Mechanisms@ especially the four bar chain and its variants@ are employed in a range of applications which include packaging@ diggers and motor vehicles to name but three. In some applications@ such as the compaction of hay or refuse@ precision may not be essential. However@ even in this case it is necessary to deduce what magnitude of tolerance would be allowable. In other situations@ for example vehicle steering (the Ackermann linkage)@ the effect of errors may have to be carefully studied. The four bar chain is possibly the most commonly used because of the diversity of outputs that can be generated by suitable sizing of links. This Item will present an analysis of the four-bar chain mechanism@ which includes derivation of: the coupler and rocker angles in terms of the link lengths@ errors in the link angles due to changes in the link lengths from their nominal values and position errors of the offsets from the coupler and rocker. An example of a simple four-bar crank-rocker linkage will be used to illustrate the analysis process@ together with the error in the coupler and rocker angles from small changes in the link lengths. The error in the position of the coupler point from small changes in the link lengths is also shown. A second example will illustrate the steering linkage of a vehicle@ known as the Ackermann linkage@ which is driven by the action of a four-bar linkage. An appendix will derive the equations of motion of a four-bar linkage with use of the constraints approach.
DWN 10019-2010 history
2011DWN 10019-2011 Effect of link length tolerances on the performance of four-bar linkages (Issue 4)
2010DWN 10019-2010 Effect of link length tolerances on the performance of four-bar linkages (Issue 2)