Glossary

NI-Motion

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Glossary

Prefixes

Symbol Prefix Value
p pico 10 -12
n nano 10 -9
µ micro 10 -6
m milli 10 -3
k kilo 10 3
M mega 10 6
G giga 10 9
T tera 10 12

Numbers/Symbols

nV nanovolts 10-9 volts
µV microvolts 10-6 volts
µΩ microohms 10-6 ohms
mΩ milliohms 10-3 ohms
MΩ megaohms 106 ohms
pA picoamps 10-12 amperes
nA nanoamps 10-9 amperes
µA microamps 10-6 amperes
mA milliamps 10-3 amperes

A

  
A amperes
A/D analog-to-digital
absolute mode Treat the target position loaded as position relative to zero (0) while making a move.
absolute position Position relative to zero.
acceleration/deceleration Measurement of the change in velocity as a function of time. Acceleration and deceleration describes the period when velocity is changing from one value to another, such as from a stop (zero velocity) to a specified speed (target velocity) or vice versa. Deceleration is also considered negative acceleration.
active closed A signal is active when current is flowing through the optocoupled input.
active high Signal is active when its value goes high (1). See also non-inverting.
active low Signal is active when its value goes low (0). See also inverting.
active open A signal is active when current is not flowing through the optocoupled input.
ADC analog-to-digital converter
address Character code that identifies a specific location, or series of locations, in memory or on a host PC bus system.
amplifier Drive that delivers power to operate the motor in response to control signals. In general, the amplifier is designed to operate with a particular motor type. For example, you cannot use a stepper drive to operate a DC brush motor.
API application programming interface
axis Unit that controls a motor or any similar motion or control device.

B

  
b bit—One binary digit, either 0 or 1.
base address Memory address that serves as the starting address for programmable or I/O bus registers. All other addresses are located by adding to the base address.
binary Number system with a base of 2.
blending Blending connects move segments while maintaining velocity within the given physical constraints. These constraints are the specific move segments being blended, for example, velocity, acceleration, deceleration, and s-curve for each move.
buffer Temporary storage for acquired or generated data (in software).
bus Group of conductors that interconnect individual circuitry in a computer. Typically, a bus is the expansion vehicle to which I/O or other devices are connected. Examples of PC buses are the ISA and PCI bus.
byte Eight related bits of data, an 8-bit binary number. Also used to denote the amount of memory required to store one byte of data.

C

  
CCW counterclockwise—Implies the direction the motor rotates in.
closed-loop Broadly applied term relating to any system where output is measured and compared to input. The output is then adjusted to reach the appropriate condition. In motion control this term applies to a motion system that uses a feedback device to provide position and velocity data for status reporting and accurately controlling position and velocity.
commutation Sequential control of switched waveforms from the power driver amplifier into the motor phase windings that causes rotation or linear motion depending on motor type. Brush type motors auto-commutate due to the brush contact with the motor windings. Brushless type motors require the advance information of position and direction to accurately provide correct waveform switching sequences. Brushless motors typically use hall-effect type sensors to generate the commutation control waveforms.
control system bandwidth Measure of a closed-loop system's response and is typically represented as a frequency range or an update period for the PID loop in a digital servo controller. For example, if a PID loop has an update rate of 250 µs, it would have a bandwidth of 4 kHz.
CPU central processing unit
CSR communications status register
CW clockwise—Implies the direction the motor rotates in.

D

  
DAC digital-to-analog converter
data acquisition The process of collecting and measuring electrical signals from sensors, transducers, and test probes or fixtures and inputting them to a computer for processing.
DC direct current
DGND digital ground
digital I/O port Group of digital input/output signals.
DIP dual inline package
DLL Dynamic link library for Windows. Provides the API for the motion control devices.
drive Electronic signal amplifier that converts motor control command signals into higher-voltage signals suitable for driving motors.
driver Software that controls a specific hardware device such as a DAQ board or a motion controller.

E

  
encoder Device that translates mechanical motion into electrical signals; used for monitoring position or velocity in a closed-loop system.
encoder resolution Number of encoder lines between consecutive encoder marker or Z-bit indexes. If the encoder does not have an index output the encoder resolution can be referred to as lines per revolution.

F

  
F farad
FIFO First-in-first-out memory buffer—the first data stored is the first data sent to the acceptor. FIFOs are often used on DAQ devices to temporarily store incoming or outgoing data until that data can be retrieved or output. For example, an analog input FIFO stores the results of A/D conversions until the data can be retrieved into system memory, a process that requires the servicing of interrupts and often the programming of the DMA controller. This process can take several milliseconds in some cases. During this time, data accumulates in the FIFO for future retrieval. With a larger FIFO, longer latencies can be tolerated. In the case of analog output, a FIFO permits faster update rates, because the waveform data can be stored on the FIFO ahead of time. This again reduces the effect of latencies associated with getting the data from system memory to the DAQ device.
filter parameters Indicates the control loop parameter gains (PID gains) for a given axis.
filtering Type of signal conditioning that filters unwanted signals from the signal being measured.
flash ROM Type of electrically reprogrammable read-only memory.
following error trip point The difference between the instantaneous commanded trajectory position and the feedback position. If the following error increases beyond the maximum allowable value entered—referred to as the following error trip point—the motor trips on following error and is killed, preventing the axis from running away.
freewheel Condition of a motor when power is de-energized and the motor shaft is free to turn with only frictional forces to impede it.
full-step Full-step mode of a stepper motor—For a two-phase motor, this refers to energizing two windings or phases simultaneously.

G

  
Gnd ground
GND ground

H

  
half-step Mode of a stepper motor—For a two phase motor, this refers to alternately energizing two windings and then only one. In half step mode, alternate steps are strong and weak, but there is significant improvement in low-speed smoothness over the full-step mode.
hex hexadecimal
holding torque Force that a motor can provide or withstand while still remaining in a fixed stop location without any rotation, translation or movement.
home switch/home position (input) Reference position in a motion control system derived from a mechanical datum or switch. Often designated as the zero position in an absolute position frame of reference. The motion controller halts the motor if it finds this switch active while performing a find home sequence.
host computer Computer in which the motion controller is installed, or that is controlling the remote system in which the motion controller is installed.
hybrid stepper motor Motor type designed to move in discrete step increments, (typically specified in degrees). Hybrid stepper motors have permanent magnet rotor elements with a coil wound stator (outer shell) and no brushes contacting between the two. The current through the coil phases is switched in a predetermined sequence (commutated) to produce the appropriate motion in a given direction.
Hz hertz—the number of scans read or updates written per second.

I

  
I/O input/output—The transfer of data to and from a computer system involving communications channels, operator interface devices, data acquisition, and/or motion control interfaces.
ID identification
import library Windows-specific file that contains information about the VIs contained in a companion dynamic link library (DLL). Windows applications are typically linked to one or more import libraries.
in inches
index Marker between consecutive encoder revolutions.
inverting Defines the polarity of a switch (limit switch, home switch, and so on) when it is in its active state. If these inputs are active low they are said to have inverting polarity. See also active low.
IRQ interrupt request
ISA industry-standard architecture

J
jerk Derivative of acceleration (change of acceleration per unit time) measured in units of counts (steps)/s3.

K

  
k kilo—The standard metric prefix for 1,000, or 103, used with units of measure such as volts, hertz, and meters.
K kilo—The prefix for 1,024, or 210, used with B in quantifying data or computer memory.

L

  
latching Signal that maintains its value while in a given state, as opposed to a signal that momentarily pulses when entering or exiting a state.
LIFO last-in, first-out
limit switch/end-of-travel position (input) Sensors that alert the control electronics that the physical end of travel is near and that the motion must stop.

M

  
m meters
MCS Move Complete Status
microstep Proportional control of energy in the coils of a stepper motor that allows the motor to move to or stop at locations other than the fixed magnetic/mechanical pole positions determined by the motor specifications. This capability facilitates the subdivision of full mechanical steps on a stepper motor into finer microstep locations that greatly smooth motor running operation and increase the resolution or number of discrete positions that a stepper motor can attain in each revolution.
modulo position Treat the position as if it is within the range of total quadrature counts per revolution for an axis.
MustOff State or bit that is forced off (False) or must be off to satisfy a condition.
MustOn State or bit that is forced on (True) or must be on to satisfy a condition.

N

  
noise An undesirable electrical signal. Noise comes from external sources such as the AC power line, motors, generators, transformers, fluorescent lights, soldering irons, CRT displays, computers, electrical storms, welders, radio transmitters, and internal sources such as semiconductors, resistors, and capacitors. Noise corrupts signals you are trying to send or receive.
non-inverting Defines the polarity of a switch (limit switch, home switch, and so on) when it is in its active state. If these inputs are active high they are said to have non-inverting polarity. See also active high.

O

  
open collector Method of output capable of sinking current, but not sourcing current.
open-loop Refers to a motion control system where no external sensors, or feedback devices, are used to provide position or velocity correction signals.

P

  
packets Command and data sent as a group over a computer bus.
PCI peripheral component interconnect—A high-performance expansion bus architecture originally developed by Intel to replace ISA and EISA. PCI is achieving widespread acceptance as a standard for PCs and workstations; it offers a theoretical maximum transfer rate of 132 MB/s.
phase angle/phase margin Value presented in PID Loop Tuning Bode Plot analysis that represents the advance or lead of an input signal to the output signal in a closed-loop servo controller. Used to determine closed-loop system stability at a given crossover frequency.
PID control loop proportional-integral-derivative control loop—A control method in which the controller output is proportional to the error, the error time history, and the rate at which the error is changing. The error is the difference between the observed and the commanded values of a variable that is under control action.
PID loop tuning/servo compensation Flexible adjustment of the Proportional, Integral, and Derivative Gain Parameters along with loop update rate or frequency to assure stable operation and appropriate dynamic response of a closed-loop servo system.
PIVff control loop proportional-integral-velocity feed forward control loop—A control method that operates with zero derivative gain and either velocity feedback or a velocity block amplifier.
port
  1. Communications connection on a computer or a remote controller.
  2. Digital port, consisting of four or eight lines of digital input, and/or output.
position breakpoint Allows a motor to stop at a given point so that another action, such as a data acquisition or an image acquisition, can take place. You can set position breakpoints in absolute or relative quadrature counts. When the encoder reaches a position breakpoint, the associated breakpoint output immediately transitions.
position resolution Typically determined by the smallest increment of motion that can be controlled. In stepper motor systems, it is determined by the number of steps per revolution, typically as a limitation of the stepper driver microstepping value or of the feedback device resolution. In servo motor systems, it is entirely determined by the resolution of the feedback device in counts per revolution of the motor.
power cycling Turning the host computer off and then back on. This resets the motion controller.
profile Instantaneous position versus time output of a trajectory generator.
pull-in move When stepper motors are run in closed-loop mode, the encoder feedback is used to verify the position of an axis when the motion ends. The motion controller then commands the axis to do a final move so that it is at the specified target position.
PWM pulse width modulation—Method of controlling the average current in a motor phase winding by varying the on-time (duty cycle) of transistor switches.
PXI PCI eXtensions for Instrumentation

Q

  
quadrature counts Encoder line resolution times four. The encoder resolution is the number of encoder lines between consecutive encoder indexes (marker or Z-bit). If the encoder does not have an index output the encoder resolution can be referred to as lines per revolution, lines per inch, lines per millimeter, and so on.

R

  
RAM random-access memory
RDB return data buffer
relative breakpoint Sets the position breakpoint for an encoder in relative quadrature counts.
relative position Destination or target position for motion specified with respect to the current location, regardless of its value.
relative position mode Treat the target position loaded as position relative to current position while making a move.
ribbon cable Flat cable in which the conductors are side by side.
ROM read-only memory—non-volatile memory used for storing code, programs, and data.
rotary axis Axis for which rotary counts are loaded. The axis moves to the target position by taking the shortest path, either forward or backwards, while remaining within the one revolution defined by the loaded modulo value.
RPM revolutions per minute—Units for velocity.
RPSPS or RPS/S revolutions per second squared—Units for acceleration and deceleration.
RTR Ready to Receive
RTSI real-time system integration bus—the National Instruments timing bus that connects controllers directly, by means of connectors on top of the controllers, for precise synchronization of functions.

S

  
s, sec seconds
servo
  1. Specifies an axis that controls a servo motor.
  2. Specifies when a servo motor becomes active.
sinusoidal commutation Method of controlling current in the windings of a brushless servo motor by using the pattern of a sine wave to shape the smooth delivery of current to three motor inputs, each 120° out of phase from the next.
slot Position where a module can be inserted into an ISA or PCI backplane.
step output rate The frequency of the step output control pulses generated by a controller/indexer and provided to an amplifier driver. The combination of step output rate (steps/s), steps per revolution (steps/rev), and time (60 s/minute) provide a basic representation of motor velocity in RPM. Linear speed may be further derived by additional mechanical data, lead screw revolutions per inch, and so on.
stepper Specifies an axis that controls a stepper motor.

T

  
toggle Changing state from high to low, back to high, and so on.
torque Force tending to produce rotation.
totem pole Method of output capable of sinking and sourcing current.
trapezoidal profile Typical motion trajectory, where a motor accelerates up to the programmed velocity using the programmed acceleration, traverses at the programmed velocity, and then decelerates at the programmed acceleration to the target position.
trigger Any event that causes or starts some form of data capture.
trigger buffer inputs Digital signal that begins the execution of a sequence of motion commands stored on the controller/indexer allowing the commands to fully execute until the end of the sequence is reached.
TTL transistor-transistor logic

U
UOM unit of measure

V

  
V volts
velocity mode Move the axis continuously at a specified velocity.

W

  
watchdog Timer task that shuts down, or resets, the motion control device if any serious error occurs.
word Standard number of bits that a processor or memory manipulates at one time, typically 8-bit, 16-bit, or 32-bit.

Z
Z-bit Marker or index between consecutive encoder revolutions.
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