Continuous thickness measurement of a moving plastic web

Claim 1

In a device for continuously measuring the thickness of a moving plastic web, said device having a pair of spaced, cooperating, parallel rollers including a support roller and an idler roller between which the web to be measured passes, said support roller and said idler roller being mounted in a roller support frame with their axes in parallel with the support roller mounted beneath the idler roller means for maintaining said idler roller in contact with said web as it passes beneath the idler roller and in which the thickness of the web is determined by sensing means associated with said idler roller, the improvement comprising: a. driving means for the support roller to rotate said support roller such that the peripheral speed of the support roller is substantially the same as the linear speed of said moving web; b. said support roller having a length which is at least equal to twice the width of said web, c. said idler and support rollers being in a fixed, relative position wherein they are immovable along their axes with respect to one another, d. means for simultaneously moving said idler roller and said support roller transversely of said web to obtain a web thickness profile, e. idler roller support means for resiliently mounting said idler roller such that it normally is urged into contact with said web under slight pressure to obviate distortion and damage to the web, said last mentioned means including a vertically extending roller support member in which the idler roller is freely journalled, a pair of substantially parallel resilient members extending rearwardly from said roller support member, the outer ends of said resilient members having a vertical support member interposed and suspended from said roller support frame such that the configuration of the idler roller support is substantially in the form of a parallelogram to provide a support structure that responds quickly and accurately to changes in web thickness with a minimum of distortion.