Superior SS2000MD4 Torque Versus Speed Characteristics, Motor Performance

Danaher Motion Superior Electric

SECTION 5: TORQUE VERSUS SPEED CHARACTERISTICS

5.1MOTOR PERFORMANCE

All stepper motors exhibit instability at their natural frequency and harmonics of that frequency. Typically, this instability occurs at speeds between 50 and 1000 full steps per second and, depending on the dynamic motor load parameters, cause excessive velocity modulation or improper positioning. This type of instability is represented by the open area at the low end of each Torque vs. Speed curve.

There are also other instabilities that cause a loss of torque at stepping rates outside the range of natural resonance frequencies. One such instability is broadly defined as mid-range instability. Usually, the damping of the system and acceleration/deceleration through the resonance areas aid in reducing instability to a level that provides smooth shaft velocity and accurate positioning. If instability does cause unacceptable performance under actual operating conditions, use the following techniques to reduce velocity modulation.

1)Avoid constant speed operation at the motors unstable frequencies. Select a base speed above the motors resonant frequencies and adjust acceleration and deceleration to move the motor through unstable regions quickly.

2)The motor winding current can be reduced as discussed in Section 4.5. Lowering the current reduces torque proportionally. The reduced energy delivered to the motor can decrease velocity modulation.

3)Use the half-step mode of operation or use microstepping to provide smoother operation and reduce the effects of mid range instability. Microstepping reduces the shaft speed for a given pulse input rate.

SS2000MD4 18 400030-043 Rev G