GRIPPER WITH TOGGLE LEVER ARRANGEMENT

Abstract

An improved gripper with a toggle lever arrangement is characterized by, among others, the following features the gripper comprises a gripper lever which is pivotable with respect to a gripper holder around a gripper axis, the gripper lever is configured as a toggle lever and comprises in addition a first and a second toggle lever leg which are pivotable relative to each other around a toggle lever axis,—in addition a force application unit is provided which acts on the second toggle lever leg pivotable around the toggle lever axis and/or on the toggle lever flap,—the force application unit is thereby configured such that during pivoting of the gripper lever from the release position into the closed- and clamping position thereof, the toggle lever flap initially touches down on the side of the gripper table lying away from the material web while prefixing the material web in this region, before the toggle lever flap reaches the final closed- and clamping position thereof during the remaining pivoting process, in which position it is force-actuated in the direction of the gripper table and holds the material web edge clamped between the gripper surfaces.

Claims

1. Gripper comprising a toggle lever arrangement for a transport system, in particular a stretching system, comprising the following features the gripper comprises a gripper lever which is pivotable about a gripper axle with respect to a gripper mounting, the gripper lever is formed as a toggle lever and comprises for this purpose a first and a second toggle lever arm which are pivotable about a toggle lever axle relative to one another, the first toggle lever arm is pivotable about the gripper axle, the second toggle lever arm comprises a toggle lever gripper on the free end thereof, a gripper base comprising a gripper base surface and a gripping face formed thereon is provided on the gripper mounting, and the two toggle lever arms of the gripper lever are pivotable between an open position and a closed, clamping position in such a way that the gripping face on the toggle lever flap and the gripping face of the gripper base are held so as to be remote from another in the open position and are held so as to be biased in contact with one another so as to fix an edge located in between of a material web in the closed position, wherein the following further features a force application apparatus is further provided, and acts on the second toggle lever arm pivotable about the toggle lever axle and/or on the toggle lever flap, the force application apparatus is formed in such a way that when the gripper lever l pivots from the release position thereof into the closed, clamping position thereof the toggle lever flap is initially placed on the side of the gripper base remote from the material web so as to pre-fix the material web in this region, before the toggle lever flap, during the further pivot process, reaches the final closed, clamping position thereof in which it holds the material web edge clamped between the gripping faces under application of force towards the gripper base.

2. Gripper according to claim 1, wherein the force application apparatus consists of or comprises a magnetic linkage apparatus.

3. Gripper according to claim 2, wherein the magnetic linkage apparatus comprises a magnet or a pole shoe which interacts with a further magnet or a further pole shoe or with ferromagnetic materials.

4. Gripper according to claim 3, wherein the magnet or a pole shoe is fixed to the second toggle lever arm pivotable about the toggle lever axle or to the toggle lever flap.

5. Gripper according to claim 4, wherein the magnet or the pole shoe is provided on the second toggle lever arm in the region of the rear face of the toggle lever.

6. Gripper according to claim 1, wherein the magnets or the pole shoe are mounted on a separate holding device which is stationary relative to the displaceable gripper, and in that the action face of the magnets or of the pole shoe follows a line or curve in space corresponding to the closing movement of the toggle lever flap.

7. Gripper according to claim 1, wherein the action faces of the magnet or of the pole shoe are arranged in such a way that a minimum gap is formed in the closest relative position, which generates maximum attraction forces, between the toggle lever flap or an action part connected thereto and the magnet or the pole shoe.

8. Gripper according to claim 1, wherein the toggle lever flap is held in a defined position in the open position of the gripper lever in that the toggle lever flap preferably strikes a stop and/or orientation piece on the face remote from the material web Viand preferably has a force applied away from the gripper base by way of the force application apparatus on the side facing the material web.

Description

[0053] In the following, the invention is described in greater detail by way of drawings, in which, in detail:

[0054] FIG. 1a is a schematic plan view of a simultaneous stretching system, in which the return side is arranged so as to extend within an oven together with the advance side;

[0055] FIG. 1b shows an embodiment modified from FIG. 1a, in which the return side is separated from the process side and extends outside an oven;

[0056] FIG. 2a is a schematic cross-sectional view through a transport part of a gripper transport unit, which is displaceable along a guide rail by means of a linear motor drive;

[0057] FIG. 2b is a corresponding cross-sectional view through a gripper part rigidly connected to and displaceable by way of a transport part according to FIG. 2a;

[0058] FIG. 3 is a view corresponding to FIG. 2b during the closing process of the gripper lever, showing an intermediate position in which a toggle lever flap is placed on a gripper base merely in a region positioned remote from the material web;

[0059] FIG. 3a is an enlarged detail of the intermediate position according to FIG. 3;

[0060] FIG. 4 is a view corresponding to FIGS. 2b and 3, but after the final closing and clamping position of the gripper is reached;

[0061] FIG. 5 is likewise a view of the gripper lever in a closing and clamping position, but in a view rotated by 90° from FIG. 4, parallel to the plane of a clamped material web;

[0062] FIGS. 6a to 6c are three views illustrating the advantages according to the invention by contrast with a solution known in the art; and

[0063] FIG. 7 is a cross-sectional view, transverse to a guide path, of an embodiment modified from the previous drawings.

[0064] The transport and/or stretching system discussed in the following is described by way of a simultaneous stretching system. The construction of the claimed clamping device (gripper) applies in principle to simultaneous, linear-motor-driven or pantograph systems, but also to sequential stretching systems comprising chain drives or generally to transport systems comprising corresponding grippers and gripper devices. These may be sliding or roller systems.

[0065] A stretching system of this type, shown in FIG. 1a, comprises two symmetrically formed drive systems, which are positioned symmetrically with respect to a central plane of symmetry SE extending perpendicular to the plane of the drawing. FIG. 1a shows the two drive systems arranged symmetrically with respect to the plane of symmetry SE in the drawing direction 1, the material web to be treated, in other words stretched, in particular in the form of a plastics film F, being moved through, in the drawing direction 1, between the two drive systems circulating on closed paths 2.

[0066] An unstretched film F (the term “film” being used in the following even through a treatment web F in general may be correspondingly treated and simultaneously longitudinally and transversely stretched by a stretching system of this type, in such a way that the invention is not limited to a plastics web) enters the stretching system in an entry region ER, where it is gripped and clamped at both edges 8 on the stretching or process side RS by grippers 6 which are discussed further in the following, such as are shown by way of example in FIG. 2b, specifically on the operator side (OS) and on the drive side (DS). The film F is subsequently heated in a downstream preheating zone PH and subsequently supplied to a stretching zone R, so as to be stretched simultaneously in the longitudinal and transverse directions therein. Subsequently, the stretched film F passes through various thermal treatment zones HT, in which the film may also be relaxed. At the output AR of the stretching system, in other words at the end of the exit zone A, the film is gripped by suitable means and subsequently leaves the simultaneous stretching system.

[0067] Otherwise—as is also shown in FIG. 1b—the guide rail may extend differently in the advance region, and thus in the stretching region, and in the return region, specifically in such a way that for example only the guide rail passes through an oven O and is guided back outside the oven on the return side RL. In this regard, reference is made to known stretching systems and associated structures.

[0068] The further construction is to be explained in the following using the example of a linear-motor-driven gripper device, specifically initially with reference to FIGS. 2a and 2b.

[0069] FIG. 2a is a cross-sectional view transverse to the guide rail of a transport part 7, which is rigidly connected via a bridge 8 to the gripper part 6 shown in FIG. 2b to form a unit. The gripper transport unit T is thus subdivided into the gripper part 6 and the transport part 7, the gripper part 6 being carried by way of the transport part 7 and displaced together therewith.

[0070] In the embodiment shown, the gripper part 6 and the transport part 7 are interconnected via a gripper bridge 8, which can be associated with the transport part or with the gripper part depending on point of view. Below this bridge part 8, there is a U-shaped opening which is open at the bottom, and by which the gripper part 6 is slightly separated from the actual transport part 7. However, any other desired constructions are also possible.

[0071] The actual construction of the linear-motor-driven simultaneous stretching system comprising the corresponding linear motor drive is known for example from EP 0 455 632 B1 or DE 44 36 676 C2, to the entire disclosure of which reference is hereby made. The cross-sectional view of FIG. 2a shows the guide and support rail 15, which consists of a horizontal running face 15a, 15b and two vertically orientated running faces 15c, 15d.

[0072] In the present embodiment, at least one pair of running rollers 505 runs on each running face.

[0073] Instead of the aforementioned running rollers or running wheels 505, however, corresponding slide elements 505′ may also be provided, for example slide elements 505′a, 505′b, 505′c and 505′d. Likewise, mixed embodiments using running wheels in part and using slide elements in part are also possible.

[0074] The corresponding transport part is driven by way of linear motors, which comprise stationary primary parts 502 and secondary parts 503 which can move together with the gripper transport parts T. In other words, the grippers, i.e. the gripper 6, along with the transport parts 7 are longitudinally displaced and moved along the guide rail 15, which in this case also simultaneously serves as a transport rail 15 (monorail), by means of the primary parts 502 and the secondary parts 503.

[0075] The aforementioned primary parts 502 are attached in parallel with the guide and support rail 15. The secondary parts 503 consist of the aforementioned permanent magnets 503a, which are each fixed in a holding cage 503b, which is in turn held on the gripper body 6.

[0076] The gripper part 6, which is rigidly connected to the aforementioned transport part, the technical details of which may be derived from EP 0 455 632, is shown in the cross-sectional drawing of FIG. 2b. In FIG. 2b, the drawing direction of the material web or plastics film is denoted MD, in other words the machine longitudinal direction extending perpendicular to the plane of the drawing. The transverse direction TD of the transport or stretching system is also shown, in other words in the direction extending transverse to the material web. Finally, th marks a vector direction perpendicular to the material web plane, in which the thickness of the film or material web clamped in the gripper is orientated.

[0077] The following description is basically identical to all grippers (clamping devices) found on the market.

[0078] The gripper part 6 comprises a gripper mechanism 25 comprising a gripper mounting 25a, which in the embodiment shown is rigidly connected to the transport part 7 via the aforementioned bridge 8 and which ultimately supports the entire gripper mechanism.

[0079] The gripper mechanism 25 comprises a gripper axle 25b, on which the actual gripper lever 25c is held so as to be pivotable about a gripper axle 25b. The gripper axle 25b is usually orientated so as to extend in parallel with the material web plane E, and thus usually more or less in parallel with the guide rail which supports the entire transport part along with the gripper part.

[0080] In addition, in the gripper mechanism, an opening or closing part 25g is provided on the free end of the gripper lever 25c. A mechanical and/or magnetic apparatus for opening and closing the gripper lever may act here, as is disclosed in principle in EP 0 782 499 B1, to which reference is hereby made.

[0081] Finally, the gripper lever 25c is tensioned by means of a spring apparatus 25h, for which purpose the spring apparatus 25h is anchored and/or suspended both on an anchoring point 25i on the gripper mounting 25a and opposite on the gripper lever on a fastening point 25j provided there. This anchoring point 25j is positioned between the pivot axle 25b and the free gripper lever end.

[0082] In the embodiment shown, the gripper lever 25c is formed as a toggle lever mechanism 60 comprising a toggle lever 60′, which thus comprises, in addition to the pivot axle 25b, a further parallel toggle lever axle 60b positioned so as to be offset therefrom.

[0083] As a result, two toggle lever arms are formed, specifically a first toggle lever arm KH-S1, in the longitudinal extension region of which the pivot axle 25b is located, and a second toggle lever arm KH-S2, which is pivotable about the toggle lever axis 60b relative to the first toggle lever arm KH-S1.

[0084] At the free end of the second toggle lever arm KH-S2 there is a toggle lever flap 60c, on the underside of which a gripping face 60d for fixing a material web or a film F is formed.

[0085] The gripper base 61 is located below the gripping face 60d of the toggle lever flap 60c, and also comprises a gripping face 61d comprising a gripper base surface 61S. This defines the clamping plane E on which a material web or a plastics film F, in other words the edge thereof, can be held in a clamped manner.

[0086] The gripper base 61 itself can be anchored and mounted by means of a gripper base mounting 61e using a screw connection 61g to the gripper mounting 25a.

[0087] Finally, an orientation piece 63a comprising a directing face 63b mounted or formed on the gripper mounting 25a is also provided, and interacts with the toggle lever flap 60c, as will be discussed in the following.

[0088] Further, a force application apparatus MK is provided, and is preferably formed as a magnetic force linkage apparatus. For this purpose, on the lower free end of the second toggle lever arm KH-S2 in the embodiment shown, directly on the rear face of the toggle lever flap 60c, a permanent magnet 62M is mounted, and is anchored there by suitable measures. On the rear face of the toggle lever flap 60c, either a further magnet cooperating therewith in attraction or at least a ferromagnetic material is provided, or else the toggle lever flap 60c itself consists of a ferromagnetic material, at least in so far as the aforementioned permanent magnet 60M can exert attractive forces on the toggle lever flap 60c in the manner described in the following. However, the relevant relationships may also be reversed, to the effect that a permanent magnet is provided on the rear face of the toggle lever flap 60c, and together with a corresponding ferromagnetic part can generate attractive magnetic forces on the second toggle lever arm KH-S2. Generally, in this regard reference is therefore merely made to a magnetic force linkage element MK which generates attractive forces.

[0089] In the following, the mode of operation of this embodiment according to the invention is described in greater detail, specifically in the case where a corresponding gripper device along with a transport part 7 and the associated gripper part 6 is supplied for example to the entry of a stretching system, the gripper lever 25c being opened at this entry for example by an electromagnetic opener, such as is disclosed in EP 0 782 499 B1, by means of a magnetic non-positive fit via the opening and/or closing part 25g positioned above.

[0090] The principle described in greater detail in the following is thus suitable both for grippers of simultaneous systems and for sequential systems, regardless of the drive technology used in relation to the transport parts, in other words the gripper transport units T.

[0091] The principle behind the invention is to be explained using the example of a linear-motor-driven gripper according to FIG. 3. The gripper lever 25c is opened at the entry by an electromagnetic opener, such as is disclosed in DE 195 19 095, by means of a magnetic non-positive fit via the opening or closing part 25g.

[0092] To make it possible to thread the film into the gripper 9 without disruption, the toggle lever flap 60c has to be moved into a defined position. For this purpose, the toggle lever is moved into the stop position thereof. In this context, the position of the toggle lever flap 60c provides that the stop face 60e thereof is orientated counter to the directing face 63b of the orientation piece 63a. The gripping face 60d of the toggle lever flap is parallel to the gripping face 61d of the gripper base coating 61S. The spacing of the two faces is configured depending on the thickness of the cast film to be stretched (or generally of a material web F to be clamped), and may for example be several mm. In addition, the toggle lever flap 60c is brought into the working region of the permanent magnet 62M and attracted thereby. The mounting in the axle 60b is configured so as to be very free-moving, so as to provide free movement of the toggle lever flap.

[0093] In FIGS. 3 and 3a, the film is threaded between the gripping faces and the gripper lever 25c is magnetically closed. According to the invention, the magnet 62M now provides that the rear face of the toggle lever flap 60c is initially placed on the edge region Fr of the film F. The placement position of the gripper lever is always placed in the same relative position on the film. The placement on the rear face leads to lower frictional forces when the blade flap is closed. This reduces the risk of the film sliding out during gripping. Since in addition the film is gripped or the gripper is closed very rapidly at high speeds, an undefined fixed position can result in resonances occurring in the toggle lever flap. The oscillation affects the thickness profile of the flexible film in an uneven manner. This leads to uncontrollable thickness fluctuations in the gripping region, and this can lead to the film tearing off or being ripped out (see FIG. 6c).

[0094] The stamp foot 6a, in other words the toggle lever flap 60c, is held in the optimum position thereof during placement on the film by the aforementioned magnet 62M (preferably in the form of a permanent magnet). After being placed on the film, the stamp 60c is rotated by the further movement of the blade flap 25c so as to be positioned on the film F. As the spacing from the magnet 62M increases, the force thereof becomes smaller, and there is barely any effect on the holding force from the magnet.

[0095] The pivot movement into the closed position is carried out until the first and the second toggle lever arm KH-S1, KH-S2 of the gripper lever 25c (blade flap 25c) in the form of the toggle lever 60′ have reached the final closed position shown in FIG. 4, in which the gripping face 60d of the toggle lever flap 60c is positioned in a direct parallel position with respect to the gripping face 61d of the gripper base 61, is held so as to be biased thereon, and thus holds the material web or the plastics film F, in other words in particular the edge Fr of this material or product web or of the plastics film F, clamped in the plane E between the two gripping faces 60d and 61d.

[0096] For this purpose, it is necessary for a gap SP (see FIG. 3a, approximately 0.1 to 0.5 mm) to be maintained between the magnet 62M and the lever flap 60c. If the holding force is too large, the release impulse results in an undesired effect on the film thickness. An additional major advantage over the prior art which may be mentioned is that the magnet system is completely maintenance-free and wear-free.

[0097] FIG. 4 shows the situation when the gripper is completely closed. After placement on the rear face of the gripper on the film edge, the closing angle α (FIG. 3) is reduced continuously, without oscillation and without release impulse, by the magnet 62M until the closed position has been achieved. The film now runs through the preheating zone PH and is subsequently stretched.

[0098] FIG. 5 shows the arrangement during the placement of the stamp foot from the TD direction.

[0099] In other words, during the closing process of the gripper, in a first step the toggle lever flap 60c, which in the initial situation is positioned with a spacing from the gripper base 61 (and is thus preferably orientated in parallel with the plane of the gripper base), is moved onto the gripper base 61 in such a way that the toggle lever flap 60c is only placed on the gripper base 61 on the edge face positioned remote from the material web or from the film F. As the gripper lever 25c is closed, the gripper lever is adjusted further in such a way that the toggle lever flap 60c carries out a pivot movement with a decreasing angle α, until the entire area thereof is positioned on the film, and the gripper base is orientated in parallel therewith, the material web or plastics film F now being held in a clamped manner between the entire area of the two gripping faces 60d and 61d.

[0100] Instead of the aforementioned magnet 62M, a pole shoe may also be used, and like the magnet 62M is mounted on the gripper lever 25c at a correspondingly suitable point, in particular on the toggle lever arm KH-S2 or else on the toggle lever flap 60c, and subsequently cooperates with a corresponding ferromagnetic material or magnet shoe or pole shoe mounted on the associated other part, as was explained above.

[0101] The effectiveness of the measure according to the invention has been demonstrated in comprehensive tests. FIG. 6a highly schematically shows a film piece F comprising the film edge Fr. The gripping face 60dF on the film is intended to correspond approximately to the gripping faces 60d and 61d of the toggle lever gripper or to the gripper base. In a prior art lever arrangement, the film is thinned considerably under the gripping faces, and the material under the area 60dF is ripped out by the stretching force. These extremely thin points were denoted KF, and were located below the gripping faces 60d, 61d when the stretching forces were introduced. In particular these thin points and the thinning of the material of the clamped material web and in particular of the plastics film below the gripping face 60dF mean that stretching forces can no longer be exerted. The film is completely ripped out of the gripper, or tears in this position.

[0102] A similar situation applies in FIG. 6b, but the extremely thin point KF is still located within the gripping region. This improvement was achieved simply by an improved placement position but without the continuous reduction of the placement angle α under the magnet effect.

[0103] The greatly improved situation of FIG. 6c is achieved by the inventive solution. The gripping face 60dF now has a uniform thickness. The material is not pulled out under the gripper 6. The given shape WF is not a thin point KF in this case, but rather a material bead WF, which is produced by the stretching in the TD and MD directions.

[0104] In the following, reference is made to a modified embodiment by way of FIG. 7.

[0105] The embodiment of FIG. 7 differs in the functional construction of the magnetic linkage device MK. By contrast with the previous embodiment, in the variant of FIG. 7 it is provided that the magnet or permanent magnet 62M disclosed and shown in the previous embodiment is not provided and/or mounted directly above the toggle lever flap 60c in the second toggle lever arm KH-S2, but instead in the form of a pole shoe 62a.

[0106] In the embodiment of FIG. 7, an arrangement is shown comprising a pole shoe 62a which is mounted in a stationary manner on the closing construction OC of the gripper.

[0107] In principle, the pole shoe is a rectangular metal sheet, on the upper face of which a plurality of rectangular magnets 62M are attached. The relevant magnets may be provided in a sufficient number and/or size. The polarity of the magnet arrangement is based on the polarity of the closing/opening arrangement OC. Normally, the X pole is directed towards the pole shoe sheet. The spacing SP between the pole shoe edge and the toggle lever flap 60c is 1-6 mm. The pole shoe edge follows the closer contour OC in terms of direction.

[0108] As a result of the pole shoe construction, closed magnetic field lines are generated, which extend over the exit face of the pole shoe edge and the end face 60′c through the toggle lever flap 60c, and thus hold the toggle lever flap 60c so as to be orientated in accordance with the mode of operation, as was explained by way of the previous embodiment.

[0109] The pole shoe 62a and the magnets 62M are fixed to the opening construction OC using a mounting 62b. The opening mechanism OC actuates the gripper lever 25c, in other words in accordance with a construction such as is known in principle from EP 0 782 499 B1 for actuating a gripper lever to open and close.

[0110] In a deviation from the pole shoe itself, however, a normal magnet may also be provided at a corresponding point, the south pole or north pole or another action face of which is orientated towards the end face of the toggle lever flap 60c so as to generate appropriate attraction forces. In this case too, a small gap or spacing SP should preferably be present between the defining faces of the pole shoe and the defining faces of any provided magnet and the toggle lever flap 60c or the end face 60′c of the toggle lever flap 60c, so as to make possible a similar force progression during the closing process to what was explained by way of the previous embodiment.

[0111] In principle, the gripping faces 60c and 61S are selected as desired within wide ranges as regards shape, configuration including surface configuration, size etc. In other words, the corresponding gripping faces 60c and 61S may preferably be round, polygonal or oval or have any other shape. Preferably, rounded edges are used for the gripping faces, in which case roundings should be configured without a transition, for example at radii of from 0.5 to 5.0 mm, preferably at a radius of r=1.5 mm.

[0112] Preferably, EPDM which is vulcanised on is used as the material for the gripping faces 60c and/or 61S. However, any other high-temperature-resistance and wear-resistant material may be used, such as Viton, polyurethane, bronze, brass or the like. The material may be attached to the toggle lever flap 60c and/or to the gripper base 61e. The connection is preferably provided by vulcanisation, but screwing, gluing, riveting etc. are also possible.

[0113] Therefore, to form the contact face, in general any material may be used which has a hardness of at most the hardness of the thermoplastic synthetic resin film to be stretched. The surface and structure (for example Ra, Rz) depends on the material pairing.

[0114] In the solution according to the invention according to FIGS. 2b to 6, a round magnet D7x3 (neodymium) is preferably glued in. The polarity is dependent on the polarity of the opener/closer OC. Normally, the N pole is located outwards towards the toggle lever flap.