Abstract:
The invention relates to a pneumatic actuator composed of cuts of a gas-tight film which are interconnected so as to form hollow film elements that are gas-tight towards the outside. The hollow film elements are interconnected by means of air ducts while forming a fan-shaped structure from a cross-sectional perspective. The actuator, which is fastened to a component, is swiveled about a common edge of the hollow film elements when compressed gas is delivered via a connection. The swiveling movement of the actuator can be used for gripping and holding objects or transmitting optical signals.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a pneumatic gripper comprising at least one pneumatic structural element. 
     2. History of the Related Art 
     The devices nearest to the present invention are known from U.S. Pat. No. 3,056,625, Timmerman (D1) and JP 05261687, Bridgestone (D2). 
     D1 describes a gripper for goods which is configured as a clamp and has grippers held movably on its lateral vertically disposed sections by means of hinges. Located between each vertically disposed section and the associated gripper is an inflatable bellows which, under pressure, pushes the gripper away from the vertical section towards the inside of the gripper so that the goods are grasped by the gripper. 
     D2 also describes a gripper configured in the manner of a clamp with lateral vertically disposed sections. A supporting arm runs parallel to each of the vertical sections, on the inner side thereof, said supporting arm for its part being movably hinged in the cross member of the gripper by means of a hinge. Inflatable cushions are provided on each supporting arm which, when filled with compressed air, press the supporting arms away towards the inside (whereby said cushions also move inwards since they are disposed on the supporting arms). 
     These known grippers have the disadvantage of a rigid structure, for example, with the consequence that they can only be used in a vertical position. 
     SUMMARY 
     The object of the present invention is to provide a pneumatic gripper which is simple and inexpensive to manufacture and use and its construction principle is constituted in such a manner that it can be flexibly configured and varied both as a kinetic and as a dynamic tool, and fulfils its task in any, even non-vertical, position and also under difficult boundary conditions. 
     The gripper should be able to satisfy various requirements such as sterilisability and the handling of sensitive objects, for example, in conjunction with a handling robot. These requirements include the easy exchangeability of a, for example, soiled or otherwise contaminated specimen. 
     The solution of the formulated object is reproduced in the characterising part of claim  1  with regard to its main features and in the following claims with regard to further advantageous embodiments. 
     An advantageous embodiment of a pneumatic actuator according to the invention is in particular characterised in that [0010] this is constructed of a plurality of interconnected layers of film cuts ( 22 ) of a flexible but barely expandable gastight film ( 1 ), [0011] the layers of the film cuts ( 22 ) are interconnected so as to form hollow film elements ( 2 ), [0012] at least one of the hollow film elements ( 2 ) has a connection ( 8 ) for compressed gas, [0013] the hollow film elements ( 2 ) thus constructed are all connected to one another so that when said hollow film elements ( 2 ) are filled with compressed gas, these interconnected hollow film elements ( 2 ) execute a pivoting movement as an actuator ( 24 ). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the method and system of the present invention may be obtained by reference to the following Detailed Description when taken in conjunction with the accompanying drawings wherein: 
         FIG. 1   a  is a pneumatic actuator in the uninflated state, 
         FIG. 1   b  is a pneumatic actuator in the state filled with pressure medium, 
         FIG. 1   c  is a top view of a pneumatic actuator, 
         FIG. 2  is a pneumatic actuator as a single-leaf gripper, 
         FIG. 3   a  is a side view of a two-leaf gripper in the empty state, 
         FIG. 3   b  is a two-leaf gripper in the state filled with pressure medium, 
         FIG. 4  is a typical film cut of a three-leaf gripper, 
         FIGS. 5   a ,  5   b  show further film cuts of the three-leaf gripper, 
         FIG. 6  is a three-leaf gripper in the activated state, i.e., filled with pressure medium, in an isometric projection, 
         FIG. 7  is a side view of a single leaf of a three-leaf gripper, 
         FIG. 8  is a single sheet according to  FIG. 7  as a single-leaf gripper, and 
         FIG. 9  is a three-leaf gripper without a base plate. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention will now be described more fully with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, the embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
       FIGS. 1   a, b, c  is a diagram of a first embodiment of the device according to the invention;  FIG. 1   a  shows a side view in the pressure-less state,  FIG. 1   b  shows a view in the state filled with compressed gas,  FIG. 1   c  shows a plan view from below (with respect to  FIG. 1   a ) in the pressure-less state. This exemplary embodiment, like the following embodiments, is constructed of film cuts  22  of a flexible but barely expandable gastight film  1 , which form a fan-shaped structure in cross-section. This film can also be a textile reinforced plastic film. At the edges, these film cuts  22  are each joined by welding or adhesive bonding and are thus closed in a gastight manner against the environment. The hollow film elements  2  thus formed are connected to one another by air ducts. Compressed gas can now be let in by means of a suitably shaped connection  8  whereby the individual hollow film elements  2  are pressed apart from one another. If this movement is restricted to one side of the hollow film elements  2 , this changes into a swivelling movement whereupon the structure constructed of the film cuts  22  and being gastight towards the outside, is deformed as an actuator  25 , as shown in  FIG. 1   b.    
       FIG. 1   c  shows the structure of the actuator viewed from below with reference to  FIG. 1   a . The inner boundaries of the film cuts  22  are shown by solid lines whilst the inner boundaries of the film cut-outs  22  of a plurality of hollow film elements  26 ,  29  formed by the inner boundaries of the corresponding film cuts  22  are depicted by dashed lines. 
     In all three  FIGS. 1   a, b  c, the film cuts  22  are placed one upon the other at the closed end and welded or adhesively bonded together. 
     A common edge  18  is thereby formed where the actuator  25  can be fixed, for example, on a stationary or movable external device. However, this is in no way compulsory: the connection  8  or, again as an example, the underside of one of the hollow film elements  26 , in this case the lowest one, can be held firmly by suitable means and measures. What is important is the relative swivelling movement of the hollow film elements  26  and  29 . 
     The actuator  25  thus configured can now be used as a kinetic actuator, still in the sense of an example of application, for example, for interrupting a light barrier or as an optical signal generator. The longest of the, in this case four, hollow film elements  29  can be relatively long since a substantially circular tube having high stiffness is formed from this hollow film element  29  when filled with compressed gas. 
     If the hollow film element  29  is designed to be approximately the same length as the other, in this case three, hollow film elements  26 , an actuator  24  exerting forces can be constructed therefrom as shown in  FIG. 2 , corresponding to  FIG. 1   b , a so-called dynamic actuator. The said swivelling movement is used for gripping or holding objects. Here, the position  23 , the welding or adhesive bonding of the film cuts  22 , is fixed on a component  30  which is shown representatively as an angle. The person skilled in the art, who is entrusted with constructive tasks, will have many other designs available with which the positive and moment engagement of the actuator  24  with one corresponding to the component  30  can be accomplished. Such a combination of actuator  24  and component  30  is suitable, for example, as a gripper for leaf-like, i.e. substantially two-dimensionally extended bodies. 
     Since both the actuator  24  and also the actuator  25  have very low inertial masses, the inertial forces associated with their acceleration are very low; rapid gripping and release is thereby easily possible. 
       FIG. 3   a b  shows a third exemplary embodiment of an actuator according to the invention. In this case, two actuators  24  are assembled, where with the aim of rational manufacture, in each case both parts of the same plane are cut on one piece. In  FIGS. 3   a, b  the two actuators are fixed by means of a fastening element  9  (in this case, shown representatively as a screw with a nut) on a base plate. The actuators  24  together form a gripper, again preferably for flat objects. 
     A gripper is formed from one or more actuators  24 ,  31  which are called gripper elements. In contrast to conventional grippers where actuators and grippers are separate components, here these are combined in one element. That surface of the gripper element  6  which touches the object to be gripped is called gripping surface  10 . In at least one of the hollow film elements  2  nearest to the base plate  5 , a connection  8  is provided for compressed gas. A plurality of possibilities is known for such a connection; for example, a hose connection at the compressed air supply  7  or a push-button-type quick coupling can be used. No mechanical parts such as pins, screws, locking devices etc. are present, whereby any risk caused by falling out or other malfunction can be eliminated. 
     By regulating the amount of through-flowing gas or the pressure, the gripping force can be adjusted and metered very precisely and free from hysteresis. The gripper elements can be positioned very precisely since the gripping process takes place free from jolts and pressure peaks (stick-slip free). The usual inaccuracy during positioning with hydraulic cylinders is lacking. The pressure or flow sensors required for this purpose and the controller are attached outside the gripper, for example, on a handling robot whereby a gripper can be exchanged independently of these. 
     The inflatable hollow film elements  2  retain a certain flexibility so that it is possible to resiliently grip sensitive objects  20  or those having complex shapes over a large area. Since the force exerted by the gripper on the body is not punctiform but is exerted so that it is distributed on a surface adapted to the object, the point stressing of the object is reduced. As a result of the large contact surface, a large retaining force can be achieved with low filling pressure. The retaining force can be further increased by using specialised surfaces  15 ,  16 ,  17 . It is also feasible to additionally protect such surface regions by a protective film or by another suitable reinforcement, for example, against mechanical or chemical damage. The flexibility of the gripping surface  10  also makes it possible to use the same gripper for different objects. Since it is partially adapted to the object, no specialised gripper need be used which is only suitable for a single type of object. The adapting capability can be achieved by additional reinforcement of the surface regions  15 ,  16 ,  17  whereby, for example movably interconnected plates are provided for reinforcement. Object-dependent reinforcements in the manner of the adapted “thimble” are also possible, which thanks to the adaptability of the gripper, still allows a non-specialised gripper to be used, then reinforced for special objects by an adapted thimble. 
     The exemplary embodiment of actuators according to the invention shown in  FIGS. 4 to 6  has a similar structure to those in  FIGS. 1 to 3 . Instead of a mirror symmetry of the actuators according to  FIGS. 3   a, b , a multiple, for example, threefold axial symmetry appears. In this case, three actuators  31  are combined to form a gripper. 
     The actuators  31  according to the invention are constructed of superposed plastic films  1  which are joined to one another at predefined seams  14 . The join can again be made by welding or adhesive bonding. The material used allows simple steam or radiation sterilisation. Such actuators  31  assembled to form a gripper  31  can be welded into a package and delivered sterile. These actuators  31  are simple and therefore inexpensive to manufacture since the plastic films  1  used comprise a flat material that can be joined to one another with flat welded or adhesive joints. Together with the low material costs, this design principle allows grippers to be manufactured at such low prices that they can be used as disposable articles. The entire gripper is made of a single material which makes disposal feasibly simple. Therefore, a contaminated gripper can easily be exchanged for a new sterile one. Expensive cleaning and sterilisation processes such as are required for conventional mechanical grippers are superfluous. In industrial applications in which grippers become contaminated, exchanging them saves complex and cost-intensive cleaning processes. Corrosion damage due to permanent contact with aggressive media can be eliminated. Exchanging also makes maintenance work which would also be necessary in a mechanical gripper due to wear effects superfluous. The elimination of all maintenance and cleaning work on the gripper substantially simplifies operation and saves a large part of the costs which would be incurred with a conventional gripper. 
     The areas of application for such a pneumatic gripper are numerous, not least because it can be manufactured and used in various sizes in the meter to the millimeter range. Its advantages also make it ideal for all areas where clean or sterile operation is required as in the pharmaceutical area or in analytical laboratories. Freedom from bacteria is also an important aspect to be satisfied in the food sector. Contamination problems can be eliminated in biotechnology or chemical applications since a contaminated gripper can be simply exchanged and disposed of. In industrial areas where the gripper is exposed to strongly aggressive media or becomes strongly contaminated such as, for example, by spray mist in painting work and cleaning would be expensive, this is eliminated. Costly repair work due to wear is also eliminated. As a result of its purely pneumatic mode of operation, it also fulfils the requirements for working areas in which explosion protection is required. 
     Furthermore, the structure of the gripper according to the invention is ideal specifically for use in contaminated areas. Under laboratory conditions or production conditions, contaminated areas are frequently spatially separated areas which are operated by remote control from outside using special tools. If openings need to be provided in enclosures or walls separating contaminated areas (or areas to be kept clean or sterile), these should be configured to be as small as possible. By suitably configuring the hollow film elements  2  or by suitably folding together and optionally by miniaturised design of a gripper according to the invention, as shown for example in  FIG. 9 , this can be passed through openings which are small compared to the inflated gripper elements  6  and are small compared to the objects to be gripped. 
     Pressure sensors and control equipment are expensive compared with the gripper. So that the gripper can be exchanged independently of these, they are attached outside the gripper. A screw or a push button, for example, can be used as a fastening element  9  to fasten the hold-down device  4  as well as the films  1  on the base plate  5 . Using a quick-coupling, for example, in the form of a push button makes exchanging the gripper very simple. 
     The basic structure of a gripper constructed of three actuators  31  according to  FIGS. 4 ,  5 ,  6  consists of polygonal elements. This structure prevents any movement of the gripper in a direction of movement (shown by the arrow) other than that desired without external stabilising elements needing to be attached for this purpose. For example, the triangular basic structures of the three-finger gripper shown in  FIG. 4  prevent any twisting of the gripper elements  6  about their longitudinal axis. Starting from the configuration of the gripper according to  FIGS. 4 ,  5  and  6 , the person skilled in the art is able to form the actuators or grippers according to the other exemplary embodiments in such a manner that external stabilising elements can be omitted. This assists the flexible range of use of such an actuator or gripper, for example, in those places where rigid external flexible elements prevent the use of an actuator or gripper for reasons of space. Thus, for example a gripper according to  FIGS. 3   a  and  3   b  can then move the gripper elements  6  only in the desired direction of movement indicated by the arrows without external stabilising elements if the fastening element  9  configured as a screw with a nut is suitably positioned; this is again the case if the nut or the washer shown in the figure firmly clamps both gripper elements  6  symmetrically (i.e. precisely centrally). A gripper according to  FIGS. 1   a  to  1   c  will have a stable direction of movement if the hollow film elements  26 ,  29  at the edge  18  are firmly connected to one another over the entire width and also if the gripping hollow film element  29  is configured to be narrower than the adjoining hollow film element  26 . The element  29  then rests centrally in the element  29 , also presses this in centrally so that the element  26  laterally supports the element  29  by means of its lateral edge zones which produces a stabilising supporting effect for said element in the sense of the desired direction of movement. This stabilising effect can be further improved if the respectively next element  26  is broader than the preceding element  26 . 
     It is found that by suitably conceiving the number of hollow film elements  29 ,  29 ;  10 ,  12 ,  13  in conjunction with their shape (polygonal, non-polygonal; narrower or wider compared with another such element) and their mutual fastening (for example, over the entire width of the respective element or not), the optimum result can be achieved with regard to the desired gripping movement or direction and the desired gripping position. A gripper can thus be specifically optimised for a certain intended use. 
     For preciseness, it should be added that the lower hollow film elements  2  located closer to the base plate  5  are shortened in their length to improve the efficiency. 
     The number of actuators  31  used for a gripper can be adapted to the intended use: a two-finger gripper according to  FIG. 3  or a one-finger gripper according to  FIGS. 3 ,  8  which presses the object  21  against a counterpart  19  is suitable for flat or planar objects  21 . 
       FIG. 8  shows an embodiment according to the invention of a one-finger gripper with an actuator  31  with which a flat object  21  can be pressed against a counterpart  19 . The configuration of the counterpart  19  is not part of the invention; it can be configured according to the nature of the object  21  and that of the machine element on which such a gripper is to be placed. 
     The actuator  31  is fastened on the counterpart  19 , designed as an angle, which at the same time serves as the base plate and closes the force flow to the actuator  31 . A force meter, for example, in the form of a strain gauge, can be attached on the counterpart  19 . For rather cylindrical or spheroidal elements, grippers having three or more actuators  31  according to  FIG. 4  are better suited since sliding away of the element in the direction tangential to the base plate  5  is prevented. 
       FIG. 6  shows a gripper consisting of three actuators  31  in isometric projection, and  FIGS. 5   a  and  5   b  show the outlines of films from which these are constructed. In this case, the thick continuous lines framing the surfaces form the seam lines  14 . Not shown is a welding allowance edge which is necessary in practice.  FIG. 7  shows in side view how the film cuts  22  shown in  FIGS. 5   a, b  are joined together to form an actuator  31 . Gripping surface  10  is that surface which touches the object to be gripped. Surface  11  forms the outer surface of the hollow film element  2  which is formed by surface  11  and the gripping surface  10 . The surfaces  12  form a bellows-like structure and surface  13  forms the base surface  13  of the gripper which touches the base plate  5 . 
     A variant to the exemplary embodiment of the actuators  31  as grippers is shown in  FIG. 9 . In this exemplary embodiment the base plate according to  FIG. 3  is replaced by at least one or more further hollow film elements  2  per gripper element  6 . When the actuators  31  are filled with compressed gas this is swivelled downwards and the three actuators  31  press towards one another in the lower part. They thereby also effect a positive and moment engagement. 
     In  FIG. 9  the central region of the three actuators  31  is again fastened with a fastening element  9  (not shown) on a mechanical component  32 —here in the sense of an example, on a tube—which on the one hand ensures the positive engagement to the gripped object and on the other hand ensures the supply and removal of compressed gas. The configuration of the component  32  is again not part of the device according to the invention and can be shaped and designed according to the intended use.