1 Introduction At present, in the machining enterprises, in order to adapt lathes to the processing of small batches, varieties, and complex parts, and to make full use of ordinary lathes, it is necessary to carry out electromechanical integration design for ordinary lathes. The main design options are as follows: First, using a microcomputer as a control unit (mainly a single-chip microcomputer), controlling the feed system of the lathe, and using a stepping motor open-loop control system; secondly, man-machine interface (HMI) and programmable controller (PLC) ) As a main control element, instead of the electrical control part of the traditional lathe relay-contactor, its purpose is to improve the reliability of the lathe electrical control system, this method is mainly used in combination lathes and special lathes on the production line; Special CNC equipment to control the servo feed system of the lathe, the servo feed system is a stepping motor open loop control system. Figure 1 Equipment diagram Figure 2 Overall layout of the lathe Stereo Audio Cable, Audio cable, stereo cable, aux plug cable Stereo Audio Cable, Audio cable, stereo cable, aux plug cable Ningbo HanCheng(HC) Electronic Co.,Ltd , https://www.hcwires.com
Each of these methods has its own characteristics: the control system of the SCM can not only control the trajectory of the lathe, but also simplify the mechanical structure of the lathe, but its interface design is complicated and its reliability is low; while the interface of the control system composed of HMI and PLC is simple and reliable. High, but can not control the trajectory of the lathe; special CNC equipment can not only simplify the mechanical structure of the lathe, but also control the trajectory of the lathe, but its expensive, not suitable for economical CNC machine tools.
In recent years, with the development of microelectronic technology, computer technology, communication technology and automatic control technology, the functions of HMI and PLC have become more and more powerful. This paper proposes to use WEINVIEW HMI to control the stepper motor and the lathe spindle to realize the numerical control of the lathe.
2, the program to determine the numerical control is to solve the relationship between the lathe and the drive chain of the part of the drive, the drive chain are: spindle drive system, feed drive system. In order to make full use of the human-machine interface functions, the scheme is designed as follows:
1) The spindle drive system adopts variable frequency speed regulation;
2) Open-loop control of stepping motor is adopted for the transverse feed and longitudinal feed transmission systems;
3) The main technical parameters: 0.05mm/step lateral feed pulse equivalent, fast forward speed 2mm/min; longitudinal feed pulse equivalent 0.001mm/step, fast forward speed 1mm/min.
The overall scheme of the lathe is shown in Figure 2:
3, mechanical part
3.1 Spindle Drive System In order to simplify the structure of the spindle box and meet the requirements of the spindle and torque, the spindle drive system uses a three-phase asynchronous motor to drive the spindle to rotate through a belt and a speed reduction gear.
3.2 Feed Drive System Both the infeed and longitudinal feed drive systems use a stepper motor to drive the ball screw pair via the reduction gear to push the carriage travel to do the interpolation movement. In order to improve the accuracy of the feed transmission, the gears use spur gears with a gap-adjusting structure, and the ball screw pair must be pre-tightened during installation.
4, control system design
4.1 Hardware Structure In order to facilitate the expansion of the system and improve the maintainability of the system, this control system adopts a modular design. It consists of four subsystems: human-machine interface display, PLC controller, inverter, stepper motor drive module. The logic diagram of its control system is shown in Figure 3. The man-machine interface uses a stable and powerful WEINVIEW MT8104. Two stepper motors use the same type of reactive stepper motor and corresponding driver.
Figure 3 logical composition of the control system
4.2 Software Structure In order to facilitate software debugging, the software structure adopts a modular structure and is mainly divided into the following sections: stepper motor control module, feed system positioning control module, data input and data transmission module, component fault detection and alarm module, and human Machine interface monitoring and display. Through MT8104, system-related parameters are set to monitor and display the system operation process in real time, achieving a friendly combination of human-computer interaction operations.
Figure 4 HMI parameter setting component fault detection has a high reliability, so most of the PLC control system faults come from the PLC external components, such as the common short circuit or the formation of a button or stroke switch contact welding and oxidation Broken circuit. The system fault information can be displayed on the touch screen in real time, and prompts how to troubleshoot and help the user to handle system electrical or mechanical faults.
5, system reliability guarantee
The system reliability mainly comes from the stable, accurate and timely response and control of the control center unit;
Man-machine interface structure and working principle: 32bit RISC 200M CPU, display unit (LCD), input unit (resistive touch panel), communication interface, data storage unit (64M DRAM/32M Flash), etc.;
Fig. 5 Man-Machine Interface Structure MT8000 series is a man-machine product independently researched and developed by WEINTEK: Touch Panel adopts high-reliability precision resistive industrial-grade touch panel, which ensures accurate touch accuracy, high surface hardness, and long touch life. Maintain at least 1 million consecutive operations.
Fig. 6 The touch panel LCD adopts internationally renowned brand manufacturers, and cooperates closely with the best suppliers, and provides accumulated 13 years of experience in the HMI industry to suppliers for project discussion and work improvement; on the motherboard, strict Do a good job of stability, anti-jamming and other aspects of the test, and plus power isolation protection to ensure the reliability of human-machine interface in the field, stability and accuracy. The CPU uses 32bit RISC 200M to respond quickly to PLC requests. The highest baud rate of the serial port can reach 115200, which ensures the communication speed between HMI and PLC.
6. Notes Because the PLC is working in a cyclic scan mode, the scan cycle is generally between a few milliseconds and several tens of milliseconds, so the stepper motor cannot operate at high frequencies, and the pulse signal frequency can only be in the range of ten to several tens of Hertz. The speed of the stepper motor is proportional to the control pulse. When the stepper motor runs at a low frequency, the pulse equivalent cannot be too large in order to ensure the positioning accuracy of the system. This means that the positioning time is too long. In order to solve this problem, the positioning process is divided into two stages with different pulse equivalents: coarse positioning and fine positioning. Two sets of speed-changing mechanisms are used on the mechanical structure. In the rough positioning stage, the stepper motor directly drives the tool post. In the fine positioning stage, the stepping motor is used to drive the tool post via the deceleration gear. The two sets of devices have the electromagnetic clutch control.
7. Concluding remarks
Designing common lathes with HMI and PLC is simple, reliable, and highly resistant to interference. According to WEINVIEW headquarters incomplete statistics, 90% of the sales in the machine tool industry, application prospects are very broad.
Shenzhen Wei Luntong Technology Co., Ltd.