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    Serial Port:
   
    A digital data communication port configured with a minimum number of signal lines. This is achieved by passing binary information signals as a time series of "1"s and "0"s on a single line.
   
   
    Servo:
   
    A system consisting of several devices which continuously monitor actual information (position, velocity), compares those values to desired outcome and makes necessary corrections to minimize that difference.
   
    Servo Amplifier/Servo Drive:
   
    An electronic device which produces the winding current for a servomotor. The amplifier converts a low level control signal into high voltage and current levels to produce torque in the motor.
   
   
    Servo System:
   
    An automatic feedback control system for mechanical motion in which the controlled or output quantity is position, velocity, or acceleration. Servo systems are closed loop systems.
   
   
    Settling Time:
   
    The time required for a step response of a system parameter to stop oscillating or ringing and reach its final value.
   
   
    Sinking Current:
   
    Refers to the current flowing into the output of the chip. This means that a device connected between the positive supply and the chip output will be switched on when the output is low.
   
    Shunt regulator:
   
    A device that clamps the power supply voltage from exceeding rated values. Shunt regulators are very useful in dealing with problems with regeneration.
   
   
    Shunt resistor:
   
    The power resistor in a shunt regulator. The shunt regulator directs excess energy into the shunt resistor to 'burn off' extra voltage.
   
    Slew:
   
    In motion control, the portion of a move made at a constant non-zero velocity.
    Slew Speed:
   
    The maximum velocity at which an encoder will be required to perform.
   
   
    Sourcing Current:
   
    Refers to the current flowing out of the output of the chip. This means that a device connected between the chip output and the negative supply will be switched on when the output is high.
   
    Static Torque (Stall Torque):
   
    The maximum torque available at zero speed.
   
    Stator:
   
    The non-rotating part of a magnetic structure. In a motor, the stator usually contains the mounting surface, bearings, and nonrotating windings or permanent magnets.
   
   
    Step Angle:
   
    The angle the shaft rotates upon receipt of a single step command.
   
    Stiffness:
   
    The ability to resist movement induced by an applied torque. Is often specified as a torque displacement curve, indicating the amount a motor shaft will rotate upon application of a known external force when stopped.
   
    Straightness of Travel:
   
    Deviation from straight line motion in a horizontal plane. Also referred to as horizontal runout. This error is usually traceable to an underlying angular error of the ways.
   
   
    Synchronism:
   
    A motor rotating at a speed correctly corresponding to the applied step pulse frequency is said to be in synchronism. Load torques in excess of the motors capacity (rated torque) will cause a loss of synchronism. The condition is not damaging to a step motor.
   
    Tachometer:
   
    An electromagnetic feedback transducer which produces an analog voltage signal proportional to rotational velocity. Tachometers can be either brush or brushless.
   
   
    T.I.R.:
   
    This stands for Total Indicator Reading, which reflects the total absolute deviation from a mean value (versus a + value which indicates the deviation from a nominal value).
   
   
    Torque:
   
    The rotary equivalent to force. Equal to the product of the force perpendicular to the radius of motion and distance from the center of rotation to the point where the force is applied.
   
   
    Torque Constant:
   
    A number representing the relationship between motor input current and motor output torque. Typically expressed in units of torque / amp.
   
   
    Torque Ripple:
   
    The cyclical variation of generated torque at a frequency given by the product of motor angular velocity and number of commutator segments or magnetic poles.
   
    Torque-to-Inertia Ratio:
   
    Defined as a motor's holding torque divided by the inertia of its rotor. The higher the ratio, the higher a motor's maximum acceleration capability will be.
   
    Transducer:
   
    Any device that translates a physical parameter into an electrical parameter. Tachometers and encoders are examples of transducers.
   
   
    Transfer Function:
   
    A mathematical means of expressing the output to input relationship of a system. Expressed as a function of frequency.
   
    Trapezoidal Profile:
   
    A motion profile in which the velocity vs. time profile resembles a trapezoid. Characterized by constant acceleration, constant velocity, and constant deceleration.
   
   
    Triggers:
   
    Inputs on a controller that initiate or €?trigger€? the next step in a program.
   
    TTL:
   
    Transistor-Transistor Logic. Describes a common digital logic device family that is used in most modern digital electronics. TTL signals have two distinct states that are described with a voltage €¡° a logical €?zero€? or €?low€? is represented by a voltage of less than 0.8 volts and a logical €?one€? or €?high€? is represented by a voltage from 2.5 to 5 volts.
   
    Under damped:
   
    In tuning, the response is considered to be under damped when there is overshoot or oscillations in the step response. In control theory this occurs when the damping ratio ¦Æ < 1.
   
   
    Unstable:
   
    Not able to hold a commanded value because of poor tuning. Characterized by large oscillations that may increase in magnitude for each successive oscillation.
   
    Unipolar driver:
   
    A step motor driver configuration that uses a unipolar power supply and is capable of driving phase current in only one direction. The motor phase winding must be center tapped (6 or 8 lead) to operate with a unipolar driver. The center tap is used instead of providing the current reversal of a bipolar driver.
   
    Unipolar Motors:
   
    These motors are composed of two windings, each with a center tap. The center taps are either brought outside the motor as two separate wires or connected to each other internally and brought outside the motor as one wire, resulting in 5 or 6 wires.
   
    Velocity:
   
    The change in position as a function of time. Velocity has both a magnitude and a direction.
   
   
    Velocity Ripple:
   
    Disturbances in the programmed velocity profile due to changes in magnetic flux and commutation switching.
   
   
    Voltage Constant: (or Back EMF Constant):
   
    A number representing the relationship between Back EMF voltage and angular velocity. Typically expressed as V / kRPM.
   
   
    Yaw:
   
    An angular deviation from ideal straight line motion, in which the positioning table rotates around the Z (vertical) Axis as it translates along its travel axis.
   
    Zero:
   
    A frequency at which the transfer function of a system goes to zero.
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