Variable eccentric cam rheometer system
View Patent ↗The present application relates generally to moving die rheometers, and more particularly to moving die rheometers that employ a variable eccentric cam. In one aspect, the eccentricity produced by the cam may be adjusted using shims of different thickness to alter the position of the post on the cam.
1. An eccentric cam for use in an oscillating rheometer system wherein the eccentric cam converts rotary motion into oscillatory motion of a die of the rheometer system, the eccentric cam comprising:
a housing operatively connected to a rotating drive shaft which is structured to rotate the housing about a central axis of rotation;
a post slidably disposed in a channel in the housing, the post being connected to the die of the rheometer system by an arm, the post extending parallel to the axis of rotation at a location which is spaced at a first desired distance from the axis of rotation;
a first shim having a fixed dimension and being disposed in the cam housing to space the post at the desired first distance from the central axis of rotation; and
at least one second shim, having a different fixed dimension than the fixed dimension of the first shim, the first shim being removable from the housing for replacement with the second shim to change the location of the post to a second desired distance from the axis of rotation to change the amplitude of oscillation of the die.
2. The eccentric cam of claim 1 further comprising:
an elongated channel in the housing, the channel passing through the central axis of rotation in a direction perpendicular to the axis of rotation; and
a lock piece slidably disposed in the channel, the lock piece having the post extending therefrom.
3. The eccentric cam of claim 2 wherein the first and second shims are inserted and removed from the channel through an opening in the housing in a direction that is perpendicular to a direction of elongation of the channel and perpendicular to the axis of rotation.
4. The eccentric cam of claim 2 further comprising a shaft that extends along the channel and through the lock piece, the shaft being threadably coupled to a face of the housing.
5. The eccentric cam of claim 4 wherein the first or second shim is disposed between the lock piece and the face of the housing and wherein a torque is applied to the shaft to thread the shaft into the face to urge the lock piece against the first or second shim and to urge the first or second shim against the face.
6. The eccentric cam of claim 5 wherein the lockpiece comprises two blocks, a first block to which the post is attached and a second block, and wherein a head of the shaft bears against the second block and the second block bears against the first block to urge the first block against the shim.
7. The eccentric cam of claim 5 wherein the face of the housing is disposed at a location spaced from the axis of rotation on a side of the axis of rotation opposite that of the post.
8. The eccentric cam of claim 6 wherein the first and second blocks bear against each other along parallel surfaces and wherein the parallel surfaces form an acute angle with respect to the shaft.
9. A method for changing the amplitude of oscillation of a moving die rheometer, in which the rheometer comprises:
a housing operatively connected to a rotating drive shaft to rotate therewith about a central axis of rotation; and
a post slidably disposed on the housing, the post being connected to one end of an arm, the other end of the arm being connected to a moving die in the rheometer, the post being spaced from the central axis and parallel thereto;
the method comprising:
selecting a first shim of a first known dimension to space the post a first known distance from the central axis of rotation to impart a first amplitude of oscillation to the die; and
changing the first known distance to a second known distance from the central axis of rotation by removing the first shim and replacing it with a second shim having a second known dimension to impart a second amplitude of oscillation to the die.