Hydraulically controlled holding device

Claim 1

A hydraulically controlled holding device for accurately locating and securely locking work pieces in position during the performance of various operations thereon, said holding device comprising a body and a thin-walled sleeve supported thereby, a closed hydraulic system within said body and in direct communication with said sleeve, means to pressurize said closed hydraulic system to a desired value whereby to uniformly distort said sleeve to a workpiece gripping position, at least two pressure releasing means shiftable between a first position wherein said desired pressure in said closed hydraulic system is maintained and said sleeve is in said gripping position and a second position wherein said pressure in said closed hydraulic system is relieved and said sleeve is relaxed to a workpiece releasing position, each of said pressure releasing means comprising a piston in a cylinder, each of said cylinders being connected to said closed hydraulic system, said pistons when in said second position being so located within their respective cylinders as to permit the bleeding of hydraulic fluid from a said closed hydraulic system into said cylinders to relieve said desired pressure in said system, said pistons when in said first position expelling said hydraulic fluid from their respective cylinders to maintain said desired pressure in said closed hydraulic system, resilient means to urge said pistons toward said first position and to normally retain them in said first position, said pistons being shiftable from said first position to said second position against the action of said resilient means by an outside force independent of said closed hydraulic system, whereby said sleeve is normally in said gripping position unless said pistons are acted upon by said outside force whereupon said sleeve is relaxed to said releasing position to return to said gripping position upon deactivation of said outside force, said pistons being in abutting relationship with a common element, said resilient means acting upon said common element, means to transmit said outside force to said common element permitting said pistons to shift to said second position, and a plurality of rod-like indicator means giving a visual indication of the pressure in said closed hydraulic system, said rod-like indicator means being evenly spaced along and affixed to said common element, each of said indicator means being slidably mounted in a perforation extending through the exterior surface of said body, the extent to which said indicators extend beyond said exterior surface comprising said visual indication, said indicators comprising said Means for transmitting said outside force to said common element.