FR2487779A1 - - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR SOLIDARIZING A CONTINUOUS BAND ON A LOAD. WE CARRY OUT AN INITIAL PHASE OF PROGRESSIVE DELIVERY OF THE BAND AND THE LOAD IN REGARD TO AND NEAR ONE OF THE OTHER IN PARTICULAR THE BAND IN RESPECT OF THE AREA OF RECEPTION OF THE LOAD AND THEN A FINAL PHASE OF PROGRESSIVE APPLICATION RECIPROCAL BAND AND LOAD TO ENSURE THEIR SOLIDARIZATION. BEFORE THE FINAL PHASE, AN INTERMEDIATE PHASE OF PROGRESSIVE DEPOSIT OF A SOLIDARIZATION MATERIAL ON THE BAND AND OR THE RECEPTION AREA.

Description

METHOD OF SOLIDARIZING A BAND CONTINUES ON A

CHARGE.

  The present invention relates to a method and a

  machine for securing a continuous band on a load.

  The loads to which the process of the machine according to the invention applies have, in particular, a generally parallelepipedal shape, the dimensions of which can vary within quite wide limits. The band considered is

  generally narrow, and placed in particular longitudinal-

  and / or transversely on the load, therefore on its

  faces or on three sides, the middle part of which

it.

  Methods and machines for

  Dare a continuous band on a load. In a first

  known embodiment, a special, adhered strip is used.

  sive on one of its faces, it gradually brings the band and the load facing and close to one another, including the band facing the load receiving zone and then performs a reciprocal application of the band and load to ensure their joining, thanks to the adhesive which is provided with the band. A machine for carrying out this method comprises means for storing a web, in particular in the form of a web, means for progressively feeding the web associated with the storage means, means for progressively feeding the web. the load such as a conveyor belt or the like, means for reciprocating the web on the load including in particular pressing rollers and means for cross-cutting the web at length. This known method and this machine have certain drawbacks

  the adhesive is generally evenly distributed over the

  tality of the tape, it is not conceivable to provide an impression of the tape before its application, because of the adhesive, it is not conceivable to carry out the drawing or retraction of the tape in particular in the case

  a load whose faces are not completely closed.

  Finally, this known method and machine involve the use of

  trade-specific bands and not any other

be material.

  Also known is a method and a machine which uses a tape previously coated with a dehydrated glue such as gum arabic. In this process, we quench

  strip it in water before applying it on the load.

  This method therefore does not make it possible to escape most

  disadvantages mentioned above. In addition, the use

  Such a band involves supports compatible with dehydration. Finally, such strips can not be used with certain charges previously coated with a plastic film. Also, a machine for implementing this method involves operating with

  a band moving essentially in the vertical direction.

  The present invention aims to remedy these inconveniences.

  by proposing a process and a machine of solidari-

  a continuous strip on a load in which we can use any type of tape including any material that is not previously coated with a dehydrated glue

  or an adhesive. This process and this machine according to

  vention also make it possible to apply an impression, which

  that it be, on the band, on both sides of this one.

  The method according to the invention also aims at allowing a discontinuous connection of the band and the load, at

  place of the continuous joining of the known methods. In-

  end, an objective for a machine according to the invention is

  it can operate both vertically and horizontally

  tal. These objectives are achieved by the joining method according to the invention in which an initial stage of progressive feeding of the bandage is first carried out.

  and the charge facing each other in close proximity to each other,

  the band next to the reception area of the car-

  and then a final phase of progressive and reciprocal application of the band and the load for

  ensure their solidarity. Before the final phase, we

  reads an intermediate phase of progressive application of a fastening material on the strip and / or the receiving zone. A machine according to the invention comprises

  means for storing a band, means for progressively feeding

  of the band associated with the storage means, means for progressively feeding the load, means for reciprocating the band on the load, means for cross-cutting the band and means for applying a band.

fastening material.

  The other features and advantages of the invention

  will result from the description that will follow as a reference

  in the accompanying drawings in which: - Figure 1 is a schematic perspective view of a

machine according to the invention.

  - Figures 2 to 7 are six schematic side views of the

  machine according to the invention in different operational phases.

  res corresponding to the phases of the process according to the invention.

  According to the invention, there is provided a method of

  joining a continuous strip 1 on a load 2.

  The load 2 is in particular a case or a case.

  Its form is notably and not exclusively parallelepiped-

  than. The charge 2 is bare or covered with a film in particular

  made of plastic The dimensions of the load 2 can

  may vary within fairly wide limits. In the remainder of the text, reference will be made by way of nonlimiting example to a load 2 of parallelepiped shape having a lower face 3, an upper face 4, an upstream vertical face 5, a downstream vertical face 6 and two vertical faces

lateral 7.

  The band 1 has two faces: the outer face or front 8 and the inner or reverse side 8a. By convention, it is considered that the backside Sa of the band 1 is applied to the load 2, the front side 8 being on the visible side. Band 1 is

  intended to be placed on the load 2 in an area of

  ception 9 of this also in the form of a strip, extends

  on at least one of the faces 3, 4, 5, 6, 7 in particular

  bind on four adjacent faces two to two opposite.

  The method and the machine according to the invention are

  in the case of a load 2 with a zone of

  unique ception, that is to say a single band or

  contrary to several zones 9 and thus several bands,

  whether or not the same faces, in particular orthogonal

they.

  In the rest of the text, reference will be made to the case of a strip 1 covering the lower part of the upstream face 5, the lower face 3, the lower part of the downstream face 6. Any other embodiment between

  naturally in the context of the invention.

  According to the invention, the band 1 can be the subject of many variations of execution. In the first place, the constituent material of the strip 1 may be of a nature

  varied: paper, plastic, metal, textile, etc.

  In the second place, the band 1 is, according to the invention, no

  previously coated with an adhesive or a dehydrating glue

  ted. Thirdly, band 1 can be subject to many variations as to its form namely

  on the one hand, its longitudinal edges which can be rectilinear

  gnes or not and on the other hand its faces 8, 8a which can be full or pierced holes or indentations, the band 1

  remaining nevertheless continuous in longitudinal direction. In fourth

  In my case, the qualities of the material constituting the strip can also be the subject of numerous variants, this material being able to be either substantially inextensible, or stretchable, or retractable. Fifthly, the band 1 can be the subject of many variations with respect to its possible treatment namely, for example, it can be printed or not, the two faces 8,8a being regarded as equivalent to such a treatment. Band 1 normally has some

  flexibility allowing it to be folded in particular to

  open two adjacent inclined faces, particularly at right angles

  2. However, band 1 may

  This band is only interested in a single face of the load 2. Sixthly, the presentation mode of the tape 1 can be the subject of many variations: a general mode of presentation is that of a coil 10. Nevertheless, it is conceivable

  other modes that also fall within the scope of the invention.

  Thus, the versatility of the process and the

  according to the invention with regard to band 1 is

  nied. In the process according to the invention, an initial stage of progressive feeding of the strip is first carried out.

  1 and load 2 facing and near one of the other

  in particular, the back 8a with regard to the zone 9. Then, a final phase of progressive and reciprocal application of the band 1 and the load 2 to achieve their joining. Progressive nature of the intake phase and the application phase is understood to mean that each

  of these phases successively concerns

  adjacent longitudinal bands of Band 1 and more

  element of a strip between an initial free end portion 11 and a terminal free end portion 12,

  after cross-section of band 1 as will be seen later

térieurement.

  The initial character of the phase of ame-

  and final character of the application phase the fact that for a given elementary section, the feed phase precedes

the application phase.

  In the process according to the invention, before the final phase of application, an intermediate phase of gradual deposition of a bonding material is carried out on the strip 1 and / or the zone 9. The progressive nature of the phase

  intermediary means in the same way as for the

  his initials and finals ie successively for

  adjacent longitudinal elementary sections of the ban-

  of 1 and / or zone 9. The intermediate nature of the deposit phase means that this phase takes place chronologically before the final phase, for an elementary section.

  band 1 and / or an elementary segment of zone 9 cor-

  corresponding to this elementary band section 1.

  Preferably, the intermediate phase of

  pote intervenes chronologically after the initial phase

  feed. However, it is also part of the

  vention the case of a deposit phase that is prior to or simultaneous with the supply phase, particularly in the case of a deposit phase concerning zone 9 of charge 2 and not the

band 1.

  The intermediate deposit phase is either continuous

  in time, for a data load, either discontinuous.

  The intermediate deposit phase concerns all or only part of the surfaces of the backside 8ade the band I and /

or zone 9 of charge 2.

  In the case of a filing phase concerning only

  part of these surfaces, this part is called the joining zone. This securing zone may consist of a succession of points that are distinct from one another and / or at least one line or strip and / or a succession of elementary zones of joining and / or

  a combination of these different variants.

  In the case of a zone of solidarity comprising

  at least one line or strip, it may be, relative to the longitudinal axis of the strip 1, longitudinal,

transverse or inclined.

  In a preferred embodiment, not limiting and illustrated by the figures, the deposition phase occurs after the initial phase, is continuous in time for a given load 2, exclusively relates to the band 1 and not the load 2 (the material of solidarization being deposited on the strip 1 and not on the load 2),

  is continued on the reverse side of band 1, concerns a

  only on the reverse side 8a the zone of

  two thick lines or longitudinal threads adjacent the longitudinal edges of the strip 1. The method according to the invention may comprise before the final phase of application, a drawing phase of

  the strip 1, the latter being designed to be stretched.

  This variant is particularly interesting in

  some particular applications, particularly in the case

  of an unclosed load 2, the band 1 coming to realize this

closing.

  According to another variant of the process according to

  vention, it comprises a retraction phase of the band 1 in particular after the final phase. This retraction phase is in particular carried out by heating, the strip 1 being made of a heat-shrinkable material and the material of

  solidarization 2 being heat-fusible.

  According to another possible variant of the method according to the invention, it comprises a printing phase of the band 1, progressive and subsequent to the initial phase but prior to the intermediate phase. According to the invention, this printing phase may interest front 8 and / or

the back 8ade the band 1.

  The present invention also relates to a

  China for securing a continuous band on a load and the implementation of the method described above which comprises means 13 for storing the band 1; means 14 for gradually feeding the band, associated

  storage means 13; means for progressively feeding

  ve of charge 2; means 16 for reciprocating the band 1 and the load 2; and cutting means 17

transverse of the band 1.

  According to the invention, the machine further comprises means 18 for depositing a bonding material on

  the band 1 and / or the receiving area 9 of the load 2.

  This machine can be placed either horizontally

(case in point) or vertically.

  This machine can be the subject of many embodiments depending on the type of strip 1 used, the type of load 2 used and the receiving area 9. It will be sufficient to describe later a form

  of preferential but not exhaustive execution of the invention

  tion, with reference to the process already described, the other variations

  you are within the reach of the skilled person.

  The storage means 13 are provided for example to receive a tape reel 10 and are constituted for example by a journal pivotally mounted about an axis 19

  extending transversely with respect to the strip 1.

  All the axes that will be discussed in the following

  text are, unless otherwise stated, parallel to axis 19.

  The belt feeding means 14 may comprise, for example, a belt drive roll 20, with an axis 21

  cooperating with a matching roller 22 of axis 23.

  The counter-roller 22 is likely to be in two positions respectively active and

  passive. In the active position, the roller 22 is applied

  than on the roller 20 and driven by it. In the state

  passive, the roller 22 is separated from the roller 20. The control

  of the state of the roller 22 is ensured by means of em-

clutch 24.

  The line of contact 25 of the two rollers 20, 22 is preferably located in a window 26 of means

guide 27 of the band 1.

  The guiding means 27 may be subject to

  many forms of execution. They present themselves, for example,

  ple in the form of two parallel surfaces and spaced transversely from each other, placed opposite one another, defining a guide space 28 for the band 1, profiled shape to the path that we wish to see follow by the strip 1. For example, the space 28 has an upstream opening upstream opening 29, an upstream portion adjacent to the opening 29, flat, horizontal, where is located the window 26, a downstream portion 31 curved in particular concavity turned upwards, for example in the form of a quarter circle and finally an extreme downstream opening 31 in particular placed horizontally and in the vicinity

supply means 15.

  The journal of the storage means 13 is rotatably mounted about the axis 19 and carried by the frame of the machine (not shown). The training roll

  is a driving roller, capable of being driven in

  in the direction allowing unwinding of the coil 10.

  The counter-roller 22 is pivotably mounted at the end of a support 33 pivotally mounted in

  its median part about an axis of articulation 34 and

  tilted at its opposite end portion about an axis 35 to a control rod or the like 36 forming part of

clutch means 24.

  The pivoting of the support 33 around the axis 34

  mnet- to the matching roller 22 to be moved closer or otherwise removed from the drive roller 20 as previously indicated. The means 15 for supplying the load comprise a

  bearing surface 37 of the load 2 and the driving means

  of it. In one possible embodiment, the bearing surface 37 serves as drive means, the feed means 15 taking the form of a feed band. In the

  case represented by the figures, there is shown schematically

  the bearing surface 37, the drive means being omitted for clarity of the drawing. These means may however be in the form of pushers acting on the upstream vertical face 5 of the load or pushers in transverse movement maintaining the load 2 by side vertical faces 7 or in any other manner. In the illustrated case

  in the figure, the bearing surface 37 is placed horizontally

  is lying. As indicated above, the machine can also be designed with a vertical support surface 37. In the

  embodiment illustrated by the figure, the surface area

  then 37 is placed at the top of the machine, the means 13, 14, 16, 17, 18 being placed substantially below or at the same level as the bearing surface 37. The supply means 14 of the strip 1 are coupled to the supply means 15 of the load 2 so that the strip 1 is fed simultaneously to the load 1 or at least that the supply of the load 2 controls that of the strip 1. For this purpose, it is for example provided a control roller 38

  axle 39, protruding slightly above the surface

  this support 37, placed in the upstream portion 40 of the surface

  of support 37 so that the passage of the load by

  horizontal clearance on the bearing surface 37 from upstream to downstream in the direction of the arrow F causes the pivoting of the

  roll 38 about the axis 39 in the direction of the arrow f.

  Kinematic drive means 41 are associated with the roller 38 and the roller 20. These means 41

  example the form of belt, pinion, etc.

  The clutch means 24 are for example in the form of a pivoting plate, hinged about an axis 42, having an arm 43 which is articulated about an axis 44 the link 36. The plate 24 is placed in the middle portion 45 of the bearing surface 37, at the location of the bearing surface 37 to be controlled by the load 2 as will be seen. Preferably, this plate clutch means 24 extends downstream

  relative to the hinge pin 42, the arm 43 being di-

ruled towards 1 upstream.

  The bearing surface 46 of the plate, in particular its upper surface is slightly inclined with respect to the bearing surface 37, projecting from it on its free downstream edge 47, the upstream free edge 48 being placed at a level at most equal to that of the bearing surface 37 so as not to hinder the displacement of the upstream load 2

  downstream. The displacement of the load 2 on the surface of ap-

  in the direction of the arrow f is therefore such that its lower face 3 firstly drives the roller 38 causing the driving roller 20 to be driven and then pressing the plate of the clutch means 24 which causes, through the rod 36 and the support 33 the application of the counter roller 22 on the roller

  20 and the effective training of the band 1.

  Preferably, the bearing surface 37 thus comprises a median free space 49, longitudinal, to allow the passage of the drive rollers 38 and the plate

clutch means 24.

  The cutting means 17 are for example in the form of cutting knives placed transversely to the right of the guide space 28, the guide means

  27 having a transverse opening 50 for this purpose

  between the upstream 30 and downstream 31 parts.

  The clutch means 24 are associated with elastic return means requesting the counterpart roller

22 to his passive position.

  The application means 16 may be subject to numerous alternative embodiments. They may comprise for example one or more pressure rollers rotatably mounted on pivotally mounted arms, biased towards the corresponding face of the load 2. In the

  In this case, these means 16 comprise an axis 51

  said downstream of the machine, supporting two arms 52a, 52b, pivotally mounted, themselves supporting at their ends two rollers 53a, 53b. Unrepresented elastic means such as springs or the like urge the rollers 53a, 53b to rest so that their line of tangency is situated on the bearing face 37, these rollers 53a, 53b being placed on either side of the bearing surface 37 so as to be able to interfere with the load 2, in particular with the downstream vertical face 6 and the lower face 3. These elastic means also urge the rollers to

  are applied to the corresponding faces of the load.

  The rollers 53a, 53b can pass from

  other of the bearing surface 37 thanks to the free space 49.

  The deposition means 18 are placed at right angles and in the vicinity of the path followed by the strip 1, in particular in the immediate vicinity of the downstream end opening 32 of the guiding means 27. The depositing means 18 are placed

  the upstream side of band 1 in relation to the direction of movement

  2. The depositing means 18 are placed

  in the immediate vicinity of the guide means 27.

  The deposition means 18 comprise means for storing a bonding material, not shown, and means for dispensing this material in communication with the storage means, taking the form in particular

  of nozzles 54 carried by a support 55 on which is connected

  the supply duct 56 of fastening material.

  The deposition means 18 may be the subject of many embodiments in the particular form given to the deposition of fastening material. Thus, the deposition means 18 may comprise one or more nozzles 54 and in particular two nozzles placed laterally with respect to the strip 1. As can be seen in the figures, the means 18 are placed in close proximity to the surface

  37 so that the strip 1 having received the material

  the network is ready to be rapidly

on the load 2.

  The machine finally comprises control means

  57 in the form of contactors placed on the means of

  born 2 of charge and commanding the functioning of the means

cutting 17.

  The operation of the machine will be described in

  Referring to Figures 2 to 7: In Figure 2, the load 2 is upstream of the machine just before interfering with the roll 38. The band 1 is stopped, its initial part being at the place of the downstream aperture 32. The counter roller 22 is applied to the drive roller and the two rollers 53a, 53b are placed against each other.

  the other as indicated previously.

  The load 2 resting by its lower face 3 on the bearing surface 37 is driven in translation from upstream to downstream in the direction of the arrow F and is interfered by its lower face 3 on the roller 38 by driving it in rotation in the direction of the arrow f as illustrated in FIG. 3. The rotation of the roller 38 causes that of the

  driving roller 20 in the direction of arrow F1.

  The counterpart roller 22 being applied to the roll is also rotated in the opposite direction along the arrow f3 which causes the scrolling of the

  At the same time, the depositing means 18 are

  dice and implemented. Strip 1 passes against the nozzles 54

  which deposit on the verso8a the fastening material.

  The movement is prolonged until the load 2 comes to interfere with the clutch means 24 in particular

  resting on the bearing surface 46 which causes the disengagement

  age of the counter roller 22 and thus the stopping of the paring of the band. Simultaneously, the initial free end portion 11 of the band 1 is applied to the load 2, especially the zone 9, in particular on the vertical face

  downstream 6 in the vicinity of the lower face 3. (Figure 4).

  The translational movement of the load 2 is

  pursued. The disengaging means 24 continue to maintain

  counterpart roller 22 spaced apart from the drive roller.

  1. The load 2 provided with the band 1 then comes into

  to interfere with the means of application 16, in particular the

  rollers 53a, 53b so that the strip 1 is correctly applied.

  2. The band 1 is then driven by the load 2, this movement being made possible by the fact that

the spool support journal 10 is freely rotatably mounted

  tion and that the counter roller 22 is disengaged. The unwinding of the strip is accompanied by a scrolling thereof facing the deposition means 18 including nozzles 54 for the deposition of the fastening material on the back 8 of the strip 1 which is then applied to the

charge 2.

  The roller 53a firstly applies to the downstream vertical face 6 of the load 2 and then to the lower face 3. Subsequently (FIG. 6) the load 2 has passed the bearing surface 46 and the plate of the disengaging means 24 is released. The roller 22 is therefore applied to the roller

  20. However, the drive control roller

  38 is not trained and therefore Band 1 is not

  not driven by the means 20, 22 but by the load 2.

  The control means 57 are then controlled by the

  ge 2, in particular by one of its faces in particular the upper face 4 which allows the implementation of the means

cutting 17.

  Finally, (FIG. 7) the translational movement of the load 2 is completed, the end free end portion 12 of the band 1 being applied to the load 2, in particular by

  53b applied to the downstream vertical face 6, in particular

  in the vicinity of the underside 3.

  The bonding material used in the

  yielded according to the invention is deposited (and stored previously) in the liquid state, pasty or semi-pasty. For this purpose, the material storage means may comprise means

  of heating. This solidarization material is in itself suf-

  to ensure the joining (without the need for further processing such as soaking for a glue

  dehydrated). Preferably, the material of solidarisa-

  tion is fast-setting and in this case the means of

  are placed in the immediate vicinity of the reception zone 9.

  This fastening material can be the subject of numerous variants such that they are compatible with the material of the strip 1, the material of the load 2

or that of its coating.

  For example, the joining material can be

a type hot melt glue.

  Where appropriate, the nature of the solidarising material

  tion is chosen according to its possible action properties on the strip 1 or the load 2, including a drawing effect. Naturally, the invention can be the subject of numerous alternative embodiments, in particular, it goes without saying that any form of deposition of the solidarization material is part of the invention (deposition, coating, spraying,

  etc ...) as well as the means 18 associated.

Claims (22)

  1. A method of joining a continuous strip to a load in which an initial phase of gradual feeding of the strip and the load is first carried out.   and close to each other, especially the band in re-   keeping the load receiving area and achieving   then a final phase of progressive and   ciproque band and load, to ensure their solidarity, characterized by the fact that before the phase   final stage, an intermediate phase of progressively   sif of a bonding material on the strip 1 and / or the reception area 9.   2. Method according to claim 1 characterized in that the intermediate phase occurs after the initial stage.   3. Process according to any one of the claims   1 and 2, characterized in that the intermediate phase   deposit is continuous in time for a charge 2 don- born.   4. Process according to any one of the claims   1 and 2, characterized in that the intermediate phase   deposit is discontinuous in time for a given charge.   5. Process according to any one of the claims   1 to 4, characterized in that the intermediate phase   deposition is continuous on tape 1 and / or charge 2.   6. Process according to any one of the claims   1 to 4, characterized in that the intermediate phase   deposit is discontinuous on band 1 and / or charge 2.   7. Process according to any one of the claims   1 to 6, characterized in that the intermediate phase   filing date concerns the whole of band 1 and / or from the reception area 9.   8. Process according to any one of the claims   1 to 6, characterized in that the intermediate deposition phase concerns only part of the strip 1 and / or   the reception zone 9, called the securing zone.   9. Process according to any one of the claims   1 to 6 and 8, characterized in that the zone of attachment comprises a succession of points which are distinct from one another and / or at least one line or strip and /   or a succession of elementary zones of solidarity.   10. Process according to claim 9, characterized   by the fact that the line or strip of the zone of solidarity   is longitudinal or transverse or inclined by   ratio to band 1 and / or receiving area 9.   11. Process according to any one of the claims   1 to 10, characterized in that before the final phase of application of the strip 1 and the load 2,   performs a stretching phase of the band 1.   12. Process according to any one of the claims   1 to 11, characterized in that it comprises a retraction phase of the band 1, in particular posteriorly in the final phase.   13. Process according to any one of the claims   1 to 12, characterized in that it comprises a printing phase of the band 1 after the initial phase.   14. Process according to any one of the claims   1 to 13, characterized in that a band 1 is used   initially not coated with a bonding material.   15. Process according to any one of the   cations 1 to 14 characterized by the fact that a bonding material is used in the form of an adhesive hot melt.   16. A machine for joining a web contir-l bare on a load comprising means for storing a tape; means for progressively feeding the strip, associated with the storage means; means for progressively feeding the load; means of reciprocal application of the band   and the charge; characterized by the fact that it comprises   In addition, means 18 for depositing a solid material   on band 1 and / or the reception area 9 of the charge 2.   17. Machine according to claim 16 characterized in that the depositing means 18 are placed in the right   and near the path of the band 1.   18. Machine according to any one of the claims   16 and 17 characterized by the fact that the deposition means 18 are placed on the upstream side of the strip 1 with respect to the direction of translation of the feed means 15 of the load 2.   19. Machine according to any one of the claims   16 to 18 characterized in that the depositing means 18 are placed in the immediate vicinity of guide means of the band 1.   20. Machine according to any one of the claims   16 to 19, characterized by the fact that the means of deposit   include means for storing a solidifying material   and distribution means of this material in communication with the storage means, in particular under the shape of nozzles 54.   21. Machine according to any one of the claims   16 to 20 characterized by the fact that along the bearing surface of the load are placed from upstream to downstream a   driving control roll 38 and means for   clutch, the roll 38 being coupled to a roll of   20 of the band 1 and the clutch means being connected by members 43, 46, 33 to a counterpart roller 22 may be pressed on the roller   drive 20 or on the contrary spaced therefrom.   22. Machine according to any one of the claims   16 to 21 characterized by the fact that the means of application   16 comprise at least one roller 53a, 53b mounted free at the end of an arm 52a, 52b mounted to pivot about I at the end of an arm 52a, 52b pivotally mounted around of an axis 51.