Page 189 - Electric Drives and Electromechanical Systems

Chapter 6 Brushless motors 183

automotive active suspension (Lee, 2009; Boldea et al., 2018). As discussed in Gieras et al.
(2012) linear brushless synchronous motors can be classified by their construction, the
most common types being the following:
Flat (planar) or tubular (cylindrical).
Single or double sided.
Slotted or slotless.
Iron or air cored.
Transverse or longitudinal flux.
In principle the operation of the motor is identical to that of its rotary equivalent. In a
flat motor, single sided motor the magnets are mounted on the stationary track, with the
coil and sensors fitted to a moving assembly, Fig. 6.13. In the figure the encoder track for
the linear encoder is glued to the side of the stationary substrate, (as discussed in
Chapter 4, Velocity and Position Transducers). As with the rotary machine the windings
are 120 electrical degrees apart. For a trapezoidal winding, Hall-effect devices are
mounted adjacent to the coils to control the commutation pattern. If sinewave com-
mutation is used, the linear encoder used for the position feedback is also to control the
commutation of the motor. During initialisation the commutation feedback may not be
in synchronised with the motor, hence a phase finding strategy based on using the hall-
effect encoders is required until synchronisation is achieved. In the tubular design the
motor windings surround a tube that contains the permanent magnets, the analysis of

FIG. 6.13 The construction of a linear, flat, single sided brushless motor. The upper diagram shows the plan of the
substrate, the lower shows a cross section through the substrate and the carriage that contains the windings.