Lets do some math:
- For a 20" diameter disc, the circumference is 62.832"
- You commanded a move of 1.5" in Mach, and since your steps per inch is 25600, then idealy 1.5x25600=38400 pulses need to be sent to the stepper for that linear movement.
The DRO in Mach should have iindicated 1.5000" change in position. The mechanical indication of that movement is relative to the pointer position as compared to the
the mark on the disc. Note that we are "relating" electrical to mechanical movement and idealy you would measure the pulses sent out the pp, the pulses recieved by the
drive, the pulses sent from the drive to the stepper, and finaly use a physical indication of the rotor positioin . I have done the this using a custom input pulse counter accurate
to parts per million which provides direct comparison. You don't have that kind of equipment, nor I, but the disc measurements although not exact, are very indicative
of the TOTAL pulses sent.
- One revolution of the disc requires 200 pulses and since you are microstepping, then, 200 x 8= 1600 total steps to rotate the disc 1 revolution.
- If 38400 pulses are recieved by the stepper, then 38400 PULSES / 1600 PULSES PER rotation of the stepper rotor = 24 rotations of the disc.
- The disc actualy rotated 24 times plus some additional amount ( .060" on the disc) which is equal to .3437 degrees too much ( approx).
- One degree on the disc, 1600 pulses per 360 deg per roatation= 1600 / 360 = 4.444 pulses / degree.
The rotor turned too much, thus 4.444 pulses per degree x .3437 degrees = 1.5274 pulses to manny. Well kind of ....readon....
Now to relate some of the above info:
- Not all drives are equal and thus there is non linearity associated with them. Not all steppers are equal on thier ability to position accurately in the microstepping.
If you read the posted links by Ian in reply #13, you would understand that when a stepper recieves a pulse to make a small move it may take more than one since
since it must overcome the detent torque and internal friction. Then depending on the magnetic field and position of the rotor it can after a few pulses then overmove.
A good example of this can be done using your disc to see how manny jogs it takes to move just .0001". May take more than calculated or rotor may move more than deisred.
In fact each position will vary over the complete revolution, won't be exactly linear and you can't tell if the drive or motor has smore influence on this.
This is just when moving in one direction, now apply the same thinking to a change in direction, and then consider that linearity will be different when going the other direction.
Do you now understand why i only wanted to do one direction moves and i also wanted you to position the rotor so that it would not need to reserse direction?
So you get some data for only a single direction move, then you get get some data on changing direction, then data on the other direction. You will then have an
understanding of how things relate and then a base do do changes to see if some settings will improve things.
Now remember that the motor needs to ramp up to speed and then also ramp down to stop. An the power supply can have an impact on that and also positioning.
Do now understand why I wanted you to do this at a slow feed rate and acceleration and only one drive at time?
BTW, pulses are on and off comming out of the PP, whole pulses, so there is no such thing as sending a 1.5274 pulse.
- The smallest move you can do, if all was ideal, is 1/25600=0.000039" for a linear move. So say, two pulses too manny were sent for example,
then your axis would be out of position by 0.0008". Is that repeatable for a one direction move?
I have lots of patience and also had problems with my mill when i started doing 3d cutting.
Your the one doing the testing ...........,
RICH
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