Patent ID: 8870253

Claim:
A lifting apparatus for lifting load along a lift axis, the apparatus comprising: an electrically operable clamping arrangement having clamping elements movable between an open and a closed position of the clamping arrangement for selectively grasping and releasing the load; an electrical lockout arrangement connected at a lower end thereof to the clamping arrangement and having an upper end thereof adapted for application of a lifting force along the lifting axis; the electrically operable clamping arrangement and the electrical lockout arrangement being cooperatively configured such that the electrical lockout arrangement precludes electrical power from being applied to open the clamping arrangement when the lifting force being applied to the upper end of the electrical lockout arrangement has reached a predetermined lockout value while the clamping arrangement is grasping the load; the electrically operable clamping arrangement and the electrical lockout arrangement also being cooperatively configured such that the electrical lockout arrangement allows electrical power to be applied to the clamping arrangement for opening the clamping arrangement when the lifting force being applied to the upper end of the electrical lockout arrangement is below the predetermined lockout value; wherein, the predetermined lockout value of the lifting force is adjustable; wherein the predetermined lockout value is a function of a spring constant of at least one spring of the electrical lockout arrangement; and wherein the at least one spring includes multiple springs arranged in a parallel arrangement relative to the spring force applied thereby.