Patent Publication Number: US-6910408-B2

Title: Linear drive with no connecting rod

Description:
This application claims priority based on an International Application filed under the Patent Cooperation Treaty, PCT/EP02/00740, filed on Jan. 25,2002, and German Patent Application No. DE 101 09 482.5, filed on Feb. 28, 2001. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a piston rod-less linear drive comprising a housing, which has a slot aligned longitudinally and having a movable force coupling member extending through it, the outer opening of the slot being provided with a covering means having at least one covering band, the covering band having an attachment section fixed to the housing on a first longitudinal side of the outer slot opening and a pivotal covering section able to be pivoted between a covering position covering the outer slot opening and a free position permitting the extension of the force coupling member through the slot. 
     BACKGROUND OF THE INVENTION 
     A piston rod-less drive of this type is disclosed in the German patent publication 3,509,891 A1. It possesses a housing in which a piston is arranged able to be slid by fluid power and is drivingly coupled with a power transmitting member extending through a longitudinal slot in the housing. In order to prevent escape of fluid the inner slot opening facing the piston receiving space of the longitudinal slot is provided with a sealing band. At the outer slot opening located at the outer face of the housing a covering band is provided, which extends along the length of the slot and is secured to the housing at an attachment section on the long side to a first longitudinal side of the outer slot opening. A covering section, pivotally connected with this attachment section, of the covering band covers the outer slot opening axially on either side of the power transmitting member in order to prevent the ingress of dirt into the longitudinal slot. At the power transmitting member the covering section is pivoted outward into a hatch-open position in order to permit the extension of the force coupling member through an opening with the function of a hatch. This hatch zone is displaced along the longitudinal slot in accordance with the movement and instantaneous position of the piston and of the force coupling member connected with it. 
     The assumption of the covering position of the covering section is in the case of the known linear drive to be ensured by a sufficient biasing effect, which automatically returns the covering section and also the correspondingly fashioned sealing band, after pivoting into the release position automatically. The biasing effect is produced by a connecting rib integrally made with the covering band and the sealing band, such rib extending through the longitudinal slot. In this case there is however the disadvantage that in the course of time material fatigue will impair reliable assumption of the covering position. 
     Similar problems occur with the covering band based on the same principles in accordance with the U.S. Pat. No. 4,555,980. Departing from the design in accordance with the German patent publication 3,509,891 A1 the covering means in this case however has two covering bands which jointly cover the longitudinal slot. 
     Admittedly there has in the said U.S. Pat. No. 4,555,980 also been a suggestion to secure the covering band by means of a releasable detent connection with the sealing band in the covering position. 
     However in this case a different type of covering band is provided, in the case of which the covering band has its full width moved clear of the longitudinal slot at the force coupling member, something which as regards the force coupling member demands a complicated structure, because it must be provided with a passage for the covering band to run through. 
     SUMMARY OF THE INVENTION 
     Accordingly one object of the present invention is to provide a linear drive of the type initially mentioned, which while having a simple structure ensures reliable covering of the longitudinal slot even after a long period of use. 
     In order to fulfill this aim detent means are provided on the pivotally moving covering section for releasable detentwise locking in the covering position and actuating means are provided kinematically coupled with the force coupling member, such actuating means acting on the associated covering band in order to bring about a detent locking effect. 
     The covering means is accordingly designed with at least one covering band, which at the instantaneous position of the force coupling member is only lifted clear on one longitudinal side from the longitudinal slot or, respectively, from the housing defining it. This does offer the advantage that there is no need for complex channel-like passages, otherwise required, in the force coupling member for the covering band. The detent connection ensures a reliable dwell of the covering section of the covering band in the covering position, without material fatigue occurring producing any disadvantageous effects. For a reliable detent holding action use is made of actuating means kinematically coupled with the force coupling member and arranged to act on the respective covering band, more particularly on the outer face of the covering band. 
     Further advantageous developments of the invention are defined in the dependent claims. 
     Optimum fixation of the covering band in the covering position is ensured if the detent means are able to cooperate with mating detent means, which are provided on the housing of the linear drive. Nevertheless there is however also certainly the possibility of providing the mating detent means on an additionally provided sealing band for the inner slot opening, something which provides the additional advantage that the sealing band is reliably held in the sealing position. 
     Preferably, the detent means are constituted by a fork-like detent section of the covering section, which is preferably located on the edge part, opposite to the attachment section, and which more particularly cooperates with mechanical detent means, which are constituted by a holding lip extending in the longitudinal direction of the longitudinal slot and located on the second longitudinal side, opposite to the first longitudinal side, of the outer slot opening. 
     It would in principle be possible to so secure the attachment section to the housing of the linear drive that it participates in the pivotal motion of the covering section and accordingly the covering band functions as a pivoting part along its entire width. However a design is preferred in the case of which the attachment section is held immovably on the housing and in which the pivotal motion of the covering section and in which during the relative movement of the covering section a relative movement between the latter and the stationarily mounted attachment section takes place. One of the advantages of this arrangement is that any resilient elasticity of the covering band may provide a contribution to the return force acting on the covering section. 
     The covering band is preferably anchored at the attachment section in an attachment groove, open toward the longitudinal slot, in the housing. Assembly and fitting together takes place more particularly by insertion from the end via one of the two end openings of the attachment groove. 
     The design in accordance with the invention is admittedly more especially suitable for a covering means with only one covering band, which covers the entire width of the longitudinal slot in the covering position. However, it is possible to provide a covering means having two covering bands placed alongside one another, each covering band having a pivotally movable covering section, both covering bands contributing jointly to the complete covering of the longitudinal slot. 
     The actuating means provided for producing the detent connection are preferably located axially on either side of the force coupling member. Furthermore it is convenient to design the actuating means in the form of a component of a guide means kinematically coupled with the force coupling member, which controls the pivoting of the covering section on opening and closing the longitudinal slot. 
     The covering band consists conveniently of elastic plastic material and more especially of elastomeric material. Furthermore, any guide means present is preferably manufactured of plastic material. 
     In the following the invention will be explained with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an end view of a first design of the piston rod-less linear drive with the housing cover removed so that the piston is visible. 
         FIG. 2  shows part of the length of the linear drive in accordance with  FIG. 1  in a perspective representation and omitting the housing. 
         FIG. 3  is an exploded view of the components as viewed in  FIG. 2  but omitting the covering band. 
         FIG. 4  shows the linear drive of  FIGS. 1 through 3  in a cross sectional representation, the plane of section being axially outside the piston and only the housing, the covering band and the sealing band being illustrated. 
         FIG. 5  shows a representation corresponding to  FIG. 4  with the covering section pivoted into the opened or released position, the plane of section extending at the force coupling member, which is not illustrated. 
         FIG. 6  shows in cross section part of a further design of the linear drive, the detent connection being provided between the covering band and the sealing band. 
         FIG. 7  shows a still further design of the linear drive in the case of which there is a covering means having two covering bands. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The piston rod-less linear drive of the working example generally referenced  1  is operated by fluid force and more particularly by compressed air. 
     The linear drive has a housing  2  with a longitudinal extent, wherein a piston receiving space  3  is formed extending in the longitudinal direction is provided having a preferably cylindrical cross sectional configuration. As a rule the housing  2  will comprise a tubular body, more particularly in the form of an extruded tubular section having terminal end covers, which in the drawing are not illustrated in detail. 
     The housing  2  possesses a longitudinal slot  5  extending approximately along length of the housing and which is more especially located in the tubular body  4 . It extends through the wall of the housing  2  in the radial direction in the circumferential part of the piston receiving space  3  so that there is an inner slot opening  6  directed into the piston receiving space  3  and an outer slot opening  7  at the outer side of the housing  2 . Both slot openings  6  and  7  extend in the longitudinal direction of the longitudinal slot  5 . 
     Inside the piston receiving space  3  there is an axially moving piston. At axially spaced positions, preferably at the two axial end parts, it is provided with a respective sealing means  12 , which cooperates with the inner face of the piston receiving space  3  in a sealing manner. Accordingly the piston receiving space  3  is divided up into three axially consecutive space parts, that is to say one middle space part between the two sealing means  12  and two outer space parts each adjoining the piston  8 , which lie between a respective means  12  and the facing end cover of the housing  2  and which have the function of working spaces able to be subjected to fluid pressure. 
     By causing an operating fluid (which is supplied by way of fluid ducts, not illustrated, extending in the housing  2 ) to act in a controlled manner in the working spaces the piston  8  may be caused to move in the longitudinal direction of the housing. The direction of movement is indicated by a double arrow  13 . 
     The linear movement of the piston  8  may be made available outside the housing  2  by a force transfer part  14 , which is secured to a force coupling member  15 , which in turn is kinematically coupled with the piston  8  in the direction  13  of motion. The force transfer part  14  possesses attachment means, not illustrated in detail, for the attachment of one or more objects to be moved. Preferably, the force transfer part  14  is guided externally on the housing  2  by a linear guide means  16  for running in the direction  13  of motion and is supported in the direction perpendicular thereto. Accordingly it is possible to prevent the piston  8  and the force coupling member  15  being subjected to excessive loads due to forces acting on the force transfer part  14 . The force transfer part  14  may be designed in the form of a slide or carriage. 
     The force coupling member  15  may be termed an entraining member and extends-like a rib radially through the longitudinal slot  5 . Attachment means  17 , for example in the form of screws, serve for the attachment on the force transfer part  14 . For the connection with the piston  8  the force coupling member  15  is provided at the end lying within the piston receiving space  3  with a forked holding section  18 , which is plugged into the piston  8  from the longitudinal side thereof. The piston  8  has for this purpose a recess  22  receiving the holding section  18 , and the dimensions of the recess  22  in the direction  13  of motion are equal to the dimensions of the holding section  18  so that there is an interlocking connection effective in the direction  13  of movement. Every axial movement of the piston  8  is accordingly transmitted free of play to the force coupling member  15 . At the same time it is possible for there to be play in and opposite to the insertion direction  23 , indicated by an arrow, of the holding section  18 , such play being between the latter and the piston  8  so that there is an automatic compensation of any lack of parallelism of the piston receiving space  3  and the linear guiding means  16 . 
     The inner slot opening  6  is provided with a flexurally elastic sealing band  24  which has the purpose of sealing off the two working spaces on either side of the piston  8  from the surroundings and preventing escape of the actuating fluid through the longitudinal slot  5 . The sealing band  24  extends along the full length of the longitudinal slot  5  and has its outer sections  25 , which are axially clear of the piston  8 , in sealing engagement with the slot flanks  26 , which delimit the longitudinal slot on either side thereof. The sealing contact is in this case generally in the transition zone between the piston receiving space  3  and the longitudinal slot  5 , the sealing band  24 , as illustrated, being able to extend fully or only partly into the longitudinal  5  from the inside. 
     At the same level as the piston  8  and accordingly in the middle space part between the two sealing means  12  the sealing band  24  is held for part of its length completely clear of the longitudinal slot  5 , that is to say from the slot flanks  26 . The lifted or moved clear section  27  of the sealing band here runs through a deflecting passage  28 , defined in the interior of the piston  8 , such passage extending underneath the force coupling member  15 . It is in this manner that the force coupling member  15  can run through the longitudinal slot  5  without hindrance by the sealing band  24 . Escape of fluid from the piston receiving space  3  is out of the question in this part, because the middle space part is separated by the sealing contact between the sealing means  12  and the sealing band  24  from the adjoining working spaces. 
     The outer opening  7  of the longitudinal slot  5  is provided with a covering means generally referenced  32 . In the working embodiment illustrated in  FIGS. 1 through 6  it comprises a single covering band  33 , which like the sealing band  24  consists of plastic material and has rubber-elastic properties. Preferably, it is a question of a covering band  33  of elastomeric material. 
     The covering band  33  extends along the full length of the longitudinal slot  5  and its purpose is to prevent access of dirt into the slot  5  from the surroundings of the linear drive  1 . 
     Independently of the actual position of the piston the covering band  33  seals of or obiturates the outer slot opening  7  on either side of the piston  8  axially, while at the same time rendering possible passage therethrough of the force coupling member  15 . Unlike the case of the sealing band  24  the covering band  33  is however not completely cleared from the longitudinal slot  5 , or the housing  2  defining it, in the vicinity of the force coupling member  15 . The covering band  33  always remains firmly connected with the housing  2  at one longitudinal side of the longitudinal slot  5  and is only moved clear on the opposite longitudinal side and accordingly directed around the force coupling member  15 . This means that there is the substantial advantage that the force coupling member  15  does not require any complex passage for the covering band  33 , and in fact the band may run past on the outer face of the force coupling member  15 . 
     As regards details the covering band  33  is divided in the longitudinal direction into two band sections adjoining each other at their longitudinal sides that is to say in an attachment section  34  and a covering section  35 . The two sections  34  and  35  are integrally connected together, the connection zone defining a pivotal zone  36  with a pivot axis extending in the longitudinal direction of the covering band  33 . 
     At the attachment section  34  the covering band  33  is fixed to a first longitudinal side  37  of the outer slot opening  7  and is therefore fixed in relation to the housing. For this purpose the attachment section  34  may be designed in the form of a bead and have a larger cross section than the adjoining covering section  35  so that the attachment section may be anchored in an attachment groove  42 , open toward the longitudinal slot  5 , in the housing  2 . In the working embodiment the attachment section  43  is circular in shape and it is seated in a correspondingly formed section of the attachment groove  42 , which merges into the narrower groove opening, through which the covering section  35  protrudes. 
     The transverse dimensions of the attachment section  34  and of the attachment groove  42  are more particularly so matched with each other that the attachment section  34  may be inserted from one end into the attachment groove  42  during assembly. With operation may take place using a light pressing force. 
     The covering section  35  is able to be so pivoted between a covering position indicated in  FIG. 4 and a  released position indicated in  FIG. 5  in relation to the attachment section  34  and accordingly in relation to the housing  2 . The pivoting movement is indicated ba a double arrow at  43 . In the covering position the covering section  35  extends between the longitudinal first side  37  and the second longitudinal side  38  opposite to it of the outer slot opening  7  and accordingly covers the outer slot  7  for its entire width. The covering section  35  may in this case partly or completely extend into the longitudinal slot  5  from the outside. 
     In the released position the covering section  35  is pivoted away from the housing  2  and accordingly uncovers the outer slot opening  7  for the passage or extension therethrough of the force coupling member  15 . 
     The transition between the covering position and the released position is controlled by a guide means  44  kinematically coupled with the force coupling member  15  axially. 
     Its structure is such that it moves the covering section  35  at the same axial level as the force coupling member  15  and in axially adjoining transitional zones  45  into the released position and following this into the covering position. The released position is in this case characterized by a different size of pivot angle of the covering section  35 , which at the level of the force coupling member  45  is at a maximum and in the course of the transitional zones  45  as far as the end of the guide means  44  and the following covering position gradually decreases. 
     A significant feature of the covering band  33  is that its pivotally moving covering section  35  possesses detent means  46 , by the intermediary of which it is releasably held in the covering position. The detent holding action is responsible for a reliable touching contact between the longitudinal edge region  41 , opposite to the attachment section  34 , of the covering section  35  and the housing  2  at the associated second longitudinal side  38 . With the detent action it is possible to achieve a bias effect between the above mentioned components, something which leads to a sealing contact to prevent the ingress of solid dirt or extraneous liquids in a reliable manner. 
     During the linear movement of the piston  8  the covering section  35  of the covering band  33  runs through the above mentioned guide means  22 , the guide means  44  causing both the disengagement and also the detent enclosure of the covering section  35 . 
     In the working examples in accordance with  FIGS. 1 through 5  the detent means  46  of the covering section  35  cooperate with the mating detent means  47 , which are provided directly on the housing  2  of the linear drive  1 . Preferably, in this case the mating detent means  47  are constituted by a holding rib  48  extending in the longitudinal direction of the longitudinal slot  5 , such rib  48  being located on the second longitudinal side  38  of the longitudinal slot  5  and extending toward the opposite slot edge. The detent means  46  comprise a forked detent section  49  of the covering section  35 , in whose trough-like opening the holding rib  38  extends in the locked state. The holding rib  48  is in this case braced between the two fork prongs  53   a  and  53   b  of the detent section  49 . 
     The inner fork prong  53   a  is deformable and is bent round during engagement and disengagement. One could speak of a snap-action connection in this case. 
     Accordingly there is the certainty of a play-free and therefore sealed detent connection, because the holding rib  48  is provided with a cross section tapering toward the free end and the intermediate space defined between the fork prongs  53   a  and  53   b  of the detent section  49  tapers in the depth direction also. This means that the detent engagement operation is more particularly aided. 
     The guide means  44  possesses actuating means  54  arranged axially on either side of the force coupling member  15 , such actuating means  54  being able to cooperate with an outer face  55 , facing away from the longitudinal slot  5 , of the covering section  35  in order to lock the covering section  35  in relation to the housing on transition from the released position into the covering position. The actuating means  54  thrust against the outer face,  55  so that the covering section  35  is pivoted inward and is forced into a detent engagement with the mating detent means  47 . 
     The actuating means  54  define the two outer ends of the transition zones  45  and are constituted by actuating faces, whose course is the same as the desired course of the covering section  35 . They are curved, their distance from the outer slot opening  7  decreasing with an increase in the distance from the force coupling member  15 . Accordingly the covering section  35  is thrust underneath the corresponding actuating face and during a corresponding direction of movement of the piston  8  is gradually thrust down onto the longitudinal slot  5 . 
     Axially between the two actuating means  54  the guide means  44  is provided with an oppositely directed guide face  56 . Starting at the end regions opposite to the actuating means, it becomes increasingly steep toward the force coupling member  15 . Since the inner face  57  of the covering section  35  runs along the guide face  56 , the course of the guide face  56  will determine the pivoting operation between the covering position and the release position. The guide face  56  is steepest in the middle of the action of the force coupling member  15 , the latter being able to constitute a direct component of the guide face  56 . 
     Apart from any component possibly present on the force coupling member  15 , the guide face  56  is like the actuating means  54  and accordingly the entire guide means  44  provided on a single component, which single component in the working example constitutes an insert  58 , which is inserted longitudinally into the piston  8 . Preferably, the insert  58  consists of plastic material, the actuating  54  and the guide face  56  being more particularly manufactured by free molding. The production of the guide means  44  on a separate component of its own offers the advantage that complex shapes of the faces may be produced independently from the manufacture of the piston  8 . 
     The fitting of the insert  58  in the piston  8  is preferably performed by plugging in place, the piston  8  possessing a recess  59  open toward one longitudinal side, into which recess  59  a foot section  62  of the insert  58  is plugged perpendicularly to the direction  13  of movement. Interlocking centering means, as for instance ribs and grooves, in this case ensure an exact fitting together. 
     The above mentioned deflecting passage is preferably arranged in the recess  59  and is partly defined by the piston  8  and partly by the foot section  62  of the insert  58 . The latter can possess a deflecting face  64  facing the sealing band  24 . 
     The force coupling member  15  could in principle be an integral component of the insert  58 . For the reasons explained above however a separate design is however more advantageous. Thus in the working example the insert  58  is provided at the level of the recess  22  in the piston  8  with a further recess  65 , which renders possible the insertion of the forked holding section  18 , the insert  58  being ultimately held by the holding section  18  straddling it. 
     On movement through the guide means  44  the actuating means  54  act as holding down means, which thrust the covering section  35  into the engaged state. The guide face  56 , placed in between, which may be made up of a plurality of sequentially following face sections, is responsible for moving the covering section  35  into the erect position in the released state for this purpose deflection around the force coupling member  15 . 
     As shown in  FIG. 6  a further design of the linear drive is possible, in the case of which the covering section  35  in the engaged state is again on the second longitudinal side  38  of the outer slot opening  7  is in clamping engagement with the housing  2 . However, the mating detent means  47  in this case are not directly provided on the housing  2 , but are on the face of the sealing band  24  facing the covering band  33 , such sealing band engaging the housing  2 . This design offers the advantage that the covering band  33  and the sealing band mutually hold each other in the covering position or sealing position. 
     The design illustrated in  FIG. 7  differs from the designs so far described to the extent that the covering means  32  has two covering bands  33   a  and  33   b  instead of only one. Each such covering band  33   a  and  33   b  possesses an attachment section  34  and a covering section  35 , its attachment sections  34  being secured on opposite longitudinal sides of the longitudinal slot  5  in relation to the housing. Starting from this position their covering sections  35  project toward each other and respectively cover part of the width of the outer slot opening  7 . In the working embodiment the arrangement is such that the longitudinal slot  5  is covered by both covering sections  35  in the covering position for half thereof. 
     The kinematic behavior of the two covering section is the same as that described above so that further explanations thereof are unnecessary. In the case of the design of the guide means  44  on the other hand the fact needs to be taken into consideration that the two covering sections  35  are pivoted in opposite directions. More particularly, each covering section  35  is provided with its own guide face so that the covering sections  35  are moved past the force transfer part  14  on opposite sides. 
     In the case of the design in accordance with  FIG. 7  there is the particular opportunity of providing the detent connection in the covering position between the covering sections  35  and the sealing band  24 . More especially, suitable detent means  46  may be formed on the mutually facing longitudinal edge regions  41  of the covering sections, such detent means cooperating with the shared mating detent means  47  of the sealing band  24 .