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Improvement of the control method of the spindle of the machine tool
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The energy consumption braking method is adopted to make the spindle motor stop; when the spindle rotates at low speed and low speed; about 0.5 s; in high-speed rotation; about 2. 5 s. current; the selected spindle motor braking method is shown in Figure 1. As shown; first disconnect KM1; then close switch KM2; then disconnect three-phase AC power; turn on DC power; delay 2. 5s; determine spindle motor stop rotation; then perform tool change or other measures.
When the spindle rotates at a different speed; the energy consumption braking method is used to make the spindle stop at different times; the same energy consumption braking timing is selected; the meaningless processing assistance time is extended; the machine tool working efficiency is reduced. Once the switch KM2 can not be closed securely; perhaps the DC power supply is safely disconnected and the DC power cannot be normally supplied; then the spindle motor can only be decelerated under the effect of friction; the braking time is very long; but the delay is after 2. 5s; the machine tool numerical control system Still determined that the spindle motor is now aborted; at this point the machine tool change or other measures simply form a fault.
Therefore, we improved the description of the spindle control of the machine tool spindle; resolved the spindle rotation; did not select the delay of 2. 5s; that is, determine the control method of the spindle motor to stop the rotation; instead, monitor the spindle rotation status in real time; At the inevitable speed; immediately announced that the spindle has completed the signal.
2 Spindle speed monitoring program installs a strip of iron on the synchronous drive shaft of the motor; rotates synchronously with the motor; detects it by the proximity switch; detects two pulse signals per revolution; after detecting the pulse signal, it is known Speed. There are two plans for detecting pulse signals.
Top plan: read the number N of pulse signals in the inevitable period Tp; PLC is a sequence manipulator; its program is executed step by step from front to back; each execution is one scan cycle; then it starts from the beginning Fulfillment. Assume that the program has 2000 steps; the execution time period of each step is 30Î¼s; the scanning period of the program is about 60ms; the scanning frequency is about 16Hz; the pulse frequency that can be accurately detected should be lower than 8Hz; when the pulse frequency of the rotation speed is greater than 16Hz; When the speed is nâ‰¥480r/min; the PLC is affected by the scanning frequency; the number of pulses cannot be accurately detected; when the condition is not good; the number of pulses detected at high speed is small; the misjudgment is that the motor is aborted. The following measures; the formation of the incident. This plan is only applicable to the monitoring of the low-speed rotation of the spindle.
The second scheme: detecting the time T at which the pulse signal continues to be "0" or "1"; when n < 60r/min; announcing that the spindle has stopped the signal. Because the PLC program fulfills the delay of the process; the CNC system receives the spindle stop Signal; and perform the following actions; the spindle has completely stopped the rotation; the time T of the pulse signal corresponding to n=60r/min continues to be â€œ0â€ or â€œ1â€ is 0. 25s; thus we set the timer for detecting the pulse signal It is set to 0. 25s. The same high speed will also show the pulse banned condition; but no matter how bad the situation is; "0" or "1" changes at least once in the time of 0. 25s; thus it can accurately distinguish whether the spindle can Stop rotation. This plan can be applied to the detection of spindle braking conditions when the spindle is rotating at high speed or low speed. In practice, we have chosen this plan.
3 PLC completes the spindle energy consumption braking control method PLC drawing program; X20. 0 is the input of the speed pulse signal; M05 is the spindle stop signal; Y50. 0 is the spindle suspension signal.
The two timers TM1, TM2 are separated from the resolution X20. The time when the 0 pulse signal continues to be "0" or "1" can reach the set time; only one time arrives; that is, R100.1 or R100. 2 change " 1"; inducing R100. 3 change "1"; M05 is "1" at this moment; inducing Y50. 0 output "1"; then declare the spindle brake completion signal; complete the exact resolution of the spindle stop.
4 Conclusion We use the improved control method to control the braking of the machine tool spindle with PLC; it can accurately distinguish the rotation condition of the machine tool spindle; avoid the wrong action of the machine tool; save the auxiliary time of the spindle machining; make the maintenance function of the machine tool tend to be more perfect.
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