#### Problem solving

Analysis and solution of stepping motor out of step
Release Date : 2019-03-08 09:44:36

Analysis and solution of stepping motor out of step：

In the process of economical CNC machine tools, the reasons for the stepping motor out of step are analyzed comprehensively, and the corresponding solutions are proposed. The open-loop CNC system consisting of stepping motor and drive circuit has been widely used in economical CNC machine tools because of its simple structure, low price and reliable performance. It plays an important role in the numerical control process of China's machine tool industry. status. Stepper motors are often used for precise positioning, thus ensuring that the motor does not lose step.

Out of step and its harm:

When the stepping motor works normally, it moves one step angle every time a control pulse is received, that is, it goes further. If the control pulse is continuously input, the motor continuously rotates accordingly. Stepping motor out of step includes lost steps and steps. When the step is lost, the number of steps the rotor advances is smaller than the number of pulses; when the step is exceeded, the number of steps the rotor advances is more than the number of pulses. The number of steps lost and stepped is equal to an integer multiple of the number of beats. When the step is lost seriously, the rotor will stay in one position or vibrate around one position. When the step is serious, the machine will overshoot. The stepping motor is an important part of the open loop feed system, and its performance directly affects the performance of the CNC system. The loss of the motor will affect the stability and control accuracy of the CNC system, resulting in a decrease in the machining accuracy of the CNC machine.

Reasons for loss of synchronization and solutions:

1. Rotor Acceleration Slow Substepping Motor Rotating Magnetic Field Rotor Force n The speed is slower than the rotating magnetic field of the stepping motor, that is, when the commutation speed is lower than the commutation speed, the stepping motor will lose the step. This is because the power input to the motor is insufficient, and the synchronizing torque generated in the stepping motor cannot cause the rotor speed to follow the rotational speed of the stator magnetic field, thereby causing out-of-step. Since the dynamic output torque of the stepping motor decreases as the continuous operating frequency increases, any operating frequency higher than this frequency will result in lost motion. This out-of-step indicates that the torque of the stepping motor is insufficient and the dragging ability is insufficient. Solution: 1 Increase the electromagnetic torque generated by the stepping motor itself. For this reason, the drive current can be appropriately increased within the rated current range; when the torque in the high frequency range is insufficient, the drive voltage of the drive circuit can be appropriately increased; and the stepping motor with a large torque can be used instead. 2 The torque that the stepping motor needs to overcome is reduced. To this end, the motor operating frequency can be appropriately reduced to increase the output torque of the motor; a longer acceleration time can be set so that the rotor obtains sufficient energy.

2. The average speed of the rotor is higher than the average rotational speed of the stator magnetic field. At this time, the stator energizes for a longer time, which is longer than the time required for the rotor step. The rotor obtains too much energy during the stepping process, so that the step The output torque generated by the incoming motor is increased to cause the motor to step out. When a stepping motor is used to drive those mechanisms that act to move the load up and down, it is more likely to cause a step-by-step phenomenon because the torque required by the motor decreases when the load moves downward. Solution: Reduce the drive current of the stepper motor to reduce the output torque of the stepper motor.

3. The inertia of the stepping motor and the loaded load is due to the inertia of the stepping motor itself and the loaded load, so that the motor can not be started and stopped immediately during the working process, but the lost step occurs at the start, and the step occurs when the stop occurs. . Solution: Start through a process of acceleration and deceleration, that is, start at a lower speed, then gradually accelerate to a certain speed, and then gradually slow down until it stops. Proper and smooth acceleration and deceleration control is the key to ensure reliable, efficient and accurate operation of the stepper drive system.

4. The stepper motor generates resonance, and resonance is also a cause of out-of-step. When the stepping motor is in continuous operation, if the frequency of the control pulse is equal to the natural frequency of the stepping motor, resonance will occur. During a control pulse period, the vibration is not sufficiently attenuated, and the next pulse comes, so that the dynamic error is greatest near the resonance frequency and causes the stepper motor to lose synchronization. Solution: Appropriately reduce the drive current of the stepping motor; use the subdivision drive method; use the damping method, including the mechanical damping method. The above methods can effectively eliminate motor oscillation and avoid out-of-step phenomenon.