Patent ID: 8517321

Claim:
A gravity compensation apparatus, comprising: a base unit; an arm pivotably attached to said base unit for swivel movement, said arm having a contact element located at a fixed distance from a pivot center of the arm; a force output device comprising: a sliding element having a sliding surface; and a torsion spring with one end held by said base unit and another end held by said sliding element, wherein a center of said torsion spring is located on said sliding element, said sliding element for pushing/pulling said torsion spring so that a rotation angle of said sliding element is the same as a rotation angle of said torsion spring; wherein said sliding element is pivotally attached to said base unit with said center of said torsion spring as a pivot center of the sliding element and said center of said torsion spring is located between a rotational path of said arm and a center of rotation of the arm; wherein when said arm rotates, said contact element of said arm slides on said slide surface of said sliding element.