Film stretcher

Abstract

A film stretcher utilizes a spring bias to clamp the film. The film stretcher may include a stretch head having one or more clamps positioned about the film in locations necessary to clamp the film for stretching in one or more axes. The clamp may utilize a spring to provide the clamping force. The stretch head may include structures that operate to counter the spring bias to move the clamp to one state and then to allow the spring bias to move the clamp to another state. Thus, the stretch head may effectively clamp and unclamp the film.

1 - 7 . (canceled) 
     
     
         8 . A method of clamping film within a film stretcher, comprising:
 applying a force against a piston with at least one spring to bias it in a clamping direction while applying a counter force against the piston to bias it in a release direction opposite the clamping direction, the counter force exceeding the force applied by the at least one spring;   placing a film against a surface of a first clamp finger;   reducing the counter force against the piston in the release direction so that the piston is biased against the surface of the first clamp finger to clamp the film.   
     
     
         9 . The method of  claim 8 , comprising:
 increasing the counter force against the piston in the release direction so that the piston is not biased against the surface of the first clamp finger to unclamp the film.   
     
     
         10 . The method of  claim 8 , wherein applying a force against the piston with the at least one spring comprises providing the spring with a fixed relationship to a second clamp finger that is fixed relative to the first clamp finger. 
     
     
         11 . The method of  claim 8 , wherein each of applying a counter force against the piston comprises moving a rocker in a first direction while reducing the counter force comprises moving the rocker in a second direction, wherein the rocker abuts an end of the piston so as to move the piston in the release direction and to allow the at least one spring to move the piston in the clamp direction. 
     
     
         12 . The method of  claim 11 , wherein moving the rocker comprises moving a slider along a surface of the first clamp finger, the slider engaging an end of the rocker to move the rocker in the first and second directions. 
     
     
         13 . The method of  claim 12 , wherein applying the counter force further comprises moving a secondary D-ring to move the slider so that the rocker moves in the first direction until reaching a detent position that holds the piston open from the surface of the first clamp, and wherein reducing the counter force further comprises moving the secondary D-ring to move the slider so that the rocker moves in the second direction until the piston abuts the film and the surface of the first clamp finger, and wherein the method further comprises after the piston abuts the film and the surface, then moving the secondary D-ring out of contact with the slider. 
     
     
         14 . The method of claim  1 , further comprising moving a primary D-ring that is mechanically linked to the first clamp finger to position the first clamp finger at a location where the film is to be clamped before stretching and moving the primary D-ring in an opposite direction after the film is clamped and before the film is unclamped to stretch the film. 
     
     
         15 - 20 . (canceled)