Abstract:
A support device for persons, such as a bed, treatment or operating table, chair, comprises:—a frame;—a first and a second movable member, which movable members can be adjusted independently of one another and which are designed to support the person or one or more parts of the person in various positions, and—a hydraulic system for adjusting the movable members, the hydraulic system comprising:—a reservoir for hydraulic liquid;—a first and a second hydraulic actuator associated with the first and second movable member, respectively, which hydraulic actuators can each be moved in two directions;—a hydraulic pump;—a pump activating member which is operatively connected to the pump in order for an operator to activate the pump;—a valve assembly which is provided in the hydraulic circuit between the pump and the respective actuators, and—a valve assembly operating member which can be mechanically operated by an operator and is mechanically connected to the valve assembly for selecting and providing a connection between one of the actuators and the pump in order to be able to selectively move a movable member by supplying pressurized hydraulic liquid to the associated actuator upon activation of the pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of PCT International Application No. PCT/NL2009/000067 filed on Mar. 19, 2009, which claims the benefit of Netherlands Patent Application No. 2001387 filed Mar. 19, 2008, both of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a support device for a person, such as a (hospital) bed, treatment or operating table, chair or the like. In particular, the invention provides a support device of this type for use in the medical field, such as in a hospital or other medical establishment, for the transportation of patients (or example in an ambulance), etc. 
         [0003]    In a particularly advantageous embodiment, the invention relates to a bed or table (in particular for a hospital) in which a patient is supported essentially in a recumbent position on a supporting surface of the bed or the table. In this case, a hydraulic system is provided for adjusting the height and the orientation of the supporting surface (or one or more sections thereof) of the bed or the table. 
       BACKGROUND OF THE INVENTION 
       [0004]    Hydraulic systems for adjusting hospital beds, for example adjusting of the supporting surface of a hospital bed in which, for example, a mattress is situated on which a patient can lie down, are generally known. For example, in U.S. Pat. No. 4,959,957 a hydraulic unit for adjusting the height of a hospital bed is illustrated. The unit: comprises a single-acting hydraulic actuator and a hydraulic plunger pump. The actuator is coupled to a height-adjustable subframe via a system of rods. The pump is operated by means of a foot-operated lever. The known hydraulic system is furthermore provided with a relief valve which can be operated separately and which relieves the actuator when it is operated, so that the subframe can be lowered. 
         [0005]    Another hospital bed with an associated hydraulic system is known from EP 0 341 358 A1. Compared to the system from U.S. Pat. No. 4,959,957, this system comprises a number of additional actuators, each of which is designed to adjust an associated adjustable section of the supporting surface. This known hospital bed has a supporting surface with adjustable back and leg sections, as is very common in practice. The hydraulic system is provided with a hand-operable valve assembly operating member which is designed in such a manner that, by being operated, it selects a specific actuator and connects the latter to the pump in order to thus adjust a specific section of the supporting surface or to set the height of the subframe. The hydraulic system known from EP 0 341 358 A1 is furthermore provided with a pump activating member in the form of a foot-operable lever which is connected to the pump. The purpose of this pump activating member is to actuate the pump so that an actuator which is selected by means of the valve assembly operating member is fed with pressurized hydraulic liquid. In addition, the known hydraulic system is provided with a further, i.e. a third, member which can be operated by an operator and which is connected to a separate relief valve. By operating this third operating member, an operator can produce a connection between a selected actuator and the reservoir and thus a return movement can be carried out. 
         [0006]    In order to operate the hydraulic system known from EP 0 341 358 A1, the operator needs at least one of his/her hands to operate the valve assembly operating member. This means that the operator is not able to use both his/her hands (if any) for treating a patient when the operator operates the valve assembly operating member. In many cases, the procedures which have to be carried out on a patient require the use of both hands by the person carrying out the procedure, which is not possible in the case of the hydraulic system known from EP 0 341 358 A1. This may lead to a reduction in care for the patient, require additional care personnel or delay the operation of the hydraulic system (which is undesirable in, for example, hospitals). 
         [0007]    The German Utility Model DE 298 15 699 U1 discloses an operating table with hydraulic adjustable members on the supporting surface. The hydraulic system of the operating table from DE 298 15 699 U1 comprises a first lever which can be displaced in a horizontal plane by means of which a hydraulic actuator which is associated with one of the adjustable members can be selected. This lever can be moved into unique positions in order thus to select a specific hydraulic actuator. Like the hydraulic system known from EP 0 341 358 A1, the hydraulic system from DE 298 15 699 U1 comprises a pump activating member in the form of a second foot-operable lever which is connected to the hydraulic pump. In addition, the hydraulic system comprises a third lever which can be foot-operated by an operator and is connected to a separate relief valve. By operating the third lever, the operator can produce a connection between a selected actuator and the reservoir and thus a return movement can be carried out. 
         [0008]    A further drawback of both EP 0 341 358 A1 and DE 298 15 699 U1 is that the positioning of the members that can be operated, in particular the foot-operated levers for actuating and relieving the hydraulic actuators, is not satisfactory from an ergonomic point of view. With both the hydraulic system from EP 0 341 358 A1 and DE 298 15 699 U1, said foot-operated levers are arranged in close proximity to one another. This may result in mistakes being made regarding which lever is to be operated by the operator, which may have highly undesirable consequences in the case of a hospital bed. 
       OBJECT OF THE INVENTION 
       [0009]    It is an object of the present invention to provide a support device for a person with an improved hydraulic system. 
         [0010]    It is furthermore an object to provide a support device for a person with a hydraulic system which can be operated easily, intuitively, reliably and quickly, in which the risk of the wrong operating member being operated is as small as possible. 
         [0011]    It is a further object of the invention to provide a support device for a person with a sturdy and reliable hydraulic system. 
         [0012]    It is a further object of the invention to provide a hospital bed or operating table provided with a hydraulic system for adjusting one or more movable members of the respective bed or table which is simple to operate. 
       SUMMARY OF THE INVENTION 
       [0013]    According to a first aspect thereof, the present invention achieves one or more of the above objects by providing a support device for a person, such as a bed, treatment or operating table, chair. The support device comprises a first and a second movable member, which movable members can be adjusted independently of one another and which are designed to support the person or one or more parts of the person in various positions. A hydraulic system is provided for adjusting the first and second movable members, the hydraulic system comprising:
       a reservoir for hydraulic liquid,   a first and a second hydraulic actuator associated with the first and second movable member, respectively, which hydraulic actuators can each be moved in two directions;   a pump;   a valve assembly which is arranged in the hydraulic circuit between the pump and the respective actuators; and   a relief element for removing hydraulic liquid from an actuator.       
 
         [0019]    The support device furthermore is provided with:
       a pump activating member which is operatively connected to the pump in order for an operator to activate the pump;   a relief-activating member which is operatively connected to a relief element for removing hydraulic liquid from a selected actuator;   a valve assembly operating member which can be mechanically operated by an operator and is mechanically connected to the valve assembly for providing a connection between a selected actuator and the pump and the relief element, in order to be able to selectively move a movable member by supplying pressurized hydraulic liquid to the selected actuator upon operation of the pump activating member or by removing hydraulic liquid from the selected actuator upon operation of the relief element, respectively.       
 
         [0023]    In the support device; according to the first aspect of the invention, the valve assembly is designed so as to provide a connection between a selected actuator and the reservoir in such a way that the selection of an actuator requires a substantially horizontal displacement of the valve assembly operating member into various positions, so that the operator selects the movable member to be moved by operating the valve assembly operating member and produces the movement by activating the pump activating member and the relief activating member, respectively. In addition, the pump activating member, the relief activating member and the valve assembly operating member are designed and arranged so as to be operated by the operator with his/her foot. In addition, they are provided in a substantially horizontal plane on a side of the support device for persons. In particular, the valve assembly operating member is situated between the pump activating member and the relief activating member. The substantially horizontal displacement of the valve assembly operating member is an operation which is simple to learn and which can be carried out easily, for example when under stress. 
         [0024]    The invention is inter alia based on the insight that and has the advantage that by placing the various operating members of the hydraulic system of the device next to one another and in particular by separating the operating members for supplying hydraulic liquid to the actuators or discharging it therefrom as much as possible from one another, yet grouping them together with the operating member for the valve assembly, it becomes possible for an operator to operate the hydraulic system of the device without using his/her hands and results in the risk of mistakes in selecting the direction of movement of the actuators being reduced to a minimum. 
         [0025]    Preferably, the valve assembly is a single multi-position valve with a valve body which can be moved at least into a number of positions corresponding to the number of positions of the valve assembly operating member. By using a single valve, the structure is relatively simple and not susceptible to malfunction. 
         [0026]    In an advantageous embodiment, an actuator is a single-acting cylinder with a piston rod which can be moved to and fro in a cylinder housing, which delimits a variable chamber in the cylinder housing, with a single main line connection being provided which is connected to the variable chamber, with the cylinder being provided with a hydraulically operated non-return valve with a control pressure line connection which is connected to the relief element and with a main line and a control pressure line being provided between the valve assembly and the actuator, in such a manner that the piston rod of the selected cylinder extends upon activation of the pump and retracts upon activation of the relief element. This embodiment ensures that rupture or leakage of a line does not result in accidental movement of the movable member, for example in lowering of the bed. In a practically advantageous embodiment, all actuators are single-acting actuators. 
         [0027]    In a preferred embodiment of the present invention, the reservoir for the hydraulic liquid, the hydraulic pump and the valve assembly are accommodated in a common housing. This eliminates a further drawback of the hydraulic system known from EP 0 341 358 A1. 
         [0028]    In the hydraulic system known from EP 0 341 358 A1, the respective parts thereof, in particular the reservoir, the pump and the valve assembly, are distributed over a frame of the hospital bed. In order to incorporate all said parts into a circuit, several hydraulic lines are required in order to connect all parts to one another. This results in a relatively complex system of lines, connections and operating members, which are distributed across said frame. In addition, constructing the known hydraulic system is consequently labour intensive, since all parts have to be fitted and connected separately. In the case of said design of the present embodiment, only the hydraulic lines from and to the actuators have to be fitted to the hospital bed. As a result thereof, it is inter alia possible to deliver the hydraulic system preassembled to whoever produces or assembles the hospital bed, which will result in a significant time saving during assembly. 
         [0029]    According to a second aspect thereof, the present invention achieves one or more of the above objects by providing a support device for a person, such as a bed, treatment or operating table, the support device comprising:
       a first and a second movable member, which movable members can be adjusted independently of one another and which are designed to support the person or one or more parts of the person in various positions; and   a hydraulic system for adjusting the movable members, the hydraulic system comprising:
           a reservoir for hydraulic liquid;   a first and a second hydraulic actuator associated with the first and second movable member, respectively, which hydraulic actuators can each be moved in two directions;   a pump;   a valve assembly which is arranged in the hydraulic circuit between the pump and the respective actuators.   
               
 
         [0036]    The support device furthermore is provided with:
       a pump activating member which is operatively connected to the pump in order for an operator to activate the pump;   a valve assembly operating member which can be mechanically operated by an operator and is mechanically connected to the valve assembly for providing a connection between a selected actuator and the pump, in order to be able to selectively move a movable member by supplying pressurized hydraulic liquid to the selected actuator upon operation of the pump.       
 
         [0039]    This device according to the second aspect of the invention provides for the mechanically operable valve assembly operating member for each of the first and the second actuators to be brought into two unique spatial positions, with one unique position corresponding to the connection of this actuator (which is thus also selected) to the pump and the other unique position corresponding to the direction of movement of said selected actuator, so that, by operating the latter, the operator selects the movable member which is to be moved as well as the direction of movement thereof and effects the movement by activating the pump activating member. 
         [0040]    As far as its second aspect is concerned, the invention is inter alia based on the insight that now, using a single valve assembly operating member, both the actuator to be operated and its direction of movement can be selected and that, by activating the pump, this movement can be effected. 
         [0041]    Preferably, the mechanically operable valve assembly operating member is designed to be able to select all hydraulic actuators of the device, i.e. in the case of three actuators, there would be six unique positions, etc. 
         [0042]    In this manner, only two elements which are to be operated by the one or more operators (for example medical personnel) are required in order to carry out all the necessary operations in order, for example, to adjust a supporting surface of a hospital bed. In addition, when selecting the actuator to be actuated, the direction of operation thereof will also have to be selected, so that, upon actuation of the actuator, it is no longer necessary to choose a respective operating member, but only one operating member is available for said purpose. 
         [0043]    Preferably, the valve assembly is a single multi-position valve with a valve body which can be moved at least into a number of positions corresponding to the number of unique positions by operating the valve assembly operating member. By using a single valve, the structure is relatively simple and not susceptible to malfunction. 
         [0044]    In an advantageous embodiment, the single valve has a valve body which is accommodated in an associated bore in a housing so as to be rotatable about an associated shaft and axially displaceable in the direction of said shaft, with the valve body having two axial positions which can be achieved by axial displacement and, in each axial position, at least two angular positions which can be achieved by rotation, with each of these positions corresponding to a selected actuator and the direction of movement thereof. 
         [0045]    Preferably, the valve assembly operating member is designed such that the selection of an actuator requires a substantially horizontal displacement of the valve assembly operating member, and that the selection of the direction of movement of an actuator requires a substantially vertical displacement of the valve assembly operating member. This is an operation which is simple to learn and which can be carried out easily, for example when under stress. 
         [0046]    In a practically advantageous embodiment, the valve assembly operating member comprises a lever connected to the valve assembly. 
         [0047]    Preferably, the valve assembly operating member is designed and arranged as a member which can be operated by an operator with his/her foot. This is advantageous as the operator can use his/her hands to do other things and/or can keep them clean, for example sterile in the case of medical personnel. This version is particularly advantageous if the activation of the pump is also carried out by foot. 
         [0048]    In a practically advantageous embodiment, the pump is a pump which can be operated mechanically by means of a foot lever, the pump preferably being provided with two foot levers which can be operated from different sides of the device. 
         [0049]    In an advantageous embodiment, the device is provided with a valve assembly operating member provided in duplicate, so that operation thereof can take place from different sides of the device. 
         [0050]    In a particularly advantageous embodiment, an actuator is a single-acting cylinder with a piston rod which can be moved to and fro in a cylinder housing, which delimits a variable chamber in the cylinder housing, with a single main line connection being provided which is connected to the variable chamber, with the cylinder, preferably in the cylinder housing, being provided with a hydraulically operated non-return valve with a control pressure line connection, a main line and a control pressure line being provided between the valve assembly and the actuator, in such a manner that if the valve assembly connects the pump to the main line, the piston rod extends upon activation of the pump, and in such a manner that if the valve assembly connects the main line connection to the reservoir, the non-return valve prevents the hydraulic liquid from the variable chamber from flowing out via the main line to the reservoir, unless the pump is activated. This embodiment ensures that rupture or leakage of a line does not result in accidental movement of the movable member, for example in lowering of the bed. In a practically advantageous embodiment, all actuators are single-acting actuators. 
         [0051]    In a preferred embodiment of the present invention, the reservoirs for the hydraulic liquid, the hydraulic pump and the valve assembly are accommodated in a common housing. This eliminates a further drawback of the hydraulic system known from EP 0 341 358 A1. 
         [0052]    In the hydraulic system known from EP 0 341 358 A1, the respective parts thereof, in particular the reservoir, the pump and the valve assembly are distributed over a frame of the hospital bed. In order to incorporate all said parts into a circuit, several hydraulic lines are required in order to connect all parts to one another. This results in a relatively complex system of lines, connections and operating members, which are distributed across said frame. In addition, constructing the known hydraulic system is consequently labour intensive, since all parts have to be fitted and connected separately. In the case of said design of the present embodiment, only the hydraulic lines from and to the actuators have to be fitted to the hospital bed. As a result thereof, it is inter alia possible to deliver the hydraulic system preassembled to whoever produces or assembles the hospital bed, which will result in a significant time saving during assembly. 
         [0053]    The present invention furthermore relates to a bed or table on which a person can be supported in a recumbent position, in particular a hospital bed, treatment or operating table, with:
       an undercarriage which stands on the ground, preferably a wheeled undercarriage,   a height-adjustable subframe;   a supporting surface which is supported by the subframe for supporting a person thereon, for example a patient, at least in a recumbent position, the supporting surface comprising at least one adjustable section for supporting a specific body part of a patient in different orientations,   a hydraulic system according to one of both aspects of the invention, in which the height-adjustable subframe and the at least one adjustable section of the supporting surface are each separately coupled to a hydraulic actuator of the hydraulic system.       
 
         [0058]    The invention also relates to a hydraulic system which is designed for a support device for persons as explained in this document. 
         [0059]    Further advantageous embodiments of the present invention will be described below with reference to the figures, in which identical parts are denoted by the same reference numerals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0060]      FIG. 1  shows a hospital bed with a hydraulic system according to a first embodiment of the invention; 
           [0061]      FIG. 2  shows a simplified representation of the hospital bed from  FIG. 1 ; 
           [0062]      FIG. 3A  diagrammatically shows a three-dimensional representation of the hydraulic system with a double valve assembly operating member; 
           [0063]      FIG. 3B  shows the system from  FIG. 3A  in a different position thereof; 
           [0064]      FIG. 3C  shows the system from  FIG. 3A  in yet another position thereof; 
           [0065]      FIG. 4A  shows the valve assembly, in cross section and in top view, of the hydraulic system of the first embodiment of the invention; 
           [0066]      FIG. 4B  shows the valve assembly from  FIG. 4A  in cross sectional side view; 
           [0067]      FIG. 5  shows a hydraulic diagram of the bed from  FIG. 1 ; 
           [0068]      FIG. 6  shows a simplified representation of the hospital bed from  FIG. 1  with an alternative hydraulic system, and 
           [0069]      FIG. 7  shows a hydraulic diagram of the hydraulic system of the bed from  FIG. 6 . 
           [0070]      FIG. 1  shows a hospital bed which is generally denoted by reference numeral  1 , with reference to which an example or a first embodiment of the present invention will be described. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0071]    The hospital bed  1  comprises a wheeled undercarriage  2  which is provided with wheels  4 . By means of a parallelogram structure  6 , a height-adjustable subframe  8  is supported on the undercarriage. The subframe  8  in turn supports a supporting surface  12  on which a person can lie. In practice, a mattress can be arranged on the supporting surface  12 . 
         [0072]    For the sake of keeping the drawing simple, parts which are normally present on a hospital bed  1 , such as mattresses, cosmetic panels, etc. have not been shown in the figure. 
         [0073]    In the illustrated embodiment, the supporting surface  12  is made up of several sections, in this case a fixedly arranged section  14  for supporting the lower back of a person, an adjustable back section  16  for supporting the back of a person and an adjustable leg section  18  for supporting the legs of a person, which is made up of two parts  18   a,b  in this case. 
         [0074]    Furthermore, the hospital bed  1  is provided with at hydraulic system  20 , a first preferred embodiment of the hydraulic diagram of which is shown in  FIG. 5 . 
         [0075]    The hydraulic system  20  comprises a reservoir  22  for storing hydraulic liquid therein. Furthermore, the hydraulic system  20  comprises several hydraulic actuators, in this case three  24 ,  26  and  28 , each for driving an associated movable member of the bed  1 . If desired, an actuator can also be replaced by a pair of parallel actuators. 
         [0076]    The actuators  24 ,  26 ,  28  are connected to a hydraulic pump  32  via lines which are not shown in  FIG. 1 . The hydraulic pump  32  is connected to the reservoir  22  and is designed for supplying pressurized hydraulic liquid to the actuators  24 ,  26 ,  28 , with the reservoir  22 , the pump  32  and the actuators  24 ,  26 ,  28  forming a hydraulic circuit. 
         [0077]    As is preferred, the pump  32  is a pump which is operated by human force, but could possibly also be an electric pump. 
         [0078]    In said hydraulic circuit, a valve assembly  34  is provided between the pump  32  and the actuators  24 ,  26 ,  28  which is designed to selectively connect in each case one actuator to the pump  32  or to the reservoir  22  so that a circuit is formed. 
         [0079]    Furthermore, a pump activating member  36  is provided in the form of a foot-operable lever which is connected to the pump  32 , which is intended exclusively for operating the pump  32 . 
         [0080]    Furthermore, a valve assembly operating member  38  is provided in the form of a lever which is connected to the valve assembly  34  and is intended exclusively for operating the valve assembly  34 . 
         [0081]    The valve assembly  34  in the embodiment illustrated in  FIG. 1  is designed to select both a selection of the actuators  24 ,  26 ,  28  to be actuated and the direction of movement thereof, the latter meaning the extension or retraction of a piston rod of the respective actuator. In this case, the valve assembly  34  is designed to switch on in each case one actuator  24 ,  26 ,  28  so that a circuit is formed, that is to say bring ii: into liquid communication with the pump  32  or with the reservoir  22 . 
         [0082]    This means that the member  38 , for each of these switching positions of the valve assembly  34 , has a unique spatial position, which position is determined by the operator. By subsequently operating the pump  32 , the intended movement is performed. 
         [0083]    As is preferred, the valve assembly  34  is designed as a single multi-position valve (a preferred embodiment of which is explained in more detail with reference to  FIGS. 4   a,b ) having a single valve body which can assume several positions. Displacement of the valve body is effected by displacement of the lever  38 . 
         [0084]    As stated, each setting of the multi-position valve of the valve assembly  34  and thus each position of the valve assembly  34  is associated with one unique combination of an actuator and the selected direction of movement thereof. 
         [0085]    Because of its direct mechanical connection to the valve assembly  34 , the lever  38  connected to the valve assembly  34  thus also always has a unique position which is associated with the position of the valve assembly  34 . Therefore, the position of the lever  38  is thus indicative of the selected actuator  24 ,  26 ,  28  and the direction of movement thereof. 
         [0086]    Various members of the hydraulic system, in particular the reservoir  22 , the pump  32  and the valve assembly  34  are preferably accommodated in a single housing, that is to say that at least the respective members are connected to one another in such a way that their respective housings form a substantially single unit. This results in a very compact assembly of hydraulic reservoir, valve assembly and hydraulic pump which can be fitted to the undercarriage  2  of the hospital bed  1  as a single unit. 
         [0087]    The internal operation of the valve assembly  34  and in particular the operation of the multi-position valve will be described in more detail with reference to  FIGS. 4A and 4B . The operation of the hydraulic system  20  and in particular the adjustment of the hospital bed  1  by means of the hydraulic system  20  will now be explained briefly. 
         [0088]    As mentioned, the subframe  8  is adjustable in height and by adjusting the height of the subframe  8 , the supporting surface  12  supported thereon can also be adjusted in height. This is desirable, in particular for hospital beds, in order to avoid nursing staff having to bend over very often so as to be able to carry out nursing and/or caring treatments. The height-adjustment of the hospital bed  1  and in particular of the supporting surface  12  is indicated in the figure by a double arrow A. 
         [0089]    Adjusting the height of the subframe  8  and thus of the supporting surface  12  is effected by actuating the actuator  24 , one end of which is connected to the undercarriage  2  and the other end of which is connected to the structure  6 . 
         [0090]    Adjustment of the hinged back section  16  takes place by means of actuator  26 , one end of which is connected to a subframe  8  and the other end of which, in the example illustrated the free end of a piston rod  26   a  (see  FIG. 3A ), is connected to the adjustable section  16 . 
         [0091]    Adjustment of the leg section  18  takes place by means of actuator  28 , one end of which is connected to the subframe  8  and the other end of which is connected to a first subsection  18   a  of the leg section  18 . The first subsection  18   a  is hingedly connected to a second subsection  18   b  via a hinge  52 . It should be noted that the position of hinge  52  will correspond approximately to the location of the knees of a person lying on a mattress arranged on the supporting surface  12  when the hospital bed  1  is in use. The second subsection  18   b  is in turn connected to the subframe  8  by its free end  18   c  via a linear guide. The first subsection  18   a  is hingedly connected to the fixed section  14  via a hinge  56 . 
         [0092]    Selecting the subsection  16 ,  18  of the supporting surface  12  to be displaced or selecting the height-adjustment of the subframe  8  is effected by moving the valve assembly  34  into the correct position by means of the lever  38 . The selection of the selected actuator  24 ,  26 ,  28  is effected by operating the lever  36  by means of a foot. 
         [0093]    As has been explained above, the position of the valve assembly  34  and thus the position of the lever  38  by means of which the valve assembly  34  can be operated, is indicative of the selected actuator  24 ,  26 ,  28  and the selected direction of movement thereof. This will be explained briefly with reference to  FIG. 2 . 
         [0094]      FIG. 2  shows a highly simplified representation of the hospital bed  1 , in which only the supporting surface  12 , the subframe  8 , the wheeled undercarriage  2  and the levers  36 ,  38  are represented (in highly diagrammatic form). In this case, the position of the supporting surface  12  substantially corresponds to the position thereof as indicated in  FIG. 1 . Furthermore,  FIG. 2  shows the various sections  14 ,  16 ,  18  which can be hinged with respect to one another via the hinges provided, as has been explained above with reference to  FIG. 1 . For the sake of simplicity of the illustration, the actuators and the hydraulic system for adjusting the hospital bed  1  are not shown in any more detail. 
         [0095]    As has been described above, the position of the lever  38 , by means of which the valve assembly  34  can be operated, is indicative of the selected actuator  24 ,  26 ,  28  and the selected direction thereof. This is illustrated diagrammatically by the positions  381 - 386  of the lever  38  shown in  FIG. 2 . Position  381 , that is to say the topmost left-hand position in  FIG. 2 , corresponds to the selection of the actuator  26  with which the back section  16  of the supporting surface  12  can be adjusted upwards (see  FIG. 1 ) in such a manner that operation, that is to say actuation, thereof by operating the lever  36  using a foot, as indicated by arrow I, will rotate the back section  16  about hinge  44  and this will thus be moved upwards. It should be noted that the lever  36  has two limit positions denoted by an upper position  361  and a lower position  362 . From the point of view of ease of operation, it is simple and comfortable for a user to press the lever  36  downwards using his/her foot (arrow I), i.e. from the top position  361  to the bottom position  362 . To this end, a restoring mechanism (not shown in any more detail) is preferably provided so that, when the lever  36  has been moved to the bottom position  362 , the lever  36  is returned to the top position  361  by releasing it or by no longer exerting any force on it with the foot. 
         [0096]    A position on the far bottom left-hand side of the lever  38 , indicated in  FIG. 2  by reference numeral  382 , indicates that the actuator  26  is selected, but that operation of the lever  36  will result in the actuator  26  (see  FIG. 1 ) being relieved and thus the back section  16  being lowered. By selecting the bottom position of the lever  38 , a connection is made in the valve assembly between the actuator  26  (see  FIG. 1 ) and the reservoir  22  (see  FIG. 1 ) instead of the pump  32  (see  FIG. 1 ). In this way, a person who wants to adjust the hospital bed  1  will recognise a far left-hand position  381 ,  382  as a position in which the back section  16  will be adjusted when the other lever  36  is operated, which back section  16  is for this person also situated on the left-hand side. 
         [0097]    In a completely analogous manner, adjusting the lever  38  to a position  385  at the top right-hand side and a position  386  at the bottom right-hand side corresponds to selecting actuator  28  (see  FIG. 1 ), more particularly to moving the leg section  18  upwards or downwards, respectively. Adjusting the lever  38  to a position  383  at the top centre and a position  383  at the bottom centre, that is to say between the left-hand and right-hand positions of the lever  38  in the figure, corresponds to selecting actuator  24  (see  FIG. 1 ) for adjusting the height of the supporting surface  12 . For the sake of clarity, adjusting the lever  38  to a position between a top and bottom position is indicated by arrow II in  FIG. 2 . In this way, only two operating elements are necessary to carry out all the necessary operations in order to adjust the supporting surface  12  of the hospital bed  1 . In addition, it is immediately clear from the position of the lever  38  which actuator will be operated and in which direction. 
         [0098]    In a preferred embodiment of the hydraulic system according to the present invention, the pump activating member  36  and the valve assembly operating member  38 , in other words the levers  36 ,  38 , are provided in duplicate, in this case in such a manner that they can be operated from each longitudinal side of the bed  1 . This is shown in more detail in  FIGS. 3A-3C . 
         [0099]      FIG. 3A  shows a simplified representation of a hydraulic system  20  according to the present invention. The purpose of the representation in  FIG. 3A  is only to clarify the operation of the hydraulic system  20 . In particular, the spatial distribution of the actuators  24 ,  26 ,  28  is only indicated diagrammatically. Thus, for example, the hydraulic lines which connect the actuators  24 ,  26 ,  28  and the valve assembly  34  are not shown.  FIG. 3A  shows that the levers  36 ,  38  are in this case provided in duplicate. The advantage thereof is that there are operating members on both longitudinal sides of a hospital bed, in this example, as is preferred, foot-operable elements, such as levers, by means of which the hospital bed can be adjusted. As can be seen in the figure, the double lever  36  is connected via a system of rods  60  to a shaft  62  of the pump  32 . Via a further system of rods  64 , the operating member  38  provided in duplicate is connected to a shaft  66  by means of which a multi-position valve in the valve assembly  34 , which valve will be described in more detail below, can be operated. 
         [0100]    In the position shown in  FIG. 3A , the lever  38  for operating the valve assembly  34  is in the position indicated in  FIG. 2  by reference numeral  381 . That is to say that when the lever  36  associated with the pump is operated, hydraulic liquid will be supplied to the actuator  26  and the piston rod  26   a  will thus be pushed out of the actuator  26 . In addition,  FIG. 3A  shows that the lever  36  has just been operated as it is in its bottom position  362  (see also  FIG. 2 ). 
         [0101]    From the position shown in  FIG. 3A , the actuator  26  can be retracted again by moving the lever  38  downwards, as has been described for  FIG. 2 . This is shown in  FIG. 3B . 
         [0102]    In  FIG. 3B , the lever  38  has been moved downwards to a position which is denoted in  FIG. 2  with reference numeral  382 . In this position  382 , the actuator  26  is connected to the reservoir  22 . By moving the lever  36  from position  361  to position  362 , the actuator  26  is retracted again under load. 
         [0103]    As another example of a position of the hydraulic system  20 , that is to say a position of the levers  38 ,  FIG. 3C  shows the position in which the levers  38  are in position  385  from  FIG. 2 . In this position, the actuator  28  is actuated when the pump is operated and thus the leg section  18  (see  FIG. 2 ) is moved upwards. 
         [0104]      FIGS. 3A to 3C  also show that the hydraulic pump  32 , the reservoir for hydraulic liquid  22  and the valve assembly  34  (to which all hydraulic lines from and to the piston-cylinder devices  24 ,  26 ,  28  which are not shown in the figures are connected) form a single unit. 
         [0105]    An example of the valve assembly  34  is shown in more detail in and described with reference to  FIGS. 4A and 4B . 
         [0106]      FIG. 4A  shows a valve assembly  34  which is designed as a single multi-position valve in cross-sectional side view. The multi-position valve  34  comprises a valve housing  70  with a blind bore  72  provided therein. The valve body  66  is accommodated in the bore  72  so as to be rotatable about a shaft and to be axially displaceable along the shaft, in which a free end  66   a  of the shaft  66  extends outside the housing  70  and can be connected to the system of rods  64  as described with reference to  FIG. 3A . At the location of the free end of the valve body  66 , a gland  74  is provided in bore  72 . On the one hand, the gland  74  serves to seal the bore  72  and, on the other hand, to seal the interior of the bore  72 , in which pressurized hydraulic liquid is situated. A second free end  66   b  of the valve body  66  comprises a mouth  76  of a through-passage  78 . The mouth  76  is in communication with a source of hydraulic liquid, so that the hydraulic liquid can flow into the through-passage  78 . The through-passage  78  ends in a space  82  between the gland  74  and a collar  80  provided on the valve body  66 , which collar  80  serves to seal the space  82 . Via the through-passage  78 , the space  82  is filled with hydraulic liquid at the same pressure as prevails at the inlet  76 . As a result thereof, the play of forces resulting from the pressure in the hydraulic liquid will keep the shaft balanced and the hydraulic pressure which prevails at the second free end  66   b  of the valve body  66  will be balanced out by the same pressure in the space  82  and the valve body  66  will not be pushed out of the housing  70 . 
         [0107]    In addition, the housing  70  is provided with connection nipples  84 , only two of which can be seen in the cross-sectional view from  FIG. 4A . The number of pairs of connection nipples corresponds to the number of actuators  24 ,  26 ,  28  present. The connection nipples  84  can be connected to hydraulic lines which run to the actuators. Via connecting ducts  86 , the connection nipples  84  can be connected to a mouth  88  (see  FIG. 4B ) in the valve body  66  and thus to the through-passage  78 . In the illustrated arrangement, the bottom connection nipple  84   a   1  is in communication with the through-passage  78  and hydraulic liquid can flow through the associated hydraulic line. In view of the configuration of the lever  38  shown in  FIGS. 3A to 3C , the valve body  66  is in its bottom position and the lever  38  will be in its highest position (see  FIG. 3A ) in this example. 
         [0108]      FIG. 4B  shows the multi-position valve  34  in cross-sectional side view. In this case, a number of connection nipples  84  are visible which are situated at the same level, that is to say the illustrated connection nipples  84  are all bottom connection nipples or top connection nipples. 
         [0109]    For the sake of convenience, it is assumed that, in this case, they are bottom connection nipples  84   a   1 ,  84   a   2 ,  84   a   3 . The connection nipples  84   a   1 ,  84   a   2 ,  84   a   3  can be connected to the connecting ducts  86  which can, in turn, be connected to the mouth  88  in the valve body  66  and thus to the through-passage  78 . At their other side, the connection nipples  84   a   1 ,  84   a   2 ,  84   a   3  are connected to lines to the respective actuators. In the illustrated example, the central connection nipple  84   a   2  is connected to the through-passage  78 . The selection of another actuator is effected by rotating the valve body  66  about its longitudinal axis. This is indicated in the figure by arrow C. By turning the valve body  66  a quarter turn clockwise, connection nipple  84   a   3  will be connected. By turning the valve body  66  a quarter turn anticlockwise, connection nipple  84   a   1  will be connected. In this way, a multi-position valve which is simple to operate is provided. 
         [0110]      FIG. 5  shows an example of the hydraulic system as has been discussed above, with pump  32 , reservoir  22 , the pressure-limiting valve  90  connected to the outlet of the pump  32  in a connection to the reservoir, and with multi-position valve  34 . These parts are accommodated in a unit. 
         [0111]    Furthermore, the actuators  24 ,  26 ,  28  can be seen, which are all designed as single-acting cylinders with a piston rod which can be moved to and fro in a cylinder housing, which delimits a variable chamber in the cylinder housing. A single main line connection  24   a ,  26   a ,  28   a , is provided for each actuator and is connected to the variable chamber. 
         [0112]    Each of the cylinders  24 ,  26 ,  28  is furthermore provided with a hydraulically operated non-return valve  24   b ,  26   b ,  28   b  with a control pressure line connection  24   c ,  26   c ,  28   c.    
         [0113]    Between the valve assembly  34  and each of the actuators, there is in each case provided a main line  91 ,  92 ,  93 , and a control pressure line  94 ,  95 ,  96 , for example in the form of a hose. 
         [0114]    If the valve assembly  34  connects the pump  32  to the main line to an actuator, the piston rod thereof will extend upon activation of the pump. 
         [0115]    If the valve assembly  34  connects one of the main line connections  24   a ,  26   a ,  28   a  to the reservoir  32 , the non-return valve  24   b ,  26   b ,  28   b  of this respective actuator prevents the hydraulic liquid from flowing out of the variable chamber via the main line to the reservoir. This blocking is only cancelled when the pump is activated, so that a control pressure reaches the respective non-return valve via the control line and opens this valve. 
         [0116]    When a line or connection ruptures or leaks, the valves  24   b ,  26   b ,  28   b  ensure that no accidental movement takes place, for example lowering of the bed  1 . 
         [0117]    It can furthermore be seen that, in this case, each actuator is also provided with a restricted outflow via a throttle and a parallel non-return valve which makes an unrestricted inflow to the variable chamber possible. 
         [0118]    Below, an alternative embodiment of the hydraulic system  20  for the hospital bed  1 , as shown and described with reference to the preceding figures, will be described with reference to  FIGS. 6 and 7 . The alternative hydraulic system largely corresponds to the hydraulic system  20  except for the differences to be discussed below. 
         [0119]    The inventors have realized that, although the embodiment of the hydraulic system for the hospital bed, as described with reference to the preceding figures, works well and is a significant improvement on the known hospital beds, it is possible, on the one hand, to simplify the valve assembly  34  and, on the other hand, to further improve the operation of the hydraulic system as regards intuitive operation. The inventors have achieved this by no longer configuring the valve assembly  34  so that it selects the actuator  24 ,  26 ,  28  to be actuated as well as the direction of movement thereof, but by configuring it solely so that it selects the actuator  24 ,  26 ,  28  to be actuated, and by providing a separate relief-activating element which is operatively connected to a non-return valve in an actuator  24 ,  26 ,  28  for removing hydraulic liquid from a selected actuator. 
         [0120]      FIG. 6  shows a highly simplified representation of the hospital bed  1  as discussed with reference to  FIG. 2  and with substantially the same members. Compared to the hospital bed from  FIG. 2 , the hospital bed  1  in  FIG. 6  comprises a third operating member  100 . The third operating member or relief-activating member  100  is operatively connected to a non-return valve for removing hydraulic liquid from a selected actuator. This will be discussed in more detail with reference to  FIG. 7 . 
         [0121]    As has been discussed before, the position of the lever  38 , by means of which the valve assembly  34  can be operated, is indicative of the selected actuator  24 ,  26 ,  28 . This is shown diagrammatically by means of the positions  381 ,  383 ,  385  of the lever  38  illustrated in  FIG. 6 . Position  381 , that is to say the position on the far left-hand side in  FIG. 6 , corresponds to selecting the actuator  26  with which the back section  16  of the supporting surface  12  can be adjusted (see  FIG. 1 ) in such a manner that operation, that is to say actuation, thereof by operating the lever  36  by foot, indicated by arrow I, will cause actuator  26  to extend and will raise the back section  16 , and operation of the lever  100  by foot, indicated by arrow II, will cause actuator  26  to retract and will lower the back section  16 . Operating the lever  100  activates, that is to say opens, a non-return valve in the actuator  26  and hydraulic liquid will flow to the reservoir  22  from actuator  26 . 
         [0122]    It should be noted that lever  36  and lever  100  have two limit positions, denoted as top position  361  and  101 , respectively, and bottom position  362  and  102 , respectively. From the point of view of ease of operation, it is simple and comfortable for a user to press the levers downwards using his/her foot (arrows I, II), i.e. from the top position to the bottom position. Preferably, a restoring mechanism (not shown in any more detail) is provided for this purpose. 
         [0123]    In this manner, the position of the lever  38  is indicative of the member  14 ,  16 ,  18   a ,  18   b  to be displaced and two separate levers are provided for, on the one hand, raising and, on the other hand, lowering the selected section. In addition, as can clearly be seen in  FIG. 6 , the levers for actuating a selected actuator and relieving a selected actuator are (spatially) separated from one another as much as possible, so that there is little chance of an operator making mistakes when operating the hydraulic system. 
         [0124]    In an entirely corresponding manner, adjusting the lever  38  to a position  385  on the right-hand side corresponds to the selection of the actuator  28  (see  FIG. 1 ) and in particular to the selection of the leg section  18  for operation. Adjusting the lever  38  to a position  383  in the centre, that is to say between the left-hand and right-hand positions of the lever  38  in the figure, corresponds to selecting the actuator  24  (see  FIG. 1 ) for adjusting the height of the supporting surface  12 . Thus, only three operating members are required to carry out all the necessary operations for adjusting the supporting surface  12  of the hospital bed  1 . In addition, it is immediately clear from the position of the lever  38  which actuator will be operated. 
         [0125]    In a preferred embodiment of the hydraulic system according to the present invention, the pump activating member  36  and the valve assembly operating member  38  or levers  36 ,  38  are provided in duplicate, in this case in such a manner that the bed  1  can be operated along each longitudinal side. 
         [0126]    It should be noted that it will be clear to the person skilled in the art how the valve assembly  34  can be modified in order to be made suitable for a hydraulic system such as that shown in  FIG. 6  and such as that which is to be discussed below with reference to  FIG. 7 . 
         [0127]      FIG. 7  shows an example of the hydraulic system as discussed above with reference to  FIG. 6 . The hydraulic system shown in  FIG. 7  essentially corresponds to the hydraulic system shown in  FIG. 5  and comprises the pump  32 , reservoir  22 , the pressure-limiting valve  90  connected to the outlet of the pump  32  in a connection to the reservoir  22 , and a multi-position valve  134 . These parts are accommodated in a unit. In addition, a control pressure pump or relief element  120  which is incorporated in a control pressure circuit  150  is provided. A pressure-limiting valve  130  which is in communication with the reservoir  22  is connected to the outlet of the control pressure pump  120 . The control pressure pump  120  is operatively connected to and can be operated by the relief operating member or lever  100 . Furthermore, the actuators  24 ,  26 ,  28  can be seen which are all designed as single-acting cylinders with a piston rod which can move to and fro in a cylinder housing, which delimits a variable chamber in the cylinder housing. A single main line connection  24   a ,  26   a ,  28   a  is provided for each actuator and is connected to the variable chamber. 
         [0128]    Each of the cylinders  24 ,  26 ,  28  is furthermore provided with a hydraulically operated non-return valve  24   b ,  26   b ,  28   b  with a control pressure line connection  24   c ,  26   c ,  28   c . Between the valve assembly or multi-position valve  134  and each of the actuators, there is in each case provided a main line  91 ,  92 ,  93 , and a control pressure line  94 ,  95 ,  96 , for example in the form of a hose. The control pressure line  150  can be connected to one of the control pressure lines  94 ,  95 ,  96  by means of the multi-position valve  134 . 
         [0129]    Furthermore, the hydraulic system comprises a return line  160  which is connected to the line of the pump  32  and is in communication with the reservoir  22 . In the return line  160 , a non-return valve  140  is provided which is situated on the control pressure line  150  and can be operated by the control pressure pump  120 . 
         [0130]    An actuator can be selected by means of the valve assembly  134 , as has been described above. Operating, that is to say activating, the pump  32  will cause the selected actuator to extend by the pump  32  supplying hydraulic liquid to the actuator in question. Operating, that is to say activating, the control pressure pump  120  will open the non-return valve of the respective actuator and non-return valve  140 , so that hydraulic liquid can flow from the actuator to the reservoir  22  and cause the selected actuator to retract. 
         [0131]    When a line or connection ruptures or leaks, the valves  24   b ,  26   b ,  28   b  ensure that no accidental movement takes place, for example lowering of the bed  1 . 
         [0132]    In a variant (not shown), an actuator may be provided for tilting the subframe in a forward or backward direction. 
         [0133]    In another variant (not shown), an emergency operating device is provided for quickly lowering the back section  16 , for example in order to carry out reanimation. To this end, a bypass valve could be provided on the actuator  26 , if desired with a direct line to the reservoir. 
         [0134]    It should also be noted that it is also possible to operate more than the three actuators that are illustrated in each case. This requires a larger number of positions and thus connections on the valve assembly. However, the principle of selecting positions of the valve assembly remains unaffected. 
         [0135]    Although the invention has been described above as a hydraulic system which is suitable for adjusting a hospital bed, it will be clear to those skilled in the art that the hydraulic system according to the present invention can also be used for different applications. In particular, the hydraulic system can be used in situations where intuitive operation of actuators is desirable.