At present, there are more and more devices with position control requirements such as CNC machine tools, and such systems generally use high-performance electric drives as power.
The numerical control device issues a position control pulse, which is controlled by the servo drive system to control the precise positioning of the servo motor, and the position control of the CNC machine tool table is achieved by the mechanical transmission system, and once the mechanical transmission chain is determined, the transmission ratio is fixed. In this way, the pulse equivalent of this CNC machine is fixed, and the pulse equivalent is the displacement moved by the numerical control device to send a pulse table. It is a very important indicator that affects the machining accuracy of CNC machine tools. In order to achieve different control precisions in such a rigid system with a fixed mechanical transmission ratio, the electronic gear can solve such a problem, and the mechanical transmission chain itself does not need to be changed, and only the frequency division ratio of the electronic gear needs to be reset. Electronic gears are therefore a very important component of high performance electric drive systems. Thanks to this new range of features, users have more room to flexibly adjust and adjust, making it easier to use and improving performance.
1 Electronic gear principle and its gear ratio setting 111 The concept of electronic gear The so-called "electronic gear" function is a function frequently used in CNC machine feed position control. The CNC system sends a feed command pulse to control the machine tool. When the feed member is moved, the mechanical reduction ratio and the number of pulses of the encoder can be ignored, and the position shift amount corresponding to the input command pulse of the numerical control system can be set to an arbitrary value to achieve the purpose of controlling the position.
112 Electronic Gear Ratio Setting (1) The elements related to the electronic gear are shown as the principle of the CNC machine feed drive system. Take the CNC lathe as an example. The system uses the SGDM servo drive and SGM series of Yaskawa. The AC servo motor is a 17-bit gain type encoder.
(2) Confirm the number of encoder pulses of the SGMGH servo motor.
Since the 17-bit gain type encoder has been selected in the foregoing, it can be found that the number of encoder pulses of the SGDHD is 32 768.
(3) Find the electronic gear ratio BA to set the reduction ratio of the motor shaft and the load shaft to nm. That is: the motor rotates m turns and the load shaft rotates n turns.
Check the machine user manual to see that the machine's X-direction reduction ratio is 22 / 45, and the Z-direction reduction ratio is 22 / 50.
The command unit is 0 1 001mm, which is the minimum unit of position data of the moving load. When the screw pitch is 10mm, the movement amount of the load shaft is rotated by one rotation (command unit) = the amount of movement after the load is rotated by one revolution. 0 1 001 = 10 000 X-direction electronic gear ratio BA = encoder pulse number × 4 movement amount of one rotation of the load shaft × mn = 32 768 × 4 10 000 × 45 22 = 36 864 1 375 Z-direction electronic gear ratio BA = encoder pulse number × 4 movement amount of one rotation of the load shaft × mn = 32 768 × 4 10 000 × 50 22 = 8 192 275 (4) Setting the user constant After dividing the electronic gear ratio by the value of BA, Select A and B as integer values ​​less than "65 535" and set them as user constants.
2 Conclusion With the development of microelectronics technology, power electronics technology, electric drive technology, control technology, computer technology, the use of electronic gear instead of mechanical gearbox to achieve accurate transmission relationship technology has been widely used, and has broad prospects.
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