Abstract:
A system for use with a mobile device includes at least one sensor to sense a variable related to tilting of the mobile device and at least one activatable system in operative connection with the sensor. The at least one activatable system increases stability of the mobile device upon actuation/change in state thereof on the basis of data measured by the at least one sensor. A variable related to tilting includes variables that indicate concurrent, actual tilting as described herein as well as variables predictive of imminent tilting. Activatable systems hereof change state upon actuation or activation to increase stability of the mobile device by reducing, eliminating or preventing tilting.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/591,238, filed Jan. 26, 2012, the disclosure of which is incorporated herein by reference. 
     
    
     GOVERNMENTAL INTEREST 
       [0002]    This invention was made with government support under the National Science Foundation Grant No. EEC 0552351, NIH Grant No. RD43HD058376-01 and VA Center of Excellence Grant No. B6789C. The government has certain rights in this invention. 
     
    
     BACKGROUND 
       [0003]    The following information is provided to assist the reader in understanding technologies disclosed below and the environment in which such technologies may typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the technologies or the background thereof. The disclosure of all references cited herein are incorporated by reference. 
         [0004]    Personal Mobility Devices (PMDs) such as electronic power wheelchairs (EPW) as illustrated in  FIG. 1A , scooters as illustrated in  FIG. 1B  and manual wheelchairs as illustrated in  FIG. 1C  are very beneficial to the people with mobility impairments. As used herein, the term “personal mobility device” or PMD refers to mobile devices to transport a person, thereby increasing the mobility of the person. However, those benefits come with some risks. One such risk lies in the stability of the PMD. A review of the US Food and Drug Administration&#39;s (FDA&#39;s) Manufacturer and User Facility Device Experience (MAUDE) database shows that one of the most frequent adverse events connected to these devices is their inclination to tip; causing the user to be thrown from the device and injured, sometimes severely. In a study done between 1975 and 1993, 25.7% of the wheelchair safety incidents reported to the FDA were from a tip and/or fall. R. Lee Kirby, S. A.-S. Wheelchair Safety-Adverse Reports to the Food and Drug Administration,  American Journal of Physical Medicine and Rehabilitation,  308-312 (1995). 
         [0005]    To help prevent these injuries the US Department of Veterans Affairs (VA), the FDA and the Centers for Medicare &amp; Medicaid Services (CMS) require that PMDs are tested for stability issues and that the results then be published in the user manual. Testing the PMDs and reporting the results do not necessarily mean that they are stable. However, the VA has become more proactive about requiring that PMDs be more stable. They have indicated in their requests for low cost EPW&#39;s that they are dynamically stable on a 6° slope. 
         [0006]    It is a good idea to change the design of the PMDs to make them more stable; however any design change may affect the performance of the device as well. Slowing the speed of the device reduces mobility and independence. Making a wider frame can limit access to narrow places. Stiff suspension reduces user comfort. Passive anti-tip devices limit some safe maneuvers and can be ineffective if not properly adjusted to the user&#39;s specifications. 
       SUMMARY 
       [0007]    In one aspect, a system for use with a mobile device includes at least one sensor to sense a variable related to tilting of the mobile device and at least one activatable system in operative connection with the sensor. The at least one activatable system increases stability of the mobile device upon actuation/change in state thereof on the basis of data measured by the at least one sensor. A variable related to tilting includes variables that indicate concurrent, actual tilting as described herein as well as variables predictive of imminent tilting. Activatable systems hereof change state upon actuation or activation to increase stability of the mobile device by reducing, eliminating or preventing tilting. The system may further include a control system in operative connection with the at least one sensor and in cooperative connection with the at least one activatable system to control whether the at least one activatable system is activated on the basis of data measure by the at least one sensor. 
         [0008]    The at least one activatable system may, for example, include at least one activatable damper system or at least one activatable brake system. In a number of embodiments, the at least one activatable system is in operative connection with a suspension system of the mobile device. In a number of embodiments, the at least one activatable system is in operative connection with at least one abutment member adapted to contact a surface upon which the mobile device is supported to increase or enhance stability or prevent instability. 
         [0009]    In a number of embodiments, the mobile device is a personal mobility device. The personal mobility device may, for example, be an electrically powered wheelchair or an electrically powered scooter. 
         [0010]    Activatable systems in operative connection with at least one abutment member adapted to contact a surface upon which the mobile device is supported to increase or enhance stability or prevent instability may, for example, be used in connection with manually powered wheelchair or powered wheelchairs. In a number of embodiments, the abutment member includes a wheel that moves up and down before activation of the activatable system, but requires more force to move upon or down or is prevented from moving up or down upon activation of the activatable system. The wheel may, for example be biased to remain in contact with a surface upon which the mobile is traveling when the activatable system in not activated. 
         [0011]    In a number of embodiments, the mobile devices (or suspension systems thereof in some embodiment) may operate independently of the activatable systems. The activatable systems hereof need not be formed integrally with systems upon manufacture thereof and are, for example, readily adapted to be attached to an existing mobile device. 
         [0012]    In another aspect, a method of operating a mobile device includes providing at least one sensor to sense a variable related to tilting of the mobile device in operative connection with the mobile device, providing at least one activatable system in operative connection with the sensor, and activating the at least one activatable system to increase stability of the mobile device on the basis of data measured by the at least one sensor. The method may further include providing a control system in operative connection with the at least one sensor and in cooperative connection with the at least one activatable system to control whether the at least one activatable system is activated on the basis of data measured by the at least one sensor. As described above, the at least one activatable system may, for example, include at least one activatable damper system or at least one activatable brake system. 
         [0013]    In another aspect, a mobile system includes an anti-tip system including at least one sensor to sense a variable related to tilting of the mobile system, and at least one activatable system in operative connection with the sensor. The at least one activatable system increases stability of the mobile system on the basis of data measured by the at least one sensor. 
         [0014]    The present devices, systems, and methods, along with the attributes and attendant advantages thereof, will best be appreciated and understood in view of the following detailed description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1A  illustrates a typical embodiment of a scooter. 
           [0016]      FIG. 1B  illustrates a typical embodiment of an electrically powered wheelchair. 
           [0017]      FIG. 1C  illustrates a typical embodiment of a manually powered wheelchair. 
           [0018]      FIG. 2A  illustrates a side view of a prototype wheelchair used in studies hereof. 
           [0019]      FIG. 2B  illustrates an enlarged or close-up view of a portion of the wheelchair frame and suspension of the wheelchair of  FIG. 1A . 
           [0020]      FIG. 2C  illustrates a front view of another embodiment of a wheelchair and an activatable system hereof for use in connection with the wheelchair. 
           [0021]      FIG. 2D  illustrates another front view of the wheelchair of  FIG. 2C  with the activatable system hereof in operative connection with each castor wheel thereof. 
           [0022]      FIG. 3A  illustrates a cross-sectional view of an embodiment of a linear brake system hereof. 
           [0023]      FIG. 3B  illustrates a perspective view of the linear brake system of  FIG. 3A . 
           [0024]      FIG. 4  illustrates a perspective view of an embodiment of a sensor support hereof via which a sensor can be attached to a mobile device at a desire initial or starting angle or orientation. 
           [0025]      FIG. 5A  illustrates an embodiment of a control system for use with the activatable systems and sensors hereof. 
           [0026]      FIG. 5B  illustrates a generalize schematic view of a system hereof including a sensor, a control system and an activatable system. 
           [0027]      FIG. 6A  illustrates a rear perspective view of a manual wheelchair including embodiments of activatable systems hereof to increase stability (reduce the likelihood of tipping or excessive tilting) wherein the activatable systems are in a non-activated state. 
           [0028]      FIG. 6B  illustrates another rear perspective view of the manual wheelchair of  FIG. 6A  wherein the activatable systems are in an activated state. 
           [0029]      FIG. 6C  illustrates a rear perspective view of a manual wheelchair including embodiments of activatable systems hereof to increase stability wherein the activatable systems are in a non-activated state. 
           [0030]      FIG. 6D  illustrates another rear perspective view of the manual wheelchair of  FIG. 6C  wherein the activatable systems are in an activated state. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    It will be readily understood that the components of the embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations in addition to the described example embodiments. Thus, the following more detailed description of the example embodiments, as represented in the figures, is not intended to limit the scope of the embodiments, as claimed, but is merely representative of example embodiments. 
         [0032]    Reference throughout this specification to “one embodiment” or “an embodiment” (or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment. 
         [0033]    Furthermore, described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, et cetera. In other instances, well known structures, materials, or operations are not shown or described in detail to avoid obfuscation. 
         [0034]    As used herein and in the appended claims, the singular forms “a,” “an”, and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a sensor” includes a plurality of such sensors and equivalents thereof known to those skilled in the art, and so forth, and reference to “the sensor” is a reference to one or more such sensors and equivalents thereof known to those skilled in the art, and so forth. 
         [0035]    In a number of represented embodiment hereof, active stability devices (ASD) hereof are discussed for use in connection with personal mobility devices for personal transportation. Such personal mobility devices may be used to transport a human user either through manual control or autonomously. However, the active stability devices hereof are suitable for use in connection with many mobile devices, including personal mobility devices such wheelchairs (both electric-motor powered and manual) and scooters, as well as mobile robotic bases and others mobile devices. 
         [0036]    In a number of embodiments hereof, active stability devices or systems for use with mobile devices are provided that do not interfere with normal operation of the mobile device, but activate only when a mobile device such as a wheelchair is in an unstable situation or is about to become unstable. Devices, systems and methods hereof may, for example, be used to increase the stability of mobile devices including personal mobility devices such as wheelchairs. In a number of embodiments, systems hereof include at least one sensor and at least one actuator. Under conditions where instability exists or is predicted, the actuator activates in a manner to increase stability (or reduce or prevent instability) of the system. In general, the term “instability” as used herein refers to tilting or tipping of a mobile device. Tilting or tipping occurs upon rotation about an axis (for example, a longitudinal axes or a latitudinal axes) of the mobile device causes at least one wheel (or other rotatable mobility elements) of the mobile device to loose contact with a surface or plane upon which the mobile device is moving. 
         [0037]    For example, in a number of personal mobility devices, a soft suspension on the device is used to increase ride comfort, but can also make the device unstable under certain dynamic situations. To preserve comfort and increase stability of such wheeled personal mobility devices, a representative embodiment of an active suspension system was developed and tested on the prototype hybrid power operated vehicle (HyPOV) chair. See, for example, U.S. Pat. No. 7,882,909 and Pearlman, J., et al., “Design, development and testing of a low-cost electric powered wheelchair for India. Disability and Rehabilitation,”  Assistive Technology,  4(1):, 42-57 (2009), the disclosures of which is incorporated herein by reference. In a number of embodiments, the representative system included a stability sensor including a tilt switch, an actuatable or activatable device or system including a magnetorheological (MR) damper, and circuitry for the power supply. 
         [0038]    Static stability and dynamic stability tests were conducted to see if the activatable system activated before the wheelchair tipped and to determine if the wheelchair would achieve a similar stability rating for the same test as the wheelchair received with the activatable MR Damper(s) fully engaged or stiffened. A low-cost linear brake device or system was also developed as an activatable system for use as an alternative to or to work in cooperation with a damper such as the MR Damper. In a number of embodiments hereof, activatable systems such as MR Dampers and/or brake devices can be retrofitted to existing personal mobility devices and other mobile devices or systems. 
         [0039]    Although the application of such a representative system hereof is ostensibly to stiffen suspension on a power wheelchair equipped with a “soft” or resilient suspension (for example, including one or more springs or other resilient devices or systems), the applications are much broader. Applications of the sensor/activatable systems hereof include both manual- and electric-powered wheelchairs, mobile robotic bases, and devices without suspension. In general, stability of mobile devices is increase via a system including of at least one sensor to sense at least one variable related to or predictive of instability (tilting or tipping) and at least one actuator activatable system in operative connection with the sensor that can be actuated or activated to reduce the likelihood of or existence of instability. In other words, under conditions where instability exists or is predicted, then the actuator or activatable system would activate in such a way as to increase stability of the system. 
         [0040]    A description of a representative embodiments of the activatable stability device or system for an electric powered wheelchair follows. One goal of the system was to develop and perform initial testing of a powered mobility active anti-tip system. As described above, a hybrid power operated vehicle (HyPOV) was used as a test-bed for this system. The HyPOV wheelchair  10  is a low-cost electrically powered wheelchair which was originally developed for use, for example, where cost may be a determinative factor. Many powered and manual wheelchairs may become unstable, for example, under certain high-speed turning situations. 
         [0041]    The current design of wheelchair  10  uses a centrally located drive or hub drive wheel  42  to maneuver. The hub motor (not shown) may be fully enclosed within the hub of drive wheel  42 . This allows for wheelchair  10  to function with only one motor as opposed to other power chairs which usually require two motor. 
         [0042]    Wheelchair  10 , which is similar to wheelchairs described in U.S. Pat. No. 7,882,909, includes a seat  12  mounted on a generally rectangular frame system  14  (see  FIG. 2B ). Frame system  14  may, for example, be made from metal or another similar rigid material. Frame  14  includes at least one rear rail  20  and side rails  22  on each side thereof. In the illustrated embodiment, side rails  22  are provided on each side, and connect between rear rail  20  and front wheel axle brackets. As described in U.S. Pat. No. 7,882,909, a solid axle joins two large freely spinning wheels  28  via wheel axle brackets. The brackets and axle solidly connect the side frame rails  22  to each other. Wheelchair  10  further includes a foot platform  70  connected to an extending member  66  via a pivotable connection  68 . 
         [0043]    Seat  12  is attached to side rails  22  of frame  14  via multiple sliding seat perches  24 ; at least one seat perch  24  (see  FIG. 2A ) on each side rail  22 . Seat  12  can be mounted to face in either direction to be adaptable for various wheelchair user needs. Terms such as “front”, “rear”, “forward”, “rearward”, “upper”, “lower” and like terms as used herein refer to the orientation of wheelchair  10  in  FIGS. 2A through 2B . 
         [0044]    As also described in U.S. Pat. No. 7,882,909, a pivot connection piece (not shown) is attached near the midpoint of the front solid axle and pivots about the axle between the large wheels  28 . An elongated center swing arm  34  is rigidly attached to the pivot connection piece at one end, and to a midpoint of front rail  20  on the other end. This swing-arm system houses the motor/brake/turning system, generally  40 . The pivot connection piece enables center swing arm  34  to pivot about the front solid axle and to move parallel to the longitudinal axis of side frame rails  22  according to the load balance on caster wheels  58  and a drive wheel  42  described below. 
         [0045]    Drive wheel  42 , which may, for example, be a hub-motor as described above, is placed in a fork  44  with a bearing (not shown) mounted near its topmost portion. Extending upwardly from the top of the bearing is a shaft  46 . Shaft  46  extends optionally through center swing arm  34  and operatively connects to a steering mechanism  80  (including, for example, a tiller  82 ). Drive wheel  42 , fork  44 , bearing and shaft may connect to center swing arm  34  so that they can be adjusted along the length thereof. This adjustment of the position of drive wheel  42  permits the force on drive wheel  42  to be increased or decreased as the force on casters wheels  58  increases or decreases. 
         [0046]    In the illustrated embodiment, a suspension link systems  50  includes upper link member  51 U and lower link member  51 L, which are connected between frame  14  and rotatable joints  54  for caster wheels  58 . In the illustrated embodiment, a caster wheel connector  56  is attached to and extends downwardly from each rotatable joint  54 . Caster wheels  58  are smaller than the two large wheels  28  and are capable of rotating 360 degrees by means of the rotatable joint  54 . Caster wheels  58  are located on one end of wheelchair  10  opposite large wheels  28 . Large wheels  28  can be located in the front of the wheelchair  10  and caster wheels  58  can be located in the rear (as illustrated) or vice versa, depending on the user&#39;s preference. 
         [0047]    In the illustrated embodiment, each caster wheel connector  56  is connected to center swing arm  34  with separate upper link members  51 U and lower link members  51 L of suspension link systems  50 . As also described in U.S. Pat. No. 7,882,909, upper link members  51 U connect and pivot about an axle located inside rear frame rail  20 . Lower link members  51 L are fixed to, for example, a polymeric or metallic torsion spring  60  not shown which links to center swing-arm  34  through an adjustable bracket system  61 . Other suspension system including other types of resilient members (for example, coil springs or leaf springs) can also be used. Such resilient members or elements allow vertical displacement of each caster wheel  58  independently and transfer force to the drive wheel  42  as caster wheels  58  encounter obstacles, bumps, uphill or downhill surfaces or any other kind of terrain. 
         [0048]    Wheelchair  10  also includes activatable systems  100  on each side thereof (only one of which is shown in  FIGS. 2A and 2B , with the other being substantially identical). Activatable systems  100  are connected at one end to lower link member  51 U in the suspension system and to side rail  22  (via connecting bracket  90 —see  FIG. 2A ) at another end thereof. In embodiments hereof, activatable systems  100  hereof may, for example, decrease the travel distance of a suspension or a portion thereof, stiffen dampers or shock absorbers to require more force for the suspension to travel, lock motion of the suspension or a portion thereof etc. In a number of embodiments, activatable systems  100  included MR (Magnetorheological) dampers. An MR damper uses a fluid that has a variable yield strength controlled by a magnetic field. When a higher voltage is passed into the controller via, for example, a control system  150  which is in operative connection with a sensor  300  as described below, the fluid stiffens which causes an increase to the damping force. However, the damper does not completely stop the linear motion. It can slow it down, but if there is enough force on the damper, it will eventually become completely stretched out or compressed. Upon activation one of activatable systems  100  including an MR damper, vertical travel of the associated caster wheel  58  is limited by the increased force required to overcome the resistance provided by the MR damper. 
         [0049]      FIGS. 2C and 2D  illustrates the use of an activatable system  100   a  hereof in connection with another embodiment of wheelchair  10   a.  Similar to wheelchair  10 , wheelchair  10   a  includes Caster wheels  58   a  located on one end of wheelchair  10   a,  opposite large wheels  28   a.  In the illustrated embodiment, however, large wheels  28   a  are located in the rear of wheelchair  10   a  and caster wheels  58  are located in the front thereof. Caster wheels  58   a  are connected to the frame of wheelchair  10   a  via a suspension system including springs  60   a.  Springs  60   a  are connected between castor wheel connecting members  53   a  and upper members  54   a,  which are operatively connected to wheelchair frame (not shown in  FIGS. 2C and 2D ). Activatable systems  100   a  are connected at one end to upper members  54   a  and at another end to castor wheel connecting members  53   a.  Upon actuation or activation of activatable system(s)  100   a,  vertical travel of the associated caster wheel  58   a  relative to the associated upper member  54   a  (and the frame) is limited or prevented. In a number of embodiments hereof, activatable systems hereof are connected between a suspended portion of a wheelchair or other mobile device (for example, a frame) and a non-suspended portion thereof (for example, a wheel) to limit or prevent relative motion between the suspended portion and the non-suspended portion. 
         [0050]    A number of activatable systems other than MR dampers are suitable for use herein. For example, an activatable system including a linear brake was designed as an alternative (or an addition) to MR dampers. As described above, MR dampers do not completely prevent the suspension from moving. MR damper only cause it to require more force to move the suspension at some speed. Moreover, MR dampers are relatively costly (for example, approximately $400). A lower-cost device for use in the activatable systems hereof may be desirable in certain circumstance (for example, in a case in which a wheelchair or other mobile device is being retrofitted with activatable systems hereof). A device or system such as a linear brake, which actually locks the suspension (preventing movement thereof) may be used and may be more effective at preventing the mobile device from tipping. An activatable brake system may, for example, be designed so that the dimensions are roughly the same as the MR dampers used in activatable systems  100  (with substantially less cost). In other embodiments, a linear or rotary brake, such as those that use electromagnets for actuation, may be used to stiffen either suspension systems or other anti-tip systems hereof to stabilize a mobile device such personal mobility device. 
         [0051]    An embodiment of a linear brake system  200  for use in the systems hereof is shown in  FIGS. 3A and 3B . In linear brake system  200 , a wedge  210  is be forced into a cone  220  within a housing  230  and which then causes wedge  210  to apply a normal force to a rod  240 . Wedge  210  is forced into cone  220  via the electromagnetic force of a coil  250 , which (upon activation) forces a plunger  260  into wedge  210 . Linear brake system  200  operates in a manner similar to a solenoid. Operation of the system can be altered and/or optimized via control of, for example, angles for wedge  210  and cone  220 , the force needed and obtainable by coil  250 , and the maximum size allowable for the linear brake system  200 . Linear brake system  200  includes a connector  248  upon a distal end of rod  240 , and a connector  270  on another end linear brake system  200  via which linear brake system  200  may be attached to, for example, be connected at one end to lower link member  51 U in the suspension system and to side rail  22 L at another end thereof as described above in connection with activatable system  100 . 
         [0052]    In a number of studies hereof, an OMRON® Model D7E-3 tilt switch  300 , available from Omron Electronic Components of Schaumburg, Ill. was used to sense instability. Examples of sensors that may be used in the systems hereof include, but are not limited to, tilt switches or sensors, gyroscopes, accelerometers, camera, microphones, force sensors, etc. Multiple sensors of different types may, for example, be used in a single system. Control thresholds may, for example, be based upon accelerations/decelerations that are in a direction not aligned with travel, or measures of roll, pitch or yaw from, for example, a gyroscope. Alternatively, one could measure the reaction force of each wheel and determine when/if one was going to lose contact, or has lost contact, with the ground. 
         [0053]    A platform or support  350  (see  FIGS. 4A and 4B ) upon which a sensor such as a tilt sensor  300  (that is, a sensor to detect orientation, inclination or tilting) may be supported was developed. Support  350  included a generally U-shaped bracket  360  to which support member  370  is connected. Sensor  300  was attached to support member  370 , which may be angled with respect to a longitudinal orientation L of bracket  360  to adjust the starting orientation or angle of sensor  300  (when no tilting is occurring). The specification sheet for one embodiment of a studied tilt sensor  300  indicated that the sensor would switch at 40 degrees, but the best angle at which wheelchair  10  should be when the switch activates activatable system  100  was unknown at the beginning of the studies hereof and may vary between different types of mobile devices. Therefore, support  350  was made to be adjustable. In that regard, side members  362  of bracket  360  were formed with curves slots or extending passages  368  formed therein. The position of connectors such as bolts used in connection slots  368  may be varied as represented by arrow A in  FIG. 4A  to vary the starting angle of sensor  300 . In a number of embodiments, tilt sensor  300  could be placed at a starting angle in the range between 15 to 45 degrees. 
         [0054]    A circuit, illustrated schematically in  FIG. 5 , for representative tilt switch sensor  300  was developed to be used in connection with activatable systems  100  including MR dampers. The circuit includes a subsystem or control system (for example, including a filter) to selectively activate activatable system  100 . Tilt switch sensor  300 , by itself, might, for example, activate activatable system  100  every time wheelchair  10  hit a bump. Even worse, tilt switch sensor  300  might deactivate activatable system  100  if wheelchair  10  hit a bump while it was on an incline. 
         [0055]    In the circuit of  FIG. 5 , a low-pass filter was used to selectively activate or actuate activatable system  100 . The low-pass filter circuit may, for example, result in activatable system  100  being activated only if tilt switch sensor  300  is on/activated more than 50% of the time or if tilt switch sensor  300  is on/activated for longer than the rise time for the filter. In a number of embodiments, actuation or activation would not occur unless tilt switch sensor  300  is open for longer than approximately one second. 
         [0056]    As illustrated schematically in  FIG. 5B , a control system with appropriate logic is desirable to activate the activatable devices or systems hereof (to, for example, stiffen or lock a suspension system) in those situations or circumstances when desired or required. Circuitry may, for example, be replaced with mechanical systems. Moreover, a processor (for example, a micro-controller or micro-processor) may also or alternatively be used to integrate sensor signals and determine when an instability is occurring or is about to occur, and in-turn trigger activatable system  100 . 
         [0057]    ANSI (American National Standards Institute) and RESNA (Rehabilitation Engineering and Assistive Technology Society of North America) [1, 2] have specific tests that are to be conducted to determine how stable a personal mobility device is and to compare different personal mobility device to each other. To test the actively controlled suspension system of wheelchair  10 , three trials were completed with each test: one with the softest possible suspension (MR Dampers off), one with the stiffest suspension (MR Dampers fully engaged), and one with the active anti-tip system enabled. The ANSI/RESNA tests that were selected to be done are shown Table 1 below. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 ANSI/RESNA Section 
               
             
          
           
               
                   
                 Direction 
                 Description 
               
               
                   
                   
               
             
          
           
               
                 Static Stability 
                   
                   
               
               
                  9.2 
                 Forward 
                 Wheels unlocked and wheelchair in least 
               
               
                   
                   
                 stable configuration 
               
               
                 10.2 
                 Backward 
                 Wheels unlocked and wheelchair in least 
               
               
                   
                   
                 stable configuration 
               
               
                 12.1 
                 Lateral 
                 Wheelchair in the least stable 
               
               
                   
                   
                 configuration 
               
               
                 Dynamic Stability 
               
               
                 10.2 
                 — 
                 Turning on a slope 
               
               
                 10.3 
                 — 
                 Turning in a circle at maximum speed 
               
               
                 10.4 
                 — 
                 Turning suddenly at maximum speed 
               
               
                   
               
             
          
         
       
     
         [0058]    The results of the static stability test are shown in Table 2 below. The results show that the performance of wheelchair  10  with the actively controlled suspension system is statistically the same as the performance with the dampers fully powered. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Static Test 
               
             
          
           
               
                   
                 Tip Angle 
               
             
          
           
               
                   
                 Suspension 
                 Forward 
                 Backward 
                 Lateral 
               
               
                   
                   
               
               
                   
                 Dampers Off 
                 24.0 
                  7.8 
                 4.3 
               
               
                   
                 Dampers on 
                 23.7 
                 10.0 
                 6.1 
               
               
                   
                 Tilt Switch Active 
                 23.8 
                  9.0 (2.0) 
                 5.8 (.9) 
               
               
                   
                   
               
             
          
         
       
     
         [0059]    The results of the dynamic stability tests show the same correlation except for the section 10.2 test. The result obtained in the 10.2 test is believed to be a result of the delay in the circuit being too long and wheelchair  10  starting to tip before tilt switch sensor  300  was activated. The time constant of the low pass filter may, for example, be decreased for wheelchair  10  to pass this test. Table 4 summarizes how the tests and results were obtained. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Dynamic Lateral 
               
             
          
           
               
                   
                 Test Scores 
               
             
          
           
               
                   
                 Suspension 
                 10.2 
                 10.3 
                 10.4 
               
               
                   
                   
               
               
                   
                 Dampers Off 
                 0 
                 2 
                 2 
               
               
                   
                 Dampers on 
                 2 
                 2 
                 3 
               
               
                   
                 Tilt Switch Active 
                 0 
                 2 
                 3 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Wheelchair test ratings 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 Full tip 
                 The wheelchair tips completely over 
               
               
                   
                   
                 (90° or more from its original 
               
               
                   
                   
                 orientation) unless caught by a 
               
               
                   
                   
                 restraining device or testing 
               
               
                   
                   
                 personnel for test purposes 
               
               
                 1 
                 Stuck on anti-tip 
                 The wheelchair anti-tip device(s) 
               
               
                   
                 device 
                 contacts the test plane, and the wheelchair 
               
               
                   
                   
                 remains stuck on the anti-tip device(s) 
               
               
                 2 
                 Transient tip 
                 Less than three wheels remain on 
               
               
                   
                   
                 the test plane at some point 
               
               
                   
                   
                 during the test and then drop back 
               
               
                   
                   
                 on the test plane, whether or not any 
               
               
                   
                   
                 anti-tip devices contact the test plane 
               
               
                 3 
                 No tip 
                 At least three wheels remain on the 
               
               
                   
                   
                 test floor at all times 
               
               
                   
               
             
          
         
       
     
         [0060]    The activatable stability devices, systems and/or methods hereof can improve the stability of mobile devices, including personal mobility devices (whether powered or manual), without substantially effecting the normal operations. In a number of embodiments, the activatable systems here prevent ratings of 0 or 1, or 0, 1 or 2 as set forth in Table 4. In that regard, in a number of embodiment, either full tilting/tipping or sticking/resting on a static anti-tip device of a mobile device or system (including personal mobility devices) is prevented or, any tipping or tilting that does occur is transient. In other embodiments, even transient tipping (wherein in wheel loses contact with the surface) is prevented. 
         [0061]    Studies of anti-tip suspensions including activatable stability devices or systems on a single side of the chair are discussed above. Use of activatable anti-tip or stabilizing devices or systems hereof on each side of, for example, a wheelchair or other mobile device will provide improved performance. Dynamic stability tests may, for example, be used in connection with a particular type of mobile device to ensure that the one or more active stability systems activate only in desired circumstances and not in other circumstances (for example, during obstacle climbing). In the case of control systems including, for example, a low pass filter, the low pass filter (or other control system) characteristics or stationary angle of the tilt sensor base may, for example, be readily adjusted to achieve improved performance. A potentiometer may, for example, be used to adjust sensitivity of the filter. Once again, one or more processors (for example, micro-controllers or micro-processors) may also be used to integrate sensor signals, and classify whether instability is occurring or about to occur. 
         [0062]    In a number of embodiments, the activatable stability device, systems and/or methods hereof may, for example, be activated to decrease travel distance of a suspension or a portion thereof, stiffen dampers or shock absorbers, lock motion of the suspension or a portion thereof etc. as described above. The activatable systems hereof need not be formed integrally with the suspension system of a mobile device. Indeed, the activatable system hereof are readily retrofitted onto mobile system such as personal mobility devices. In a number of embodiments, such mobile systems include a suspension system comprising one or more resilient members such as springs. 
         [0063]    Although representative embodiments of the use of activatable stability devices and/or systems hereof in connection with a suspension system of a mobile device or system are discussed above, the activatable stability devices, systems or methods hereof may be used in connection with manual personal mobility devices (for example, manually operated wheelchairs) and need not be used in connection with a suspension system.  FIG. 6A and 6B  illustrate a representative embodiment of activatable stability systems  500  hereof which includes two activatable devices attached to the rear of a manual wheelchair  10   b.  Each of activatable systems  500  is in operative connection with an abutment member  510  or anti-tip device which is rotatably or pivotably attached to wheelchair  10   b.  In the non-activated state as illustrated in  FIG. 6A , activatable systems  500  maintain abutment member  510  in a first, non-activated or non-actuated state in which abutment member  510  are maintained at a suitable height to prevent interference with normal operation of wheelchair  10   b.  In  FIG. 6B , the activatable system have been activated or actuated (via, for example, a sensor system and control system as described above) to rotate or pivot abutment members  510  to a lower position to increase stability and reduce the likelihood of or prevent tipping. In the illustrated embodiment, abutment members  510  are lowered and raised via actuatable or activatable cylinders  520  which may, for example, be solenoids or hydraulic cylinders. Additional or alternative activatable devices and cooperating abutment members may, for example, be placed at other positions on the wheelchair (for example, on the front and/or sides thereof). 
         [0064]      FIGS. 6C and 6D  illustrate another representative embodiment of activatable stability systems  600  hereof which includes two activatable devices attached to the rear of a manual wheelchair  10   c.  Each of activatable systems  600  is in operative connection with an wheel  610  which is rotatably attached to an extending or outrigger member  620 . In the non-activated state as illustrated in  FIG. 6C , wheels  610  are free to move up and down relative to a surface upon which wheelchair  10   c  is travelling via extending members or rods  630  which move telescopically through cylinders  640 . Rods  630  may, for example, be biased to assist in maintaining wheels  610  in contact with the surface. Upon actuation of activatable system  600 , rod  630  is locked in position or requires increased force to move relative to cylinder  640 , thereby maintaining wheels  610  in contact with the surface and prevent or limit movement thereof up or down relative to the surface. Activatable systems  600  may be activated or actuated via, for example, a sensor system and control system as described above to increase stability and reduce the likelihood of or prevent tipping. Additional or alternative activatable devices and cooperating abutment members may, for example, be placed at other positions on wheelchair  10   c  (for example, on the front and/or sides thereof). In general, manual wheelchairs such as wheelchair  10   c  are unlikely to tip in a lateral direction, but one or more activatable systems similar in operation to activatable systems  600  may, for example, be placed on one or both sides of a powered wheelchair to prevent lateral tipping. Activatable system  600  may, for example be operated to limit tipping and/or to prevent even transient tipping as discussed above. 
         [0065]    The foregoing description and accompanying drawings set forth a number of representative embodiments at the present time. Various modifications, additions and alternative designs will, of course, become apparent to those skilled in the art in light of the foregoing teachings without departing from the scope hereof, which is indicated by the following claims rather than by the foregoing description. All changes and variations that fall within the meaning and range of equivalency of the claims are to be embraced within their scope.