f2424 stepper motor problem

[mwchildress]

I just purchased the F2424 board and we are trying to run a stepper motor (vexta PK268) directly from the board.  At stepspeed 50-450 the motor sounds an rotates smoothly.  Over 450 - 800 pps the motor sounds dirty.  Over 800 pps the motor will no longer rotate. We have tried just about every combination of ramp speed with no change in motor rotation over 800 PPS. We need this motor spinning at 4000 pps .  We have unhooked the motor from the rotary table and hooked the wires directly to the board.  We have verified the correct wiring of the motor several times.   We have moved to a simple program that only moves the motor  and we have installed the diodes as dictated by the manual.  The motor is powered by the same 24 volts as the board.  Any suggestions you might have would be greatly appreciated.
 
 
Michael

[support]

Most stepper motor maximum stepping rate is about 600 to 1000ppm. This is limited by the physics of stepper motor. Stepper motor drivers that claim to output many thousands of pps is actually doing "microstepping" which means they break a single step into say 8 to 256 "microstep" which is achieved by applying different voltages on the winding to turn it slightly away from its normal step. However, the actual stepping rate of the motor is still limited by what the motor can achieve.

You can try half step mode to achieve smoother operation. You probably can drive it up to 1600 pps smoother than full step mood. You still can't drive it beyond its maximum ability to spin. If faster speed is required, use a gear box.

[mwchildress]

That may be true however,  This motor was running through a driver UDK2120a at 3800 pps full steps for several weeks.  The driver went bad and we chose to upgrade to the f2424 from the 888 for about the same price as the driver. Now I have a machine down and it only rotates at a fraction of what it was before.Its current RPM at 450 PPS is 135.  This motor was spinnig at 1140 rpm before the change well within what vexta states this motor is capable of.  I need to get this motor spinning to the level it was.  

[support]

What we learn is that in order to drive the stepper motor above the standard max pps limit it will need to be over-driven with higher than rated voltage but with carefully controlled current (via or PWM or chopped current technique) in order to prevent burning out of the motor coil or the driver. The dedicated stepper motor driver you used may have employed one of these techniques as well as micro-stepping in order to achieve the needed speed-torque curve.

Unfortunately on the F-series PLC the stepper motor outputs send pulses only as pure square waves and do not employ any over-driving technique to achieve beyond the standard rated maximum pps.

However, F-series PLC can be programmed as "controller" mode and send pulse and direction signal under program control to external micro-stepping motor driver that may drive the motor a higher speed.