WO2009084722A1

WO2009084722A1 - A closing and opening apparatus of a tenter clip, and defective tenter clip detecting method and device

Info

Publication number: WO2009084722A1
Application number: PCT/JP2008/073940
Authority: WO
Inventors: Hiroshige Kuzuno
Original assignee: Tonen Chemical Corporation
Priority date: 2007-12-28
Filing date: 2008-12-25
Publication date: 2009-07-09
Also published as: JP5749780B2; JP2011507722A; JP2014024351A; JP5646995B2

Abstract

A tenter clip closer of the present invention has a first closer comprising a cam and a second closer comprising a freely rotatable disk. A tenter clip opening apparatus of the present invention comprises plate-shaped opener fixed rotatably and also driven by a forcing means to resist clip arm, and when an abnormal force acts on the plate-shaped opener because of malfunctioning clips, the plate-shaped opener pivots away from the malfunctioning clip against the forcing means. A device used for detecting defective tenter clips of the present invention has at least one tenter clip actuator for opening or closing the tenter clips. When the force exceeds a reference value, a signal from the monitoring means automatically activates a counter for automatically counting the number of clips that have contacted the actuator after the malfunctioning clip.

Description

DESCRIPTION

A CLOSING AND OPENING APPARATUS OF A TENTER CLIP, AND

DEFECTIVE TENTER CLIP DETECTING METHOD AND DEVICE

FIELD OF THE INVENTION

[0001] The present invention relates to an apparatus and method for stretching a polymeric web, e.g., a film or extmdate. More particularly, the invention relates to an apparatus which comprises a driven conveyor comprising tenter clips that hold opposing edge portions of the web and thereby convey the web through the tenter machine. Automatic closers and openers are provided at the upstream and downstream ends of the apparatus respectively for closing and opening the clips. The tenter clips have a clamping surface and a pivotable clamping arm, wherein the clamping arm has an upper end comprising a cam follower and a lower end comprising a gripping surface for gripping the web between the gripping surface and the clamping surface. The clamping arm is actuated by a first closer comprising a cam to pivot the cam follower in order to grip the web. A second closer located downstream of the first clip close contacts the at least partially pivoted cam follower to close clips that are not fully closed after the first closer.

[0002] The present invention also pertains to a method and a device used for detecting tenter clips having rotation defects in clip arms, particularly for detecting malfunctioning tenter clips. A malfunctioning tenter clip, e.g., one whose clip arms have poor rotation are detected by means for monitoring the force between the tenter clips and at least one tenter clip actuator. When the force exceeds a reference value, a signal from the monitoring means automatically activates a counter for automatically counting the number of clips that have contacted the actuator after the malfunctioning clip. The machine can be halted, and by counting the number of clips from the actuator the malfunctioning clip can be identified. The malfunctioning clip can be repaired or replaced, thereby preventing damage to, e.g., the stretching equipment.

BACKGROUND OF THE INVENTION [0003] Tenter-type stretching equipment can be used to stretch a web of polymeric material, e.g., extrudate or film. The stretching can be uniaxial (stretching along one planar axis of the web), or biaxial. When biaxial stretching is used, the stretching can be sequential, i.e., in stretching in one direction and then another, simultaneous, i.e., stretching in both planar directions at the same time, or combinations thereof.

[0004] Conventional tenter equipment as described, e.g., in U.S. Pat. No. 4, 065,838, generally includes a plurality of tenter clips mounted on two endless chains guided by a pair of diverging tracks to convey the tenter clips. The tenter clips are adapted to shift from an open position to a closed position to grip the edges of the web of material such as polymeric extrudate or film. As the web is moved in the machine direction being gripped by the clips which are moving on the diverging tracks, the web can be stretched simultaneously in both planar directions of the web, i.e., the machine direction and the transverse direction. [0005] In the operation of conventional tenter equipment, means are provided to move the tenter clip into position to receive an edge of the web. Means are also provided to shift each clamping arm to the closed position so that the web gripped. The web is then stretched as the tenter clips follow their divergent tracks. Finally, means are provided to shift each clamping arm open again to release the web as each clip follows its path around the endless chain. Such opening and closing means are well known to those skilled in the art. See, for example, U.S. Pat. No. 4,065,838 and U.S. Pat. No. 4,193,175. [0006] Conventional closing means include, for example, closing cams which are provided on opposite sides of the entrance of the tenter machine. Likewise, opening cams can be provided on opposite sides of the exit end of the machine to release the web after stretching. Both pairs of cams, entering end and exit end, are in operational position to actuate the respective cam followers on the tenter clips attached to the endless chain conveying the tenter clips. See, for example, U.S. patent No. 4,193,175.

[0007] Thus, in the typical operation of a tenter machine there is a constantly repeated opening and closing of the tenter clips as the continuous web is moved through the machine. The repeated opening and closings lead to degradation of the clips, sometimes to the point of failure. In one failure mode, where the cam follower is opened but becomes rigidly fixed in the open position, interference between the tenter clip and the clip closer at the downstream end of the tenter machine can result in further damage to the clip, and other components of the tenter machine, such as the bearings, pantograph, and drive.

[0008] Tenter clip degradation was referred to in U.S. Pat. No. 2,096,283, which suggests the improvement of reducing the number of tenter clip openings and closings per circuit from four to two and thus cut the problem in half. Other improvements focused on the tenter clips themselves, e.g., by adding flexibility to the cam follower mechanism of the tenter clip to reduce clip degradation. See, e.g., EP212985. Still other improvements focused on improving the clip closers or openers to reduce wear and tear on the clips. For example, U.S. Patent 4,065,838 discloses a driven disk with a padded perimeter, where the perimeter contacts the clip arm to actuate the tenter clip. U.S. Patent No. 5,781,974 discloses a magnetic apparatus for actuating the tenter clips. [0009] Japanese Patent Applications No. 2001-162681 and 2002-18691 utilize the perimeter of a freely-rotating disk as the clip opening device to prevent localized wear of the clip arm. Other clip actuators, e.g., those disclosed in Japanese Patent Application No. S59-48123, comprise a free- rotating disc which contacts the closing arm of the clip to close the clip. The disk is held in position by a bracket and spring, which allow the disk to pivot away from the clip arm of a damaged clip, and then return to position by action of the spring.

[0010] While there have been gradual improvements in the design of tenter- type stretching, there is still a need for improved tenter clip closing and opening devises that are able to withstand or prevent damage from defective tenter clips. Particularly there is a need for improved tenter clip closing devices that are able to close the clips more completely with less wear on the clips. [0011] As a method for detecting malfunctioning clips, Japanese Patent Application No. 2006-130770 discloses a method analyzing the footprint of the tenter clip's grip on the edges of the film using a grip trace detector. When an abnormal footprint is found, the machine is halted, and the malfunctioning clip is repaired or replaced. Another reference, Japanese Patent Application No. H06-247615, discloses comparing the profile of a clip at a point along the tenter machine and comparing the profile of the clip to the profile of adjacent clips or to a reference profile. If the clips profile differs from the profile of the neighboring clip or from the reference profile, the tenter machine is halted and the malfunctioning clip is repaired or replaced.

[0012] While it is an improvement, the method of the 770 reference is difficult to practice because it requires continuous monitoring of the tenter clip's footprint on the film during the entire operating duration of the tenter machine. The method of the '615 reference also requires continuous monitoring. Moreover, Neither reference is suitable for identifying clips which fail as they are toggled by the clip opener from the closed to the open position. Such a clip has opened properly, i.e., it has left an appropriate footprint on the edge of the film and it has the appropriate profile. But since the clip has malfunctioned during opening, it might not close properly when it is recirculated to the downstream end of the tenter machine, thereby damaging the tenter machinery. There is therefore a need for further improvements. SUMMARY OF THE INVENTION

[0013] The first apparatus for stretching a polymeric web of the present invention comprising:

(a) a driven conveyor comprising tenter clips that hold opposing edge portions of the web and convey the web along a machine direction within the apparatus from an upstream gripping region of the apparatus to a downstream stretching region; the tenter clips being adapted to controllably open and close;

(b) a first tenter clip closer located in the gripping region for at least partially closing the tenter clips in order to grip the web; and (c) a second tenter clip closer located in the gripping region but downstream of the first tenter clip closer to further close the tenter clips. [0014] In an embodiment, the invention relates to a continuous process for stretching a polymeric web, the process comprising

(a) conducting the polymeric web to a stretching apparatus which comprises (i) a plurality of tenter clips, the tenter clips comprising a clamping surface and a pivotable clamping arm, wherein the clamping arm has an upper end comprising a cam follower and a lower end comprising a gripping surface,

(ii) opposed tracks along which the plurality of tenter clips travel, the opposed tracks defining an upstream gripping region and a stretching region downstream of the gripping region;

(b) contacting in the gripping region the cam followers of opposed sequential pairs of the tenter clips with a pair of opposed first clip closers in order to at least partially close the tenter clip and thereby grip successive portions of the web along opposite edges of the web with opposed pairs of the tenter clips in order to convey the web into the stretching zone; and

(c) contacting the cam followers of opposed sequential pairs of the tenter clips with a second pair of opposed clip closers located in the gripping region but downstream of the first clip closers; and then (d) conveying the web along the opposing tracks to the stretching region and stretching the web within the stretching region.

[0015] The first tenter clip closer of the present invention can be placed at the entrance region (also called a gripping region) of a tenter which conveys a web gripped by the tenter clips. The tenter clips can be continuously conveyed along a pair of looped rails provided on either side of the web. The first tenter clip closer actuates the tenter clip to the closed or partially closed position that the tenter clip grip the web, e.g., by rotating a pivotable clip arm on the tenter clips by making contact with it. A second tenter clip closer is located downstream of the first tenter clip closer. The second tenter clip closer provides an additional closing force to more completely close the tenter clips, particularly those tenter clips that have become resistant to complete closure by, e.g., the accumulation of debris in the pivot region. [0016] In an embodiment, the first tenter clip closer is a cam and the second tenter clip closer is a disk. The tenter clip can be actuated to the closed position by the action of the cam or disk against a cam follower which can be part of the tenter clip.

[0017] The cam of the first tenter clip closer can be, e.g., in the shape of an elongated rectangular plate or wedge. In an embodiment, the cam has a curved surface that bends slightly outward with respect to the direction of web travel from upstream to downstream. For example, the cam can have the shape of a longitudinal plate tilted downward in the inner direction or the shape of a horizontal plate having an outer surface that is tilted gradually outward with respect to the direction of tenter clip travel. The cam can be a metallic cam. The disc of the second tenter clip closer can be an abrasion-resistant resinous disk.

[0018] In an embodiment, the disc of the second tenter clip closer is mounted axially, where the mounting axis is perpendicular to the plane of the disk and tilted at an acute angle with respect to the plane of the web in the tenter machine. For example, the disc can be mounted so that the side (or planar) surface of the disc bears on the cam follower of the tenter clip to more completely close the clip.

[0019] The second apparatus for stretching a polymeric web of the present invention comprising: a driven conveyor comprising tenter clips that hold opposing edge portions of the web and convey the web along a machine direction of the apparatus into a through a stretching region, the tenter clips being adapted to controllably open and close; and at least one pivotable tenter clip opener, the tenter clip opener comprising a fixed cam for at least partially opening the tenter clips in order to release the web and a pivot connected to the fixed cam for pivoting the fixed cam away from the tenter clip.

[0020] In an embodiment, the invention relates to a continuous process for stretching a polymeric web, comprising

(ii) opposed tracks along which the plurality of tenter clips travel, the opposed tracks defining a gripping region, a stretching region downstream of the gripping region, and a releasing region downstream of the stretching region; (b) contacting in the gripping region the cam followers of opposed sequential pairs of the tenter clips with at least one pair of opposed first clip closers in order to at least partially close the tenter clips and thereby grip successive portions of the web along opposite edges of the web with opposed pairs of the tenter clips in order to convey the web into the stretching zone;

(d) conveying the web along the opposing tracks to the stretching region and stretching the web within the stretching region; and (e) contacting in the releasing region the cam followers of opposed sequential pairs of the closed tenter clips with at least one pair of opposed clip openers in order to at least partially open the tenter clips and thereby release the gripped successive portions of the web, the clip openers comprising a fixed cam for at least partially opening the tenter clips in order to release the web and a pivot connected to the fixed cam for pivoting the fixed cam away from the tenter clip.

[0021] The third apparatus for stretching a polymeric web of the present invention comprising:

(a) a driven conveyor comprising tenter clips that hold opposing edge portions of the web and convey the web along a machine direction of the apparatus into a through a stretching region, the tenter clips being adapted to controllably open and close;

(b) at least one tenter clip actuator for at least partially opening or closing the tenter clips in order to grip or release the web, the tenter clip actuator being adapted for movement away from the tenter clip toward a stop which when contacted by the tenter clip actuator prevents further movement of the tenter clip actuator; and

(c) a counter automatically activated by the stop for counting a number of tenter clips conveyed to the tenter clip actuator following activation. [0022] The present invention also relates to a method for identifying a malfunctioning tenter clip in continuous process for stretching a polymeric web, comprising:

(a) conducting the polymeric web to a stretching apparatus which comprises

(i) a plurality of functioning tenter clips for gripping opposing edge portions of the web and conveying through the stretching apparatus, the tenter clips being adapted to controllably toggle open and close, and the malfunctioning tenter clip which resists such toggling;

(ii) at least one tenter clip actuator for toggling the functioning tenter clips closed or open to grip or release the web, the tenter clip actuator being adapted for movement away from the tenter clip toward a stop and which contacts the stop when the malfunctioning tenter clip is toggled by the actuator but which does not contact the stop when a functioning tenter clip contacts the actuator, the stop being adapted to prevent further movement of the tenter clip actuator; and (iii) a counter automatically activated by the contacted stop for counting a number of tenter clips conveyed to the tenter clip actuator following activation;

(b) contacting the malfunctioning clip and the tenter clip actuator thereby moving the tenter clip actuator to the stop and activating the counter;

(c) halting the conveying of the tenter clips; and (d) counting the number of tenter clips between the actuator and the malfunctioning tenter clip as provided by the counter to identify the malfunctioning tenter clip.

[0023] In an embodiment, the positions of the defective clip or clips is determined directly from the counter. In another embodiment, a reference clip is used, and counter values from a second counter establish a unique tenter clip number for each tenter clip. The location of malfunctioning clip can be determined by its reference number and the position of the reference clip by addition or subtraction, which can be accomplished automatically, e.g., by a computer or other automated data processing equipment. The computer can be used in combination with means for controlling the tenter clip conveyance drive, in order to automatically halt the machine when a malfunctioning clip is detected.

[0024] The reference clip can be identified automatically by, e.g., using a magnetic member (e.g., a magnetic bolt) on the clip or proximate to the clip (e.g., on a pantograph arm) which can be sensed by a sensor capable of detecting a change in electromagnetic field.

[0025] The clip actuator can be a clip opener, a clip closer, or both. Clip openers are generally used as one or more opposed pair of clip openers on each edge of the web. Similarly, clip closers are generally used as one or more opposed pair of clip closers on each edge of the web.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of an embodiment of a tenter machine equipped with the first and second tenter clip closers and openers of the present invention.

[0027] Figure 2 provides side views of a tenter clip of the tenter in Figure 1; wherein, (a) shows an open tenter clip, (b) shows a partially open/partially closed tenter clip, and (c) shows a closed tenter clip. [0028] Figure 3 is an oblique view of an embodiment the first and second tenter clip closers of Figure 1. This figure also shows a compliant mount attached to the first and second tenter clip closers. The compliant mount, as shown, is adapted to pivot the first and second tenter clip closer away from the tenter clips when an abnormal force is applied to the first or second tenter clip closer, e.g., when a broken or defective tenter clip acts on with closer or both.

[0029] Figure 4 is a plan view of the tenter clip closer in the embodiment of

Figure 3.

[0030] Figure 5 is a side view of the tenter clip closer in the embodiment of

Figure 3. [0031] Figure 6 is an oblique view showing the tenter clip opening apparatus of Figure 1.

[0032] Figure 7 is an oblique view showing another example of a tenter clip opening apparatus in the present invention. [0033] Figure 8 is a plan view showing the tenter clip opening apparatus in

Figure 7.

[0034] Figure 9 is a schematic diagram illustrating an example one embodiment of the invention, comprising an apparatus for detecting and identifying a malfunctioning tenter clip.

[0035] Figure 10 is an oblique view illustrating a representative reference clip detecting sensor.

[0036] Figure 11 is an enlarged partial plan view of the tenter and sensing portions of a representative apparatus for assigning a unique clip identification number to each tenter clip, the unique clip identification number for each tenter clip being referenced to the reference clip.

[0037] Figure 12 is an oblique view illustrating a tenter clip closing apparatus of Figure 9.

[0038] Figure 13 is a diagram schematically illustrating the stress variations as a tenter clip is conveyed through the tenter machine and contacts a clip actuator.

[0039] Figure 14 is an oblique view illustrating a tenter clip opening apparatus of Figure 9.

[0040] Figure 15 is a schematic diagram of a conventional tenter machine having a first but no second tenter clip closer.

[0041] Figure 16 is a schematic diagram of a conventional disk-type tenter clip closer.

DETAILED DESCRIPTION OF THE INVENTION [0042] [1] A TENTER CLIP CLOSING APPARATUS

[0043] A tenter clip closing apparatus of the present invention is based in part on the discovery that tenter clips can be repeatedly actuated with less wear and tear by distributing the closing action over two tenter clip closers, i.e., a first upstream closer to at least partially close the tenter clips and a second tenter clip closer downstream (in the machine direction of the web) of the first tenter clip closer which more completely closes clips that were only partially closed by the first closer and which contacts even the fully closed clips to ensure firm gripping of the web. When the first tenter clip closer comprises a cam in the shape of an elongated (in the machine direction) rectangular plate, the cam can have, e.g., a curved surface and/or a tilted surface that bends outward away from the web so that the upstream end of the cam is further from the web than the downstream end of the cam. It has been discovered that a curved, elongated cam is desirable because it more gently imparts a closing force to the clip over a longer distance (and longer time) than is the case for a disc-shaped closer.

Consequently, the impulse on the tenter clip from the cam is comparatively mild, resulting in less wear and tear on the clips. Since tenter clips are generally actuated by a toggle action of the clip arm pivoting on the tenter clip, a discshaped second tenter clip closer is desirable to impart a relatively sharp impulse, particularly to clips that are only partially closed by the first tenter clip closer, since the sharp impulse is effective for actuating the toggle motion of the arm. This is particularly the case with second tenter clip closers comprising a freely- rotating closer disc. It has also been discovered that it can be advantageous to bias the first and/or second tenter clip closer by an appropriate force (e.g., a force generated by a spring, an air cylinder, or both) so that the plate-shaped closer and the disk-shaped pusher can retreat when an abnormal force acts on either closer, such as might occur when a defective tenter clip is acted on by the first or second tenter clip closers. [0044] Figure 15 shows conventional tenter equipment of the type commonly used for stretching a continuous plastic film in the film's planar directions, i.e., the transverse and machine directions. The tenter comprises a pair of looped rails 100 and 100 that are provided on either side of film 400, pantographs that circulate along said rails via bearings, a plurality of tenter clips 121 that are attached to pantographs at regular intervals, longitudinal plate-shaped tenter clip closers 250 and 250 each having a curved surface that bends slightly outward with respect to the machine direction that are placed at the entrance region of the tenter, and longitudinal plate-shaped openers 300 and 300 each having a curved surface that gradually bends inward with respect to the machine direction that are placed at the tenter exit region (also called the releasing region) of the tenter. The tenter is driven by drive means (e.g., chain drive, belt drive, gear drive, etc.) to convey tenter clips 121 are conveyed from the gripping region at the upstream end of the tenter toward the downstream stretching region. [0045] When the closing arms 121 ' of clips 121 come into contact with closers 250 at the tenter entrance part as tenter clips 121 are advanced, open clips 121 are closed so as to grab the edge of film 400, and film 400 is stretched as clips 121 are advanced in the machine direction. When arms 121' of tenter clips 121 come into contact with openers 300, clips 121 are opened so as to release stretched film 400. [0046] In order for the web (e.g., film) to be firmly gripped by the tenter clip, the closer actuates the closing arms 121' of the tenter clip 121 by forcing the arms in the transverse direction away from the film. Since considerable force is needed to close the tenter clips for gripping the web, the closers 250 can severely abrade the clip arms 121 ', particularly if both are metallic, resulting is the formation of metallic particulates which can enter various parts of the tenter (e.g., the tenter clip arm pivots, causing deterioration). The film being stretched can also be contaminated, which is particularly problematic for films that might be used as battery separators since the metallic particulates can cause short circuits in the battery. In addition, when a single strong force is used to actuate clip arms 121', the pantographs and the bearings that are used to run the pantographs on the rails are also subjected to a relatively heavy load, resulting in additional wear and tear, and deterioration of the pantographs and the bearings connecting the pantograph to the tenter clips. It has been discovered that this problem is particularly acute for defective cams, e.g., those with the clip arm stuck in the open position, since the action of the closer 250 on a stuck clip arm of tenter clip 121 can result in such a large closing force that not only closers 250 but also pantographs and the bearings are deformed or damaged. [0047] To overcome this difficulty, Japanese Patent Application No. S59[1984]-48123 discloses a tenter clip closer of the type shown in Figure 16. The closer comprises a wearable disk 260 that is placed in contact with clip lever 131, arm 261 that supports the disk in a freely rotatable fashion, retainer 263 for retaining compression spring 262, and supporting bracket 264 that is integrally formed with retainer 263 while pivotably supporting one end of arm 261, wherein one end of retainer 263 is supported by the other end of arm 261. This clip closer is adapted to retreat when an abnormal force acts upon it. In this device, wearable disk 260 pushes clip lever 131 while the disk is turning in order to close the tenter clip. When an abnormal tenter clip (e.g., one frozen or stuck in the open as a result of a fouled clip-arm pivot) contacts the disk 260 retreats when connecting arm 261 pivots under application of the force applied by the abnormal tenter clip.

[0048] It has now been discovered that when only the disk-shaped closer is used, as in the prior art, the contact time between the tenter clip's clip arm and the disk is so brief that the clip arm cannot always be pushed sufficiently to completely close the clip and grip the web.

[0049] Figure 1 shows one embodiment of an improved tenter machine which overcomes this difficulty. In an embodiment, the improved tenter comprises a pair of looped rails 1 that are provided on either side of film 4, a plurality pantographs that circulate along said rails via bearings, and a plurality of tenter clips 11 that are attached to pantographs at regular intervals; a pair of tenter clip closer assemblies 2 are placed in the entrance region of the tenter machine; and a pair of tenter clip openers 3 are placed in the exit region of the tenter machine. The pair of rails 1 spread apart in the stretching region of the tenter machine as the film 4 advances from upstream to downstream in the machine direction. The film is thus stretched as the tenter clips gripping the film are conveyed into and through the stretching region. [0050] One embodiment of a tenter clip compatible with the invention is shown in Figure 2. Tenter clip 11 comprises (a) C-shaped frame 11a; (b) pivotable clip arm 1 Ib that is pivoted on the frame; (c) a pivotable gripping member l ie that is pivoted at the bottom of the clip arm, (d) a cylindrical upper tooth (having a gripping surface) 1 Id that is attached to said movable member in a freely rotatable fashion; (e) cylindrical lower tooth l ie (having a clamping surface for clamping the web against the gripping surface when the clip is closed) that is fixed to the lower arm of C-shaped frame 1 Ia; (!) a tubular

(preferably cylindrical) member 1 If that is pivoted on the C-shaped frame 1 Ia at a first end while pivoted on projection 110b of clip arm 1 Ib at a second end; and (g) a spring Hg (generally in compression) that is fitted around the cylindrical member 1 If so as to bias clip arm 1 Ib. With the appropriate selection of the spring 1 Ig, the clip arm 1 Ib should toggle between positions for gripping and releasing the web, i.e., the "closed" and "open" positions. A first end of the clip arm l ib can comprise a cam follower configured so that the cam of at least the first clip closer acting on the cam follower with cause the clip arm 1 Ib to pivot on shaft 111b about the clip arm pivot thereby at least partially moving the clip arm 1 Ib from the open position to the closed position. The tenter clip can comprise a second cam follower for contacting the tenter clip opener in the releasing region of the tenter machine. In an embodiment, the second cam follower is on the or near the first end of the tenter clip's pivotable arm, generally opposed to the first cam follower. [0051] Figures 3-5 show details of an embodiment of one of the pair of the tenter clip closer assemblies 2 disposed on opposing sides of the web. As discussed, each tenter clip closer comprises a first tenter clip closer and a second tenter clip closer downstream of the first tenter clip closer. In an embodiment, tenter clip closer assembly 2 comprises (a) support arm 20 that extends toward film 4 along the film's transverse direction and has a leg part at an outer end; (b) support body 200 that comprises two inverted J-shaped side plates 200a and 200a that sandwich support arm 20 and upper plates 200b and 200b that connect the side plates in parallel; (c) a pivotable arm 21 (21a shows a pivot), which can be in the shape of an elongated rectangular member, that is pivotable about a pivot on the support body, e.g., on the lower end of the support body 200 below support arm 20 as shown, such that the pivotable arm can pivot about the support body like a seesaw; (d) a first tenter clip closer attached to a first end of pivotable arm 21, the first tenter clip closer comprising a cam 2a which has a curved surface that bends gradually outward with respect to the machine direction and is also tilted toward the plane of the film; (e) a second tenter clip closer 2b, e.g., one shaped in the form of a disk mounted in a freely rotatable fashion, e.g., on U-shaped support member 211, wherein the second and first tenter clip closers are attached to pivotable arm 21 via link 210; (f) forcing means 22 (e.g., a spring or a piston driven by compressed gas or fluid), that is attached at a first end to support body 200 and attached at a second end to pivotable arm 21 for pivoting the pivotable arm toward or away from the tenter clip as shown; (g) a stop 201 to prevent pivoting of the pivotable arm past a defined stop point; and (h) a linear gauge 202 that is provided proximate to the second end of pivotable arm 21 and used to measure the position of , e.g., disk- shaped pusher 2b.

[0052] Referring to figures 3, 4, and 5, first tenter clip closer 2a can comprise a cam having a curved surface that bends gradually outward with respect to the direction of clip 11 travel while tilted downward in the inner direction. Consequently, when tenter clip 11 is advanced and the cam follower of arm 1 Ib on open clip 11 (Refer to Figure 2(a)) comes into contact with the cam of first tenter clip closer 2a, the cam following action of clip arm l ib causes the clip arm 1 Ib to pivot as the clip arm is pushed outward away from the film, and clip 11 closes as shown in Figures 2(b) and (c). As clip arm 1 Ib pivots, cylindrical member 1 If pivots, and the bottom part of clip arm 1 Ib is biased by compression spring 1 Ig, so that clip 11 toggles closed while film 4 is gripped between upper tooth 1 Id and lower tooth l ie. [0053] The size, curvature, tilt angle, and layout position of longitudinal plate-shaped closer 2a are selected such that clip 11 can be brought from its open state to the closed state to grip film 4. More specifically, because clip arm 1 Ib is closed by the biasing force of compression spring 1 Ig when it is pivoted to an angle beyond its neutral position (i.e., the state when the apex of projection 110b is placed on the axial line of cylindrical member 1 If as shown in Figure 2(b)), the size, curvature, tilt angle, and layout position of the cam of the first clip closer 2a should be set such that clip arm l ib can be pressed at least to an angle beyond the neutral position.

[0054] While the cam of the first tenter clip closer 2a is illustrated as having a curved surface, this is not required. The cam can have any convenient surface for actuating the cam follower on the tenter clips. In an embodiment, the cam is metallic, but this is not required.

[0055] After clip 11 has been at least partially closed by making contact with the first tenter clip closer, clip arm 1 Ib is further actuated during contact with the second tenter clip closer 2b, which is generally in the form of a disk-shaped pusher as shown. The disk of second tenter clip closer 2b is generally supported in a freely rotatable fashion on a tilted spindle so as to allow its outer surface to make contact with the upper portion (generally the cam follower portion) of clip arm 1 Ib. As the tenter clip is conveyed in proximity to the second tenter clip closer, the disk acts on the cam of clip arm 1 Ib further toggling the at least partially closed clip into the closed position. The disk of 2b continues to rotate as the tenter clip advances in the machine direction, generally until the clip has passed the tenter clip closing assembly. The size and layout position of disk-shaped pusher 2b are not critical, and can be selected such that clip arm 1 Ib is pushed deeper into film 4 that is gripped by clip 11. Although it is not required, the diameter of disk-shaped pusher 2b can be, e.g., in the range of about 10-30 cm. While not required, the disk of 2b can be made of an abrasion resistant resin for improved durability, e.g., hard nylon. [0056] In an embodiment, the biasing force applied by forcing means (e.g., air cylinder) 22 is selected such that the second tenter clip closer 2b overcomes the resistance created by contact with clip arm 1 Ib in order to tilt clip arm 1 Ib to an angle beyond the neutral position. It can be desirable to increase this force further, e.g., so that clip arm 1 Ib is pushed further into film 4, which has been grabbed by clip 11, by disk-shaped pusher 2b. The force applied by the forcing means should not be so great that it doesn't prevent articulation (e.g., pivoting) of the first or second tenter clip closer out of the way of a defective or malfunctioning tenter clip as the defective tenter clip is conveyed in the gripping region of the tenter machine. For example, the biasing force created by forcing means 22 can be set such that the biasing force will be overcome when either (or both) of the first and second tenter clip closers contact a defective tenter clip. In that case, pivotable arm 21 pivots in the manner shown in Figure 5 in order to allow the tenter clip closer assembly to pivot away from a defective tenter clip, e.g., as when an abnormal pressure is applied to the first or second tenter clip closer as a result of the tenter clip's clip arm being frozen in the upright (i.e., open) position. Such a condition might occur when the tenter clip arm's pivot becomes fouled, corroded, or unduly worn. In practice, the appropriate force can be selected by measuring, e.g., with a load cell or strain gage, the force from ION to 300N needed to close functioning tenter clips using the first and/or second tenter clip closer. It is desirable that the force of the second tenter clip closer is higher than the force of the first tenter clip closer. In an embodiment, the force of from ION to 5ON is needed to close tenter clips using the first tenter clip closer. In an embodiment, the force of from 5ON to 300N is needed to close tenter clips using the second tenter clip closer, preferably from IOON to 200N. [0057] It has been discovered that at least partially closing the tenter clip with the first tenter clip closer and then contacting the closing arm of the tenter clip with the second tenter clip closer provides for more reliable and more complete closing of the tenter clips, particularly for closing tenter clips that have become difficult to toggle close as a result of, e.g., toggle spring wear, tenter clip arm pivot wear, debris in the clip arm pivot, clip arm pivot corrosion, etc. Moreover, since clip arm l ib does not have to be completely closed by the first tenter clip closer, the frictional force between the clip arm's cam follower and the cam of the tenter clip closer can be reduced compared to cam/cam follower arrangements that must completely close the clip. Consequently, the relatively sharper impulse of the second clip closer can drive the toggle action of the tenter clip to the fully closed position without significantly increasing the wear of the clip arm cam. With the tenter clip in the completely closed position, there is less risk of damage to the tenter machine, particularly. And since the first and/or second tenter clip closer can articulate away from the a defective or malfunctioning tenter clip, the risk of damage to the first tenter clip closer, the second tenter clip closer, the pantographs, and the bearings can be greatly reduced or prevented. [0058] The invention is compatible with the tenter stretching of a wide range of film thicknesses, e.g., from a thickness of 10 micrometers or less to a thickness of 10 mm or more. The either the first or second tenter clip closer or a tenter clip assembly comprising the first and second tenter clips closers can be adapted to position sensors to sense the position of either closer or both during tenter clip closing. For example, the position of disk-shaped pusher 2b can be monitored using linear gauge 202 that comprises scale plate 202a and indicator 202b, and an increase/decrease in the gap between upper tooth 1 Id and lower tooth l ie can be monitored based on the determined position of disk-shaped pusher 2b. When the gap exceeds a prescribed value, the biasing force of forcing means 22 can be increased in order to increase the pressing force of disk-shaped pusher 2b. The pressing force of disk-shaped pusher 2b can in this way be regulated according to the thickness of film 4.

[0059] As shown in Figures 2(b) and (c), when clip 11 advances to the exit part of the tenter (the releasing region), clip arm 1 Ib can be pushed inward (toward the film) by a tenter clip opener 3 in order to toggle clip 11 to the open position as clip 11 advances further. Because cylindrical member 1 If rotates as clip arm 1 Ib is turned and the upper part of clip arm 1 Ib is biased by compression spring 1 Ig (refer to Figure 2(a)), clip 11 releases film 4. While a normally open clip is used for illustration, the invention is compatible with normally closed tenter clips also. While the invention has been described in terms of a tenter clip actuated from open to closed and vice versa by a toggle action (i.e., having a relatively unstable neutral position compared to the open and closed position), the invention is not limited thereto, and tenter clips having a stable or relatively stable neutral position are compatible with the invention. [0060] It has been discovered that it can be advantageous to run the tenter machine for a "warm-up" period without film, e.g., lubricate or adjust the machine before the start of film stretching. The invention is useful during such a warm-up period since the first or second tenter clips can be retracted away from the tenter clips, e.g., by tilting movable arm 21 by reducing the biasing force of forcing means 22. The closing of a tenter clip during the warm-up period would cause upper tooth 1 Id to bear directly against lower tooth lie with no film situated therebetween, and damage to the upper tooth 1 Id and/or lower tooth l ie can result. Consequently , it is advantageous to operate the articulating tenter clip closers or tenter clip closer assemblies (e.g., the one illustrated in figure 3) during warm-up.

[0061] [2] A TENTER CLIP OPENING APPARATUS [0062] A tenter clip opening apparatus of the present invention is based on the discovery of a tenter clip opening apparatus capable of articulating away from a defective or malfunctioning tenter clip. In an embodiment, the clip opener comprises an elongated fixed cam, i. e., it is not a rotating wheel or rotating cam. Even though the cam is fixed (no free or driven rotation), it is pivotable in order to provide a degree of articulation, but less than 360° about the pivot, and generally less than about 10°. In general, the cam bears against forcing means in response to the force applied to the clip opener by the clip during clip opening. The forcing means is selected to force the cam against the clip sufficiently to open a normally-operating clip, but not so much force as not to prevent the pivoting of the tenter clip opener away from a defective or malfunctioning clip. In one embodiment, the cam of the clip opener has the shape of an elongated rectangular member, which, for example, can curve away from the tenter clips in proximity to the cam (and also from the edge of the web). It has been discovered that such an articulating elongated cam opens the tenter clip more gently than a rotating wheel or fixed cam since a lower camming force can be applied over a longer time and since the cam can articulate away from a malfunctioning clip stuck in the closed position.

[0063] As shown in Fig. 15, in order for the web (e.g., film) to be released by the tenter clip, the opener 300 of the conventional tenter contacts the actuating means (e.g., pivotable clip arms) 121' of the tenter clip 121 by forcing the arms in the releasing direction (transversely direction toward the web for the tenter clips illustrated in Figure 2). Since considerable force can be needed to move the clip actuating means from the closed to the open position to release the web, the openers can severely abrade the clip arms 121 ', particularly if both are metallic, resulting is the formation of metallic particulates which can enter various pails of the tenter (e.g., the tenter clip arm pivots), causing deterioration. The web being stretched can also be contaminated with the particulates, which is particularly problematic for films as described above. In addition, when a rigid cam is used to actuate clip arms 121', wear and tear and deterioration of the pantographs and the bearings are increased as described above. It has been discovered that this problem is particularly acute for malfunctioning tenter clips, e.g., those with the clip arm stuck in the open position, since the action of the clip opener 300 on a stuck clip arm of tenter clip 121 can result in such a large opening force that not only opener 300 but also pantographs and the bearings are deformed or damaged. [0064] Rigid clip openers such as the rotatable disk-shaped clip openers disclosed in Japanese Patent Application No. 2001-162681 cannot overcome the difficulty presented by a defective or malfunctioning tenter clip because the clip opener does not retract under an abnormally large force from the malfunctioning tenter clip. [0065] In an embodiment, the clip opener of the invention comprises a fixed cam that is pivotably attached to the tenter so that the clip opener can pivot away from a malfunctioning tenter clip. For example, the clip opener can comprise an elongated rectangular cam having a first end and a second end, the second end being attached to a pivotable arm. The pivotable arm has a first end attached to the cam and a second end attached to the forcing means. The pivot is located between the first end and the second end. Depending on the configuration of the cam and pivotable arm, a first torque developed by the force of a malfunctioning tenter clip against exceeds a second torque developed by the forcing means acting on the second end of the pivotable arm times the distance between the pivot and the point on the second end where the forcing means acts on the pivotable arm. When the first torque exceeds the second torque, the cam will pivot away from the malfunctioning tenter clip.

[0066] In another embodiment, the tenter clip opener comprises a fixed cam in the shape an elongated rectangular wedge. A first end of the cam moves freely and the second end of the cam (generally the wider end) is engaged with the forcing means. The pivot is located between the first and second ends of the cam. As the clip is conveyed past the opener, the actuating means on the clip contacts the cam first near or at the upstream end and then the point of contact gradually advances toward the downstream end of the cam. As the tenter clip advances, the camming force gradually increases in order to actuate the tenter clip from the closed position to the open position. Similar to the preceding embodiment, a first torque equal to the camming force times the distance between the tenter clip's point of contact with the cam and the pivot is balanced by a second torque equal to the force of the forcing means times the distance between the point of contact of the forcing means on the cam and the pivot. When an abnormally large force is applied by a malfunctioning tenter clip, the first torque exceeds the second torque and the cam articulates away from the malfunctioning tenter clip. [0067] In an embodiment, the cam is in the form of an elongated rectangle or wedge having a cam surface (for contacting the tenter clip's actuating means) curing away from the web along the cam surface from downstream to upstream. While not required, the cam surface can be inclined at a positive angle with respect to an axis perpendicular to the plane of the web. In other words, a first edge of the cam closest to the frame of the tenter clip is inclined toward the web and a second edge of the cam (the edge farthest from the frame of the tenter clip) is inclined away from the tenter clip. For the purpose of illustration, such an inclination, when made gradually over the length of the cam can impart a twist to the cam 3 a as shown in figure 6. The material selected for the cam is not critical, and can be, e.g., metal or an abrasion-resistant resin.

[0068] While not required, the tenter clip opener can further comprise stopping means such as a mechanical stop or limit to prevent articulation of the cam about the pivot past a defined annular range of, e.g., +/- 10° from the cam's equilibrium position (the first and second torque are in balance), or +/- 20°, or +/- 45°, or +/- 60°. It is preferable that the tenter clip opening apparatus in the present invention have a stopper that holds the aforementioned plate-shaped opening in a fixed position. An elastic body (e.g., a spring) or a piston driven by a compressed gas or fluid (e.g., an air cylinder) can provide the forcing means. [0069] The invention will now be described in terms of the embodiments selected for illustration in the figures. As shown in Fig. 6, the first embodiment of one of the pair of the tenter clip opening apparatuses (or tenter clip openers) 3 comprises the following components: (a) Means for anchoring the tenter clip opener to the tenter machine, such as a support member 30 that extends from a first end away from the edge of the film to a second end.

(b) A pivot mount, e.g., a clevis such as the U-shaped support member 304 affixed in proximity to the downstream side of the first end of support arm 30. (c) A pivotable arm 31, such as the "z" shaped arm illustrated in figure 6. The illustrated arm has a first portion 31a approximately parallel to the machine direction, a second portion 31b extending from a first end attached to the upstream end of portion 31a to a second end, and a third portion 31c extending from a first end attached to the downstream end of 31a to a second end attached to the downstream end of the opening cam. As shown the pivot is of the pivotable arm is located proximate to the intersection of the first and second portions (for example on the second portion proximate to the second portion's downstream end), the pivot 3 Id being contained within the pivot mount of (b) above by, e.g., a clevis pin. (d) A cam 3 a having a free first end and a second end downstream of the first end, the second end being connected to the second end of portion 31c of the pivotable arm. As shown in the figure, the cam can have the form of an arcuate curving laterally away from the film from the cam's first end to the second end. The curvature of the arcuate can be, e.g., one or more of parabolic, circular, elliptical, or hyperbolic. As illustrated, the cam is in the form of an elongated rectangle (or rectangular member) which can have a gradual left hand twist moving downstream from the second end toward the first end. The twist imparts a tilt to the cam surface moving the long edge of the cam nearer to the film closer to the edge of the film and the long edge farthest from the film away from the edge of the film. Generally only a fraction of one revolution of twist (e.g., 1/64, 1/32, 1/16, or 1/8 of a revolution) of the cam surface is used over the length of the cam. Gently toward the inside relative to the direction of advance of tenter clips 11 and that is inclined to the inside and downward. (e) Means for anchoring forcing means, such as foot 301, can be attached to the downstream face of support arm 30.

(f) Further anchoring means, such as support base 302 can be used, e.g., extending from foot 301 downstream in the machine direction as shown.

(g) Forcing means, e.g., a tension spring 32 having a first end is attached to an L-shaped member 303 attached to support base 302 and a second end attached to the downstream face of portion 31b of movable arm 31, the forcing means providing sufficient tension to keep the downstream portion of cam 3 a approximately parallel to the machine direction, as shown, (h) Stopping means, such as mechanical stopper 33 furnished on support base 302 to prevent portion 31b of pivotable arm 31 from advancing downstream under the tension of the forcing means.

(i) Alarm means, such as normally-closed limit switch 34, which can be furnished proximate to the downstream face of the portion 31b of pivotable arm 31. Opening of the limit switch, which would occur as the downstream face of pivotable arm pivots away from the limit switch when the first torque (as define above) exceeds the second torque, can be used to provide a signal to automatic control means to halt conveyance of the tenter clips. [0070] Referring again to Figure 6, cam 3a can have a curved surface projecting gently toward the inside relative to the direction of advance of tenter clips 11 in the machine direction and that is inclined to the inside and downward, e.g., slightly twisted. When a clip 11 is conveyed in proximity to the opener, the opening cam follower of clip 1 Ib of the closed or partially closed tenter clip 11 (refer to Figure 2 (c)) contacts the camming surface (film side) of the cam thereby urging clip arm l ib toward the film as shown in Figures 2 (a) and (b) to at least partially open tenter clip 11 and release the film. In other words, as clip arm l ib pivots, tubular member 1 If articulates and the first end of clip arm 1 Ib urged by presser spring 1 Ig to toggle tenter clip 11 to the open position thereby releasing the film 4. The size, curvature, angle of inclination, and installation position of longitudinal plate-shaped opener 3 a are set so that clip 11 can be readily toggled from the closed position to an open position. As opening cam follower of the clip arm 1 Ib pivots under the urging of the cam, the clip arm toggles with the assistance of the forcing means provided in this case by pressure spring 1 Ig from the closed position through the neutral position (Figure 2(b)) to the open position (Figure 2(a)).

[0071] While this embodiment has been illustrated with reference to a curved cam, the invention is not limited thereto. For example, cam 3a can instead have a camming surface inclined gently to the inside relative to the direction of advance of tenter clips 11. Cam 3a can be metal, thought this is not critical. [0072] Referring again to Figure 6, forcing means, e.g., spring 32 acts on pivotable arm 31 to resist the force applied by the cam 3 a against opening cam follower of clip arm lib. The force selected for tension spring 32 in its equilibrium position against stop 33 is a force that is approximately equal to and opposed to the camming force that would otherwise cause pivotable arm 31 to articulate about pivot 31 d. In other words, a first torque is developed by the greatest camming force of cam 3 a against the opening cam follower of a functioning tenter clip as it toggles from the closed to the open position times the distance between the pivotable arm's pivot 3 Id and the point on the cam surface where the greatest camming force is generated. Similarly, a second torque is developed by the action of the forcing means against portion 3 Ib times the distance between the pivot 3 Id and the point at which the forcing means is applied to portion 31b. The forcing means is selected to provide a second torque that slightly exceeds the first torque for toggling open functioning tenter clip. When a defective or otherwise malfunctioning clip in the closed or partially closed position is conveyed in proximity to the opener, an abnormally large camming force will cause the first torque to exceed the second torque, and the pivotable arm 31 will articulate away from the stop 33 and the cam 3 a will articulate away from the cam follower of clip arm 1 Ib, thereby reducing or preventing damage to the tenter machine. While not required, the forcing means 32 can be selected to prevent cam 3a from articulating under the influence of a functioning tenter clip arm requiring the least force to toggle from the open to the closed position. The downstream face of portion 3 Ib will then articulate away from stop 33 when a functioning tenter clip having a slightly stiffer toggle is conveyed past the opener. This might be the case for functioning tenter clips which have clip arms that have become slightly stiffer with age and normal wear and tear. In this embodiment, spring 32 will ensure that only the minimum force needed to open a functioning tenter clip will be applied by cam 3 a. Since only a minimum camming force is used to toggle the clip, this embodiment results in less wear and tear on the clip, pantograph, bearings, etc. A second stop and second limit switch can be used opposite the first stop and first limit switch to prevent further articulation and to provide an alarm signal in the event a defective or malfunctioning tenter clip is conveyed in proximity to cam 3 a. [0073] Figures 7 and 8 show a second embodiment of the tenter clip opening apparatus. In this embodiment, tenter clip apparatus 3' comprises the following components:

(a) A support arm 35 terminating in a pivot mount (e.g., a clevis) and extending laterally away from the film 4. (b) An elongated wedge-shaped cam 3 a' that can pivot freely at or near a first end of the cam the inside the pivot mount of support arm 35. The pivot can be provided by, e.g., a clevis pin 3 Ia' as shown. The cam has first and second surfaces approximately parallel to the surface of the film and each other and a camming surface that inclines slightly toward the film from the downstream (first) end of the cam to the upstream (second) end. The cam has a fourth face substantially parallel to the machine direction when the cam is in its equilibrium position.

(c) An elongated rectangular-shaped member 350 having a first surface opposed to the fourth surface of the cam, a second surface in substantially the same geometric plane as the first surface of the cam, and a third surface in substantially the same geometric plane as the second surface of the cam.

(d) A tubular member 36 that passes through plate member 350 and contacts or nearly contacts the fourth surface of cam 3a', in which tubular member is fit- mounted forcing means such as a presser spring 360 for forcing the camming surface of cam 3 a¹ against the opening cam follower of the tenter clip in proximity to the tenter clip opener.

(e) Stopping means (which can also be guiding means, as shown) such as stopper 351 attached to the second surface of member 350 and the first surface of cam 3a' for holding the second surface of member 350 in substantially the same plane as the first surface of cam 3 a' as the cam pivots about clevis pin 31a'. Curved slot 351a') and guide pin 30a' can be used to guide the cam as it pivots, for example.

(f) Alarm means, such as limit switch 38 actuated by member 37 attached to the second end of the cam for providing an alarm signal as described in the first embodiment.

[0074] The opener of the second embodiment has a wedge-shaped cam which inclines gently toward the film as the tenter clips 11 advance in the machine direction. The selection of the pivot position and the calibration of the forcing means is the same as described in connection with the first embodiment. Accordingly, tenter clip and tenter wear and tear are reduced when the minimum force needed to toggle the tenter clip from closed to open is used. In an embodiment, an opener can retreat when the force is higher than 2ON, preferably 5ON. [0075] In a related embodiment, cam 3a' is not a wedge, but instead is a member having a camming surface in the form of an arcuate as described in connection with the first embodiment. As in the first embodiment, cam 3a¹ can be metal, although this is not required. Other materials such as abrasion- resistant resin (e.g., hard nylon) can be used for the camming surface or the entire cam.

[0076] When properly calibrated, forcing means 360 (which can be, e.g., a spring or a piston driven by compressed gas or fluid) is set to oppose the camming force of the tenter clip's cam follower against cam 3a¹. The position at which forcing means 360 bears on the fourth surface of cam 3a' can be selected as the position of maximum camming force as the tenter clip traverses the tenter clip opener. Generally, this position is proximate to the downstream end of cam 3a', as shown. When this position is opposed to the position of maximum force applied by the cam follower on the camming surface, the lever arms of each force about pivot 3 Ia' are equal, and the first and second torques are relatively easy to calculate compared to the first embodiment. Although it is not required, the forcing means 360 can be selected in a range so that clip arm 1 Ib of a damaged or malfunctioning clip stuck in the closed position is not overly forced, thereby damaging one or more of the tenter machine components, but instead the cam 3 a' pivots away from the malfunctioning clip against the forcing means.

[0077] As described above, the second apparatus, too, has a function whereby cam 3a' can pivot away slightly under an abnormally large force from a functioning tenter clip to prevent or reduce wear and tear on the tenter components including the clips. The position at which the tenter clip toggles open merely moves downstream along the camming surface of 3 a'. Further elongation of the cam can be used if needed as the equipment ages, generally with a substitute cam. [0078] [3] DEFECTIVE TENTER CLIP DETECTING METHOD AND DEVICE [0079] A method and a device used for detecting defective tenter clips of the present invention will be described. In one embodiment, the invention relates to an apparatus and system for detecting malfunctioning tenter clips, e.g., tenter clips that from wear and tear or the accumulation of detritus have become resistant to opening or closing. The apparatus can be adapted to the tenter described above. When a malfunctioning clip is conveyed in proximity to the tenter clip actuator for opening or closing, the malfunctioning clip's resistance to actuation (generally resistance to toggling) causes the actuator to move against the stop. The motion of the actuator is calibrated so that a functioning clip, (offering significantly less resistance to actuation than a malfunctioning clip) will not cause the clip actuator to contact the stop. The stop is adapted to serve two functions: first the stop prevents further movement of the tenter clip actuator away from the tenter clip past a calibrated point, and second the stop, at a second calibrated point that can be but is not necessarily the same as the first calibrated point, automatically activates a tenter clip counter to count the number of tenter clips conveyed past the actuator following the malfunctioning clip. The position of the malfunctioning tenter clip can be determined directly from the value on the counter by counting (automatically or manually, or otherwise) from the tenter clip in proximity to the tenter clip actuator forward (downstream) to the malfunctioning tenter clip. The functions of the stop

(means for preventing articulation of the actuator away from the tenter clips and means for generating an alarm and/or alarm signal for activating the counter) can be achieved by separate but linked stop and alarm components (e.g., a hard limit and an electric limit switch) or combined into a single stop component. [0080] Means for counting the clips can be automatic, e.g., as provided by automatic data processing equipment, such as a computer. Control means can be provided to automatically control the tenter drive, and to automatically halt the tenter after a malfunctioning clip is detected by the stop. The control means and counting means can be combined, e.g., in automatic process control equipment, such as a computer-based process controller. [0081] Accordingly, in another embodiment, the invention relates to a method for identifying a malfunctioning tenter clip in continuous process for stretching a polymeric web, comprising

(a) conducting the polymeric web to a stretching apparatus which comprises an apparatus of the previously described-embodiments;

(b) contacting the malfunctioning clip and the tenter clip actuator thereby moving the tenter clip actuator to the stop and activating the counter; (c) halting the conveying of the tenter clips; and

(d) counting the number of tenter clips between the actuator and the malfunctioning tenter clip as provided by the counter to identify the malfunctioning tenter clip. The automated data processing and control means can be used to automatically halt the tenter drive. Mechanical linkages in the tenter are such that the machine will not halt immediately, but will continuously advance for a period of time until the machine's momentum is spent. It is an advantage of this invention that the counting means will continue to count tenter clips during this interval so that the malfunctioning clip can be identified even if it has moved away from the proximity of the tenter clip actuator. In an embodiment, the method of the invention is practiced where the actuator instrumented with the stop and counter in accordance with the invention is at least one of the opposed tenter clip closers. In this embodiment, a malfunctioning clip can be identified before it is recirculates along the loop rails to the gripping region where it could potentially damage the clip opener, the pantograph, the bearings, etc. The system and method of the invention is advantageous that it is activated only when a malfunctioning clip is in proximity to the instrumented actuator. It is therefore more efficient than the prior art systems and methods which are activated continuously as tenter clips advance through the system. [0082] In another embodiment, (1) one of the tenter clips circulating on the same loop-shaped rail is selected as a reference clip, (2) a reference clip detecting sensor that only detects said reference clip and a clip counter that counts all of the tenter clips are arranged along the loop-shaped rails; (3) signals containing the tenter information detected by said reference clip detecting sensor and said clip counter are conducted to automatic data processing equipment, e.g., a computer, which upon receipt of such reference clip signal establishes and records a unique sequential number to each tenter clip of the tenter; (4) the tenter clip closing apparatus comprising at least one tenter clip closer located in the gripping region, the tenter clip closer comprising (a) a closing cam to rotate the cam follower (and clip arm) of the tenter clip about the clip arm's pivot in order to at least partially close the tenter clip and grip the web between the gripping surface and the clamping surface as the tenter clip is conveyed in proximity to the tenter clip closer and optionally a second closer downstream of the first closer, and (b) a stop that holds at least one of the first or second closers in a fixed position; (5) the force applied to the stop of the tenter clip closing device in response to the action of the closer's cam against the tenter clip's cam follower is measured by force sensing means (e.g., a load cell or a strain gauge) for all tenter clips, and a signal from the sensing means is conducted to the computer; and if the sensed force is below a prescribed threshold value, the corresponding clip is recorded as a malfunctioning clip; (6) a correspondence is established between (a) the unique clip number of each tenter clip and (b) the signal from the sensing means, in order to identify the unique clip number or numbers of the malfunctioning clip or clips; (7) the tenter clip opener apparatus comprises (a) at least one tenter clip opener, e.g., a fixed or rotating cam and/or wheel, for at least partially opening the tenter clips in order to release the web and a pivot for articulating the tenter clip opener away from the tenter clip as the cam follower of the tenter clip contacts the clip opener and (b) a stop that holds the opener in a fixed position; (8) the force applied to the stop of the tenter clip opener in response to the action of the opener's cam and/or wheel against the tenter clip's cam follower is measured by second force sensing means (e.g., a load cell or a strain gauge) for all tenter clips, and a signal from the second force sensing means is conducted to the computer; and if the sensed force is below a prescribed threshold value, the corresponding clip is recorded as a malfunctioning clip; (9) a correspondence is established between (a) the unique clip number of each tenter clip and (b) the signal from the second sensing means, in order to identify the unique clip number or numbers of the malfunctioning clip or clips. Even though all of the preceding aspects can be practiced together, if (4), (5), and (6) are used, (7), (8), and (9) can be optional, and vice versa. The aspects are all compatible with the system, apparatus, and method of the invention. As might be appreciated, aspects of this embodiment can be practiced in combination with the preceding embodiments. [0083] Aspects of the invention can be described with reference to the figures, although the invention is not limited thereto.

[0084] Figure 9 shows one embodiment of a device used for embodying the defective tenter clip detecting method disclosed in the present invention. The tenter has a pair of continuous loop-shaped rails 1, 1, pantographs, tenter clips 11, tenter clip closing apparatus 2, 2, and tenter clip opening apparatus 3, 3 in the same way the above. Pantograph has an arm that can extend and retract freely and a plurality of parallel arms 10b supported on said arm. Tenter clips 11 are installed on parallel arms 10b.

[0085] In an embodiment, a clip counting sensor 5a connected to computer 6 is arranged on the outer side of loop-shaped rail 1. An optical sensor (for example an infrared sensor) can be used as clip counting sensor 5a. The digital information detected by clip counting sensor 5a is conducted to computer 6. [0086] In an embodiment, reference clip detecting sensor 5b (which detects reference clip 11' only) is arranged on the inner side of loop-shaped rail 1. One of the plurality of tenter clips 11 conveyed on pantograph is selected as reference clip 11'. Figure 10 shows an example of reference clip detecting sensor 5b. A dummy bolt 10c made of a magnetic material is attached at the end on the inside on parallel arm 10b bearing reference clip 11'. Reference clip detecting sensor 5b is set at a position such that dummy bolt 10c passes in proximity to the sensor. The invention will be described in terms of magnetic means for identifying the reference clip. While a magnetic bolt/electromagnetic or magnetic sensor can be used to detect the reference clip, this is not required, and other identifying means, e.g., optical means, can be used. The electromagnetic or magnetic sensor is set at an appropriate height so that dummy bolt 10c is within the detection range, while parallel arm 10b is outside the detection range. Since parallel arm 10b is generally magnetic, the electromagnetic or magnetic sensor is generally set at a height effective for detecting the bolt 10c, but not arm 10b. As shown in Figure 9, reference clip detecting sensor 5b is connected to computer 6. The digital information detected by reference; clip detecting sensor 5b is conducted to computer 6 in the form of an analog signal which can be digitized, for example. [0087] In an embodiment, as shown in Figure 11, clip counting sensor 5a and reference clip detecting sensor 5b are arranged such that they sandwich rail 1, but this is not required. Reference clip detecting sensor 5b can be arranged downstream or upstream of clip counting sensor 5a. For example, the position clip counting sensor 5a can be such that it is between reference clip 11' and the next clip 11 when "dummy" bolt 10c is directly below reference clip detecting sensor 5b. [0088] When the signal from reference clip detecting sensor 5b that is provided when dummy bolt 10c is detected is conducted to computer 6, the clips count value obtained from clip counting sensor 5a is reset. The counter value (an integer) is recorded sequentially starting from the clip 11 next to reference clip 11 '. Sequential numbers can be uniquely assigned to all tenter clips 11 in this way. Resetting of the count value and assigning of numbers to clips 11 is repeated in conjunction with the conveyance of clips 11. The unique numbers assigned to clips 11 at the position of clip counting sensor 5a can be displayed sequentially on monitor panel 7, and stored in the computer. [0089] As discussed, malfunctioning clips such as those which have become defective clips on account of poor rotation of clip arms 1 Ib can be detected by tenter clip closing device (or apparatus) 2 and opening device (or apparatus) 3. [0090] Figures 12 shows details of one of the pair of the tenter clip closer assemblies 2. This tenter clip closer assembly 2 is the same as the embodiment shown in Figs. 3 to 5, except that this has sensing mean 203 engaged with an end of stop 201. The force sensing mean 203 can be used to measure the force applied to stop 201.

[0091] Force sensing means 203 can be installed at an end of stop 201, as shown. As shown in Figure 12, since the articulating portion of movable arm 21 is energized upward by forcing means 22, when closers 2a and 2b are in fixed positions, and an almost constant force is applied to stop 201 even if there is slight change due to contact between closers 2a and 2b and any of the functioning clips 11. When a malfunctioning clip contacts closer 2a and 2b, the malfunctioning clip's resistance to toggling results in a closing force exceeding that the closing force applied during the closing of a functioning clip, and the force sensed by force sensor 203 is reduced. Consequently, malfunctioning clips can be directly from the force measured by force sensor 203. In an alternative embodiment, a strain gauge is used on stop 201 instead of load cell 203. [0092] As shown in Figure 9, the signal from load cell 203 can be conducted to computer 6. The digital information in the signal can be recorded by the computer 6 for all tenter clips 11. The force measured by load cell 203 can be monitored continuously, and if that force drops below a prescribed threshold value, the corresponding clip will be identified by the computer as a malfunctioning clip. For example, as shown in Figure 13, a threshold value Pi is set that is lower than the force Pi measured when a functioning clip 11 is conveyed in proximity to the closer. When the force measure by the sensor less than Pi (e.g., 75% of P₁, 50% of Pi_, 25% of Pi_, or 10% of Pi) the clip can be identified as a malfunctioning clip. This, however, is not the only choice. [0093] Figure 14 shows details of one of the pair of the tenter clip opening apparatuses 3 compatible with the invention. This tenter clip opening apparatus 3 is the same as the embodiment shown in Fig. 6, except that this has a force sensing mean 330. Force sensing mean 330 can be used for measuring the force applied to stop 33 during stretching of the film. [0094] Force sensing means, e.g., load cell 330, can be installed at the end of stop 33. Load cell 330 makes contact with the downstream face of portion 31b of movable arm 31. Since movable arm 31 is energized by tension spring 32 to offer resistance to clip arms l ib, normally when longitudinal plate-shaped opener 3a is in a fixed position, an almost constant force is applied to stop 33 (see Figure 14). However, if a malfunctioning clip is conveyed to the opener, a relatively higher force is applied, and the force applied to stop 33 is reduced. Consequently, a malfunctioning clip can be detected. As in the case of the closer, a strain gauge can be used instead of or in addition to load cell 330 on stop 32. [0095] As shown in Figure 9, the signal from load cell 330 can be conducted to computer 6 for all tenter clips 11. When the stress measured by load cell 330 is constantly monitored and that stress drops below a prescribed threshold value Pi¹, the corresponding clip can be identified (e.g., automatically) as a malfunctioning clip. It is preferred to set threshold value Pi' within the range of 75%, or 50%, or 25%, or 10% of the initial stress P₀ ¹ (the stress when there is no contact between longitudinal plate-shaped opener 3a and clip 11). [0096] In an embodiment, malfunctioning clips can be detected by tenter clip closing device 2, where the value calculated by subtracting the number of clips between clip counting sensor 5a and tenter clip closing device 2 from the clip number counted by clip counting sensor 5 a at the moment that the malfunctioning clip is detected by tenter clip closing device 2 is taken as the number of the malfunctioning clip.

[0097] In an embodiment, malfunctioning clips can be detected by tenter clip opening device 3, where the value calculated by subtracting the number of clips between clip counting sensor 5 a and tenter clip opening device 3 from the clip number counted by clip counting sensor 5 a at the moment that the malfunctioning clip is detected by tenter clip opening device 3 is taken as the number of the malfunctioning clip. [0098] The numbers of the defective clips identified by tenter clip closing device 2 and/or opening device 3 can be shown on monitor panel 7, and the drive means can be halted so the identified clip can be retrieved from its identified position for replacement or repair. [0099] While not required, the apparatus can be programmed so that a warning is generated directly when defective clips are detected by tenter clip closing device 2 and/or opening device 3. For example, as shown in Figure 13, it is programmed appropriately so that a warning is generated when the stress drops below threshold value Pi. The operator can stop the tenter after the warning is generated, checks the states of the identified clips, and replace/repair the clips if necessary, or this can be done automatically as described above, e.g., by acting on a command for stopping the tenter if the force from either sensing means drops below threshold value P₂ lower than threshold value Pi. While not critical, the threshold value P₂ can be set within the range of 75%, or 50%_; or 25% _, or 10% OfP₀. [0100] The present invention has been explained with reference to figures. However, the present invention should not be interpreted as being restricted to the illustrated embodiments.

[0101] The invention will now be further described with reference to the following non-limiting embodiments. [0102] 1. An apparatus for stretching a polymeric web, comprising

(b) a first tenter clip closer located in the gripping region for at least partially closing the tenter clips in order to grip the web; and

(c) a second tenter clip closer located in the gripping region but downstream of the first tenter clip closer to further close the tenter clips. [0103] 2. The apparatus of embodiment 1, wherein the tenter clips each comprise a clamping surface and a pivotable clamping arm, wherein the clamping arm has a first end comprising a cam follower and a second end comprising a gripping surface for gripping the web between the gripping and clamping surfaces when the tenter clip is at least partially closed. [0104] 3. The apparatus of embodiment 1 or 2, wherein the first tenter clip closer comprises a cam to pivot the tenter clip's cam follower in order for the tenter clip to grip the web between the gripping surface and the clamping surface as the tenter clip is conveyed in proximity to the first tenter clip closer. [0105] 4. The apparatus of any of embodiments 1 - 3, wherein the second tenter clip closer comprises a freely rotatable disk which contacts the at least partially pivoted cam follower as the tenter clip is conveyed in proximity to the second clip closer.

[0106] 5. The apparatus of any of embodiments 1 - 4, wherein the conveyor in the stretching region is configured for the tenter clips to travel in divergent paths to stretch the web.

[0107] 6. The apparatus of any of embodiments 2 - 5, further comprising a pivotable member having a first end and a second end with a pivot situated therebetween, wherein either the first tenter clip closer, the second tenter clip closer, or both are attached to the first end of the pivotable member, the second end of the pivotable member is fixed in position by a force Fi acting in a direction perpendicular to the web's planar surface.

[0108] 7. The apparatus of embodiment 6, further comprising a defective tenter clip which applies an abnormal force F₂ from the cam follower against the first or second tenter clip closer, wherein the pivotable member bears away from the tenter clip until a first torque generated by force F₂ about the member's pivot is equal and opposed to a second torque generated by force Fi about forcing means.

[0109] 8. The apparatus of any of embodiment 6 or 7, wherein the cam of the first tenter clip closer has a curved surface that extends upstream in the gripping region and bends away from the web, and a cam face having an upper edge tilted toward the web.

[0110] 9. The apparatus of any of embodiments 6 - 8, wherein the cam is metal and the disk is an abrasion-resistant resin. [0111] 10. The tenter clip closer described of any of embodiments 6 -9, wherein the side of the disc contacts at least partially pivoted cam follower.

[0112] 11. A continuous process for stretching a polymeric web, comprising

(c) contacting the cam followers of opposed sequential pairs of the tenter clips with a second pair of opposed clip closers located in the gripping region but downstream of the first clip closers; and then

(d) conveying the web along the opposing tracks to the stretching region and stretching the web within the stretching region.

[0113] 12. An apparatus for stretching a polymeric web, comprising: a driven conveyor comprising tenter clips that hold opposing edge portions of the web and convey the web along a machine direction of the apparatus into a through a stretching region, the tenter clips being adapted to controllably open and close; and at least one pivotable tenter clip opener, the tenter clip opener comprising a fixed cam for at least partially opening the tenter clips in order to release the web and a pivot connected to the fixed cam for pivoting the fixed cam away from the tenter clip.

[0114] 13. The apparatus of embodiment 12, wherein the tenter clip opener further comprises forcing means for opposing the pivoting of the fixed cam. [0115] 14. The apparatus of embodiment 12 or 13, wherein (a) the tenter clip comprises a clamping surface and a pivotable clamping arm, wherein the clamping arm has a first end comprising a cam follower and a second end comprising a gripping surface for gripping the web between the gripping and clamping surfaces when the tenter clip is at least partially closed; (b) the apparatus further comprises (i) a gripping region upstream of the stretching region, and

(ii) at least one tenter clip closer located in the gripping region, the tenter clip closer comprising a closing cam to rotate the cam follower about the pivot in order to at least partially close the tenter clip and grip the web between the gripping surface and the clamping surface as the tenter clip is conveyed in proximity to the tenter clip closer; and

(c) the cam of the tenter clip opener rotates the cam follower about the tenter clip's pivot in order to release the web held between the gripping surface and the clamping surface as the tenter clip is conveyed in proximity to the tenter clip opener.

[0116] 15. The apparatus of embodiment 14, wherein the tenter clip opener is located in a releasing region downstream of the stretching region, and wherein the tenter clip opener further comprises a pivotable member, the pivotable member having a first end attached to the cam of the tenter clip opener, a second end coupled to the forcing means, and wherein the tenter clip opener's pivot is located on the pivotable member.

[0117] 16. The apparatus of any of embodiments 12 - 15, wherein the cam of the tenter clip opener has the shape of an elongated rectangular plate or the shape of an elongated wedge .

[0118] 17. The apparatus of embodiment 16, wherein the cam and the cam follower contact at a camming surface of the plate, and wherein the camming surface is an arcuate curving laterally away from the film from the plate's first end to the second end. [0119] 18. The apparatus of embodiment 17, wherein at least one section of the arcuate has a parabolic, circular, elliptical, or hyperbolic curvature. [0120] 19. The apparatus of embodiment 15 , wherein the forcing means comprises one or more of a spring or a piston driven by a fluid or gas. [0121] 20. The apparatus of any of embodiments 13 - 19, wherein the forcing means bears on the downstream end of the cam of the tenter clip opener and wherein the downstream end of the cam of the tenter clip opener pivots away from the tenter clip's cam follower as the cam forces the cam follower, the pivoting being opposed by the forcing means. [0122] 21. The apparatus of any of embodiments 14 - 20, wherein the tenter clip opener further comprising at least one mechanical limit for restricting movement of the cam about the tenter clip opener's pivot to an angle of +/- 45° from equilibrium. [0123] 22. A continuous process for stretching a polymeric web, comprising

(ii) opposed tracks along which the plurality of tenter clips travel, the opposed tracks defining a gripping region, a stretching region downstream of the gripping region, and a releasing region downstream of the stretching region;

(b) contacting in the gripping region the cam followers of opposed sequential pairs of the tenter clips with at least one pair of opposed first clip closers in order to at least partially close the tenter clips and thereby grip successive portions of the web along opposite edges of the web with opposed pairs of the tenter clips in order to convey the web into the stretching zone;

(d) conveying the web along the opposing tracks to the stretching region and stretching the web within the stretching region; and

(e) contacting in the releasing region the cam followers of opposed sequential pairs of the closed tenter clips with at least one pair of opposed clip openers in order to at least partially open the tenter clips and thereby release the gripped successive portions of the web, the clip openers comprising a fixed cam for at least partially opening the tenter clips in order to release the web and a pivot connected to the fixed cam for pivoting the fixed cam away from the tenter clip. [0124] 23. An apparatus for stretching a polymeric web, comprising:

(c) a counter automatically activated by the stop for counting a number of tenter clips conveyed to the tenter clip actuator following activation. [0125] 24. The apparatus of embodiment 23, wherein the tenter clip actuator is pivotable tenter clip opener, the tenter clip opener comprising a fixed cam for at least partially opening the tenter clips in order to release the web and a pivot connected to the fixed cam for pivoting the fixed cam away from the tenter clip, and forcing means for opposing the pivoting of the fixed cam. [0126] 25. The apparatus of embodiment 24, wherein

(a) the tenter clip comprises a clamping surface and a pivotable clamping arm, wherein the clamping arm has a first end comprising a cam follower and a second end comprising a gripping surface for gripping the web between the gripping and clamping surfaces when the tenter clip is at least partially closed; (b) the apparatus further comprises

(i) a gripping region upstream of the stretching region, and (ii) at least one tenter clip closer located in the gripping region, the tenter clip closer comprising a closing cam to rotate the cam follower about the pivot in order to at least partially close the tenter clip and grip the web between the gripping surface and the clamping surface as the tenter clip is conveyed in proximity to the tenter clip closer;

(c) the cam of the tenter clip opener rotates the cam follower about the tenter clip's pivot in order to release the web held between the gripping surface and the clamping surface as the tenter clip is conveyed in proximity to the tenter clip opener; and

(d) the stop is connected to a load cell or strain gage, the signal from the load cell or strain gage being adapted to activate the counter.

[0127] 26. The apparatus of embodiments 24 or 25, wherein the tenter clip opener is located in a releasing region downstream of the stretching region, and wherein the tenter clip opener further comprises a pivotable member, the pivotable member having a first end attached to the cam of the tenter clip opener, a second end coupled to the forcing means, and wherein the tenter clip opener's pivot is located on the pivotable member. [0128] 27. The apparatus of any of embodiments 24 - 26, wherein the cam of the tenter clip opener has the shape of an elongated rectangular plate or the shape of an elongated wedge.

[0129] 28. The apparatus of any of embodiments 24 - 27, wherein the cam and the cam follower contact at a camming surface of the plate, and wherein the camming surface is an arcuate curving laterally away from the film from the plate's first end to the second end.

[0130] 29. The apparatus of embodiment 28, wherein at least one section of the arcuate has a parabolic, circular, elliptical, or hyperbolic curvature. [0131] 30. The apparatus of any of embodiments 26 - 29, wherein the forcing means comprises one or more of a spring or a piston driven by a fluid or gas.

[0132] 31. The apparatus of any of embodiments 24 - 30, wherein the forcing means bears on the downstream end of the cam of the tenter clip opener and wherein the downstream end of the of the cam of the tenter clip opener pivots away from the tenter clip's cam follower as the cam forces the cam follower, the pivoting being opposed by the forcing means. [0133] 32. The apparatus of any of embodiments 28 - 31, wherein the tenter clip opener further comprising at least one mechanical limit for restricting movement of the cam about the tenter clip opener's pivot to an angle of +/- 45° from equilibrium.

[0134] 33. A method for identifying a malfunctioning tenter clip in continuous process for stretching a polymeric web, comprising

(a) conducting the polymeric web to a stretching apparatus which comprises (i) a plurality of functioning tenter clips for gripping opposing edge portions of the web and conveying through the stretching apparatus, the tenter clips being adapted to controllably toggle open and close, and the malfunctioning tenter clip which resists such toggling; (ii) at least one tenter clip actuator for toggling the functioning tenter clips closed or open grip or release the web, the tenter clip actuator being adapted for movement away from the tenter clip toward a stop and which contacts the stop when the malfunctioning tenter clip is toggled by the actuator but which does not contact the stop when a functioning tenter clip contacts the actuator, the stop being adapted to prevent further movement of the tenter clip actuator; and (iii) a counter automatically activated by the contacted stop for counting a number of tenter clips conveyed to the tenter clip actuator following activation;

(b) contacting the malfunctioning clip and the tenter clip actuator thereby moving the tenter clip actuator to the stop and activating the counter; and (d) counting the number of tenter clips between the actuator and the malfunctioning tenter clip as provided by the counter to identify the malfunctioning tenter clip.

[0135] 34. The method of embodiment 33, wherein the stretching apparatus further comprises (iv) a pair of continuous rails disposed on either side of the web for conveying the tenter clip from a gripping region downstream to a stretching region and continuing downstream to a releasing region, wherein at least one actuator in the gripping region is a tenter clip closer and wherein at least one actuator in the releasing region is a tenter clip opener; (v) at least one reference tenter clip ; (vi) a reference clip sensor that senses the reference clip ; (vii) a second counter for providing the number of tenter clips that have passed the second counter following the reference clip; (viii) a data processor for reading the second counter and identifying each of the plurality of tenter clips with respect to the reference clip; and wherein the method further comprises (c) halting the conveying of the tenter clips;

(e) establishing a correspondence between the numbers from the second counter and each clip, thereby identifying each clip by a unique clip number representing the number of clips between the unique clip and the reference clip, and

(f) identifying the malfunctioning clip by its unique clip number. [0136] 35. The method of embodiments 33 or 34, wherein the malfunctioning clip contacts the tenter clip opener, and the unique number of the malfunctioning clip is determined by subtracting the number of clips between the second clip counter and the tenter clip opener, or the malfunctioning clip contacts the tenter clip closer, and the unique number of the malfunctioning clip is determined by subtracting the number of clips between the second clip counter and the tenter clip closer.

[0137] 36. The method of any of embodiments 33 - 35, wherein the plurality of tenter clips are installed in a pantograph, which has a pantograph arm that can extend and retract freely and a plurality of parallel arms supported by the pantograph arm, which pantograph circulates along said loop-shaped rails; a magnetic reference member on the on the parallel arm proximate to the reference clip; the reference clip sensor is a magnetic sensor adapted so that the reference member is within the detection range of the sensor but the parallel arm is outside the sensor's detection range.

Claims

1. An apparatus for stretching a polymeric web, comprising

(c) a second tenter clip closer located in the gripping region but downstream of the first tenter clip closer to further close the tenter clips.

2. The apparatus according to claim 1, wherein the tenter clips each comprise a clamping surface and a pivotable clamping arm, wherein the clamping arm has a first end comprising a cam follower and a second end comprising a gripping surface for gripping the web between the gripping and clamping surfaces when the tenter clip is at least partially closed.

3. The apparatus according to claim 1 or 2, wherein the first tenter clip closer comprises a cam to pivot the tenter clip's cam follower in order for the tenter clip to grip the web between the gripping surface and the clamping surface as the tenter clip is conveyed in proximity to the first tenter clip closer.

4. The apparatus according to any one of claims 1-3, wherein the second tenter clip closer comprises a freely rotatable disk which contacts the at least partially pivoted cam follower as the tenter clip is conveyed in proximity to the second clip closer.

5. The apparatus according to any one of claims 1-4, wherein the conveyor in the stretching region is configured for the tenter clips to travel in divergent paths to stretch the web.

6. The apparatus according to any one of claims 1-5, further comprising a pivotable member having a first end and a second end with a pivot situated therebetween, wherein either the first tenter clip closer, the second tenter clip closer, or both are attached to the first end of the pivotable member, the second end of the pivotable member is fixed in position by a force Fi acting in a direction perpendicular to the web's planar surface.

7. The apparatus according to claim 6, further comprising a defective tenter clip which applies an abnormal force F₂ from the cam follower against the first or second tenter clip closer, wherein the pivotable member bears away from the tenter clip until a first torque generated by force F₂ about the member's pivot is equal and opposed to a second torque generated by force Fi about forcing means.

8. The apparatus according to any one of claims 3-7, wherein the cam of the first tenter clip closer has a curved surface that extends upstream in the gripping region and bends away from the web, and a cam face having an upper edge tilted toward the web.

9. The apparatus according to any one of claims 3-8, wherein the cam is metal and the disk is an abrasion-resistant resin.

10. The apparatus according to any one of claims 4-9, wherein the side of the disc of the second tenter clip closer contacts at least partially pivoted cam follower.

11. A continuous process for stretching a polymeric web, comprising

12. An apparatus for stretching a polymeric web, comprising: a driven conveyor comprising tenter clips that hold opposing edge portions of the web and convey the web along a machine direction of the apparatus into a through a stretching region, the tenter clips being adapted to controllably open and close; and at least one pivotable tenter clip opener, the tenter clip opener comprising a fixed cam for at least partially opening the tenter clips in order to release the web and a pivot connected to the fixed cam for pivoting the fixed cam away from the tenter clip.

13. The apparatus according to claim 12, wherein the tenter clip opener further comprises forcing means for opposing the pivoting of the fixed cam.

14. The apparatus according to claim 12 or 13, wherein (a) the tenter clip comprises a clamping surface and a pivotable clamping arm, wherein the clamping arm has a first end comprising a cam follower and a second end comprising a gripping surface for gripping the web between the gripping and clamping surfaces when the tenter clip is at least partially closed; (b) the apparatus further comprises (i) a gripping region upstream of the stretching region, and

15. The apparatus according to any one of claims 12-14, wherein the tenter clip opener is located in a releasing region downstream of the stretching region, and wherein the tenter clip opener further comprises a pivotable member, the pivotable member having a first end attached to the cam of the tenter clip opener, a second end coupled to the forcing means, and wherein the tenter clip opener's pivot is located on the pivotable member.

16. The apparatus according to any one of claims 12-15, wherein the cam of the tenter clip opener has the shape of an elongated rectangular plate or the shape of an elongated wedge.

17. The apparatus according to claim 16, wherein the cam and the cam follower contact at a camming surface of the plate, and wherein the camming surface is an arcuate curving laterally away from the film from the plate's first end to the second end.

18. The apparatus according to claim 17, wherein at least one section of the arcuate has a parabolic, circular, elliptical, or hyperbolic curvature.

19. The apparatus according to claim 15, wherein the forcing means comprises one or more of a spring or a piston driven by a fluid or gas.

20. The apparatus according to claim 15 or 19, wherein the forcing means bears on the downstream end of the cam of the tenter clip opener and wherein the downstream end of the cam of the tenter clip opener pivots away from the tenter clip's cam follower as the cam forces the cam follower, the pivoting being opposed by the forcing means.

21. The apparatus according to any one of claims 12-20, wherein the tenter clip opener further comprising at least one mechanical limit for restricting movement of the cam about the tenter clip opener's pivot to an angle of +/- 45° from equilibrium.

22. A continuous process for stretching a polymeric web, comprising

(e) contacting in the releasing region the cam followers of opposed sequential pairs of the closed tenter clips with at least one pair of opposed clip openers in order to at least partially open the tenter clips and thereby release the gripped successive portions of the web, the clip openers comprising a fixed cam for at least partially opening the tenter clips in order to release the web and a pivot connected to the fixed cam for pivoting the fixed cam away from the tenter clip.

23. An apparatus for stretching a polymeric web, comprising:

(c) a counter automatically activated by the stop for counting a number of tenter clips conveyed to the tenter clip actuator following activation.

24. The apparatus according to claim 23, wherein the tenter clip actuator is pivotable tenter clip opener, the tenter clip opener comprising a fixed cam for at least partially opening the tenter clips in order to release the web and a pivot connected to the fixed cam for pivoting the fixed cam away from the tenter clip, and forcing means for opposing the pivoting of the fixed cam.

25. The apparatus according to claim 24, wherein

(a) the tenter clip comprises a clamping surface and a pivotable clamping arm, wherein the clamping arm has a first end comprising a cam follower and a second end comprising a gripping surface for gripping the web between the gripping and clamping surfaces when the tenter clip is at least partially closed;

(b) the apparatus further comprises

(i) a gripping region upstream of the stretching region, and (ii) at least one tenter clip closer located in the gripping region, the tenter clip closer comprising a closing cam to rotate the cam follower about the pivot in order to at least partially close the tenter clip and grip the web between the gripping surface and the clamping surface as the tenter clip is conveyed in proximity to the tenter clip closer; (c) the cam of the tenter clip opener rotates the cam follower about the tenter clip's pivot in order to release the web held between the gripping surface and the clamping surface as the tenter clip is conveyed in proximity to the tenter clip opener; and (d) the stop is connected to a load cell or strain gage, the signal from the load cell or strain gage being adapted to activate the counter.

26. The apparatus according to claim 24 or 25, wherein the tenter clip opener is located in a releasing region downstream of the stretching region, and wherein the tenter clip opener further comprises a pivotable member, the pivotable member having a first end attached to the cam of the tenter clip opener, a second end coupled to the forcing means, and wherein the tenter clip opener's pivot is located on the pivotable member.

27. The apparatus according to any one of claims 24 - 26 , wherein the cam of the tenter clip opener has the shape of an elongated rectangular plate or the shape of an elongated wedge .

28. The apparatus according to claim 27, wherein the cam and the cam follower contact at a camming surface of the plate, and wherein the camming surface is an arcuate curving laterally away from the film from the plate's first end to the second end.

29. The apparatus according to claim 28, wherein at least one section of the arcuate has a parabolic, circular, elliptical, or hyperbolic curvature.

30. The apparatus according to any one of claims 24 - 29, wherein the forcing means comprises one or more of a spring or a piston driven by a fluid or gas.

31. The apparatus according to any one of claims 24 - 30, wherein the forcing means bears on the downstream end of the cam of the tenter clip opener and wherein the downstream end of the of the cam of the tenter clip opener pivots away from the tenter clip's cam follower as the cam forces the cam follower, the pivoting being opposed by the forcing means.

32. The apparatus according to any one of claims 24 - 31, wherein the tenter clip opener further comprising at least one mechanical limit for restricting movement of the cam about the tenter clip opener's pivot to an angle of +/- 45° from equilibrium.

33. A method for identifying a malfunctioning tenter clip in continuous process for stretching a polymeric web, comprising

(a) conducting the polymeric web to a stretching apparatus which comprises

(i) a plurality of functioning tenter clips for gripping opposing edge portions of the web and conveying through the stretching apparatus, the tenter clips being adapted to controllably toggle open and close, and the malfunctioning tenter clip which resists such toggling; (ii) at least one tenter clip actuator for toggling the functioning tenter clips closed or open grip or release the web, the tenter clip actuator being adapted for movement away from the tenter clip toward a stop and which contacts the stop when the malfunctioning tenter clip is toggled by the actuator but which does not contact the stop when a functioning tenter clip contacts the actuator, the stop being adapted to prevent further movement of the tenter clip actuator; and

(iii) a counter automatically activated by the contacted stop for counting a number of tenter clips conveyed to the tenter clip actuator following activation;

34. The method according to claim 33 wherein the method further comprises (c) halting the conveying of the tenter clips.

35. The method according to claim 33 or 34, wherein the stretching apparatus further comprises

(iv) a pair of continuous rails disposed on either side of the web for conveying the tenter clip from a gripping region downstream to a stretching region and continuing downstream to a releasing region, wherein at least one actuator in the gripping region is a tenter clip closer and wherein at least one actuator in the releasing region is a tenter clip opener;

(v) at least one reference tenter clip ; (vi) a reference clip sensor that senses the reference clip ;

(vii) a second counter for providing the number of tenter clips that have passed the second counter following the reference clip;

(viii) a data processor for reading the second counter and identifying each of the plurality of tenter clips with respect to the reference clip; and wherein the method further comprises

(e) establishing a correspondence between the numbers from the second counter and each clip, thereby identifying each clip by a unique clip number representing the number of clips between the unique clip and the reference clip, and (f) identifying the malfunctioning clip by its unique clip number.

36. The method according to claim 35, wherein the malfunctioning clip contacts the tenter clip opener, and the unique number of the malfunctioning clip is determined by subtracting the number of clips between the second clip counter and the tenter clip opener, or the malfunctioning clip contacts the tenter clip closer, and the unique number of the malfunctioning clip is determined by subtracting the number of clips between the second clip counter and the tenter clip closer.

37. The method according to claim 35 or 36, wherein the plurality of tenter clips are installed in a pantograph, which has a pantograph arm that can extend and retract freely and a plurality of parallel arms supported by the pantograph arm, which pantograph circulates along said loop-shaped rails; a magnetic reference member on the parallel arm proximate to the reference clip; the reference clip sensor is a magnetic sensor adapted so that the reference member is within the detection range of the sensor but the parallel arm is outside the sensor's detection range.