— 1-3 —
1.2. Functional Principle
1.2.1. Motor
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By virtue of its unique design, the Megathrust Motor System is capable of producing extremely
high thrust force at low speeds suitable for direct drive applications. Furthermore, it can produce
these force 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 a stator and a rack base construction. The stator is constructed of laminated iron
sheets with several 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 some 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 along with the stroke of the Motor. (The
number depends upon the rack base length.) The rack base is an iron plate with the same tooth
structure, but without windings or pole pieces. The rotor serves to conduct the magnetic field
from the stator through the rack base, and back again to the adjacent pole piece on the stator. The
rack base teeth also serve to focus the magnetic field into discrete points along with the stroke of
the rack base, and the combined effect of these points of focused magnetic field around both the
stator and the rotor act like electronic gear reduction, multiplying the force 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 moves through one magnetic cycle
which is the distance between adjacent teeth. There is one(1) electrical cycle per 4.096 mm
stroke. 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 move.
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 force 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 Megathrust 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 Megathrust Motor System in position, velocity
or force control modes are contained in the Driver Unit. These circuit functions are:
à
Digital microprocessor
à
Power amplifier
à
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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