Abstract:
A method of controlling an exoskeleton bracing system to walk includes identifying an expected current stance, receiving a tilt signal from a tilt sensor, and receiving a ground force signal from ground force sensors. Motorized joints are actuated to forwardly extend a leg brace when the expected stance includes standing with the leg braces together, the tilt signal indicates tilting forward, and the ground force signal indicates leaning on an opposite leg brace. Motorized joints are actuated to extend a trailing leg brace forward beyond a forwardly extended leg brace when the expected stance includes a forwardly extended leg brace and a trailing leg brace, the tilt signal indicates tilting forward, and the ground force signal indicates leaning on the forwardly extended leg brace. Motorized joints are actuated to converge both leg braces to a standing stance when the ground force signal indicates leaning on a trailing leg brace.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 12/250,155, filed Oct. 13, 2008 now U.S. Pat. No. 8,096,965, which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to control of a device for assistance with locomotion. More particularly, the present invention relates to a locomotion assisting device and method. 
     BACKGROUND OF THE INVENTION 
     Motorized locomotion assisting exoskeleton devices have been proposed for assisting people with disabilities to walk or to perform other tasks. In addition to enabling the performance of the tasks, enabling a person to walk may also impart therapeutic benefits. However, a major difficulty with such devices has been the lack of ability to control such devices in an effective, safe, and intuitive manner. 
     U.S. Pat. No. 7,153,242 (Goffer) describes an apparatus for enabling a person with handicapped lower limbs to walk. The apparatus attaches to parts of the lower portion of the person&#39;s body, possibly up to the torso, and includes motorized means of propelling the parts of the body to which it is attached. The apparatus includes sensors for measuring the angles of the joints, and a sensor for measuring the tilt angles of the upper body. The person using the apparatus selects a mode of operation, such as a gait. Initiation and maintaining of a gait is indicated by the tilt of the upper body of the person using the apparatus. For example, leaning forward triggers a forward step, and swinging the upper body from an upright position to a forward bend maintains a walking gait sequence wherein the apparatus performs the required sequence of movements of the lower limbs, including lifting, extending, bending, and lowering. However, such control by means of measuring the tilt of the upper body may be insufficient. For example, tilting the upper body does not enable the user of the apparatus to indicate with which leg to initiate the gait. Thus, user control is limited. In addition, such an apparatus does not provide control feedback for monitoring the phases and progress of the gait, and cannot alert the user to hazardous situations such as a forbidden arrangement of the feet. 
     Another powered exoskeleton, called a “hybrid assistive limb” or “HAL,” is described by Boyd in “Bionic suit offers wearers super-strength” (New Scientist, issue 2494, 9 Apr. 2005). Two control methods are described. In the first method described, sensors on the skin detect electric nerve signals from the brain to the leg muscles that indicate intention to move a leg. The device guides movement of the legs in accordance with the user&#39;s intentions. In the second described method, sensors detect when the user has started to move. The device then activates itself automatically to augment the power of user&#39;s muscles. Neither control method may be used by a paraplegic user whose nerves do not transmit signals from the brain to the legs. 
     It is an object of the present invention to provide an apparatus and method for controlling a locomotion assisting exoskeleton device in an intuitive and natural manner by a paraplegic or other user, and for providing feedback with regard to performance. 
     It is a further object of the present invention to provide an apparatus and method for enhancing the safety of a locomotion assisting exoskeleton device. 
     Other aims and advantages of the present invention will become apparent after reading the present invention and reviewing the accompanying drawings. 
     SUMMARY OF THE INVENTION 
     There is thus provided, in accordance with some embodiments of the present invention, an exoskeleton bracing system. The system comprises: a trunk support for affixing to the trunk of a disabled person, leg braces for connecting to the legs of the person with each leg brace including limb segment braces, motorized joints adapted to provide relative angular movement between the limb segment braces of the leg braces and between the leg braces and the trunk support, one or more ground force sensors designed to sense ground force exerted on each of the leg braces, and a controller for receiving sensed signals from the ground force sensors. An algorithm identifies a stance from the sensed signals and, based on the identified stance, actuates the motorized joints to perform an action relating to a mode of locomotion selected from a set of predefined actions corresponding to the identified stance 
     Furthermore, in accordance with some embodiments of the present invention, the algorithm includes selecting an action comprising actuating the motorized jointed limb braces of one leg, when the sensed signals are indicative of the person leaning on the opposite leg. 
     Furthermore, in accordance with some embodiments of the present invention, the algorithm includes selecting an action comprising actuating the motorized jointed limb braces of one leg, when the sensed signals are indicative of the person leaning on the same leg. 
     Furthermore, in accordance with some embodiments of the present invention, the algorithm includes selecting an action comprising ending a currently performed action when the sensed signals are indicative of substantially equally loading both legs. 
     Furthermore, in accordance with some embodiments of the present invention, the algorithm includes selecting an action comprising ending a currently performed action when the sensed signals are indicative of the person leaning on a trailing leg. 
     Furthermore, in accordance with some embodiments of the present invention, the system comprises an alerting device, the algorithm includes selecting an action comprising generating an alert from the alerting device. 
     Furthermore, in accordance with some embodiments of the present invention, the system comprises an alerting device, the action of generating an alert from the alerting device is performed when the sensed signals are indicative of the person falling 
     Furthermore, in accordance with some embodiments of the present invention, the system comprises an alerting device, the action of generating an alert from the alerting device is performed to indicate that the user is to change the stance. 
     Furthermore, in accordance with some embodiments of the present invention, the algorithm includes selecting an action comprising continuing a currently performed action when the sensed signals are indicative of increasing ground force. 
     Furthermore, in accordance with some embodiments of the present invention, the algorithm includes selecting an action comprising continuing a currently performed action when the sensed signals are indicative of decreasing ground force. 
     Furthermore, in accordance with some embodiments of the present invention, the system comprises a mode selector for selecting the mode of locomotion from a set of predefined locomotion modes. 
     Furthermore, in accordance with some embodiments of the present invention, the mode selector is adapted to communicate with the controller via wireless communication. 
     Furthermore, in accordance with some embodiments of the present invention, the mode selector includes a strap for strapping on a wrist. 
     Furthermore, in accordance with some embodiments of the present invention, the mode selector includes controls for selecting modes of locomotion from a group of locomotion modes consisting of: walking, standing from a sitting position, sitting from a standing position, climbing a stair and descending a stair. 
     Furthermore, in accordance with some embodiments of the present invention, the system comprises a tilt sensor to sense tilt of the trunk of the person with respect to the vertical and to communicate with the controller. 
     Furthermore, in accordance with some embodiments of the present invention, the identified stance is determined from the signals received from said one or more ground force sensors and a signal from the tilt sensor. 
     Furthermore, in accordance with some embodiments of the present invention, the action is selected from a group of actions consisting of: initiating a gait, maintaining a gait, halting a gait, climbing a stair, and descending a stair. 
     Furthermore, in accordance with some embodiments of the present invention, the action comprises enabling continuation of the mode of locomotion. 
     Furthermore, in accordance with some embodiments of the present invention, there is provided a method of controlling an exoskeleton bracing system that includes a trunk support for affixing to the trunk of a disabled person, leg braces for connecting to the legs of the person, each leg brace including limb segment braces, motorized joints adapted to provide relative angular movement between the limb segment braces of the leg braces and between the leg braces and the trunk support, and a controller. The method comprises: providing one or more ground force sensors designed to sense ground force exerted on each of the leg braces, receiving sensed signals from the ground force sensors, identifying a stance from the sensed signals, and actuating the motorized joints based on the identified stance to perform an action relating to a mode of locomotion selected from a set of predefined actions that relates to the identified stance. 
     Furthermore, in accordance with some embodiments of the present invention, the step of identifying the stance comprises identifying a stance determined by the person. 
     Furthermore, in accordance with some embodiments of the present invention, the identified stance comprises leaning on one leg and the selected action comprises actuating the motorized jointed limb braces of the opposite leg. 
     Furthermore, in accordance with some embodiments of the present invention, the identified stance comprises leaning on one leg and the selected action comprises actuating the motorized jointed limb braces of the same leg. 
     Furthermore, in accordance with some embodiments of the present invention, the identified stance comprises standing on both legs and the selected action comprises ending a currently performed action. 
     Furthermore, in accordance with some embodiments of the present invention, the identified stance comprises leaning on a trailing leg and the selected action comprises ending a currently performed action. 
     Furthermore, in accordance with some embodiments of the present invention, the selected action comprises generating an alert. 
     Furthermore, in accordance with some embodiments of the present invention, the system comprises an alerting device, the action of generating an alert from the alerting device is performed when the sensed signals are indicative of the person falling 
     Furthermore, in accordance with some embodiments of the present invention, the system comprises an alerting device, the action of generating an alert from the alerting device is performed to indicate that the user is to change the stance. 
     Furthermore, in accordance with some embodiments of the present invention, the identified stance comprises falling and the selected action comprises generating an alert. 
     Furthermore, in accordance with some embodiments of the present invention, the method comprises detecting increasing ground force to verify the selected action. 
     Furthermore, in accordance with some embodiments of the present invention, the method comprises detecting decreasing ground force to verify the selected action. 
     Furthermore, in accordance with some embodiments of the present invention, the method comprises providing at least one tilt sensor, sensing the tilt of a body part of the person, and using the sensed tilt in the step of actuating the motorized joints. 
     Furthermore, in accordance with some embodiments of the present invention, the action is selected from a group consisting of: initiating a gait, maintaining a gait, halting a gait, climbing a stair, and descending a stair. 
     Furthermore, in accordance with some embodiments of the present invention, the mode of locomotion is selected from a group of locomotion modes consisting of: walking, standing from a sitting position, sitting from a standing position, climbing a stair and descending a stair. 
     Furthermore, in accordance with some embodiments of the present invention, the action comprises enabling continuation of the mode of locomotion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to better understand the present invention, and appreciate its practical applications, the following Figures are provided and referenced hereafter. It should be noted that the Figures are given as examples only and in no way limit the scope of the invention. Like components are denoted by like reference numerals. 
         FIG. 1A  shows a locomotion assisting exoskeleton device in accordance with embodiments of the present invention. 
         FIG. 1B  shows a control panel unit associated with the locomotion assisting exoskeleton device shown in  FIG. 1A . 
         FIG. 1C  is a block diagram of the locomotion assisting exoskeleton device shown in  FIG. 1A  and  FIG. 1B . 
         FIG. 2A  is a diagram of a control process for initiating a step from a standing position, in accordance with embodiments of the present invention. 
         FIG. 2B  is a flow chart of the control process illustrated in  FIG. 2A . 
         FIG. 3  is a diagram of a control process for initiating a step from a standing position using only ground force sensors, in accordance with embodiments of the present invention. 
         FIG. 4A  is a diagram of a control process for maintaining a gait, in accordance with embodiments of the present invention. 
         FIG. 4B  is a flow chart of the control process illustrated in  FIG. 4A . 
         FIG. 5  is a diagram of a control process for maintaining a gait using only ground force sensors, in accordance with embodiments of the present invention. 
         FIG. 6  is a diagram of a control process for standing from a sitting position, in accordance with embodiments of the present invention. 
         FIG. 7  is a diagram of a control process for sitting from a standing position, in accordance with embodiments of the present invention. 
         FIG. 8A  is a diagram of a control process for ascending a stair, in accordance with embodiments of the present invention. 
         FIG. 8B  is a flow chart of the control process illustrated in  FIG. 8A . 
         FIG. 9A  is a diagram of a control process for descending a stair, in accordance with embodiments of the present invention. 
         FIG. 9B  is a flow chart of the process illustrated in  FIG. 9A . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     In accordance with embodiments of the present invention, an apparatus and method are provided to enable effective control and monitoring of a motorized locomotion assisting exoskeleton device by means of ground force measurement. By “ground force measurement” is meant a local measurement of the force that is exerted by an area of a supporting surface that counters the force exerted on that area of the surface by the user. The supporting surface may be a floor, or ground, below the user, or any other horizontal or non-horizontal surface that supports the weight of, or otherwise supports or stabilizes the user, or counters a force exerted by the user or the locomotion assisting exoskeleton device. The ground force may be a force applied directly by the supporting surface on a component of the locomotion assisting exoskeleton device, or may be transmitted via a body or object that is between the supporting surface and the component. 
     The locomotion assisting exoskeleton device includes braces and supports that may be strapped on, or otherwise attached or affixed to, the trunk and sections of limbs and body parts in the lower portion of the body of a user. The various braces and supports are connected to one another by means of joints that enable relative movement between the braces and supports. The locomotion assisting exoskeleton device may include motorized actuation assemblies or joints for moving parts of the user&#39;s body, such as for bending joints in order to propel various limbs of the user&#39;s body. The locomotion assisting exoskeleton device may also include sensors for measuring relative situation of various components of the device, and thus of the body parts to which they are attached. Such sensors may measure, for example, the angle between the brace sections on either side of a joint. 
     In addition, the locomotion assisting exoskeleton device may include one or more sensors that sense or measure tilt. For example, such a sensor affixed to the upper portion of the user&#39;s body may measure the tilt of that portion of the body. 
     The user of the locomotion assisting exoskeleton device is provided with a set of controls that communicate with the locomotion assisting exoskeleton device. By means of the controls, the user may select a locomotion mode for the device. Available modes may include walking, climbing a stair, descending a stair, sitting, and standing from a sitting position. 
     In accordance with embodiments of the present invention, the locomotion assisting exoskeleton device includes a foot brace that is positioned under a foot of the user. The foot brace supports the foot of the user, and applies force to the user&#39;s foot that counters the force of the weight of the user on the foot brace. The foot brace is provided with one or more ground force sensors. Ground force sensors are known in the art. For example, a ground force sensor may be based on a force sensitive resistor, such as a piezoresistive force sensor. A ground force sensor generates a signal that indicates the force that is applied to it. The amount of force applied to the ground force sensor depends on the posture or stance of the user, or on the activity of the user. 
     When a locomotion mode is selected, the locomotion assisting exoskeleton device awaits an instruction before initiating the appropriate motion sequence. In accordance with embodiments of the present invention, instructions are provided in accordance with signals generated by the ground force sensors of a foot brace. By shifting the weight of the user&#39;s body, perhaps with the aid of crutches, the user may increase or decrease the force applied to one or more of the ground force sensors. 
     For example, if a walking gait mode was selected and the user wishes to begin walking with the right foot, the user slightly leans on the left foot (perhaps with concurrent use of crutches). A ground force sensor on the right foot brace may then generate a signal indicating decreased force and a force sensor of the left foot brace may indicate increased force. The locomotion assisting exoskeleton device then initiates the walking gait by lifting and extending the right foot brace. The locomotion assisting exoskeleton device continues to monitor the signals generated by the ground force sensors. Thus, the user retains control over the gait. By leaning or otherwise controlling the force on the ground force sensors in an expected manner, the user continues to enable the gait. If, however, the weight of the user shifts in a manner inconsistent with the current phase of the gait, the locomotion assisting exoskeleton device may alert the user or halt the gait or converge to a stance until further instructions are received. 
       FIG. 1A  shows a motorized locomotion assisting exoskeleton device that is controlled in accordance with embodiments of the present invention. Locomotion assisting exoskeleton device  20  is powered and controlled by controller pack  22 . Controller pack  22  incorporates a controller in the form of a programmable processor, and a battery or other power supply (shown schematically in  FIG. 1C ). Controller pack  22  is generally worn on the back of a person using locomotion assisting exoskeleton device  20 . Alternatively, the various components of controller pack  22  may be attached to or incorporated in various components of exoskeleton device  20 . For example, components of controller pack  22  may be incorporated into braces  24 . 
     Controller pack  22  may communicate with a tilt sensor  23  that is fixed to a location on the upper portion of the user&#39;s body. For example, tilt sensor  23  may be worn on a shoulder strap that holds controller pack  22  to the user&#39;s torso, and thus senses the degree of tilt of the torso. The tilt sensors may include accelerometers, gyroscopes, or any other sensors capable of being incorporated in a locomotion assisting exoskeleton device and designed to sense tilt. The tilt sensor generates a signal that indicates whether the user&#39;s upper portion of the body is leaning or is upright with respect to the vertical 
     Braces  23   a  are affixed by means of straps  25  to segments of the user&#39;s lower limbs and to the pelvis, torso, or other parts of the user&#39;s body. Braces  23   a  incorporate motorized actuation assemblies  24 . Each actuation assembly  24  includes a motorized actuator (not shown) that, in response to commands transmitted by controller pack  22 , causes a joint that connects between individual braces  23   a  to bend or extend. Bending or extending a joint may propel or move a limb to which an adjoining brace is attached. When the lower limbs of the user are affixed to braces  23   a , each of the user&#39;s feet is placed on a foot brace  26 . Foot brace  26  may be movable by means of a separate motorized actuation assembly (not shown) to lift, guide, and lower a foot of the user. Alternatively, foot brace  26  may include a coil, spring, or other elastic anti-drop mechanism associated with ankle joint  27 . The anti-drop mechanism associated with ankle joint  27  holds foot brace  26  substantially horizontal when foot brace  26  is raised above, and is not supported by, a supporting surface. 
       FIG. 1B  shows a control panel unit associated with the motorized locomotion assisting exoskeleton device shown in  FIG. 1A . Control panel unit  30  communicates with controller pack  22  via a wireless or other communications channel. Typically, control panel unit  30  is strapped to the user&#39;s wrist by means of straps  34 . Control panel unit  30  includes one or more touch-sensitive buttons or keys  32 . The touch-sensitive buttons  32  may serve as a mode selector to select a mode of locomotion, to verify a command, or to communicate other instructions to controller pack  22 . 
     One or more ground force sensors  28  are mounted on each foot brace  26 . Each of ground force sensors  28  is capable of generating a signal that indicates the force applied to that sensor. Signals generated by ground force sensors  28  are transmitted to controller pack  22 . Controller pack  22  receives signals transmitted by control panel unit  30  and by ground force sensors  28 . On the basis of the received signals and in accordance with programmed instructions, controller pack  22  transmits instructions to actuation assemblies  24 . The instructions transmitted to actuation assemblies  24  may cause one or more of braces  23   a  to move, propelling any limbs attached to the units. 
     By activating buttons  32  and by adjusting the force on ground force sensors  28 , a person may control locomotion assisting exoskeleton device  20  to assist in performing a desired task. Examples of controlling a locomotion assisting exoskeleton device in accordance with embodiments of the present invention are described below. 
       FIG. 1C  is a block diagram of the locomotion assisting exoskeleton device shown in  FIG. 1A  and  FIG. 1B . Power supply  15  is located in controller pack  22 . Main supply  16  provides power to main processor  12 , actuation assemblies  24 , and motors  38 . Main supply  16  may include a rechargeable battery that may be charged by means of charger unit  18  that may be connected to main supply  16  through protection circuit  19 . When necessary, an appropriate alternative external power source, such as an auxiliary battery, may be connected to auxiliary connection  17 . 
     Main processor  12  may receive signals from tilt sensor  23  and ground force sensors  28 . Main processor  12  may communicate with control unit  30  over a wireless connection through wireless communications board  14 . Main processor  12  communicates with actuation assemblies  24  via communications channels, such as controller-area network (CAN) bus  37 . Each actuation assembly  24  includes a control board  36 . Each control board  36  controls a motor  38  that determines the motion of actuation assembly  24 , and thus of a brace or joint to which actuation assembly  24  may be attached. 
     In general, a user of locomotion assisting exoskeleton device  20  selects a mode of operation. Modes of operation may include selection of a task to be carried out. Examples of such tasks may include walking with a particular gait, sitting, standing from a sitting position, climbing stairs, and descending stairs. 
     The locomotion assisting exoskeleton device may include one or more alerting devices for alerting the user of situations demanding the user&#39;s attention. Such alerting devices may generate audible, visible, or tactile alert signals. The alerting devices may be incorporated into one or more components of the locomotion assisting exoskeleton device. Situations requiring user attention may include contradictory or unexpected movements or foot loading, falling, and points during the execution of a procedure where user verification is required for safety purposes. 
     Depending on the details of the control algorithm for the motorized locomotion assisting exoskeleton device, the ground force sensor values used in controlling the locomotion assisting exoskeleton device may represent a signal generated by a single sensor, or may be a representative value of the signals based on processing the outputs generated by part or all of an array of sensors associated with a single foot brace. Alternatively, the value used may represent a pattern or map of forces applied to the sensors of one or both foot braces. 
     For the sake of simplicity in the discussion below, the values of forces measured by the ground force sensors, or foot loadings, may be classified into one of four loading categories. The ranges of sensor signals to be included within each loading category may vary from user to user, or from one mode of operation to another. The loading categories may also be defined relative to one another. The category representing the range of the smallest forces may be labeled “foot off” (FO), and is associated with a foot brace that is not touching the ground. The category representing the next larger range of forces may be labeled “foot touching” (FT), associated with a foot brace that is touching the ground, but with minimal loading. The category representing the next larger range of forces labeled “foot lightly loaded” (FLL), may represent light loading on a foot brace, associated with a situation where the user is standing on both feet, and load of the weight of the body is shared with the other foot brace. Finally, a category representing the range of greatest forces may be labeled “foot heavily loaded” (FHL). FHL is associated with a user leaning on one foot brace, with that foot brace supporting most of the weight of the user&#39;s body. 
     In addition to the signal output of ground force sensors, control of the locomotion assisting exoskeleton device may utilize a measurement of the tilt of the upper part of the user&#39;s body. The tilt measurement may be used to check whether the tilt of the user&#39;s body is consistent with the current phase of an activity. In addition, depending on the control algorithm of the locomotion assisting exoskeleton device, the user may use body tilt, in addition to applying force to the ground force sensors, to control the locomotion assisting exoskeleton device. 
     Loading on a particular foot, the right or the left foot is indicated in the discussion below by preceding the abbreviation for a loading category with the letter R or L, respectively. For example, the right foot lightly loaded may be designated RFLL. The left foot touching may be designated LFT. 
     Various combinations of loading on the right and left legs may indicate various stances. A stance is to be understood as including any posture of the body, such as, for example, standing, sitting, or a phase of a walking gait, including an unstable or falling posture, and not only a stable standing posture. For example, a loading combination RFLL and LFLL may indicate that the user is standing straight or otherwise placing approximately equal loading on both legs. A combination of RFHL with lighter loading on the left leg, LFLL, LFT, or LFO, may be indicate that the user is leaning on the right leg. Conversely, a combination of LFHL with RFLL, RFT, or RFO may indicate leaning on the left leg. Leaning on a leg is understood to include standing on one leg with the other leg being held above the ground. Any combination of FLL, FT, or FO loading on one leg, combined with FT or FO loading on the other leg, may indicate falling. Falling may also be indicated by a tilt sensor. During falling, the tilt sensor may indicate that the upper body is tilted at an angle indicative of falling, or may indicate acceleration indicative of falling. 
     In the diagrams discussed below, the left leg is designated LG, the right leg is designated RG, and ground force sensors are designated GF. In the examples of the control methods described below, the user may coordinate the action of the locomotion assisting exoskeleton device with the use of crutches. However, the role of the crutches is not indicated in the Figures. 
       FIG. 2A  is a diagram of the control process for initiating a step from a standing position, in accordance with embodiments of the present invention.  FIG. 2B  is a flow chart of a control method for the process illustrated in  FIG. 2A . By means of the controls on the control panel unit of the exoskeleton skeleton device, the user indicates the intention to initiate a walking gait (step  140 ). The control system of the locomotion assisting exoskeleton device then checks whether tilt sensors indicate that the user is leaning forward (step  142 ). If not (step  57 ), the system checks whether a predetermined time has elapsed since step  140  (step  144 ). If the time has elapsed, the process of initiating a walking gait times out and is halted (step  58 ). If not, the system continues to wait for an appropriate signal from the tilt sensors (return to step  142 ). 
     The user initiates the walking gait by leaning forward (step  41 ). The user may be initially standing with weight distributed approximately equally between both legs (as in step  40 , RFLL and LFLL, loading). If no change in loading is detected by the ground force sensors within a predetermined period of time (step  150 ), the process of initiating a walking gait times out and is halted (step  58 ). The user may lean on the right leg (RFHL loading, step  42 ) to instruct the locomotion assisting exoskeleton device to begin a walking gait, stepping with the left leg first. Leaning on the right leg is a relatively intuitive way of indicating that the user wishes to start walking by stepping with the left leg. When the control system detects leaning on the right leg, the system executes an algorithm (step  44 ) causing the locomotion assisting exoskeleton device to extend the left leg. The user is then standing with left leg extended (step  46 ). The system records that a walking step was made with the left leg (step  146 ) and the gait maintenance process (described below) begins (step  48 ). If the user prefers to start the gait with the right leg, the user leans on the left leg (LFHL loading, step  50 ). This initiates a walking step with the right leg (step  52  and step  54 ) that is recorded by the system (step  148 ). During the process of initiating a gait, the locomotion assisting exoskeleton device continues to monitor the ground force sensors. Should the ground force sensors indicate falling (step  56 , FLL, FT, or FO loading on one leg combined with a FT or FO loading on the other), or a tilt sensor indicate falling, the walking gait initiation procedure is halted (step  58 ). 
     Alternatively, initiating a gait by the locomotion assisting exoskeleton device may be controlled by means of activating the ground force sensors alone, without waiting for a signal from a tilt sensor.  FIG. 3  is a diagram of control for initiating a step from a standing position using only ground force sensors, in accordance with embodiments of the present invention. Leaning on either leg initiates the gait initiation process. If the ground force sensors do not indicate that the user has leaned on either leg within a predetermined period of time, the gait initiation process times out and is halted. 
       FIG. 4A  is a diagram of the control process for maintaining a gait, in accordance with embodiments of the present invention.  FIG. 4B  is a flow chart of a control method for the process illustrated in  FIG. 4A . Before initiating another walking step of the gait, the system checks if the tilt sensors indicate that the user is leaning forward. If not (step  57 ), and a predetermined time period has elapsed (step  144 ), the gait maintenance process times out. When the process times out, an algorithm is executed (step  70 ) to bring both legs to a standing position (step  40 ) and the process is halted (step  58 ). 
     The user indicates the intention to continue the walking gate by continuing to lean forward (step  47 ). If the previous step of the gait was executed with the left leg, the user may be standing in the position of step  46 , with left leg extended forward. The user leans on the extended left leg (step  60 ) to instruct the locomotion assisting exoskeleton device to continue the walking gait by extending the right leg (step  62 ). The system records that the last step of the gait was executed with the right leg. The user is now in the position of step  54 , with right leg extended. On the other hand, while standing in the position of step  46 , the user may lean on the trailing right leg (step  68 ) or on both legs with about equal force. Continuing to lean on the trailing right leg or on both legs for a predetermined time interval (step  150 ) instructs the locomotion assisting exoskeleton device to halt the walking gait. The system executes an algorithm (step  70 ) to bring the user&#39;s legs together to a standing stance, to the position of step  40 . The walking process is then halted (step  58 ). 
     If the previous step of the gait was executed with the right leg so that the user stands with right leg extended (step  54 ), the user may lean on the extended right leg to instruct the locomotion assisting exoskeleton device to continue a forward gait by extending the left leg (step  64 ). The locomotion assisting exoskeleton device then executes a step of the gait with the left leg forward (step  66 ) so that the user is standing with the left leg extended (step  46 ). The system records that a step was executed with the left leg (step  146 ). On the other hand, while still standing in the position of step  54 , leaning on the trailing left leg (step  74 ) or about equally on both legs (step  40 ) for a predetermined time interval (step  150 ) instructs the locomotion assisting exoskeleton device to bring the user to a standing position (step  70  and step  40 ) and to stop the gait maintenance process (step  58 ). 
     After taking a step of the gait, with the having one leg extended (step  46  or step  54 ), the system again checks for tilt (step  142 ) and repeats the step process. If during execution of a step of the gait, the ground force sensors or a tilt sensor indicate that the user is falling (step  56 ), the gait maintenance process is halted (step  58 ). Alternatively, the process of maintaining a walking gait of the locomotion assisting exoskeleton device may be controlled by means of activating ground force sensors alone, without waiting for a signal from a tilt sensor.  FIG. 5  is a diagram of the control process for maintaining a gait using only ground force sensors, in accordance with embodiments of the present invention. Leaning on the extended leg signals continuation of the gait maintenance process. If the ground force sensors do not indicate that the user has leaned on the extended leg within a predetermined period of time, the gait maintenance process times out, the legs are brought together to a standing-straight position, and the process is halted. 
       FIG. 6  is a diagram of the control process for standing from a sitting position, in accordance with embodiments of the present invention. The user, in a sitting position, uses the control panel unit of the locomotion assisting exoskeleton device to signal the locomotion assisting exoskeleton device that the user wishes to stand. In order to instruct the locomotion assisting exoskeleton device to initiate the standing procedure, the user places both feet on the ground (step  80 , FT loading on both legs). The locomotion assisting exoskeleton device initiates a standing procedure algorithm (step  82 ). The locomotion assisting exoskeleton device begins straightening the user&#39;s legs (step  84  and step  86 ), bringing the user to a standing position (step  88 ). While executing the standing procedure, the locomotion assisting exoskeleton device monitors the output signals of the ground force sensors. If the standing procedure proceeds as expected, the ground force sensors measure increasing force during steps  84  and  86  until the full standing position of step  88  is attained (RFLL and LFLL loading). Alternatively or additionally, progress of the standing procedure may be monitored by means of sensors that sense the angles of the various joints, and that are incorporated in the actuation assemblies of the locomotion assisting exoskeleton device. Deviation from the expected increase in force, or change in joint angle, for a predetermined interval of time may be interpreted as indicating a problem with the standing procedure. In such a case, the locomotion assisting exoskeleton device may alert the user, and may halt or suspend the standing procedure until further instructions are received or may return the user to a sitting position  80 . 
     Another safety means may involve a tilt sensor that senses the tilt angle of a part of the upper body of the user. If the tilt sensor indicates that the user is falling, the locomotion assisting exoskeleton device may act to attempt to prevent or mitigate the effects of the fall. For example, the locomotion assisting exoskeleton device may cause the user to sit back. 
       FIG. 7  is a diagram of the control process for sitting from a standing position, in accordance with embodiments of the present invention. While standing in front of a surface on which the user wishes to sit, the user uses the control panel unit to instruct the locomotion assisting exoskeleton device to execute a sitting procedure. The user stands straight, with approximately equal force (FLL loading) on both legs (step  90 ). This signals the locomotion assisting exoskeleton device to initiate a sitting procedure algorithm (step  92 ). The locomotion assisting exoskeleton device bends the user&#39;s legs (step  94  and step  96 ), bringing the user to a sitting position (step  98 ). While executing the sitting procedure, the locomotion assisting exoskeleton device continues to monitor the ground force sensors. It is expected that the ground force sensors will indicate decreasing ground force until a full sitting position is attained (RFT and LFT loading). Alternatively or additionally, progress of the sitting procedure may be monitored by means of sensors that sense the angles of the various joints, and that are incorporated in the actuation assemblies of the locomotion assisting exoskeleton device. A deviation from the expected decrease in force, or change in joint angle, for a predetermined interval of time may be interpreted as indicating a problem with the sitting procedure. The procedure may then be stopped or paused until further instructions are received. If a tilt sensor indicates that the user may be falling during the sitting procedure, the sitting procedure may be stopped, and action may be taken to prevent, or mitigate the effects of, the fall. 
       FIG. 8A  is a diagram of the control process for ascending a stair, in accordance with embodiments of the present invention.  FIG. 8B  is a flow chart of a control method for the process illustrated in  FIG. 8A . To ascend a stairway of several stairs, the control process is repeated for each consecutive stair. To initiate the process of ascending a stair, a user standing below a stair to be ascended uses the control panel unit to instruct the locomotion assisting exoskeleton device to execute a stair ascending procedure (step  160 ). The system then checks if the ground force sensors indicate that the user is leaning on a single leg (step  162 ). The user leans on one leg to instruct the locomotion assisting exoskeleton device to initiate the procedure by placing the opposite leg on top of the stair. If the user does not lean on a single leg but continues to stand on both legs, the locomotion assisting exoskeleton device alerts the user (step  163 ). 
     In this example, the user leans on the left leg (step  100 ). For simplicity, we limit the discussion here to an example in which the user leans on the left leg in order to begin the ascent with the right leg. However, the description of the procedure remains valid if right and left legs are interchanged throughout. In response to leaning on the left leg, the locomotion assisting exoskeleton device executes an algorithm for lifting the right leg and extending it forward above the stair (step  102 ). With the right leg positioned above the stair, the ground force sensors are expected to indicate that the user is standing on the left leg (step  104 ). The locomotion assisting exoskeleton device then executes an algorithm to lower the right leg (step  106 ), checking the ground force sensors on the right foot brace (step  170 ) until the sensors indicate that the right foot has touched the top of the stair (RFT loading) while leaning on the left leg (step  108 ). At this point the output signals from the ground force sensors are monitored to check whether the right foot is fully resting on the stair (step  172 ). For example, input signals from sensors in both the toe and heel of the right foot brace may be checked to verify that all sensors indicate at least minimal contact (FT loading). If the sensor signals indicate that all or part of the right foot is not resting on top of the stair within a predetermined time interval, the algorithm assumes that the procedure has failed. In the event of such failure, the locomotion assisting exoskeleton device may return the right foot to its original position as at the beginning of the procedure (step  173 ), i.e. the position of step  100 . The procedure is then halted until further instructions are received (step  58 ). 
     If the sensors indicate that the procedure has continued as expected, and that the right foot is fully resting on top of the stair, the locomotion assisting exoskeleton device may alert the user to this by generating an audible or other signal. For safety reasons, the locomotion assisting exoskeleton device may then await acknowledgment or verification from the user before proceeding to the next step in ascending the stair (step  174 ). The user may indicate verification by means of a control button, or by any other appropriate control or signaling means known in the art. Once verification is received from the user, system checks whether the user is leaning on the right leg (step  176 ). In addition, the system may verify that a tilt sensor indicates that the user&#39;s torso is leaning forward. If the user leans on the right leg (step  110 ), the system executes an algorithm to lift the left leg and the user&#39;s body to the top of the stair (step  112 ). Failure to lean on the right leg, or to lean forward, within a predetermined time interval may indicate the user&#39;s stance is inconsistent with safely proceeding with the ascend stair procedure. Therefore, failure to lean on the right leg, or to lean forward, may cause the locomotion assisting exoskeleton device to alert the user and to stop the procedure until further instructions are received (step  178 ). When step  112  is complete, the left leg is brought into line with the right leg on top of the stair. The user is then standing on top of the ascended stair (step  114 ). At this point, the user may use the control panel unit to instruct the locomotion assisting exoskeleton device to execute a procedure to begin a walking gait, to ascend another stair, or any other appropriate action. Throughout the stair ascending procedure, the stability and safety of the user may be achieved by concurrent use of crutches or a hand railing. During execution of the stair ascending procedure, the ground force sensors or a tilt sensor may indicate that the user is falling. The locomotion assisting exoskeleton device may then take action to prevent, or mitigate the effects of, a fall. For example, the locomotion assisting exoskeleton device may attempt to restore balance to prevent a fall, may cause the user to collapse in such a manner as to reduce the impact of a fall. 
       FIG. 9A  is a diagram of the control process for descending a stair, in accordance with embodiments of the present invention.  FIG. 9B  is a flow chart of a control method for the process illustrated in  FIG. 9A . To descend a stairway of several stairs, the control process is repeated for each consecutive stair. To initiate the process of descending a stair, a user standing on an upper level above a stair to be descended uses the control panel unit to instruct the control system of the locomotion assisting exoskeleton device to execute a stair descending procedure (step  182 ). The user leans on one leg to instruct the locomotion assisting exoskeleton device to initiate stair descent procedure with the opposite leg. If the user does not lean on a single leg (step  184 ) but continues to stand on both legs, the locomotion assisting exoskeleton device alerts the user (step  186 ). 
     In this example, the user leans on the left leg (step  120 ). For simplicity, we limit the discussion here to an example in which the user leans on the left leg in order to begin the descent with the right leg. However, the description remains valid if right and left legs are interchanged throughout. In response to leaning on the left leg, the system executes an algorithm for extending the right leg forward above the stair (step  122 ). While extending the right leg, the system continues to check if the right foot is no longer touching the upper level (RFO loading, step  190 ). When the right leg is extended above the stair, the ground force sensors are expected to indicate RFO loading on the right foot, and that the user is standing on the left leg (step  124 ). At this point, for reasons of safety, the system may wait for an acknowledgement signal indicating verification by the user (step  192 ). Verification from the user may be understood to indicate that crutches are properly positioned, or other precautions have been taken, to assure proper support of the user&#39;s body during the next steps of the procedure. If verification is received, the locomotion assisting exoskeleton device then executes an algorithm for bending the left knee (step  127 ), lowering the right leg. During execution of the algorithm of step  127 , the ground force sensors may indicate a state equivalent to falling, with a combination of RFO and LFLL or LFT loading (step  126 ). However, in reality, the weight of the user is being supported by crutches or other means. During this phase of descending a stair, a true state of falling may be indicated only by a tilt sensor or similar sensor, and not by the ground sensors. While bending the left knee, the system checks the ground force sensors for RFT loading (step  194 ) that may indicate that the right foot has made contact with the top of the stair. When RFT loading is indicated, the right foot is expected to rest on the top of the stair the algorithm of step  127  ceases to execute. The ground force sensors are checked to verify that the user is leaning on the right leg (step  196 ). If not the user is alerted (step  198 ). When the user leans on the right leg (step  128 ), the system begins execution of an algorithm to remove the left leg from the upper level (step  130 ). The locomotion assisting exoskeleton device lifts the left leg at the hip and bends the left knee to remove the left foot from the upper level. This action continues as long as the ground force sensors indicate LFT loading (step  131 ). When the ground force sensors indicate LFO, the left foot is expected to be positioned above the stair, with the user leaning on the right leg (step  132 ). The system then executes an algorithm that causes the locomotion assisting exoskeleton device to lower the left foot until the left foot touches the top of the stair (step  134 ). When step  134  is complete, the user is standing with both legs on top of the stair (step  136 ). At this point, the user may use the control panel unit to instruct the locomotion assisting exoskeleton device to execute a procedure to begin a walking gait, to descend another stair, or any other appropriate action. Throughout the stair descending procedure, the stability and safety of the user may be achieved by concurrent use of crutches or a hand railing. 
     It should be understood that in the above descriptions of examples of control processes, steps of the processes may have been omitted for the sake of clarity and simplicity. Also, variations of the processes and procedures described above may be apparent to one skilled in the art, and are to be considered as falling within the scope of the present invention. 
     Examples of such variations are: additional or different points during a procedure where user verification may be required, different means of indicating user verification or monitoring a procedure, additional timeout intervals that were not indicated in the above discussion, use of tilt sensor output in procedures where such use was not described in the above discussion, use of angle sensor output, changing the order of individual steps of the procedure, and other variations. 
     Thus, as described above, a system for the convenient, safe, and intuitive control of a locomotion assisting exoskeleton device is provided. 
     It should be clear that the description of the embodiments and attached Figures set forth in this specification serves only for a better understanding of the invention, without limiting its scope. 
     It should also be clear that a person skilled in the art, after reading the present specification could make adjustments or amendments to the attached Figures and above described embodiments that would still be covered by the present invention.