directing attention to fig7 , the present invention provides chair 100 having a seat 102 that is manipulated through a large number of different angular motion paths . the seat moves in a synchronized motion path employing two or more degrees of freedom , depending on the embodiment . this motion system consists of two drive wheels 104 , 106 . drive wheel 104 is driven from gear motor 108 . drive wheel 106 is driven by chain 110 connected to drive wheel 104 ( fig9 ). the ratio between the diameters of drive wheels 104 , 106 determines the motion paths for seat 102 . if the diameters of drive wheels 104 , 106 are equal , a circular tilting pattern will occur and the seat will never be in a horizontal position . thus , in a preferred embodiment , drive wheels 104 , 106 are of different diameters to generate a periodic path of varying ellipsoidal tilting motions . the number of tilting motion iterations per repeating pattern is determined by the ratio between drive wheels 104 , 106 . if the ratio is not equal the seat of the chair will be horizontal or nearly horizontal two times during each period . in a preferred embodiment , the present invention utilizes a ratio of 7 : 6 between drive wheels 104 , 106 . a useful range of ratios is about 1 : 20 to about 20 : 1 , excluding the ratio of 1 : 1 . a ratio close to 1 : 1 will make the number of roll to pitch tilts per repeating motion paths more equal . directing attention to fig8 , in an embodiment , seat 102 supported by support 112 connected to universal joint 114 ( fig1 ). universal joint 114 allows seat 102 to pivot about a central point . eccentric member 116 is connected to drive wheel 104 to provide an off - center connection point for linkage 118 that is connected between eccentric member 116 and a side mounting point of seat 102 . the front of seat 102 is driven by crankshaft 120 that is supported by idler bearings 122 . at the end of crankshaft 120 , eccentric member 124 provides an off - center connection for linkage 126 . linkage 126 is connected between eccentric member 124 and a mounting point beneath the front of seat 102 . both eccentric member 116 and eccentric member 124 may have a plurality of off - center mounting points located at different radii from the center of rotation , to provide adjustments to the magnitude of vertical change to seat 102 by linkages 118 , 126 , respectively . while in a preferred embodiment , drive wheels 104 , 106 are sprockets that are connected by a roller chain , in alternative embodiments , drive wheels 104 , 106 can be pulleys and chain 110 can be substituted with a drive belt connecting drive wheels 104 , 106 . in another embodiment , drive wheels 104 , 106 can be gears that interface directly with each other , or through intermediate gearing . in yet another embodiment , drive wheel 104 and crankshaft 120 can be independently powered by separate drive motors that turn drive wheel 104 and crankshaft 120 at respective rotational speeds to achieve the same motion paths generated by drive wheels 104 , 106 having the range of diameter ratios between about 1 : 20 through 20 : 1 . the motion paths generated in the present invention cause seat 102 to tilt between a level , horizontal position and various tilted positions . the deterministic and repeatable complex angular motion path generated by the present invention allows seat 102 to tilt in a much larger range of positions than the circular path methods of the prior art . this complex angular path is illustrated in a graphical plot in fig1 . as shown in fig1 , seat 102 is moved in accordance with a lissajou pattern . to generate the path in fig1 a drive wheel ratio of 7 : 6 was used . this path consists of six cycles . a more detailed graphical representation of each cycle of this path is shown in fig1 through fig1 . directing attention to fig1 ( 5 ) the x indicates the location where seat 102 is level . with a ratio of 7 : 6 the seat becomes level twice during the six angular path cycles this ratio generates . this ratio metric angular motion path has the ability to reverse direction without reversing the direction of the motor . in fig1 ( 2 ) the direction of the angular motion changes from clockwise to counter clockwise and reverses again to clockwise in fig1 ( 3 ). comparing fig1 to the angular path of the prior art in fig1 it should be obvious the angular path of this invention provides a much larger range of angular motions than the prior art circular motion method . while ratio of 7 : 6 was used in this invention , a much larger set of other ratios will generate many desirable angular motion paths . different ratio metric ratios will produce different repeating angular paths and a different number of cycles before the pattern repeats . in an embodiment , motor 108 ( and thus the motion of seat 102 ) is controlled by speed control mechanism 130 , which is adjustable by speed adjustment mechanism 132 . in an embodiment , motor timer 134 is included to also provide periods where motion of seat 102 is temporarily suspended . this allows the motion to be stopped when seat 102 is level and thus constant postural changes are not required . returning to fig9 , in an embodiment , the present invention detects when seat 102 is level with respect to pitch and roll . to detect when seat 102 is level , two horizontal seat sensors are disposed proximate to drive wheels 104 , 106 . sensor 136 determines when seat 102 is horizontal with respect to left / right tilt . in an embodiment , sensor 136 utilizes a stationary , mechanically activated electrical switch such as a limit switch . sensor 136 is triggered when a lobe on cam 138 makes contact with sensor 136 . cam 138 is attached to protrude radially from drive wheel 104 and revolves as drive wheel 104 rotates . the lobe on cam 138 is positioned to contact sensor 136 when seat 102 is horizontal with respect to left / right tilt . a similar sensor and cam are disposed proximate to drive wheel 106 to determine when seat 102 is level with respect to front / back tilt . in an embodiment , sensor 140 utilizes a stationary , mechanically activated electrical switch such as a limit switch . sensor 140 is triggered when a lobe on cam 142 makes contact with sensor 140 . cam 142 is attached to protrude radially from drive wheel 106 and revolves as drive wheel 106 rotates . the lobe on cam 142 is positioned to contact sensor 140 when seat 102 is horizontal with respect to front / back tilt . when both sensors 136 , 140 are activated , seat 102 is level with respect to pitch and roll . in an embodiment , when motor timer 134 is in the seat on mode , motor 108 is powered on and drives drive wheels 104 , 106 . when motor timer 134 is in the seat off mode and horizontal seat sensors 136 and 140 are triggered , motor 108 is powered off . in an embodiment , motor timer 134 contains logic that allow an adjustable interval during which sensors 136 and 140 are serially activated and motor 108 is powered off when seat 102 is in a position that is close to level with respect to pitch and roll but contains a slight tilt in either pitch , roll , or both . this is especially useful for accommodating individual needs such as an injury where the seated person finds comfort in a slightly off - level position . since the motion of seat 102 can be stopped , chair 100 may be used as a regular level chair . the motion of seat 102 can be automatically stopped for periodic level seat time out periods . while the preferred embodiment of the present invention uses a drive wheel ratio of 7 : 6 ( gearing 14 : 12 ), reversing this ratio to 6 : 7 will yield similar results . while chair 100 is illustrated herein as a conventional chair , chair 100 is also particularly useful when incorporated into the design of a wheelchair , and is also useful in vehicles such as automobiles , airplanes , or any other application where a person remains seated for prolonged periods of time . while in the preferred embodiment linkages 118 and 126 are attached to the bottom side of the seat and the bottom front of the seat respectively , in an alternative embodiment , linkages 118 , 126 are connected directly to support 112 rather than to seat 102 . in this alternative embodiment , linkages 118 and 126 are still orthogonal with respect to each other . in this alternative embodiment , the seat motion is the same as in the preferred embodiment . in this alternative embodiment , motor 108 , sprockets 104 , 106 , eccentric 116 and chain 110 are rotated 90 degrees to assume a horizontal orientation . eccentric 124 is attached directly to drive wheel 106 . crankshaft 120 and bearings 122 - 1 , 122 - 2 are replaced by an idler bearing . while various embodiments of the dynamic chair of the present invention have been described and illustrated in detail , it is to be understood that many changes to the embodiments can be realized without departing from the spirit of the invention .
the present invention provides a dynamic chair having a deterministic motion path that allows a variety to different paths to be selected depending of needs of user . by changing the ratio between drive wheels that control the pitch and roll of the seat , motion paths can be selected to help a person assume and / or avoid certain postures while seated . embodiments of the present invention move the seat of the dynamic chair through a deterministic path to dictate how often and when the seat is in a level position with respect to pitch and roll .