Abstract:

ESDU 90022 gives three strategies for estimating the reaction forces at joints connecting rigid links of single-degree-of-freedom, multibar, linkages. They are static force analysis, in which inertia forces are ignored (so it can only be used for very slowly moving mechanisms), kinetostatic analysis in which it is assumed the motion of the input link is known (frequently taken as constant speed), and dynamic analysis in which the external driving force or torque is assumed to be known as a function of the input link velocity or position. The joint forces are needed to stress the links, to select appropriate bearings, and to assess the shaking effect of the linkage on the frame. Guidance is given on the choice of method and the steps required to determine joint forces. Each strategy uses the equilibrium equations and the kinematic relations to derive a set of equations for computer solution. To illustrate each procedure the equations required for an offset slider-crank linkage are derived in full. Finally, explicit expressions derived by kinetostatic analysis are provided for all four-bar linkages (crank-rocker, slider-crank and offset swinging block). A numerical example compares the effectiveness of the three different approaches applied to a typical design problem. A computer program for the kinetostatic force analysis of a four-bar linkage is provided as ESDUpac A9022.