The technical level of CNC machine tools and the percentage of metal cutting machine tool output and total ownership are one of the important indicators to measure the overall level of a country’s industrial manufacturing. CNC lathe is one of the main varieties of CNC machine tools. It occupies a very important position in CNC machine tools. It has been widely valued by countries all over the world for decades and has developed rapidly. Among them, the spindle movement is an important content of the CNC lathe, and its power accounts for about 70% to 80% of the power of the whole lathe. It plays a very important role in improving processing efficiency, expanding the range of processed materials, and improving processing quality. The basic control is forward, reverse and stop of the main shaft, with automatic shifting and stepless speed regulation. The effective control of the main shaft by frequency converter and plc is an important link in the process of technological transformation of CNC lathes. This article mainly introduces the application of plc and frequency converter in the drive control of CNC lathe spindle.

Plc and Frequency Converter in CNC

1. Process requirements

CNC lathes generally process rotary surfaces, threads, etc. It is required that its actions are generally fast forward, work forward, and fast rewind in the x and z directions. During the processing process, automatic, manual, external circle turning and thread turning can be converted; and single-step operation can be performed.

CNC lathes are processed with a constant linear speed function, and the processing procedures are:
(1) Press the start button to cut part ①, the motor rotates forward at a speed of 2400r/min, and the spindle rotates forward.

(2) Cutting ②, the motor rotates forward, the speed is 1500r/min, and the spindle rotates forward.

(3) Process ③Drilling, the motor rotates forward at a speed of 2700r/min, and the spindle rotates forward.

(4) Process ④ Tapping, the motor rotates forward at a speed of 600r/min, and the spindle rotates forward.

(5) Process ⑤ Exit the tap, the motor reverses, the speed is 1200r/min, and the spindle reverses.

(6) Press the stop button, the motor stops and the spindle stops.

2. Control requirements

(1) Use plc and inverter to control the AC motor to work, and the AC motor drives the spindle of the CNC lathe to run. The change of the AC motor’s working speed is shown in Figure 2, and it should be able to run continuously.
(2) The spindle motor can also be selected to rotate at a constant speed at any speed.
(3) The spindle motor can also be controlled by forward and reverse jogging, which is convenient for maintenance or adjustment, and the motor speed is selected to be 600r/min.
(4) Frequency converter frequency setting estimation formula f=np/60. f is the inverter setting frequency, n is the motor speed, and p is the number of pole pairs (set p=1).

3. Frequency converter selection and parameter setting

In this system, Mitsubishi series inverters are selected, the inverters are controlled by external terminals, and the parameters of the motor speed are set through the inverters. The forward and reverse operation of the motor is controlled by the peripheral through the str, stf and plc programs of the frequency converter.

(1) Basic parameters: pr.7=2 (acceleration), pr.8=2 (deceleration); pr.9=set the rated current of the motor;

(2) Operation mode: pr.79=3;

(2) Set the speed parameters of each stage; pr.4=40hz (1 stage), pr.5=35hz (2 stages), pr.6=45hz (3 stages), pr.24=10hz (4 stages), pr.25=20hz (5 segments).

For the spindle motor of CNC lathe, PLC and frequency converter are used to control, which has the following significant advantages: soft start and stepless speed regulation can be realized, and acceleration and deceleration control can be conveniently performed, which enables the motor to obtain high performance, greatly saves electric energy, and greatly saves power. Significantly reduce maintenance costs; achieve high-efficiency cutting and high processing accuracy; achieve strong torque output at low and high speeds.

The technical level of CNC machine tools and the percentage of metal cutting machine tool output and total ownership are one of the important indicators to measure the overall level of a country’s industrial manufacturing. CNC lathe is one of the main varieties of CNC machine tools. It occupies a very important position in CNC machine tools. It has been widely valued by countries all over the world for decades and has developed rapidly. Among them, the spindle movement is an important content of the CNC lathe, and its power accounts for about 70% to 80% of the power of the whole lathe. It plays a very important role in improving processing efficiency, expanding the range of processed materials, and improving processing quality. The basic control is forward, reverse and stop of the main shaft, with automatic shifting and stepless speed regulation. The effective control of the main shaft by frequency converter and plc is an important link in the process of technological transformation of CNC lathes. This article mainly introduces the application of plc and frequency converter in the drive control of CNC lathe spindle.

Plc and Frequency Converter in CNC

1. Process requirements

CNC lathes generally process rotary surfaces, threads, etc. It is required that its actions are generally fast forward, work forward, and fast rewind in the x and z directions. During the processing process, automatic, manual, external circle turning and thread turning can be converted; and single-step operation can be performed.

CNC lathes are processed with a constant linear speed function, and the processing procedures are:
(1) Press the start button to cut part ①, the motor rotates forward at a speed of 2400r/min, and the spindle rotates forward.

(2) Cutting ②, the motor rotates forward, the speed is 1500r/min, and the spindle rotates forward.

(3) Process ③Drilling, the motor rotates forward at a speed of 2700r/min, and the spindle rotates forward.

(4) Process ④ Tapping, the motor rotates forward at a speed of 600r/min, and the spindle rotates forward.

(5) Process ⑤ Exit the tap, the motor reverses, the speed is 1200r/min, and the spindle reverses.

(6) Press the stop button, the motor stops and the spindle stops.

2. Control requirements

(1) Use plc and inverter to control the AC motor to work, and the AC motor drives the spindle of the CNC lathe to run. The change of the AC motor’s working speed is shown in Figure 2, and it should be able to run continuously.
(2) The spindle motor can also be selected to rotate at a constant speed at any speed.
(3) The spindle motor can also be controlled by forward and reverse jogging, which is convenient for maintenance or adjustment, and the motor speed is selected to be 600r/min.
(4) Frequency converter frequency setting estimation formula f=np/60. f is the inverter setting frequency, n is the motor speed, and p is the number of pole pairs (set p=1).

3. Frequency converter selection and parameter setting

In this system, Mitsubishi series inverters are selected, the inverters are controlled by external terminals, and the parameters of the motor speed are set through the inverters. The forward and reverse operation of the motor is controlled by the peripheral through the str, stf and plc programs of the frequency converter.

(1) Basic parameters: pr.7=2 (acceleration), pr.8=2 (deceleration); pr.9=set the rated current of the motor;

(2) Operation mode: pr.79=3;

(2) Set the speed parameters of each stage; pr.4=40hz (1 stage), pr.5=35hz (2 stages), pr.6=45hz (3 stages), pr.24=10hz (4 stages), pr.25=20hz (5 segments).

For the spindle motor of CNC lathe, PLC and frequency converter are used to control, which has the following significant advantages: soft start and stepless speed regulation can be realized, and acceleration and deceleration control can be conveniently performed, which enables the motor to obtain high performance, greatly saves electric energy, and greatly saves power. Significantly reduce maintenance costs; achieve high-efficiency cutting and high processing accuracy; achieve strong torque output at low and high speeds.

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