Glossary of Terms
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top A

Ampere abbreviation.

Absolute encoder
A rotary encoder which outputs absolute rotary position information in the form of a binary number.

Absolute positioning
Positioning commands relative to a fixed zero starting point.

AC current
Alternating Current. The type of current where all electrons flow back and forth, typically at either 50 or 60 cycles per second.

AC line filter
Connected to the incoming AC line to control electrical noise from affecting electronic devices on the machine from being affected.

AC servo
A general term referring to a motor drive that generates sinusoidal shaped motor currents.

Rate of change in velocity over time. In motion control systems this is sometimes referred to the acceleration “ramp" which is the time for the motor to go from rest to set speed.

The measured difference between the expected position and actual position of a motor or mechanical system.

Acme screw
A common and standardized type of friction leadscrew utilizing a trapezoidal shaped thread form.

Any device that produces rotary or linear motion by electromechanical means.

Ambient temperature
The temperature of the medium immediately surrounding a particular device.

Ampere (Amp)
Unit of electrical current.

Electronic device that converts command signals (analog or digital) to higher power switching to run motors.

Analog servo
A servo system that utilizes analog control and feedback systems such as voltage.

After Receipt of Order. “Delivery 3 weeks ARO" (With conditions at time of quotation the usual delivery time is 3 weeks after the date of order placement.

Analog signal
A communication within the system that is accomplished by means of a signal that varies in direct relation to the intensity or magnitude of the external quality being measured.

Angular accuracy
The measurement of rotary shaft positioning accuracy on a motor.

Arc minute
An angular measurement unit equal to 1/60th of a degree.

American Standard Code for Information Interchange. This code assigns a number to each numeral and letter of the alphabet so that information can be communicated in binary language.

Application Specific Integrated Circuit. An integrated circuit designed to perform a particular function by defining the interconnection of a set of basic circuit building blocks.

Axial play
Axial shaft displacement occurring during a reversal of an axial force on the shaft.

A principal direction along which movement of a tool, component or workpiece occurs.

top B
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Back drive
When the force which keeps the lead screw stationary is over come by the force of the load, driving the screw in reverse of current position.

Back EMF
Back Electro Magnetic Force. The reversed voltage bias generated in a motor by rotation of the magnetic field across a stator's windings.

Back EMF constant
The constant corresponding to the relationship between the induced voltage in the phases of a motor and it's rotational speed.

The "play" or "slop" in a mechanical system.

Ball screw
A type of lead screw that use ball bearings rolling in a channels machined or rolled into the screw and mating nut.

A data transmission rate. The maximum amount of information (bits/second) that can be transmitted along a channel.

Base speed
The highest rated speed of a motor.

Baud rate
The number of binary bits transmitted per second on a serial communication link (such as RS-232).

Binary Coded Decimal. An encoding technique used to describe the numbers 0 through 9 with four digital (on or off) signal lines.

Bifilar winding
Refers to the winding configuration of a stepper motor where each stator pole has a pair of windings.

Numbering system in which the base is two, each number being expressed in the powers of two, by 0 or 1.

Bipolar drive
A step motor drive which reverses the magnetic polarity of the poles by electronically switching the polarity of the current to the windings.

Bit (binary digit)
A unit of information equal to 1 binary unit having a value of 0 or 1.

Block diagram
A simplified schematic representing components and signal flow through a system.

Bode plot
A graph of system gain and phase versus input frequency used to graphically illustrates the steady state characteristics of the system.

Breakaway torque
The torque required to start a machine in motion. Almost always greater than the running torque.

A motor may have or more pairs of brushes which serve as the positive and negative voltage terminals to the motor.

Brushless motor
A class of motors that operate using electronic commutation of phase currents rather than brushes.

The temporary memory storage of information flow to compensate for a difference in rate of flow of data, or time of occurrence of events, when transmitting data from one device to another.

A group of parallel connections carrying pre-assigned digital signals.

A cylindrical metal sleeve inserted into a machine part to reduce friction between moving parts.

A group of 8 bits treated as a whole, with 256 possible combinations of ones and zeros, each combination representing a unique piece of information.

top C

A serial bus system which was originally developed for automotive applications in the early 1980's.

CANopen is a CAN-based higher layer protocol developed as a standardized embedded network with highly flexible configuration capabilities.

A measurement of a devices to store an electrical charge. Units are Farads (F).

Device which stores and electrical charge.

C-face mount
A standard NEMA motor mounting design where mounting holes in the face are threaded to receive the mating mount.

Chopper drive
A constant current step motor drive which rapidly turns on an off the voltage to the windings (chopping) to maintain a specified current level.

Class B insulation
Motor insulation rated for operation up to 130 degrees C internally.

Class H insulation
Motor insulation rated for operation up to 180 degrees C internally.

Closed loop
A motion control system where velocity or position sensors are monitored during motion and corrections signals generated to achieve desired parameters.

Coefficient of friction
Defined as the ratio of the force required to move a given load to the magnitude of that load.

A term used to describe non-uniform angular velocity which appears as jerky motion, especially at low speeds.

An electronic pulse, signal, or set of signals to start, stop, or continue some operation.

Controlling power to the windings of a motor. DC motors commutate with brushes, DC brushless commutate electronically with position feedback sensors.

Corrective action in a feedback loop system which is used to improve system performance characteristics.

The amount of displacement per unit of applied force.

Constant current drive
Electronically controlling the current in motor windings to maintain a prescribed current level.

Continuous rated current
The maximum allowable continuous current a motor can handle without exceeding the motor temperature limits.

Continuous stall toque
The maximum output torque a motor can continuously produce without exceeding the motor temperature limits.

An electronic device that instructs a motor drive or amplifier to perform a prescribed move or sequence of moves.

The ability of a motion control to follow smooth rounded paths on a XY plane, such as an XY table (stage).

Coordinated motion
Multi-axis motion where the position of each axis is dependent on the other axes.

A device which connects the motor to a part that the motor is turning. An example is a motor turning a lead screw. The “coupling" is used to connect the motor shaft to the machined end of the lead screw.

Critical damping
Tuning a system such that the response to an incremental change in desired velocity or position is achieved in a minimum amount of time with minimum overshoot.

Critical speed
Rotational speed of a leadscrew at which vibrations (whipping) will occur.

The flow of electrons through a conducting material typically measured by number of amps.

Current constant
The constant corresponding to the relationship between motor current and motor output torque.

Current limit
A drive containing a current limit, restricts the amount of electrical current following to a motor, thereby preventing potential damage.

Current loop
Refers to the inner control loop on a servo amplifier (drive). The current loop is sometimes called torque control.

When motion is repeated (move and dwell) such as repetitive back-and-forth motion.

top D

Daisy chain
The linking of several devices in sequence, such that a single communication signal stream flows through all of them, each device having its own address.

A device that attaches to a stepper motor shaft to absorb energy and damped step oscillations.

An indication of the rate of decay of a signal to its steady state of value. Related to settling time.

DC current (Direct current)
The type of current where all electrons are flowing in the same direction continuously.

Dead band
A range of input signals in which there is no system response.

A logarithmic measurement of gain.

The change in velocity as a function of time, going from a higher speed to a lower speed.

Demag current
The current level at which the motor magnets will be demagnetized. This is an irreversible effect which will alter the motor performance.

Derivative gain
A damping control on a servo system which controls torque in proportion to the rate of change in positional error.

Detent position
The resting position of a step motor with its windings unenergized.

Detent torque
The maximum torque that can be applied to an unenergized step motor without causing continuous rotating motion.

Digital servo
A servo motor (see AC servo and Analog servo) which utilizes binary coding for all parameter generation and feedback.

An electronic device that controls torque, speed and/or position of an AC or brushless motor.

An electronic device which convert step and direction inputs into control of a step motors windings to create motion.

Duty cycle
For a repetitive cycle, the ratio of on time to total cycle time.

Dwell time
Time within a move cycle where no motion occurs.

Dynamic braking
A passive technique for stopping a permanent magnet brush or brushless motor.

Dynamic Braking
A passive technique for stopping a permanent magnet brush or brushless motor. The motor windings are shorted together through a resistor which results in motor braking with an exponential decrease in speed.

Dynamic Torque
Dynamic Torque is also known as running torque or pullout torque. Dynamic torque varies by the speed of the motor.

top E

Eddy Currents Losses
Currents induced when a conductor is rotated in a magnetic field. Power is dissipated in the form of heat loss.

Electrically Erasable Programmable Read Only Memory.

The ratio of power output to power input.

Electrical time constant
Transient response time to current flowing to the armature.

Electronic gearing
Using one axis to control another by use of feedback, usually encoder, to scale another axis motion.

Undesirable electromagnetic emission or any electrical or electronic disturbance which causes and undesirable response.

Feedback device used to convert mechanical motion into electrical signals.

Encoder index
Signal used on some incremental encoders to indicate a once-per revolution reference point.

End play
Axial movement of the shaft resulting from an external force.

High speed computer interface.

Nominal current or voltage required to hold or move a motor.

top F

Feed Forward
Control technique to compensate for known errors in a control loop.

A signal which is transferred from the output back to the input for use in a closed loop system.

Feed forward compensation
A control action that predicts error and sends a compensating signal.
Non-conductive ceramic compounds derived from iron oxides or magnetite as well as other metals.

Field Effect Transistor.

An electrical device used to remove unwanted parts of an electrical signal.

Machine code which is stored in non volatile memory which give an electronic device to be powered on and off without loss of basic control functions.

Floating ground
When an electrical system has no electrical ground referenced to earth ground. Most electric and electronic systems will display erratic behavior if there is a floating ground.

Following error
The difference between the commanded signal and feedback signal.
The action of one body against another.

Form Factor
Ratio of RMS (root mean square) current to average current.

Four Quadrant
Refers to a motion system which can operate in all four quadrants; i.e., velocity in either direction and torque in either direction.

A resistance to motion caused by contact with a surface. Friction can be constant with varying speed (Coulomb friction) or proportional to speed (viscous friction).

Friction torque
Torque caused by frictional force. Occurs when two objects in contact begin to move.

Full step
The full mechanical movement of a stepper motor for each digital pulse. (i.e. - 1.8 degrees for a 200 step motor)

top G

The ratio of system output signal to system input signal.

A multiaxis position system which is designed to work above the product to be serviced by the motion control system.

G code
Software language specifying motion profiles generally used in the Machine Tool industry.

A mechanical device used to transfer energy from one device to another.

Ground Loop
Unwanted current in a conductor with different potentials causing electrical noise and interference.

Graphical User Interface.

top H

Half Step
Half mechanical step for each digital pulse.

Hall sensor (Hall effect sensor)
Feedback device used in servo applications to provide information to the controller to commutate the motor.

A unit of frequency, i.e. 60 hertz = 60 times per sec.

High pass filter
Electrical device which allows frequencies above a set value to pass, usually used in servo systems.

Human Machine Interface.

Holding torque
Maximum external torque that can be applied to an energized motor (coil) without causing the motor to rotate.

Home position
A reference point in a motion control system, usually a limit switch or encoder position.

Rating determining a motors torque and speed capabilities.

Hunting, Oscillation
Instability in a system does not allow it to achieve a steady position or state.

Hybrid motor
Features a combination of permanent magnet and variable reluctance motors.

Difference in actual and commanded position in a bidirectional move.

Hysteresis losses
Loss of power due to magnetic flux.

top I

Conventional abbreviation of Inputs/Outputs.

Insulated Gate Bipolar Transistor. Used for output power in high voltage and high current devices.

Incremental encoder
Provides position in pulses relative to the amount of movement.

Incremental motion
Term describing one step of motion for each step command.

Electronics that convert host computer commands into step and direction pulses used by a stepper motor drive.

Property of a coil of wire and its characteristic to resist a change of state. Current flow resistance in a circuit resulting in back EMF.

A measure of an object’s resistance to a change in velocity.

Inertia match
Inertia of the load equals the inertia of the motor rotor.

A device which sense digital or analog status (or state).

Inrush current
Initial current surge when a piece of equipment is turned on.

Insulation class
Insulation rating.

Integral compensation
Algorithm used to determine and offset the accumulative error in the feedback loop.

A math function that defines the area under a curve.

To calculate the value between two points. Linear interpolation is used when a control device calculates a straight line between two points on a XY stage. Circular interpolation calculates a curve on a two axis device.

top J

The affect of acceleration on the object being accelerated.

top K

Velocity loop proportion gain. Used to tune velocity error in a servo system.

Position loop gain. Used to tune the positional error in a servo system.

top L

L/R Drive
Constant voltage drive.

A stamped form of electrical steel used to form the stack in most motors. Sometimes used as stator (stepper) or armature (DC brush motor).

The linear distance a nut travels on a lead screw in one revolution.

Lead screw
An externally treaded screw coupled with an internally threaded nut. Converts rotary motion to linear motion.

Sensors that signal to the controller end of travel or end of move has been reached.

Linear actuator
A device that develops force in a linear motion.

Linear encoder
Sensor or transducer paired with a scale that encodes linear position.

Linear slide
Linear motion device. Stationary base and moving carriage. Move mounted loads across a given axis.

Linear step increment
Amount of linear travel in one step of a stepper motor using a lead screw.

Term used in a speed control system to measure, in percentage of speed, the maximum deviation between actual and commanded speed.

Any resistance attached to a motor.

Logic ground
Electrical reference voltage used by control signals in a system.

Loop Gain
Filter used in a velocity loop in analog drives. Allows frequencies below a set value to pass.

Loop feedback
Control method used to determine error between commanded and desired position.

top M

The amount of matter an object contains.

Master slave control
Coordinated motion control. Master axis generates slave axis position commands.

Maximum running torque
Maximum torque load a stepper can move without missing a step.

Maximum temperature rise
Maximum temperature rise test. Done by suspending the motor, unmounted, while applying steady state D.C. current.

Mechanical time constant
The time required by an unloaded motor to reach a speed of 63% from a standstill.

A semiconductor which has properties to perform calculations and logic tasks.

One millionth of a second.

Increases a step motor's position resolution and velocity smoothness by appropriately scaling the phase currents. Microstepping reduces or eliminates the effects of system resonance at low speeds.

Microstepping drive
Drive that divides full steps into smaller steps.

Mid range instability
Condition where a step motor falls out of synchronism due to a loss of torque at mid-range speeds. Torque loss is due to interaction between drivers electronics and motors electrical characteristics.

One thousandth of a second.

Metal Oxide Semiconductor Field Effect Transistor.

Move profile
A definition via a program in an indexer (controller) which defines how a motion control device may move. Often times a simple profile will define acceleration, top velocity and deceleration over time.

Mean Time Between Failure.

Allows communication between multiple devices on a single communication line.

top N

One billionth of a second.

National Electrical Manufactures Association. Set standards for motors and electrical equipment.

Neodymium iron boron
Rare-earth permanent magnet material.

No load current
Current consumption of motor, no-load conditions, nominal voltage.

No load speed
Maximum motor speed at a given voltage with no additional torque load.

Usually used to describe electrical signal interferenceAudible noise is measured in decibels.

Nominal voltage
The normal or designed voltage level for a motor.

Non Recurring Engineering, or Non Recurring Expense (Fee).

top O

Original Equipment Manufacturer.

Open collector
An output signal of a transistor that acts as a switch closure to ground when activated.

Open loop
A control system where there are no feedback sensors. It is assumed in this system that the motor/load completes its move as commanded.

Signal is transmitted optically rather than electrically. Used for isolation in a noisy signal environment.

A change in value or position in relationship to a mean value.

Output power
As it relates to a motor there are two implied meanings. First the mechanical power in terms of speed and torque, and the second in term often used is the rate of transferring energy express in watts or horsepower.

Relates to the motor passing the commanded position. In terms of shaft angle in a step motor overshoot, which results in ringing, and potentially instability.

top P

Peak torque
The maximum torque a motor can produce. In a servo system this may apply to an instantaneous current in rush, which allows the motor to reach momentary torques in excess of normal torque. Special care should be given to thermal considerations during this time.

Permanent magnet
A magnet that has been magnetized for use in a motor, yielding high torque at relatively low cost.

As it relates to a motor, the phase is the electrically excited poles allowing the motor to rotate.

Phase angle
Relates to the angle of the stator to the rotator as the difference between the two yielding motion.

Proportion/Integral/Derivative relating to the ""tuning"" (compensation) used in a closed loop servo system.

In screw it is the distance between threads.

Programmable Logic Control, a class of products used in machine control.

PMDC motor
Permanent Magnet Direct Current motor. Generally referring to a motor with a magnet non rotating portion of a motor and a rotating winding called the armature, with brushes carrying the current to the rotating portion.

In a motor the poles are the magnetic paths generated.

Positional error
The difference between the theoretical commanded position and the actual position.

Position loop
In a servo system this allows for adjustment (correction) of positional error.

Positive logic
An input to a device where the absence of voltage, zero volts produces a false input and a voltage above a certain voltage produces a true signal. That is in a 0-5V system 0 is false 5 is true.

Abbreviation for potentiometer

An electrical device that allows a variation in resistance.

A measure of the rate of doing work. See output power.

Power factor
Ration of actual power dissipated to the input power.

Prime ratio
The ratio of stator to rotor teeth in a step motor.

Program mode
Refers to the mode in a controller to accept command instructions.

Term used to describe a graphical depiction of a movement is a motion system.

A math function which compares two variables to a fix value.

Proportional compensation
In a servo system the "tuning" (compensation) of the error of the feedback loop. Adjusts the accuracy and responsiveness of the system.

Pull in torque
Maximum torque a step motor can generate without losing synchronization when accelerated instantly.

Pull out torque
Maximum torque a step motor can generate at a constant speed for a given system without losing synchronization.

Pulse per second
The number or commanded steps for a step motor every second.

Pulse rate
The number of pulses per second (pps) applied to the step motors windings.

Pulse width modulation, refers to the drive (amplifier) technique for switching current to the motor windings.

top Q

In an encoder a single set of "lines" has two sensing elements, 90 degrees offset electrically to generate two sets of outputs offset by 90 degrees. Generally used in encoders to increase resolution and sense rotational direction.

top R

Random Access Memory.

Technique for accelerating a motor and its load smoothly to the desired rate of rotation. Generally acceleration and deceleration are on the same "ramp", but more sophisticated systems allow for independent control.

Rated current
The maximum rated current for continuous operation of a motor.

Reflected inertia
The inertia at the motor output shaft see when a speed reduction or increase when there is a gear train between the motor and load.

Refers the ability to use the motors windings to act as a generator while decelerating a load. This energy may be returned to the amplifier.

Refers to the ability of a motor or positioning system to duplicate a speed or position.

Measure of resistance to current flow in an electrical circuit.

Smallest increment of position a system can reach. May be rotational or linear depending on the motion system.

A rotating device which generates a sign wave proportional to shaft position.

A system oscillation based on a mechanical system. In a step motor resonance will often cause a reduction in torque available or complete loss of synchronization.

Read only memory.

Radio Frequency Interference. Often causes "noise" issues with sensitive electronic devices.

System oscillation occurring when there is a sudden change in state.

Rise time
Time for a servo system signal to rise from 10% of the final value to 90% of the final value.

Return Material Authorization.

RMS current
Root Mean Square current is the value in an intermittent duty cycle application which produces an equivalent motor heating over a period of time.

RMS torque
Root Mean Square torque is the value in an intermittent duty cycle application which produces an equivalent motor heating over a period of time.

The rotating part of a motor.

Rotor inductance
Inductance limits the rate of change in current to a DC motors rotor windings.

Rotor inertia
The moment of inertia created by the rotating part of a motor including the shaft.

top S

S curve
An acceleration ramp the minimizes jerk to the object being moved. The graphical depiction of this ramp appears as a portion of the “S" shape.

Servo amplifier
A device which takes a low voltage reference signal in and produces a high voltage signal out to control a servo motor.

Servo system
A motion system the gives automation feedback for speed, position, and acceleration. Typically the feedback device is an encoder.

Settling time
The required for a system to stop oscillation and come to rest at its commanded position.

The portion of a rotor around which rotation occurs. Typically extends through the bearings supporting the rotor.

Shielded cable
A cable bundle which as a metallic sleeve or braided metal sleeve surrounding to wire conductors. Use to minimize electrical noise generation, or protect against external electrical noise.

Shock load
The peak torque experienced during the highest system acceleration.

Shunt resistor
An electrical device used to dissipate energy from motor regeneration during system deceleration.

Sinking input
An input in which current flow into the input.

Sinking output
Current flows into the output.

Single ground point
A common electrical ground for all system electrical connections.

Single step response
Time required for one step to occur in a step motor system.

Sinking current
In an electrical device the connection between the positive supply and the chip output will switch on when output is low.

Slave axis
Describes an axis in a motion control system in which one axis follows another synchronously by some scale factor.

The portion of a motion control profile at which the motor is rotating at a constant speed.

Slew speed
See Slew.

Sourcing input
Used with sinking output.

Sourcing output
Used with sinking input. Current flows out of output.

The rotational or linear velocity of a motion system.

Speed constant
The velocity per volt applied to the motor phases.

Stall torque
The amount of torque developed with voltage applied to the motor when the motor shaft is locked (prevented from rotating).

Static torque
The maximum torque a motor will produce when the motor shaft is at standstill. Sometimes called holding torque.

The non rotating part of a motor.

The angular movement of a step motor shaft when the motor receives a pulse.

Step Angle
Rotation of the motor for a given pulse stated in degrees.

Step and direction
A control input which uses two lines, one indicates the direction of rotation, and the frequency of the other input indicates speed.

Step Motor
Motor which translated electrical inputs to precise incremental movement.

Steps per revolution
Number of pulses needed to rotate a motor 360 degrees.

A ratio of rotor movement to a given externally applied torque.

Refers to a PWM (pulse width modulation) device.

The rotation of a motor at the same frequency as the commanded signal.

top T

An electrical device which produces an analog voltage proportional to the speed at which it is rotated.

Thermal resistance
The opposition to the flow heat between to materials.

Thermal time constant
Time required for a motor to attain 63% of its final temperature for a fixed input current.

A measure of linear force.

A measure of angular force.

Torque constant
An angular force measured at a distance.

Torque to inertia ratio
Holding torque divided by rotor inertia.

Torque limit
An electrical setting which limits the current supplied to a motor, thereby limiting torque generation. These may be active limitations or preset.

Transistor to transistor logic.

A fully integrated system.

top U

Unifilar winding
Step motor stator poles each have one set of windings (4 lead motor).

Unipolar drive
Drive technique that utilizes current to one phase of the motor in sequence. This simple drive technique which is generally used with 6 lead step motors results in a 30% lower torque than an equivalent bipolar drive.

Unipolar motor
A unipolar motor is generally distinguished by having 6 leads, two of which are “center taps."

top V

Variable reluctance motor
A variable reluctance motor is differentiated from a hybrid motor by the fact that there is no permanent magnet in the motor. In a step motor a “VR" motor generally has a step size of 7.5 to 15 degrees per step. Most simple AC motors are variable reluctance motors.

The change in position as a function of time. Rotational speed of the motor.

Viscous damping
A device which retards the torque during rotation of the motor. Sometimes used to reduce ringing in a step motor.

Voltage constant
Voltage constant is sometimes called the “Back EMF constant" (V/kRPM). When motors are operating they will generate a voltage proportional to speed which opposes the applied voltage. As the “Back EMF" approaches the supplied voltage, the motor will not have the ability to increase its RPM past that point.

top W

A unit of power which may refer to electrical power or thermal capabilities in a power device such as a drive or motor. That is the products ability to dissapate heating.

Winding inductance
See Inductance.

Winding resistance
See Resistance.