Hi,
I am trying to determine at what speed does one need to apply an acceleration ramp and deceleration ramp to a stepper motor drive. All the books say you should have one but really, it would depend on how fast things are moving no?
If I am stepping at 1 step/second, then clearly no acceleration ramp is needed. If I am at 1000 steps / second, ya you should have acceleration and deceleration ramps. But what about 100 steps/second? Basically running the motor at 2 RPM. Is it needed? How can you determine this?
Thanks for any insite.
Tom
There is no simple answer to that. It depends on the load on the motor and the torque of the motor relative to the torque needed for moving the load.
I think the only reliable solution is trial and error with the actual application.
I guess the safe solution is to use acceleration unless there is some reason not to.
I have been wondering, but have not got around to testing, if a step-wise acceleration would be sufficient - for example get to 1000 steps/second by first running at 350 and then 700 and then 1000.
Of course you also need to consider whether the application can accept rough treatment.
...R
think about it
motor at rest so rotational velocity equals zero
motor then receives a single step command
it could be argued that at that instant the requested accelation is "infinite" and only limited by the inertia of the motor rotor
so in answer to the question, acceleration ramp rate may always be applicable, irrespective of step rate, but the value may be irrelevant to the particular operation, so only you can decide
Momentun doesnt go away at low speeds, max acceleration always applies, however if the top speed is reached in about one step you get away with it
You need to control the step rate acceleration when the step torque is less than the torque needed to overcome:
- the driven inertia i.e. resistance to changing speed (not momentum!)
- frictional losses
- electrical and magnetic losses
- any work load.
The step torque depends primarily on the motor specifications and current flowing, the torque and will decrease with speed for various reasons so the acceleration limit at higher speeds will be lower to the point where it will not be possible to accelerate at all.
You can calculate the acceleration limits at different RPM by computer modelling the system, or you can find out empirically.
If the rate of change (acceleration or decelleration) of the stepping frequency is too great then angular steps will get missed and the stepper motor will not turn through the expected angle.
I've done some applications without acceleration and my experience suggests to definitely use acceleration in all cases.
Try the excellent AccelStepper library by Mike McCauley - makes it really easy