DK3097898T3 - A MEDICAL WHEELCHAIR EQUIPPED WITH A SYSTEM TO HELP PATIENTS TO SET UP AND TRAVEL - Google Patents

Description

Description

The invention relates to the field of invalid chairs, more particularly to chairs equipped with movable seats that help persons of reduced mobility and/or of reduced muscle strength (hereinafter called "patients") to sit down and stand back up.

Sitting down and standing back up are complex movements which involve the joints of the ankle, knee and hip, the muscles of the calves (anterior leg muscle), the thighs (quadriceps), the buttocks and the dorsal (lumbar) vertebrae, and which additionally presuppose a correct function of the inner ear, which is the organ of balance of the human body.

For patients affected by psychomotor disadaptation syndrome or PDS (especially the elderly, or persons suffering from bone or muscle injuries or balance problems), sitting down and standing back up pose considerable risks of falling and therefore of sustaining injury. On the subject of this syndrome, see in particular the article by P. Manckoundia et al. "Syndrome de désadaptation psychomotrice" in Gériatrie et Psychologie Neuropsychiatrie du Vieillissement, volume 12, March 2014, and the paper by N. Meesmaecker "Etat des lieux a propos du syndrome de désadaptation psychomotrice au sein d'un centre spécialisé en gériatrie", Institut de formation en masso-kinésithérapie, Rennes, 2011.

In most patients affected by PDS, one observes postural symptoms referred to as retropulsion (a tendency to fall backwards when moving from a seated posture to a standing posture) and oppositional hypertonia (reflex muscle tension opposing the envisaged movement). These symptoms are often accompanied by those of stasibasiphobia (fear of standing, adopting a vertical posture and walking), which leads the patient to fear the action of standing back up from a seated posture .

To sit down and stand back up, patients can use their arms for support on the armrests with which invalid chairs are generally equipped, but this requires a certain amount of strength. Patients may also obtain assistance from nursing staff, but the latter are then exposed to various musculoskeletal problems (especially lumbago) on account of a combination of the following factors: an uncomfortable posture, the repetition of manoeuvring procedures, and the weight of the patients.

Various chairs and recliners provided with telescopic seats have been proposed to help patients sit down and stand back up. There are chairs with an electric motor governed by a remote control that can be operated by the patient.

This technology, illustrated by the United States patent US 7 090 297 (La-Z-Boy), is not without its disadvantages: first, to be supplied with electricity, the chair has to be connected to the mains network and cannot therefore serve as a wheelchair; second, because it is powered electrically, this chair is relatively heavy, which makes things difficult if it has to be moved (e.g. from one room to another).

There are also chairs available which are provided with restoring means of the mechanical type (spring) or of the pneumatic type (jack), which are lighter and do not require any external power supply. This technology is illustrated in particular by the British patent GB 1 406 420 (Warwick), which describes a medical chair provided with a movable seat that is controlled by a spring mechanism. However, this chair may be found to be lacking in terms of ergonomics, since the movement followed by the seat during its articulation is quite different from the movement of the legs of the patient, who then risks losing balance when sitting down or standing back up. A first object is therefore to make available a medical chair that is safer for patients. A second object is to make available a medical chair by which patients who have lost the habit of sitting down and standing back up unaided (particularly patients affected by PDS) can recover this ability. A third object is to make available a medical chair that is reliable and relatively light, allowing it to be easily moved about.

To this end, an invalid chair is made available comprising: a chassis equipped with a base, a seat movable with respect to the base and including a front-half seat and a rear-half seat which are mutually articulated about an axis A, and a mechanism which permits articulation of the seat and is able to adopt a folded configuration, placing the seat in a down position near the base, and a deployed configuration, placing the seat in an up position at a distance from the base, this mechanism comprising: • a lower frame mounted rotatably with respect to the base about an axis B, and with respect to the front-half seat about an axis C situated near a front edge thereof; • an upper frame mounted rotatably with respect to the lower frame about an axis D situated between the axes B and C, and with respect to the rear-half seat about an axis E situated near a rear edge thereof; • a coupling arm mounted rotatably with respect to the base about an axis F, and with respect to the front-half seat about an axis G at a distance from the axis C; an elastic return member which stresses the articulation mechanism towards its deployed configuration; the axes A, B, C, D, E, F and G being parallel and defining, in a plane perpendicular to them: the axes B, C, G, F: a deformable lower quadrilateral; the axes A, C, D, E: a deformable upper quadrilateral; the axes A, B, C, D, E, F and G being positioned in such a way that the lower quadrilateral is convex in the folded configuration and concave via the axis G in the deployed configuration .

Various additional features may be provided, alone or in combination : the sum of the inter-axis distances FG and CG is less than or equal to the inter-axis distance BC; the angle between the planes defined respectively by the axes A and C on the one hand and C and G on the other hand is between 70° and 120°; the angle between the planes defined respectively by the axes A and C on the one hand and C and G on the other hand is about 90°; the inter-axis distance DE is greater than or equal to the inter-axis distance AC; the inter-axis distance CD is less than or equal to the inter-axis distance BD; the inter-axis distance AE is greater than or equal to the inter-axis distance CD; the return member is a gas spring; the gas spring is of the blockable type; the gas spring comprises a body fixed to the lower frame, and a rod fixed to the upper frame.

Other objects and advantages of the invention will become clear from the following description of an embodiment and by reference to the attached drawings in which:

Figure 1 is a perspective view of an invalid chair, shown on its own, with the seat in the down position;

Figure 2 is a view of the chair from Figure 1, with a patient seated on it;

Figure 3 is a perspective view of the chair from Figure 1, with the seat in the up position;

Figure 4 is a view of the chair from Figure 3, with a patient in the process of standing back up from or sitting down on the chair;

Figure 5 is a side view of the seat in the down position, and of its articulation mechanism in the folded configuration;

Figure 6 is a kinematics diagram illustrating the articulation mechanism in its folded configuration;

Figure 7 is a side view of the seat in the up position, and of its articulation mechanism in the deployed configuration;

Figure 8 is a perspective view, from the rear, of the seat in the up position and of its articulation mechanism in the deployed configuration;

Figure 9 a kinematics diagram illustrating the articulation mechanism in its deployed configuration;

Figure 10 is a longitudinal section showing the seat in the up position and illustrating the return member with, in the inset, an enlarged detail centred on an adjustable limit stop;

Figure 11 shows a diagram illustrating the different positions of the seat between its down position and its up position;

Figure 12 is a comparative diagram illustrating the different positions of the seat of the chair from the patent GB 1 406 420, between its down position and its up position.

In Figure 1, an invalid chair 1 is shown which is intended for elderly persons or for persons suffering from bone or muscle injuries or from problems affecting their balance (these persons being more simply called "patients" hereinbelow) . This chair 1 is intended not only to allow them to adopt a seated position but also to make it easier for nursing staff to move them about.

The chair 1 comprises a chassis 2 composed of tubular elements made of metal (in particular of steel or of aluminium alloy). This chassis 2 includes a carriage 3 provided with wheels 4, permitting movement of the chair 1, a base 5 mounted on the carriage 3, an upright 6 fixed adjustably (particularly in inclination) on the base 5, and, as illustrated, tubes 7 extending laterally from the base 5 in order to permit the adjustable mounting of armrests 8. The carriage 3 comprises, for example, a main crosspiece 9 and a pair of longitudinal members 10, at the ends of which the wheels 4 are fixed.

The chair 1 comprises a backrest 11 mounted on the upright 6 and, optionally, a headrest 12 mounted at an upper end of the upright 6, on top of the backrest 11. Moreover, as in the example illustrated, the chair 1 is preferably equipped with a handlebar 13 formed by a transverse bar fixed to the upper end of the upright 6, in order to make it easier for nursing staff to move and manoeuvre the chair 1. In the description below, "rear" defines a location towards the backrest 11; by contrast, "front" defines an opposite location. "Down" defines a location towards the wheels 4; by contrast, "up" defines an opposite location. Generally speaking, the terms "rear", "front", "down" and "up" are employed in the context of a normal position and use of the chair 1, as it is commonly used from day to day. The same applies to the terms "vertical" and "horizontal", it being assumed that the chair 1 rests on a horizontal floor.

The chair 1 comprises a seat 14 which is movable, with respect to the base 5, between a down position (Figures 1, 2, 5 and 6), in which the seat 14 extends near the base 5 in order to allow a patient 15 to be comfortably seated in the chair 1 as illustrated in Figure 2, and an up position (Figures 3, 4, 7, 8, 9 and 10), in which the seat 14 is spaced apart from the base 5 in order to help the patient 15 to stand back up by pushing him behind his thighs or, by contrast, to help him sit down by accompanying his movement.

The base 5 can be fixed immovably to the carriage 3 or, as in the example illustrated, can be adjustable at least in height and, if appropriate, in rotation, by way of a jack 16 provided with a blocking mechanism that can be actuated by means of a protruding lever 17 within the reach of the patient 15. In the example illustrated, the base 5 is in the from of a metal component comprising a horizontal plate 18 and lateral flanges 19 folded at right angles to the horizontal plate 18.

It is preferable that the base 5 (and thus the seat 14 and the armrests) is (are) blocked in rotation while the patient 15 is sitting or standing up, so as to safeguard the patient. To this end, and as is illustrated in particular in Figure 1, at least one of the tubes 7 is provided with a leg 20 which abuts against the crosspiece 9.

According to an embodiment illustrated in Figures 1 to 4, the chair 1 is equipped with a footrest 21 which is vertically displaceable between a lower position (illustrated in the figures), in which the footrest 21 extends close to the floor to allow the patient 15 to find support when sitting down and standing back up, and an upper position, in which the footrest 21 is spaced apart from the ground in order to keep the feet of the patient away from the ground, which avoids the feet rubbing against the latter during the movements of the chair 1. As will be seen in particular in Figures 1 to 4, the chair 1 is provided with a mechanism 22 for actuating the footrest 21, including a control lever 23 at the foot and a rod 24 coupling the lever 23 to the footrest 21, the tilting of the control lever 23 placing the footrest 21 in its upper position or, conversely, in its lower position. Advantageously, the actuating mechanism 22 simultaneously controls the locking of at least two of the wheels 4 (e.g. the rear wheels) in the lower position of the footrest 21, so as to avoid the chair 1 sliding away when the 15 patient stands up or sits down.

The seat 14 is in two parts: it comprises a front-half seat 14A for supporting the thighs of the patient 15, and a rear-half seat 14B for supporting the pelvis. The seat halves 14A, 14B are mutually articulated about a common axis A, which is situated near a rear edge of the front-half seat 14A and near a front edge of the rear-half seat 14B.

As is illustrated in the figures, and in particular in Figures 5 and 7, the front-half seat 14A comprises a front metal front plate 25 provided with flanges 26; likewise, the rear-half seat 14B comprises a rear metal plate 27 provided with flanges 28.

In the example illustrated, the axis A is formed by a pair of bolts 29 via which the plates 25, 27 are mounted rotatably with respect to each other.

The seat 14 comprises a flexible cushion 30 having a front part 30A mounted on the front plate 25 via a front panel 31A slidably mounted thereon, and a rear part 30B mounted on the rear plate 27 via a rear panel 31B slidably mounted thereon and articulated with respect to the front panel 31A about a hinge 32.

The cushion 30 is preferably made of a foam, e.g. a viscoelastic foam (commonly referred to as shape-memory foam) . The panels 31A, 31B can be made of plastic, of wood or, advantageously, of a material derived from wood (typically agglomerated, medium, laminated).

The chair 1 further comprises a mechanism 33 for articulation of the seat 14, designed to be able to adopt a folded configuration placing the seat 14 in its down position (Figures 5 and 6) , and a deployed configuration placing the seat 14 in its up position (Figures 7, 8 and 9) .

This mechanism 33 comprises, firstly, a lower frame 34 mounted rotatably with respect to the base 5 about an axis B and with respect to the front-half seat 14A about an axis C situated near a front edge thereof. In the example illustrated, the axis B is formed by a pair of bolts 35 via which the lower frame 34 is mounted rotatably on the flanges 19 of the base 5.

The lower frame 34 could be formed by a pair of parallel rods interconnected by a spacer. However, in the example illustrated in the figures, and in particular in Figure 8, the lower frame 34 is present in the form of a one-piece metal component comprising a rectangular plate 36 provided with a recess 37 (of which the function will become clear hereinafter), and lateral edges 38 folded at right angles to the plate 36.

According to an embodiment illustrated in the figures, and in particular in Figures 5, 7 and 8, the axis C is formed by a tube 39 integrated in the lower frame (e.g. by being welded to the plate at a front edge thereof) and rotatably mounted between two bearings 40 which are fixed (e.g. by screwing) to the front-half seat 14A, laterally either side thereof.

The articulation mechanism 33 comprises, secondly, an upper frame 41 mounted rotatably, on the one hand, with respect to the lower frame 34 about an axis D situated between the axes B and C, and, on the other hand, with respect to the rear-half seat 14B about an axis E situated near a rear edge thereof .

The upper frame 41 could be formed by a pair of parallel rods interconnected by a spacer. However, in the example illustrated in the figures, and in particular in Figure 8, the upper frame 41 is present in the form of a one-piece metal component comprising a rectangular plate 42 provided with a central slit 43 (of which the function will become clear hereinafter), and lateral edges 44 folded at right angles to the plate 42.

In the example illustrated, the axis D is formed by a pair of coaxial bolts 45 via which the upper frame 41 is rotatably mounted on the side edges of the lower frame 34. According to a preferred embodiment, the axis D extends in the plane formed by the axes B and C (in other words, the axes B, C and D are coplanar) . The axis E, for its part, is formed by a pair of coaxial bolts 46 via which the upper frame 41 is rotatably mounted with respect to the rear-half seat 14B, and more specifically on tabs 47 formed projecting from the rear plate 27.

The articulation mechanism 33 comprises, thirdly, a coupling arm 48 mounted rotatably on the one hand with respect to the base 5 about an axis F and, on the other hand, with respect to the front-half seat 14A about an axis G spaced apart from the axis C and situated on the side thereof opposite the front plate 25.

The coupling arm 48 could be in the form of a single central rod (that is to say extending in a longitudinal plane of symmetry of the chair 1) . However, in the example illustrated, the coupling arm 48 comprises a pair of rods 49 disposed laterally on either side of the base 5 and made integral with each other by means of a spacer 50 (here in the form of a transverse bar).

As can be seen from the figures, the rotation axis F of the coupling arm 48 is offset with respect to the rotation axis B of the lower frame 34, both forwards and downwards, the arm 48 itself being offset forwards with respect to the entire lower frame 34. The axis F is formed, for example, by a pair of bolts 51 via which each connecting rod 49 is rotatably mounted with respect to a flange 19 of the base 5.

As is additionally seen in Figures 5, 7 and 8, the arm 48 is rotatably coupled to the front-half seat 14A by way of a tab 52 which projects from the front plate 25 and to which it is secured (e.g. by welding). According to an embodiment illustrated in these figures, the tab 52 is horn-shaped, and the rotation axis G of the arm 48 with respect to the front-half 14A is fixed to an end of the tab opposite thereto. In the example illustrated, the axis G is formed by a pair of coaxial bolts 53.

The axes A, B, C, D, E, F and G are parallel to one another and extend transversely, that is to say perpendicularly with respect to a general plane of symmetry of the chair 1.

In this way, the axes A, B, C, D, E, F and G define in any plane perpendicular to them (particularly in the general plane of symmetry of the chair 1): the axes B, C, G, F: a deformable lower quadrilateral BCGF; the axes A, C, D, E: a deformable upper quadrilateral ACDE .

Since the tab 52, which carries the axis G, is secured to the front plate 25, the side AC of the upper quadrilateral ACDE and the side CG of the lower quadrilateral BCGF are rigidly connected. Moreover, since the axes B and F are fixed and the axis D is secured to the lower frame 34 (that is to say on the side BC of the lower quadrilateral BCGF) , the deformations of the quadrilaterals BCGF and ACDE are linked, each configuration of the lower quadrilateral BCGF having a corresponding unique configuration of the upper quadrilateral ACDE, and vice versa.

However, the articulation mechanism 33 is not free, otherwise gravity would keep it in its folded configuration. The chair 1 comprises an elastic return member 54, which stresses the articulation mechanism 33 to its deployed configuration, such that, in the absence of any resistive force counteracting the deformation of the return member 54, the deployed configuration is the one that the articulation mechanism 33 occupies by default.

According to an advantageous embodiment, the return member 54 is interposed between the lower frame 34 and the upper frame 41 and tends to separate these from each other. The return member 54 is, for example, a gas spring, and in this case it comprises a jack body 55 which, in the illustrated example, is fixed to the lower frame 34 (and more specifically to a yoke 56 secured thereon) by being hinged relative thereto, and a rod 57 slidably mounted with respect to the body 55 and fixed to the upper frame 41 through the recess 37 and the slit 43, being articulated with respect to the upper frame 41.

As is illustrated in Figure 8, the recess 37 and the slit 43 provide an angular clearance for the rod 57, to permit the pivoting thereof that accompanies the tilting of the upper frame 41 with respect to the lower frame 34 during the deployment (or, conversely, the folding) of the articulation mechanism 33.

As is illustrated in Figure 10, and more particularly in the inset detail, the articulation mechanism 33 can be provided with an adjustable stop 58 for adjusting the deployed configuration of the mechanism 33 (and therefore the up position of the seat 14) . As in the illustrated example, this stop 58 can be in the form of a knurled wheel 50 in the bar 50 spacing apart the connecting rods 49 of the coupling arm 48. The stop 58 has a mushroom-shaped handle 59 and a stem 60, at the end of which a hemispherical pad 61 is mounted. In the deployed configuration, the plate 36 of the lower frame 34 abuts against the pad 61, which blocks the articulation mechanism 33 in position. By screwing (or unscrewing) the rod 60 in the bar 50 by means of the handle 59, the position of the pad 61 is adjusted, which makes it possible to adjust the deployed configuration of the articulation mechanism 33 (and therefore the up position of the seat 14) to the morphology (in particular the height) of the patient 15.

The movable seat 14 (with its articulation mechanism 33) can thus accompany and assist the actions of the patient 15 that are involved in sitting down from the standing posture and, conversely, standing back up from the seated posture.

We will now describe the movement of the articulation mechanism 33, starting first of all from the standing posture of the patient 15 and from the deployed configuration (adjustable, as we have just seen) of the articulation mechanism 33 (and therefore the up position of the seat). In this configuration, illustrated in Figures 3 and 4, it is assumed that the wheels 4 of the chair 1 are locked and that the footrest 21 is lowered.

The patient 15 has his back to the chair 1 and, with his feet on the lowered footrest 21, gently bends his legs. He can use his arms for help by gripping the armrests 8 (of which the height is preferably adjustable), as illustrated in Figure 4, which tensions, however moderately, the extensor muscles of the elbow (in particular the brachial triceps) . The back of the thighs (hamstring muscles) coming to rest on the front-half seat 14A, and the pelvis (and glutes) on the rear-half seat 14B, the patient 15 can then allow himself to sit down by relaxing his muscles, without fear of bumping the coccyx, since the spring 54 damps his movement.

To this end, the spring 54 is chosen to slow (and therefore to damp, but not resist) the folding movement of the articulation mechanism 33, specifically for a sample group of patients with weights varying between a minimum value (e.g. of the order of 35 to 40 kg) and a maximum value (e.g. of the order of 80 to 90 kg). It is possible to choose a gas spring 54 of adjustable force in order to adapt it to the weight of the patient 15. Alternatively, it is conceivable to provide several models of chairs 1, each adapted to a limited weight range and together covering a wide range of weights, and to select a model depending on the weight of the patient.

Once the patient 15 is seated, a helper can unlock the wheels 4 and raise the footrest 21 in order to freely move the chair 1 (with the patient) using the handlebar 13.

Conversely, starting from the sitting posture of the patient and from the folded configuration of the articulation mechanism 33 (and assuming that the wheels 4 are locked and the footrest 21 lowered; Figures 1 and 2), the patient 15, in order to start the movement involved in standing back up, begins by leaning the upper body forwards, thereby moving his centre of gravity forwards and transferring part of his weight to his feet, reducing the resistant force counter to the deployment of the articulation mechanism 33 under the effect of the return spring 54.

The patient can use his arms for help by gripping the armrests 8 and pressing down on them, which further lightens the weight supported by the seat 14, to the point where the spring 54 can freely stretch, deploying the articulation mechanism 33, which pushes the patient both upwards (by the rear-half seat 14B) and forwards (by the front-half seat 14A) and further lightens the weight supported by the seat 14. The patient 15, assisted in this way, can then easily reach the posture illustrated in Figure 4 where, although his legs are still slightly bent, the effort that the patient 15 needs to make to fully extend them is modest.

The articulation mechanism 33 is not only designed to provide the patient 15 with a thrust force allowing him to stand up; it is designed to perform an ergonomic support movement, that is to say a movement closer to the kinematics of the human body when going from a seated posture to a standing posture, and vice versa.

To this end, the axes A, B, C, D, E, F and G are positioned (that is to say the lower frame 34, the upper frame 41, the front-half seat 14A, the rear-half seat 14B and the coupling arm 48 are dimensioned) such that the lower quadrilateral BCGF is convex in the folded configuration of the mechanism 33 and concave, via the axis G, in the deployed configuration of the mechanism 33.

It will be remembered that a quadrilateral is called convex when its diagonals are included in the perimeter defined by the quadrilateral, and concave when one of its diagonals is situated outside this perimeter. In other words, the lower quadrilateral BCGF being concave via the axis G signifies that the angle between the segments GF and GC, measured from the inner side to the quadrilateral BCGF, is greater than 180° .

It is in fact found that: as long as the lower quadrilateral BCGF is convex, the segment AE (and with it the rear-half seat 14B) is driven, upon the deployment or folding of the articulation mechanism 33 during a phase called a translatory phase (labelled T in Figure 11), in a substantially vertical translational movement (arrow FI in Figure 6) as far as an intermediate configuration in which the segments GF and GC are aligned; then, beyond the intermediate configuration, when the lower quadrilateral BCGF becomes concave, the segment AE (and with it the rear-half seat 14B) is driven, upon the deployment or folding of the articulation mechanism 33 during a phase called a rotatory phase (labelled R in Figure 11), in a substantially rotational movement from the rear forwards (in the case of deployment, the arrow F2 in Figure 9) or, conversely, from the front rearwards (in the case of folding).

The movement of the articulation mechanism 33 (and therefore of the seat 14) is thus subdivided into two phases.

During the translatory phase T, the rear-half seat 14B accompanies the vertical translational movement of the pelvis (and buttocks) of the patient 15, either when he initiates the movement involved in standing back up from the seated posture or when he ends the movement involved in sitting down. As for the front-half seat 14A, it is driven in a combined movement of vertical translation and of low-angular amplitude rotation that accompanies both the rise (in the case of transition to the upright posture) or fall (in the cause of transition to the seated posture) of the knee joint and the rotation of the thighs about the latter. In the deployment movement of the articulation mechanism 33, the axis C is driven, during the translatory phase T, in a rotational movement of large amplitude upwards, centred on the axis B (arrow F3 in Figure 6).

It will be noted that, during the translatory phase T, the whole seat 14 moves rearwards in translation. This movement provides reassurance (thus promoting relaxation of the muscles) to patients who have retropulsion symptoms and who are inclined by reflex to lean their body back during the transition from the seated posture to the standing posture.

During the rotatory phase R, the complete seat 14 (front- half seat 14A and rear-half seat 14B) accompanies the rotational movement of the pelvis and thighs of the patient 15 about the knee joint, which remains at a substantially constant height. In the deployment movement of the articulation mechanism 33, the axis C is driven, during the rotatory phase R, in a low-amplitude rotational movement downwards, centred on the axis B (arrow F4 in Figure 9) , which frees the knee joint and allows the patient 15 to extend his legs without obstruction in order to stand up.

It will also be noted that, during the rotatory phase R, the entire seat 14 moves forwards in translation, which, after the translatory phase T rearwardly accompanying the patient with retropulsion symptoms, conversely propels him forwards at the end of the movement and allows him definitively to stand upright.

To obtain these complex kinematics, at least one of the following conditions a) to e) must be satisfied: a) The sum of the inter-axis distances FG and CG is less than or equal to the inter-axis distance BC:

FG + CG < BC b) The angle, labelled a, between the planes defined respectively by the axes A and C on the one hand and C and G on the other hand is between 70° and 120°: 70° < a < 120° (In the example illustrated, the angle a is approximately 90°) c) The inter-axis distance DE is greater than or equal to the inter-axis distance AC:

DE > AC d) The inter-axis distance CD is less than or equal to the inter-axis distance BD:

CD < BD

In other words, the anchoring point of the upper frame 41 on the lower frame is nearer the axis C than the axis B. e) The inter-axis distance AE is greater than or equal to the inter-axis distance CD:

AE > CD

Two, three or four of the conditions a) to e) can be jointly satisfied. In the example illustrated, all the conditions a), b), c), d) and e) are jointly satisfied.

By way of example, a list of parameters and of their corresponding numerical values is given below, for which the articulation mechanism 33 operates correctly, that is to say it allows the translatory phase and the rotatory phase to be

obtained, to the benefit of patient safety, and makes it possible to provide an ergonomic seat. In the table below, a sequence of two contiguous letters, among the letters A, B, C, D, E, F and G, corresponds to the distance separating the axes defined by their respective letters. Thus, BC designates the inter-axis distance (that is to say the shortest distance) defined between the axes B and C.

Bfx designates the distance between the vertical planes passing through the axes B and F, and BFz designates the distance between the horizontal planes passing through these same axes .

In Figure 12, by way of comparison, a similar diagram to that of Figure 11 has been traced in order to illustrate the different positions of the seat of the chair from the patent GB 1 406 420 between its extreme positions shown in Figures 2 and 3 of said patent. In the diagram of Figure 12, of which the orientation is the reverse of that in Figures 2 and 3 of said patent, the front of the seat is on the right. It will be seen that the rear part of the seat is driven in a substantially vertical translational movement and forwards, without any appreciable rotation component, while the front end of the seat is driven in a substantially translational movement always directed rearwards, including at the end of the movement. Such kinematics do not follow the movement of the human body, and in particular they do not provide the PDS patient with the forward momentum which, at the end of the movement, is needed for him to stand back up .

By contrast, thanks to the movement being divided into two phases, namely a substantially translatory phase followed (or preceded, depending on whether the patient is sitting down or standing back up) by a substantially rotational phase, the articulation mechanism 33 of the chair 1 described above is adapted to the kinematics of the human body. This results in enhanced safety of the PDS patient 15, whose symptoms of retropulsion, of oppositional hypertonia and stasibasiphobia can thus be effectively combatted.

Tests conducted with this chair 1 show that patients who have lost the habit of sitting down and standing up without help can recover this habit through daily use of the chair.

It is possible to go beyond mere assistance in the movements involved in standing up and sitting down (for example gradually during a rehabilitation programme) by limiting the travel of the articulation mechanism 33 (and therefore of the seat 14) by means of a system for locking the spring 54.

This locking system acts, for example, on a valve that closes a pressure relief vent of the spring 54, thereby blocking the rod 57 in position, whatever this position might be. The locking system is actuated, for example, via the handlebar 13 by means of a manually operable handle 62 connected to the spring 54 by a cable 63, in the manner of a bicycle brake.

The articulation mechanism 33 does of course add weight by comparison with a chair that does not have this mechanism, but this weight can be kept contained, since the components from which it is constructed are relatively few in number and quite light. The chair as a whole can be kept relatively light. Moreover, if the bodies forming the axes A, B, C, D, E, F and G are sufficiently greased, the mechanism 33 provides the chair 1 with a high degree of reliability and therefore a long service life.

Claims (10)

A medical wheelchair comprising: - a chassis (2) equipped with a bottom (5) - a seat (14) movable with respect to the bottom (5) and including a front half-seat (14A) and a a rear semicircular (14B) rotatable about an axis A; and a low positron when the bottom (5), and capable of assuming an unfolded configuration, placing the seed (14) in a high positron at a distance from the bottom (5), the mechanism (33) comprising: a lower frame (34 ) rotatably mounted relative to the bottom (5) about an axis B and with respect to the front semitrailer (14A) about an axis C located near a leading edge thereof; An upper frame (41) pivotally mounted relative to the lower frame (34) about an axis D located between axes B and C and pivotally mounted relative to the rear semicircle (14B) about an axis E, there is a rear edge thereof; A coupling arm (48) rotatably mounted relative to the bottom (5) about an axis F and relative to the front half-way (14A) about an axis G at a distance from the axis C; - an elastic return member (54) which tightens the pivot mechanism (33) to its unfolded configuration; where axes A, B, C, D, E, F and G are parallel and define in a plane perpendicular to them: - the axes B, C, G, F: a deformable lower square BCGF; - axes A, C, D, E: a deformable upper square ACDE; wherein the axes A, B, C, D, E, F and G are arranged such that the lower square BCGF is convex in the folded configuration and concave via the axis G in the folded configuration. The wheelchair (1) according to claim 1, characterized in that the sum of the distances between the axes FG and CG is less than or equal to the distance between the axes BC. Wheelchair (1) according to claim 1 or claim 2, characterized in that the angle between the planes defined by axes A and C respectively on one side and C and G on the other side is between 70 ° and 120 °. The wheelchair (1) according to claim 3, characterized in that the angle between the planes defined respectively by the axes A and C on one side and C and G on the other side is approx. 90 °. Wheelchair (1) according to one of the preceding claims, characterized in that the distance between the axes DE is greater than or equal to the distance between the axes AC. Wheelchair (1) according to one of the preceding claims, characterized in that the distance between the axes CD is less than or equal to the distance between the axes BD. Wheelchair (1) according to one of the preceding claims, characterized in that the distance between the axes AE is greater than or equal to the distance between the axes CD. Wheelchair (1) according to one of the preceding claims, characterized in that the return element (54) is a gas spring. The wheelchair (1) according to claim 8, characterized in that the gas spring (54) is of the lockable type. Wheelchair (1) according to claim 8 or claim 9, characterized in that the gas spring (54) comprises a body (55) attached to the lower frame (34) and a rod (57) attached to the upper frame (41).