Tech Briefs Magazine - August 2023 - MD-13

motor coil must be flat, parallel, and
mounted with a particular air gap between
them. The moving coil rides on a
carriage connected to parallel precision
linear bearing rails above the magnetic
track. The position encoder with a linear
scale and read head is another critical
part of a linear motor that demands
proper alignment procedures and a robust
mounting design to withstand accelerations
up to 5 Gs. With modular
linear motors, these details are already
accounted for and pre-engineered out
of the box.
Sophisticated motion controllers and
The components of a linear motor design need to be machined and assembled with high precision and
repeatable processes. Proper alignment of these parts is critical and requires significant design detail and
assembly skill. (Image: Dizfoto/Shutterstock)
* A motor coil
* A permanent magnetic track (normally
neodymium magnets)
* A carriage that connects the motor coil
to the load
* Linear bearing rails that the carriage is
guided on and connect to the base
* A linear encoder for position feedback
* End stops
* A cable track
* Optional bellows to protect the magnet
track, encoder, and linear rails
from environmental contamination.
Control Loop
The components of a linear motor
design need to be machined and assembled
with high precision and repeatable
processes. Proper alignment of these
parts is critical and requires significant
design detail and assembly skill. For example,
the magnetic track and moving
servo drives are used to control the motion
of the linear motor. Linear motors
hold a definite advantage regarding stiffness
and frequency response. In certain
frequency ranges, they exhibit a stiffness
that surpasses traditional ball screws by a
remarkable factor of 10 or more. With
this attribute, linear motors can handle
high position and velocity-loop bandwidths
with impressive precision, even
with external disturbances. Unlike ball
screws, which often encounter resonant
frequencies between 10 and 100 Hz, linear
motors operate at higher frequencies,
placing their resonances well beyond
the position loop bandwidth.
However, there is a trade-off associated
with the removal of mechanical transmission.
Mechanical components, such as
ball screws, help decrease disturbances
from machine forces, natural resonant
frequencies, or
cross-axis
vibrations.
Their elimination leaves linear motors
directly exposed to such disruptions.
Modular linear motor systems like the one shown are used when precise, high-speed, and repeatable linear motion
is needed. The system is an alternative to ball screw, belt, and rack and pinion actuators. (Image: Yaskawa America)
Motion Design, August 2023
Consequently, compensating for these
disturbances becomes the responsibility
of the motion controller and drive electronics,
which must tackle them head-on
- acting directly on the servo axis.
That's where today's sophisticated closedloop
motion algorithms come into play
to eliminate resonances and provide remarkable
position loop control.
Within the realm of linear actuators,
linear motors provide exceptional technical
prowess. The motors' ability to
exhibit superior stiffness and operate at
higher frequencies sets them apart
from traditional alternatives. By defying
resonant frequencies and maintaining
high precision even in the presence of
external disruptions, linear motors
offer a compelling solution.
Nevertheless, the absence of mechanical
transmission necessitates
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Tech Briefs Magazine - August 2023

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