Abstract:
A vacuum operated lifting apparatus includes a piston having a pressure side and a suction side, respectively, and being movably received in a cylinder, wherein a piston shaft projects through a bottom of the cylinder from the pressure side of the piston and having a through passage for connecting the piston pressure side with the atmosphere. An axially compressible space is connected to a vacuum source for evacuation of the chamber and sealed in air-tight attachment to the piston suction side, the space being confined within the wall of a flexible bellows.

Description:
TECHNICAL FIELD OF INVENTION 
     The present invention relates to a lifting apparatus operated by negative pressure, and by which articles may be gripped and lifted to be displaced and transferred to a new position. Specifically, the invention relates to a vacuum operated lifting apparatus that is designed to have durable operation also in polluted or dusty environments. 
     As used herein, the term “vacuum operated” refers to a lifting apparatus that is operated by negative pressure, such that a pressure difference between a piston pressure side and a piston suction side causes a movement in the piston, that is utilized for lifting purposes. The word vacuum is therefore to be understood as including also other conditions than conditions, completely free of pressure. 
     Lifting apparatus as mentioned above are known per se in process industry and used for shifting articles between work stations or process steps, e.g. In many such industries, such as the engineering industry, graphic or chemical industries, high demands are raised in aspects of durability also in harsh operational conditions. These conditions may include oil or grease, frequently combined with dust, grindings and fibers, that may intrude between slide surfaces and ports, thus reducing the operational capacity of the lifting apparatus. 
     OBJECT OF INVENTION 
     The object of the present invention is to provide a vacuum operated lifting apparatus that is designed for reliable service and durable function also in harsh operational conditions. 
     By the way this object will be met by the invention, there is also provided a vacuum operated lifting apparatus having great versatility in implementation, and by which installation is facilitated. 
     SUMMARY OF THE INVENTION 
     In the present invention there is suggested a lifting apparatus comprising a cylinder, wherein a moving piston has a pressure side and a suction side. A piston shaft runs through a bottom of the cylinder and has a passage that connects the piston pressure side to the atmosphere. In accordance with the invention, the piston suction side defines a chamber that is connected to a vacuum source. Said chamber is designed to be evacuated from air and is axially compressible. In radial directions, the chamber is defined between the walls of flexible bellows, that are arranged concentrically about the piston shaft. 
    
    
     DRAWINGS 
     The invention is more fully described below, reference being made to the attached drawings. In the drawings: 
     FIG. 1 is a longitudinal section through the lifting apparatus in a rest position; 
     FIG. 2 is a section similar to FIG. 1, showing the lifting apparatus in operative position when the piston shaft is extended, and 
     FIG. 3 is a similar section showing the piston shaft under extraction for a lifting sequence. 
    
    
     DETAILED DESCRIPTION 
     By reference to the drawings, an embodiment of the inventive lifting apparatus is shown diagrammatically. 
     A cylinder has a surrounding wall  1 , enclosing a cylinder space that is axially defined by a top plane  2  and a bottom  3 , respectively. An evacuation chamber  4  is connected to a vacuum source through a discharge opening  5 , and a passage  6  connects the inner space of the cylinder to the evacuation chamber  4 . A piston shaft  7  is received in the cylinder and runs through the cylinder bottom  3  to be extendable and retractable, respectively. A piston  8  is attached in an inner end of the piston shaft  7  and caused to move as a result of a difference in pressure, generated by the vacuum source, and acting on the top face or bottom face, or the pressure side and suction side, respectively, of the piston. A grip means, such as a suction cup for holding an article, is attached in the outer end of the piston shaft  7 . A passage  9  runs axially through the piston shaft  7  to open in the top face of the piston  8 , thereby connecting the cylinder space above the piston top face to atmospheric pressure. A ring shaped seal, not further disclosed, may be received in the top face of the piston for dampening the piston motion in the extracted, extreme end position. 
     In accordance with the present invention,the bottom face of the piston  8  rests on upper ends of two bellows  11 , 12 , the bellows being supported on the bottom plane  3  of the cylinder. Said bellows  11 , 12  are flexible to be axially compressible, and may thus be produced from rubber or synthetic material, or a composition material including rubber and synthetics. By their construction and choice of material, the bellows  11 , 12  are urged to the extended position shown in FIG.  1 . 
     The bellows  11 , 12  extend concentrically about the piston shaft  7 , such that an outer and an inner annular space  13  and  14 , respectively, is defined within the bellows  11 , 12 . The outer annular space  13  is connected to the vacuum source through an annular passage  15 , opening in the upper face of the cylinder bottom  3 . The inner annular space  14  is connected to the atmosphere via one or more axial through holes  16 , passing through the cylinder bottom  3 . 
     When activating the vacuum source, see FIG. 2, a negative pressure is produced in the outer annular space  13 , that acts on a radially outer area of the piston suction face, whereas atmospheric pressure acts on the whole area of piston pressure face. While compressing the bellows  11 ,  12 , the piston  8  together with piston shaft  7  are thus driven outwards until the passage  9  of the piston shaft is closed, when the suction cup  10  contacts a surface of an article F (see FIG.  3 ). As atmospheric pressure no longer is admitted into the cylinder space above the piston  8 , the pressure difference between the piston pressure side and the piston suction side is gradually vanishing. This is secured by a passage  17  connecting the cylinder space and the evacuation chamber  4 , the latter preferably being extended substantially the whole axial length of the cylinder. 
     Concurrently, atmospheric pressure acts on the inner annular space  14 , which is connected to the atmosphere via through holes  16 . Thus, the piston suction face is exposed to a pressure that gradually exceeds the pressure acting on the pressure side of the piston. Accordingly, the piston  8 , piston shaft  7  and the gripped article are lifted upwards as illustrated by the arrow of FIG.  3 . 
     In one alternative embodiment, one or several load springs may be arranged inside the bellows for providing added lift capacity thereof, when lifting heavy articles. Reinforcing ring elements may likewise be internally arranged in the bellows  11 , 12  to provide them more stiffness. 
     In another embodiment, a set screw  18  may be arranged to provide an adjustable restriction of the passage  17  in order to adjust the speed of extension and retraction, respectively, of the piston shaft  7 . 
     In yet another embodiment, a set screw  18 ′ may likewise be arranged in the passage  6  for restricting the connection between the evacuation chamber  4  and the annular groove  15 , in order to adjust the speed of extension and retraction, respectively, of the piston shaft  7 . 
     In a second aspect of the invention, a transverse and horizontal partition wall  19  may be arranged to separate bellows  11  and  12 , arranged on top of each other. Said partition  19  forms an annular connection member  19  for a modular configuration of the lifting apparatus to a desired length or height, and comprises a central through hole for the piston shaft  7  as well as openings (not shown) for axial flow connection between spaces, enclosed by the bellows  11 , 12 . 
     Annular recesses  20  are formed in the lower face of the piston  8 , as well as in the upper face of cylinder bottom  3  and on both faces of the connection member  19  for receiving the ends of the bellows. Each annular recess  20  has a peripheral wall  21  running in the axial direction, so that the ends of the bellows  11 , 12  are radially supported by the wall. At least the ends of the inner bellows  12  may be formed to have a supporting shoulder  22  extended in radial direction, resting in the bottom of the recess  20 . Said shoulder  22  prevents air from leaking out from the annular spaces  13 , 14  during operation of the vacuum source. 
     A vacuum operated lifting apparatus as shown schematically in this embodiment provides good operating capacity also in harsh environments. The guidance of the piston shaft  7  through the cylinder bottom  3  may include a certain clearance to make the lifting apparatus less sensitive to particles and dirt. Impurities, which may enter the space within the inner bellows  12  via the through holes  16  will not be able to effect the operation, and the piston  8  may likewise be provided a clearance from the cylinder wall. Hence, the lifting apparatus of the invention is substantially insensitive to problems related to frictional wear, and will meet high demands on operation also in polluted or otherwise harsh locations.