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    Lead Compensation Algorithm:
   
    A mathematical equation implemented by a computer to decrease the delay between the input and output of a system.
   
    Lead Screw:
   
    A device for translating rotary motion into linear motion, consisting of an externally threaded screw and an internally threaded carriage (nut). Typically leadscrews are inefficient when compared to Ball Screws or Belt Drives.
   
    Limits:
   
    Motion control systems may have sensors called limits that alert the control electronics that the physical end of travel is being approached and that motion should stop.
   
   
    Linear Coordinated Move:
   
    A coordinated move where the path between endpoints is a line.
   
   
    Linearity:
   
    For a speed control system it is the maximum deviation between actual and set speed expressed as a percentage of set speed.
   
    Load:
   
    Any external resistance (static or dynamic) to motion that is applied to the motor.
   
    Logic Ground:
   
    An electrical potential to which all control signals in a particular system are referenced.
   
    Loop, Feedback Control:
   
    A control method that compares the input from a measuring device, such as an encoder or tachometer, to a desired parameter, such as position or velocity and causes action to correct any detected error. Several types of loops can be used in combination (i.e. velocity and position together) for high performance requirements.
   
   
    Loop Gain, Open:
   
    The product of the forward path and feedback path gains.
   
   
    Loop, PID:
   
    Proportional, Integral, and Derivative Loop: Specialized very high performance control loop which gives superior response.
   
   
    Loop, Position:
   
    A feedback control loop in which the controlled parameter is motor position.
   
   
    Loop, Velocity:
   
    A feedback control loop in which the controlled parameter is mechanical velocity.
   
   
    Master Slave Motion Control:
   
    A type of coordinated motion control where the master axis position is used to generate one or more slave axis position commands.
   
   
    Mechanical Time Constant:
   
    The time for an energized DC motor to reach 2/3rds of its set velocity. Based on a fixed voltage applied to the windings.
    Mid-range Instability:
   
    Designates the condition resulting from energizing a motor at a multiple of its natural frequency (usually the third orders condition). Torque loss and oscillation can occur in underdamped open-loop systems.
   
    Microstepping:
   
    An electronic control technique that proportions the current in a step motors windings to provide additional intermediate positions between poles. Produces smooth rotation over a wide speed range and high positional resolution.
   
    Mid-Range Instability:
   
    A phenomenon in which a stepping motor can fall out of synchronism due to loss of torque at mid-range speeds. The loss of torque is due to interaction between the motor's electrical characteristics and the driver electronics. Some drivers have circuitry to eliminate or reduce this phenomenon.
   
   
    MOSFET:
   
    Metal-Oxide Semiconductor Field-Effect Transistor. Used as the output power devices in PWM drives. MOSFET's are good for lower voltage and lower current drives.
   
    Motor, AC:
   
    A device that converts electrical alternating current into mechanical energy. Requires no commutation devices such as brushes. Normally operated off commercial AC power. Can be single or multiple phase.
   
   
    Motor, AC Asynchronous or Induction:
   
    An AC motor in which speed is proportional to the frequency of the applied AC. Requires no magnets or field coil. Usually used for non-precise constant speed66 applications.
   
   
    Motor, AC Synchronous:
   
    Another term for brushless DC motor.
   
    Motor Constant:
   
    The ratio of the motor torque to motor input power.
   
   
    Motor, DC:
   
    A device that converts electrical direct current into mechanical energy. It requires a commutating device, either brushes or electronic. Usually requires a source of DC power.
   
   
    Motor, DC Brushless:
   
    A type of direct current motor that utilizes electronic commutation rather than brushes to transfer current.
   
   
    Motor, DC Permanent Magnet:
   
    A motor utilizing permanent magnets to produce a magnetic field. Has linear torque speed characteristics.
   
   
    Motor, Stepping:
   
    A specialized AC motor that allows discrete positioning without feedback. Normally used for non-critical, lowpower applications, since positional information is easily lost if acceleration or velocity limits are exceeded. Load variations can also cause loss of position. If encoders are used, these limitations can be overcome.
   
    National Electrical Manufacturer's Association (NEMA):
   
    The acronym for the organization that sets standards for motors and other industrial electrical equipment.
   
    NC, Numerical Control:
   
    Usually refers to any type of automated equipment or process used for contouring or positioning.
   
    No Load Speed:
   
    Motor speed with no external load.
   
    NTC - Negative Temperature Coefficient:
   
    A negative temperature coefficient thermistor is used to detect and protect a motor winding from exceeding its maximum temperature rating. Resistance of the device decreases with an increase in temperature.
   
   
    Open Collector:
   
    A term used to describe a signal output that is performed with a transistor. An open collector output acts like a switch closure with one end of the switch at ground potential and the other end of the switch accessible.
   
    Open-Loop System:
   
    A system where the command signal results in actuator movement but, because the movement is not sensed, there is no way to correct for error. Open lop means no feedback.
   
   
    Operator Interface:
   
    A device that allows the operator to communicate with a machine. This device typically has a keyboard or thumbwheel to enter instructions into the machine. It also has a display device that allows the machine to display messages.
   
   
    Optical Encoder:
   
    A linear or angular position feedback device, typically providing incremental two channel information in quadrature format (sine or square waves with a 90-degree phase shift between each channel). Such two channel information allows simple counter circuits to function as absolute position indicators.
   
   
    Opto-isolated:
   
    A method of sending a signal from one piece of equipment to another without the usual requirement of common ground potentials. The signal is transmitted optically with a light source (usually a Light Emitting Diode) and a light sensor (usually a photosensitive transistor). These optical components provide electrical isolation.
   
    Orthogonality:
   
    The degree of perpendicularity, or squareness, between the two axes in an X-Y or X-Z table. This parameter is usually measured in arc-seconds or microradians.
   
   
    Oscillation:
   
    An effect that varies periodically between two values.
   
    Overload capacity:
   
    The ability of a drive to withstand currents above its continuous rating. It is defined by NEMA as 150% of the rated full-load current for "standard industrial DC motors" for one minute.
   
    Overshoot:
   
    The amount that the parameter being controlled exceeds the desired value for a step input.