T100MD step motor speed control

[hareldvd]

Hi,

We need an accurate step motor speed control to run a pump in a speed range of  20-500 pps so we will have accurate flow.
We discovered that step motor speed is not increasing smoothly rather in gaps of about 4% of the current speed. That is if the speed is about 200 pps the next speed I can get is 208 pps.
We measured the step motor output channel using Frequency counter to reassure our findings but you can also hear the sound of the motor. If you increase the  speed by incrementing pps value in stepspeed command you will here that if starting from 200 pps the sound doesn't change until it reaches 208.
We also thought of changing step motor steps to 1 eighth step and increase the pps value in the plc that is:
stepspeed 1, e*8, 5
but that didn't help because that 4% gap was still on on hight speed values.
Is there any measure I can take to increase speed accuracy?

[AlbertMartinez]

What are the exact STEPSPEED and STEPMOVE commands parameter values that you are using to control Step Motor.

Are you executing STEPSPEED command first before executing STEPMOVE command?

Are you waiting until current STEPMOVE command is compleated before executing the next STEPMOVE command?

Is your STEPMOVE "count" parameter value at least twice the STEPSPEED acceleration parameter value?

Albert Martinez
martinezalbert@yahoo.com

[support]

Stepper motor final speed is only an approximate figure and it depends on the number of steps it takes to accelerate to the final speed. Try with more acceleration steps to get finer resolution of the stepper speed. The motor may run smoother that way too.

[hareldvd]

I fail to identify replies on this forum and for some reason I do not get a mail notification. Is there some kind of mailing list I can be a member of instead of this forum?

And now for the real thing.

The command I do to start the motor is in a function called 53-MotorStart. it is performed only once and has this code in it:
stepspeed 1, 1, 1
stepmove 1, 2147483647, 10

In function called 51-Operate and in function 52-Calibrate I recalculate the speed according to changes in fluid level measured from analog input 1. (code further below).

The motor rotates all the time only the speed is changed and that is also very gradually. (would the motor reach end of track I restart it using relay 10 as a trigger).

Code snip:
call FluidLevel

' calculate the new exit motor speed
' fluid level     Motor spec   Definition of 100% fluid level
'                   400          3000
if (dm[52] > 0 and dm[53] > 0)
  e =  dm[53] *     dm[51]   /   dm[52]
else
  x$ = "Fluid level 0 !!  "
  call ShowErr
endif

' set the motor speed
if (e > 0)
  stepspeed 1, e, 1
  stepmove 1, 2147483647, 10
else
  stepstop 1
endif

[support]

I understand what you are trying to use it for.  What you need is a precision pulse generator that can generate pulses of desired frequency. Unfortunately, the stepper channels were actually designed for motion control and the main purpose is to move a motor a precise number of steps and to accelerate/decelerate a number of steps to/from  the maximum desired speed. We were less concern with the exact speed of the motor at any one time.  The stepper motor controllers is not designed to be precision pulse generator and therefore is not exactly suitable for your application.