Microstepping is a technique to control stepper motors, usually used to gain higher resolution or smoother motion at low speeds.
What is Stepper Motors?
Stepper motors are open-loop, cheap, user-friendly, and robust motors. They offer numerous advantages over other electric motors:
- They have high torque at low speeds and stall mode.
- Their speed is easy to control via modulation of pulse widths (PWM).
- They have pretty good accuracy.
- They have a great response to start/stop.
When precise and reliable positioning is needed at a low cost, then stepper motors are the obvious choice. What is Microstepping?
What is Microstepping?
Consider decreasing torque while micro-stepping a stepper motor for precision.
Microstepping is achieved by dividing full steps into smaller steps and this is the reason for the smoothness of motors rotation at low speeds.
For example, if you divide a 1.8-degree step 256 times, it will provide a step angle of (1.8/256)=0.0007 degrees or 51,200 micro-steps per revolution.
For example, if you divide a 1.8-degree step 256 times, it will provide a step angle of (1.8/256)=0.0007 degrees or 51,200 micro-steps per revolution.
Why Microstepping in Stepper motors?
Microstepping has three major benefits: - reduced Mechanical Noise.
- gentler Actuation Mechanically.
- reduces Resonances Problems.
Full Step Position Vs. Time |
Microstepping Position Vs. Time |
Microstepping significantly reduces positioning oscillations.
Images credit: Dover Motion
What is the downside of micro-stepping in
stepper motors?
- Torque Vs. Shaft Position:
Dotted line: Suitable response for precise micro-stepping positioning. Blueline: Distorted curves. |
The real downside is that the incremental torque/micro-step drops off considerably if you increase the number of micro-steps per full step. A few stepper motors have a clean sinusoidal torque vs. shaft position and every stepper has higher-order harmonics which results in distorted curve and accuracy (see graph below).
- Incremental Torque per Microstep/Full Step:
Where:
μPFS = Number of Micro steps per Full Step [Integer]
N = Number of Micro steps Taken [Integer]
N Less than or equal to μPFS
MHFS= Holding Torque-Full Step [Nm]
MINC = Incremental Torque per Microstep [Nm]
MN = Incremental Torque for N Micro steps [Nm]
N Less than or equal to μPFS
Table 1 dramatically quantifies the significant impact of the incremental torque per micro-step as a function of the number of micro-steps per full step. A full step is considered one micro-steps per full step for Equations 1 and 2.
Incremental Torque per Microstep as the Number of Micro steps per Full Step Increase:
Summary
There are pros and cons to micro-stepping. To decide if it's right for your application, you need to understand these pros and cons. Microstepping is not for everyone, but it can be useful for certain applications.
Incremental Torque per Microstep as the Number of Micro steps per Full Step Increase:
Comments
Post a Comment