Technical information

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Glossary
Closed Loop
A broadly applied term relating to any system where the output is measured and compared to the input. The
output is then adjusted to reach the desired condition. In motion control the term is used to describe a system
wherein the actual velocity or position (or both) is used to generate correction signals by comparison with
the command to achieve the desired results.
Cogging
A term used to describe non-uniform angular velocity caused by the motor rotor’s tendency to prefer certain
repeatable angular positions. Cogging appears as a jerkiness especially at low speeds. (see Torque Ripple).
Command Position
The desired angular or linear position of an actuator.
Commutation
A term which refers to the action of directing currents or voltage to the proper motor phases so as to produce
optimum motor torque. In brush type motors, commutation is done electro-mechanically using the brushes
and commutator. In brushless motors, commutation is done by the switching electronics using rotor position
information typically obtained by Hall sensors, resolvers or an encoder.
Commutator
A rotating multi-position switch usually constructed like a mechanical cylinder consisting of alternating
angular segments of conductive and insulating material. This cylinder used in DC motors passes currents
from the brushes into the rotor windings and performs motor commutation as the motor rotates.
Compensation
The corrective or control action in a feedback loop system which is used to improve system performance
characteristics such as accuracy and response time.
Compensation, Derivative
A control action which depends on the amount of error per unit time. It is used to improve system stability
and accuracy.
Compensation, Feedforward
A control action which depends on the command only (and not the error) to improve system response time.
Compensation, Integral
A control action which monitors and generates correction signals to the motor according to the amount of
time that the feedback error does not match the command. It is usually used to reduce static error.
Compensation, Lag
A control action which causes the phase to lag at low frequencies and tends to increase the delay between
the input and output of a system while decreasing static error.
Compensation, Lead
A control action which causes the phase to lead at high frequencies and tends to decrease the delay between
the input and output of a system.
Compensation, Lead Lag
A control action which combines the characteristics of lead and lag compensations.