— 1-3 —
1.2. Functional Principle
1.2.1. Motor
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By virtue of its unique design, the Megatorque Motor System is capable of producing extremely
high torque at low speeds suitable for direct drive applications. Furthermore, it can produce these
torque levels without using an undue amount of power, so it can sustain these torque levels
indefinitely under most conditions without overheating.
Motor Construction
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This Motor is of dual stator construction with rotor between them. Each stator is constructed of
laminated iron sheets with eighteen poles stamped into the laminations. Each pole has one set of
copper windings around it which provide the magnetic field. The windings are wired in series so that
there are three sets of windings seen by the power amplifier, each winding consisting of six (four for
0408 type Motor) pole pieces. The face of each pole piece has many teeth, resembling a stepping
motor (in appearance, not in function). The teeth serve to focus the magnetic energy into a series of
discrete points along the pole face. In total there are hundreds of these points around the full turn of
the Motor. (The number depends upon the Motor size.) The rotor is a thin cylindrical ring,
constructed of the same iron laminations and with the same tooth structure, but without windings or
pole pieces. The rotor serves to conduct the magnetic field from the inner stator across the rotor to
the adjacent pole piece on the outer stator, and back again. The rotor teeth also serve to focus the
magnetic field into discrete points around the circumference of the rotor, and the combined effect of
these points of focused magnetic field around both the stators and the rotor act like electronic gear
reduction, multiplying the torque hundreds of times while reducing the speed by the same amount.
Brushless Microprocessor Commutation
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For each full electrical cycle of commutation, the Motor rotates through one magnetic cycle which
is the angular distance between adjacent teeth. In most Motor sizes, there are 150 electrical cycles
per Motor revolution; some smaller sizes such as 0408 type have 100 cycles per revolution. The
commutation of the Motor phases is performed without brushes by direct control of a high speed
microprocessor in the Driver Unit, and it is the phase relationship of the three Motor phases, not
current polarity, that determine the direction of rotation.
Why No Magnets?
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No magnets are used in the Motor, since the Motor uses the teeth to focus the magnetic field. This
contributes to the robustness of the Motor and to the high torque levels which are produced. Since
demagnetization is not a worry, it is possible to develop high magnetic flux densities within the Motor
which would weaken permanent magnets. Unlike motors which use permanent magnets, the
Megatorque Motors do not weaken with age.
1.2.2. Driver Unit
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All of the circuits that are needed to operate the Megatorque Motor System in position, velocity or
torque control modes are contained in the Driver Unit. These circuit functions are:
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Digital microprocessor
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Power amplifier
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Resolver interface
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The resolver interface and the digital microprocessor are on the control board, a single printed
circuit board which is accessible to you on the right side of the Driver Unit.
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