The present invention relates to an apparatus according to the preamble of the independent claim.

In the employment of lifting apparatuses which include a scissor mecha¬ nism for realizing the lifting force, the problem exists that, in the lowest lifting position of the apparatus, the vertically directed com¬ posant of force is very slight in relation to the horizontally directed composant. As a result, there is a need in certain practical applica¬ tions to be able, at the lowest lifting position of the apparatus, to provide a larger vertically directed composant of force. Since, in many contexts, solutions are also sought for in which the lifting table of the lifting apparatus can be permitted to descend to a very low level, there is thus but a very limited space available for disposing the operative parts for the lifting movements. The above problem, condi¬ tioned by the laws of mechanics, constitutes a serious drawback.

The present invention relates to an apparatus in which the lifting force is multiplied at the initial stage of the upwardly directed displacement of a part disposed on the apparatus and in which scissor devices are employed for lifting this part. The lifting apparatus is intended to be used for many different practical applications such as lifting tables, beds, working platforms, frames for supporting these and other parts, etc.

There are numerous prior art solutions to this problem in which an extra vertical composant of force is given in the lowest position of the scis¬ sor mechanism. In, for example, US,A, 4890 692, there is disclosed a lifting apparatus including a scissor mechanism and in which a vertical composant of force is applied in the initial phase of the lifting move¬ ment via a lever. The lever carries a roller which acts on a cam surface on the scissor mechanism. The drive means for the lifting apparatus is joumalled obliquely inclining, which entails that the possibility of contracting the lifting apparatus together to a low level is restricted.

In addition, the movement of the drive means is transferred to the scis¬ sor mechanism in a manner which is different from that called for ac¬ cording to the present invention.

The contemplated solution is attained by means of an apparatus which is defined by the independent claim.

Expedient embodiments of the present invention are also disclosed in the appended subclaims.

The present invention will now be described in greater detail herein- below, with reference to a number of Drawings. In the accompanying Draw¬ ings:

Fig. 1 is a side elevation of the apparatus in its lowermost position;

Fig. 2 is a view corresponding to that of Fig. 1 in which the displacement of the lifting portion of the apparatus has been commenced;

Fig. 3 is a view corresponding to that of Figs. 1 and 2 in which the lifting portion of the lifting apparatus has reached its highest position;

Figs. 4a,b are perspective views of a detail of one end region of the scissor mechanism of the apparatus;

Fig. 5 is a perspective view in detail of the other end region of the scissor mechanism of the apparatus.

In the Figures, there is shown a chassis 10 with longitudinal beams and cross beams. In the illustrated embodiment, wheels 14 support the chas¬ sis 10. A prime mover consisting of a motor 15 and a reciprocator 16 is secured in the chassis. The prime mover extends substantially horizon¬ tally.

A first scissor pair 20 formed of first arms 22a,22b and a second scis¬ sor pair 21 formed by second arms 23a,23b carry a frame 30 on which are disposed anchorage devices 31 when coupling the frame, for example, to a lifting platform or to a bed. In alternative embodiments, the scissor pairs 20,21 support lifting tables, beds, work platforms, additional scissor pairs, etc. directly, without employing a frame. A first, upper crossbar 26 connects two of the opposed arms 22a,23a and a second upper crossbar 28 connects the other two opposed arms 22b,23b in the one end regions of the arms. A first lower crossbar 29 connects the opposed arms 22b,23b connected with the second upper crossbar 28, and a second lower crossbar 27 connects the two first-mentioned opposed arms 22a,23a in their other end regions. A journal 24 rotatably connects the first arms to one another, and a journal 25 rotatably connects the second arms to one another so as to form the scissor pairs 20 and 21, respectively.

The crossbars are located pairwise 26,29;27,28 above one another in a vertical direction on either side of the journals 24,25 of the scissor pairs. The pair consisting of the first upper and lower crossbars 26,29 is rotatably joumalled in the chassis 10 and in the frame 30, respec- tively. The second pair of crossbars 27,28 is displaceably and rotatably connected to the chassis 10 and the frame 30, respectively. Those paths 32,34 in which the crossbars are displaced are directed substantially transversely of the direction of displacement of the frame 30. The first upper crossbar 26 is fixedly disposed in rotary journals 32 supported in the frame 30, and the first lower crossbar 29 is fixedly disposed in rotary journals 35 supported in the chassis 10. The second lower cross¬ bar 27 is displaceably disposed in rotary journals which are displaced in the chassis 10 in paths 33. The second upper crossbar 29 is dis¬ placeably disposed in rotary journals which are displaced in the frame 30 in paths 34. Thus, the crossbars 26-29 are rotatably joumalled in relation to the chassis 10 and the frame 30, respectively, while the crossbars 26-29 and the scissor arms 22a,b;23a,b are rigidly intercon¬ nected with one another. A person skilled in the art will deduce from this description that it is possible to proceed conversely, i.e. allow the crossbars to be rigidly connected to the chassis in the frame, re¬ spectively, while the arms are rotatably joumalled on the crossbars, without deviating from the inventive concept.

In one alternative embodiment, the upper crossbars 26,28 are dispensed with, in which event the lifting table, bed, etc., is supported via wheels disposed on two scissor arms and via the other two scissor arms rotatably joumalled direct in the supported portion or in parts con¬ nected with the supported portion (not shown).

In the illustrated embodiment, the prime mover consists of an electric motor 15 which operates a reciprocator 16. In other embodiments, the prime mover may comprise, for example, a hydraulic piston, a pneumatic piston, a ball screw or a gear rack. The type of prime mover which is selected principally depends upon the relevant field of application and those power sources which are available.

Via an arm 36, the reciprocator 16 is rotatably connected to a sleeve 37 which is rotatably disposed on the first lower crossbar 29. An obliquely upwardly directed mechanical transmission device, shown in Fig. 3 as an obliquely upwardly directed rod 43 and an abutment member 45 disposed furthest out on the rod 43 is fixed to the sleeve 37. The mechanical transmission device 43,45 is disposed in a predetermined angular rela¬ tionship to the arm 36 of the sleeve, the size of the angle being adapted to that moment of force which is sought for in connection with rotation of the sleeve in relation to the first lower crossbar 29. Thus, the arm 36 of the sleeve constitutes a lever for the prime mover 15,16 around the sleeve and the crossbar 29, and the force of the prime mover is transmitted via the mechanical transmission device 43,45. For maximum moment of force, the arm 36 is completely vertical in the initial posi¬ tion.

When the frame of the apparatus is located in its lowermost position, raising of the frame is commenced in that the motor 15 draws the recip¬ rocator 16 to the left in the Figures, in which event the sleeve 37 is rotated about the crossbar 29. The reciprocator 16 is joumalled to the sleeve 37 via the arm 36. On rotation of the sleeve 37, the upwardly directed rod 43 is displaced in a direction away from the prime mover, in which event the rod 43, with its connected transmission device 45 exercises, by the abutment of the transmission device against an arrest

member 41, an upwardly directed force thereagainst. The arrest member 41 is fixed to parts of the scissor arms 22a, 3a located above the sleeve 37 and connected to the first upper crossbar 26. There will hereby be achieved the sought-for increase of the lifting force in the initial stage of the raising of the frame from its lowermost position. In the illustrated embodiment, the arrest member 41 consists of two parts each connected to a scissor arm 22a,23a, respectively. The arrest members 41 are fixed with a certain inclination on the scissor arms 22a,23a, this inclination determining how quickly the lifting apparatus lifts. As long as the arrest members 41 rest on the mechanical transmission device, the lifting force is transferred this way.

A stop 44 is disposed on the crossbar 29 in order to stop rotation of the rod 43 when additional force is no longer required from the trans- mission device 43,45. The rotation of the sleeve 37 about the crossbar 29 connected to the prime mover thus ceases on contact with the stop 44. This takes place when a mechanical element 38 disposed on the sleeve 37 moves against the stop 44. The arrest of movement takes place at the earliest when the angle between the arms 22a,22b and 23a,23b, respec- tively, in the scissor pairs 20,21 is approx. 20° and preferably takes place when the angle is approx. 25° and most preferably when the angle is approx. 30°.

When the mechanical element 38 moves against the stop 44, lifting force is no longer transmitted via the mechanical transmission device 43,45. The continued lifting then takes place in that the motor 15, with the. aid of the reciprocator 16, moves the lower crossbars 27,29 towards one another, i.e. the second lower crossbar 27 moves in the paths 33 in the chassis 10. The height difference between the lowest and highest height of the lifting apparatus is regulated by regulating the stroke length of the reciprocator 16.

In one alternative embodiment (not shown), the sleeve 37 which carries the mechanical transmission device 43,45 is joumalled on the displace- able lower crossbar 27, in which event the arrest members 41 are fixed to parts of the scissor arms 22b,23b located above the sleeve 37 and connected to the second upper crossbar 28. As one alternative, the ar-

rest member 41 is occasionally placed on a frame portion or the like instead of on the scissor arms.

In the illustrated embodiment, the wheels 14 which support the lifting apparatus and make it mobile are each provided with a parking brake in order to prevent unintentional movement.

The above detailed description has referred to but a limited number of embodiments of the present invention, but a person skilled in the art will readily perceive that the present invention encompasses a large number of embodiments without departing from the spirit and scope of the appended claims.