Piece of Seating Furniture with a Longitudinal Axis Above the Seating Surface

The present disclosure relates to seating furniture, including office chairs, having a seating surface and a vertical plane of symmetry, where the seating surface can be swiveled about a longitudinal axis with respect to a base of the seating furniture.

A piece of seating furniture is disclosed by EP 1 090 568 that proposes to support a seating surface by means of spherical or ball-shaped rolling elements on an at least approximately spherical base. The instantaneous swivel point, the instantaneous center, which is therefore not fixed in relation to the base, is approximately at chest height of a user, but can also sink. Due to this position, the center of gravity of the combination of user and (movable part of the) furniture is always below the instantaneous center, so that the seating surface and user are always pushed into the upright, stable, “resting position.”

EP 2 381 816 discloses various swiveling piece of seating furniture, some of which have their pivot point in the floor region, some just below the seating surface. Above the seating surface, the position in the thoracic-lumbar spine region is mentioned in order to avoid rotation around this axis when sitting in order to avoid degenerative phenomena when sitting for long periods of time, only one example with an exactly horizontal, physically formed, longitudinal axis is provided.

Seating furniture is known from DE 40 06 608 and EP 780 073 in which longitudinal axes for the seating surface are provided directly below the seating surface.

From WO2016/042127 of the applicant, a piece of seating furniture is known in which a longitudinal axis is virtually formed in the form of a spherical bearing above the seating surface. The kinematics are as follows: at the base, a series of three arms that can be swiveled relative to one another and are arranged in series is formed, the last of which is firmly connected, directly or indirectly, to the seating surface, and the three swivel axes of which intersect each other at one point, the central point, often only in a central region. This central point is located above the seating surface, preferably in the pelvic region of the presumed user, particularly preferably approximately at the height of the user's center of gravity in the plane of symmetry of the seating furniture. Since a spherical motion around this central point is possible, a motion around the (virtual) longitudinal axis is possible without being predetermined or preferred. The three-arm kinematics used, often and actually more accurately referred to as three-axis kinematics, is already known from WO 2012/123102 by the same inventor.

A completely differently structured seating furniture with a “real” longitudinal axis is known from EP 3 890 558 B1. A cantilever that extends diagonally upwards is rotatably mounted on a vertical support. A swivel arm is movably mounted on the cantilever, which can also be swiveled around an axis of rotation lying in a vertical plane, according to its longitudinal axis. The seating surface is then accordingly attached to this swivel arm. The rotation axis or longitudinal axis forms an angle of approximately 65° with a horizontal plane and lies practically entirely below the seating surface. A chair built according to this principle and commercially available from the patent proprietor has a rotation axis/longitudinal axis with an angle of approximately 75° relative to the horizontal plane. This axis lies mostly above the seating surface, the swivel point formed by the vertical axis of rotation lies far above the center of gravity of a user, who is thus always forced into a stable, upright, resting position.

In both cases, a turning motion is only possible in the manner mentioned, the usual “simply leaning back” is not possible.

Due to their spherical bearing, the seating furniture with a virtual longitudinal axis can also perform swiveling motions about a transverse axis and rotational motions about the vertical axis (and due to the nature of the spherical bearing, about any other assumed axis as well), but this is not relevant in the context of the present disclosure. It is also irrelevant for the purposes of the present disclosure whether a backrest and/or armrests are provided and how these are mounted/attached with respect to the seating surface.

What is needed is a piece of seating furniture that helps avoid the health disadvantages of long periods of sitting. Such a chair should be designed to encourage continuous motion and thus stimulate the metabolism and support the cardiovascular system of the user without making the user feel unsafe or unstable.

The present disclosure is directed to seating furniture that facilitates movement by the user, promoting the health of the spine, and supporting the back muscles. The seating furniture disclosed herein encourage a natural pelvic and lumbar motion, while keeping the head and shoulders in a stable position.

In one example, the seating furniture of the present disclosure defines a plane of symmetry, and includes a lower part, where the lower part includes a base or is formed with a base in an upper region of the lower part; a seating surface that is swivelably connected to the base via a kinematics, such that the seating surface is swivelable about a longitudinal axis by means of the kinematics; where when the piece of seating furniture is in a resting position the longitudinal axis lies in the plane of symmetry in an angular range of between 5° in a backward and downward direction and 75° in a forward and downward direction, relative to a horizontal plane; where the longitudinal axis, when considered in a region of a vertical projection P of the seating surface, or optionally when considered in a region of a vertical projection P of the seating surface combined with a rear seating surface part, lies above the seating surface along more than 50% of the length of the vertical projection P; and further including a restoring device with an energy accumulator disposed between the base and the seating surface, the restoring device configured to exert a restoring torque on the seating surface when the seating surface is deflected about the longitudinal axis from the rest position.

The features, functions, and advantages of the disclosed seating furniture may be achieved independently in various embodiments of the present disclosure, or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings.

The present disclosure relates to a piece of seating furniturewith a plane of symmetryand with: a lower partwhich has or is formed with a basein its upper region, and a seating surfacewhich is swivelably connected to the baseabout a longitudinal axisby means of a kinematics, where the longitudinal axislies in the plane of symmetryin the resting position of the piece of seating furniture and is inclined relative to the horizontal from 5° backwards, downwards to 75° forwards, downwards, preferably by 45°±30°, most preferably between 40° and 50° forwards, downwards. Additionally, the longitudinal axisis optionally formed virtually, and the longitudinal axisin the region of the vertical projection P of the seating surface, optionally in combination with a rear seating surface part, lies above the seating surface, optionally in combination with the rear seating surface part, along more than 75% of the length thus defined.

The seating furniture of the present disclosure include a seating surface and a vertical plane of symmetry, wherein the seating surface can be swiveled by means of kinematics with respect to a base of the piece of seating furniture about a longitudinal axis which, in the rest position, is in an angular range which lies between 5° backwards, downwards and 75° forwards, downwards, preferably by 45°±30° forwards, downwards, very particularly preferably by 45°±20° forwards, downwards in the plane of symmetry and at least predominantly above the seating surface. The longitudinal axis can also be formed virtually, for example by a spherical bearing of the seating surface around a swivel point above the seating surface, which allows rotation around “all” axes. For the sake of simplicity, in the following usually only the “longitudinal axis” is mentioned. In most cases this is inclined forwards at an angle of 45°±30° (or ±20°) to the horizontal, but a greater inclination of up to 75° (technically precise, not mathematically) is also possible. The kinematics that bring about this are explained in detail in the inventor/applicant's publications discussed below and therefore require no further explanation here.

In one example, the seating furniture of the present disclosure is characterized in that a restoring devicewith an energy accumulatoris provided between the baseand the seating surface, which exerts a restoring torque about the longitudinal axison the seating surface when the seating surfaceis deflected about the longitudinal axisfrom the rest position.

In another example, if the longitudinal axis of the disclosed seating furniture is inclined by up to 30° relative to the horizontal, the longitudinal axislies entirely above the seating surfacein the region of the vertical projection (P).

In another example, if a backrestis provided for the seating furniture of the present disclosure, the longitudinal axis, regardless of its inclination, lies at least in the region extending up to 120 mm in front of the backrestabove the seating surface.

In another example, an inclination of the longitudinal axisof the disclosed seating furniture that is backwards, or downwards, is possible, but is reasonable only in special cases (medical applications, etc.) and within narrower limits (up to 5°) than when the inclination is forwards, downwards.

With regard to the term “plane of symmetry”, it should be noted that this only applies with a grain of salt, because the individual components and handles of seating furniture, for example office chairs, are certainly one-sided, but there is nevertheless a plane of symmetry for the seating surface and, if present, the backrest and armrests, which runs vertically when the seating furniture is at rest and is swiveled along with the seating surface. It is this plane that will be referred to as the plane of symmetry.

With regard to the term ‘seating surface’, it should be noted that this can be divided, with the two parts being able to swivel relative to each other about a horizontal axis normal to the plane of symmetry and with the rear part being firmly or elastically connected to a backrest. In this case, the kinematics can be connected either to the backrest and thus to the rear part of the seating surface, or to the front part of the seating surface. The seating surface, divided or undivided, can also be upholstered; the position of the longitudinal axis “above” the seating surface is not affected by this; in extreme cases it lies above the cover of the seating surface. If, in the case of an extreme inclination, the front part of the longitudinal axis comes to lie below the seating surface, then, in the rest position, the greater portion of the part of the longitudinal axis which lies within the irregular cylinder formed by the outline of the seating surface in the direction of the vertical lies above the seating surface.

In relation to the use of such seating furniture, hereinafter usually referred to as “chair” or “office chair”, the following must be mentioned:

Almost every day we are confronted with headlines warning about the health risks of sitting. Articles such as “Sitting makes you sick” from Norddeutscher Rundfunk (2022), “Sitting is the new smoking” by Juliet Starrett (2016), “Lack of exercise makes millions sick” from Tagesschau (2022) or “Those who sit longer die sooner!” “Get out of the seating surface trap” by MDR (2022) can be found in both digital media and the traditional press. The World Health Organization (WHO) also emphasizes the importance of regular exercise and recommends standing, walking or exercising more often (2020).

For decades, doctors and experts have warned about the consequences of a lack of exercise and prolonged sitting, including back pain (Lis, Black, Korn, & Nordin, 2007), shortness of breath and digestive disorders (BAuA, 2011), as well as an increased risk of type 2 diabetes and heart attacks (Latza, Bucksch & Wallmann-Sperlich, 2020). These can lead to impaired well-being (Atkin et al., 2012), promote mental illness (Kilpatrick et al., 2013) and promote depression (van Uffelen et al., 2013).

Despite repeated warnings, the number of illnesses caused by excessive sitting continues to rise, according to health insurance reports (e.g. DKV Report, 2021). In Germany, people sit for an average of around 8.5 hours on working days, which is one hour more than in 2018, while young adults (18 to 29 years) reach the peak at 10.5 hours. This contributes to an increase in musculoskeletal disorders, which, together with mental illnesses, contribute significantly to work absences (Techniker Krankenkasse, 2022).

The design of our workplaces contributes to this problem. Around 59% of employees in Germany spend at least half of their working time at an office workplace, mostly sitting (Industrieverband Büro und Arbeitswelt, 2020). Work is also often done sitting down at workbenches and in production. The short break to go to the coffee machine offers little compensation for the physical strain, and there is often a lack of active balance in leisure time too.

Previous approaches to the problem have proven to be ineffective and have not been able to significantly reduce the symptoms mentioned. We therefore take the approach that necessary motions must take place during working hours and therefore while sitting. The office chair must allow for ample motions in order to relieve and load the intervertebral discs, which promotes the supply of nutrients and the maintenance of the health of the spine. In addition, the back should be supported by a suitable backrest in order to avoid permanent static strain on the back muscles.

Many chairs available on the market allow a tilting motion of the pelvis, but do not meet the requirements for a healthy sitting posture. Critical points include the fact that the swivel point is below the seating surface and motions do not follow the human anatomy. This can make it difficult to concentrate on work, as the head and upper body move, requiring the eyes to constantly refocus. In addition, working on texts or tables can be impaired by motions.

An ideal ergonomic chair should mimic the natural pelvic and lumbar motion that occurs when walking, while keeping the head and shoulders in a stable position. In healthy adults, this rolling swiveling motion when walking occurs around an axis directed forwards and downwards at approximately 45°, which passes through the region of the ninth to twelfth, preferably the eleventh thoracic vertebrae. The angular range depends on various circumstances, such as age, general and current physical condition, speed of motion and many more, so that ranges of 45°±30°, at least ±20° and especially ±10° or 5° are favorable.

These ranges are advantageously to be used in seating depending on the habits and constitution of the user. A positioning of the user's center of gravity above the central point is here very advantageous, and a position of the larger part of the longitudinal axis in the seating surface cylinder above the seating surface is necessary.

When sitting, the feet should be firmly on the floor to ensure a stable posture. Traditional chair concepts that use swivel points below the seating surface do not adequately imitate human motion dynamics.

Scientific studies, including the work of R. Kuster (Physiological motion axis for the seat of a dynamic office chair—PMC (nih.gov)) and the as yet unpublished dissertation by Mark Buhrer, have found that the ideal swivel point is at the level of the upper abdomen, near the eleventh thoracic vertebra (thus in the region of the ninth to twelfth, preferably at the level of the eleventh thoracic vertebra). These findings emphasize the importance of seating furniture that promotes the natural motions of the human body when sitting and are illustrated in, showing the motion of the pelvis in and across the sitting direction around an instantaneous center at the level of the upper abdomen.

show in detail in the four individual representations the specific kinematics of the pelvic motion of a useron the seating furniture, a chair with a divided seating surface, the rear part of which is a fixed or elastic part of the backrest, based on the representation of the user's bones. With regard to such a piece of furniture, it should be noted that a lower part of the furniture (chassis, gas spring, etc.) (not shown here) is connected to the backrest via a kinematics, and the actual (front) seating surface is connected to the rear seating surface part, which is firmly or elastically connected to the backrest, so that it can swivel about a transverse axis. A further kinematics is responsible for the relative position (angular position) between these two parts, as described in detail in the applicant's WO 2022/174945.

The arrow(approximately horizontal and lying in the plane of symmetryof the seating furniture, which of course does not take into account details such as the mechanics of the kinematics, etc.) points to the part of the spine in which the bending can be viewed in concentrated form. The arrowthus also symbolically represents, with a grain of salt, the respective motion component around the axis indicated by it.shows upright sitting with “force-less” contact with the backrest, the knee also representing this.visualizes the forward leaning of the upper body and the changed leg position; in the illustrated construction of the piece of seating furniture, the position of the backrestand the relative position of the two parts of the seating surfacechange. The change in the curvature of the spine is recognizable.

The lowerillustrate the lateral tilt of the pelvis to the left and right respectively. It is a precisely isolated motion of the pelvis, again localized by an arrow, arrow, but this time running approximately horizontally in a transverse direction and again pointing to the symbolic “bending point” of the spine. The inclination of the pelvis follows the defined axis of rotation of the chair and thus remains stationary with respect to the seating surface; the pelvis thus moves synchronously with the seating surfaceand the backrest, while the shoulders and head of the seated person remain relatively stable in space.

This (double) motion dynamic of the pelvis on the chair, characterized by specific angles around the rotation axis(es) in the three spatial dimensions, imitates the natural walking motion of humans. This correlation is demonstrated in the study “Patterns of spinal motion during walking” by Jack Crosbie, Roongtiwa Vachalathitib and Richard Smith, published in December 1994. The study identifies consistent motion patterns: “We found consistent patterns within and between segments and motions, with an obvious follow-up motion of the trunk following pelvic displacements. This suggests that the spinal motions associated with walking are linked to the primary motions of the pelvis and lower limbs.” This observation by the authors was supported by the later measurement studies by R. Kuster.

show, only as a counterexample and for explanation, in the upper illustrations, the situation when the user“immovably” follows the motion of the seating surfaceand the backrestduring the sideways swiveling. For this reason, instead of an arrow, only a line was drawn to the now non curved spine region.

shows the userleaning more strongly against the backrest than in, which can also be seen from the relative position of the two parts of the seating surfacein comparison. Finally,shows the fully reclined position for completeness.

Based on these findings, a special kinematics was developed that allows the construction of a chair the swivel point of which—following scientific recommendations—is located in the region of the upper abdomen, above the seating surface. This allows motion around all three swivel axes around this central point without the need for back or armrests, as described in WO2016/042127 mentioned above. In addition, a lifting of the front edge of the seating surface can be avoided in an embodiment of this kinematics, as can be seen from WO2022/174945 of the applicant. This also shows, in particular in, the different possible orientations of the longitudinal axis, which has the reference numeralthere.

After development, prototypes of these chairs were manufactured and further optimized over a period of two years. These prototypes were made available to people with musculoskeletal problems. The feedback from these test subjects was predominantly positive. A noticeable reduction in pain was noted in some patients after only a short period of use. After a few months, many test subjects reported a significant improvement or even a complete disappearance of their symptoms. The symptoms examined included lumbago, hip pain, sacroiliac joint problems and aftercare for disc surgery. Although the medical benefits still need to be proven by more extensive studies, feedback to date suggests that chairs of this design may offer significant potential for alleviating health problems such as those caused by a lack of exercise while sitting.

Unfortunately, many test subjects find it difficult to feel safe on a chair with such kinematics. It may take several weeks for this uncertain feeling to diminish or disappear. Some subjects rejected this motion completely. This is especially true if the physical limitation was not yet so pronounced and the suffering was not yet great enough to accept this habituation phase. On the other hand, these were patients who had only recently undergone surgery, especially on the intervertebral disc. They were understandably afraid that their situation could worsen and were consistently unwilling to accept this unusual motion.

Since the test subjects reported that they got used to this motion after some time, but also reported that some of them actually felt sick in the chair during the first few hours, it was initially assumed that this was only a problem with the balance organ, which has to combine the motion of the hips with a stable head. Since the motion of the hips corresponds to a walking motion and people are used to the head moving forward when walking, this was considered the most likely solution for a long time.

In fact, there was a second approach. This was based on the observation that this insecurity was significantly reduced or even disappeared completely as soon as the arms were resting on the desk in order to operate the keyboard of a PC, for example. So it was concluded that this all has something to do with the current motion of a person. If the person moves on the chair as if they were walking, i.e. if they swing or circle their hips around the swivel point of the chair, the insecurity disappears. However, if the same test subject sits freely on the chair in the room, i.e. moves his arms freely, uncertainty arises again. Therefore, the motion in the two situations was examined more closely.

As mentioned, when sitting at a desk and using a PC, the arms rest on the desk and the pelvis moves—so all moving mass points below the chair's swivel point are in stable equilibrium. The person feels safe. However, as soon as a person sits freely, he or she moves the entire upper body rather than the chair. Since not only the pelvis and part of the spine move with the seating surface, but also the body with the shoulders, head and arms remains rather rigid on the chair, the center of gravity of the moving mass moves upwards. The center of gravity then lies above the swivel point (the longitudinal axis, the central point) of the chair—an unstable equilibrium is created, which makes people feel insecure. This is illustrated in, which show the motion of the entire upper body during free sitting analogous to.

In response, the swivel point of the chair was first adjusted (moved upwards) so that the user's center of gravity always remains in a stable equilibrium (below the longitudinal axis or central point) even during rigid upper body motions (this leads to a situation similar to the office chair sold by Bergardi mentioned above). Although this adjustment reduced the uncertainty among the test subjects, it led to a new problem: wobbling in the shoulder and head region occurred, similar—although less pronounced—to that experienced with a swivel point located under the chair surface (longitudinal axis). The reason for this was that the swivel point of the chair did not coincide with the physiological swivel point of the pelvis, although it was shifted in the opposite direction, namely downwards. Therefore, this adaptation was not a satisfactory solution because, although it solved one problem, it created a new one.

To overcome this dilemma, the possibility of applying a counter-torque was considered. This would make it possible to keep the swivel point (the longitudinal axis) of the chair close to the physiological swivel point of the pelvis, while at the same time generating a torque counteracting the unstable equilibrium, which would bring the system—the chair or its seating surface—into a stable equilibrium. A critical point with this solution, however, was that the counter-torque also acts on pure pelvic motions, thus counteracting the motion of the test person. However, a key feature of the chair is its ability to respond to pelvic motions with great ease, so this effect has been viewed critically.

Tests showed that test subjects performed up to 60 pelvic motions per minute, which underscores the mobility of the chair. This effect should by no means be lost, because the continuous motion stimulates the metabolism and the cardiovascular system, which, in addition to positive effects on the musculoskeletal system, also improves the user's concentration and productivity and can be expected to have other health benefits. Despite this challenge, the decision was made to implement a simple spring mechanism in order to investigate the effects in more detail. Such a chair according to the present disclosure with a simple spring accumulator for building up a counter torque is shown in.

show (without taking the seating surface height into account) a piece of seating furniturewith a lower part, supporting or forming a base, and a kinematics provided between the baseand an (undivided) seating surface, designated overall by, and a backrestwhich is elastically connected to the seating surface. The kinematicsprovide a central pointaround which the seating surface is spherically movable, wherein a longitudinal axisis also formed in the sense explained above.

This kinematicscorresponds to the kinematics explained in detail in WO2016/042127 of the applicant and in WO 2012/123102 of the inventor and therefore does not require any further description here (a brief explanation is given in).

Advantageously, a restoring device, the effect of which is adjustable, is provided between the baseand the seating surface, which is shown inin the installed state, without the sleeve for the springs in order to show them, whileshows an exploded sketch to explain the structure. This restoring deviceis constructed as follows: a flat intermediate bladeis articulated so as to be rotatable about a first axiswhich is approximately horizontal in the exemplary embodiment and stationary with respect to the base, on which blade a flat actuatorwith a main plane is arranged so as to be rotatable about a second axisparallel to the first axis. A spring mechanismis arranged on the actuatorso as to be rotatable about an actuator axiswhich, in the illustrated exemplary embodiment, runs normal to the main plane of the actuator. Furthermore, a rotating armis articulated on the actuatorabout a rotating arm axisparallel to the actuator axis.

At the free end of the rotating arm, a connecting pieceis spherically articulated, which is firmly connected to the seating surface. Instead of this spherical connection, it is possible to arrange a universal joint, which then also blocks the “internal rotation” around the vertical axis, which is explained below, without the need for an additional mechanism. This block is necessary to avoid singularities in the kinematics. Also in the region of the free end of the rotary arm, a coupling rod of the spring mechanismis articulated, which carries an adjusting plateat its other end.