| 摘要 |
A counterbalanced adjustable height load bearing support structure (20) comprises a spring biased arm (42) having a cam surface (44) thereon cooperates with a follower (46) of a vertically movable support assembly (26) supporting a load bearing surface (32). The cam surface (44) in preferred form is generally concave upwardly and has a profile defined by the expressions: Rx' = r cos.gamma. + (d-r) cos (.beta. + .theta.), Ry' = r sin.gamma. + (d-r) sin (.beta. + .theta.) where Rx' and Ry' are a local coordinate system on the cam arm (42), r represents the distance between the cam surface (44) and the center of rotation of the cam arm, .gamma. is the angle of rotation of the r vector with respect to the x' coordinate system, .theta. is the angular rotation of the cam arm, .beta. is an angle normal to the cam surface at its point of contact with the follower as measured relative to the world coordinate system, d is the distance to the center of curvature of the cam profile and r is the radius of the cam follower.
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