Abstract:
A driving assembly for moving one unit with respect to another, for instance, a working unit with respect to a frame unit. Preferred practical applications for the driving assembly are lifting platforms or presses. The driving assembly includes a flat, enclosed, flexible container or bladder disposed between the two units. End wall portions of the container comprise the major surface area thereof. When pressure is introduced into the container, the walls thereof bear entirely against opposed bearing portions of the respective units and against a limiting wall. The invention allows for use of a very thin walled container for lifting large loads.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a driving assembly adapted to actuate a unit in relation to a frame unit, such as in the case of lifting platforms to raise a working portion in relation to a platform or as in the case of press devices to move a press member in relation to a machine frame. 
     2. Description of the Prior Art 
     It is previously known to use driving assemblies of elastic material for the abovementioned purposes. The prior art driving assemblies, however, have essential limitations as far as capacity and/or safety of operation is concerned. Thus, for instance, thinwalled driving assemblies in the first place are inclined to expand in other directions than the working direction whereas driving assemblies of the thickwalled, doublewalled or reinforced type exert a great resistance and therefore require special high pressure in order to overcome this resistance. 
     The present invention has for its purpose to remove these drawbacks by means of a simple apparatus. 
     SUMMARY OF THE INVENTION 
     The driving assembly of the present invention includes a first unit and a first bearing portion with a first bearing surface. A second unit is moveable relative to the first unit. The second unit has a second bearing portion including a second bearing surface. The units are so disposed relative to each other that the first and second bearing surfaces are in opposed, spaced, face-to-face relationship. A flat, enclosed, flexible container engages the first and second units and is disposed therebetween. The enclosed flexible container has an outer surface area and an inner, expansible chamber. The enclosed flexible container has a pair of opposite end wall portions comprising the major portion of the outer surface area. The remaining outer surface area is defined by a side wall portion, at least when the container is in a pressurized condition. Means are coupled with the container for effecting communication with a pressure source. The shape of the flexible container is changeable, in response to introduction of fluid pressure, to move the first unit with respect to the second unit. A limiting wall cooperates with the opposite bearing surfaces, these surfaces and the limiting wall defining an enclosed area within which the enclosed, flexible container is entirely disposed. The end wall portions of the enclosed, flexible container bear substantially entirely against the bearing surfaces of the first and second units. The side wall portion of the enclosed flexible container bears against the limiting wall at least when the container is in a pressurized condition. Thus, movement of the container, in a direction other than the direction of relative movement between the units, is limited. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be explained in more detail in the following specification with reference to the enclosed drawings in which 
     FIG. 1 by means of a sectional view shows a driving assembly according to the invention adapted to lift the working portion of a lifting platform, and 
     FIG. 2 by means of a sectional view shows said driving assembly in the ineffective position thereof with the lifting platform in the retracted position thereof. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The lifting platform 1 shown in the drawings is provided with one unit including a frame portion 2 and a working portion or working unit 4 connected to the frame portion by means of a lever system 3. The lever system 3 preferably comprises two pairs of crosslaid levers 5, 6 (in the drawings only one pair is shown) which by means of pivot pins 7, 8 are pivotally connected to the frame portion 2. The lever include pins 9, 10 which slidably engage slots 11, 12 in the working portion 4. The working unit 4 is raised and lowered in relation to the frame portion 2 by means of a driving assembly 13. This is provided with a bladder 14 for a pressure medium, and the chief object of the invention is to make it possible to use a thinwalled bladder 14 so as to exert the smallest possible resistance during expansion and to be inexpensive manufacture. Moreover, the bladder 14 should allow a reliable operation of the power aggregate and, despite a simple and inexpensive construction, to allow lifting of large loads. 
     For this purpose the power aggregate 13 according to the invention in principle consists of the bladder 14 which has a flat shape and is adapted by increase of the pressure on the medium within the container to expand in direction (A) partly increasing the distance between two opposite end walls 15, 16 which are the surfaces of the bladder having essentially the largest areas. The end walls form pressure surfaces in that they substantially entirely bear against oppositely positioned bearing portions 17 and 18, respectively, of the units 2 and 4, respectively, and exert pressure against said portions, and partly changing the shape of wall portions 19, 20. These wall portions connect the end walls 15, 16 and are positioned within at least one limiting wall 21 adapted to limit expansion of the bladder 14 in other direction. 
     The following combination of features achieve what is sought: the bladder 14 is flat, it has end walls forming relatively very large pressure surfaces, and walls connecting the side walls and changing their shape are supported by at least one limiting wall. 
     In order to make the parts enclosing the bladder 14 simple and to enhance convenience, the bearing portion 18 of one (4) of the units forms the bottom of a preferably downwardly open container the side walls 21 of which form limiting walls for the shape changing, side wall portions 19, 20 of the flat bladder 14. Said container preferably is guided by the frame unit 2 in that the side walls 21 cooperate with the other unit. 
     In order to provide a simple and expedient structure also as far as portions of the frame unit 2 are concerned, said unit is provided with a bearing portion 17 having portions 22 and 23 extending from the bearing side, the side walls 21 of the open container extending along and adapted to be guided by said portions 22, 23. That is, the entireties of side walls 21 of unit 2 are disposed in parallel relationship with the entireties of walls 23 and 24 of unit 4 as is readily apparent from the drawing. As is also readily apparent from the drawing, the major portions of walls 21, on the other hand, and walls 22 and 23, on the other hand, overlap each other in face-to-face relationship when bladder 21 is in the de-pressurized condition. See particularly FIG. 2. 
     A particularly simple, expendient and very stable structure is provided when the bearing portions of the units 2, 4 consist of box-shaped containers in which the flat bladder 14 is mounted between the bottoms of the portions 17, 18 forming said containers. In that case a suitable guiding of the one container is provided in that the wall portions 21 and 22, 23 bear against each other either directly or by means of guiding rollers (not shown). 
     In order to allow simple assembly and removal, respectively, the bearing portion 18 of one (4), of the units may consist of a separate part guided by the other unit 2. This part cooperates with the lever system 3 connecting the frame unit 2 with the working unit 4. The levers 5, 6 of the lever system 3 may bear against the open container 18, 21 in a suitable manner either directly (for instance against the outside of the bottom 18 of the container) or by means of rollers 24 mounted on the container walls 21. 
     As appears from FIG. 2 the lifting platform 1 in the retracted position thereof has a total height which corresponds to or only slightly exceeds the total height of the working unit 4, and this is achieved in that the working unit 4 directly bears against the frame unit 2. In order to cover and to protect all of the movable parts of the lifting platform 1 in collapsed position thereof the working unit 4 is shaped as a container which is open towards the frame unit 2. The container thus formed covers said movable parts and also the frame portion 2. Due to the fact that the working unit 4 with its bottom is spaced from the frame unit 2 only by the end walls 15, 16 of the flat bladder 14 when they bear against each other or practically bear against each other, an extremely low profile is provided when the lifting platform 1 is collapsed. It is important that the flat bladder 14 is not charged when the lifting platform is collapsed but that said bladder 14 is completely unloaded. This is achieved in that the units have portions forming stops. Thus, for instance, the height of the wall 21 may be higher than the height of the walls 22, 23 to an extent that a space for the flat bladder 14 is formed when the wall 21 bears against the frame unit 2. 
     The bladder 14, consists of an elastic, flexible or ductile material such as rubber, plastic, impregnated paper or the like. In order to expand the same a pressure medium, such as air, oil, water or any other liquid or gas may be used. The pressure is generated by means of a suitable pressure source 25 connected to the flat bladder 14 by means of a conduit 26. For the shutting off and/or throttling of the pressure medium, the conduit 26 may be provided with a conventional valve means 27. As is clearly apparent from the drawing, the conduit 26 passes through an opening 26a in bearing portion 17 of the lower container and extends into the cavity formed by that container. As is also clearly apparent from the drawing, there is a coupling device 26b in conduit 26, the coupling device being disposed in the cavity formed by walls 17, 22 and 23 of the lower container. 
     In the lifting platform 1 described above, the details may be carried out in many ways within the scope of the invention. As examples of different alternatives, the levers 5, 6 of the lever system 3 may be locked to the working unit 4 in different positions of displacement, as far as the elements 9, 10 in relation to the slots 11, 12 are concerned, by means of any type of locking device (not shown). Furthermore, in order to eliminate hazards of clamping a screen 28 may be used which is coupled to the units 2, 4 and unfolded when the working unit 4 is raised to cover all of the movable parts at the sides when the working unit 4 has been raised. Moreover, the pressure source 25 may be provided with a pressure plate (not shown) which in case of an exterior loading, for instance when a vehicle is driven onto the same, will compress a container of a plastic material, said bladder being connected to the flat container so that an increase of the pressure therein will cause a pressure increase in the flat bladder. The flat bladder 14 for instance may be adapted to cooperate with a wheel undercarriage (not shown) so that the wheels occupy their running position for driving the frame unit 2 over an underlayer when the flat bladder 14 is in its collapsed position and so that the wheels occupy the resting position when the flat bladder 14 is in its inflated position. 
     From the above it is seen that a lifting platform using the driving assembly 13 according to the invention may include a great deal of valuable characteristic features the details of which however have not been more specifically explained. The lifting platform also is provided with means ensuring a parallel movement of the working unit in relation to the frame unit 2. However, this is not the subject matter to which the present invention is directed, and therefore it has not been more specifically described. 
     The driving assembly according to the invention may be used in connection with other structures than lifting platforms. By and large, the driving assembly may be used in connection with all kinds of structures where one unit is to be moved in relation to a frame unit, such as presses in which a press member is to be moved in relation to a machine frame.