GB2055754A - An actuator mechanism for lifting and lowering the supporting surface of piece of furniture, such as a bed or chair, having a locking mechanism for maintaining the supporting surface in a vertical position obtained by means of the actuator mechanism - Google Patents

Abstract

An actuator mechanism (14) for lifting and lowering the supporting surface (3) of a piece of furniture, such as a hospital bed or a dentist's chair, comprises an energy accumulating spring means (15), preferably having a gently sloping spring characteristic, the spring force of which is transmitted to the supporting surface (3) via a linkage consisting of a push rod (17) and a first link (19). A second link (24) connects the hinge point (18) between the push rod (17) and the first link (19) with a second hinge point (23), which is connected to a fixed point (22) of the furniture frame via a pivotal adjustment arm (21). By pivoting the adjustment arm (21) to various angular positions it is possible to vary the moment of the spring force about the second hinge point (23) in such away that, given the value of the spring force, the lifting force acting on the supporting surface varies. The lifting force can thus be adapted to precisely balance the variable total weight of the movable parts of the piece of furniture whereby lifting and lowering of the supporting surface can be effected either manually or by a slight pivoting of the adjustment arm. <IMAGE>

Description

SPECIFICATION An actuator mechanism for lifting and lowering the supporting surface of a piece of furniture, such as a bed or chair, having a locking mechanism for maintaining the supporting surface in a vertical position obtained by means of the actuator mechanism The present invention relates to an actuator mechanism for lifting and lowering the supporting surface of a piece of furniture, such as a bed or chair, having a locking mechanism for maintaining said surface in a vertical position obtained by means of the actuator mechanism.

Mechanisms of this kind are known, e.g. for beds used in hospitals or nursing homes or for dentists's chairs, in which the supporting surface is lifted by means of a pedal activated mechanical or hydraulic jack directly connected to the supporting surface.

Disadvantages of these known mechanisms are that the movements of the supporting surface occur in jerks which can be highly unpleasant to a patient, and that the lifting requires rather high forces and consumes much energy. Normally it is impossible for a patient to operate the mechanism without help.

According to the present invention there is provided an actuator mechanism of the kind referred to, characterized in that it comprises (a) a spring means located below the supporting surface and having a protruding push rod which is guided for longitudinal movement in a guide means capable of pivoting about a horizontal axis extending perpendicular to the longitudinal axis of the push rod, (b) a first link hingedly connected to the protruding end of the push rod at a first hinge point and connected, for transmission of force, to the supporting surface at a point located at a higher level than said first hinge point and the pivot axis of said guide means, (c) a second link hingedly connected to the push rod and to the first link at said first hinge point, and hingedly connected at a second high point to an adjustment arm pivotally connected to the furniture frame at a fixed point thereof and extending from that frame point towards the pivot axis of said guide means, and (d) means for pivoting said adjustment arm about said frame point between upper and lower end positions and for retaining the arm in a selected angular position, the component parts of the actuator mechanism being dimensioned such that in any angular position of said adjustment arm and at any vertical position of the supporting surface, said second hinge point is located at a higher level than the line connecting said first hinge point with the pivot axis of said guide means.

In an actuator mechanism of th is construction a pivoting movement of the adjustment arm will result in that the geometry of the linkage, which consists of the push rod and the two links and through which the force exerted by the spring means tends to lift the supporting surface, is altered such that the ratio of the resulting lifting force to the spring force varies from a maximum value occurring in the uppermost position of the adjustment arm, to a minimum value in the lowermost position of the arm. This implies that it is possible, when the supporting surface assumes its lowermost position, to adjust in advance the angular position of the adjustment arm such that the spring force is just sufficient to ensure lifting of the supporting surface plus patient, bed clothes etc.

The lifting movement will be accompanied by a straightening of the linkage due to the connection, via the second link, of the first hinge point with the second hinge point, which latter becomes a fixed point when the adjustment arm is locked. As a consequence it is possible to obtain a lifting force which notwithstanding the decreasing spring force is by and large constant during the upward movement and which in any event does not drop below its original value. Since the movement of the supporting surface starts already at the moment when the adjustment arm passes by that position in which there is balance or equilibrium between the weight to be lifted and the lifting force exerted through the linkage, it is possible to obtain a perfectly smooth and jerk-free lifting movement created solely by the energy accumulated in the spring means.Similarly, a lowering of the supporting surface can be effected without jerks, either in response to a slight pivoting of the adjustment arm towards the lowermost position thereof whereby the balancing force decreases, or by manually depressing the surface. As long as the total weight of the supporting surface and the load thereon is constant, the small pivoting movements of the adjustment arm, which are sufficientto initiate lifting and lowering, respectively, of the supporting surface, result in only very small changes in the amount of energy accumulated in the spring means.Consequently, only a correspondingly small force has to be exerted in order to move the supporting surface up and down and as long as the piece of furniture is used by the same patient, it is in practice possible to operate the mechanism with a by and large constant angular position of the adjustment arm determined by the weight of the patient.

In a preferred embodiment the spring means is a gas-cushion spring, the piston rod of which constitutes the push rod while its housing constitutes the guide means for the push rod. An advantage of this embodiment is that the force of the gas-cushion spring decreases only slightly when its piston and piston rod move outwardly during the lifting of the supporting surface. Alternatively, a mechanical spring may, however, be used provided its spring rate or stiffness is sufficiently low.

It is expedient that the component parts of the actuator mechanism are furthermore dimensioned such that in any angular position of the adjustment arm said first hinge point is located close to said fixed frame point when the supporting surface assumes its uppermost position, and that irrespective of the level of the supporting surface the distance from the pivot axis of the guide means to the first hinge point decreases when the adjustment arm is pivoted from its lowermost to its uppermost end position. A consequence thereof is that a change in the "degree of balancing" brought about by pivoting the adjustment arm when it is desired to lowerthe supporting surface from its uppermost position, results in only a minor change of the compression of the spring means and thus of the accumulated amount of energy.A further consequence is that the longitudinal travel of the push rod and, hence, the spring member's capability of accumulating potential energy liberated by the lowering of the supporting surface, is utilized to a maximum extent when the adjustment arm assumes its uppermost angular position corresponding to a require mentfor maximum available lifting force.

The mechanism may comprise a control member adapted to activate a mechanical or hydraulic jack for pivoting the adjustment arm towards the uppermost position thereof and to simultaneously release the mechanism for locking the supporting surface.

This feature contributes to simplifying the operation ofthe mechanism.

In addition the mechanism may comprise a second control member which is movable from a rest position, in which the supporting surface is locked, via an intermediate position in which the locking mechanism is released, to an extreme position in which additionally the jack is released to permit pivoting of the adjustment arm towards the lowermost position thereof.This feature ensures that unnecessary loss of energy from the spring means functioning as energy accumulator is avoided when the supporting surface is lowered, because only in case the spring force is too high, so that the supporting surface does not start sinking spontaneously when the control member is moved to its intermediate position thereby releasing the locking mechanism, it is necessary to release the adjustment arm - by moving the control member to its extreme position - and thus dissipate accumulated energy from the spring means.

The invention will now be described in more detail with reference to the highlyschematical accompanying drawings, in which Figure 1 is an elevation, partly in section, of a hospital bed equipped with an actuator mechanism embodying the invention, Figures Paare fractional views which on a larger scale show the actuator mechanism in four different positions, Figures 6 and 7 are further fractional views on a smaller scale for illustrating the transmission of force from the spring means to the supporting surface of the bed, and Figure 8 is a detail of the mechanism for locking the supporting surface and of a common control memberforthe locking mechanism and the adjustment arm of the actuator mechanism.

In Figure 1 a hospital bed is very schematically illustrated by means of a bottom frame consisting of longitudinal beams 1 and transverse beams 2, and a vertically displaceable upper frame 3, which likewise is composed of longitudinal beams 4 and transverse beams 5, and on which the supporting surface (not shown) of the bed including bed frame, mattress etc.

rests. Bottom frame 1,2 is supported by schematically shown wheels 6, which may be of conventional design.

Bottom frame 1,2 and upper frame 3 are connected together by means of two parallel, identical linkages 7, each provided at one long side of the bed.

Each linkage, of which only one is shown in Figure 1, comprises an arm 8 which at one end is connected to the bottom frame at a hinge point 9 while its upper end is hingedly connected to a link 10 which in turn is hinged to the upper frame, and a second arm 11 which at its upper end is hinged to the upper frame and at its lower end hinged to one end of a second link 12, the opposite end of which is hinged to the bottom frame. Intermediate their ends arms 8 and 11 are pivotally connected at a hinge point 13. By suitable dimensioning of the component parts of linkage 7 it is possible to obtain a practically exactly vertical movement of upper frame 3 without undesired simultaneous displacement in the longitudinal direction of said frame.

Associated with each linkage is an actuator mechanism generally designated by 14 which includes an energy accumulator formed by a gascushion spring 15, the housing of which is mounted on the bottom frame for pivoting about a transverse horizontal axis which in Figure 1 has been illustrated by a fixed frame point 16. The gas-cushion spring 15 may be of conventional design and for that reason it has not been shown in detail. At one end thereof, viz.

the righthand end of Figures 1-6, it contains a chamber wherein an amount of gas is trapped between the bottom of the housing and a freely movable piston. A further piston defines, together with the opposite face of the first piston and the lefthand end portion of the spring housing, respectively, two mutually connected chambers wherein an amount of liquid is trapped. The last mentioned piston is rigidly connected to a piston rod 17 protruding from the housing of the gas-cushion spring.

At a hinge point 18 the free end of piston rod 17 is connected to one end of a first link 19, the opposite end of which is connected with arm 8 at a hinge point 20. One end of an adjustment arm 21 is pivotally connected to the bottom frame 1,2 of the bed at a fixed frame point 22 while the opposite end of arm 21 is hingedly connected, at a hinge point 23, to a second link 24, the opposite end of which is hinged to piston rod 17 and link 19 in the associated hinge point 18.

The cylinder of a hydraulic jack 25 is pivotally connected at its lowermost end to bottom frame 1,2 at a point 26, and the upwardly protruding piston rod 27 of the jack is hinged, at a point 28, to each adjustment arm 21 intermediate the ends thereof.

The piston (not shown) of the jack, which is secured to piston rod 27, is lifted by pumping in oil below the piston by means of a pump 29, see Figure 8, which is activated from a pedal 30. Pedal 30 also operates the mechanism, to be described below, for locking linkage 7 and thus permits maintaining upper frame 3 in an arbitrary vertical position.

The locking mechanism comprises a gas-cushion spring 31, see Figure 8, the cylinder of which is hinged to arm 8, while its piston rod 32 is hinged to the bottom frame of the bed at a fixed point 33.

While in the gas-cushion spring 15 discussed above the liquid chambers on opposed faces of the liquid piston communicate permanently, gas-cushion spring 31 comprises a valve between said two chambers. This valve is normally closed whereby the gas-cushion spring locks arm 8 and, hence, upper frame 3, but the valve can be opened by means of a release pin 34 which protrudes through piston rod 32 and which is operated by a pivoted lever 35 actuated from pedal 30 through a compression spring 36.

When the valve is open, the upper frame 3 is unlocked and gas-cushion spring 31 functions as a damped spring which permits lifting and lowering of frame 3.

For pivoting adjustment arm 21 from its uppermost position as shown in Figures 2 and 3 to its lowermost position as shown in Figures 4 and 5, the bed comprises a further pedal (not shown) which normally assumes an upper rest position from which it can be depressed to a lowermost end position.

During its travel the pedal passes by an intermediate position in which it actuates the release pins 34 of the two gas-cushion springs 31 and, thus, unlock upper frame 3, similar to pedal 30. When the further pedal is depressed to its lowermost position it, furthermore, opens a valve, which permits the outflow of oil from jack 25 so that arms 21 can pivot towards their lowermost positions shown in Figures 4 and 5.

Figures 6 and 7 are intended to illustrate how the compression force acting on piston rod 17 protruding from gas-cushion spring 15 is transformed to a lifting force acting on arm 8 of linkage 7. The component parts of the actuator mechanism are shown in a position corresponding approximately to that shown in Figure 4, i.e. with the upper frame 3 in its lowermost position and the piston rod 27 of jack 25 almost fully retracted corresponding to a low "degree of balancing".

Since piston rod 27 and, thus, adjustment arm 21 are immobilized, hinge point 23 constitutes a fixed frame point of the actuator mechanism. The spring force acting on piston rod 17 tends to pivot link 24 clockwise about point 23 with a moment designated by M. In the position of point 23 as shown the lever arm about that point is small and, consequently, moment M is relatively small. When adjustment arm 21 is pivoted towards the uppermost position thereof as shown in Figures 2 and 3, the lever arm and hence also the magnitude of the moment exerted by a given spring force increases.Moment M is transferred to arm 8 through link 19 in the form of a moment M1 about the pivot point 9 of the arm, and by a suitable choice of the geometry of linkage 8, 19, 24 it is possible to obtain that the ratio of M, to M varies only relatively little, typically about 10% of its maximum value, irrespective of the vertical position of upper frame 3 and the angular position of adjustment arm 21. It will also be seen from Figures 2-5 that, for a given location of point 23, the lever arm of the spring force about point 23 does not vary substantially when the angular position of arm 8 and hence the level of upper frame 3 varies.Consequently, moment M1 and hence the lifting force acting on upper frame 3 depends essentially only on the degree of balancing which is determined by the angular position of arm 21, but not on the level of the upper frame, provided the spring force is relatively constant during the travel of piston rod 17, which as mentioned above is especially true of a gas-cushion spring but which can also be obtained with mechanical springs when their spring rate or stiffness is suitably low.

When the entire system has been dimensioned such that the total lifting force exerted on arms 8 by the two actuator mechanisms is capable of overcoming the maximum total weight of the movable parts of the bed, the release of gas-cushion springs 31 by actuating the further pedal (not shown) described above when upper frame 3 assumes its lowermost position corresponding to that shown in Figure 2, will cause piston rods 17 to be extended from the housings of gas-cushion springs 15 and thus, via links 19, pivot arms 8 upwardly, maximally to the position shown in Figure 3 which corresponds to the highest level of the upper frame. It will be understood that the upward movement can be stopped at any desired intermediate level by locking the pistons of gas-cushion springs 31.

When adjustment arm 21 assumes its lowermost position shown in Figures 4 and 5, the lifting force acting on arm 8 is just sufficient to lift the minimum total weight of the movable parts to the highest level. The movement is controlled in the same way as just described.

If upper frame 3 is to be lifted, from its lowermost position or from an intermediate position, and if the lifting force acting on arms 8 is insufficient, pedal 30 is actuated whereby - as described above - oil is pumped into jack 25 so that adjustment arm 21 pivots counterclockwise to a higher position and thus a higher degree of balancing. At the moment when the lifting force, which is represented by moment M1 shown in Figure 7 and which increases with the pivoting of arm 21, exceeds the weight of the load, upper frame 3 starts rising gradually and jerk-free whereby gas-cushion springs 31, furthermore, act as dampers as long as pedal 30 is kept depressed so as to actuate release pins 34. When the pedal is released, the valves of the gas-cushion springs close following which the frame is locked at the level obtained.If the frame is to be subsequently lowered, it is possible by operating the other pedal (not shown) to discharge so much oil from jack 25 that adjustment arm 21 pivots clockwise until the degree of balancing has decreased so much that the upper frame and the load thereon, if any, starts sinking.

When the angular position of adjustment arms 21 corresponds to a perfect balancing of the weight of the movable parts by means of the moments acting on arms 8, it will normally be possible to manually alter the level ofthe upper frame after release of locking mechanisms 31,32 but without any pivoting of arms 21 and thus without loss of accumulated energy in gas-cushion springs 15.

Among the several modifications of the mechanism described, which are possible within the scope of the invention, it may be mentioned that the pedals, which control the jack, can be replaced or supplemented by handles arranged such that they can be operated directly by a bedridden patient. It will also be possible to combine the activating functions of the two pedals described within a single pedal and/or single handle. The motive powerforthe pivoting adjustment arm could also be provided by an electric motor, which can be battery driven in view of the relatively low power necessary for pivoting the arm.

Claims (6)

1. An actuator mechanism for lifting and lowering the supporting surface of a piece offurniture such as a bed or chair, having a locking mechanism for maintaining said surface in a vertical position obtained by means of the actuator mechanism, characterized in that the actuator mechanism comprises:: (a) a spring means located below the supporting surface and having a protruding push rod which is guided for longitudinal movement in a guide means capable of pivoting about a horizontal axis extending perpendiculartothe longitudinal axis of said push rod, (b) a first link hingedly connected to the protruding end of said push rod at a first hinge point and connected, for transmission of force, to the supporting surface at a point located at a higher level than said first hinge point and the pivot axis of said guide means, (c) a second link hingedly connected to the push rod and to the first link at said first hinge point and hingedly connected art a second hinge point to an adjustment are pivotally connected to the furniture frame at a fixed point thereof and extending from that frame point towards the pivot axis of said guide means, and (d) means for pivoting said adjustment arm about said frame point between upper and lower end positions and for retaining the arm in a selected angular position, the component parts of the actuator mechanism being dimensioned such that in any angular position of said adjustment arm and at any vertical position of the supporting surface, said second hinge point is located at a higher level than the line connecting said first hinge point with the pivot axis of said guide means.

2. An actuator mechanism as claimed in claim 1, characterized in that said spring means is a gascushion spring, the piston rod of which constitutes said push rod while its housing constitutes said guide means for the push rod.

3. An actuator mechanism as claimed in claim 1 or 2, characterized in that its component parts are, furthermore, dimensioned such that in any angular position of the adjustment arm said first hinge point is located close to said fixed frame point when the supporting surface assumes its uppermost position, and that irrespective of the level of the supporting surface the distance from the pivot axis of the guide means to the first hinge point decreases when the adjustment arm is pivoted from its lowermost to its uppermost end position.

4. An actuator mechanism as claimed in any of claims 1-3, characterized in that the means for pivoting the adjustment arm is a mechanical or hydraulic jack, and in that the mechanism comprises a control member adapted to activate said jack for pivoting the adjustment arm towards its uppermost position and simultaneously release the locking mechanism.

5. An actuator mechanism as claimed in claim 4, characterized by a second control member which is movable from a rest position in which the supporting surface is locked, via an intermediate position in which the locking mechanism is released, to an extreme position in which additionally the jack is released to permit pivoting of the adjustment arm towards the lowermost position thereof.

6. An actuator mechanism for lifting and lowering the supporting surface of a piece of furniture, substantially as hereinbefore described with reference to the accompanying drawings.