Abstract:
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.

Description:
RELATED APPLICATION 
   This application is a continuation of co-pending U.S. patent application Ser. No. 11/088,011, filed Mar. 22, 2005, which claims priority to U.S. provisional patent Ser. No. 60/581,099, filed Jun. 17, 2004, both of which are incorporated herein by reference in their entirety. 

   FIELD 
   The present invention relates broadly to chairs having powered motion. Specifically, the present invention relates to a chair seat that travels through a preferred range of motion to distribute pressure over a large area beneath a seated person. 
   BACKGROUND 
   In a seated position, a very small area under the buttocks supports the majority of a person&#39;s weight. In this small area, capillaries and soft tissue are compressed. Blood circulation is restricted and soft tissue is put under stress. Prolonged sitting over time can damage the tissue being compressed. The simple solution is to avoid sitting for prolonged periods, but such a solution is not realistic for many people who must sit for prolonged periods to perform many necessary functions such as driving or working. 
   Two major factors that contribute to the physical detriments described above are time and compressive pressure. Reducing one or both of these factors reduces the stress on the soft tissue. If the compressive pressure under the buttocks is shifted back and forth between two locations, then the duration of compressive pressure experienced at one position is reduced by half. This would allow some measure of periodical relief of the pressure points. If the compressive pressure point could be rotated between several positions over time, then the time of tissue stress at each position can be further reduced. As the number of pressure points is increased, the period of stress is reduced at each pressure point. In order to obtain the maximum number useful pressure points, the pressure points need to be evenly distributed over the entire buttocks area. 
   One solution to this problem is a seat that tilts in two dimensions with a pivot that is located under the center of the seat. Such a seat can continuously rotate in a circular manner, thus distributing pressure over a large number of pressure points, as shown in the motion path illustrated in  FIG. 1 . The problem with this method is that all pressure points are limited to only one circular path under the buttocks area. This simple motion path misses the majority of possible pressure point locations. 
   U.S. Pat. No. 5,976,097 to Jensen and U.S. Pat. No. 5,113,851 to Gamba both disclose a chair having a seat that is permanently tilted at a fixed angle with respect to the center of the seat. The chair seat is motor-driven to rotate this tilted fixed angle in a circular manner with respect to the center of the seat. It is important to point out that the seat does not rotate. It is the seat&#39;s tilting fixed angle that rotates around the center of the seat. The direction of this circular tilting motion remains constant and the circular tilt pattern repeats identically on each rotation. Since the seat is always tilted, the seat needs to be always in motion or a seated person will be sitting in a twisted fashion, trying to compensate for the static, tilted nature of the chair. While the purpose of the chairs described in Jensen and Gamba is to prevent sitting in a static position and thus holding the same posture for prolonged period of time, sitting in these chairs requires continuous posture adjustments.  FIG. 1  illustrates a graphical plot of the circular tilted motion generated by the chairs described in Jensen and Gamba. At location  1 , seat  10  is tilted backwards only, as shown in  FIGS. 2A and 2B . At location  2  of  FIG. 1 , seat  10  is tilted to the right side only, as shown in  FIGS. 3A and 3B . At location  3  of  FIG. 1 , seat  10  is tilted to the right and tilted forward, as illustrated in  FIGS. 4A and 4B . At location  4  of  FIG. 1 , seat  10  is tilted forward only, as shown in  FIGS. 5A and 5B . For seat  10  to be level, as shown in  FIGS. 6A and 6B , seat  10  travels through a path taking it through location  5  of  FIG. 1 . But because the seats of Jensen and Gamba rotate at a fixed angle, they never pass through this horizontal position. 
   While Jensen and Gamba both address part of the problem described above, and it is desirable for a seated person to change posture and not sit in a static position for extended periods of time, it is not desirable to be forced to make continuous postural changes while seated over prolonged periods of time. Due to the fixed angle of the chairs described in Jensen and Gamba and their inability to ever become level, these seats always need to be moving, thus requiring constant posture changes for a seated person, and the seat cannot be used as a regular level chair. Also, neither Jensen nor Gamba disclose or suggest any manner in which the seat can be easily stopped, or how the seat can be stopped periodically. 
   U.S. Pat. No. 6,033,021 to Udo discloses a self-tilting seat that utilizes two independent, unsynchronized tilting mechanisms to generate a path from two separate motors. There is no disclosure in Udo for detecting a level position. If a level position of the seat is ever reached it is achieved randomly, and not in a repeatable manner, as the two independent tilting mechanisms are not synchronized. There is a heartfelt need for a dynamic chair having a repeatable and deterministic motion path to generate a known range of postural changes to alleviate compressive pressure at as many pressure points as possible. 
   SUMMARY 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. 
   The present invention provides a dynamic chair providing automatic motion in a seat. The chair includes a base, a seat having a bottom, the seat bottom having first and second mounting points on the bottom of the seat, a support disposed between the base and the seat bottom, and a drive motor. A first drive wheel is driven in a rotational manner by the drive motor, and has a first mounting point offset from the center of the first drive wheel. A first control provides a first rotational degree of freedom of movement to the seat, and is attached between the first offset mounting point and the first seat bottom mounting point. A second drive wheel is driven in a rotational manner by the first drive wheel. A crankshaft has one end connected to the second drive wheel and is rotatably driven by the second drive wheel, and the second end has an eccentric providing a second offset mounting point offset from the center of the second crankshaft end. A second control provides a second rotational degree of freedom of movement to the seat, and is attached between the second offset mounting point and the second seat bottom mounting point. The first drive wheel and the second drive wheel are configured in a nonequal ratio of diameters within a range of 20.0:1.0 and 1.0:20.0, such that a changing, substantially ellipsoidal pattern of movement is produced in the seat bottom. 
   In an embodiment, the first seat bottom mounting point is offset 90 degrees from the second seat bottom mounting point with respect to the location of the support. The first offset point is disposed at a first distance from a center of rotation of the first eccentric for the seat and the second offset point has a second distance from the center of rotation of the second eccentric for the seat. The first distance determines a range of rotation of the seat&#39;s first rotational degree of freedom, and the second distance determines a range of rotation of the seat&#39;s second rotational degree of freedom. The first and second ranges of rotation are within −5 degrees to +5 degrees. 
   In an embodiment, the support incorporates a universal joint and an attached extension arm, and the seat bottom is attached to the extension arm and the base is attached to the universal joint. The support provides a first degree of linear freedom of linear movement for the seat and a second degree of linear freedom of linear motion for the seat, with the first degree of freedom of linear motion orthogonal to the second degree of freedom of linear movement. The length of the extension arm determines a radial distance from the universal joint to the seat, so that as the universal joint rotates, the radial distance and a rotational angle of the universal joint determine a first linear travel distance for the first degree of freedom of linear motion and a second linear travel distance for the second degree of freedom of linear motion. 
   In an embodiment, the first control and the second control are connected to the first seat mounting point and the second seat mounting point, respectively, such that the seat is moved through the changing, substantially ellipsoidal pattern of movement, such as a Lissajou pattern. 
   In various embodiments, the dynamic chair of the present invention can include a motor speed controller that controls the rotational speed of the first drive wheel, a motor timer that provides periodic motor stop time, and a plurality of level sensors that indicate that the seat is level with respect to pitch and roll so that the chair motion can be temporarily halted when the seat is level. 
   Many other features and advantages of the present invention will be realized upon reading the following detailed description, when considered in conjunction with the accompanying drawings. 

   
     BRIEF DECRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a graphical plot of a range of motion in an existing chair. 
       FIGS. 2A and 2B  illustrate a profile view and elevation view, respectively, of a position of an existing chair that corresponds with a point on the plot of  FIG. 1 . 
       FIGS. 3A and 3B  illustrate a position of an existing chair that corresponds with a point on the plot of  FIG. 1 . 
       FIGS. 4A and 4B  illustrate a profile view and elevation view, respectively, of a position of an existing chair that corresponds with a point on the plot of  FIG. 1 . 
       FIGS. 5A and 5B  illustrate a profile view and elevation view, respectively, of a position of an existing chair that corresponds with a point on the plot of  FIG. 1 . 
       FIGS. 6A and 6B  illustrate a profile view and elevation view, respectively, of a position of a chair that corresponds with a level point on the plot of  FIG. 1 . 
       FIG. 7  illustrates the dynamic chair of the present invention. 
       FIG. 8  illustrates a plan view of elements used in an embodiment of the present invention. 
       FIG. 9  illustrates the drive system of the dynamic chair of the present invention. 
       FIG. 10  illustrates the chair support and universal joint used in the dynamic chair of the present invention. 
       FIG. 11  illustrates a motion path of six cycles of the dynamic chair of the present invention when configured with drive wheels having a 7:6 ratio. 
       FIG. 12  illustrates a motion path of the first of six cycles of the dynamic chair configured in accordance with  FIG. 11 . 
       FIG. 13  illustrates a motion path of the second of six cycles of the dynamic chair configured in accordance with  FIG. 11 . 
       FIG. 14  illustrates a motion path of the third of six cycles of the dynamic chair configured in accordance with  FIG. 11 . 
       FIG. 15  illustrates a motion path of the fourth of six cycles of the dynamic chair configured in accordance with  FIG. 11 . 
       FIG. 16  illustrates a motion path of the fifth of six cycles of the dynamic chair configured in accordance with  FIG. 11 . 
       FIG. 17  illustrates a motion path of the sixth of six cycles of the dynamic chair configured in accordance with  FIG. 11 . 
       FIG. 18  illustrates a motion path of 20 cycles of the dynamic chair of the present invention when configured with drive wheels having a 1:20 ratio. 
       FIG. 19  illustrates a motion path of 20 cycles of the dynamic chair of the present invention when configured with drive wheels having a 20:1 ratio. 
   

   DETAILED DESCRIPTION 
   Directing attention to  FIG. 7 , 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  ( FIG. 9 ). 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  FIG. 8 , in an embodiment, seat  102  supported by support  112  connected to universal joint  114  ( FIG. 10 ). 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  FIG. 11 . As shown in  FIG. 11 , seat  102  is moved in accordance with a Lissajou pattern. To generate the path in  FIG. 11  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  FIG. 12  through  FIG. 17 . Directing attention to FIG.  11 ( 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 FIG.  13 ( 2 ) the direction of the angular motion changes from clockwise to counter clockwise and reverses again to clockwise in FIG.  16 ( 3 ). Comparing  FIG. 11  to the angular path of the prior art in  FIG. 1  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  FIG. 9 , 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.