Cutting tool exhibits at the hottest emo99 Exhibit

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The tool exhibit at emo99 exhibition

1 introduction

generally, when the spindle motor of machine tool is braked, the energy consumption braking mode is adopted to input DC power to phase ab of the motor

use energy consumption braking to stop the spindle motor. When the spindle rotates at low speed in low gear, it takes about 0.5s, and when it rotates at high speed in high gear, it takes about 2.5s. At present, the braking method of the spindle motor is shown in Figure 1. First disconnect KM1, and then close the switch km2, so as to disconnect the three-phase AC power supply, connect the DC power supply, delay 2.5s, confirm that the spindle motor stops rotating, and then change the tool or other actions

when the spindle rotates at different speeds, the time required to stop the spindle by using the energy consumption braking method is different. The same energy consumption braking time is used to prolong the meaningless processing auxiliary time and reduce the working efficiency of the machine tool. In addition, once the switch km2 cannot be reliably closed, or the DC power fuse is disconnected and cannot normally provide DC power, the spindle motor can only decelerate under the action of friction, and the braking time needs to be very long. However, after a delay of 2.5s, the CNC system of the machine tool still recognizes that the spindle motor has stopped rotating. At this time, the tool change or other actions of the machine tool are likely to cause accidents

therefore, we have improved the design of the spindle braking control mode of the machine tool to judge the spindle rotation state. Instead of using the control mode of 9. Piston stroke: 150mm, delaying 2.5s, that is, identifying the spindle motor to stop rotating, we monitor the spindle rotation state in real time. When the spindle rotation is lower than a certain speed, we immediately send out the spindle stop signal

2 spindle speed monitoring scheme

install a strip iron on the synchronous transmission shaft of the motor, rotate synchronously with the motor, and detect it by the proximity switch. Two pulse signals are detected per revolution, and its speed is known through the detection of the pulse signal. There are two ways to detect pulse signals

scheme 1: read the number of pulse signals n within a certain period TP. PLC is a sequence controller. Its program is executed step by step from front to back. Each execution is a scanning cycle, and then it is executed from the beginning. If the program has 2000 steps, the execution time cycle of each step is 30 μ s. Then the scanning cycle of the program is about 60ms, the scanning frequency is about 16Hz, and the pulse frequency that can be accurately detected should be lower than 8Hz. When the pulse frequency of the rotating speed is greater than 16Hz, that is, when the rotating speed n ≥ 480r/min, PLC cannot accurately detect the number of pulses due to the influence of its scanning frequency. When the situation is not good, there will be a small number of pulses detected at high speed, and the following action will be taken when the motor is basically stopped and the test piece is close to damage, Cause accidents. This scheme is only applicable to the monitoring of the low-speed rotation state of the spindle

the second scheme: detect the time t when the pulse signal continues to be "0" or "1". When n < 60r/min, send the signal that the spindle stops. Due to the delay of the PLC program execution process, when the CNC system receives the spindle stop signal and performs the following actions, the spindle has completely stopped rotating. The time t when the pulse signal corresponding to n=60r/min continues to be "0" or "1" is 0.25s, so we set the timer for detecting the pulse signal to 0.25s. Similarly, pulse uncertainty also occurs at high speed, but no matter how bad the situation is, the "0" or "1" changes at least once in 0.25s, so it can accurately judge whether the spindle stops rotating. This scheme can be applied to the detection of spindle braking state when the spindle rotates at high speed or low speed. In practical application, we adopt this scheme

3 PLC realizes the control of spindle energy consumption braking. 5. Refrigeration auxiliary parts: the main refrigeration accessories and controller parts adopt the imported original method. In the PLC design program, x20.0 is the input of speed pulse signal, M05 is the spindle stop signal, and y50.0 is the spindle stop signal

two timers TM1 and TM2 respectively judge whether the time when the x20.0 pulse signal continues to be "0" or "1" reaches the set time. As long as there is a time, that is, r100.1 or r100.2 changes to "1", resulting in r100.3 changing to "1", at this time M05 is "1", resulting in y50.0 outputting "1", then a spindle braking completion signal is sent, realizing the accurate judgment of spindle stop

4 conclusion

we use an improved control method to control the braking of the machine tool spindle with PLC, which can reliably distinguish the rotation state of the machine tool spindle, avoid the misoperation of the machine tool, save the auxiliary time of spindle processing, and make the protection of machine tools similar to illite more perfect

author unit

pan yuedou (Department of industrial electrical automation, College of automation, Tianjin University, zip code: 300072)

Xu Zhenlin (Tianjin University)

Yu Zhihuo (Beijing Machine Tool Research Institute)

Cao Zhentao (Beijing Machine Tool Research Institute)

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