Methods and apparatus for tensioning sheet material

Claim 3

A method according to claim 1 in which said vibration is imparted to said piece by exposing it to sound waves impinging on a surface thereof.

Claim 4

A method according to claim 2 in which said sound waves are constant in frequency.

Claim 5

A method according to claim 2 which said sound waves are constant in amplitude.

Claim 6

A method according to claim 1 in which said parameter of said vibration is the amplitude thereof.

Claim 7

A method according to claim 1 in which said vibration is caused by said changing force to vary from a condition of non-resonant vibration of said piece to a condition of resonant vibration thereof, and in which said terminating of further change in said force is effected upon said vibration arriving at said resonant condition.

Claim 8

A method according to claim 1 in which said material is electret sheet material.

Claim 9

A method according to claim 1 in which said force radially tensions said piece to develop said tensile stress therein.

Claim 10

A method according to claim 1 in which said vibration is and remains substantially constant in frequency during the applying to said piece of said changing force.

Claim 11

A method according to claim 1 further comprising the steps performed after said terminating step of (a) bonding to a surface of said piece a rigid tension-retaining ring so that such ring surrounds and is surrounded by, respectively, a central portion of said piece and a fringe portion thereof, and so that said ring fixedly retains in said central portion the tensile stress existing in said piece after said terminating step while said force continues to be applied, and (b) subsequently discontinuing application of said force.

Claim 12

A method according to claim 1 in which said force changes by progressively increasing from an initial value therefor of zero, and in which said increasing force causes said vibration parameter to vary from initial value characterizing non-resonant vibration of said piece to a subsequent value characterizing resonant vibration thereof.

Claim 17

The method according to claim 13 in which said holding is effected by positioning said sheet on support means so that said first portion of said sheet registers with a recess in said support means, and sheet material around said first portion registers with a bearing surface provided by such support means and ringing said recess, and advancing a ring shaped clamping means towards such bearing surface to squeeze such material between said clamp means and bearing surface to thereby grip such sheet around said first portion.

Claim 18

Apparatus for tensioning part of a sheet of material comprising, means for holding material of said sheet surrounding the circumferential margin of a first portion thereof so as by such holding, to preclude radially inward slippage at such margin of such surrounding material, a tension-producing ring adapted to contact a ring shaped area of said sheet disposed within said first portion and surrounding a second portion of said sheet, movable pressing means adapted by movement thereof to press said ring against said area with a changing force so as to develop in said second sheet portion a correspondingly changing radial tensile stress, means to concurrently impart to said second sheet portion a vibration having a parameter which varies as a function of said changing stress, means responsive to said vibration to monitor said varying parameter so as to permit determination of when said changing stress causes said variable parameter to reach a preselected value therefor, and means adapted upon said parameter reaching such value to terminate further change in said force while continuing said pressing of said ring against said area so as to retain in said second portion the tensile stress then existing therein.

Claim 19

Apparatus for tensioning part of a sheet of material comprising, means for holding material of said sheet surrounding the circumferential margin of a first portion thereof so as by such holding, to preclude radially inward slippage at such margin of such surrounding material, a tension-producing ring adapted to contact a ring shaped area of said sheet disposed within said first portion and surrounding a second portion of said sheet, movable pressing means adapted by movement thereof to press said ring against said area with a changing force so as to develop in said second sheet portion a correspondingly changing radial tensile stress, means to concurrently impart to said second sheet portion a vibration having a parameter which varies as a function of said changing stress, means responsive to said vibration to monitor said varying parameter so as to permit determination of when said changing stress causes said variable parameter to reach a preselected value therefor, and means adapted upon said parameter reaching such value to terminate further change in said force while continuing said pressing of said ring against said area so as to retain in said second portion the tensile stress then existing therein.

Claim 20

Apparatus according to claim 15 in which said holding means comprises, sheet support means having a bearing surface ringing a recess formed in said support means, said sheet being positionable on said support means so that a first sheet portion registers with said recess and sheet material around such portion registers with such surface, and ring-shaped clamping means movable towards said surface to squeeze said such material between such means and said surface to thereby grip such sheet around said first portion.

Claim 21

Apparatus according to claim 16 in which said recess is provided by an aperture formed in said support means, and in which said apparatus further comprises, movable ring transporting means adapted to carry at its front a tension-retaining ring having adhesive thereon, said transporting means being adapted after said termination of further change in said force to move such ring within said aperture towards and then against said sheet so as produce between such ring and a corresponding ring shaped area of said sheet within said second portion a bonding by said adhesive of said ring and sheet, which bonding fixedly retains in a third portion of said sheet ringed by such area the tensile stress existing in said third portion as of the time of such termination.

Claim 22

Apparatus according to claim 15 in which said vibration imparting means comprises electroacoustic transducer means adapted in response to excitation thereof by alternating electrical energy to generate sound waves constant in amplitude and frequency and to direct said waves onto said second sheet portion to thereby impart said vibration thereto.

Claim 23

Apparatus according to claim 15 in which said vibration monitoring means comprises vibration sensing means adapted to be optically coupled with said second sheet portion by a light beam which is intensity modulated by said vibration, and optolectronic means responsive to said modulated light beam to electrically indicat the amplitude of said vibration.

Claim 24

Apparatus according to claim 15 further comprising control means responsive to an indicating by said monitoring means of a reaching by said vibration parameter of said preselected value to stop the movement of said pressing means so as to thereby effect said termination of further change in said force.

Claim 25

Apparatus for tensioning part of a sheet of material comprising, sheet support means having a bearing surface ringing a recess formed in said means, said sheet being positionable on said support means so that a first sheet portion registers with said recess and sheet material around said portion registers with said surface, ring-shaped clamping means movable towards said surface to squeeze said material between it and said surface to thereby grip said sheet around said first portion thereof, a tension-producing ring adapted to contact a ring shaped area of said sheet disposed within said first portion and surrounding a second portion of said sheet, movable pressing means adapted by movement thereof towards said support means to press said ring against said area with increasing force so as develop in said second portion an increasing radial tensile stress, means operable during such tensioning of said second portion to impart thereto a constant frequency vibration of which the amplitude is caused by said increasing stress to increase, vibration monitoring means responsive to said vibration to produce a running indication of the value of the amplitude thereof as said amplitude increases, and control means responsive to the reaching by said amplitude of a preselected value for stopping the movement of said pressing means to terminate further increase in said force while continuing said pressing by said ring of said second portion so as, thereby, to retain the tensile stress then existing therein.

Claim 26

Apparatus for tensioning part of a sheet of material comprising, sheet support means having a bearing surface ringing a recess formed in said means, said sheet being positionable on said support means so that a first sheet portion registers with said recess and sheet material around said portion registers with said surface, ring-shaped clamping means movable towards said surface to squeeze said material between it and said surface to thereby grip said sheet around said first portion thereof, a tension-producing ring adapted to contact a ring shaped area of said sheet disposed within said first portion and surrounding a second portion of said sheet, movable pressing means adapted by movement thereof towards said support means to press said ring against said area with increasing force so as develop in said second portion an increasing radial tensile stress, means operable during such tensioning of said second portion to impart thereto a constant frequency vibration of which the amplitude is caused by said increasing stress to increase, vibration monitoring means responsive to said vibration to produce a running indication of the value of the amplitude thereof as said amplitude increases, and control means responsive to the reaching by said amplitude of a preselected value for stopping the movement of said pressing means to terminate further increase in said force while continuing said pressing by said ring of said second portion so as, thereby, to retain the tensile stress then existing therein.