Abstract:
According to the present invention there is provided a module for use with a chair having a seat portion supported by a support portion, for triggering movement of a person sitting thereon. The module is adapted for attachment to the chair between the seat portion and the support portion, and comprises a driving motor, a base platform adapted for fixed attachment to the seat portion, and an angled axis system (AAS). The AAS has a main rotary element having a main axis, and an auxiliary rotary element having an auxiliary axis and coupled with the first rotary element so that the auxiliary axis is oriented at an angle to the main axis. The module is designed such that when the main rotary element rotates about its main axis, the auxiliary rotary element also rotates about the main axis. The base platform is coupled to the auxiliary rotary element so that the rotation of the auxiliary axis moves the base platform entailing the seat portion to perform an oscillating combined rotary-tilting motion, the amplitude of the movement being defined by the angle. The motor is adapted to rotate either of the main rotary element or auxiliary rotary element to provide desired oscillation frequency so that the person seated on the seat portion is triggered to operate his joints and muscles to compensate for the movement in order to remain focused on a target. The frequency and the amplitude being such that the compensation of the movement by the person allows the person to remain focused on the target.

Description:
This is a National Phase Application filed under 35 U.S.C. 371 as a national stage of PCT/IL2007/000491 filed on Apr. 18, 2007, an application claiming the benefit under 35 USC 119(e) U.S. Provisional Application No. 60/792,652 filed on Apr. 18, 2006, the content of each of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to moveable seat, in particular seats in which the seat portion thereof may be adapted for motorized movement. 
     BACKGROUND OF THE INVENTION 
     In modern life, mostly in office jobs, laboratory work etc. the majority of work is done sitting on a chair. Sitting for long periods of time is blamed for having several harmful effects on the human body, one major effect being various forms of back pain. 
     Walking has been suggested as a way of avoiding some of the above effects, being known for its ability to relieve back pain in many cases. However, since walking is not always possible during the work day, most people do not walk enough during a day to gain its benefit. 
     Some other activities are also known for their ability to relieve back pain such as: riding a horse especially at a walk gait, some dancing movements, swimming etc. Individuals may benefit from one activity better than from another. All of these activities induce motion to the pelvis and the vertebras and this is the trigger for their cure mechanism. 
     Several devices have been disclosed in order to either treat the symptoms of prolonged sitting or in order to prevent their occurrence in the first place: 
     U.S. Pat. No. 5,113,851 to Gamba discloses a chair with a ‘singing seat’ which is adapted to continuously swing and change the position of a person sitting thereon. 
     U.S. Pat. No. 6,033,021 to Udo discloses a chair with an automatic seat adapted for cyclical inclination. 
     U.S. Pat. No. 5,735,575 to Harza discloses an apparatus for periodically lifting one hip of a seated person and then the other. 
     WO 2005/072564A1 discloses a sitting support and a sitting surface determined thereon. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a module for use with a chair having a seat portion supported by a support portion, for triggering movement of a person sitting thereon, said module being adapted to be attached to said chair between said seat portion and said support portion, and comprising a driving motor, a base platform adapted for fixed attachment to said seat portion, and an angled axis system (AAS) having a main rotary element having a main axis, and an auxiliary rotary element having an auxiliary axis and coupled with said first rotary element so that the auxiliary axis is oriented at an angle to said main axis and so that, when the main rotary element rotates about its main axis, the auxiliary rotary element also rotates about said main axis, said base platform being coupled to the auxiliary rotary element so that the rotation of the auxiliary axis moves the base platform entailing the seat portion to perform an oscillating combined rotary-tilting motion having an amplitude defined by said angle; said motor is adapted to rotate either of said main rotary element and said auxiliary rotary element to provide desired oscillation frequency so that the person seated on said seat portion is triggered to operate his joints and muscles to compensate for said movement in order to remain focused on a target, said frequency and said amplitude being such that the compensation of said movement by said person allows the person to remain focused on the target. 
     In order to allow the above compensation and at the same time to allow the person to maintain his steady visual orientation, e.g. reading, working in front of a computer monitor, performing office work, laboratory work etc. the oscillation frequency of said movement may range between about 0.25 Hz÷2 Hz, and more particularly between 0.5÷1.5 Hz., and its amplitude may range between about ±0.25÷6°, in particular, between ±0.4÷3° and even more particular between ±0.5÷1.5°. 
     Said auxiliary axis may intersect said main axis at an intersection point which determines a point in the module-seat-person system which is not displaced during the operation of the module 
     By changing at least one of the frequency, amplitude and location of the intersection point, the module may simulate walking on an irregular surface, rough terrain etc. having various influences on the back than monotonic motion like walking on a straight track. 
     Said chair may be a swivel chair, to which the module is adapted to be attached, and it may comprise, like most swivel chairs, a pneumatic piston normally constituting the leg of said swivel chair. Such swivel chairs also often comprise a chair mechanism adapted for controlling height of the seat portion thereof (by controlling the pneumatic piston), inclination of the seat portion, etc. Such mechanisms are usually assembled so that their bottom end rests on said pneumatic piston and their top end supports the seat portion of said swivel chair. A majority of swivel chairs of the above type also comprise a backrest usually attached to said chair mechanism. 
     For the purpose of the specification and claims that the term ‘chair’ should be understood in its broadest form to refer to a variety of seating assemblies, and may include vehicle seats, airplane seats, train seats etc. 
     The module may be attached to said swivel chair in either of two positions: between said chair mechanism and said seat portion, or between the top end of said gas piston and said chair mechanism. In the latter case, the module is adapted to be fitted with a handle for controlling the movement of the pneumatic piston. Alternatively, the module may be integrally formed with the chair mechanism, in which case, it is adapted to fully replace an existing chair mechanism. When assembled with the chair, the operation of said module may be adapted for imposing movement on the seat portion alone without affecting the backrest. 
     According to one embodiment of the present invention, the main axis of said AAS may be disposed substantially transverse manner, parallel to the base of a chair to when the module is attached thereto. 
     The base platform may comprise a fixed unit and a movable unit, said fixed unit being adapted for fixed attachment to the support portion of said chair while said movable unit is adapted for fixed attachment to the seat portion of the chair. The base platform is designed such that the movable unit is free to move with respect to the fixed unit, allowing the seat portion to perform said movement. 
     Both said fixed and said moveable unit may be in the form of a plate. The fixed plate may be in the form of a substantially flat plate, i.e. with a planar surface, and two shoulders extending perpendicular to said surface. Each of the shoulders may be formed with a lead hole and a bearing therein, so that when the fixed plate is mounted onto said support portion, said planar surface is essentially parallel to the plane defined by a base on which said chair is positioned, and the centers of the lead holes define a main axis, parallel to said planar surface, and transverse thereto. The fixed plate may also be formed with a place for the motor to be attached thereto. 
     The movable plate may also be formed as an essentially flat plate, having two extensions extending perpendicular to the plate, which may be located at one end of the plate, e.g. at its end which is associated with the front area of the seat portion. 
     Each extension may be formed with a lead hole, each of said lead holes also being equipped with bearings, similar to said fixed plate. 
     According to the currently described embodiment, said main rotary element may be in the form of a main rod having a longitudinal axis constituting said main axis, and said second rotary element may be in the form of two protrusions extending from each side of said main rod. The protrusions may extend along an axis constituting said auxiliary axis. In this case, the intersection point between the main and auxiliary axes may be located along the fro-aft line of the chair, whereby said movement will be symmetrical with respect to the left and right sides of the person&#39;s body. 
     The main rod may also be formed with a drive receiving member adapted for a connection of the driving motor thereto, in order to allow the motor to rotate the main rod about its major axis. The drive receiving member may be in the form of a strap receiver adapted for a strap connecting said motor to said main rod to be placed thereon. Alternatively, said receiving member may be in the form of a gear, etc. Alternatively, said main axis may serve as an axle of the driving motor. 
     According to a design variation of said embodiment, the motor may be coupled with the protrusions forming said auxiliary rotary element, i.e. the torque is given to the auxiliary axis. In this case, the motor body will be engaged to the movable plate. 
     In assembly, for example when the module is attached to a swivel chair having a chair mechanism, the fixed plate may be fixedly attached to, for example, the top end of said chair mechanism. The main rod may then be positioned so that each end thereof is inserted into the lead hole of said fixed plate, whereby an axis passing through said lead holes and the main axis of the main rod may be co-aligned. In this position, the protrusions of said main rod protrude from the shoulders of said fixed plate on each side thereof, so that, for example, the protrusion on one end of the main rod may face downward and backward while the protrusion on the other end of the main rod may face upward and forward. 
     The movable plate may then be positioned over the fixed plate such that each protrusion of said main rod is positioned within the lead hole of said movable plate, whereby the auxiliary axis of said protrusions may be co-aligned with an axis defined between the centers of said lead holes. In this position, the movable plate may not be parallel to the fixed plate and may be angled thereto in the horizontal plane and/or in the vertical plane. 
     It should be noted that both said fixed and said movable plate may be formed with their lead holes positioned in various locations along the shoulders or extensions thereof. Thus, for example, the lead holes of said fixed plate may be so disposed as to allow positioning of the main rod essentially angled (not perpendicular) to the fro-aft line of the swivel chair. This, for example, may allow the module to be to be aligned with the seat portion when the module is not operating. 
     Various options of dynamic positioning of the main rod in the up-down and fro-aft directions may facilitate various movements of the movable plate, consequently causing the muscle operation of a user to simulate various motions, e.g. walking on rough terrain, etc. 
     The module may further comprise a spacer positioned between the fixed plate and the movable plate adapted to still allow relative movement of said movable plate with respect to said fixed plate, while maintaining a fixed vertical distance therebetween at the location where the spacer is positioned. The spacer may be in the form of a connecting rod with a ball joint at each end, each joint connected to one of said fixed and said movable plates, or in the form of a ball confined between the two plates. Alternatively, the spacer may be made of flexible material, e.g. rubber. 
     In operation, the motor causes a rotation of said main rod, as a result of which, the entire auxiliary axis defined by the two protrusions is urged to rotate about the main axis defined by the main rod. Consequently, the protrusions of the main rod may also perform a continuous circular motion, inducing said movement of the movable plate. 
     Due to the above continuous motion, and the angle between said main and auxiliary axes, said rotary-tilting movement imposed on the plate will be the combination of the following motions:
         a rotary, left &amp; right motion about a vertical axis parallel to a height axis of the chair, caused by the protrusions periodically switching places—one being in front of the other and visa versa;   a tilting up &amp; down motion about the intersection point of said main and said auxiliary axes, caused by the protrusions periodically switching places—one being above the other and visa versa.       

     The movement of the movable plate is therefore such that it causes each of the right and left ends thereof to perform a periodical and opposite rotary and tilting circular motions, i.e. when the left end of the plate is displaced forward, the right end of the plate is displaced backward, and when the left end is displaced upwards, the right end is displaced downwards. 
     According to one embodiment of the present invention, the main axis of said AAS may be disposed substantially vertical manner, perpendicular to the base of a chair to when the module is attached thereto. 
     The AAS may be formed of a circular disc having top and bottom surfaces angled to one another and being formed with a top and bottom cylindrical portions protruding from said top and bottom surfaces respectively. Said circular disc and its bottom cylindrical portion constitute said main rotary element and their common rotary axis constitutes said main axis. Said top cylindrical portion constitutes said auxiliary rotary element and its rotary axis constitutes said auxiliary axis angled to the main axis and, optionally intersecting therewith at said intersection point. Said bottom surface of the circular disc may be substantially perpendicular to said main axis, and said top surface may be perpendicular to said auxiliary axis. 
     It should be noted that, although in the present example, the circular disc and bottom cylindrical portion constitute the main rotary element and define the main axis, and the top cylindrical portion constitutes the auxiliary rotary element and defines the auxiliary axis, this is not compulsory. According to a different design, the arrangement is visa versa, i.e. the circular disc and top cylindrical portion constitute the main rotary element and define the main axis, while the bottom cylindrical portion constitutes the auxiliary rotary element and defines the auxiliary axis. 
     The location of the intersection point between the auxiliary axis and the main axis may vary, in accordance with which various possible movements of the seat portion of the chair may be obtained. 
     For example, the intersection point may be located in the plane of the circular disc. Alternatively, the intersection point may be a virtual point located outside the AAS in which case the cylindrical portions will be offset from one another. For example, when the intersection point is located at the center of the seat portion, the seat portion will then have a fixed point, i.e. a point which doesn&#39;t move during operation of the module. This may cause every point on the seat portion to be displaced only up and down but remain substantially in place. However, if the intersection point is located, for example, above the seat portion, during operation of the module the seat portion will perform, in addition, a circular motion about the main axis. In this position, the location of the intersection point may be determined to be at the height of any desired vertebra of the person sitting on the seat, causing opposite direction forces to body parts above and below this point. 
     If the intersection point is located below the seat or even below the bottom cylindrical portion, the oscillations will push the whole body sideways, thus the intransient tilt is aimed at triggering an active reaction in order to balance the body. Therefore the ability to change the intersection point height creates a range of movement that can be adapted to any individual preferences. 
     Each of said top and bottom portions may be partially retained by a top and bottom bearings respectively, i.e. articulated to the inner ring of the bearings, allowing free rotation of said portions therein. 
     The bearings used may be deep groove bearings adapted to support axial loads resulting by the weight of a person seated on the seat, while still allowing free rotation of the cylindrical portions therein. The use of deep groove bearings may remove the need for further securing means for supporting the weight of said person. 
     The fixed unit of said base platform may be adapted to connect to the outer ring of said bottom bearing, and may be, for example, formed with a round shaped cavity for this purpose. The moveable plate of said base platform may be adapted to connect to the outer ring of said top bearing, and may have a similar round shaped cavity for this purpose. 
     The moveable unit may be formed with a conical protrusion at its top portion, adapted to be inserted into a chair mechanism, should the chair have one. The fixed unit may be formed with a conical hole adapted for attachment to the support portion of the seat or to the pneumatic piston in case of a swivel chair. 
     The module may further comprise a retention member adapted to prevent said moveable plate and said fixed plate from rotating with respect to each other during operation of the module, while still allowing said movement. 
     The retention member may be in the form of a strap made of flexible material, e.g. metal, plastic etc., which connects said fixed and said moveable units. The structure of the strap may allow the strap a high resistance to rotation between the units while enabling movement in other directions. Alternatively, the retention member may be in the form of an external hinge formed of two prolonged hinge members articulated to one another at one end, and to said fixed and moveable units at another end respectively. 
     According to yet another design, the retention member may be a coil passing through a cavity formed within the AAS, and may be attached to the fixed unit at one end, and to the moveable unit at another end. The resistance of the coil to a torque applied thereto may be adapted to prevent the two units from rotating with respect to one another. 
     The motor may comprise a driving wheel adapted to partially extend between said fixed and said moveable units and mesh with the side surface of said circular disc, such that rotation of the driving wheel causes the circular disc to rotate about its main axis. It should also be noted that a variety of motor couplings may be used, e.g. spur gear, worm gear, chain, belt etc. 
     In assembly, the fixed unit may be connected to the pneumatic piston of the swivel chair, and the moveable unit may be connected to the seat portion thereof. 
     In operation, when the motor rotates the circular disc, subsequent rotation of the top and bottom cylindrical portions takes place. Since the axis of the bottom cylindrical portion is collinear with that of the circular disc, the bottom cylindrical portion performs a simple rotary motion in place. 
     Due to the above rotary motion and the angle between the axes of said top cylindrical portion and said bottom cylindrical portion, said rotary-tilting movement imposed on the moveable unit will be the combination of the following motions:
         a rotary motion about a substantially vertical axis caused by the rotation of the moveable unit about the intersection point of the main and auxiliary axes; and   a tilting up &amp; down motion about the top cylindrical portion caused by the rotation of said top cylindrical portion with the bearing.       

     According to a design variation on the above described embodiment, the top and bottom cylindrical portions may be essentially hollow, said top and bottom cylindrical portions adapted for connection to a top and bottom bearing respectively, i.e. the inner surface of the hollow is connected to the outer ring of the bearings. In this case, the fixed unit may be adapted to be connected to the inner ring of said bottom bearing while the moveable unit is adapted to be connected to the inner ring of said top bearing. 
     In assembly, the support portion of the chair, e.g. a pneumatic piston of a swivel chair, may be connected to the fixed unit so that the main axis of the bottom cylindrical portion is essentially perpendicular to the plane defined by a base of the chair. 
     In the above described design variation, the retention member may be in the form of a universal joint connecting said fixed unit and said moveable unit. 
     It should be understood that a variety of retention members may be used for all previously described embodiments of the present invention. 
     With regards to all the above embodiments of the module of the present invention, when a person is seated on a chair on which said module is mounted, said movement of the seat portion induces a motion of said person&#39;s pelvis, which is usually undesired during working. As the person keeps his eyes on the target, such as a television screen or a computer monitor, the head remains almost stable while the pelvis is moved by the seat portion, and the person will naturally tend to perform counter movements among the vertebras, to compensation the seat motion. This coerces the small muscles surrounding and connecting between successive vertebras to act. This muscle activity is virtually similar to that exerted by said person during walking, and may help maintain good blood circulation at the vertebra vicinity. 
     It should be noted that the movement of the seat portion with the frequency and amplitude as described above, is sufficiently mild, so that the operation of the muscles in order to compensate for said movement does not interfere with the person&#39;s working mentioned above. This, in turn, means that the person may easily perform his/her required office work while spontaneously operating his muscles, almost on an unconscious level. 
     With regards to all previous embodiments of the present invention, the module may further comprise a controller for controlling the operation thereof, whereby the module may be set to work automatically in predetermined time intervals, e.g. work for five minutes, then stop for 25 minutes, then work again. This operation mode of the module may allow efficient power consumption as well as prevention of strain on the vertebra for too long periods of time. The module may also comprise an over-ride button allowing a user to fully control the module, e.g. staring its operation when the module is at rest, exercising for longer or shorter periods of time than those of said predetermined time intervals, etc. 
     The module according to the present invention may further comprise a sensor adapted for detecting whether a person is seated on the seat portion, and may prevent operation of the module in the negative. 
     The motor of the module may be operated either by connection to electricity or by providing a battery driving the motor. In the latter case, power consumption of the module proves to be very efficient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
         FIG. 1A  is an exploded isometric view of a module according to one embodiment of the present invention; 
         FIG. 1B  is a side view of a main rod used in the module of  FIG. 1A ; 
         FIG. 1C  is an isometric bottom view of the module of  FIG. 1A  when attached to a swivel chair; 
         FIG. 1D  is a cross section view of the attached module of  FIG. 1C ; 
         FIG. 1E  is a side view of a different design of the module embodiment shown in  FIG. 1A ; 
         FIG. 1F  is rear view of the module of  FIG. 1E ; 
         FIG. 2A to 2D  are schematic cross section views of various designs of the module according to a different embodiment of the present invention; 
         FIGS. 2E to 2G  are schematic cross section illustrations of various positions of the intersection point of an AAS used in the module of  FIG. 2A to 2D ; and 
         FIG. 3  is a cross-sectional view of another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1A  shows an exploded isometric view of a module  10  comprising a driving motor  20 , an angled axis system (AAS)  30 , and a base platform  40 . The module  10  is adapted to be attached to a chair  60  partially shown) comprising a seat portion  62  and a support portion ( FIG. 1C ,  1 D). 
     In general, the chair described with respect to the drawings is a swivel chair  60 , and comprises, like most swivel chairs, a seat  62  constituting the seat portion of the chair, a pneumatic piston  64  constituting the support portion of the chair  60 , and a chair mechanism  66  adapted for controlling height of the seat  62  thereof (by controlling the pneumatic piston), inclination of the seat  62 , etc. Such chair mechanisms  66  are usually assembled so that their bottom end is articulated to the pneumatic piston  64  and their top end supports the seat  62  of the chair  60 . A majority of swivel chairs  60  of the above type also comprise a backrest  68  usually attached to the chair mechanism  66 . 
     The module  10  may be attached to said swivel chair  60  in either of two positions: between the chair mechanism  66  and the seat  62 , or between the top end of the pneumatic piston  64  and the chair mechanism  66 . In the latter case, the module  10  is adapted to be fitted with a handle for controlling the movement of the pneumatic piston  64 . Alternatively, the module  10  may be integrally formed with the chair mechanism  66 , in which case, it is adapted to fully replace an existing chair mechanism  66  of a swivel chair  60 . 
     Turning to  FIG. 1B , the AAS  30  comprises a main rotary element constituted by a main rod  32  having a major longitudinal axis Mx constituting the main axis of the AAS  30 , and an auxiliary rotary element constituted by two protrusions  34  extending from each side of said main rod  32 . The protrusions extend along a minor axis Ax constituting the auxiliary axis of the AAS  30 . The intersection point  38  between the main and auxiliary axes Mx and Ax respectively is located in the middle of the main rod  32 , and as will be evident later, is located under the fro-aft line of the chair. The intersection point  38  is a point in the module-seat-person system which is not displaced during the operation of the module. 
     The main rod  32  is further formed with a drive receiving member  36  adapted for a connection of the driving motor  20  thereto, in order to allow the motor  20  to rotate the main rod  32  about its major axis Mx. The drive receiving member  36  is in the form of a strap receiver adapted for receiving a strap  22  connecting the motor  20  to the main rod  32  to be placed thereon. 
     Reverting to  FIG. 1A , the base platform  40  comprises a fixed unit  42  and a moveable unit  52 . The fixed unit  42  is adapted for fixed attachment to the support portion of the chair  60  and the moveable unit  52  is adapted for fixed attachment to the seat portion  62  of the chair. In the present example, the chair  60  is a swivel chair comprising a chair mechanism  66 , and the fixed unit  42  is adapted to be attached to the top end of the chair mechanism  66 . 
     The fixed unit  42  is in the form of a substantially flat plate  44 , i.e. with a planar surface, and two shoulders  46  extending perpendicular to the plate  44 . Each of the shoulders  46  is formed with a lead hole  48  and a bearing  49  therein, so that when the fixed unit  42  is mounted onto the support portion of the chair it is essentially parallel to the plane defined by the base on which the chair is positioned. The lead holes  48  are formed such that the axis extending between the centers thereof is parallel to the plate  44 . 
     The moveable unit  52  is also be formed as an essentially flat plate  54  having two extensions  56  extending perpendicular to the plate  54 , which are located at one end of the plate  54 , e.g. at its end which is associated with the front area of the seat  62  of the chair  60  when the module  10  is assembled thereto. Each extension  56  is formed with a lead hole  58 , each of the lead holes  58  being equipped with bearings  59 . 
     The base platform  40  further comprises a spacer  45  positioned between the plate  44  and the plate  54  and adapted for maintaining a fixed distance ‘d’ between said plates, at the point where the spacer  45  is located. This allows preventing the moveable unit  52  from vertical movement with respect to the fixed unit  42  during operation of the module  10 , while still allowing a certain degree of freedom and relative movement of the plates with respect to one another. The spacer  45  is made of flexible material, e.g. rubber. The spacer  45  may also be in the form of a connecting rod with a ball joint at each end, a ball confined between the two plates, etc. 
     The module  10  further comprises a bottom cover  55  adapted to be attached to the plate  44 , largely covering the chair mechanism  66 . This is done mostly for esthetic reasons. 
     Turning to  FIG. 1C , in assembly, for example when the module  10  is attached to a swivel chair having a chair mechanism  66 , the plate  44  is fixedly attached to the top end of the chair mechanism  66 . The main rod  32  is then positioned so that each end thereof is inserted into the lead hole  48  of the plate  44 , whereby the axis passing through the lead holes  48  and the major axis Mx of the main rod  32  are co-aligned. In this position, the protrusions  34  of the main rod  32  protrude from the shoulders  46  of said plate  44  on each side thereof, so that, for example, the protrusion  34  on one end of the main rod  32  faces downward and backward while the protrusion  34  on the other end of the main rod  32  faces upward and forward. 
     The moveable unit  52  is then positioned over the fixed unit  42  such that each protrusion  34  of the main rod  32  is positioned within the lead hole  58  of the moveable unit  52 , whereby the auxiliary axis Ax of the protrusions  34  is co-aligned with the axis defined between the centers of said lead holes  58 . In this position, the moveable unit  52  may not be parallel to the fixed unit  42  and may, for example, be angled thereto in the horizontal plane and/or in the vertical plane. 
     It should be noted that both the fixed unit  42  and the moveable unit  52  may be formed with their lead holes  48 ,  58  positioned in various locations along the shoulders  46  or extensions  56  thereof. Thus, for example, the lead holes  48 ,  58  of the plate  44  may be so disposed as to allow positioning of the main rod  32  essentially angled (not perpendicular) to the fro-aft line of the swivel chair. Various options of positioning the main rod  32  may facilitate various movements of the moveable unit  52 , consequently causing the muscle operation of a user to simulate various motions, e.g. walking on rough terrain, etc. 
     The driving motor  20  is located below the chair mechanism  66  and is connected to the main rod  32  through a driving strap  22  positioned on the drive receiving member  36  thereof, so that the motor  20  is able to rotate the main rod  32  about its axis Mx. 
     In operation, the driving motor  20  causes a rotation of said main rod  32 , as a result of which, the entire auxiliary axis Ax defined by the two protrusions  34  is urged to rotate about the main axis Mx. As a result the protrusions  34  also perform a continuous circular motion, inducing movement of the moveable unit  52 , and consequently of the seat  62 . 
     Due to the above continuous motion, and the angle between said main axis Mx and the auxiliary axis Ax, a rotary-tilting movement is imposed on the plate  54  which is a combination of the following motions:
         a rotary, left &amp; right motion about a vertical axis parallel to the axis of the pneumatic piston  64  caused by the protrusions  34  periodically switching places—one being in front of the other and visa versa;   a tilting up &amp; down motion about the intersection point  38  of the main axis Mx and the auxiliary axis Ax, caused by the protrusions  34  periodically switching places—one being above the other and visa versa.       

     The movement of the plate  54  is therefore such that it causes each of the right and left ends of the plate&#39;s front to perform a periodical and opposite rotary and tilting circular motions, i.e. when the left end of the plate  54  is displaced forward, the right end of the plate  54  is displaced backward, and when the left end is displaced upwards, the right end is displaced backwards. Thus, the seat  62  attached to the plate  54  is free to move with respect to the plate  44 , allowing it to perform a movement along all three axes. 
     In operation, the motor may rotate the main or in either direction, e.g. forwards or backwards, however, when the rod rotates backwards, the pattern of motion caused by the user compensating for the movement of the module simulate very closely the pattern induced by walking, especially when choosing the parameters of f and A as suggested above. 
     In order to allow the above compensation and at the same time to allow the person to maintain steady visual orientation, e.g. reading, working in front of a computer monitor etc. the oscillation frequency f of is designed to be in the range of about 0.25 Hz÷2 Hz, and more particularly between 0.5÷1.5 Hz. The amplitude A may range between about ±0.25÷6°, in particular, between ±0.4÷3° and even more particularly between ±0.5÷1.5°. 
     By changing at least one of the frequency f, amplitude A and location of the intersection point  38 , the module  10  may simulate walking on an irregular surface, rough terrain etc. having various influences on the back than monotonic motion like walking on a straight track. 
     With reference to  FIGS. 1E and 1F , a design variation on the above embodiment is shown in which main rod  32  is positioned under the rear end of the seat portion  62  and the spacer  45  is positioned in the front. Also, the motor  20  is positioned between the plate  44  and the plate  54 . 
     Turning to  FIG. 2A , another embodiment of a module  100  according to the present invention is shown comprising a driving motor  200 , an asymmetric element  300  constituting the AAS, and a fixed and a moveable unit  420  and  440  respectively. 
     The asymmetric element  300  is in the form of a circular disc  310  having angled bottom and top surfaces  312 ,  314  respectively. The surfaces  312 ,  314  are formed with a bottom and top cylindrical portions  320 ,  340  protruding from the bottom and top surfaces  312 ,  314  respectively. The circular disc  310  and its bottom cylindrical portion  320  constitute the main rotary element of the module  100  and their common rotary axis Mx constitutes the main axis. The top cylindrical portion  340  constitutes the auxiliary rotary element and its rotary axis Ax constitutes the auxiliary axis, which is angled to the main axis and, optionally intersecting therewith at said intersection point  380 . The bottom surface  312  is substantially perpendicular to the main axis, and the top surface  314  is substantially perpendicular to the auxiliary axis. 
     It should be noted that, although in the present example, the circular disc  300  and bottom cylindrical portion  320  constitute the main rotary element and define the main axis, and the top cylindrical portion  340  constitutes the auxiliary rotary element and defines the auxiliary axis, this is not compulsory. According to a different design (not shown), the arrangement may be visa versa, i.e. the circular disc  300  and top cylindrical portion  340  constitute the main rotary element and define the main axis, while the bottom cylindrical portion  320  constitutes the auxiliary rotary element and defines the auxiliary axis. 
     The fixed and moveable units  420 ,  440  are connected to the outer rings  429   a  and  449   a  of bearings  429 ,  449  respectively. The bearings  429 ,  449  are in turn adapted for connection to the bottom and top cylindrical portion  320 ,  340 , through their inner rings  429   b,    449   b,  allowing their rotation therein. The fixed and moveable units  420 ,  440  are adapted for attachment to the pneumatic piston  64  of the swivel chair, and to chair mechanism  66  of the chair respectively. 
     The fixed unit  420  is formed with a conical hole  425  adapted for attachment to the pneumatic piston  64  of the chair, the conical form of the hole  425  allowing the attachment of the module  100  to a variety of pneumatic piston sizes. The moveable unit  440  may be formed with a conical protrusion  445  at its top portion adapted to be inserted into the seat  62  or the chair mechanism  66 . 
     The motor  200  comprises a driving wheel  220  adapted to partially extend between the fixed and moveable units  420 ,  440  and mesh with the side surface  316  of the circular disc  310 , such that rotation of the driving wheel  220  causes the circular disc  310  to rotate about its main axis Mx. It should also be noted that a variety of motor couplings may be used, e.g. spur gear, worm gear, chain, belt etc. as mentioned above. 
     The module  100  further comprises a retention member  500  adapted to prevent the fixed and moveable units  420 ,  440  from rotating with respect to each other during operation of the module  100 . The retention member  500  is in the form of a strap made of flexible material, e.g. metal, plastic etc., which connects the fixed and moveable units  420 ,  440 . The structure of the strap may allow the strap a high resistance to rotation between the units  420 ,  440  while enabling movement in other directions. 
     In operation, when the motor  200  rotates the circular disc  310 , whereby subsequent rotation of the top and bottom cylindrical portions  320 ,  340  takes place. Since the bottom cylindrical portion  320  is of an axis collinear with that of the circular disc  310 , the bottom cylindrical portion  320  performs a simple rotary motion in place. 
     Due to the above rotary motion and the angle between the planar surface  342  of the top cylindrical portion  340  and the planar surface  314  of the circular disc, said rotary-tilting movement imposed on the moveable unit  440  is a combination of the following motions:
         a rotary motion about a vertical axis parallel to the height axis of the chair caused by the rotation of the planar surface  342  of the top cylindrical portion  340  about the intersection point  380  of the main axis Mx of the circular disc  310 ; and   a tilting up &amp; down motion of the moveable unit  440  caused by the rotation of the top cylindrical portion  340  within the bearing.       

     Turning to  FIG. 2B , the retention member  510  is in the form of an external hinge formed of two prolonged upper hinge members  512  articulated to a prolonged bottom hinge member  514 . 
     According to yet another design shown in  FIG. 2C , the retention member  520  is a coil  522  passing through a cavity  330  formed within the AAS, and is attached to the moveable unit  440  at one end  447 , and to the fixed unit  420  at another end  427 . The coil&#39;s  522  resistance to torque is adapted to prevent the two units  420 ,  440  from rotating with respect to one another. 
     Turning to  FIG. 2D , the top and bottom cylindrical portions  320 ′,  340 ′ are formed with a cavity  1400  therein. The top and bottom surfaces  312  and  314  previously provided by the circular disc  300  and providing the angle between the bearings  429 ,  449 , are now provided by inner shape of the cavity  1400 , formed with two inclined inner surfaces  1412  and  1414 . Thus, the top and bottom cylindrical portions  320 ′,  340 ′ are now connected to the outer rings  429   a,    449   a  of the bearings  429 ,  449 . The fixed unit is  420 ′ and the moveable unit  440 ′ are connected to the inner rings  429   b,    449   b  of the bearings  429 ,  449 , and are free to rotate therein. 
     The retention member  540  in this case is a universal joint between the fixed and moveable units  420 ′,  440 ′. In this example, the intersection point  380  between the main and auxiliary axes Mx, Ax is located at the coupling point. 
     With reference to  FIGS. 2E to 2G , the location of the intersection point  380  between the auxiliary axis Ax and the main axis Mx may vary, in accordance with which various possible movements of the seat  62  of the chair  60  may be obtained. 
     For example, the intersection point  380  may be located in the plane of the circular disc as shown in  FIG. 2F . Alternatively, the intersection point  380  may be a virtual point located outside the AAS.  FIG. 2E  shows an arrangement in which the intersection point  380  is above the plane of the circular disc  310 . For example, when the intersection point  380  is located at the center of the seat  62 , the seat will then have a fixed point, i.e. a point which doesn&#39;t move during operation of the module  100 . This may cause every point on the seat  62  to be displaced only up and down but remain substantially in place. 
     If the intersection point  380  is located, for example, above the seat  62  and is offset from its center thereof, during operation of the module the seat  62  will perform, in addition, a circular motion about the main axis Mx. In this position, the location of the intersection point  380  may be determined to be at the height of any desired vertebra of the person sitting on the seat  62 , causing opposite direction forces to body parts above and below this point. 
     However, if the intersection point  380  is located below the seat or even below the bottom cylindrical portion  320  as shown in  FIG. 2G , the oscillations will push the whole body sideways, thus the intransient tilt is aimed at triggering an active reaction in order to balance the body. Therefore the ability to change the intersection point&#39;s  380  height creates a range of movement that can be adapted to any individual preferences. 
     Turning to  FIG. 3 , a further embodiment of the present invention is shown in which the motor  200  is directly connected to the main axis of rotation Mx. An external retention member  560  in the form of a coil prevents the rotation of the moveable unit with respect to the fixed unit as previously described. 
     With regards to all the above embodiments of the module of the present invention, when a person is seated on a chair  60  on which the module is mounted, the lo movement of the seat  62  induces a motion of the person&#39;s pelvis, which is usually undesired during working. As the person keeps his eyes on a target, such as a television screen or a computer monitor, the head remains almost stable while the pelvis is moved by the seat  62 , and the person will naturally tend to perform counter movements among the vertebras, to compensation the seat  62  movement. This coerces the small muscles surrounding and connecting between successive vertebras to act. This muscle activity is virtually similar to that exerted by said person during walking, and may help maintain good blood circulation at the vertebra vicinity. 
     It should be noted that the movement of the seat  62  with the frequency f and amplitude A as described above, is sufficiently mild, so that the operation of the muscles in order to compensate for said movement does not interfere with the person&#39;s working mentioned above. This, in turn, means that the person may easily perform his/her required office work while spontaneously operating his muscles, almost on an unconscious level. 
     With regards to all previous embodiments of the present invention, the module may further comprise a controller for controlling the operation thereof, whereby the module may be set to work automatically in predetermined time intervals, e.g. work for five minutes, then stop for 25 minutes, then work again. This operation mode of the module may allow efficient power consumption as well as prevention of strain on the vertebra for too long periods of time. The module may also comprise an over-ride button allowing a user to fully control the module, e.g. starting its operation when the module is at rest, exercising for longer or shorter periods of time than those of said predetermined time intervals, etc. 
     The module according to the present invention may further comprise a sensor adapted for detecting whether a person is seated on the seat portion, and may prevent operation of the module in the negative. 
     Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations, and modifications can be made without departing from the scope of the invention, mutatis mutandis.