The degree to which an actuator is able to move to a specific commanded point. On the bullseye below, notice that all the holes are centered around the middle of the target, but the grouping is not very close together. Good accuracy does not require good repeatability. (see repeatability & accuracy

Acme Screw/Nut

Threaded screw and nut design which utilizes sliding surfaces between the two. Typical efficiencies are between 60-70%.

Auto-phasing

The drive function that determines the motor’s angular rotor position for commutation without the need for Hall Effect switches.

Axial Loading

Load where the force is acting along the axis of actuator (bearing) in any direction.

Back EMF

Voltage produced across a motor winding due to the winding turns being cut by a magnetic field. This voltage is directly proportional to rotor velocity and is opposite in polarity to the applied voltage.

Backlash

Linear distance which is lost in positioning the nut or carrier when the screw direction of rotation changes.

Bending Moment

Equivalent torque produced by a force displaced by a known distance from the carriage. Ex. Mx, My, Mz, Fz

Dead length

Result of subtraction of stroke length from overall length of an actuator.

Deflection

Amount of displacement of a point on rodless actuator carrier or rod actuator tooling plate, under load by forces or bending moments, measured in the direction perpendicular to actuator axis.

Duty Cycle

Ratio of on time to total cycle time. Duty Cycle = On Time (On Time + Off Time)

Dwell Time

A pause of motion within a move cycle.

Efficiency

Ratio of power output to power input.

Encoder

Device used to provide relative position and velocity information to a drive or controller by sensing mechanical motion and providing a corresponding pulse rate as output.

Flatness

When traveling in a straight horizontal line, the vertical deviation above or below the horizontal plane of travel of the carrier.

Gantry

A method of connecting two actuators together by a drive shaft so one motor can operate both actuators.

Holding Torque

Maximum external torque that can be applied to a stopped, energized motor without causing the rotor to rotate.

Incremental move

A positional move referenced from the current position.

Inertia

Measure of an object’s resistance to change in motion that is a function of the object’s mass and shape.

Inertia Match

If the reflected inertia of the load is equal to the rotor inertia of the motor, the system will operate optimally for efficiency and dynamic performance.

Lead

Linear travel of a lead screw nut or carriage for every one full rotation of the lead screw expressed in inches per rev.

Maximum static load

Maximum load of constant magnitude acting in one direction that a static actuator (component) can withstand without permanent deformation.

Repeatability & accuracy

The measure of how close to a programmed point the actuator can come, and how close it gets to that same point again. The repeatability of industrial actuators is usually much better than the accuracy. Notice on the bullseye below that the points are centered around the middle of the target and are grouped close together. This is good accuracy and repeatability.

Stepper Motor

Motor which translates electrical pulses into motion, where the pulse rate controls velocity and position.

Vector drive

A class of drives that sense motor current in each individual motor phase and resolves these readings into two current vectors. One vector is the torque producing current and other is the waste current. The current control algorithm then works to drive the non-torque-producing component to zero. This result in a high bandwidth torque response over the full speed range without the phase lag and tolerance issues that place older drive technologies.

Actuator

A mechanism for moving or controlling something indirectly instead of by hand.

Auxiliary Carrier

An option for band cylinders or linear slides that increases the load capacity of the cylinder as well as increasing the capacity of bending moment about the Y axis. Note: internal cushion will not work when auxiliary carrier ordered without piston, it will be necessary to add external shock absorbers.

Center of Gravity

(Center of Mass) The point a which the entire weight of a body may be considered as concentrated so that if supported at this point the body would remain in equilibrium in any position.

Configurator

Name given to the software that uses the configuration string to give instructions to the factory with correct specifications to create your built-to-order actuator.

Configuration String

A series of code letters and numbers that Tol-O-Matic uses to create built-to-order actuators.

Hall-effect D.C. Switch

A magnetically-controlled transistor switch controlling DC power. It has no moving parts and theoretically unlimited contact life.

Inch-Pound

A unit of measure of torque. It is derived from a given force in pounds acting at a given radius in inches (pounds multiplied by inches = inch-pounds). An inch-pound is 1/12th of a foot-pound. Inch-pounds may be converted to the IS Metric equivalent of Newton-meters by multiplying them by 0.1129848. Newton-meters may be converted to inch-pounds by multiplying them by 8.850748.

Anodizing

Protective treatment for aluminum that involves subjecting the metal to electrolytic action in a chemical bath, to create a protective film of aluminum oxide with a very smooth finish.

Tube Deflection

Due to the nature of loads and aluminum extrusions tube deflection will occur if cylinder (linear slide) is supported only on the ends without tube supports at recommended intervals along length of cylinder.

Units

U.S. Standard: A system of weights and measures based on the pound and inches. Metric: A decimal system of weights and measures based on the kilogram and meter.

Ball Screw/Nut

Screw and nut design utilizing a nut that contains one or more circuits of recirculating steel balls which roll between the screw and nut.

Baud Rate

Number of binary bits transmitted per second in a serial communication system.

Breakaway Torque

Torque required to start an actuator in motion. In an electric actuator, this consists primarily of the torque to overcome the preload of the lead screw nut assembly and the static friction of the carrier bearings.

Brushless DC Servo

Motor/drive that generates trapezoidal motor currents and trapezoidal back EMF in a brushless motor.

Carrier

Moving part of a rodless actuator providing a mounting surface for a load.

Closed Loop (Feed Back)

System where the output is measured and compared to the input. If this system is capable of making corrections to minimize the difference it is classified as a servo.

Commutation

Switching of drive voltage to the motor windings necessary to provide continuous rotation. A brush motor uses mechanical switching through a brush-bar contact. Brushless motors use separate devices such as Hall Sensors to sense the rotor position. This information is then processed by the drive to determine the switching sequence.

Continuous torque

Another term for RMS torque. See RMS torque

Critical Speed

Rotational speed of a lead screw at which the screw begins to oscillate or whip. This speed is dependent on the screw length and diameter.

Cycle

A complete motion of actuator’s carrier or tooling plate from start to finish and back.

Cycle Rate

Total number of complete cycles in a specific period of time.

Load

A mass or weight supported by the carrier (rodless cylinders) or tooling plate (rod type cylinders). Ex. Fz

Maximum dynamic Load

Load of constant magnitude acting in one direction that results in a nominal life (travel) of a linear motion actuator (component).

Maximum dynamic Load

Load of constant magnitude acting in one direction that results in a nominal life (travel) of a linear motion actuator (component).

Microstepping

Type of drive that proportions the current in a step motor’s windings to provide intermediate positions between full steps. Advantages over full and half stepping include smoothness of rotation and higher position resolution.

Moment Load

Rotational forces applied to the carrier equal to the linear force applied (weight) multiplied by the distance between the location of the force (center of gravity) and the surface center of the carrier. Typically expressed as yaw (Mz), pitch (Mx) and Roll (My). (See illustration with “LOAD”).

Motion Profile

Definition of an objects position and velocity relationships in time during a move.

Open Loop

Motion control system where no position or velocity signals are provided for correction. Typically, stepper systems run as open loop systems.

Optically Isolated

Transmission of a signal from one device to another with a light source (emitted) and sensor (received), in order to avoid direct electrical contact

Pitch

Number of revolutions required by a leadscrew to move the nut or carrier one inch, expressed in revs/per inch

PLC

(Programmable logic controller) A digital electronic device that uses to store instructions and to implement functions such as logic sequencing, timing and counting in order to control machines and processes.

PWM

Pulse Width Modulation is a method of controlling current in the windings of a motor by on-off switching of transistors to vary the duty cycle.

Radial Load

Load where the force is acting perpendicular to the axis of actuator (bearing) in the direction of actuator (bearing).

Regeneration

Characteristic of a motor to act as a generator when the CEMF (counter electromotive force) is larger than the drive’s applied voltage.

Regeneration braking

The technique of slowing or stopping a drive by regeneration.

Repeatability

The degree to which an actuator can return to a reference location. Notice on the bullseye on the next page that the holes are close together, however the grouping is far from the bullseye. Repeatability can be thought of as how tight of a grouping can be made. Unidirectional repeatability, measured by approaching a position from a single direction, hides errors caused by backlash and hysteresis effects. Bidirectional repeatability, measured by approaching a position from opposing directions, includes these effects, and provides a more meaningful specification.

Resolution

The smallest position increment that can be achieved.

Resolver

A feedback device consisting of a stator and rotor that provides position and velocity information to the drive for commutation.

Reverse radial load

Load where the force is acting perpendicular to the axis of actuator (bearing) in the direction opposite from actuator (bearing).

RMS Torque

In an intermittent application, this is the torque provided to generate equivalent motor heating to one operating in a steady state. Trms= where: Ti= Torque during interval i ti= Time of interval i

RS232

A standard for data communication that defines voltages and time requirements for information to be transferred on a single line in sequential format.

Servo

System that compares the output of a device (by monitoring position, velocity, and/or torque) with the desired outcome and makes corrections to minimize the difference.

Servo Motor

Motor used in closed loop systems where feedback is used to control motor position, velocity, and/or torque, usually expected to have high torque/inertia ratio.

Slew

Constant non-zero velocity portion of a motion profile.

Stall Torque

Maximum torque available at zero speed.

Stiffness

System ability to maintain accuracy when subject to disturbance.

Straightness

When traveling in a straight horizontal line, the side to side deviation within the horizontal plane of travel of the carrier.

Stroke length

The distance that the carrier and its load will move on the actuator.

Thrust

Measurement of linear force