Mechanisms for Position Guidance:
A mechanism might be needed to provide guidance to a body in a prescribed manner. Letting a problem where a rigid body need to be so guided that it acquired three particular positions throughout its movement as illustrated in Figure.
This may be attained by a four bar linkage for which this body behaves as the coupler. The fixed hinges O2 & O4 are the centres of the circles passing through the points A1, A2, A3 and B1, B2, B3 respectively. Join A1 with A2 and A2 with A3. Draw perpendicular bisectors of A1 A2 & A2 A3. These perpendicular bisectors shall meet at O2. Join B1 through B2 & B2 with B3. Draw perpendicular bisectors of B1 B2 and B2 B3. These bisectors shall meet at O4. Therefore the four bar mechanism O2 A1 B1 O4 so constituted ensures that the guided body takes up the specified positions in succession.