Abstract : Based on the analysis of the structure, working mechanism, and performance of a linear motor driven stamping press, a system identification device for this press was designed. This device can be used to analyze the relationship between linear motor parameters and transient impact force, thus providing a basis for the optimized design and control of the linear motor stamping press. Keywords : Linear motor; Electromagnetic stamping press; System identification 1 Introduction The novel electromagnetic stamping press (linear motor punch press) utilizes linear motor technology to directly convert electrical energy into mechanical force, realizing the reciprocating motion of the punch. However, linear motor-driven stamping presses also have many problems in practical applications, such as: ① When the stamping press is randomly triggered (i.e., the initial closing angle is uncertain), the transient impact force varies greatly, sometimes even by several times; ② When the conduction time of the stamping press is too long, the motor remains in the conducting state after generating an effective transient impact force. At this time, the motor is in a stalled state, and the effective value of the current in the motor increases rapidly, causing the motor temperature to rise too quickly and reducing the motor's performance. When the conduction time is too short, the stroke of the stamping press is very short, and the transient impact force it generates is very small, sometimes even failing to contact the die. This causes the stamping press to work abnormally. Therefore, it is necessary to develop an identification device for linear motor stamping presses to find the trigger angle and conduction time at the maximum transient impact force, and obtain the system control model through identification analysis experiments. [b]2 Identification Device System Design 2.1 Identification Device System Structure[/b] The identification system for the impact force of a linear motor-driven stamping press mainly consists of three parts: a control system, a linear motor-driven stamping press, and a testing and analysis system. The control system mainly includes an 89C51 microcontroller system and an amplification and drive section; the testing and analysis system mainly includes a force sensor, an acceleration sensor, a charge amplifier, a strain amplifier, an A/D acquisition card, an industrial computer, and a CRAS signal testing and analysis system. The system structure diagram of the identification device is shown in Figure 1. 2.2 Control System Saddle Component Design The control circuit is required to implement the following functions in software: ① For each input data, it should be able to determine whether it is within the correct range and provide a prompt to the user; ② Convert the input frequency into a period, calculate the linear motor de-energizing time based on the conduction time, and determine whether it is within the correct range; ③ When the upper and lower limits of the initial closing angle are not equal, the initial closing angle should be increased incrementally with each press, and when it reaches the upper limit, it should start from the lower limit again; ④ The given gate angle should be accurate to the degree; ⑤ During operation, the press can be terminated by pressing a button. The program flowchart is shown in Figure 2. The program consists of a variable initialization module, a keyboard query module, a main module, and a software trap module . 2.3 Control System Hardware Design The principle block diagram of the control circuit is shown in Figure 3. Take any phase of the three-phase voltage of the linear motor (taking phase A as an example), first step down the voltage, then pass it through a comparator to convert the sine wave into a square wave, and then through an optocoupler to convert the analog signal into a digital signal, which is then sent to the microcontroller. After receiving the working signal, the microcontroller starts to detect the zero point of the rising edge of the input voltage. After detecting the zero point, it sends a conduction signal after a period of time. The signal is transmitted to the solid-state relay through the optocoupler, which makes the linear motor start working. The pulse width of the conduction signal is determined by the conduction time. Once the conduction time is up, the microcontroller sends a power-off signal. After the power is off, the downward thrust of the linear motor disappears, and the press resets under the action of the spring. 3. Test Experiments and Result Analysis Since the force sensor is a self-designed strain gauge and cylindrical force sensor, static and dynamic calibrations were performed before testing. Using a 10kN linear motor-driven press as an example, the static and dynamic calibration coefficients KF of the sensor were 0.07258V/kN and 0.07351V/kN, respectively, with a relative error of 1.3%. Therefore, it can be assumed that the force sensor has the same static and dynamic output characteristics. During testing, the force sensor was fixed on the base of the linear motor-driven press and press was performed. When the force sensor was subjected to the transient impact force of the press, it immediately generated a weak pulse signal. After amplification, conversion, and detection processing, this signal became the required transient force waveform. The magnitude of this transient force can be directly observed through the test analysis system. As auxiliary data, an acceleration sensor was installed at the top of the press rod. By utilizing the correspondence between the transient force signal and the acceleration signal, the noise signal can be easily distinguished from the transient force signal. By controlling and changing the magnitude of the impact force, the impact force and acceleration signal at different impact forces can be measured, as shown in Figure 4(a) and Figure 4(b). Through the test experiment, and from the test curve, it can be seen that (1) the transient response characteristics of the force sensor are very good; although the impact time is very short, the force measuring device can accurately detect the impact force; (2) the sensitivity is quite high, meeting the design requirements; because after the control parameters are changed, the slight change in impact force can be clearly detected; (3) the real-time performance of data acquisition is quite good; because the synchronization of force and acceleration signals is very good; (4) the system has a very good shielding against interference signals, because the detected signal is relatively clear and basically free of interference signals. This identification device, combined with a single-chip microcomputer control system, can accurately obtain the trigger angle and conduction time at the maximum transient impact force through experiments. 4 Conclusion and Prospect The development and application of linear motors will inevitably lead to revolutionary changes in the structure and performance of machine tools. However, considering that there are still some problems with linear motors that have not been solved, their design models, design theories, manufacturing processes and control aspects still need to be improved. At present, the application is limited to high-speed and high-precision machining tools that cannot be satisfied by rotary motor transmission, and it is only in the initial stage of application. However, with the emergence of new magnetic materials and special cooling methods for motors, and with the further development of high-speed and precision machine tools, the application of linear motors in machine tools will definitely become more and more widespread. The linear motor driven stamping press system identification device developed in this paper can accurately measure the relationship between transient impact force and motor trigger angle and conduction time. It can effectively complete the system identification of linear motor driven stamping press, which is of great significance for the optimization design and precision control of linear motor stamping press. It is believed that the performance of linear motor stamping press will become more and more perfect and the application range will become wider and wider. References [1] Ye Yunyue, Chen Yongxiao, Lu Qinfen. Research and application of linear electric motor driven stamping press [J]. Journal of Electrical Engineering, 1999, 14(5). [2] Lu Qinfen. Disturbance design simulation and transient force control of linear motor for new stamping machine [D]. Hangzhou: Zhejiang Journal, 1998. [3] Ye YY, Chen YX, Yang X C. Research and application of the punching machine driven by linear induction motor [A]. 1EE/, LDIA'98, Tokyo, 1998. 62 65. [4] Ye Yunyue. Principle and application of linear motor [M]. Beijing: Machinery Industry Press, 2000. 6. [b][align=center]For details, please click: Design of identification device for linear motor driven stamping machine[/align][/b]