9.9 TORQUE COMPENSATION CAMS
way to balance torque on a camshaft is to add one or more cams driving dummy
loads (essentially springs) that are designed to provide an approximately equal
and opposite torque to the shaft, as is generated by the actual driving cams
that do the machine’s
If the motivation is simply to hide the cyclic torque fluctuations from the
driving motor (as with a flywheel), then only one torque compensation cam is
needed to counteract the sum of the torques of all the driving cams on a given
camshaft. If on the other hand, one wishes to reduce the torsional stresses and
deflections in the camshaft, then it may be necessary to add a compensating cam
adjacent to each driving cam, thus cancelling the torque locally before it has
an effect on the relative angular positions between driving cams.
9-27 shows such an arrangement in the form of a test fixture designed and built
to test the efficacy of this approach to torque compensation. The two cams,
one representing a “driving” cam and the other a “compensating” cam are seen at
the right end of the camshaft each moving a translating, spring-loaded follower
train. In a real situation, one of these would be driving tooling and the other
driving a dummy load. At the left end of the shaft is a flywheel serving as an
inertial reference, friction driven by a speed-controlled DC motor. Each free
end of the shaft is fitted with a 5000 count per revolution shaft encoder.
Their difference measures the instantaneous end-to-end torsional deflection of
the shaft. The shaft is made in three sections. The two ends that,
respectively, support the cams and flywheel are large in diameter for good
torsional stiffness, and the long center section is small in diameter, thus
torsionally compliant to exaggerate the cam-induced torsional deflections for
ease of measurement.
Copyright (C) 2002 Industrial Press Inc.