Application of the most popular PLC in CNC flat he

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The application of PLC in CNC flat head equipment

1. Preface

we all know that the smoothness and flatness of the flat head surface will be affected by many factors, such as the accuracy of the tool and the proficiency of the operator, when the traditional flat head equipment is used for flat head operation of the workpiece. In view of this problem, we have developed a CNC flat head machine, which can work continuously according to the input feed curve, and always maintain high precision and efficiency, so as to fully ensure the quality of flat head

2. Control requirements

the control requirements of CNC flat head machine are:

(1) the control system shall be able to adjust the cutting head processing program

(2) different processing speeds and depths can be selected for different processing stages. The feed curve during idle travel is shown in Figure 1, and the feed curve during machining is shown in Figure 2

(3) the spindle speed shall be adjustable and the range shall be wide

(4) high machining accuracy, and the smoothness of the machined material plane shall be RA ≤ 1.6 μ m;

(5) sizing accuracy: ± 0.5mm

Fig. 1 feed curve at idle travel

Fig. 2 feed curve at machining

3. Hardware design of the system

according to the control requirements of the system, the hardware is configured as follows:

programmable controller: a S-Series cpu222plc of Siemens

man machine interface: 1 dp210

peripherals: 2 stepper motors, 2 stepper motor drivers, 2 three-phase motors, 1 frequency converter, 1 em222, 8 electromagnetic switches, 4 photoelectric sensors and 1 hall sensor

3.1 i/o point allocation of the system

according to the hardware structure diagram, the system requires 5 input points and 14 output points Cpu222plc has 8 input points and 6 output points, so an expansion module needs to be added. The digital quantity expansion module em222 with 8-point output is selected The input point is i0.0-i0.7; The output points are q0.0-q0.5 and q1.0-q1.7. See the following table 1 and table 2 for the allocation: Table 1 input terminal allocation table

Table 2 output terminal allocation table

3.2 controller

the key equipment of the system is PLC. PLC is a computer device with single chip microcomputer as the core, which is specially used for industrial process automation control. It has very high reliability and stability. This system, also known as electrochemical capacitors, is a new type of energy storage device with energy density and power density between traditional capacitors and batteries. The S-Series cpu222plc of Siemens is selected as the control core, and two independent 20kHz high-speed pulse outputs of cpu222 are used to control the movement of stepping motors. This high-speed pulse signal can not directly drive the stepping motor. It can only work after the power is amplified by the stepping motor driver. Five digital inputs are respectively connected with five sensors to judge the position of stepping motor, workpiece and cutter head. Among the 14 digital outputs, 6 are used to control the stepper motor driver and 8 are used to control the solenoid valve switch

plc has a communication port, which is a standard RS-485 interface. When PLC communicates with the upper computer, it is necessary to convert the RS-485 interface into a standard RS-232 interface, which can be converted by using the isolated plc/ppi cable provided by four doors. The cable has a dial switch for setting. After writing the control software on the upper computer, download the program through this line and monitor the operation of the program. In order to reduce the cost, after the program is debugged, it is not necessary to use the upper computer for operation and control, but to use a simple operation panel. Dp210 operation panel is selected for this system

3.3 peripheral of the system

according to the high requirements of the system for tool machining accuracy, stepper motor is selected to control the machining program. The stepping motor can be accurate to one pulse. In this system, the accuracy of one pulse is 0.005mm. The stepping motor driver is used to drive the stepping motor, so as to control the action of the cutter head and complete the flat head. The stepping motor driver receives signals from PLC, including CP stepping pulse signal, dir direction signal and free offline signal, which are output to the two-phase stepping motor connected later after passing through its internal power amplifier circuit and processing circuit. The stepping motor generates corresponding actions according to the signal number. The solenoid valve is directly controlled by PLC, which means that consumers get a good visual experience and the safety and environmental protection guarantee number acts. In addition, PLC directly receives the signal from the sensor and determines the output through the operation and logical judgment of the internal program

the frequency converter is used to control the rotation speed of the three-phase motor of the spindle. In this system, the frequency converter adopts the basic parameter operation mode, the operating frequency is set by the potentiometer, and the start and stop of the frequency converter are controlled by the external terminal According to the characteristics of different workpieces, the rotation speed of the spindle motor is changed by rotating the potentiometer, and the signal of the external terminal is controlled by the 12th digital output of PLC

4. Software design of the system

the software of the system includes the human-computer interface dp210 program and the main control program of the system. Dp210 program completes the dialogue between the operator and PLC, mainly the mutual conversion between various operation screens and the control bits of PLC program corresponding to each key action in each operation screen. The program screen should be adapted to the work flow of the production site. The more the front screen is, the higher the utilization rate is

plc program, after receiving the operation signal from dp210, controls the whole cutter head according to the work requirements. Main Ningbo is the process of "national new material achievement transformation and industrialization base" approved by the Ministry of science and technology, as shown in Figure 3. The core control in the PLC main control program is the control of the stepping motor. The program for starting 1\; stepping motor is shown in Figure 4, and the program for controlling the motor direction is shown in Figure 5

Fig. 3 main program flow chart

Fig. 4 1stepper motor startup program

Fig. 5 1stepper motor direction selection program

(2stepper motor motion control is similar to 1stepper motor)

5. Conclusion

the system designed in this paper has simple operation, wide range of processing products and high processing precision, and has been successfully applied to production practice. At present, the flat head machine has been used in a material factory for flat head of regular geometry. Since the beginning of production, the system has operated stably, the product quality has been significantly improved, and the scrap rate has decreased significantly. At the same time, it greatly reduces the labor intensity of operators, improves the production efficiency, and can also be used for the flat head of other devices. In addition, we design a certain range of cutter head size to adapt to the flat head action of different workpiece sizes, and it has the replaceable function. (end)

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