Specifications

Acceleration to IR Compensation
Acceleration/Deceleration The time rate of change in velocity; accel-
eration refers to an increase in velocity, while deceleration refers to a
decrease in velocity. Generally expressed as radians/sec/sec. Board-
mounted trimmer potentiometers let users adjust the time it takes for the
motor to reach set speed.
Actuator A device that converts various forms of energy, when given an
input, to rotating or linear mechanical motion such as a motor.
Air-Gap The area between the rotating and stationary members of an
electric motor.
Alternating Current (AC) Electrical current flow, usually generated by
the utilities at 60 Hz, which continuously reverses direction in the middle
of its cycle. Mathematically, it follows a sine wave; it travels from zero,
then reaches a maximum in one direction, decreases to zero, then revers-
es to reach a maximum in the opposite direction.
Ambient Temperature The temperature of the medium, usually air,
around a device such as a motor or drive.
Ampere (AMP) The standard unit of electrical current, or rate of elec-
tron flow. A closed-loop electrical circuit with one volt of potential differ-
ence across one Ohm of resistance causes one ampere of current to flow.
Armature The armature is the rotating member of an electric motor. In
brush-type DC motors, it consists of the main current carrying windings
(conductors) in the rotor. The commutator switches the power supply to the
armature windings to generate a magnetic field.
Back-Emf Also known as counter emf (cemf), it is the voltage produced
across motor windings, due to the winding turns being cut by a magnetic
field, during rotation of the motor. The back-emf is directly proportional to
rotor velocity and opposite in polarity to the applied voltage. This static
voltage arises from the generator action in a motor, even if the motor
windings are not energized.
Backlash In a mechanical system, backlash is the relative motion
between two devices, connected by a coupler, gear, screw, etc.
Bridge Rectifier A section of the DC drive that converts the AC power
supply into a DC source.
Brushes The current conducting material, usually carbon or graphite,
which rests directly on the commutator of brush-type DC motor. They
transmit current from the power supply to the armature.
Capacitor A device which holds electrical charge for a period of time,
prevents the flow of direct current and allows the flow of alternating cur-
rent. These components serve as filters in DC drives to provide a “clean-
er” DC signal to the motor.
Chassis Open construction of a drive for mounting within a customer’s
existing enclosure or control console.
Choke A filter device consisting of an inductor and a resistor. Although
more expensive than a typical RC filter, they exhibit better performance.
Closed-loop A system that uses feedback information to regulate the
output response. The output feeds back to a controller for comparison to
the input command; any difference results in a corresponding change in
the input command. Thus, the accuracy increases.
Cogging Cogging refers to shaft rotation occurring in jerks or increments
rather than smooth continuous motion. The non-uniform (“jerky”) rotation
results from the armature’s propensity to certain discrete angular posi-
tions. The interaction of the armature coils entering and leaving magnetic
fields, produced by the field coils or permanent magnets, causes speed
changes. The armature tends to speed up and slow down as it cuts
through the fields during rotation. Cogging is very apparent at low speeds,
and determines a motor’s speed range.
Commutator A device mounted on the armature shaft and consisting of
a number of wedge shaped copper segments arranged around the shaft.
These segments are insulated from the shaft and from each other. The
motor brushes ride on the periphery of the commutator, and electrically
connect and switch the armature coils to the power source.
Conductor Any material, such as copper or aluminum, which offers lit-
tle resistance to the flow of electric current.
Current Limit (Torque Limit) This feature permits the operator to adjust
the maximum current the motor can draw. This, in effect, limits the maxi-
mum torque the motor will produce.
Dynamic Braking A way of quickly stopping a motor by discon-
necting the power source. The rotating motor then becomes a gener-
ator. When connected to a resistor, the energy of rotation is then dis-
sipated as heat in the resistor.
Duty Cycle The ratio of operating time versus total cycle time of a
motor. A motor has a continuous duty rating if it continues to operate
for an indefinite amount of time and its normal operating tempera-
ture remains within the temperature limits of its insulation system. A
motor has an intermittent duty rating if it never reaches a steady tem-
perature, but is allowed to cool between operations.
Enclosure A description of the motor or drive housing. The selected
enclosure depends on the application’s environment and heat gener-
ated by the device.
Encoder A feedback device that translated mechanical motion into
an electronic signal or combination of signals (pulses).
Field Motor field windings provide the magnetic field, located in the
stator of DC shunt-wound motor, which interacts with the armature
field to produce torque. PM motors use magnets, instead of windings,
to produce the stator field.
Filter An electrical device used to suppress electrical noise, or to
improve the DC output to a DC motor.
Flyback Diode This is a super fast recovery diode that snubs cur-
rent and voltage spikes as a result of the fast transients that occur
when IGBT, and MOSFETS are turned on and off quickly.
Form Factor Form factor indicates how much AC component
resides in the DC output from DC drives. Represented mathematical-
ly as the ratio of a signal’s root-mean square current value to its aver-
age current value. Any form factor value greater than one means that
some of the current produces heat instead of torque.
Four-quadrant This term refers to a drive’s ability to control the
velocity and torque of a motor in either direction of rotation. The
direction of torque can be in the opposite direction of the velocity for
applications requiring braking or deceleration. Single-quadrant dri-
ves, on the other hand, only produce torque and velocity in the same
direction of rotation.
Frequency Frequency refers to how often a complete cycle occurs
in a unit of time. Frequency is usually measured in cycles per second,
or Hertz, where 1 cycle/second equals 1 Hz. The standard AC power
supply in the USA is 60 Hz, while 50 Hz remains common in many
other countries of the world.
Friction The resistance to motion between surfaces
Fuse A device connected to an electrical circuit designed to melt and
open the circuit in the event of excess current flow.
Gearhead A mechanical device that converts speed and torque to
values required by the application. Output torque increases, and out-
put speed decreases proportionally to the gear ratio.
Generator A machine that converts mechanical energy into electric
energy.
Hall Effect Sensor These feedback devices, commonly used in
brushless motors, provide information for the amplifier to electroni-
cally commutate the motor. The sensors generate commutation sig-
nals by sensing the position of a magnetized wheel on the rotor.
Horsepower The rate at which work is performed. It equals the
speed multiplied by torque, and a constant, depending on the units
selected.
Inductance A property of an electric circuit that represents its abili-
ty to resist changes in current flow.
Inertia A function of the mass and shape of an object. The inertia
represents the property of an object that resists a change in motion.
An object’s inertia increases directly with an increase in the object’s
mass; also, increasing inertia loads require more force to accelerate
and decelerate them.
Inverter (Variable Frequency Drives) AC drive that varies the
frequency and voltage applied to an AC motor to vary motor speed.
IR Compensation It varies the mount of voltage to the armature in
response to current (load) changes. It is adjustable via a
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REFERENCE