glossary
A-B-C-D-E-F-G-H-I-J-K-L-M-N-O-P-Q-R-S-T-U-V-W-X-Y-Z
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.
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.