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Locking universal support arm

  • US 5,683,064 A
  • Filed: 06/07/1995
  • Issued: 11/04/1997
  • Est. Priority Date: 06/10/1994
  • Status: Expired due to Term
First Claim
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1. A support arm for movably positioning a surface relative to a base structure, comprising:

  • a base member attachable to the base structure;

    a platform defining the surface;

    at least one connecting arm disposed between the base member and the platform;

    at least one joint coupling the connecting arm to one of the base member and the platform, wherein said at least one joint is rotatable on a substantially horizontal axis, the joint having rotatable couplings between the connecting arm and said one of the base member and the platform along two mutually perpendicular axes, thereby forming a universal joint;

    locking means engaging the rotatable couplings for maintaining an angular relationship between the connecting arm and said one of the base member and the platform for both said two mutually perpendicular axes, the locking means having rotational engagement surfaces facing one another axially along each of the two axes and means for applying tension to draw the rotational engagement surfaces axially together, and for releasing said tension to allow relative rotation between the connecting arm and said one of the base member and the platform;

    resilient means in at least one of the joints mounted to urge the rotational engagement surfaces axially apart, the resilient means being normally loaded by said means for applying tension such that the rotational engagement surfaces come into contact, and unloaded upon easing of the tension such that the couplings are free to rotate;

    control means for simultaneously releasing the locking means in both said two mutually perpendicular axes; and

    a counterbalance spring disposed inside said connecting arm and coupled by a counterbalance cable which is passed around at least one pulley housed in said connecting arm and extends tangentially to an attachment point spaced from the horizontal axis and provided on a fitting mountable over a range of positions on said joint such that rotation of the joint applies varying tension to the cable, and wherein the spring resists said tension to offset at least part of a weight of the support arm.

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