pivoted to ground (i.e., the crank and rocker). When external forces are applied to the
coupler link, the transmission angle tells nothing about the linkage's behavior.
Holte and Chase [1] define a joint-force index (IPl) which is useful as an indicator
of any linkage's ability to smoothly transmit energy regardless of where the loads are
applied on the linkage. It is applicable to higher-order linkages as well as to the fourbar
linkage. The IPI at any instantaneous position is defined as the ratio of the maximum
static force in any joint of the mechanism to the applied external load. If the external
load is a force, then it is:
The