Thomson bearings and
profile rails used in test and
measurement equipment,
robotics and pick & place
equipment provide the
length, durability and
accuracy design engineers
need for their systems
Feature: Linear motion technology
A basic linear motion system integrates
a power component, such as a motor; a
thrust mechanism, such as an actuator;
and a guidance infrastructure, such as a
rail. There are numerous subsystems within
these categories and understanding your
options will help determine the ideal linear
motion technology for your application.Power components overview
The power components of the linear sys-
tem include its motors, drives and con-
trols. These convert electrical energy into
mechanical energy and assist in position-
ing the device.The mechanical energy can be rota-
ry-to-linear or direct-to-linear motion. Ro-
tary-to-linear drives will convert the rotary
torque of a motor into axial travel through
a gearhead/gearmotor or actuator con-
nection. Electrical linear motors produce
direct linear motion without rotary com-
ponents. The motor driving the system
can be controlled to provide the desired
velocity, acceleration, torque and position
to yield optimal performance.Drive options include servo motors, which
enable the most accurate position con-
trol in multiple poles and axes; stepper
motors, which provide accurate position
management but for a limited range of po-
sitions; and variable speed drives, which
can control speed only.Achieving positioning accuracy is done by
integrating controls, switches, sensors and
optical encoders. A servo motor, for exam-
ple, has so many poles that determining
location at any point requires an encoder to
generate pulses that indicate the exact po-
sition of the rotating shaft. Controllers use
such information to calculate discrepancies
between the actual system position and the
desired location. Control systems such as
programmable logic controllers (PLCs) can
then be programmed to drive corrective
actions based on reported anomalies or to
drive complex operational sequences such
as multi-axis movements. As power drive
components become increasingly digitised,
encoding functionality that conventionally
required external devices can be integrated,
reducing complexity and footprint.Moving the load
Powered by motors and drives and under
the control of PLCs or other controllers, lin-
ear thrust mechanisms provide the physical
contact that moves a load from one position
to another. Because they “actuate” the load,
they are often generally called actuators,
but thrust mechanisms might also be ball
screws, lifting jacks, cylinders, solenoids,
belt drives or any other device that that con-
vert rotary motion (torque) into linear thrust
on one or more axes.Guidance and support
The guidance portion of a linear system
controls the direction of the thrust mecha-
nism’s movement while also supporting it.
These guidance components can include
round rails – also called shafting – or square-
like profile rails, either of which may ride on
lubricated bearings mounted in a metal
block, or, for example, a dual ball guide
version that runs on hardened steel shafts,
as offered by Thomson Industries. All these
alternatives and the bearing blocks that ride
on them provide support for the system as
well as directional control.The bearing blocks fasten to a carriage and
may often be referred to as bearing hous-
ings, bushings or trucks. The carriage itself
is also known as a saddle, platen or table.
In a machining application, the carriage mayW
hen manufacturing processes require high precision, high-
speed repeatability and flexibility for applications such as CNC,robotics and material handling, production engineers often specify
linear motion technologies.
Choosing
linear motion
technology
for high precision applications
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