Danaher Motion Superior Electric
Section 5: Torque Versus Speed Characteristics
SS2000 D3 AND D6
15
SECTION 5: TORQUE VERSUS SPEED
CHARACTERISTICS
5.1 M
OTOR
P
ERFORMANCE
All stepper motors exhibit instability at their natural frequency and harmonics
of that
frequency. Typically, this instability occurs at speeds between 50 and 500 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
.
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