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Escape Cam

IP.com Disclosure Number: IPCOM000075300D
Original Publication Date: 1971-Aug-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

van Ee, H: AUTHOR [+2]

Abstract

An improved design for dwell cams of uniform diameter has been found. Such a cam of known design, shown on the left, has been used in an escapement mechanism for incrementing a paper tape (cf. USP 3,139,763). Due to its unfavorable dynamic behavior, the cam had to run in an oil bath. The new design, shown on the right, features continuity of the cam's contour up to the second derivative, thereby eliminating discontinuous accelerations causing vibrations in the mechanism, so that the oil bath can be dispensed with.

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Escape Cam

An improved design for dwell cams of uniform diameter has been found. Such a cam of known design, shown on the left, has been used in an escapement mechanism for incrementing a paper tape (cf. USP 3,139,763). Due to its unfavorable dynamic behavior, the cam had to run in an oil bath. The new design, shown on the right, features continuity of the cam's contour up to the second derivative, thereby eliminating discontinuous accelerations causing vibrations in the mechanism, so that the oil bath can be dispensed with.

The cam on the left is composed of six circular arcs fitted continuously to the first derivative at the six points A ... F. The drive shaft is centered at 0, which point will be used as origin of cartesian coordinates x,y and polar coordinates r,psi. There are three distinct centers of curvature 0, K, and M, which define an equilateral triangle, and about which the circular arcs have either of two radii, R1 or R2, respectively. Thus, the uniform diameter of the cam is S = R1 + R2. When assembled, the cam is enclosed between two parallel edges of a yoke, a distance S apart, and operates to oscillate the yoke, while the arcs CD and FA provide dwell time for punching the tape. The escapement comprises two such cams and yokes, mounted 180 degrees apart, driving the pin wheel alternatingly while the inactive one returns idle. For backspacing the tape, he return strokes are used while the forward strokes are idle.

In the new cam design, the arcs CD and FA are to be preserved. The top B, where dy/dx = 0, may be shifted horizontally but not vertically to preserve the symmetry about the X-axis, and the points K and M lose their identify as centers of curvature. Assume a suitable selection for the abscissa of top B has been made. Then we know six boundary conditions for the curve AB, necessary and sufficient to provide continuity up to the second derivative, as follows. In point A (psi = 5 pi/6) we have r = R1, dr/d psi = 0, d/2/r/d psi/2/ = 0 (or, stated in cartesian coordinates, y = -x/square root of 3 = 1/2 R1, dy/dx = square root of 3, d/2/y/dx/2/ = -8/R1); these provide a f it to the circle arc FA.

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