Abstract : This paper introduces a simple, inexpensive, and powerful microcontroller control system, and uses it to implement adaptive control of the feeding device of a punch press, achieving good results. Keywords : Microcontroller, Adaptive control, Feeding device. A factory produces medical aluminum bottle caps using aluminum strip material, which is manufactured in a single stroke on a punch press through a blanking-drawing compound die. Its automatic feeding device uses a front double-roller support and a rear double-roller pulling method. The intermittent rotational motion of the rear roller is derived from the movement of the punch press crankshaft, achieved by a connecting rod and ratchet-pawl mechanism. However, due to structural limitations, it is difficult to externally implement this mechanism in some punch presses. Therefore, we adopted an adaptive feeding device driven by a stepper motor controlled by a microcontroller. 1. Composition of the Control System The control system, as shown in Figure 1, utilizes the state-of-the-art 51 series microcontroller AT89C2051. It has few pins (only 20), simple peripheral circuitry, yet powerful functionality. Besides bidirectional serial/parallel ports and two 16-bit internal timers, it also features a 2K electrically erasable flash EPROM (for storing the control program) and 128 bytes of RAM (for data storage). The external crystal oscillator frequency can reach up to 24MHz, enabling a single instruction execution time of only 0.5–1μs, suitable for fast real-time control applications. The external power supply is 3–6V, offering strong adaptability. Furthermore, its low cost makes it ideal for building small control systems. Figure 1. Circuit Principle of Control System In this system, the toggle switch is used to set the feeding length; S is the punch travel switch used to send a start feeding signal to the microcontroller when the punch drops and then lifts; MC1413 is the driver to provide sufficient operating current to the LED of the optocoupler; G is the optocoupler to isolate the microcontroller from interference from high voltage; M is the stepper motor. 2. Working Principle of Control System After power-on, the system first sets the initial state and reads the set value of the feeding length from the toggle switch. This value is then calculated and converted into the number of steps for the stepper motor, which is stored in RAM as the step count memory. After confirming that the punch has dropped and lifted, the microcontroller sends a pulse signal, which is amplified and drives the stepper motor to rotate. The system uses software to construct a ring distributor and automatically handles acceleration and deceleration. When the number of steps the stepper motor rotates equals the value in the step count memory, the stepper motor stops rotating and waits for the next punch drop and lift signal. The program flowchart is shown in Figure 2. Figure 2. Flowchart of the microcontroller's operation The feeding length adjustment must be performed in the power-off state by toggling a toggle switch. 3. Stepper Motor and its Driver Amplifier This device uses a 75BF003 stepper motor, 3-phase, 4A, step angle 1.5°/3°, maximum static torque 0.882 N*m, and no-load starting frequency 1250Hz. The stepper motor driver uses a chopper constant current power amplifier circuit. Figure 3 shows one phase, where W is the stepper motor winding, VT is a high-power MOS field-effect transistor, RS is a sensing resistor, CP is a comparator (the output jumps to a high level when the voltage on RS exceeds the voltage set by potentiometer RP), F1 is a NAND gate, F2 is an inverting driver, R1 and D are the energy discharge circuits for W when VT is off, and R2 and C are the protection circuits for VT. This power amplifier circuit is simple, efficient, has high output torque, and high operating frequency. Figure 3 Chopper constant current power amplifier circuit 4 Roller feeding mechanism The working principle of this mechanism is shown in Figure 4. The rear roller is made of 45 steel with knurled outer surface to increase friction and ensure feeding accuracy. The lower roller is connected to the output shaft of the stepper motor; the upper roller presses on the scrap and the lower roller under the action of the spring. The front roller plays a tensioning and positioning role, and is made of rubber-metal composite roller and polished to prevent damage to the surface of the aluminum strip. This mechanism is simple and practical. [b][align=center] Figure 4 Working principle of roller feeding mechanism[/b][/align] 5 Features The single-chip microcomputer controlled punch press feeding device has the following advantages: (1) Compact structure and few control circuit hardware. (2) Strong anti-interference ability and can adapt to the environment of the stamping workshop. (3) High cost performance. (4) The control part adopts speed lifting treatment, which can effectively prevent the stepper motor from losing steps. (5) The feeding length can be adjusted within a wide range. (6) The control system shown in Figure 1 can itself be used as a programmable controller in other industrial control systems.