| WO/1996/032037 | AN ARTICLE OF FURNITURE |
| WO/1993/018686 | UNITARY CHAIR WITH RESILIENT BOTTOM AND BACK |
| WO/2020/146206 | CHAIR |
| WO1994027472A1 | 1994-12-08 |
| DE832053C | 1952-02-21 | |||
| US4880272A | 1989-11-14 |
Technical problem This invention solves the problem of automatically adjusting chairs with anatomical chair back shape, having a concentrated pressure on the low back of a sitting person. Since a comfortable and anatomically correct sitting requires that a concentrated pressure of the persons back on the chair back should be in the point of the low back (lumbal zone), it is necessary to find a way to adjust this position for users of various body heights, i. e. various low back heights, as well as to find a way of adjusting when changing the sitting position forward-backward (by moving the lower part of the body back and forward on the seat).
Background art It is well known that a modern man spends most of his time sitting, so that it is necessary to make sitting more comfortable and anatomically correct, specially as regards the backbone position. The most important function of the chair back is to provide support to the lumbal zone of the backbone. This concave low part of the backbone stretches approximately from the waist till the middle of the backbone. From that reason the chair back has to be co-ordinated with the backbone profile in the lumbal zone, which enables support of the lumbal zone by the chair back.
There are two problems to be solved in order to realize this necessity. The first one is how to provide the correct leaning of lumbal zone for a greater number of users 1 of various body heights, having also various heights of lumbal zone 2 in relation to the seat surface level, according to the figure 1.
The second problem is that the sitting itself, being a dynamical activity, involves temporary a spontaneous changing of sitting position by moving back and forward on the seat.
Simultaneously with body moving, the point of backbone support in relation to the chair back is also changed. The figure no. 2 shows the chair type with the fixed chair back. If, by an upright sitting position of user 1, the position of the lumbal zone 2 corresponds to the most convex point on the chair back, i. e. to lumbal support 3 (since they are at the same height as shown in the figure 2), it means that the condition of a comfortable, i. e. anatomical correct support by sitting is fulfilled. When the user 1 spontaneously moves forward on the seat, he takes the position shown with the broken line, so that the lumbal zone comes into the position 4 and loses contac with the support, while the point of back support is located in the point 5, so that the condition of an anatomical support is no longer fulfilled. Similar happens also with the chair back shown in the figure 3, although the distance between the new point of back support 6 and the new lumbal zone position 7 is smaller.
According to criteria of adjustment to condition of anatomical support, the existing chairs can be divided into the following groups: 1. Most chairs are designed with fixed seat und fixed chair back and in no case consider the necessity of supporting the lumbal zone, for example the chairs with flat chair back.
2. There are also chairs with fixed seat and fixed chair back with anatomical chair back profile in the lumbal zone. However, this does not solve the problem of adaptation for users of various body heights. It also does not solve the problem of adaptation when moving on the seat, as shown in the fig. 2. This is the reason why this type of chairs is convenient for only a small number of users and is not suitable for various sitting positions.
3. There are also some chair types with seats and chair backs adjusted by means of some elements such as screws, springs and similar, which are used for fixing and unfixifing seats and chair backs. For such adjustments, it is necessary to have an active user's action. Such adjustment is only partly comfortable, in case when a user takes a seat and adjusts the chair for himself, but becomes rather uncomfortable for compensation of spontaneous moving of the body during the sitting.
4. There are also chairs with various solutions of self-adjustment while changing sitting position.
These are mainly solutions with flexible chair back, where the moving axis of the chair back is located in seat surface level or in the level of the lumbal zone (as shown in the figure 3). Such solutions are not meant to solve any of the mentioned problems or they solve them only partly, such as the chair shown in the figure 3 which solves the problem by reducing the distance the support point and the lumbal zone (points 6 and 7) in comparison to the simple chair shown in the figure 2 (points 4 and 5).
Disclosure of Invention Here described invention represents a method which solves the problem of self adjustment of lumbal zone support height for users of various body heights and in various sitting positions, without an active user's action, by using a chair seat construction of cantilever type fixed on the front side of the chair, with free end on the back side of the chair. This function of self-adjustment is based upon assumption that a great number of users have height and weight, that can be approximated by a linear dependence (the taller the user-the larger the weight.). Since the cantilever deformation depends upon the applied force, a taller and havier user will cause larger deformation, which with most users enables direct leaning of the lumbal zone on the lumbal support. Solution of the problem of chair self adjustment for user's moving forward- backwards on the seat, is based on the fact that cantilever deformation decreases by shortening of effective cantilever length (with the same vertical pressure on the seat). When users move forward, the effective length of cantilever (and it's deformation) decreases, and the height of lumbal support in relation to the seat level also decreases, so that the position of the lumbal zone center comes very close to lumbal support center, when moving back or forward to any sitting position. In this way the chair offers a comfortable, i. e. anatomically correct support for most users and most sitting positions.
Brief Description of the Drawings The invention is described in detail in the following drawings: Fig. 1-Various heights of lumbal zone in relation to the seat surface level, depending upon user's body height (technical problem) Fig. 2-A chair with the fixed chair back (background art) Fig. 3-A chair with the flexible chair back (background art) Fig. 4-Schematic longitudinal section of the chair through the seat and the chair back with various cantilever loads.
Fig. 5-Schematic longitudinal section of the chair for users of various body heights Fig. 6-Schematic longitudinal section of the chair through the seat and the chair back with a different cantilever load point Fig. 7-Schematic longitudinal section of the chair showing the user in various sitting positions Fig. 8-A chair with multi layer cantilever Fig. 9-A chair with multiple cantilever Fig. 10-A real solution-a chair with flexible chair back Fig. 11-A real solution-a chair with flexible chair back Detailed description of invention Here described invention solves the problem of self adjustment of lumbal support height for users of various body heights and in various sitting positions without an active user's action, only by using chair seat construction of cantilever type fixed on the front side of the chair, and with a free end on the back side of the chair. This function of self-adjustment is shown on the figures 4,5,6 and 7. Fig. 4 shows the schematic longitudinal section of the chair through the seat and the chair back. It can be seen that the seat-cantilever 20 has the fixed point 21 on the front side of the chair. At the same time the free part of the seat- cantilever can take various positions 22 and 23, which depends upon various loads shown as vertical vector force 24 and 25. Solving the problem of self-adjustment is based upon assumption that a great number of users have height and weight, that can be approximated by a linear dependence (the taller the user-the larger the weight). And according to that, the height of the lumbal zone (height in relation to the seat surface level by upright sitting position) is approximated by a linear dependence to the weight. Fig. 5 shows that a taller user 26 (shown with full line) will make a larger cantilever deformation than a smaller and thinner user 27 (shown by broken line). Since the cantilever deformation depends upon the applied force in the same load point, so does the distance between seat (cantilever) 20 from lumbal support 3 depend in the same linear way. According to this, the height 28 is suitable for person 26, and height 29 is suitable for person 27 (Fig. 4 and 5). With proper choice of cantilever stiffness (relation force- deformation) one can make lumbal zone 2 to be leaned directly on lumbal support 3 with most users of various body heights, which makes sitting comfortable with anatomically correct support.
By solving the problem of chair self-adjustment while user moves back and forward on the seat, we use the fact that cantilever deformation decreases simultaneously with effective cantilever length (with the same load). Fig. 6 and 7 show that the load point represents the vertical projection of the lowest pelvic bone part on the seat. When a user in upright sitting position moves forward on the seat, the load point is moved from position 31 into position 32.
Since by such moving the effective cantilever length decreases from the length 33 to the length 34, so will cantilever deformation be smaller in the front position 32.
Fig. 6 shows an ideal case when user moves forward on the seat and the lumbal zone 2 does not move in relation to the lumbal support 3, what means that distance of load points 31 and 32 its the same in relation to the support point 3. In this ideal case, if we suppose that positions 31 and 32 are extreme positions (upright and the most distant position), it is necessary that the intermediate positions make a part of a circle between points 31 and 32, with a center in the point 3. This ideal case is not real because of seat flexibility (point 3 moves) and because of backbone bending by changing of the sitting position. In a real case, however, the center of the lumbal zone 2 will be very close to lumbal support 3 for all forward-backwards moving positions.
By real cantilever construction the relation force-deformation on the free end will be chosen according to the weight and lumbal zone height range with most users. For a given force- deformation relation (for example 7 cm for user of 90 kg), the proper cantilever deformation (while moving forward) might be adjusted by proper choice of cantilever length-by moving the cantilever fixed point back towards free end. It means that by choice of various users'heights and various sitting positions we can use two free parameters, the cantilever length and stiffness.
Relation deformation-moving (forward-backwards) can also be adjusted by changing specific stiffness along the cantilever. This adjustment is possible in many ways, for example the multy layer cantilever as shown in fig. 8 or multiply cantilever as shown in fig. 9. The essence of invention will not be changed by using such or similar solutions.
For the real chair construction one can use various solutions with flexible chair back, making sitting more comfortable, as shown in fig. 10 and 11. In this case, when the user moves forward on the seat, lumbal support 3 on the chair back is moved backwards, as shown in the fig.
10, or forward as shown in the fig. 11. Such moving will be compensated by adjusting relation deformation-moving (forward) in constructing the cantilever-seat, keeping the constant distance of support points on the seat 31 and 32 from lumbal support 3. It is obvious that the chair construction with flexible chair back won't change the essence of invention.
It is apparent to those skill in the art that many modifications of the chair shape, chair back and seat can be made, which does not mean changing essence of invention.