Answer: The spindle of the CNC lathe and boring machine requires reversible operation. The Yun motor can run in the forward and reverse directions. The methods of controlling the forward and reverse rotation of the DC Tawei motor can be divided into two categories: one is to change the direction of the armature voltage, and the other is to change the direction of the armature voltage. Change the direction of the excitation voltage.
The spindle speed control system of the original Czech WHC boring machine is to change the direction of the excitation magnetic flux, so that the DC motor can run reversibly. Generally speaking, the excitation power of the DC motor is only 1% -5% of the rated power of the motor. Therefore, the capacity of the two sets of thyristor converters required for excitation is relatively small, and only one set of large-capacity devices is used on the armature circuit. Due to the large inductance of the excitation winding, the process of the excitation reversal is much slower than the armature reversal, and during the reversal process, when the magnetic flux decreases, the armature voltage should be made zero (that is, the speed control system should be blocked regulator and trigger pulse of the armature control loop) to avoid “overspeed” due to loss of field
(or “flying car”) phenomenon, which increases the dead zone of the reverse process and increases the complexity of the control system.
The excitation reversible DC speed regulation system can not only realize the forward and reverse operation of the motor, but also enable the motor to realize regenerative braking, and convert the mechanical energy (including inertial energy and potential energy) on the motor shaft into electrical energy and send it back to the power grid. At the same time, the electromagnetic torque of the motor becomes the braking torque. The numerical control lathe draws the working condition of the motor in the four quadrants of the excitation reversible DC speed regulation system. Assuming that the motor runs forward in the first quadrant, the armature converter is in a rectifying state. The excitation is powered by the I bridges, and the motor gets power from the grid at this time. If the CNC lathe needs to be reversed, the motor should be braked quickly first, and the direction of the armature current must be changed or the direction of the motor back EMF must be changed, but for the armature converter, there is only one set of rectifier bridges, and the current cannot be reversed. flow, so it can only be achieved by changing the direction of the excitation direction to change the direction of the motor back EMF.
This requires the excitation to be switched from the original I group bridge power supply to the II group bridge power supply, and the armature rectifier bridge works in the inverter state (when the conduction angle of the rectifier bridge “< 90′, the rectifier bridge works in the rectifier state; the inverter angle When p < 90′, the rectifier bridge works in the inverter state). The inverter voltage UdB of the armature rectifier bridge of the CNC lathe is connected with the same polarity as the motor back EMF Ed, so that the motor braking current Id=IED-UdBI/R The numerical value is limited within the allowable range. At this time, the motor of the CNC lathe enters the second quadrant for forward power operation, and the electromagnetic torque becomes the braking torque, and the mechanical energy on the motor is converted into AC power through the armature rectifier bridge to feed back to the grid. By changing the value of the inverter angle, the degree of braking of the motor can be changed.
In order to keep the motor with sufficient braking torque during the braking process, the CNC lathe should generally continuously adjust the angle of the motor as the speed of the motor decreases. value, make it from small to large until p = 90′, the motor is braked in the forward direction, and the motor is stationary. If the quarrel continues to increase, it means a<90., then the armature rectifier bridge will work in the rectification state, and the motor will start Reverse, enter the reverse electric operation of the third quadrant.
The above process is the whole process of the motor from forward to forward braking until reverse. Similarly, the motor from the reverse to the reverse braking until the forward rotation, the process by the third quadrant through the fourth quadrant and finally run in the first quadrant r.
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