Abstract: This paper analyzes the necessity of modifying the C650.2 lathe. Based on the actual situation of the lathe, a PLC and frequency converter are applied to its modification. The modification strengthens and improves the control of the machine tool, making its operation more convenient, safe, efficient, and environmentally friendly.
Keywords : Programmable Logic Controller; Frequency Converter; Retrofit; Ladder Diagram
The C650.2 lathe is a common machine tool that uses a relay control system and a gearbox for speed change. It is widely used in small and medium-sized enterprises. However, the relay control system has complex wiring, the contacts are easily burned out, the control response is slow, the functions are limited, fault diagnosis and troubleshooting are difficult, and maintenance is very time-consuming and labor-intensive. In addition, the gearbox speed change method of the C650.2 lathe brings many inconveniences to daily operation, and the noise during operation is mainly caused by it. There is also vibration during operation, which has a significant impact on machining accuracy. It also has high energy consumption, which seriously affects the use of the machine tool and the processing quality of the products. Therefore, it is necessary to modify it.
Programmable Logic Controllers (PLCs) are general-purpose industrial automatic control devices that integrate microcomputer technology, automation technology, and communication technology. They are highly reliable, have a high performance-price ratio, and are easy to use, making them a powerful tool for realizing industrial automation. This article mainly introduces the application process and methods of PLCs and frequency converters (VVVFs) in the retrofitting of a C650.2 lathe. PLC control is used to replace traditional relay control, and frequency converters are used to replace the spindle gearbox speed change mechanism.
1. System Modification Technical Requirements
During the modification of the C650-2 lathe, in addition to inheriting the original relay control function and spindle gearbox speed change function, the reliability and ease of operation of the machine tool were further enhanced and improved. Specific modification technical requirements are as follows:
(1) Power supply closing and disconnection control.
(2) Spindle speed control. There are 16 speed positions for both forward and reverse rotation of the spindle, and these 32 speed values can be reset at any time according to the user's needs.
(3) The spindle’s forward rotation, reverse rotation, stop, and jog control can only have one of these four actions being performed at the same time, and the principle of priority for the later one is implemented.
(4) Emergency stop control should be provided to prevent accidents. This is achieved by reverse braking of the motor. When the emergency stop button is pressed, the PLC can intelligently determine whether the spindle is rotating forward or backward and perform reverse braking. This function is something that relay control cannot do.
(5) When machining a workpiece, the coolant must be activated after the spindle rotates and before the tool feeds. After the workpiece is machined and the tool retracts, the coolant should stop working.
(6) The main motor M1, the tool feed motor M2, and the coolant pump motor M3 should all have short-circuit and overload protection. If any one motor is overloaded or short-circuited, the other motors should stop working.
(7) The working status of the lathe should be indicated by corresponding indicator lights.
For details, please click: C650-2 Lathe Retrofit Based on PLC and Frequency Converter
