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    Control Area Network (CAN):
   
    Is a serial bus system, which was originally developed for automotive applications in the early 1980's. The CAN protocol was internationally standardized in 1993 as ISO 11898-1 and comprise the data link layer of the seven layer ISO/OSI reference model.
   
    CANopen:
   
    CANopen is a CAN-based higher layer protocol. It was developed as a standardized embedded network with highly flexible configuration capabilities. CANopen was designed motion oriented machine control networks, such as handling systems. It is used in many various fields, such as medical equipment, off-road vehicles, maritime electronics, public transportation, building automation, etc.
   
    C-face mounting:
   
    A standard NEMA mounting design, where the mounting holes in the face are threaded to receive the mating mount.
   
    Class B insulation:
   
    A NEMA insulation specification. Class B insulation is rated to an operating (internal) temperature of 130°C.
   
    Class F insulation:
   
    A NEMA insulation specification. Class F insulation is rated to an operating (internal) temperature of 155°C
   
    Class H insulation:
   
    A NEMA insulation specification. Class H insulation is rated to an operating (internal) temperature of 180°C.
   
   
    Closed Loop System:
   
    In motion control, this term describes a system wherein a velocity or position (or both) sensor is used to generate signals for comparison to desired parameters. For cases where loads are not predictable, the closed loop feedback from an external encoder to the controller may be used for stall detection, position maintenance or position verification.
   
    Closed Loop:
   
    A broadly applied term relating to any system where the output is measured and compared to the input. The output is then adjusted to reach the desired condition. In motion control, the term describes a system wherein a velocity or position (or both) transducer is used to generate correction signals by comparison to desired parameters.
   
    Constant Current driver:
   
    A control or device for adjusting the voltage to force or maintain design current in the winding when switching from one winding to another.
   
    Coefficient of Friction:
   
    This is defined as the ratio of the force required to move a given load to the magnitude of that load. Typical values for the ball and crossed roller slides are 0.001 to 0.005.
   
    Cogging:
   
    A term used to describe non-uniform angular velocity. Cogging appears as a jerkiness especially at low speeds.
   
    Command Position:
   
    The desired angular or linear position of an actuator.
   
    Commutation:
   
    The switching sequence of drive voltage into motor phase windings necessary to assure continuous motor rotation. A brushed motor relies upon brush/bar contact to mechanically switch the windings. A brushless motor requires a device that senses rotor rotational position, feeds that information to a drive that determines the next switching sequence.
   
    Commutator:
   
    A mechanical cylinder consisting of alternating segments of conductive and insulating material. This cylinder used in DC motors passes currents from the brushes into the rotor windings and performs motor commutation as the motor rotates.
   
    Compensation:
   
    The corrective or control action in a feedback loop system which is used to improve system performance characteristics such as accuracy and response time.
   
    Compensation, Feedforward:
   
    A control action which depends on the command only and not the error to improve system response time.
   
    Compensation, Integral:
   
    A control action which is proportional to the integral or accumulative time error value product of the feedback loop error signal. It is usually used to reduce static error.
   
    Compensation, Lag:
   
    A control action which causes the lag at low frequencies and tends to increase the delay between the input and output of a system while decreasing static error.
   
    Compensation, Lead:
   
    A control action which causes the phase to lead at high frequencies and tends to decrease the delay between the input and output of a system.
   
    Compensation, Lead Lag:
   
    A control action which combines the characteristics of lead and lag compensations.
   
    Compensation, Proportional:
   
    A control action which is directly proportional to the error signal of a feedback loop. It is used to improve system accuracy and response time.
   
    Compliance:
   
    The amount of displacement per unit of applied force.
   
    Continuous rated current (ICR) (Amperes):
   
    The maximum allowable continuous current a motor can handle without exceeding the motor temperature limits.
   
    Continuous rated torque (TCR) (lb-in.):
   
    The maximum allowable continuous torque a motor can handle without exceeding the motor temperature limits.
   
    Continuous stall current (ICS) (Amperes):
   
    Amount of current applied to a motor (at locked rotor conditions), which results in rated temperature rise. Refer also to definition of "Continuous stall torque".
   
    Continuous stall torque (TCS) (lb-in.):
   
    The amount of torque at zero speed, which a motor can continuously deliver without exceeding its thermal rating. Determined by applying DC current through two windings with rotor locked, while monitoring temperature. Specified with motor windings at maximum rated temperature, with motor in 25 degrees C ambient, mounted to a heat sink. Refer to individual specs for heat sink size.
   
    Controller:
   
    A term describing a functional block containing an amplifier, power supplies, and possibly position-control electronics for operating a servomotor or step motor.
   
    Current at peak torque (IPK) (Amperes):
   
    The amount of input current required to develop "peak torque". This is often outside the linear torque/current relationship.
   
    Current, Rated:
   
    The maximum allowable continuous current a motor can handle without exceeding motor temperature limits.
   
    Coordinated Motion:
   
    Multi-axis motion where the position of each axis is dependent on the other axis such that the path and velocity of a move can be accurately controlled (requires coordination between
    axes).
   
    Critical Damping:
   
    A system is critically damped when the response to a step change in desired velocity or position is achieved in the minimum possible time with little or no overshoot.
   
    Crossover Frequency:
   
    The frequency at which the gain intercepts the 0 dB point on a Bode plot (used in reference to the open-loop gain plot).
   
    Daisy-Chain:
   
    A term used to describe the linking of several RS-232C devices in sequence such that a single data stream flows through one device and on to the next. Daisy-chained devices usually are distinguished by device addresses, which serve to indicate the desired destination for data in the stream.
   
    Damping:
   
    An indication of the rate of decay of a signal to its steady state value. Related to settling time.
   
    Damping Ratio:
   
    Ratio of actual damping to critical damping. Less than one is an underdamped system and greater than one is an overdamped system.
   
    DC Adjustable-Speed Drive:
   
    All equipment required to adjust the speed or torque of DC motor(s) by controlling the voltages applied to the armature and/or field of the motors.
   
    DC Drive:
   
    An electronic control unit for running DC motors. The DC drive converts AC line current to a variable DC current to control a DC motor. The DC drive has a signal input that controls the torque and speed of the rotor.
   
    Dead Band:
   
    A range of input signals for which there is no system response.
   
    Decibel:
   
    A logarithmic measurement of gain. If G is a system's gain (ratio of output to input), then 20 log G = gain in decibels (dB).
   
    Demag current:
   
    The current level at which the motor magnets will start to be demagnetized. This is an irreversible effect, which will alter the motor characteristics and degrade performance. Also known as peak current.
   
    Detent Torque:
   
    The minimal torque present in an unenergized motor. The detent torque of a step motor is typically about 1% of its static energized torque.
   
    Drive, Analog:
   
    Usually referring to any type of motor drive in which the input is an analog signal.
   
    Drive, Digital:
   
    Usually referring to any type of motor drive in which the tuning or compensation is done digitally. Input may be an analog or digital signal.
   
    Drive, Linear:
   
    A motor drive in which the output is directly proportional to either a voltage or current input. Normally both inputs and outputs are analog signals.
   
    Drive, PWM:
   
    A motor drive utilizing Pulse-Width Modulation techniques to control power to the motor. Typically a high efficiency drive that can be used for high response applications.
   
    Drive, Servo:
   
    A motor drive which utilizes internal feedback loops for accurate control of motor current and/or velocity.
   
    Drive, Stepper:
   
    Electronics which convert step and direction inputs to high power currents and voltages to drive a stepping motor. (The stepping motor drive is analogous to the servomotor amplifier).
   
    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.
   
    Direct Drive Servo:
   
    A high-torque, low-speed servo motor with a high resolution encoder or resolver intended for direct connection to the load without going through a gearbox.
   
    Duty Cycle:
   
    For a repetitive cycle, the ratio of on time to total cycle time. Duty Cycle = On Time/(On Time + Off Time) x 100%
   
    Electromagnetic Interference (EMI):
   
    An electromagnetic disturbance, phenomenon, signal or emission that causes or can cause undesired response of electrical or electronic equipment.
   
    Efficiency:
   
    The ratio of power output to power input.
   
    Electrical Time Constant:
   
    The ratio of armature inductance to armature resistance. The time it takes for a step current input to the coil to reach 63% of its value by overcoming the resistance and the inductance of the coil.
   
    Encoder:
   
    A device that translates mechanical motion into electronic signals used for monitoring position or velocity. Typical encoders are designed with a printed disc and a light source. As the disc turns with the actuator shaft, the light source shines through the printed pattern onto a sensor. The light transmission is interrupted by the patterns of the disc. These interruptions are sensed and converted to electrical pulses. By counting these pulses, actuator shaft position is determined.
   
    Encoder, Absolute:
   
    A digital position transducer in which the output is representative of the absolute position of the input shaft within one (or more) revolutions. Output is usually a parallel digital word.
   
    Encoder, Incremental:
   
    A position encoding device in which the output represents incremental changes in position.
   
    Encoder, Linear:
   
    A digital position transducer which directly measures linear position.
   
    Encoder Marker:
   
    A once-per-revolution signal provided by some incremental encoders to specify a reference point within that revolution.
   
    Encoder Resolution:
   
    A measure of the smallest positional change which can be detected by the encoder.
   
    Explosion-proof:
   
    A motor classification that indicates a motor is capable of withstanding internal explosions without bursting or allowing ignition to reach beyond the confines of the motor frame.
   
    Feedback:
   
    A signal which is transferred from the output back to the input for use in a closed loop system.
   
    Feedforward:
   
    Feedforward control gives corrective action before the disturbance affects the output.
   
    Filter (Control Systems):
   
    A transfer function used to modify the frequency or time response of a control system.
   
    Firmware:
   
    Firmware is programming that has been permanently or semi-permanently stored. Firmware is commonly stored in flash or EEPROM memory which both have the ability to keep their information, even when powered off. It is also easy to re-program flash and EEPROM memory when new firmware updates become available. When used in devices that are frequently powered off, firmware allows these devices to turn on again without having to be re-programmed.
   
    Floating ground:
   
    A ground that is not referenced to earth ground. Floating grounds can make dangerous or exciting situations if not handled correctly. For example, when 120VAC is rectified into DC, the ground is considered to be a floating ground. Any attempt to tie the rectified AC ground to earth ground would likely blow a breaker or a fuse. The solution in this case is to first isolate the AC using a transformer before rectification.
   
   
    Flatness of Travel:
   
    Deviation from ideal straight line travel in a vertical plane, also referred to as vertical runout.
   
    Following Error:
   
    The positional error during motion resulting from use of a position control loop with proportional gain only.
   
    Form Factor:
   
    The ratio of the RMS value of a harmonic signal to its average value in one half-wave. This number is a measure of the current ripple in a SCR or other switch-mode type of drive. Since motor heating is a function of RMS current while motor torque is a function of average current, a form factor greater than 1.00 means some fraction of motor current is producing heat but not torque.
   
    Friction:
   
    A resistance to motion. Friction can be constant with varying speed (Coulomb friction) or proportional to speed (viscous friction).
   
    Full Load Current:
   
    The armature current of a motor operated at its full load torque and speed with rated voltage applied.
   
    Full Load Speed:
   
    The speed of a motor operated with rated voltage and full load torque.
   
   
    Full Step:
   
    For 2-phase stepping motor, this means that the shaft will rotate 1.8 degree (3-phase is 1.2 degree.) mechanically for each digital pulse received by the driver. In full step mode, the motor requires 200 (3-phase is 300.) digital pulses to move one shaft revolution divide 360 degree by 1.8 degree (3-phase is 1.2 degree.).
   
    Gain:
   
    The ratio of system output signal to system input signal. The control loop parameter that determines system performance characteristics.
   
    Gearbox:
   
    A system of gears that transmits mechanical power from a prime mover such as an electric motor to a typically rotary output device at a lower momentum but at a higher torque.
   
    Graphical User Interface (GUI):
   
    A type of user interface that allows people to interact with a computer and computer-controlled devices which employs graphical icons, visual indicators or special graphical elements, along with text labels or text navigation to represent the information available to the user.
   
    Ground Loop:
   
    A ground loop is any part of the DC return path (ground) that has more than one possible path between any two points.
   
    Half Step:
   
    For a 2-phase stepping motor, this term means that the motor shaft will move a distance of 0.9 degree (400 steps per shaft revolution) instead of moving 1.8 degree per digital pulse.
   
    Hall Sensors:
   
    A feedback device which is used in a brushless servo system to provide information for the amplifier to electronically commutate the motor. The device uses a magnetized wheel and hall-effect sensors to generate the commutation signals.
   
    Hertz:
   
    A unit of frequency in units of 1/s. 60Hertz is 60/s or 60 times per second. 20kHz is 20,000 times/second.
   
    Hybrid Motors:
   
    Hybrid stepper motors feature the best characteristics of PM and VR motors. Hybrid steppers are best suited for industrial applications because of high static and run torque, a standard low step angle of 1.8°, and the ability to Microstep. Hybrid stepper motors offer the ability to precisely position a load without using a closed-loop feedback device such as an encoder.
   
   
    Holding Torque:
   
    Sometimes called static torque, it specifies the maximum external force or torque that can be applied to a stopped, energized motor without causing the rotor to rotate continuously.
   
    Home Position:
   
    A reference position for all absolute positioning movements. Usually defined by a home limit switch and/or encoder marker. Normally set at power up and retained for as long as the control system is operational.
   
    Horsepower (HP):
   
    One horsepower is equal to 746 watts. Since Power = Torque x Speed, horsepower is a measure of a motor's torque and speed capability (e.g. a 1 HP motor will produce 35 in-lb. at 1,800 RPM).
   
    Host Computer:
   
    An auxiliary computer system which is connected to a controller or controllers. The host computer in distributed control systems is frequently involved with controlling many remote and distributed motion control devices. It may also be used for off-line
   
    Hunting:
   
    The oscillation of the system response about a theoretical steady-state value.
   
    Hybrid Stepping Motor:
   
    A motor designed to move in discrete increments or steps. The motor has a permanent magnet rotor and wound stator. These motors are brushless and phase currents are commutated as a function of time to produce motion.
   
    Hybrid Servo:
   
    A brushless servo motor based on a conventional hybrid stepper. It may use either a resolver or encoder for commutation feedback.
   
    Hysteresis:
   
    For a system with an analog input and digital output, the output value is dependent on both the input value and output state such that there is an input range over which the output can be high or low.