glossary

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A
Acceleration ramp

Gradual change in control frequency of a stepping motor to move from one given speed to another (e.g.: acceleration ramp, deceleration ramp).

Accuracy

Measurement of the difference between the expected theoretical position and the actual position reached. For a stepping motor, accuracy is independent of the number of steps of displacement.

B
Back e.m.f.

Voltage created at the motor coil terminals when the rotor turns. Back e.m.f. is proportional to the speed and number of turns in the coil.

C
Controller

Logic stage of a control circuit. The controller generates signals to control the driver.

D
Detent torque

Torque produced by the motor when it is not powered and its coils are not in short-circuits. It is therefore the torque needed to turn the rotor when the motor is completely disconnected.

Driver
Power stage in a control circuit.


Duty cycle
This is the ratio between duration of use of a motor (ton) and total duration of the control cycle (ton + toff).


E
Efficiency

Ratio between mechanical output power and electrical input power.


Electrical time constant
Time needed for the current to reach 63.2 % of the final asymptotic value set by a voltage scale. The electrical time constant equals the ratio of inductance to resistance: L/R


F
Full step

Elementary displacement of the rotor when the motor power moves from one phase to the next.


H
Holding torque

Maximum torque produced by the motor when it is powered at rated current. This torque is measured in static mode.


I
Increment

Linear displacement obtained by a full step rotation of a motor.


Inertia
Measurement of resistance of bodies to any change of speed.


L
Linear actuator

Electromechanical system producing a force and linear displacement by means of a motor and movement conversion.


M
Micro-step

Subdivision of a full step used to obtain better resolution and reduce torque oscilla­tion.


P
Period-electrical period

Constant time interval separating two successive passages of the variable conside­red by the same value, with the same direction of variation.
The electrical period is the time needed to perform one control cycle, i.e. the equi­valent of 4 full steps.


Phase
Set of poles and coils producing torque.


Pitch
Linear displacement of a screw after a single revolution.


Pull-in torque
Maximum acceptable torque for starting the motor at a given speed.


Pull-out torque
Torque generated by the motor at a given speed, at the limit of loss of synchro­nism.


PWM (Pulse Width Modulation)
Technique for regulating current, using a variation of duty cycle for the motor phase voltage.


Q
Quadrature

Said of two sinusoidal signals of the same period but phase-shifted by a quarter of a period with respect to each other.
The two phases of a two-phase stepping motor are said to be in quadrature be­cause the torque they produce is the same amplitude and period but phase-shifted by a quarter of an electric period (90°).


R
Reflected inertia

Equivalent inertia seen by the motor shaft, when using a mechanical transmission component (gear box, screw-nut system, pulley,…).


Resonance
Motor vibration occurring at certain speeds, particularly depending on the load applied and its method of control.


S
Start-stop speed

Maximum speed at which the motor can be controlled without an acceleration ramp and without step loss, from rest. The start-stop speed notably depends on inertia.

Steps per second or pulses per second [pps]
Motor speed expressed as a function of the number of steps made per second.

T
Tin-Can

Another term sometimes used to designate ”permanent magnet” or ”steel shell” motors.