An adjustable chair for medical use

Abstract: A chair for medical use comprising a base (1) supporting a seat (2) to which seat (2) a backrest and a legrest (4) are hinged. Movement and adjusting means (5) of the seat (2) are hinged between the base (1) and the seat (2) and comprise a first four-bar linkage (6, A-B-C-D) and a second four-bar linkage (7, C-D-E-F) of the same length and constrained to each other at a common smaller side (C-D). The first bar linkage (6) is connected at a remaining smaller side (A-B) to the base (1) and can move by an angle alpha, while the second bar linkage (7) is constrained by a remaining smaller side (E-F) to an end of the seat (2). Two bidirectional kinematic connectors (8) are positioned between the first and the second bar linkages (6 and 7) and are each solid to one large side (A-D, F-C) of the bar linkages (6, 7) so as to determine at an angle alpha of the first bar linkage (6) an angle 2 alpha between facing large sides (B-C, E-D) of the two bar linkages (6, 7).

Description: The invention relates to an adjustable chair for use in the field of medicine, especially dentistry. The chair exhibits three basically flat portions, namely a backrest, a seat and a legrest, which are hinged in sequence. Chairs with three portions, very commonly used in the medical field, usually offer a wide range of positional adjustments, necessary for the needs of the medical professional who by adjusting the portions perform his or her operations comfortably and without the patient's having to strike awkward postures. Some types of prior art chair (see US patent US 3,414,324 or GB patent GB 2,016,915) envisage that the seat be indirectly connected to a base, whereat are situated appropriate adjustment controls of the hydraulic kind (a classic vertically-arranged piston) which are activatable from the outside, directly by the doctor. These controls adjust the chair height and are aided in this task by the presence of a pantograph positioned bilaterally to the said means and constrained at one end to the chair and at the other to the base. Also present is a pair of motorised worm-nut groups, placed horizontally below the chair and permitting of inclining (with respect to the floor) both the chair and the backrest and legrest, being linked to relative independent articulations placed at the ends of the chair surfaces. Such solutions as the one described above are now obsolete since they provide only limited movement possibilities, the range of height adjustments from minimum to maximum depending on the excursion range of the piston and the mass of the chair itself, which can hamper the work of the doctor or dentist. One solution, FR 2,339,390, attempts to increase movement range while reducing the mass of the base in constraining an end of the surface defining the seat of the chair to the base by means of a motorised four-bar linkage. This solution actually increases the height range of the chair, bringing the patient's head to a height whereat the doctor or dentist can operate comfortably, as well as enabling the chair to be brought down to a height which presents no difficulty to even the shortest patient when climbing into or out of it. A similar technical improvement can be seen in patent DE 2,809,269: here, as above, the four-bar linkage principle is used, but is applied to the front end of the seat, near to where it is hinged to the legrest. This means that the entire chair can be rotated without the angular configuration of its constituent elements having to change. Obviously, the tilt axis of the chair is beneath the patient's knees. Thanks to its ability to bring the patient's head down very low, a dentist can operate while sitting in a normal chair. The two above solutions confer a better adjustment range, especially in situations where the patient's head has to be low to the ground, but they present the drawback that the positions are reached by translating the chair (and obviously the backrest also) towards the ground, shifting the vertical axis of the chair laterally, so that the patient's head is moved horizontally by a considerable distance. This translation of the patient's position poses a series of practical problems to the dentist. In a typical dentist's surgery, there are numerous apparatus arranged more or less in an arc centring on the dentist's seated position, obviously so that he or she can swiftly and easily reach each instrument. With the patient's head in a translated position with regard to the original, the dentist has also to move and is therefore no longer in his or her ideal position. In US-A-3,804,460 there is disclosed an adjustable chair for use in the field of medicine, and in particular in field of dentistry, according to the preamble of claim 1. This adjustable chair is not able to achieve a very low height, because the parts of the chair or its base interfere in the adjustments. The invention therefore proposes a dentist's chair wherein it is possible to obtain large height adjustments by means of a kinematism which keeps the chair on a same vertical axis independently of any angular adjustments made on the constituent parts of the chair itself. A further aim of the invention is to be able to adjust the chair to a very low height without the parts of the chair or its base interfering in the adjustments. Further characteristics and advantages of the present invention will better emerge from the detailed description that follows, of an embodiment of the invention, illustrated in the form of a non-limiting example in the accompanying drawings, in which: Figure 1 shows the adjustable dentist's chair in a completely raised position, and in a lateral view with some parts removed better to evidence others; Figure 2 shows the adjustable chair of figure 1 in a posterior frontal view with some parts removed better to evidence some technical details; Figure 3 shows the chair at a very low height from the ground and in a plan view from above with some parts removed better to evidence others; Figures 4 and 5 show the adjustable chair in its lowest mass configuration, both figures being lateral views with several parts removed better to evidence others; Figure 6 shows the lower part of the adjustable chair in an intermediate configuration, in a perspective view of the front side; Figure 7 shows the lower part of the adjustable chair in its configuration of smallest mass, in a perspective view from the back side. With reference to the figures of the drawings, and with particular reference to figure 1, the adjustable chair is of known type and comprises a base 1 to which are hinged: movement and adjusting means 5 supporting a seat 2 to which are hinged, at their ends, a backrest 3 and a legrest 4. As can be seen in the figure, the chair is shown without padding so that the structures composing the object of the invention can be more clearly described herein. In figure 1, the movement and adjusting means 5 enable the seat 2 to be raised and lowered vertically by means of a ratiomotor 9 between a minimum and a maximum position with respect to a reference plane P on which the base 1, usually constituted by the surgery floor. The movement and adjustment means 5 are constituted (see figures 1 and 2) by a first bar linkage 6 with ends A-B-C-D and a second bar linkage 7 with ends at C-D-E-F, all of equal length and constrained to each other at their common smaller side, C-D. Still with reference to figures 1 and 2, the two bar linkages 7 and 7 are each constituted by two arm pairs 6a, 6b and 7a, 7b, equipped at their common side C-D, with a parallel pair of pivots 33 and 34 which are rotatable about axis C-D. The pivots 33 and 34 define the ends of the smaller side C-D and have centrally inserted on them a pair of parallel and axially fixed bushings 35 and 36 realising a rigid connecting frame for the arm 6a, 6b, 7a, 7b ends of the relative bar linkages 6 and 7. Further bushings 37 and 38 are arranged at the sides of the bushings 35 and 36, which bushings 37 and 38 are rotatable about the pivots 33 and 34, to which bushings 37 and 38 the ends of the arms 6a, 6b, 7a, 7b are solid. The first bar linkage 6 is hinged at its smaller side A-B to the base 1 and is thus mobile with respect to plane P by a variable angle alpha. The second bar linkage 7 is constrained, by means of its smaller side E-F, to an end of the seat 2. More precisely, the smaller side E-F is hinged to a frame 19, which is constituted by two vertical columns 19a and 19b on which the second bar linkage 7 is hinged, and by an upper support 19c, solid to the colums and hinged, at VB, to the front end of the seat 2. To obtain a correct hinged link between the first and the second 6 and 7 bar linkages, pair of bidirectional kinematic connectors 8 are interpositioned between the first 6 and the second bar linkages 7. These bidirectional kinematic connectors 8 are each solid, one to greater base A-D and another to greater base F-C of the bar linkages 6 and 7 such as to determine at an angular value alpha of the first bar linkage 6 a consequent angular value 2 alpha between the facing greater sides B-C and E-D of the two bar linkages 6 and 7. Apart from that and owing to the equality of the two bar linkages 6 and 7, the seat 2 can be raised while all the time staying on a same vertical axis, indicated by Y (see figures 1, 4, 5). With reference to figures 1, 2 and from 4 to 7, the bidirectional kinematic connectors 8 are constituted by two enmeshed pairs of cogged sectors 10 and 11. Each pair of cogged sectors 10 and 11 is solid to a relative bushing 37 and 38, whereat the relative arm 6a and 7a belonging to the relative bar linkage 6 and 7 is fixed. The motor 9 powering the first and second bar linkages 6 and 7 is constituted by a known ratiomotor 13 activating a worm screw 14 coupled with a threaded bushing 15 hinged to the central bushing 35 of the second bar linkage 7. To enhance the inclinations of the second bar linkage 7, the ratiomotor 13 and the lower end of the worm screw 14 are hinged to the base 1, as can be seen in figures 2, 4 and 5. The seat 2 is provided with two motors 17 and 18 in order to guarantee tilt adjustment of the seat 2, the backrest 3 and the legrest 4. The first of the motors 17 is a ratiomotor of known type, supported on the frame 19 and acting on the seat 2 to tilt it with respect to plane P. It can also bring the patient into the Trendelembourg position; that is, with the head lower than the legs. The second ratiomotor 18 is structurally the same as the first 17 but is supported directly on the front part of the seat 2 and acts, by means of the known worm screw 40 - threaded bushing 41 coupling, on the backrest 3 so as to tilt it independently of the seat. As can be seen in figures 1, 4 and 5, the backrest 3 is hinged at two points: first, at LL, by a rod 43 connecting the lower end of the backrest 3 to the seat 2, and second, at H, directly to the end of the backrest 3 through the threaded bushing 41. Movements between the backrest 3 and the legrest 4 are coordinated by a first horizontal rod 20 hinged, at one or its ends, to the end of the backrest 3 linked to the bushing 41, while the other of its ends is slidably inserted in a fork 21. The fork 21 is provided at its other end with a second horizontal rod 22 hinged at its free end to the upper end of the legrest 4, and thus can be adjusted by pushing or traction (see arrow N in figures 4 and 5) to correspond with the inclination of the backrest 3. In other words, on raising the backrest 3 with respect to plane P the legrest 4 is lowered, and vice versa. 23 denotes springs acting between the first rod 20 and the fork 21 which springs keep the rod 20 and the fork 21 close together, so that the rod 20 cannot slide axially internally of the fork 21, except in a special case which will be described hereinunder. Figures 4 and 5 show how the seat 2 can be lowered until it is very close to plane P, thanks to the closeability of the bar linkages: for this reason, as well as to prevent the vertical legrest 4 stopping the descent of the chair, adjustment means 24 are provided to incline the legrest 4 gradually as the seat 2 descends. The adjustment means 24 are positioned between the seat 2 and the second bar linkage 7 and act when the seat is lowered towards a minimum height configuration of the two bar linkages 6 and 7. The adjustment means 24 are in fact a first L-shaped arm 25 pivoted at an intermediate point to the lower frame 19 and superiorly provided with a first cam-follower roller 26 in contact with a relative cam device 27 fixed to the second rod 22 linked with the legrest 4. The first L-shaped arm 25 is hinged at M to the end of a second arm 28 provided with a second cam-follower idle roller 29 at its free end, which, when the seat 2 and therefore the bar linkages 6 and 7 are lowered, contacts a fixed arc-shaped striker 30 exhibited on the greater side F-C of the second bar linkage 7. This contact causes the second arm 28 to rotate the first L-shaped arm in an anticlockwise direction (see figures 4 and 5), which arm 25 in turn pushes on the cam device 27 so a to advance the second rod 22 (see arrow R in figures 4 and 5), which then tilts the legrest 4. During the tilting, the backrest 3 stays as it was before: to stop it from following the movements of the legrest 4, the first rod 20 and the fork 21 are distanced one from the other by the sliding of the first rod 20 internally of the fork 21. The two elements 20 and 21 are held by the spring 23 which stretches to enable the sliding and distancing of the first rod 20 with respect to the fork 21 up until there is an adjustment of the legrest 4. When the chair is raised, the spring 23 causes the first rod 20 and fork 21 to retreat into the original configuration. The fork 21 is solid to an arched support structure 31 developing below the front end of the seat 2. The support structure 31 exhibits a straight portion 32 hinged at G to the seat 2, which develops in the same direction as the legrest 4 so that it crosses the end of the seat 2. This type of hinge is designed to allow a correct rotation of the legrest 4 without the patient's legs sliding on the legrest 4. The centre of rotation O of the legrest 4 (see figure 1) corresponds substantially to the point of rotation of the patient's knees, thanks to the special arched shape of the support structure 31. A chair of this type can be operated by means of an external command panel acting on all of the ratiomotors 13, 17 and 18 in order to raise the chair from a position corresponding to plane P in figures 4, 5 and 7, to a position of maximum height with respect to plane P, see figures 1 and 2. Apart from the above-described movement the chair's configuration can be changed by activating the third ratiomotor 18, which enables the backrest and the legrest to be tilted, and the second ratiomotor 17, which enables the chair to be brought into the Trendelembourg position. All of the ratiomotors are interconnected by means of endrun microswitches (not illustrated since of known type) which cut off the motor when a position of minimum or maximum excursion has been reached, and then switch the power to another ratiomotor, should the dentist wish to continue the adjustment operation. The chair as it is structured herein allows a wide variety of movements, and it can especially be adjusted to maximum and minimum heights which exceed the performance of chairs presently in use, thanks to the kinematism of the double bar linkage. The adjustment is effected while the seat remains on the same vertical axis, which makes the dentist's work easier if the patient has to be moved up or down during operations, with the dental instruments already set out in ideal positions for the dentist's reach.

Claims: An adjustable chair for use in the field of medicine, and in particular in the field of dentistry, comprising a base (1) of a seat (2) to which seat (2) are hinged a backrest (3) and a legrest (4); movement and adjustment means (5) being provided for at least the seat (2) and being hinged to the base (1) and to an end of the seat (2), the movement and adjusting means (5) being provided with motorisation (9) and having a function of raising and lowering the seat (2) between a minimum and a maximum heights with respect to a reference plane (P) on which the base (1) rests; the movement and adjustment means (5) being constituted by a first four-bar linkage (6, A-B-C-D) and a second four-bar linkage (7, C-D-E-F), both of the same length and constrained to each other at a common smaller side (C-D); the first bar linkage (6) being further connected at its end constituting another small side (A-B) to the base (1) and being mobile through an angle (alpha), and the second bar linkage (7) being constrained, by a remaining smaller side (E-F) to an end of the seat(2); two bidirectional kinematic connectors (8) being provided between the first (6) and the second (7) bar linkages, each bidirectional kinematic connector (8) being solid to a relative larger side (A-D, F-C) of the bar linkages (6, 7) such as to determine, at an angle (alpha) of the first bar linkage (6), an angle (2 alpha) which is twice the first (alpha) between facing larger sides (B-C, E-D) of the two bar linkages (6, 7), characterized in that the bidirectional kinematic connectors (8) are constituted by two pairs of enmeshed cogged sectors (10, 11); each said pair of enmeshed cogged sectors (10, 11) being solid to a relative bushing (37, 38) representing an end point of the larger sides (A-D, F-C) of the respective bar linkage (6 or 7), and in that the motorisation (9) is a rectilinear actuator, which ends are hinged at the base (1) and to a central bushing (35) defining an end point of the second bar linkage (7) approximating its rotation axis (C). A chair as in claim 1, characterised in that the motorisation (9) is a ratiomotor (13) activating a worm screw (14) screwably coupled with a threaded bushing (15) hinged to said central bushing (35); the ratiomotor (13) and the end of the worm screw (14) being hinged at the said base (1). A chair as in claim 1, characterised in that the seat (2) is provided with two second motorisation means (17, 18), the first (17) being supported on a frame (19) positioned between the seat (2), to which it is hinged, and the second bar linkage (7), which is also hinged to the frame (19), and causing the seat (2) to tilt with respect to plane (P); the second (18), identical to the first (17), being supported directly on the seat (2) and acting on the backrest (3) such as to cause it to tilt independently of the seat (2) tilting movement; the backrest (3) being further connected to the legrest (4) by means of a first horizontal rod (20) hinged at one end to the end of the backrest (3) and at the other end being slidably inserted in a fork (21), which fork (21) has at its other end a second rod (22) hinged at its free end to an end of the legrest (4) such as to regulate the tilting of the legrest (4) to correspond with that of the backrest (3); a spring (23) being provided, acting between the first rod (20) and the fork (21), to keep the first rod (20) and the fork (21) close together. A chair as in claim 3, characterised in that tilt adjustment means (24) of the legrest (4) act between the seat (2) and the second bar linkage (7) when the seat (2) is in a minimum height configuration with respect to the plane (P); the tilt adjustment means (24) being constituted by a first L-shaped arm (25) pivoted at an intermediate point to the frame (19) and provided superiorly with a first cam-follower idle roller (26) contacting with a cam device (27) fixed to the second rod (24) connected to the legrest (4); the first arm (25) being hinged, at a free lower end (M) to the end of a second cam-follower idle roller (29) which contacts a fixed striker (30) exhibited by the second bar linkage (7) when the seat (2) is at a minimum height, such as to cause a rotation of the first arm (25) and thus tilt the legrest (4). A chair as in claim 1, characterised in that the legrest (4) is solid to an arched support structure (31) developing beneath the front end of the seat (2) and exhibiting a straight portion (32) hinged at (G) to the seat (2) and developing in the direction of the legrest (4) such as o clear the end of the seat (2).

Inventors: LENZI GINO, LENZI, GINO
Applicants: TECNODENT S P A, TECNODENT S.P.A.
Application year: 1993
Main classification: A61G15
IPC codes: A61G15