Looking for references to drive step motor (acceleration/deceleration)... - Page 1
Forum section: electronics / projects

author: ElektroQuark
author_rank: Unknown
timestamp: June 07, 2016, 10:52:20 am
content: Hi,New with steppers here.Do you have any link to reliable information on how to drive a step motor? By driving I mean how to accelerate, decelerate.I'm using the motor with a TI DRV8834.

author: mubes
author_rank: Regular Contributor
timestamp: June 08, 2016, 09:03:39 pm
content: You don't say what the application is, but GRBL is a good first reference;https://github.com/grbl/grblSmoothieware is the great grandchild of GRBL;http://smoothieware.org/These are intended for machine control, but the principles are general.DAVE

author: Skashkash
author_rank: Regular Contributor
timestamp: June 08, 2016, 09:23:18 pm
content: I had luck with the following app note.http://www.atmel.com/images/doc8017.pdf

author: Siwastaja
author_rank: Super Contributor
timestamp: June 09, 2016, 06:08:54 am
content: IMHO (I know some people will disagree), any resource that talks about full or half stepping a stepper motor, showing a "step sequence" and the square waves, should be totally ignored (except for historical context).It is true that stepper motors have been traditionally used this way (the name "stepper motor" suggests it too), but it is physically wrong and often totally unsatisfactory due to horrible vibration. The reason has been the simplicity using the 80's tech, and direct control from a microcontroller. For the same reason, unipolar stepper motors exist.In essence, a stepper motor is a 2-phase synchronous AC motor, and is best excited with sine waves. Phase2 is simply 90 degrees out of Phase1. These sine and cosine waves define a magnetic field with a nicely turning phasor. This turns the motor.Traditional "stepping" table is just an extremely crude approximation. The magnetic field takes huge steps, causing severe vibration, also limiting maximum speed and torque because the mechanical oscillation easily makes it slip from the position (skip steps). Some "stepper motors" cannot be "stepped" like this practically at all, while some very small motors, designed for this, are just fine for limited applications.Today, we have integrated ICs that work as switch mode converters to produce the sine wave at a great efficiency. These also provide current limitation, which is great because it automatically provides the V/f scaling; the fact that you need higher voltage with higher speeds to get the same current and hence, torque. With these drivers, you only need to configure the current rating of the motor and off you go!So, stepper motors today are almost always controlled by a sine wave generated with high frequency switching. But as you still want to have discrete "steps" you can count (so that you can position the motor at a known position relative to the previous positions), this sine wave is quantized in a number of discrete "microsteps". You can often configure the number of microsteps the driver IC produces; typically, 64 or 128 microsteps per "actual step" is more than good enough for smooth operation.

author: ElektroQuark
author_rank: Unknown
timestamp: June 09, 2016, 07:25:59 am
content: Time to read. Thank you.