Stepper Motor starting pulses
Stepper Motor starting pulses
(OP)
Hi!
Would someone please answer what are starting pps(pulses per second?) parameter of a stepper motor. This parameter is different than that while it is running?
Thanks in advance,
Zahid
Would someone please answer what are starting pps(pulses per second?) parameter of a stepper motor. This parameter is different than that while it is running?
Thanks in advance,
Zahid





RE: Stepper Motor starting pulses
RE: Stepper Motor starting pulses
(this is another way of asking the same question of 4 msec. per step time)I shall be grateful for the reply.
Zahid
RE: Stepper Motor starting pulses
If you input a step pulse frequency to the drive at around this resonant frequency, the motor can oscillate pretty wildly and lose synchronism. This can even occur if you are ramping the pulse frequency through this resonant frequency.
For this reason, some stepper indexers and smart drives permit you to set a starting frequency, so you can start above the problem frequency. Rather than ramping to full speed from zero, as a servo system would typically do, there is a velocity step to this frequency followed by a ramp to the full frequency of the move.
Of course, the velocity step creates its own problems, as it is a request for infinite acceleration, so you have to be careful with this.
Curt Wilson
Delta Tau Data Systems
RE: Stepper Motor starting pulses
What effects the resonance of the motor have on the driver?
sincerely,
Zahid
RE: Stepper Motor starting pulses
The full speed PPS is limited by the ability to drive current into the step motor phase inductances.
The spec numbers are usually no load numbers and often reflect the best case situation (salesman numbers). The performance in a system is usually )a lot) lower.
RE: Stepper Motor starting pulses
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Stepper Motor starting pulses
As to the effects of motor resonance on the drive itself, they should be minimal to non-existent. A stalled motor will have much less back EMF at the terminals, and you won't have a consistent pattern of inductance changes, but these won't really affect the drive.
The key issue is the motor's inability to follow command sequences when the pulse rate is near the resonant frequency.
Curt Wilson
Delta Tau Data Systems
RE: Stepper Motor starting pulses
Zahid
RE: Stepper Motor starting pulses
Curt Wilson
Delta Tau Data Systems
RE: Stepper Motor starting pulses
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Stepper Motor starting pulses
RE: Stepper Motor starting pulses
Thinking of the issue in the time domain: Because there is almost no damping in the motor's response to a step, one period of the resonant frequency after the step command is given, you will be almost back to the starting position. In a full-step system, if you try to issue the next step at this time, you will have virtually zero torque. One step like this, and you could lose sync and not recover.
By the way, this is one of the key problems that microstepping was invented to solve. In my opinion, the fact that microstepping solves this problem is probably more significant for most applications that the increase in final positioning resolution.
Curt Wilson
Delta Tau Data Systems
RE: Stepper Motor starting pulses
At one time I worked on a floppy drive tester. One test was to do track seeks in which you could specify how many tracks to jump and how many times. All drives would mis-step if you found the found the correct frequency and did it long enough. And the tester had a Random Mode just to find the combination to make this happen.
RE: Stepper Motor starting pulses
The starting pps setting on a controller is there so you can start the motor moving at a speed at which it will reliably move the load without losing steps, and ramp up smoothly from there. For a size 23 stepper and a load you can hold in your hand 100pps works okay as a starting point.
With a controller you can make from something primitive like an 8048, you can ramp an average load by changing the timing by about 3 pct per step, and not much more. With dynamic analysis of the _exact_ load you intend to move, much faster ramp rates are possible. (The analysis basically uses the ringing from step N as the start of step N+1). Google Taft, Gauthier, University of New Hampshire)
There's not much damping in the motor or mechanical parts of the drive, but there's often damping in the circuit that drives the motor coils... that circuit has a huge effect on motor performance, so motor comparisons should all be made with the same circuit.
The other reasons for starting at a (mechanically high) pps like 100Hz are to save time, and to avoid exciting the building you're in. Ramp a stepper up at 3pct per step from 1 Hz, and you'll excite the building as you pass near 4 Hz, getting everyone's attention. Don't believe me; you'll be locally famous for a while.
Mike Halloran
Pembroke Pines, FL, USA
RE: Stepper Motor starting pulses
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com