Patent Publication Number: US-7222887-B2

Title: Fluid operated contractile drive

Description:
This application claims priority based on an International Application filed under the Patent Cooperation Treaty, PCT/EP03/01781, filed on Feb. 21, 2003, and German Patent Application No. DE 202 05 719.4, filed on Apr. 11, 2002. 
     FIELD OF THE INVENTION 
     The invention relates to a fluid operated contractile drive comprising a contractile hose extending between two head pieces, and contracting longitudinally when its internal hose space defined by it is acted upon by fluid pressure to exert axial tension forces on the head pieces drawing them together, the contractile hose being attached to at least one head piece by having its respective end section clamped in an annular clamping gap defined between clamping surfaces, extending at least partially inclined in relation to the longitudinal axis of the contractile hose and of a first clamping unit having a force output means serving for external force output and a second clamping unit able to be shifted axially in relation to the first clamping unit. 
     BACKGROUND OF THE INVENTION 
     In the case of a known contractile drive disclosed in the German patent publication 10,034,389 A1 a contractile hose extends between two head pieces which are respectively provided with two clamping units and which are screwed together like a gland nut. Between the clamping units an annular clamping gap is defined, in which the contractile hose is clamped at its associated end region. If the internal space of the contractile hose is charged with a pressure medium subject to a certain actuating pressure, the contractile hose will expand radially and will simultaneously pull the two head pieces toward one another. It is in this manner that it is possible for external structures or, respectively, components, which are fixed on the force output means of the head pieces, to be moved relatively toward each other and/or clamped together. 
     In the case of the known contractile drive there was the problem that owing to its liability to deformation the contractile hose could be pulled out of the clamping gap. Therefore the two clamping units were designed to be adjusted in the longitudinal direction of the contractile drive and the tightening faces were so contrived that owing to frictional effects between them and the contractile hose a certain entraining effect is produced with the result that on actuation of the contractile hose there is an automatic reinforcement of the gripping or clamping action between the two clamping units. 
     It has however now been discovered that there are still certain shortcomings with the known clamping attachment, which are more particularly significant at raised temperatures or in the case of the use of relatively soft hose materials. The material then tends to creep and in the worst case the contractile hose may slip out of the head piece completely. 
     SUMMARY OF THE INVENTION 
     Accordingly one object of the present invention is to provide a contractile drive of the type initially mentioned with a further improvement of the connection between the contractile hose and one or both of the two head pieces. 
     The design for achieving this object is characterized by loading means provided in addition to the contractile hose and effective between the two clamping units and acting on the clamping units to reduce the width of the clamping gap. 
     It is in this manner that it is possible to ensure that the end section, placed in the clamping gap, of the contractile hose will always remain firmly clamped reliably, even if owing to fatigue of the hose material or for some other reason there is a tendency to creep, which would inherently reduce the clamping action. Owing to the loading means the two clamping units are automatically reset to a degree dependent on the reduction in the wall thickness of the clamped end section of the contractile hose so that the desired clamping action may be permanently maintained even despite the effect of unfavorable environmental conditions. 
     In principle it would be possible to so design the loading means that they only take effect following or at the occurrence of certain events, for example when the temperature of the surroundings has exceeded a certain value. Such a design could be realized by the use of so-called memory metal. The simplest and at least presently most economic design is one in which the loading means are so designed that they are always in action. This is something which may be more particularly achieved by the use of loading means having resiliently elastic properties, more especially in the form of a structure corresponding to a mechanical spring means. Particularly compact dimensions may in this case be produced by having mechanical spring means, which comprises a belleville washer stack. 
     Furthermore structures of the design are possible in the case of which the action of the loading means is produced, or at least aided, by the fluid pressure medium employed for the operation of the contractile drive. For this purpose an actuating space may be provided between axially opposite actuating faces of the two clamping units, such space being constantly connected with the inner space of the hose. The clamping action produced will in this case be dependent directly on the pressure action on the contractile drive so that the clamping action increases with an increase in the load on the contractile drive. 
     In the case of a preferred embodiment of the invention the clamping faces so run together at an angle within the clamping gap that their distance from the longitudinal axis of the contractile hose increases toward the outer end region, axially opposite to the contractile hose, of the respective head piece. The diameter of the annular clamping gap then preferably increases toward the outer end region of the head piece. 
     It has been found to be particularly advantageous if at least one of the clamping faces is designed with a corrugated cross sectional outline. It is then a question here preferably of that clamping face which acts on the contractile hose at the inner periphery. 
     Preferably the respective head piece is provided with holding means serving to load the two clamping units to maintain a basic clamping effect on the contractile hose irrespectively of the fluid actuating effect in the inner space of the hose. The holding means may for example be in the form of a screw connection, which is provided between a clamping nut and the force output part of the first clamping unit. 
     A particularly compact arrangement is produced if the loading means responsible for the active clamping effect of the contractile hose are located in a region which is within the contractile hose. 
     In connection with the design in accordance with the invention furthermore an advantageous safety feature may be produced. Since owing to the reliable fixation and automatic resetting of the clamping attachment slipping of the contractile hose out of the head piece is prevented, when there is an increase in overloading here will be the effect such that the hose material in the clamped region, which becomes thinner, will become slightly porous. Air may escape through the fine holes so that overloading of the hose material or even splitting thereof is avoided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following the invention will be described with reference to the accompanying drawing in detail. 
       The single FIGURE thereof shows a preferred embodiment of the invention in the form of an actuating means, partly in longitudinal section. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The contractile drive illustrated comprises the two (first and second) spaced apart head pieces  2  and  3 , only one head piece  2  being illustrated completely in order to make the drawing more straightforward. 
     The two head pieces  2  and  3  are connected with each other by way of a contractile hose  4 . At least in the non-activated state of the contractile drive the contractile hose  4  possesses a cylindrical tubular configuration. The longitudinal axis of the contractile drive, which at the same time represents the longitudinal axis of the contractile hose  4 , is indicated at  9 . 
     The contractile hose  4  possesses an elongated hose body  5  preferably manufactured of a material having rubber-like properties. As a material use is preferably made of rubber or an elastomeric material having similar properties. A strand structure  1 , only indicated in the drawing in chained lines, is embedded in the material of the hose body  5  and such structure is preferably completely surrounded by the hose body material and possesses an arrangement which is coaxial to the hose body  5 . The structural form of the contractile hose  4  can more particularly be as disclosed in the German patent publication 29,906,626 (utility model) or in the European patent publication 0 161 750 B1. 
     The contractile hose  4  has its two axial end sections  10  so fixed at the associated head pieces  2  and  3  that on the one hand there is a fluid-tight connection between the hose body  5  and the respective head piece  2  and  4  and on the other hand the stand structure  1  is in a position of exerting tension forces on the respective head piece  2  and  3 . Instead of the strand structure  1  other suitable means could be employed to transmit the axial tension forces. 
     The contractile hose  4  delimits an internal hose space  13 , which at the end is terminated by the two head pieces  2  and  3 . Into the space  13  in the hose there opens at least one fluid duct  14 , that in the working example extends preferably coaxially right through the first head piece  2  shown in its entirety. The fluid duct  14  is able to be connected with a fluid line, not illustrated in detail, which leads to a source of pressure medium. By the use of an intermediately placed control valve arrangement there is the possibility of feeding a fluid pressure medium into the inner space  13  of the hose or of letting off such medium from it. Preferably the contractile drive is operated with gaseous pressure medium, more especially compressed air. It is also readily suitable for operation using a hydraulic fluid for example oil or water. 
     Each head piece  2  and  3  is provided with force output means  17  at a position accessible from the outside. Such means are in the working example constituted by a threaded section of the respective head piece  2  and  3  and render possible an attachment of the respective head piece  2  and  3  to some component, not illustrated in detail. For instance it would be possible to use the force output means  17  of the first head piece  2  to join it to the frame of a machine and to connect the other head piece  3  with a machine part moved in relation to the machine frame. The contractile drive is suitable for practically all applications, in which two components are to be shifted in relation to one another or to be clamped. 
     The connection with the corresponding component may be directly by way of the force output means or with the interposition of an adapter part, not illustrated in detail, which is fixed to the force output means  17 . 
     For activation of the contractile drive by way of the fluid duct  14  pressure medium at the predetermined operational pressure is fed into the interior  13  of the hose. Owing to such gage pressure the wall of the contractile hose  4  is thrust radially outward so that there is an action in the form of a radial widening of the contractile hose  4 . The consequence of this is that the contractile hose  4  is simultaneously acted upon to perform an axial contraction, axial tension forces produced by the contractile hose  4  causing an opposite movement together of the head pieces  2  and  3 . This in turn means that the components held by the force output means  17  of the head pieces  2  and  3  are acted on to move together. Dependent on the particular circumstances this is accompanied by a greater or lesser opposite movement together of the two head pieces  2  and  3 , the displacement of the head pieces  2  and  3  in relation to each other being termed the stroke. 
     For deactivation of the contractile drive the pressure medium is at least partly let off from the interior space  13  of the hose. The contractile hose  4  then contracts back to its original length so that the head pieces  2  and  3  return to the original position. This return movement may if necessary be aided by additional measures, as for example using return springs. 
     The particular movement and deformation properties of the contractile hose  4  are ensured in the working example by the strand structure  1 . The structure involved here is for example as described in the said German patent publication 29,906,626 (utility model) or in the European patent publication 0 161 750 B1. Preferably the strand structure  1  comprises a plurality of bendable strands, which have a high degree of flexibility and simultaneously a high tensile strength in the form of one or more fibers, a type being preferred, in which the strands extend helically and peripherally around the hose body  5  between the head pieces  2  and  3  and more particularly are arranged crossing over so that rhombic grid regions are formed. Owing to the action of the internal pressure in the contractile hose  4  a change of the rhomb angle is caused, something which ultimately means that axial tension forces are established in the strand structure at the end sections  10  of the contractile hose, such forces being transmitted to the head pieces  2  and  3 . 
     The force transmission to the head pieces  2  and  3  is possible because the contractile hose  4  is firmly held in place at its end sections  10  in the respectively associated head piece  2  and  3 . For this purpose the head pieces  2  and  3  are provided with a particularly advantageous clamping device  18 , which is preferably identically provided in the case of both head pieces. However, there is also the possibility of only providing one such clamping device  18 . 
     The clamping device  18  is a direct component of the respective head piece  2  and  3 . It comprises a first clamping unit  22 , which is provided with the force output means  17  and furthermore possesses a second clamping unit  23  separate from the first clamping unit  22 , such second unit not having any force output means  17 . 
     The two clamping units  22  and  23  fit coaxially into one another, a first tightening face  24  provided on the first clamping unit  22  being placed radially opposite to a second tightening face  25  on the second clamping unit  23 . The two tightening faces  24  and  25  being are orientated athwart the longitudinal axis  9  and facing each other. 
     Between the two clamping faces  24  and  25  the two clamping units  22  and  23  define an annular clamping gap  26 . Such gap is open toward the inner end side, facing the respectively other head piece, the contractile hose  4  having its end section  10  concentrically fitting into the clamping gap  26  from the open end. 
     The two clamping units  22  and  23  are so firmly clamped together on assembly of the contractile drive that they exert a clamping force (termed the basic force) on the wall of the end section  10 , lying between them. The clamping faces  24  and  25  then contact on the one hand the inner face and on the other hand contact the outer face of the hose body  5 , against which they are firmly braced. 
     The end section  10  of the contractile hose  4  is externally surrounded by the first clamping unit  22 . The second clamping unit  23  extends from the end face coaxially into the contractile hose  4 . 
     The second clamping unit  23  is in the working example constituted by a conical element, whose enveloping face constituting the second clamping face  25  has, for part of the length and preferably for the entire length, a configuration tapering conically toward the contractile hose  4 . However, the second clamping face  25  preferably is not smooth but corrugated in cross section in its outline. As a result there is an outer face with an axial sequence of alternating annular hills and valleys. 
     The first clamping unit  22  is multi-part in design and possesses a force output part  28  provided with the force output part  17  and furthermore a tightening nut  29  designed in the form of a gland nut. The force output part  28  has an axially extending, central bearing tailpiece  32  fitting into a complementary bearing recess  33  in the second clamping unit  23 , such bearing recess  33  preferably being constituted by a stepped access opening  34  extending through the full length of the second clamping unit  23 . The force output part  28  also possesses an axial through hole  35 , which together with length section, adjoining the bearing tailpiece  32 , of the through opening  34  constitutes the fluid duct  14  and is provided with the force output means  17  as a female screw thread. 
     The two clamping units  22  and  23  are designed to move in relation to each other in the longitudinal direction of the contractile hose  4 , the possible direction  36  of motion being indicated by a double arrow. Here the bearing recess  33  together with the bearing tailpiece  33  surrounding it constitute an axial slide guide. 
     The tightening nut  29  has a sleeve-like structure with a first clamping section  42  defining the inwardly directed first tightening face  24  and an attachment section  43  axially adjoining it, which externally extends over the force output part  28  at a flange-like section. Between the tightening nut  29  and the force output part  28  there are holding means  44 , which define a screw connection rendering possible a variation of the relative axial position of the two components. Instead of the screw connection other holding means with the same function could be selected. 
     The first tightening face  24  provided on the tightening nut  29  has the same slope as the second tightening face  25  turned toward it. It preferably has a smooth surface or only a slight degree of roughness. 
     In the case of both tightening faces  24  and  25  the obliqueness is such that the distance from the longitudinal axis  9  becomes larger on getting closer to the outer end region, axially opposite to the contractile hose  4 , of the head piece  2 . The diameter of the annular clamping gap  26  consequently becomes greater from the inner end of the head piece  2  axially outward. 
     The clamping device  18  additionally comprises, besides the components described so far, loading means  45  effective between the two clamping units  22  and  23 , which loading means are in a position of acting on the two clamping units  22  and  23  to reduce the width B of the clamping gap  26 . In the working embodiment the loading means  45  have resiliently elastic properties and are constituted by a mechanical spring means, which is arranged coaxially between the second clamping unit  23  and the force output part  28  of the clamping unit  22 . 
     Preferably the loading means  45  comprises a belleville washer. 
     For the sake of having a compact and space-saving structure the loading means  45  are in the working example in a region located within the contractile hose  4 . They are seated in a actuating space  46 , which is placed to the fore of the bearing tailpiece  32  toward the second clamping unit  23 , it being defined by a widened section of the through opening  34 . 
     The actuating space  26  is delimited by two axially opposite actuating faces  47  and  48  of which the first actuating face  47  is provided on the end face of the bearing tailpiece  32  and the second actuating face  48  is opposite to it on the second clamping unit  23 . Radially to the outside the actuating space  46  is directly delimited by the second clamping unit  23 , which fits over the bearing tailpiece  32  like a gland sleeve. 
     The loading means  45  acted simultaneously on the two actuating faces  47  and  48  and so thrust the second clamping unit  23  away from the force output part  28  causing the second tightening face  25  to move toward the first tightening face  24 . 
     By way of the through opening  34  the actuating space  46  is furthermore constantly connected with the interior  13  of the hose. 
     During assembly of the contractile drive firstly after previous insertion of the loading means  45  the second clamping unit  23  is slipped onto the bearing tailpiece  32  of the force output part  28 . No tightening nut  29  is fitted in this case. Then the end section  10  of the contractile hose  4  is plugged on as far as engagement with an abutment  52  onto the second clamping unit  23 . The contractile hose is then flared out like a trumpet. After this the tightening nut  29  previously slipped onto the contractile hose  4  is pushed over the unit comprising the force output part  28  and the second clamping unit  23  so that the second clamping unit  23  assumes a position coaxially within the tightening or loading nut  29 . The tightening nut  29  is now screwed on the force output part  28 , the first tightening face  24  thrusting from the outside against the contractile hose  4 , which bears internally against tightening face  25 . The supporting force of the second tightening face in this case is due to the loading means  45 , which bear against the two clamping units  22  and  23 , between which they are placed. 
     The tightening nut  29  is tightened until the desired basic clamping action of the contractile hose  4  is achieved. During this operation the second clamping unit  22  is slipped coaxially over the bearing tailpiece  32  and simultaneously the intermediately arranged loading means  45  are compressed so that a return force is built up, which is constantly effective and supplies the opposite force for the clamping in position of the contractile hose  4 . 
     Previously performed empirical measurements serve to ensure that the desired basic clamping action is reached when the tightening nut  29  has been screwed to a certain extent on the force output part  28 . 
     The contractile hose  4  is now anchored in the clamping gap  26 , the hose material being deformed in accordance with the configuration of the tightening faces  24  and  25 . 
     If during operation of the contractile drive creep of the material of the hose body should occur the loading means  45  will prevent a reduction in the holding force with the preselected basic clamping action. Any reduction in the wall thickness of the contractile hose  4  within the clamping gap  26  will be immediately and automatically compensated for because the second tightening face  25  is caused to follow up by the force of the loading means  45 . The clamping gap will be closed somewhat, but the clamping forces are maintained. Even un unfavorable conditions this means that the contractile hose  4  will be prevented for slipping out of the head pieces  2  and  3 . 
     As an alternative to the constantly acting loading means  45  a design would be possible in which the action of the loading means would only begin when a certain event takes place, as for instance when a particular temperature is reached. This would more particularly allow the use of memory-metal with the properties of assuming particular configurations in a manner dependent on temperature. 
     In the working embodiment there is a further effect. This effect involves the use of a supporting fluid force for the effect of the loading means  45  on the basis of the fact that the fluid pressure obtaining in the interior space  13  of the hose simultaneously acts in the actuating space  46  as well and has a tendency to thrust the two actuating faces  47  and  48  away from each other. 
     A seal  53  placed between the two clamping units  22  and  23  and preferably between the bearing tailpiece  32  and the second clamping unit  23  prevents pressure medium from escaping between the relatively movable parts and into the surroundings. 
     Departing from a design, in which only friction forces between the head piece and the contractile hose serve to cause a reduction in the size of the clamping gap, the installation of separate loading means  45  in addition to the contractile hose  4  offers the advantage of high efficacy under all operational states even in the case of changes in the properties of the material of the hose body  5 . 
     Owing to the clamping device  18  a secure hold of the contractile hose  4  is achieved, even if the wall thickness is substantially reduced owing to deformation of the material. The fact that even in the case of a substantial reduction in the thickness of the wall bursting of the contractile hose is not to be feared is dependent on the fact that fine holes are produced in the thin hose material creeping out of the clamping gap  26 , such holes permitting an escape of fluid under gage pressure. It is in this manner that the design in accordance with the invention takes a certain safety aspect into account as well.