Abstract:
A selectively lockable orthotic joint is provided in which a pressure sensor having a thin layer of variably resistive material generates a control signal when an actuation force is applied to the sensor. An electronic circuit operatively connects the sensor to a mechanical orthotic joint that can be selectively locked and unlocked in response to the control signal. The control signal may be uniform in strength selectively locking and unlocking the joint. The control signal may also be variable in strength wherein the orthotic joint provides increasing or decreasing resistance to motion responsive to a corresponding increase or decrease in control signal strength. The device is suitable for use as a foot/ankle/leg orthotic having a foot sensor which selectively operates a mechanical knee joint.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This is a continuation-in-part of U.S. patent application Ser. No. 10/205,714, filed Jul. 26, 2002, now U.S. Pat. No. 6,770,045 which is a continuation of U.S. patent application Ser. No. 09/398,332, filed Sep. 17, 1999, now U.S. Pat. No. 6,517,503, which claims the benefit under 35 U.S.C. § 119 (e) of U.S. Provisional Application Ser. No. 60/101,084, filed Sep. 18, 1998. 

   FIELD OF THE INVENTION 
   This invention relates generally to orthoses for providing assistance in walking. More particularly, the present invention relates to an improved foot sensor and knee joint for such an orthosis. 
   BACKGROUND OF THE INVENTION 
   An orthosis is a brace or other orthopedic device that is applied or secured to a segment or part of a human body for the purpose of assisting in the restoration or improvement of its function. Orthoses can provide assistance in walking to persons having any of several types of walking disability. One known type of orthosis is a knee/ankle/foot orthosis which controls the motion and alignment of a knee and an ankle when a person attempts to walk. Such orthoses can be made of molded plastic materials or of metal and leather parts. Various knee and ankle joints can be added to achieve the desired function. 
   There are many reasons for wearing such an orthosis, including knee injuries, arthritis, stroke, brain injuries, spinal cord injury and post-polio treatment. A person who is not able to properly move his leg and/or knee joint in a sufficiently functional manner to ambulate may wear a knee/ankle/foot orthosis to stabilize his leg and allow for ambulation. 
   A need exists for an effective knee orthosis that is able to automatically lock and unlock during ambulation without direct manual patient intervention. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with the present invention, there is provided an orthosis for assistance in walking. 
   More particularly, in accordance with one aspect of the invention, the orthosis includes an orthosis system which comprises a foot plate including at least one pressure sensor that senses the pressure exerted by a patient&#39;s foot on the foot plate, a circuit connected to at least one pressure sensor in the foot plate and a knee joint which is selectively locked and unlocked by the circuit. To this end, the knee joint is electrically operated. 
   In accordance with the present invention, a selectively lockable orthotic joint is provided that is capable of locking and unlocking during ambulation by the wearer. The selectively lockable orthotic joint includes at least one pressure sensor which can be used to sense a person&#39;s weight or a portion thereof, and may be a sensor to be associated with a person&#39;s foot, for example. An electronic circuit is provided that is associated with the pressure sensor for generating a control signal indicative of pressure or weight sensed by the sensor. At least one mechanical orthotic joint that incorporates a locking mechanism is included which orthotic joint can be selectively locked and unlocked in response to the control signal. 
   More particularly, in accordance with one embodiment of the invention, the mechanical orthotic joint of the selectively lockable orthotic joint invention includes an energizable electromagnetic coil, a spring washer deflectable in an axial direction when the electromagnetic coil is energized and an arrangement of first and second plates. The first plate has a face or an operative surface composed of a plurality of spaced teeth. The second plate also has a face or an operative surface having a plurality of spaced teeth that are complementary to the plurality of spaced teeth of the first plate. The second plate is mounted so that it is deflectable in an axial direction such that the plurality of spaced teeth of the second plate can engage the plurality of spaced teeth of the first plate when the electromagnetic coil is energized. The engagement of the first and second plates locks movement of the orthotic joint in at least one direction when the first and second plates are engaged. 
   In accordance with one embodiment, the first and second plates are complementary and each comprise ratchet plates allowing the orthotic joint to move only in one direction when the joint is in a locked position. More specifically, in one embodiment, when unlocked the orthotic joint is movable in a flexion direction and an extension direction and when the orthotic joint is locked, it is movable only in the extension direction. 
   The first and second plates may comprise a low hysteresis magnetic material. 
   In accordance with another aspect of the present invention, a method for selectively locking and unlocking an orthotic joint is provided. One embodiment locks the orthotic joint to permit movement only in the extension direction. 
   In accordance with another aspect of the invention, any suitable knee joint can be utilized in conjunction with the pressure sensor and electronic circuit as long as the knee joint can be selectively locked and unlocked by operation of the electronic circuit during ambulation by the wearer. 
   In accordance with the method, an orthotic joint of the type previously described is utilized. Pressure is sensed by the pressure sensor and an electronic control signal is generated with the electronic circuit that is indicative of pressure sensed by the pressure sensor. In response to the electronic control signal, the orthotic joint locks through its locking mechanism. 
   One advantage of the present invention is the provision of a knee joint which allows patients, who are currently walking stiff legged with a locked knee joint in a knee/ankle/foot orthosis, to walk with a more normal gait. 
   Another advantage of the present invention is the provision of an orthosis which will make sifting and standing much safer and easier for any patient forced to manually unlock his knee joint. 
   Still another advantage of the present invention is the provision of an orthosis system that senses the pressure placed by a patient&#39;s foot on a foot plate or portion of the orthosis and can automatically trigger a knee joint of the orthosis to lock and unlock. The knee joint will be locked when pressure is placed by the patient&#39;s foot on the foot plate, such as pressure above a threshold amount. It will be unlocked when the patient&#39;s foot no longer exerts pressure on the foot plate which may be the same or a different pressure from the threshold amount. 
   In accordance with another aspect of the invention, a selectively lockable orthotic joint is provided. The selectively lockable orthotic joint includes an electronic circuit for providing at least one control signal indicative of a value. At least one mechanical orthotic joint is provided that includes a locking mechanism that is in communication with the circuit. The locking mechanism can be selectively locked and unlocked in response to the control signal. The control signal provided by the electronic circuit can originate from a variety of sources other than by sensing pressure or weight. For example, the control signal can originate from EMG signals in leg muscles, from EEG signals, from a sensor that detects distance between the ground and the bottom of a shoe or other article, such as a cane, for example. In addition, a controller could be provided for operation by the user, such as a joy stick or other type of switch in order to generate or otherwise provide the control signal for locking and/or unlocking the locking mechanism of the mechanical orthotic joint. 
   In accordance with another aspect of the invention, the control signal is generated responsive to a compressive force detected by a pressure sensitive foot sensor. The foot sensor includes a layer of variably resistive material which resistance changes, typically decreases, in electrical resistance when a compressive force having a force component above a threshold force normal to the layer is applied thereto. The variably resistive material becomes conductive upon the application of a force above a threshold force whereupon conductive elements in communication with either side of the variably resistive material close the circuit thereby generating the control signal. The variably resistive material may have either uniform or variable resistance resulting in either a uniform or variable control signal. In one embodiment of the invention, presence of the uniform control signal locks the mechanical joint and absence of the uniform control signal unlocks the joint. 
   In an alternative embodiment, an orthosis composed of a foot sensor and an electronic circuit that generates a signal or signals proportional to or related to the force sensed by the foot sensor, together with any suitable knee joint as may be known in the art capable of providing varying degrees of resistance to movement or rotation is provided in which a variable control signal proportional to the force applied to the foot sensor may either resistively close the mechanical joint (increase the resistance to movement of the joint) or fully lock the mechanical joint. As greater force is applied to the sensor, the control signal increases in strength increasing the resistance to movement of the mechanical joint or locking the joint altogether. A decrease in the force applied to the sensor reduces the resistance of the mechanical joint with an absence of the control signal or a signal below a threshold eliminating all resistance. 
   In accordance with another aspect of the invention, the conductive elements are shaped to contact the variably resistive material at discrete zones. The zones correspond to contact points along the underside of the foot and may include a heel zone, a metatarsal zone and a toe zone. Each region may be further divided into sub-zones. 
   In accordance with another aspect of the invention, the variably resistive material may be divided into discrete regions as desired, for example, corresponding to contact areas of the foot such as the toe region, the metatarsal region and the heel region. The regions may have differing threshold forces. Each region may also be configured to generate either a uniform or variable control signal based on the needs of the orthotic wearer. 
   Still other benefits and advantages of the invention will become apparent to those of average skill in the art upon a reading and understanding of the following detailed specification. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangements of parts, various preferred embodiments of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof and wherein: 
       FIG. 1A  is a side elevational view in cross section along line  1 A- 1 A of  FIG. 13  of a knee joint according to the present invention in an unlocked condition; 
       FIG. 1B  is a side elevational view in cross section of the knee joint of  FIG. 1A  in a locked condition; 
       FIG. 2A  is a top plan view of the toroidally shaped housing of the joint of  FIG. 1A ; 
       FIG. 2B  is a cross-sectional view taken along line  2 B- 2 B of  FIG. 2A ; 
       FIG. 3A  is a top plan view of a bottom ratchet plate of the knee joint of  FIG. 1A ; 
       FIG. 3B  is a side elevational view in cross section along line  3 B- 3 B of  FIG. 3A ; 
       FIG. 4A  is a bottom plan view of a top ratchet plate of the knee joint of  FIG. 1A ; 
       FIG. 4B  is a side elevational view in cross section along line  4 B- 4 B of  FIG. 4A ; 
       FIG. 5A  is a top plan view of the top end portion of the knee joint of  FIG. 1A ; 
       FIG. 5B  is a side elevational view in cross section taken along line  5 B- 5 B of  FIG. 5A ; 
       FIG. 6  is a top plan view of an inner retaining ring of the knee joint of  FIG. 1A ; 
       FIG. 6A  is a cross-sectional view along lines  6 A- 6 A of  FIG. 6 ; 
       FIG. 7  is a top plan view of the retaining cap of the knee joint of  FIG. 1A ; 
       FIG. 7A  is a cross-sectional view along line  7 A- 7 A of  FIG. 7 ; 
       FIG. 8  is a top plan view of an outer retaining ring of the joint of  FIG. 1A ; 
       FIG. 9  is a top plan view of a spring washer of the joint of  FIG. 1A ; 
       FIG. 10  is an exploded perspective view of components of the knee joint of  FIG. 1A ; 
       FIG. 11  is a circuit diagram of a circuit which is employed with the knee joint of  FIG. 1A  and the force or pressure sensor of  FIG. 12 ; 
       FIG. 12  is a perspective view of the force or pressure sensor employed with the joint of  FIG. 1A ; 
       FIG. 13  is a perspective view of an orthosis in accordance with the invention incorporating the joint of  FIG. 1A  and the sensor of  FIG. 12 ; 
       FIG. 14  is a fragmentary perspective exploded view of an alternate embodiment joint in accordance with the invention; 
       FIG. 15  illustrates a cross-sectional schematic view of a portion of the alternate embodiment of  FIG. 14 ; 
       FIG. 16  illustrates a perspective view of an alternate embodiment of a foot sensor in accordance with the invention; 
       FIG. 17  is a sectional view of the foot sensor taken along line  17 - 17  of  FIG. 16 ; 
       FIG. 18  is an exploded schematic view of the foot sensor of  FIG. 16 ; 
       FIG. 19  is a perspective view of an alternate embodiment of the foot sensor in accordance with the present invention; and 
       FIG. 20  is a perspective view of an alternate embodiment of the foot sensor in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to the drawings wherein the drawings are for purposes of illustrating preferred embodiments of the invention only and not for purposes of limiting same,  FIGS. 1A and 1B ,  10  and  13 , for example, show a knee joint  10  which is used in an orthosis  10 ′ or orthopedic appliance, for example in  FIG. 13 . It is evident that two such knee joints would need to be employed for the two legs of a patient, one joint for each leg of the patient. Perhaps, even four knee joints could be used, one on either side of the knee of each leg of the patient. It is to be understood that joint  10  could be used other than as a knee joint, for example. 
   Joint  10  includes a toroidally shaped housing  12 . Toroidally shaped housing  12  is depicted individually in  FIGS. 2A and 2B . With reference now to  FIGS. 2A and 2B , the toroidally shaped housing  12  has an inner wall  14 , a base wall  16  and an outer wall  18  which together define a cavity  20 . A plurality of spaced teeth  22  protrude upwardly from the inner wall  14 . Preferably, eight such teeth are provided, although any suitable number of teeth can be utilized. A continuous flange  24  extends upwardly from the outer wall  18 . A rib  26  extends radially inwardly from the inner wall  14  into a central opening  28  to form a toroidal ledge  26 ′ approximately half way up the height of the inner wall. 
   With reference again to  FIGS. 1A and 1B  and  10 , an electromagnetic coil  30  is located in cavity  20 . Electromagnetic coil  30  is formed around a plastic bobbin  32 . Positioned on either side of rib  26  are a first bearing  34  and a second bearing  36 . The bearings can be conventional roller bearings or other suitable bearings, as desired. A bottom ratchet plate  38  is also provided for the knee joint. Bottom ratchet plate  38  is depicted in greater detail in  FIGS. 3A and 3B . Bottom ratchet plate  38  includes a planar bottom surface  40 , as illustrated in  FIG. 3B , and a top face  42  having a plurality of radially extending spaced teeth  44  protruding therefrom. As is evident from  FIG. 3A , sixty such teeth  44  are preferably located on the top face  42  with each tooth being spaced from the adjacent teeth by slots, although any suitable number of teeth can be utilized. Preferably, the teeth  44  are cut in a saw tooth pattern radially at a 30 degree is slope. A set of eight spaced slots  46  are cut into the bottom ratchet plate  38 . The slots extend radially outwardly from a central opening  48  of the plate  38  as is evident from  FIG. 3A . 
   The joint of  FIGS. 1A and 1B  is further provided with a top ratchet plate  50 , which is shown in more detail in  FIGS. 4A and 4B . Top ratchet plate  50  is preferably constructed of a magnetically soft material, for example a low hysteresis, solenoid quality magnetic stainless steel. Bottom plate  38  may be constructed of similar material. With reference now to  FIG. 4B , top ratchet plate  50  includes a top face  52  ( FIG. 4B ) and a bottom face  54 . A plurality of spaced teeth  56  are cut into the bottom face  54 . Preferably sixty such teeth are provided. As with the bottom plate  38 , the teeth  56  in the top plate are cut in a saw tooth pattern radially at a 30 degree slope such that a tip of each tooth is separated from a tip of each adjacent tooth by 6 degrees. Teeth  56  of top ratchet plate  50  are meant to be and should be of suitable design and number to engage and mesh with teeth  44  of bottom ratchet plate  38  when the two ratchet plates are brought into contact with each other. Also provided on top ratchet plate  50  is a slot  58  which circumscribes the teeth  56 . A plurality of spaced apertures  60 ′ extend through top ratchet plate  50 . These apertures are positioned radially outwardly of slot  58 . As is evident from  FIGS. 1B and 10 , suitable fasteners  60  can extend into the top ratchet plate apertures. 
   With reference now to  FIGS. 1A ,  1 B and  10 , a shaft  62  is also provided. As shown in  FIGS. 5A and 5B  shaft  62  includes a stem portion  64  and an enlarged top end  66  having a set of spaced apertures  68  extending therethrough. Note that in  FIGS. 5A and 5B , the diameter of flange  66  is illustrated smaller than the diameter illustrated in the other figures. A bottom end of the stem portion  64  is provided with a centrally located aperture  70 . Each of these apertures accommodates suitable fasteners  60  and  61 . Referring to  FIGS. 1A and 1B , also provided is an inner retaining ring  72 . As detailed in  FIG. 6 , inner retaining ring  72  has a central aperture  72 ′ for accommodating stem portion  64  and includes a set of apertures  74  extending therein. Each of apertures  74  is also meant to accommodate a suitable fastener  60 . A retaining cap  76  is also provided. As shown in  FIGS. 7 and 7A , retaining cap  76  has a centrally extending aperture  78  for accommodating a suitable fastener  61 . Fasteners  60  and  61  can be threaded fasteners or any other suitable type of fastener, for example. 
   Joint  10  is also provided with an outer retaining ring  80 . As shown in  FIG. 8  a set of apertures  82  extend through retaining ring  80  to accommodate suitable fasteners  60 . As shown in  FIGS. 1A ,  1 B,  9  and  10 , a spring washer  84  is further provided. Spring washer  84  is preferably comprised of a plurality of very thin pieces of metal which, when assembled, is very compliant in an axial direction while maintaining a high rigidity in torsion. For example, spring washer  84  may consist of approximately 60 pieces of 0.001 inch thick stainless steel disks. The axial compliance allows the spring washer to be deflected at relatively low electromagnetic forces allowing the upper ratchet plate to mesh with the lower ratchet plate. Spring washer  84 , further depicted in  FIG. 9 , has a set of outer apertures  86  for accommodating a suitable first set of fasteners  60  and a set of inner apertures  88  similarly for accommodating a suitable second set of fasteners  60 . Spring washer  84  also has a central opening  90  to accommodate stem portion  64  of shaft  62 . 
   Spring washer  84  is very compliant in the axial direction, permitting deflection of upper ratchet plate  50  even with relatively low electromagnetic attraction forces, typically deflecting about 1/16 th  of an inch in an axial direction with an electromagnetic force of several pounds. Thus, the significant axial deflection that is obtained with low electromagnetic forces permits operation of joint  10  at low power consumption levels which is important for battery-operated use. Spring washer  84 , however, is strong and stiff in torsion, providing the necessary reaction torque to support the moments required in an orthotic application. Any suitable washer that performs the function of spring washer  84  can be utilized in accordance with the invention. 
   As is evident from  FIGS. 1A ,  1 B and  10 , shaft  62  is located in central opening  28  of toroidally shaped housing  12 . Retaining cap  76  is fastened to shaft  62  by fastener  61 . In this way, two bearings  34  and  36  can be secured in place in central opening  28  of housing  12 . Bottom ratchet plate  38  is seated on inner wall  14  of housing  12 . To this end, several spaced slots  46  in bottom ratchet plate  38  accommodate several spaced teeth  22  in housing  12 . More particularly, eight slots  46  and eight teeth  22  are provided in housing  12 . It is apparent that no keying is necessary since bottom ratchet plate  38  can be rotated in relation to the housing to any desired extent so long as the slots  46  are aligned with teeth  22 . 
   Top ratchet plate  50  is positioned above bottom ratchet plate  38 . In the condition illustrated in  FIG. 1A , top ratchet plate  50  is spaced from bottom ratchet plate  38 . This allows a movement of joint  10  in either rotational direction (flexion or extension). In the position illustrated in  FIG. 1B , the teeth of top ratchet plate  50  engage the teeth of bottom ratchet plate  38  to prevent any further rotation of the joint. Preferably, the two ratchet plates are spaced from each other as indicated when in the unactuated state as shown in  FIG. 1A . 
   With reference again to  FIG. 1A , spring washer  84  is fastened to flange  66  of shaft  62  via inner retaining ring  72 . Spring washer  84  is also fastened to top ratchet plate  50  and outer retaining ring  80  by fasteners  60 . In this way, top ratchet plate  50  is normally spring-biased away from bottom ratchet plate  38 . However, top ratchet plate  50  is pulled into contact with bottom ratchet plate  38  when electromagnetic current is flowing through electromagnetic coil  30 . 
   With reference now to  FIG. 11 , a controller  101  which includes an integrated circuit  100 ′, which can be a Microchip Model No. PIC16C715, is employed to control the operation of joint  10 . The integrated circuit is preferably powered by a pair of 3 volt batteries  102  and  104 . Electromagnetic coil  30  is preferably powered by a pair of 1.5 volt batteries  106  and  108 . 
   With reference now to  FIG. 12 , an insole pressure or foot force sensor  110  is also used in connection with the joint  10 . More particularly, a set of output lines  112  lead from a set of sensors  114  in the insole to circuit  100 . Batteries  102  and  104  provide a reference signal for the sensors. A pair of output lines  116 ′ from circuit  100  extend to the electromagnetic coil  30 . The pair of 1.5 volt batteries  106  and  108 , which are of relatively higher power than the power of the 3 volt batteries, are meant to power the electromagnetic coil. 
   Insole pressure sensor  110  is preferably provided with five sensors which detect pressure by a voltage drop across very thin resistors, for example the foot force sensor provided by Cleveland Medical Devices, Inc. It should be apparent to one skilled in the art that more or less sensors may be used. The insole is slipped inside a patients shoe. The signal from the insole is translated through wires  112  to circuit  100 . Integrated circuit  100 ′ also contains a programmable microprocessor. Any suitable microprocessor can be utilized. The processor determines a threshold level and sends a signal to the joint  10  attached to a knee joint as depicted in  FIG. 13 . However, the joint need not be limited to a knee joint, but may also be an ankle, wrist or elbow joint. Any suitable pressure or force sensor can be used in accordance with the invention. 
   With the orthosis of the present invention, when a person puts his foot on the floor, the sensors  114  in insole sensor  110  sense a pressure and can trigger the joint  10  to lock by energizing electromagnetic coil  30  thereby bringing the top ratchet plate  50  down into contact with bottom ratchet plate  38  engaging respective teeth  56  and  44 . Preferably, this action prevents any further rotation of the joint in one rotational direction, however, this may lock the joint entirely from rotating. More particularly, top ratchet plate  50  and shaft  62  cannot rotate via bearings  34  and  36  in relation to bottom ratchet plate  38  and housing  12  toward a bent knee position. Preferably, when the teeth of the upper and lower ratchet plates are engaged, the joint allows incremental slip (ratcheting) in a joint extension. However, when no more pressure is sensed by sensors  114  of the insole sensor  110 , controller  101  will unlock the knee joint by ceasing the flow of electric current in the electromagnetic coil. 
   Once this occurs, spring washer  84  will pull top ratchet plate  50  out of engagement with bottom ratchet plate  38 . This will allow a rotation of the knee joint in both directions. In particular, top ratchet plate  50  and shaft  62  are again capable of rotating in relation to bottom ratchet plate  38  and housing  12 . Thus, the joint is unlocked when pressure of the patient&#39;s foot is no longer exerted on the insole sensor  110 . This invention will allow a user who is currently wearing stiff legged knee/ankle/foot orthoses to walk with a more normal gait. In addition, it will make sitting and standing safer and easier for any user currently forced to manually unlock their knee joint. 
   When a threshold level is reached, a magnetic field is generated by electromagnetic coil  30  to pull top ratchet plate  50  into engagement with bottom ratchet plate  38 , no longer allowing the two ratchet plates to rotate freely in relation to each other. This locks the knee joint and prevents it from bending into flexion. However, the joint will still allow extension. As an example, if the patient is attempting to stand and gets stuck halfway up, the joint will block flexion and prevent the patient&#39;s knee from buckling. But, it will still ratchet into extension and allow the patient to continue moving vertically. Thus, a very important advantage of the present invention is the provision of a knee joint in which flexion is prevented when the top ratchet plate  50  meshes with bottom ratchet plate  38  but extension is still allowed. This is accomplished due to the orientation of the meshing teeth  44  and  56  of the bottom and top ratchet plates  38  and  50  respectively. 
   As a second example, a user, when he takes a step, will have the insole read the floor contact and lock the knee for the user. The knee remains locked through the step and then unlocks when the user initiates swing through, i.e. takes the pressure off the first leg and puts the pressure on the second leg. The knee joint will then lock again at the next initial floor contact. 
   Sensors  114  could be wired in series or in parallel for the signal which is sent through wires  112  to controller  101 . Preferably, the output of all of sensors  114  is summed together. If a set point is reached, electromagnetic coil  30  is triggered and the knee joint is locked. However, the logic of the chip on the integrated circuit could be programmed to differentiate between, e.g. a heel strike and a toe strike of the foot plate. The logic of the circuit may also provide that given patterns of pressure, for example placing pressure on only inner or outer pressure sensors, detected by the sensors could disengage the teeth in the joint permitting an individual to sit. 
   Joint  10  according to the present invention can be attached to any conventional knee/ankle/foot/elbow/wrist orthosis or any knee brace as long as the brace is fabricated to the joint size specification. A person skilled in the art should realize that the orthotic joint of the present invention supports passive locking arrangements wherein the joint is locked until the coil is magnetized which unlocks the joint as opposed to the active locking embodiment of the joint as described above. 
     FIGS. 14 and 15  illustrate an alternate embodiment of an electronically controlled orthotic joint according to the present invention. This embodiment as shown in  FIGS. 14 and 15  provides an electromagnetic coil  118  located within a housing  120 . Actuating portion  122  is provided as well as opposing teeth inserts  124  and  126 . Engagement of the teeth inserts  124  and  126  is actuated by energizing coil  118 . The coil is energized under control of a microprocessor (not shown) as in the above embodiment. Energizing the coil produces an axial force on actuating portion  122  which forces teeth insert  124  into engagement with teeth insert  126 . In this embodiment, a passive spring (not shown) causes the teeth of teeth inserts  124  and  126  to disengage upon interruption of current through coil  118 . This embodiment can also provide for incremental slip in a single rotational direction as desired. Further, teeth inserts  124  and  126  are constructed of non-magnetic material so that they may be made of a more durable material, for example tool steel. This embodiment also provides a spline interface (not shown) between outer support ring  130  and actuating element  122 . This spline interface is on the internal surface of outer support ring  130  and the external surface of actuating element  122 . This spline interface permits axial translation of actuating element  122  while enabling large torques to be transmitted from outer support ring  130  to actuating element  122 . This arrangement permits application of large torques from outer support ring  130  to the opposite outer support ring  128  as follows. Torques are transmitted from element  130  to element  122  via the spline interface. Torques are thus transmitted from actuator element  122  to teeth insert  124 , which is fastened rigidly to element  122 . When engaged due to actuation (axial translation of element  122 ), teeth insert  124  meshes with teeth insert  126  enabling transmission of torques that oppose knee flexion. Teeth insert  126 , rigidly fastened to housing  120 , transmits torques to housing  120  via its fasteners. Finally, housing  120 , which is rigidly fastened to outer support ring  128 , transmits torque to outer support ring  128  via fasteners (not shown). In this manner, torques can be transmitted from support arm  132  of outer support ring  130  to support arm  134  of the opposite outer support ring  128 . Support arms  132  and  134  provide a convenient structure to mechanically interface the locking mechanism to orthotic bracing. One skilled in the art should recognize that an equal and opposite torque is transmitted to outer support ring  128  and support arm  134  in a similar manner. 
   Referring to  FIG. 14 , a stop  136 , which can be integral to outer support arm  132 , and a complementary stop (not shown), approximately 180° away from stop  136 , acts to interface with arm  134  to mechanically limit the range of relative rotation between outer rings  128  and  130 . This feature can be used to prevent hyperextension. 
     FIG. 14  depicts how joint  117  is integrated into an orthotic device. Outer support rings  128  and  130  house joint  117 . As shown in  FIG. 14 , joint  117  is comprised of an electromagnetic coil  118 , housing  120 , actuating portion  122 , and teeth inserts  124  and  126 . The outer support rings are constructed of non-magnetic metallic material. Outer support ring  130  has an attached support arm  132  which attaches to a limb portion of a patient. Similarly, outer support ring  128  has a support arm  134  that attaches to the same limb portion of a patient as support arm  132 , but joint  117  is aligned with the patient&#39;s joint which is to be supported. 
     FIGS. 16-20  show alternate embodiments of foot sensors in accordance with the present invention. These foot sensors can be utilized in orthosis  10 ′ in place of foot force sensor  110  together with any desired or needed changes to or replacements for controller  101  or circuit  100 , or to joints  10  or  117 , as will be evident to those skilled in the art. In  FIGS. 16-18 , a foot sensor  200  is provided and may be configured in the general shape of a shoe insole suitable to fit into the shoe of a person wearing orthosis  10 ′. Foot sensor  200  preferably includes moisture barrier  202   a  and  202   b , conductive layers or plates  204   a  and  204   b , and a layer  206  of variably resistive material as best seen in  FIG. 18 . Layer  206  is typically elongated and relatively thin. Layer  206  of variably resistive material includes a plurality of small conductive particles dispersed or suspended as normally discontinuous phase within a resilient compressive material such as rubber. The conductive particles may be any suitable conductive material as is commonly known in the art. Examples include, but are not limited to, conductive metal, carbon or graphite. The material of layer  206  displays high resistance or is otherwise insulative when in an uncompressed state. When a compressive force or pressure above a threshold force is applied normal to an area of layer  206 , the conductive particles contact each other, lowering the resistive state in that area, making the variably resistive material of layer  206  conductive in that area. Within design limits or variations for the material, a force or pressure equal to or below the threshold force in that area may compress layer  206  to some extent. It is understood, however, again within design limits or variations for the material, that a force equal to or below the threshold force will not adequately lower the resistance of layer  206  to make layer  206  conductive. Layer  206  can be continuous or discontinuous and its presence in a particular area of foot sensor  200  provides an area that will sense pressure. 
   Conductive layers or plates  204   a  and  204   b  sandwich the layer  206  of variably resistive material so as to be in operative communication with layer  206  as shown in  FIGS. 17 and 18 . Plates  204   a  and  204   b  are preferably thin, malleable sheets of metal foil with resilience to withstand compressive forces from the foot of a person during activities such as standing, walking, climbing stairs and moving from a sitting to a standing position or vice versa. It is understood that any type of metal or conductive material may be used for conductive plates  204   a  and  204   b  with brass, copper, aluminum, steel or stainless steel preferred. Most preferred are 0.002 inch brass plates  204   a  and  204   b . Each conductive plate  204   a  and  204   b  may take other forms including, but not limited to, a mesh, a screen, a wire, a plurality of wires or any combination of the same. 
   Electrodes  208   a  and  208   b  ( FIG. 17 ), which may be integral to conductive plates  204   a  and  204   b  respectively, extend from plates  204   a  and  204   b  respectively to provide a surface upon which wires  209   a  and  209   b  may be attached. Wires  209   a  and  209   b  extend to controller  101  as cord  211 . Contact between electrodes  208   a  and  208   b  and wires  209   a  and  209   b  may be established by any suitable means as commonly known in the art, including but not limited to, soldering or securing in place with insulative tape. Electrodes may be protected by means commonly known in the art such as with insulative tape or a plastic sleeve, for example.  FIG. 16  shows electrodes  208   a  and  208   b  extending from the heel portion of sensor  200  although it is understood that electrodes  208   a  and  208   b  can extend from any area of sensor  200 . 
   Moisture barriers  202   a  and  202   b  encase the layer  206  of variably resistive material and conductive plates  204   a  and  204   b . Moisture barriers  202   a  and  202   b  are made from a water-resistant or water repellent material such as, but not limited to, rubber or flexible plastic. This protects plates  204   a ,  204   b  and layer  206  from foot moisture, or external types of wetness typically encountered when wearing shoes outdoors such as water seepage from rain or puddles, for example. Moisture barrier  202   a  is attached to moisture barrier  202   b  by any suitable means as is commonly known in the art such as adhesively bound, stitched or a combination thereof. Alternatively, moisture barriers  202   a  and  202   b  may be integral to each other. In any event, moisture barriers  202   a  and  202   b  are made of an insulative, non-conductive material. One suitable moisture barrier is marketed under the name DYCEM® by Dycem USA of Rhode Island. 
   Provision of a force above the threshold force by the foot of a person onto sensor  200  (i.e., normal to the surface of sensor  200 ) brings the conductive particles of layer  206  into contact yielding a conductive path or a plurality of conductive paths through layer  206 . This establishes a closed circuit between conductive plates  204   a  and  204   b  and controller  101 . Controller  101  then generates and sends a control signal to orthotic joint  10  as long as a compressive force greater than the threshold force, i.e., an actuation force, is maintained on sensor  200 . A compressive force less than or equal to the threshold force fails to adequately reduce the resistance of layer  206  thereby opening the circuit between conductive plates  204   a  and  204   b . This terminates generation of the control signal by controller  101 . It is understood that plates  204   a  and  204   b  may be considered one component which closes the circuit when an actuation force is applied upon sensor  200 . 
     FIGS. 17 and 18  show one embodiment of sensor  200  wherein plates  204   a ,  204   b  are substantially coextensive with the layer  206  of variably resistive material. An actuation force anywhere on the surface of plate  204   a  coextensive with plate  204   b  and layer  206  will close the circuit between plate  204   a , layer  206  and plate  204   b  and thereby generate a control signal. In like manner, a plurality of actuation forces anywhere upon the surfaces of plates  204   a  and  204   b  will close the circuit between plates  204   a  and  204   b . The skilled artisan will recognize that layer  206  may incorporate any number of resilient compressive materials thereby providing a wide range of possible resistances and concomitant actuation forces as desired. 
   In an alternate embodiment, a sensor  210  comprises a conductive plate or layer  212  in communication with layer  206  of variably resistive material as shown in  FIG. 19 . Conductive plate  212  is shaped to communicate with layer  206  at discrete zones or contact points. Conductive layer  212  comprises a heel zone  214 , a front zone  216  and a connecting portion  218  connecting the two zones. It is understood that the conductive plate on the underside of sensor  210  may be the same shape as conductive plate  212  or may be substantially coextensive with layer  206  or to the entire overall extent of sensor  210 . Similarly, layer  206  may be modified to conform to the shape of conductive plate  212  or to only portions thereof (not shown), for example, such as to only a portion of heel zone  214  and front zone  216 . An actuation force or a plurality of actuation forces occurring anywhere along the surfaces of zones  214  and  216  or connecting portion  218  where layer  206  is present will produce a closed circuit with layer  206  and the underside conductive plate thereby generating a control signal. Sensor  210  may be enclosed in a water-resistant material as previously described. 
     FIG. 20  depicts an alternate embodiment of a sensor  220  in accordance with the invention. A conductive plate  222  communicates with layer  206  of variably resistive material at a plurality of toe zones  224   a - c , a heel zone  226  and a connecting portion  228 . The conductive plate (not shown) on the underside of layer  206  may be the same shape as conductive plate or layer  222  or may be substantially coextensive with material  206 . Alternatively, layer  206  may be modified to replicate the shape of conductive plate  222  or desired portions thereof, such as toe zones  224   a - c  and heel zone  226 . Thus, layer  206  may be discontinuous. An actuation pressure or a plurality of actuation pressures anywhere along the surfaces of toe zones  224   a - c , heel zone  226  or connection portion  228  (if layer  206  is present thereunder) will produce a closed circuit through at least a portion of layer  206  and the underside conductive plate is thereby producing a control signal. Sensor  220  may be encased with a water-resistant material as previously described. 
   A suitable material for layer  206  is sold under the name ZOFLEX by Xilor, Inc. of Knoxville, Tennessee. ZOFLEX is a pressure sensitive conductive rubber having high resistance when an applied force or pressure is below the actuation pressure. Typical thickness for such material is in the range of about 0.02 to 0.06 inches. 
   The control signal generated when an actuation force is placed upon the sensor may be uniform or variable. A uniform control signal is generated when the pressure sensitive conductive component has uniform resistance. In this arrangement, layer  206  acts as an on/off switch and remains in a non-conductive state until a compressive force greater than the threshold force is applied to the sensor. When an actuation force is applied to the sensor, the circuit is closed between the conductive layers or plates and controller  101 . Consequently, controller  101  generates a constant control signal uniform in signal strength. Hence, regardless of the sensor area exposed to the actuation force or the magnitude of the actuation force in excess of the threshold force, the signal produced by controller  101  remains constant. In this arrangement, the control signal pulls the top ratchet plate  50  into contact with bottom ratchet plate  38  thereby locking joint  10  in at least one rotational direction. Orthotic joint  10  may be configured to allow extension but prevent flexion or prevent extension and allow flexion or prevent both extension and flexion as desired. A force less than or equal to the threshold force terminates generation of the control signal thereby unlocking joint  10 . 
   In an alternate embodiment, the control signal may be variable in strength. This occurs when the layer of variable resistant material has a variable resistance as a function of a pressure or force applied thereto in a direction normal to the surface of the layer. In other words, the conductivity of layer  206  is proportional to the compressive force applied to the sensor. Once the threshold force is exceeded, additional compressive force applied to the sensor or an increase in the area of the sensor exposed to an actuation force increases the conductivity of layer  206 . In this embodiment, controller  101  produces a low strength control signal when a force just above the threshold force is applied. The control signal gains in strength as the compression force upon the sensor increases. The greater the compression of layer  206 , the greater the control signal strength and vice versa. The size of the sensor area exposed to the actuation force may also be used to determine the control signal strength in like manner. In any case, an orthotic joint may be configured and used to receive the variable control signal. An orthotic joint may be configured in a manner known in the art to produce incremental or gradual resistance to motion proportional to the strength of the control signal. For example, top plate  50  and bottom plate  38  may have rounded or smooth teeth or no teeth at all. As the magnitude of the actuation force increases, top plate  50  and bottom plate  38  contact each other to provide resistance to motion in at least one rotational direction. This resistance to motion increases as the actuation force increases and decreases as the actuation force decreases. Joint  10  may be configured to fully lock upon reception of a defined control signal strength or maximum signal strength. Alternatively, a frictional resistance type joint may be used where the amount of frictional resistance is proportional to the strength or weakness of the control signal as desired. 
   One of ordinary skill in the art will realize that many factors may influence the threshold force of the sensor. For example, it is desirable to adjust the threshold force of the sensor to accommodate the size and/or weight of the person using or wearing orthotic device  10 ′. The threshold force may be adjusted by selecting materials having differing resistances for the variably resistive material component or by programming controller  101 . Correspondingly, the sensor threshold force may be lower for a child or an elderly person than for an adult male, for example. The anticipated activity of the wearer may also be taken into account and the device adjusted accordingly. 
   In addition, the sensor may be adapted to accommodate the degree of ambulation and/or gait of the orthotic wearer. The pressure points upon the foot sensor may vary dramatically between wearers. For example, a person having a foot or a foot/leg prosthesis may have a different foot pressure profile than a person having a natural foot. In an alternate embodiment, the sensor comprises a layer of variably resistive material divided into a plurality of discrete regions. The regions may be directly adjacent to each other. Alternatively, any space between the discrete regions of variably resistive material may be filled by a non-conductive substrate shaped to conform to the insole of a shoe. Each region may correspond to foot pressure points adaptable to the specific needs of the user. The regions may include, but are not limited to, a toe region, a metatarsal region, and a heel region, for example. Each region may be further divided into sub-regions—i.e., a region for each toe or front and rear heel sub-regions, for example. Each region or sub-region may comprise variably resistive material having differing threshold forces as dictated by the needs of the orthotic device wearer. In addition, the sensor may include regions composed of variably resistive material having either uniform or variable resistance. Thus, the combinations between types of variably resistive material, the number and size of regions, and the threshold force for each region is virtually unlimited. For example, variably resistive material having uniform resistance may be used at strong pressure point regions, such as the heel region or the metatarsal region. This arrangement is useful so that ordinary leg and foot movement that occurs during sitting will not yield an actuation force and subsequent generation of a control signal. As the wearer begins to stand, the shift in weight to the foot sensor produces an actuation force and a concomitant uniform control signal. Device  10 ′ is preferably configured to prevent flexion but allow extension movement upon receipt of this control signal. 
   During walking, an actuation force anywhere along the sensor may generate a uniform control signal. It is understood that different regions of the sensor may comprise variably resistive material requiring differing actuation forces. For example, the heel region may require a greater actuation force than the toe region. 
   Alternatively, variably resistive material with variable resistance may also be used on the heel region, the metatarsal region and the toe region. Each region may be configured to require a different actuation force as desired. During the walking cycle, for example, an actuation force on the heel region may occur as the heel first contacts the walking surface. This initial force may generate a variable control signal limiting, but not preventing, flexion movement of the lower leg with the signal gaining in strength as the heel region receives greater force. As the walker&#39;s weight transfers to the metatarsal region of the foot, an actuation force may generate a variable signal which combines with the signal from the heel region to completely lock joint  10 . As weight transfers off of the heel region to the metatarsal region and toe regions, the reduction in force on the heel region may reduce the signal strength of the control signal thereby allowing flexion movement. Continuing through the walking cycle, a reduction in force on the metatarsal region may further reduce the signal strength allowing more flexion movement. As pressure is relieved from the toe region, the control signal may terminate allowing unrestricted movement of the lower leg. As a safety feature, the orthotic device may be equipped with an override switch that either locks or unlocks the knee joint regardless of whether a control signal is present. 
   The sensor may be readily applied to other orthotic devices. For example, the foot sensor may be connected to an ankle orthosis having a selectively lockable ankle joint. A control signal may be generated to lock or otherwise restrict movement in the ankle joint upon the occurrence of an actuating pressure on the foot sensor. Similarly, the sensor may also be adapted to an elbow orthotic device. An actuating pressure on variably resistive sensors located on the palm and/or fingers of a hand or hand prosthesis may send a control signal to a selectively lockable elbow joint restricting or preventing movement of the elbow. The hand sensors may also send a control signal to a selectively lockable wrist joint in a similar manner. In like manner, a back brace may be configured with a sensor wherein the threshold pressure is exceeded restricting movement when the back brace wearer is in the sitting or prone position. 
   While the invention has been described with respect to certain preferred embodiments, as will be appreciated by those skilled in the art, it is to be understood that the invention is capable of numerous changes, modifications and alterations that are within the scope of the appended claims.