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    Absolute Positioning:
   
    Refers to a motion control system employing position feedback devices (absolute encoders) to maintain a given mechanical location.
   
    Absolute Position:
   
    Position referenced to a fixed zero position.
   
    Absolute Programming:
   
    A positioning coordinate referenced wherein all positions are specified relative to some reference, or zero position. This is different from incremental programming, where distances are specified relative to the current position.
   
    Abbe Error:
   
    A linear positioning error caused by a combination of an angular error in the ways, and an offset between the precision determining element (lead screw, feedback device, etc.) and the actual point of interest.
   
    AC Adjustable-Speed Drive:
   
    All equipment required to adjust the speed or torque of AC electric motor(s) by controlling both frequency and voltage applied to the motor(s).
   
    Acceleration feedforward:
   
    In the velocity loop, acceleration feedforward acts to inject additional torque/force to compensate for delays inherent during high rates of change in velocity.
   
    AC line filter:
   
    A filter that connects to the incoming AC on a machine. Intended to keep the electrical noise produced in the machine from polluting the AC in the building.
   
    AC Servo Drive:
   
    A servo drive used to control either or both synchronous or induction AC motors.
   
    Actuator:
   
    A device which creates mechanical motion by converting various forms of energy to mechanical energy.
   
    Adaptive Control:
   
    A technique to allow the control to automatically compensate for changes in system parameters such as load variations.
   
    Amplifier:
   
    Electronics which convert low level command signals to high power voltages and currents to operate a servomotor.
   
    AC Servo:
   
    A general term referring to a motor drive that generates sinusoidal shaped motor currents in a brushless motor wound as to generate sinusoidal back EMF.
   
    Acceleration:
   
    The change in velocity as a function of time. Acceleration usually refers to increasing velocity and deceleration describes decreasing velocity.
   
    Accuracy:
   
    A measure of the difference between expected position and actual position of a motor or mechanical system. Motor accuracy is usually specified as an angle representing the maximum deviation from expected position.
   
    ACME Screw:
    The most common type of lead screw found in machine tool applications. The ACME thread is a particular type of thread. Compared to a ball screw, ACME lead screws have very high friction and backlash, both of which are undesirable attributes for high performance applications.
   
    Ambient Temperature:
   
    The temperature of the cooling medium, usually air, immediately surrounding the motor or another device.
   
    ASCII:
   
    American Standard Code for Information Interchange. This code assigns a number series of electrical signals to each numeral and letter of the alphabet. In this manner, information can be transmitted between machines as a series of binary numbers.
   
    Application Specific Integrated Circuit (ASIC):
   
    An integrated circuit designed to perform a particular function by defining the interconnection of a set of basic circuit building blocks drawn from a library provided by the circuit manufacturer.
   
    Arc Minute:
   
    An angular measurement equal to 1/60th of a degree.
   
    Axial Play:
   
    The axial displacement of the shaft due to a reversal of an axial force.
   
    Bandwidth:
   
    A measure of system response. It is the frequency range that a control system can follow.
   
    Back EMF:
   
    The voltage produced across a winding of a motor due to the winding turns being cut by a magnetic field while the motor is operating. This voltage is directly proportional to rotor velocity and is opposite in polarity to the applied voltage. Sometimes referred to as counter EMF.
   
    Backlash:
   
    Backlash is any kind of unexpected play in an axis due to clearance or looseness of mechanical parts. When the axis is commanded to move, the driver motor may turn briefly before movement begins.
   
    Ball Screw:
   
    A lead screw which has its threads formed as a ball bearing race; the carriage contains a circulating supply of balls for increased efficiency.
   
    Baud Rate:
   
    The number of binary bits transmitted per second on a serial communication link (such as RS-232).
   
    BCD:
   
    Binary Coded Decimal is an encoding technique used to describe the numbers 0 through 9 with four digital (on or off) signal lines. Popular in machine tool equipment, BCD interfaces are now giving way to interfaces requiring fewer wires such as RS-232C.
   
    Bit:
   
    Abbreviation of Binary Digit, the smallest unit of memory equal to 1 or 0.
   
    Bipolar chopper driver:
   
    A class of step motor driver which uses a switch mode (chopper) technique to control motor current and polarity. Bipolar indicates the capability of providing motor phase current of either polarity (+ or -).
   
    Bipolar Motors:
   
    These motors are composed of two windings and have four wires with no center taps. Current flow is bidirectional and runs through an entire winding at a time instead of just half of the winding. As a result, bipolar motors produce more torque than unipolar motors of the same size.
   
    Breakaway torque:
   
    The torque required to start a machine in motion. Almost always greater than the running torque.
   
   
    Brushless Motors:
   
    Brushless Motors are a class of motors that operate using electronic commutation of phase currents, rather than electromechanical (brush-type) commutation. Brushless motors typically have a permanent magnet rotor and a wound stator.
   
    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 which graphically illustrates the steady state characteristics of the system.
   
    Break Frequency:
   
    Frequency(ies) at which the gain changes slope on a Bode plot (break frequencies correspond to the poles and zeroes of the system).
   
    Brush:
   
    Conducting material which passes current from the DC motor terminals to the rotating commutator.
   
    Brushless DC Servo:
   
    A general term referring to a motor drive that generates trapezoidal shaped motor currents in a motor wound as to generate trapezoidal Back EMF.
   
    Brushless Servo Drive:
   
    A servo drive used to control a permanent magnet synchronous AC motor. (may also be referred to as AC Servo Drive.)
   
    Bus:
   
    A group of parallel connections carrying preassigned digital signals. Buses usually consist of address and data information and miscellaneous control signals for the interconnection of microprocessors, memories, and other computing elements.
   
    Byte:
   
    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.