1. Introduction :
Programmable logic controllers (PLCs) are highly programmable, versatile, adaptable, designed for industrial control, and reliable. They also have excellent self-diagnostic capabilities and are easy to maintain. As a result, small PLCs offer high cost-effectiveness and play an extremely important role in the design and modification of control circuits for ordinary lathes.
2. Electrical control requirements:
Before feeding, the motor must stop. When the material reaches the sealing position, the sealing end faces downwards. After the sealing end is reached, feeding continues until the sealing end is reached. At this point, the chuck on the spindle clamps the tool, retracts the material, and then the main motor is driven to rotate at high speed via the frequency converter. Next, according to the selected function, the cutting, working feed, chamfering, and finally the return to the original position completes the machining process. Based on the machining process, the following requirements are put forward for the electrical control:
1) The main motor is a three-phase asynchronous motor, controlled by a frequency converter, and is required to start and stop quickly; and due to the fast processing speed and frequent start and stop, a 400Ω, 260W braking resistor is required.
2) Both the oil pump motor and the spindle motor should have necessary short-circuit protection and overload protection;
3) Three modes are available: manual, single cycle, and automatic. Single cycle and automatic operation can only be started when the oil pump and motor clutches are engaged.
4) There are 10 functions, which can be selected by DIP switch. In single cycle and automatic operation, changing the function by changing the DIP switch will not work. You need to switch to manual function to change it.
5) An emergency stop button is required to prevent accidents during startup or operation.
3. PLC-based system design:
3.1 Hardware Design
To meet the electrical control requirements of the lathe, the FBS series of Taiwan Yung-Hong PLC, model FBS-40MAT, was selected. It has 40 I/O points, including 24 inputs and 16 outputs. Its I/O wiring diagram is shown in Figure 1.
Figure 1 PLC I/O Wiring Diagram
The PLC input and input I/O allocation tables are shown in Table 1 and Table 2.
Table 1 Input Signal Address Allocation Table
Table 2 Output Signal Address Allocation Table
3.2 Software Design
The control approach is as follows: First, the PLC reads the status setting function of the DIP switch and classifies the actions used by each function. The main program framework is written using step instructions. At each step, the corresponding subroutine is called according to the different functions to complete the processing technology.
The program was written according to the system's technical requirements and lathe manufacturing process. It was then tested on the machine tool on-site, and the system is operating normally, reliably, and safely. Ten functions are available, as listed in Table 3.
Table 3. List of Dual-Cylinder Rear Feeding Functions
When the DIP switch is set to 0: Cylinder A is grooved first, and Cylinder B is grooved later.
When the DIP switch is set to 1: Cylinder A has a flat head, and Cylinder B has a groove cut at the rear.
When the DIP switch is set to 2: Cylinder B is grooved first, and Cylinder A is grooved later.
When the DIP switch displays 3: Cylinder A is flattened, and Cylinder B remains stationary.
Subsequent actions will follow the same pattern.
Function Selection Program
Calling a subroutine
4. Conclusion
The multi-functional automatic lathe designed based on Yonghong PLC is operating well and can process a variety of workpieces. The automatic cycle time for processing each workpiece is only 4 seconds, which improves production efficiency and product quality. It is a practical and feasible control method.
References
1. Liu Jinqi. Automatic Electrical Control of Machine Tools (2nd Edition) [M]. Harbin: Harbin Institute of Technology Press, 1999.
2. Yung-Hong FBS Series Programmable Controller User Manual I
