Reading LSM Specs

Abbe Error
Motion errors caused by angular moments
between the measuring feedback element and the
point of interest.

Abbe Offset
The linear distance between the measuring
feedback element and the point of interest.

Absolute Move
A move referenced from a fixed zero position.

Acceleration
Change in velocity as a function of time, going from
slower to faster.

Accuracy
Difference between expected position and
achieved position.

Back EMF
The peak phase-to-phase voltage generated when
the motor is traveling at a velocity of 1m/s.

Backlash
The non-responsive lost motion between a drive
screw and its nut that occurs at the point of change
in rotation direction.

Brushless Servomotor
A class of servomotors, which operates using
electronic commutation of phase currents rather
than electromechanical (brushes) commutation.

Cantilevered Load
A load that has its center of mass offset from the
balance point of a bearing system.

Closed Loop
Implementing feedback to regulated position and/or
velocity with respect to commanded.

Cogging
A term used to describe non-uniform angular
velocity. Cogging appears as jerkiness, especially
at low speeds. Changes in force at low velocity,
caused by magnetic “detenting” forces created by
relative motion between a motor's permanent
magnets and its ferrous core coil windings.

Commutation
The switching sequence of drive voltage into motor
phase windings necessary to ensure continuous
motor movement. A brushed motor relies upon
brush/bar contact to switch the windings
mechanically. A brushless Linear Shaft Motor
requires a device that senses forcer position
information relative to the shaft, and then feeds that
data to a drive, which determines the next
switching sequence.

Commutation, Sinusoidal
The three phase currents applied to a motor closely
follow the sine wave shape of the motor's natural
back emf waves, thereby providing the lowest
velocity ripple and the smoothest possible motion.
This is a very important factor for scanning
applications. Sinusoidal commutation is
electronically generated at the servo controller.

Commutation, Trapezoidal
The three phase currents applied to a motor
resemble a trapezoidal profile. Slight force ripple is
present due to the mismatch between the three
phase trapezoidal shape and the motor's back emf
sinewave profile. Trapezoidal commutation is
typically generated by Hall effect sensors secured
near the motor's moving coils. Trapezoidal
commutation is suitable for most high-speed motion
applications.

Continuous Current
The current required to heat the motor phases to
their maximum operating temperature when the
ambient temperature is 25°C, the motor is not
moving, and there is no cooling.

Continuous Force
Continuous force is the force produced when the
continuous current is applied to the motor. It is the
product of Force constant X Continuous current.
The motor is not moving and there is no cooling.

Continuous Working Voltage
The maximum allowable continuous voltage
between any two phases or between any phase
and the motor safety earth.

Counts per Meter
Counts per Meter is equal to 1 divided by resolution
on encoder (Example for 50nm encoder: Pulses
per Meter = 1/(50*10^-9)=20000000)

Coefficient of Kinetic Friction (μk)
It is the proportional value of the force required to
maintain motion to the normal force of the mass
being moved.

Coefficient of Static Friction (μs)
It is the proportional value of the force required to
overcome static friction, to the normal force of the
mass to be moved.

Cosine Error
Results from a parallel misalignment between a
linear bearing system and the linear feedback
element.

Current
The value of current when two motor phases are
joined, and a current is passed between those two
phases and the third. Example, a current of 1
ampere means that 1 ampere will be flowing in one
phase and 0.5 ampere in each of the other two
phases.

Current/Torque Amplifiers
Current/Torque amplifiers produce a force
proportional to the command signal. The speed
with which the motor will move is therefore
controlled entirely by the external servo controller.
The most common type of programmable digital
servo controller used with current amplifiers
employs a PIDF algorithm to control the position of
the motor.

Deceleration
Change in velocity as a function of time, going from
faster to slower.

Duty Cycle, Motion
The percentage of the time in motion to the total
time (motion time ÷ total time) x 100%.

Duty Motor Power
The percentage of the application process power to
a motor's continuous power limits [(IRMS ÷ ICont)2
x 100%]. This value should not exceed 100% for a
prolonged period of time.

Electrical Time Constant
The time taken for a step current input to the motor
to reach 63.2% of its value.

Encoder
A position-sensing device that translates
mechanical motion into electronic signals used for
monitoring position or velocity.

Flatness
The deviation from the theoretically perfect line of
travel, and is measured as displacement in the
vertical plane.
Note that the frame or mounting surface to which
the module or gantry system is fixed will affect the
flatness of the system.

Friction
Resistance to motion of two surfaces that touch.

Force Constant
Force constant is the k force produced when 1
ampere flows into one phase and 0.5 ampere flows
out of the remaining two phases

Forcer
The coil assembly of the Linear Shaft Motor. It is
typically available in one of five configurations: D,
two sets of windings; T, three sets of windings; Q,
four sets of windings; H, six sets of windings, S,
one sets of windings, or X, eight sets of windings.

Hall Sensors
A feedback device, which is used in some
brushless servo systems to provide information for
the amplifier to electronically commutate the motor.
In a Linear Shaft Motor, the hall sensors sense the
position of the forcer and send a signal to the driver
to switch on the next sequential winding (the
process of commutation) in the forcer, which
causes linear movement.

Hysteresis
The non-responsive lost motion which may occur at
the point of change in direction. The composite
error results from many contributing factors
(backlash, elasticity of structure, etc.).

Incremental Move
A move referenced from the current position.

Inductance
The property of an electric circuit by which an
electromotive force is induced in it as the result of a
changing magnetic flux. This electrical
characteristic is an indicator of how fast the current
can rise and fall when voltage is applied to the
windings.

Inertia
The property of an element's mass and shape that
resists changes in velocity when exposed to an
outside force. The larger an object's mass, the
greater its inertia and the greater the magnitude of
force required to accelerate it at a given rate.

Intelligent Amplifiers
Servo amplifiers do not require external control
signals in order to position the motor. Depending
on the unit, they can perform very simple point to
point moves up to very sophisticated moves with
external synchronization and I/O handling.
Generally, they can operate in either
position/velocity, or force control modes.

Limits or Limit Switches
Properly designed motion control systems have
sensors called limits, or limit switches, which alert
the control electronics that the physical end of
travel is being approached and that motion should
stop. These are safety devices at each end of the
movement to prevent damage due to over travel of
the forcer.

Linear Bearing
A support device that allows a smooth, low friction
motion between two surfaces loaded against each
other.

Magnetic Pitch (Pole Pitch)
The distance in millimeters for one complete
electrical cycle (between like magnetic poles).
Example: North to North.

Maximum Phase Temperature
The maximum operating temperature for the motor
phases. It is limited to provide a safe operating
temperature for the coil.

Open Loop
A motion system which does not utilize a feedback
element.

Orthogonality
The degree to which stages are aligned with their
motion at right angles to one another. Motion of an
X-Y system is typically 90° apart in a single plane.
X-Y-Z systems are all mutually at a 90° relationship
in a 3D space. The specification is typically the
angle measured between the best-fit-straight-line of
X-axis motion and the best-fit-straight-line of Y-axis
motion.

Parallelism
The deviation between the perpendicular distance
between axes (with one being the reference axis).

Peak Current
The current that can be applied for short periods of
time for accelerating or decelerating. The peak
current can be safely applied the Linear Shaft
Motor for a maximum of 40 seconds, before the
motor phases reach their maximum operating
temperature when the ambient temperature is
25°C, the motor is not moving, there is no and no
additional heat sinking.

Peak Force
The force produced when the peak current is
applied to the Linear Shaft Motor. It is the product
of Force constant X Peak current. The motor is not
moving, there is no cooling and no additional heat
sinking.

Pulses per Meter
Pulses per Meter is equal to1 divided by resolution
on encoder divided by 4 (Example for 50nm
encoder: Pulses per Meter = 1/(50*10^-
9)/4=5000000)

Repeatability, Bi-directional
The error from nominal when repeatedly
approaching a position from opposite directions.
Repeatability, Uni-directional
The error from nominal when repeatedly
approaching a position from the same direction.

Resistance
The opposition to the flow of charge through a
conductor.

Resonance
Oscillatory behavior in a mechanical body when
subjected to a periodic force occurring at its natural
frequency.

Resolution, Electrical
The smallest increment that can be commanded by
a servo system. The value results from the
feedback's precision (encoder, laser, etc.) and the
controller's logic multiplication factor.

Resolution, Mechanical
The smallest increment that can be controlled by a
motion system. The value is affected by friction,
static friction, driving mechanism precision, etc.

Scale Error
Errors associated with the precision of the
feedback elements.

Settling Time
The time it takes after a move completes to settle to
within a specified tolerance band (i.e.: to within ±
1μm).

Servo Driver
A three phase brushless DC servomotor driver
used to drive and control the position of a servo
motor. It is comprised of a servo controller and
amplifier combination. There are many different
makes and models of amplifiers available, but they
tend to fall into one of three possible categories:
1. Intelligent amplifiers that have built in servo
controllers
2. Velocity amplifiers capable of controlling
only the velocity of the motor
3. Current/Torque amplifiers that control only
the force of a linear motor (torque in a
rotary motor)

Shaft
The magnetic assembly of the Linear Shaft Motor.
It is typically is a stainless steel shaft and not
designed to be load bearing.

Straightness
The deviation from the theoretical perfect line of
travel, and is measured as displacement in the
horizontal plane.

Stiction
Frictional resistance to initial motion.

Thermal Resistance
The equivalent thermal resistance of the motor,
determined by the ratio of coil temperature rise to
the total power motor losses in the three phases.

Velocity
A change in position as a function of time (speed).

Velocity amplifiers
Servo amplifiers are used to move the motor at a
velocity determined by an analog command. The
unit requires an external servo controller to
determine the move profiles. In addition, some are
available where the command can be input to the
drive through a serial link. Units of this nature can
sometimes be given a position set point that can be
used to move the motor to a defined position. The
motor will move towards the required position at a
predefined velocity and acceleration.
Encoder feedback is required to calculate the
motor’s velocity. The advantages of using such a
system is that the processing by the main controller
is reduced, and the update time within the amp for
the velocity loop can usually be much higher than
the servo controller.

Weight
The force of gravity acting on a body. Weight
equals mass x acceleration due to gravity.

Working Envelope
The effective area available for the system to
operate, without interfering with other parts of the
system.

Yaw
Angular motion of a linear stage, about an axis
which is between to the bearing system and which
is at right angles to the direction of travel.