Design of controllable electric wrench controller based on STC12C5A60S2

According to statistics from equipment management authorities, more than 50% of equipment failures are caused by bolt problems, and the number of major accidents caused by bolt problems is also very alarming. Therefore, new equipment installation and maintenance specifications have very strict requirements on bolt tightening torque, especially for heavy machinery equipment that bears loads and strong impact and vibration. It is necessary to accurately control the preload of the connecting bolts. However, the required preload is very large, and due to space conditions, large-size tools cannot be used, so a torque wrench must be used. The controller, as a key component of the torque wrench, has a great impact on its performance. This article provides a solution for an electric wrench controller that can accurately display the tightening torque value and angle value, and can tighten the bolts according to the preset torque value and angle value.

1. Hardware design of controllable electric wrench controller

The hardware circuit block diagram of the controllable electric wrench controller is shown in Figure 1.

Figure 1 Hardware circuit diagram of controllable electric wrench controller

1.1 Digital potentiometer, button and display control circuit

The single-chip microcomputer uses STC12C5A60S2 as the core controller. This machine is a single-clock/machine cycle single-chip microcomputer, a new generation of 8051 single-chip microcomputer with high speed, low power consumption and super anti-interference. The instruction code is fully compatible with the traditional 8051, the operating voltage range is 5.5 V ~ 3.3 V; the operating frequency range is 0 ~ 35 MHz, equivalent to 0 ~ 420 MHz of ordinary 8051; 1 280 B on-chip RAM data storage; four 16-bit timers; programmable clock output function; full-duplex asynchronous serial port (UART), compatible with the serial port of ordinary 8051; advanced instruction set structure, compatible with ordinary 8051 instruction set. The level conversion chip uses LM2575, which outputs 5 V DC voltage as the power supply. The circuit diagram is shown in Figure 2. The LCD display uses the LCM 128645ZK module, and uses five buttons to control the forward rotation, reverse rotation, torque setting, angle setting and zeroing of the stepper motor. The digital potentiometer is used to set the torque value and angle value. The circuit is shown in Figure 3.

Figure 2 Level conversion circuit [page]

Figure 3 Keyboard and display circuit

1.2 Stepper Motor Control Circuit

The stepper motor driver uses the UDK5214NW-M5 phase stepper driver produced by HP. The driver control uses the ULN2003 chip. The three output ports of the chip are used to control the stepper motor reversing control relay, the stepper motor driver work stop relay and the alarm work, and then control the stepper motor driver through the relay. The driver step pulse is output by the P1.4 port of the single chip to drive the stepper motor. The stepper motor control circuit is shown in Figure 4.

Figure 4 Stepper motor control circuit diagram

[page]

1.3 Torque detection circuit

The torque sensor uses a BS914 torque wrench special signal coupler. The coupler can directly output a 1 V to 5 V voltage signal. The torque feedback signal is input into the microcontroller through the P1.5 port, converted into a digital signal by the microcontroller, and then compared with the torque setting value to control whether the stepper motor rotates. The connection circuit diagram is shown in Figure 5

Figure 5 Torque detection circuit

2 Controllable Electric Wrench Controller Software Design

The software of the controllable electric wrench controller consists of a controller initialization program, a keyboard scanning and processing program, a stepper motor control program, a torque detection program, etc. The controller detects whether the torque and angle values ​​are input through the keyboard scanning and processing program, and determines the direction of motor rotation. If it is forward rotation, the stepper motor forward rotation control program controls the motor to rotate forward, and the torque detection program detects the output torque until the torque and angle reach the predetermined value; if it is reverse rotation, the stepper motor reverse rotation control program controls the motor to reverse until the angle reaches the predetermined value. Torque detection uses the P1.5ADC port of the STC12C5A60S2 microcontroller. When in use, set the port as an open-drain input and use it as an ADC port. The program mainly completes the functions of ADC port conversion start, data reading, software filtering, and output display.

The controllable wrench controller designed in this paper uses STC12C5A60S2 single-chip microcomputer as the central processing chip and uses fewer peripheral devices to make its structure simple. The prototype is tested and the test results show that the prototype has stable performance, accurate measurement, easy use, and the technical parameters meet the design requirements, which has certain practical value.