Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

34 Chapter 1 Motor and Motion Control Systems
Figure 1-29 A linear ironless
servomotor consists of an ironless
magnetic way and an ironless coil
assembly.
sequently, very little magnetic flux exists outside the motor, thus minimizing
residual magnetic attraction.
Epoxy-core motors provide exceptionally smooth motion, making
them suitable for applications requiring very low bearing friction and
high acceleration of light loads. They also permit constant velocity to be
maintained, even at very low speeds.
Linear servomotors can achieve accuracies of 0.1 µm. Normal accelerations
are 2 to 3 g, but some motors can reach 15 g. Velocities are limited
by the encoder data rate and the amplifier voltage. Normal peak
velocities are from 0.04 in./s (1 mm/s) to about 6.6 ft/s (2 m/s), but the
velocity of some models can exceed 26 ft/s (8 m/s).
Ironless linear motors can have continuous force ratings from about 5
to 55 lbf (22 to 245 N) and peak force ratings from about 25 to 180 lbf
(110 to 800 N). By contrast, iron-core linear motors are available with
continuous force ratings of about 30 to 1100 lbf (130 to 4900 N) and
peak force ratings of about 60 to 1800 lbf (270 to 8000 N).
Commutation
The linear motor windings that are phased 120º apart must be continually
switched or commutated to sustain motion. There are two ways to
commutate linear motors: sinusoidal and Hall-effect device (HED), or
trapezoidal. The highest motor efficiency is achieved with sinusoidal
commutation, while HED commutation is about 10 to 15% less efficient.