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The application of frequency converter in lathe spindle control system


the technical level of numerical control machine tools and their percentage in the output and total ownership of metal cutting machine tools are one of the important symbols to measure the national economic development of a country and the overall level of manufacturing industry that has made significant contributions to this utilization field. CNC lathe is one of the main varieties of CNC machine tools. It occupies a very important position in CNC machine tools. For decades, it has been widely valued by countries all over the world and has developed rapidly. The spindle is an important part of the lathe, which plays an important role in improving the processing efficiency, expanding the range of processing materials and improving the processing quality. Most economical CNC lathes cannot change speed automatically. When you need to change speed, you can only stop the machine and then change speed manually. The main transmission system of full-function CNC lathe mostly adopts stepless speed change. At present, there are mainly two kinds of CVT systems: variable frequency spindle system and servo spindle system. DC or AC spindle motor is generally used. Drive the spindle to rotate through the belt drive, or drive the spindle to rotate through the belt drive and the reduction gear in the spindle box (to obtain greater torque). Due to the wide speed regulation range of the spindle motor and stepless speed regulation, the structure of the spindle box is greatly simplified. Due to the high cost performance of frequency converters, frequency converters are widely used on lathes. Common faults of delta M Series 1: with its unique performance and superior cost performance, the frequency converter has risen rapidly in the application of CNC machine tools, and has become a powerful new force in the current market

introduction to the performance of delta M series frequency converter

m series frequency converter can meet the requirements of CNC machine tools for stepless speed change of the main transmission system. Its main characteristics are: small volume, belonging to "mini" products, and occupying less space in the control cabinet; The control mode is sine wave SPWM (providing speed feedback vector control), and the control performance is greatly improved compared with VF control mode, especially in terms of low-speed torque to meet the needs of machine tool spindle, and the starting torque can reach more than 150% at 5Hz; Carrier frequency range kHz, low noise; Provide standard V analog interface (input impedance 47Kohm, output impedance 250kohm), which is compatible with most CNC system interfaces and has strong versatility; Strong overload capacity, more than 150% of the rated output current for more than one minute; Provide multi-functional output terminal signals, such as zero speed signal, running signal, speed arrival signal, fault indication, to meet the system's monitoring of spindle speed status; Automatic torque compensation to meet the machining requirements of the machine tool spindle at low speed; Three groups of abnormal records are provided for maintenance personnel to understand the actual operation status of the machine tool spindle from the side; The automatic setting function of motor parameters can identify motor parameters and ensure the stability and accuracy of the system

lathe spindle control system

principle of lathe spindle control system

wiring diagram of control system is shown in Figure 1. The optional motor is 3.0kw/50hz/380v, the selected frequency converter model is vfd037m43, and the braking resistance is 400w/150ohm

the avi/gnd terminal of the frequency converter provides speed analog quantity to the NC system. Avi is connected to the positive signal of the analog quantity interface of the NC system, GND is connected to the negative signal, and the signal is v analog voltage signal, which controls the spindle speed. M5. Transmission system: there are two important types of transmission of electronic universal experimental machine: 1. Circular arc synchronous gear with fine lead screw pair transmission; 2. Popular belt drive 0/m1/gnd is the forward/reverse signal terminal of the frequency converter. Usually, the numerical control system sends forward signal FWD or reverse Rev to drive the intermediate relay. The normally open contact of the intermediate relay is connected to the frequency converter m0/gnd or m1/gnd, so as to control the forward and reverse rotation of the lathe spindle

control system parameter debugging

in the process of parameter adjustment, attention should be paid to: p00 parameter, select the main frequency input and set it as the analog signal V input (1); P01 parameter, operation signal, set to external terminal signal control (2); P03, maximum operating frequency selection, corresponding to the output frequency of the frequency converter when the analog signal is 10V input. Since the speed is adjusted within the rpm range, considering the mechanical reduction ratio, this parameter can be set to 184hz; P04 and P05 are set according to the motor nameplate, p04=50hz, p05=380v; P10 and P11 are acceleration time and deceleration time. According to the customer's requirements, p10=5s, p11=5s; P105 is the selection of control mode. Select vector control, p105=1

it should be noted that since the vector control needs to provide motor parameters (impedance), the frequency converter provides the motor parameter self-tuning function p103. Select p103=2, and the frequency converter will operate automatically through the panel operation key. In the process of automatic operation, in addition to calculating the motor parameters, it can also detect the no-load current. These parameters can make the vector control show high performance, and this process will last for more than ten seconds

test and operation

the actual test results of the system are shown in Table 1 and table 2: Table 1: no-load current test results

Table 2: load current test results

it can be seen from table 1 and table 2 that in the frequency band (Hz) of constant torque output, the no-load current of vector control is almost half that of VF control, and the current under load is also smaller than VF; And when cutting with load, VF control has obvious speed drop in the initial stage, and there is a large difference between no-load speed and load speed. Compared with vector control, although the spindle speed will also decrease at the initial stage, the decrease value is small, and the speed will quickly rise. Finally, the difference between no-load speed and load speed is not very obvious. After the above adjustment, special attention should be paid to the effective stroke of the electronic tension machine and the interview of the sample fixture. Compared with the VF control, the performance has been greatly improved. No matter from the no-load current, low-speed torque, or the change of speed, the effect is very obvious, which can fully meet the needs of CNC machine tools. After putting into operation, the application effect is satisfactory, which shows that the application of delta M series inverter in the lathe spindle control system is successful. (end)

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