Noncircular drive

Abstract

Noncircular drives, including chain drives with noncircular sprockets, achieve a desired functional relationship and minimize slack variation in the elongate flexible member thereof. Noncircular gears having the desired functional relationship are first designed. Noncircular members having the same pitch curve or operative surface configuration as the pitch curves of the noncircular gears are theoretically located at the desired center-to-center distance of the noncircular rotational members of the drive being designed. The noncircular members are manipulated such that points initially in contact on the gears are not joined by a common tangent. Using a computer, the drive is incremented with the common tangent acting as the driving span of the flexible member. At each increment functional relationship error and overall length of a taut elongate flexible member are calculated. The variation in taut flexible member length is the slack variation. In the event of excess functional relationship error, the design procedure is iterated modifying the functional relationship on which the original gear pair was based by adding the functional relationship error. This iterative procedure is continued until functional relationship is acceptable. If the slack variation is excessive, the same procedure continues with the other span, i.e., common tangent, driving until again the functional relationship is acceptable. If slack variation is still unacceptable, the design procedure continues using first the one run of the flexible member and then the other until both functional relationship and slack variation is acceptable.