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142   Electric Drives and Electromechanical Systems

























             FIG. 5.5 A family of brushed printed circuit motors capable of proving a peak torque in the range of 1Nm
             to 15Nm at ;3000 rpm. The motor diameters are 120 mm, 152 mm and 215 mm with respective length of 26 mm,
             30 mm and 32.6 mm. Reproduced by permission of Printed Motor Works Limited, Alton, United Kingdom (sales@
             printedmotorworks.com).


             their high coercivity rate, has made them highly suitable replacements for Alnico.
             However, there is a significant price penalty when these materials are used; but this is
             only one element in the total system cost and the enhanced performance of this class of
             motor must also be considered. The technical advantages of these materials over a
             conventional iron-rotor motor are summarised in Table 5.1. It can be concluded that the
             printed-circuit construction provides some significant advantages for system designers,
             including:
               A low-inertia armature, due to the low mass and thickness; this results in a motor
                with an exceptional torque-to-inertia ratio, and a typical motor can accelerate to
                             1
                3000 rev min , within 10 ms and 60 of rotation.

                Table 5.1  Comparison between iron rotor and printed-circuit rotor brushed
                d.c. machines.
                Property                Conventional iron-rotor motor      Printed-circuit motor
                Magnetic material       Ferrite                            Neodymium
                Rated torque            1.1 Nm                             1.1 Nm
                Rated speed             2700 rev   1                       3000 rev min   1
                Peak torque             6 Nm                               11.62 Nm
                Inertia                 1.1   10  3  kg m 2                1.3   10  4  kg m 2
                Length                  206 mm                             27 mm
                Diameter                102 mm                             140 mm
                Weight                  5.1 kg                             2.8 kg
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