SUMMARY & GLOSSARY

Summary

Stepper motors have been used in a wide array of applications for many years. With trends towards miniaturization, computer control and cost reduction, “can-stack” style steppers are being used in an ever increasing range of applications. In particular the use of linear actuators has rapidly expanded in recent years. These precise, reliable motors can be found in many applications including blood analyzers and other medical instrumentation, automated stage lighting, imaging equipment, HVAC equipment, valve control, printing equipment, X-Y tables, integrated chip manufacturing, inspection and test equipment. This attractive technical solution eliminates the use of numerous components and the associated costs related to assembly, purchasing, inventory, etc. The applications for these motors are only limited by the designer’s imagination.

Terminology

Detent or residual torque:
The torque required to rotate the motor’s output shaft with no current applied to the windings.

Drives:
A term depicting the external electrical components to run a Stepper Motor System. This will include power supplies, logic sequencers, switching components and usually a variable frequency pulse source to determine the step rate.

Dynamic torque:
The torque generated by the motor at a given step rate. Dynamic torque can be represented by PULL IN torque or PULL OUT torque.

Holding torque:
The torque required to rotate the motor’s output shaft while the windings are energized with a steady state D.C. current.

Inertia:
The measure of a body’s resistance to acceleration or deceleration.
Typically used in reference to the inertia of the load to be moved by a motor or the inertia of a motor’s rotor.

Linear step increment:
The linear travel movement generated by the leadscrew with each single step of the rotor.

Maximum temperature rise:
Determined by the resistance rise method, motor unmounted in free air and energized with a steady state D.C. current.

Pull in torque:
The load a motor can move without missing steps when started at a constant pulse rate.

Pull out torque:
The load a motor can move when at operating speed. This is normally substantially greater than the Pull in torque.

Pulse rate:
The number of pulses per second (pps) applied to the windings of the motor. The pulse rate is equivalent to the motor step rate.

Pulses per second (PPS):
The number of steps that the motor takes in one second (sometimes called “steps per second”). This is determined by the frequency of pulses produced by the motor drive.

Ramping:
A drive technique to accelerate a given load from a low step rate, to a given maximum step rate and then to decelerate to the initial step rate without the loss of steps.

Single step response:
The time required for the motor to make one complete step.

Step:
The angular rotation produced by the rotor each time the motor receives a pulse. For linear actuators a step translates to a specific linear distance.

Step angle:
The rotation of the rotor caused by each step, measured in degrees.

Steps per revolution:
The total number of steps required for the rotor to rotate 360°.

Torque to inertia ratio:
Holding torque divided by rotor inertia.