Microstepping
Micro stepping
Micro stepping is a method of moving the stator plug of the stepper motor more smoothly than it is in the full or half step drive mode.
The process of micro stepping helps in reducing the vibration and produces noiseless stepping as low as 0 Hz. It even make the step angle smaller and the positioning becomes much better.
In general ther are number of microstepping mode such as with the step lenght from 1/3 full step
micro stepping process
down to 1/32 full step or even less.
We need to clarify are cocept about the two topics full stepping and half stepping first
Full stepping
As we know that the stepper motor drives the motor winding with either full positive, full negative or no current. In this operation the current which is required by each winding is either -Im or +Im. 4 full step makes up one complete cycle.
Half stepping
The current required by each winding is -Im, 0 or +Im. 8 half step makes up the complete cycle. In this case the motor moves just half of what it moves in the full stepping.
full and half stepping process
Micro stepping implementation
For the implementation of the micro stepping the driver should deliver variable amount of current to the motor winding which requires a PWM type or a chopper such that it implementaion becomes much complex as compared to full or half stepping method. It is to be noted that the motor winding current is either sine or cosine of the peak current(Ip) called micro step. Such that the motor is made to move in equal and small micro step before a complete full step can be completed. It is the best method of driving a stepper motor as compare the above two as there is no low speed vibrations if each of the micro step choosen carefully and the implementation with the chopper or PWM type is done properly.
Actual expression for incremental torque single micro step
Tin= THS *sin(90/mfs)
The expression for incremntal torque for n micro step.
Tn = THS*sin((90n)/mfs)
Where ,
Tin – incremental torque per micro step
Tn– incremental torque for n micro step
n- no. of micro step taken
mfs– no. of micro step per full step
THS- holding torque per full step.
It is to be noted that n<= mfs.
Why micro step is choosen?
The usage of micro step result in
1. Reduced mechanical noise
2. Reduced vibration problem
3.Gentle mechanical actuation
However in spite of the above advantages the proper accuracy is not realized in micro stepping. In many application micro stepping lowers down the complexity of the system and cause, even increases the system performance.
Improved system accuracy
A micro stepping can be used to increase the stepper motor position accuracy. For this one needs design a microprocessor based micro stepping system. This technique can be used when maximum step accuracy is th emost important design criteia. If this technique is used the system has to use a rotor home position indicator to synchronize the rotor with the compensation profile.
What affects micro stepping performance?
Actually lots of phenomenon affects the performance some of them are related to the motor and other to the driver.
Remedy measure
High precision driver with the combination of TBM 3960 and PBL 3771 or any of its equivalent are used then the errors with the motor can be neglected.
Related question and answer
1. What is micro stepping?
Ans: Micro stepping is a method of moving the stator plug of the stepper motor more smoothly than it is in the full or half step drive mode. The process of micro stepping helps in reducing the vibration and produces noiseless stepping as low as 0 Hz. It even makes the step angle smaller and the positioning becomes much better.
2. Advantages of micro stepping.
Ans: 1. Reduced mechanical noise
2. Reduced vibration problem
3.Gentle mechanical actuation
3. How micro stepping is better then full stepping and half stepping approach?
Ans: For the implementation of the micro stepping the driver should deliver variable amount of current to the motor winding which requires a PWM type or a chopper such that it implementation becomes much complex as compared to full or half stepping method. It is to be noted that the motor winding current is either sine or cosine of the peak current(Ip) called micro step. Such that the motor is made to move in equal and small micro step before a complete full step can be completed. It is the best method of driving a stepper motor as compare the other two as there is no low speed vibrations if each of the micro step chosen carefully and the implementation with the chopper or PWM type is done properly.
4. What is the drawback of microstepping and how can be remove it?
In spite of the various advantages the proper accuracy is not realized in micro stepping.
Important for electrical students.A stepper motor (or step motor) is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor’s position can then be commanded to move and hold at one of these steps without any feedback sensor (an open-loop controller), as long as the motor is carefully sized to the application.
A short note on Microstepping , it is a concept of Motor.There are two types of microstepping half and full whose respective diagrams are also added in post and explained. Going through the post can be helpful !!!
Microstepping is a sheer technical concept, related to stepper motor! It would be important for the related field’s engineers to know it in order to work on improvisation.