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Glossary

GLOSSARY OF TERMS

• Acceleration

The change in velocity as a function of time. Acceleration usually refers to increasing velocity. Generally refers to the rate of change in instantaneous velocity. In common speech, the term acceleration is only used for an increase in speed. In physics, acceleration is defined as the rate of change of velocity, or as the second derivative of position (with respect to time). In SI units, acceleration is measured in meters/second² (m•s2).

• Back EMF

Back Electro-Motive Force (BEMF) occurs in motors or Counter Electro-Motive Force (CEMF) occurs in inductors. BEMF is a voltage produced across a winding of a motor due ot the winding turns being cut by a magnetic field while the motor is operating. This voltage is directly proportional to rotor velocity and is opposite in polarity to the applied voltage.

• Damping

Related to settling time is an indication of the rate of decay of a signal to its steady state value.

• Deceleration

The change in velocity as a function of time. Deceleration usually refers to decreasing velocity. Generally refers to the rate of change in instantaneous velocity. In common speech, the term deceleration is only used for a decrease in speed. In physics, deceleration is defined as the rate of change of velocity, or as the second derivative of position (with respect to time). In SI units, acceleration is measured in meters/second² (m•s2).

• Detent Torque

Remnant positioning holding torque of unenergized motor with permanent magnets.

• Holding Torque

Also, called Static Torque. Maximum external force that can be applied to a stopped but energized motor without causing the rotor to rotate.

• Microstepping

An electronic control technique that proportions the current in a step motor’s windings to provide additional intermediate positions between poles. Produces smooth rotation over a wide speed range and high positional resolution.

• Mid-Range Instability

Designates the condition resulting from energizing a motor at a multiple of its natural frequency (usually the third orders condition). Torque loss and oscillation can occur in under damped open-loop systems.

• Pull-In Torque

Maximum torque that motor can overcome to accelerate stopped load to the synchronous speed.

• Pull-Out Torque

Maximum frictional torque the motor can overcome on the rotating load before the load in pulled out of step by the friction.

• Pulse Rate

The frequency of the step pulses applied to a motor driver. The pulse rate multiplied by the resolution of the motor/driver combination (in steps/revolution) yields the rotational speed in revolutions per second.

• Ramping

The acceleration or deceleration of the motor. May also refer to the change in frequency of the applied step pulse train.

• Resolution

The smallest positioning increment that can be achieved in motor/driver combination. Usually defined as the number of steps required for a motor’s shaft to rotate one complete revolution.

• Step Angle

The angle the shaft rotates upon receipt of a single step pulse.

• Torque

Force tending to produce rotation.

Fundamental information about step motors can be find here: http://www.designnews.com/author.asp?section_id=1365&doc_id=271183