Stepper Motor Step Lost Reason And Solution
This paper explains the causes of stepping motor step lost in the process of economic CNC machines,and puts forward the
corresponding solution.Stepper motor and drive circuit are composed of open-loop CNC system,because of its simple structure,low price and reliable performance,are widely used in the economic CNC machine tools and have important status in China's machine tool industry process.Stepper motors are often used for precise positioning,so ensure that the motor does not lose step very critical.
Step Lost and its harm
When the stepper motor is operating normally,after receive one control pulse,and it moves a step angle,that is forward one step.If the control pulse is continuously input,the motor rotates continuously.Stepping motor out of step includes step lost and step skip.When the step is lost,the number of steps advanced by the rotor is less than the number of pulses.Step skip,the number of steps advanced by the rotor is more than the number of pulsed.Number of pitches of one step lost and step skip is equal to an integer multiple of the number of runs.When step lost is serious,the rotor will stay in a position or around a position to vibrate.Step skip is more serious,the machine will be overshoot.Stepping motor is an important part of open loop feed system,its performance directly affects the performance of CNC system.The motor step lost will affect the stability of the CNC system and control accuracy,resulting in CNC machining accuracy decreased.
Out of step reasons and solution
1. Rotor accerlation is slower than the rotating magnetic field of stepper motor
The torque of the rotor is slower than the rotational magnetic field of the stepping motor,that is,lower than the commutation
speed,stepping motor will lose step.It is because the input power to motor is insufficient,and the synchronizing torque generated by the stepping motor can not make the rotor speed to follow the rotational speed of the stator magnetic field,causing step lost.Since the dynamic output torque of the stepping motor decreases as the continuous operating frequency increases,all operating frequencies that are higher than the frequency will result in lost steps.This step lost indicates that the torque of the stepping motor is insufficient and drag capability is not enough.
Solution: ①stepper motor itself increase to generate electromagnetic torque.To achieve this,the drive current can be increased in the rated current range.When the torque is insufficient in the high frequency range,the driving voltage of the driving circuit can be appropriately increased;use a large torque stepping motor.② make stepper motor overcomimg small torque reduce.To achieve this,the motor operating frequency can be appropriately reduced in order to increase the output torque;a longer acceleration time is set so that the rotor obtains sufficient energy.
2. The average speed of the rotor is higher than the average rotation speed of the stator magnetic field
The average speed of the rotor is higher than the average rotation speed of the stator magnetic field,at this time the stator is energized for a long time and longer than the time required for the rotor step one step,the rotor obtains too much energy during the stepping process so that the stepping motor output torque increases,thereby causing the motor to skip step.When the stepping motor is used to drive the mechanism that operate load upper and down,it is easier to produce a step skip phenomenon because the torque required for the motor is reduced as the load moves downward.
Solution: Reduce the drive current of the stepper motor in order to reduce the output torque of the stepper motor.
3.Stepping motor and the load exist inertia
As the stepper motor itself and the load exist inertia,make the motor can not start and stop immediately at working,but lose step at start time,and skip step at stop.
Solution:through an acceleration and deceleration process,that is,start at a lower speed,and gradually accelerate to a speed operation,then gradually slow down till stop.Reasonable and smooth acceleration / deceleration control is the key to ensure the reliable,efficient and accurate operation of the stepping drive system.
4.The stepping motor generates resonance
Resonance is also a cause of out of step.When the stepper 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.In a control pulse period,the vibration is not fully attenuated,the next pulse to come,so the maximum near the resonance frequency dynamic error and will lead to stepping motor out of step.
Solution: appropriate to reduce the stepper motor drive current;use micro-step drive;use damping method,including mechanical
damping method.The above methods can effectively eliminate the motor oscillation,to avoid step lost phenomenon.