Paul,
Your actual rate of acceleration will depend on your power supply's ability to deliver the pulse current necessary and your load inertia. In many cases what's possible may be in excess of what you want because of the large reaction forces rapid acceleration imposes. It tends to bang mechanisms about at the limits of what can be achieved.
To a lesser degree the rate of acceleration also depends on the spectral purity of the step pulses. Raggedy-ass step pulses have large pulse-to-pulse period variations. These impose ripple accel and decel loads that robs the motor of torque that otherwise would be applied to the load. It's like drag-racing your car while hitting the brake and gas in rapid succession; not the best way to win a race while the other guy stands on the gas pedal only.
To give an idea of what's possible, we have used a G2002 controller (very pure step pulses) with an ordinary 500W NEMA-34 motor. Unloaded, it was able to accelerate to 3,000 RPM in 20mS (0 to 3,000 RPM in 180 degrees of shaft movement), then back to zero RPM in another 20mS. Exactly one revolution of the motor in 1/40th of a second.
To look at it, you couldn't see the motor move. It was too quick. The only thing to give it away was the way the motor would shake the test stand and bench. This is one puppy you would not want loose when you do this. Ask me how I know.:-)
Mariss  |