Method for increasing torque of stepping motor at high speed
First, increase the voltage of the drive circuit: to maintain the high torque at high speed, it is necessary to keep the current unchanged, so that the chopper works in a constant current state. To keep the current constant, only increase the pulse frequency. When the output speed of the stepping motor reaches a certain high speed, it can only work in the constant voltage state due to the voltage limitation. If the input voltage is increased, it can still work in the constant current state at high speed, thereby improving the high speed. Torque.
Second, reduce the current when the drive circuit is turned off: When the current in the coil is turned off, due to the large current change rate, a very large induced voltage will be generated in the coil, and the power tube may be broken down, usually There is a protection circuit, which is composed of the following figure. In the figure, 1 is a freewheeling diode structure. When the power tube is turned off, the back EMF generated by the coil forms a release current path through a closed loop composed of a freewheeling diode and a coil. This current is in the rotor. The torque generated in the opposite direction to the steering is the braking torque, which causes the dynamic torque to drop. Correspondingly, 3 a resistor is connected in the diode branch to reduce the current that generates the braking torque.
The figure below shows the speed-torque characteristics of the 1 and 6 circuits in the above figure for the same stepper motor drive. The drive circuit 6 adds a resistor and a capacitor to the A and (bar A) phase-current circuits to reduce the current release. The speed-torque characteristics of circuits 1 and 6 are quite different. From this, it is seen that the structure of the drive circuit has a great influence on the dynamic torque of the stepping motor.