Some parasitic deflexions in parallel spring movements

This paper analyses some parasitic departures from parallel and rectilinear movement in simple and compound assemblies. The following factors are considered: accuracy of construction, geometrical proportions, spring variations, spring distortion, platform bending, clamp distortion, and gravity effects. It is shown that the "ideal" height at which to drive a parallel spring element is at half the spring height, and it is concluded that while spring tolerances are surprisingly "easy," care must be taken with the platforms and clamps if the highest performances are to be achieved. In compound movements, the possibility of "slaving" the intermediate platform, suggested by Plainevaux, has been tested in practice with good results.