Another query re Mitsubishi FX RAMP funtion

Hi again,
I'm using an FX2 with the Ramp funtion to drive a step-motor driver (via PLSY) and having problems with the motor either not finishing its accel or decel in the expected time or not achieving its required speed.
I'm using a fixed scan period (longer than the measured max D8012) and the Ramp "Hold" mode to maintain speed after acceleration.
Does anyone know how the Ramp function actually deterines the ramp rate?

The instruction is "RAMP S1 S2 D n"

Does it say, divide the range (S2-S1) by n and increment (or decrement) S1 by this ammount on each scan (like the PLSR function).
Or does it do something more sophisticated like apply some non-linearity to the a-d ramp.
Any help appreciated.

Been a while since I used the PLSY. Are you monitoring M8029 to see if the pulse count finished? Maybe your motor is losing steps/ stalling?

Hi Tommy, thanks for responding.
As I'm ramping down to very low speeds (the "fast" speeds aren't particularly fast) and there's very little load on the motor, I thought it unnecessary - but I'll give that a try when I'm next at the machine (in a few days time).
Having thought a lot about it I'm now wondering if the problem may be because OF THE low speeds....
I'm trying to decelerate within 160mS; the period of the lowest frequency is about 20mS and the fastest about 2mS, so if, as I suspect, the ramp period is equally divided by "n" program scans (40 in this case), that'd only be 4mS per increment - yet I'm trying to generate a 25mS period in the last one (and probably greater than 4mS in the few before that)!! If so, I'm sure that could be what's screwing things up.
I'm using really low speeds initially so I can try to see what's happening but even then, the final design speeds aren't going to be significantly faster.

Dave

Remember stepper motors have a resonant band and they have to be ramped though quickly to avoid. I always had problems starting from a zero setting, needs to be started from a value above 0. I will look at a past application tonight to see if I have any other words of wisdom- still clearing out some cobwebs from years ago.
-tt

Thanks again

Dave, Sorry it took a few days, but...
I looked at my old program for stepper. I used an FX1S, so your FX2 should work. I did not use the ramp. I used the DDRVI and DDRVA commands (incremental and/ or absolute moves). These allow you to input a bias value, min and max speeds into registers allocated for the command. If you have the programming manual II, look at page 5-158. If you need to download it:

http://meau.com/Files/JY992D88101-D.PDF

For my application, I used for the first rung:
M8000 (N.O. CONTACT)
MOVP K250 D8145
MOVP K20000 D8146
MOVP K500 D8148
M8028 (ON)

This set up the main function, so in the command line, use something like this:
M (START MOVE) DDRVI K4000 K6000 Y0 Mx

This did work very well, and solves a lot of problems with the ramp command.

Good Luck,
tt