Determination of Relative Pole for Slider Crank Mechanism:
The point B reciprocates along slider in Figure by a horizontal distance say's'. The process for finding the relative pole R12 is as:
(a) Illustrate two parallel lines l1 & l2 at a distance equivalent to the eccentricity 'e'.
(b) Plot line segment O2E of length (s/2) on line l2 such as this segment is measured in a direction opposite to the motion of the slider.
(c) Illustrate perpendicular lines p1 and p2 at O2 and E respectively to the line l2.
(d) Rotate p2 around O2 by angle (θ12) /2 at point O2 in a sense opposite to the rotation of O2 A.
Use of Relative Pole for Design of Mechanism
The relative pole may be utilized to design a mechanism graphically.
If three positions of input link θ1, θ2 & θ3 and three positions of follower link φ1 φ2 and φ3 are known, R12 may be resolute considering θ12 = (θ2 - θ1 ) and φ12 = (φ2 - φ1 ) R13 may be find out by letting θ13 = (θ3 - θ1 ) and φ13 = (φ3 - φ1 ) . The angle subtended by O2 O4 at R12 is say ψ = 1 /2(θ 12- φ 12) and at R is say ψ = 1 /2(θ 13- φ 13). Now construct angles ψ12 & ψ13 at R12 & R13 respectively in arbitrary positions such as the arms of the angles intersect at A & B. Join A & B to get coupler AB. Join A having O2 and B along O4 to obtain input and follower links.