Glossary of Terms F through L

Feedback: necessary for closed-loop control, it is the signal that provides the motor output information (e.g., speed, position, etc.) to the controller.

Feedthru: device that physically interfaces one side of a separating surface to the other (e.g., an electrical feedthru passes electrical signals from one side of a wall to the other).

Friction: resistance to motion due to contacting surfaces.

Gear ratio: ratio of the motor input speed to the gearhead output speed.

Gearhead: device that reduces motor speed and increases motor torque.

Gearhead efficiency: actual torque output divided by theoretical torque output (i.e., torque input times the gear ratio).

Hall sensors: feedback device used for commutation.

Hazardous duty: Empire Magnetics hazardous duty (PT) motors and related products can be designed into a system that meets NFPA class I, II, and/or III requirements.

Holding torque: maximum torque the motor can provide to hold itself in a fixed position; also called static torque.

Horsepower: measurement of power, usually mechanical.

Hybrid step motor: class of step motors that utilizes a permanent magnet to polarize soft iron pole pieces around the rotor.

Hysterisis: describes a type of error whereby the system response to an increasing input signal is not equal and opposite to a decreasing input signal of equal magnitude.

Idle current reduction: drive feature that reduces the motor current at a standstill to reduce motor heating; a typical value is 50% for a step motor drive.

Incremental: refers to an output that is measured in known increments from a known reference point; e.g., a step motor provides incremental motion based on an initial position and an incremental encoder provides incremental feedback information based on a known zero point.

Indexer: electronics that convert high level computer or PLC commands to step and direction pulses.

Inductance: measurement of a conductor's ability to resist a change in current flow; analogous to an object's ability to resist a change in velocity.

Inertia match: refers to the ratio of the reflected load inertia to the rotor inertia; a general rule is that this ratio should be no more than 10:1 for an inertia match.

Inertia: measurement of an object's ability to resist a change in velocity, this property is dependent upon the mass and shape of the object.

IP: European rating system for specifying equipment compatibility with dust, water, and shock; also recognized in the U.S.

Lamination: material that holds the soft iron pole pieces and permanent magnet around the rotor.

Linear actuator: refers to an assembly that transfers the rotary motion of a motor to linear motion.