Technical information
185
Glossary
Incremental Programming
A coordinate system where positions or distances are specified relative to the current position.
Inertia
The property of an object to resist changes in velocity unless acted upon by an outside force. Higher inertia
objects require larger torque to accelerate and decelerate. Inertia is dependent upon the mass and shape of
the object.
Inertial Match
An inertial match between motor and load is obtained by selecting the coupling ratio such that the load
moment of inertia referred to the motor shaft is equal to the motor moment of inertia.
Inhibit
An input which, when true, prevents a circuit from functioning.
Inrush Current
The current surge generated when a piece of equipment such as a servo-amplifier is connected to an AC
line. This surge is typically due to the impulse charging of a large capacitor located in the equipment.
Instability
Undesirable motion of an actuator that is different from the command motion. Instability can take the form
of irregular speed or hunting around the desired final position.
Ke
(see Voltage Constant.)
Kt
(see Torque Constant.)
Lead Screw
A device for translating rotary motion into linear motion consisting of an externally threaded screw and an
internally threaded carriage (nut). Usually describes an ACME type threaded screw which exhibits sliding
friction between screw and nut.
Least Significant Bit
The bit in a binary number that is the least important or having the least weight.
LED
Light Emitting Diode.
Limits
Motion control systems may have sensors called limits that alert the control electronics that the physical end
of travel is being approached and that motion should stop.
Load Inertia-to-Rotor Inertia Ratio
The ratio of the load inertia to the motor rotor inertia. For a high performance, relatively fast system, load
inertia reflected to the motor should generally not exceed the rotor inertia by more than 10 times. Load
inertia in excess of 10 times the rotor inertia can result in unpredictable behavior and should be avoided.
Logic Ground
An electrical potential to which all control signals in a particular system are referenced. In many, but not all
cases, this is the same potential as analog ground.