting plate and meshes with the gear. During operation, the main shaft of the stepper motor rotates and the slider slides on the guide rail through the above connection relationship, thereby driving the pressure rod to move up and down.

[0007] The control unit includes a microcontroller and a stepper motor micro-step drive module. After power-on, the microcontroller automatically detects and sets the reference point position and the working point position of the pressure rod through an initialization program. During normal operation, the position control mode is used to quickly move the pressure rod down to the working point position, and the pressure control mode is switched to perform spot welding processing. After the processing is completed, the position control mode is switched to quickly return the pressure rod to the reference point position. During the entire control process, the microcontroller sends corresponding pulses to the stepper motor micro-step drive module. The stepper motor micro-step drive module controls the rotation of the stepper motor spindle according to the received pulses, and controls the pressure rod through transmission.

[0008] Furthermore, in the position control mode, the microcontroller determines the pulse direction and calculates the total number of pulses required based on the current position and target position of the stepper motor rotor. Combined with the speed requirements, a pulse sequence is generated in an acceleration-constant speed-deceleration mode (by setting the number of pulses and pulse period in each stage), and these pulses are sent to the stepper motor microstep drive module in sequence to control the rotation of the stepper motor spindle so that the pressure rod reaches the target position.

[0009] Furthermore, the microcontroller needs to calculate the current misalignment angle of the stepper motor before sending each pulse. i ,like- i m ≤ i ≤ i m , then send the pulse normally; otherwise, postpone sending the pulse and try to send it again after a certain interval. i m = is the offset angle corresponding to the maximum output torque. This ensures that the stepper motor offset angle remains within a safe range, avoids step loss, and enables the stepper motor to achieve maximum output torque.

[0010] Furthermore, when the microcontroller has finished sending the pulse sequence, it starts the target position positioning mode and periodically compares the current position of the stepper motor rotor. D and target location D 1. IfD < D 1- e , the microcontroller sends a positive pulse to the stepper motor micro-step drive module; if D > D 1+ e , the microcontroller sends a reverse pulse to the stepper motor micro-step drive module; if D 1- e ≤ D ≤ D 1+ e , it means the positioning is successful and the target position is reached. e The allowable deviation of the set position.

[0011] Furthermore, the current position and target position of the stepper motor rotor are represented by an encoder in the form of pulse counts.

[0012] Furthermore, in the pressure control mode, the microcontroller regularly compares the current output torque of the stepper motor. T and target torque T 1. If T < T 1- s , the microcontroller sends a positive pulse to the stepper motor micro-step drive module; if T > T 1+ s , the microcontroller sends a reverse pulse to the stepper motor micro-step drive module; if T 1- s ≤ T ≤ T 1+ s , it means that the target pressure is reached. s The permissible deviation of the set torque.

[0013] Furthermore, the current output torque T and target torque T The calculation expression of 1 is as follows:

[0014]

[0015]

[0016] in: T max is the maximum output torque of the stepper motor at rated current, i m is the misalignment angle corresponding to the maximum output torque, i is the current offset angle of the stepper motor, r is the pitch circle radius of the gear, F 1 is the target pressure.

[0017] Furthermore, in the initialization program, the microcontroller uses the pressure control mode to send pulses to the stepper motor micro-step drive module, and the pressure rod is gradually moved upward by rotating the stepper motor main shaft. When the output torque of the stepper motor reaches the target torque, T 2. The slider is held by the limit block at the upper end of the guide rail. At this time, the current position of the stepper motor rotor plus an appropriate deviation is used as the reference point position of the pressure rod. Then the microcontroller also adopts the pressure control mode to rotate the stepper motor spindle to make the pressure rod gradually move downward. When the output torque of the stepper motor reaches the target torque, T At 3 o'clock, the pressure rod is supported by the workpiece to be spot welded. At this time, the current position of the stepper motor rotor minus the appropriate deviation amount is used as the pressure rod working point position.

[0018] Furthermore, the target torque T 2=- K 2× T max , target torque T 3= K 3× T max ,in K 2 and K 3 is the proportional coefficient set between 0 and 1.

[0019] Based on the above technical solution, the present invention has the following beneficial technical effects:

[0020] 1. The present invention can realize the precise control of the position, pressure and processing time of the ultrasonic spot welding machine pressure rod, greatly improving the processing quality and processing speed of ultrasonic spot welding.

[0021] 2. The spot welding machine of the present invention has a simple structure and low cost. Compared with the solution using a servo motor and a pressure sensor, the microcontroller, stepper motor micro-step control module and stepper motor with encoder used in the present invention are all widely used and low-cost products in the market.

[0022] 3. The spot welding machine of the present invention has an automatic detection function of the processing position and is easy to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of the mechanical device of the ultrasonic spot welding machine of the present invention, in which 1 is a base plate, 2 is a stepping motor with an encoder, 3 is a gear, 4 is a connecting plate, 5 is a rack, 6 is a slider, 7 is a guide rail, 8 is an upper limit block, 9 is a lower limit block, and 10 is a pressure rod.

[0024] Figure 2 Schematic diagram of the control flow of the microcontroller in the present invention. DETAILED DESCRIPTION

[0025] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1 As shown, the ultrasonic spot welding machine driven by a stepper motor and with controllable position and pressure of the present invention includes a mechanical device and a control unit. The mechanical device includes: a base plate 1, a stepper motor 2 with an encoder, a gear 3, a connecting plate 4, a rack 5, a slider 6, a guide rail 7, an upper limit block 8, a lower limit block 9, and a pressure rod 10; the control unit includes a microcontroller and a stepper motor micro-step drive module.

[0027] The stepper motor 2 is fixed on the base plate 1, the gear 3 is fixed on the main shaft of the stepper motor 2, the rack 5, the slider 6 and the pressure rod 10 are fixed on the connecting plate 4, the guide rail 7 is installed on the side of the base plate 1, and the upper limit block 8 and the lower limit block 9 are fixed on the guide rail 7.

[0028] Stepper motor 2 uses a two-phase hybrid stepper motor model 42BYG47-2004-M1000 with a step angle of 1.8 degrees ( i m =1.8 degrees), rated current 2A, maximum holding torque T max =0.5Nm, 1000-line encoder (two-phase quadrature mode 4000PPR).

[0029] Pitch circle radius of gear 3 r =10mm, maximum telescopic stroke of the robotic arm L =150mm;

[0030] The microcontroller model used is STM32F103VET6, the advanced timer TIM1 is configured in 16-bit quadrature encoder mode, the position register of TIM1 is TIM1_CNT, and the other timer TIM2 is configured in software timer mode to send pulse sequences in timed interrupt mode.

[0031] The stepper motor microstepping driver module uses the model TB6600, which is set to a constant current 1 / 16 microstepping function (64 beats / tooth, equivalent to 3200 pulses / turn of the motor), with an output current peak of 2A.

[0032] like Figure 2 As shown, in this embodiment, the microcontroller needs to complete the following initialization after power-on:

[0033] (1) Define the clockwise rotation direction of the motor as the positive direction, and the downward movement of the robot arm as the positive direction;

[0034] (2) Configure the advanced timer TIM1 to the orthogonal encoder mode, and the clockwise direction of the motor is the encoder positive counting direction;

[0035] (3) Configure timer TIM2 to software timer mode;

[0036] (4) Enable TB6600 output;

[0037] (5) Initialize the stepper motor rotor position angle i R and the electron current vector angle i I ;

[0038] At this time, the pressure rod has no load and the stepper motor is at a near zero torque output, and it can be initialized. i R = i I =0, the count value of the position register TIM 1_ CNT =0X8000, the specific calculation formula is as follows:

[0039]

[0040]

[0041] Where: Δ i i The motor stator current vector angle corresponding to the pulse command i I Change value, n is the number of pulses; i When it is a positive pulse command, Δ i i =360 / 3200; pulse i When it is a reverse pulse instruction, Δ i i =-360 / 3200.

[0042] In this embodiment, the maximum stroke of the pressure rod L =150mm, gear pitch circle radius r =10mm, so the range of the quadrature encoder timer count value within the full stroke is:

[0043]

[0044] TIM 1_ CNT After initialization, the value 0X8000 is guaranteed to be within the full range. TIM 1_ CNT The value is within the range of 16-bit unsigned number expression, which is convenient for processing.

[0045] (6) Automatically detect and set the pressure rod reference point P 0;

[0046] The microcontroller executes the stepper motor torque control program, and the TIM2 interrupt program (timed interrupt interval 0.1ms) calculates the current output torque. The specific calculation formula is as follows:

[0047]

[0048] if T <-0.75 T max , send a positive pulse command; if T >-0.65 T max , send reverse pulse command; until -0.75 T max ≤ T ≤-0.65 T max , the stepper motor reaches the target torque and the pressure rod reaches the upper limit position.

[0049] Distance below the upper limit L 0=1mm is set as the reference point P 0, the specific calculation formula is as follows:

[0050]

[0051] (7) Automatically detect and set the working point position P 1 (judgment basis is that the downward resistance of the pressure rod reaches 0.7 T max );

[0052] The microcontroller executes the stepper motor torque control program and sets the target torque T 1=0.7 T max , the pressure rod moves downward to the working limit point (i.e. it contacts the workpiece to be spot welded) and moves at a distance above the working limit point. L 1=0.5mm is set as the working point, and the specific calculation formula is as follows:

[0053]

[0054] (8) Return to the reference point P 0;

[0055] The microcontroller executes the stepper motor position control mode and calculates the target position. The specific calculation formula is as follows:

[0056]

[0057] Calculate the number of pulses required to reach the target position from the current position N =( TIM 1_ CNT - P 0)×3200 / 4000, combined with the speed requirements, calculate the pulse sequence data (including the total number of pulses in each stage of acceleration, constant speed, and deceleration and the period of each pulse) according to the acceleration-constant speed-deceleration mode, start the TIM2 timer interrupt, and send these pulses to the stepper motor micro-step drive module in sequence to control the stepper motor rotation and drive the pressure rod to reach the target position.

[0058] Before each pulse is sent, the microcontroller calculates the current offset angle of the stepper motor i = i I(n) - i R ,if- i m ≤ i ≤ i m , send the pulse normally; otherwise, postpone sending the pulse and try again when the next interruption occurs.

[0059] After all pulse sequences have been sent, the control system enters the target position positioning process. The specific process is as follows:

[0060] if TIM 1_ CNT < TIM 1_ CNT 1-2, send forward pulse command;

[0061] if TIM 1_ CNT > TIM 1_ CNT 1+2, send reverse pulse command;

[0062] if TIM 1_ CNT 1-2≤ TIM 1_ CNT ≤ TIM 1_ CNT 1+2, the stepper motor reaches the target position and the positioning action is completed.

[0063] After initialization, the ultrasonic spot welding machine pressure rod control system enters the normal working mode. After receiving the working instruction, the stepper motor enters the position control mode and quickly moves down to the working point position. P 1; Arrive at the working point P 1 After that, the stepper motor enters the torque control mode, and the target torque T 1= F 1 / r (r is the gear pitch circle radius, F 1 is the target pressure); after reaching the target pressure, the processing time countdown begins. When the countdown ends, the stepper motor enters the position control mode and quickly returns to the pressure rod reference point. P 0, one job is completed.

[0064] In summary, the ultrasonic spot welding machine driven by a stepper motor and with controllable position and pressure can realize automatic detection of welding position, controllable welding pressure, and controllable welding time.

[0065] The above description of the embodiments is intended to facilitate understanding and application of the present invention by those skilled in the art. It is apparent that those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without requiring creative effort. Therefore, the present invention is not limited to the above embodiments. Any improvements or modifications made by those skilled in the art based on the disclosure of the present invention should fall within the scope of protection of the present invention.

Claims

1. An ultrasonic spot welder driven by a stepper motor with controllable position and pressure, consisting of a mechanical device and a control unit, characterized by: The mechanical device includes a stepper motor with an encoder, a base plate, a gear, a rack, a guide rail, a slider and a pressure rod. Limit blocks are provided at both ends of the guide rail. The stepper motor and the guide rail are mounted and fixed on the base plate. The gear is fixed on the main shaft of the stepper motor. The slider is arranged on the guide rail. A connecting plate is fixed on the slider. The pressure rod is mounted on the bottom of the connecting plate. The rack is mounted on the side of the connecting plate and meshes with the gear. When working, the main shaft of the stepper motor rotates and the slider slides on the guide rail through the above connection relationship, thereby driving the pressure rod to move up and down. The control unit includes a microcontroller and a stepper motor micro-step driving module. The microcontroller automatically detects and sets the reference point position and the working point position of the pressure rod through an initialization program after power-on. During normal operation, the pressure rod is quickly moved down to the working point position through the position control mode, and the pressure control mode is switched to perform spot welding processing. After the processing is completed, the position control mode is switched to enable the pressure rod to quickly return to the reference point position. During the entire control process, the microcontroller sends corresponding pulses to the stepper motor micro-step driving module. The stepper motor micro-step driving module controls the rotation of the stepper motor spindle according to the received pulses, thereby realizing control of the pressure rod through transmission. In the position control mode, the microcontroller determines the pulse direction and calculates the total number of pulses required based on the current position and target position of the stepper motor rotor. In combination with the speed requirement, the microcontroller generates a pulse sequence in an acceleration-constant speed-deceleration mode and sends these pulses in sequence to the stepper motor microstepping drive module to control the stepper motor spindle to rotate so that the pressure rod reaches the target position. The microcontroller needs to calculate the current offset angle of the stepper motor before sending each pulse. θ ,like- θ m ≤ θ ≤ θ m , then the pulse is sent normally; Otherwise, postpone sending this pulse and try to send it again after a certain period of time. θ m is the misalignment angle corresponding to the maximum output torque; When the microcontroller has sent all the pulse sequences, it starts the target position positioning mode and periodically compares the current position of the stepper motor rotor. D and target location D 1. If D < D 1- ε , the microcontroller sends a positive pulse to the stepper motor micro-step drive module; if D > D 1+ ε , the microcontroller sends a reverse pulse to the stepper motor microstep drive module; like D 1- ε ≤ D ≤ D 1+ ε , it means the positioning is successful and the target position is reached. ε The allowable deviation of the set position; In the pressure control mode, the microcontroller regularly compares the current output torque of the stepper motor T and target torque T 1. If T < T 1- σ , the microcontroller sends a positive pulse to the stepper motor micro-step drive module; if T > T 1+ σ , the microcontroller sends a reverse pulse to the stepper motor micro-step drive module; if T 1- σ ≤ T ≤ T 1+ σ , it means that the target pressure is reached. σ is the set torque allowable deviation; In the initialization program, the microcontroller uses the pressure control mode to send pulses to the stepper motor micro-step drive module, and the pressure rod is gradually moved upward by rotating the stepper motor main shaft. When the output torque of the stepper motor reaches the target torque, T 2. The slider is held by the limit block at the upper end of the guide rail. At this time, the current position of the stepper motor rotor plus an appropriate deviation is used as the reference point position of the pressure rod. Then the microcontroller also adopts the pressure control mode to rotate the stepper motor spindle to make the pressure rod gradually move downward. When the output torque of the stepper motor reaches the target torque, T At 3 o'clock, the pressure rod is supported by the workpiece to be spot welded. At this time, the current position of the stepper motor rotor minus the appropriate deviation amount is used as the pressure rod working point position.

2. The ultrasonic spot welding machine driven by a stepper motor and with controllable position and pressure according to claim 1, characterized in that: The current position and target position of the stepper motor rotor are represented by an encoder in the form of pulse counts.

3. The ultrasonic spot welding machine driven by a stepper motor and with controllable position and pressure according to claim 1, characterized in that: The current output torque T and target torque T The calculation expression of 1 is as follows: ; ; in: T max is the maximum output torque of the stepper motor at rated current, θ m is the misalignment angle corresponding to the maximum output torque, θ is the current misalignment angle of the stepper motor, r is the pitch circle radius of the gear, F 1 is the target pressure.

4. The ultrasonic spot welding machine driven by a stepper motor and with controllable position and pressure according to claim 3, characterized in that: The target torque T 2=- K 2× T max , target torque T 3= K 3× T max ,in K 2 and K 3 is the proportional coefficient set between 0 and 1.

Images