generally stated the present invention is concerned with the simulation of human locomotion . fig1 schematically illustrates the mechanical components of a human locomotion simulator 20 according to an illustrative embodiment of the present invention . the human locomotion simulator 20 is mainly concerned with locomotion patterns of the human body by the fully coordinated simulation of the pelvic structure , the hip joint and the thigh segments with longitudinal displacement of the ground including 3 - d mobility of the ground . this mechanical framework is completed by the connection of an above knee leg prosthesis equipped with at least a motorized knee joint and a motorized or a passive ankle joint in order to complete the simulation of the locomotion movements with the knee joint and the ankle joint motions . of course other uses of the human locomotion simulator described herein are possible , such as , for example , the testing of footwear . it is to be understood that in the foregoing the words “ vertical ” and “ horizontal ” are to be construed broadly . for example , generally orthogonal orientations would be encompassed thereby . the human locomotion simulator 20 consists of a five degrees of freedom ( dof ) system which are actively controlled by a controller or a computer network running a control software ; the vertical and the horizontal linear axes of the pelvic structure , the hip - thigh mechanism ( hip joint and the thigh segment ) of the simulator itself , the knee joint of the motorized leg prosthesis and longitudinal displacement of the ground . optionally , the human locomotion simulator 20 could also include the four vertical displacement pistons of the treadmill to allow for the 3 - d variable positioning of the ground and a controlled ankle joint in the case where the leg prosthesis includes a active ankle joint . referring to fig1 , the mechanical components of the human locomotion simulator 20 include a base 22 onto which is mounted a conventional treadmill 24 , a vertical post 26 mounted to the base 22 , a pelvic structure 29 composed of a vertically movable support 28 mounted to the vertical post 26 as to produce the vertical displacement of the pelvic structure 29 and a horizontally movable support 30 so mounted to the vertically movable support 28 as to move the pelvic structure 29 horizontally , a hip - thigh mechanism 33 including a hip joint 40 represented by a pivot pin and a thigh segment assembly 38 ( schematically illustrated in fig1 ) mounted on the horizontally movable support 30 of the pelvic structure 29 providing the rotational mobility at the hip joint 40 of the thigh segment assembly 38 . fig1 also illustrates a schematic prosthesis leg 32 provided with a knee joint , a shank segment , a ankle joint and a foot mounted to the thigh segment assembly 38 . the hip - thigh mechanism 33 is illustrated in fig3 . it is designed to allow easy installation and maintenance of all it &# 39 ; s components . the unit can be completely assembled before attaching to the rest of the system . and all it &# 39 ; s sub - assemblies can be assembled or disassembled individually . calculations have been done to ensure that the hip - thigh mechanism 33 can provide the required level of torque and speed with the torque and speed range of the motor . the calculation ( equation 1 ) is also used in the control software to translate the hip angle into linear displacement along the motor axis . the variables used in equation 1 are shown in fig2 . ρ =√{ square root over (( l 2 + l 4 · sin θ ) 2 +( l 4 · cos θ − l 1 ) 2 )} equation 1 returning to fig3 , the hip - thigh mechanism 33 includes a hip frame assembly 34 , a hip joint motor assembly 36 and a thigh segment assembly 38 with a connector or attachment member 39 for mounting the prosthesis leg 32 . the hip frame assembly 34 is configured and sized to be mounted to the horizontally movable support 30 of the pelvic structure 29 as will be described hereinbelow . the hip joint motor assembly 36 shown in fig4 is pivotally mounted to the hip frame assembly 34 . the hip joint motor assembly 36 and the thigh segment assembly 38 are interconnected by a hip joint ball - nut assembly 42 shown in fig5 . similarly , the thigh segment assembly 38 is pivotally mounted to the hip frame assembly 34 via a hip pivot pin 40 ( fig3 ) that simulates the biomechanical axis of the human locomotion structure at the hip . fig4 illustrates the hip joint motor assembly 36 in an exploded view . the hip joint motor assembly 36 includes a hip motor 44 , a hip joint ball - screw holder 46 and a ball screw 48 . the hip motor 44 is fixedly mounted to the hip joint ball - screw holder 46 that is itself pivotally mounted to the hip frame assembly 34 of fig3 via bearings 54 and a fastener 52 ( see fig3 ). the ball screw 48 is mounted to the hip motor 44 to rotate therewith , passing through the angular - contact bearings set 55 . the hip joint ball - nut assembly 42 is shown in an exploded view in fig5 . it includes a body 50 that is pivotally mounted to the thigh segment assembly 38 via bearings 57 and a threaded element 52 fixedly mounted to the body 50 . the threaded element 52 is so internally threaded as to receive the externally threaded ball screw 48 . the hip joint motor assembly 36 provides a linear motion to the hip joint ball - nut assembly 42 , which induces a rotational movement to thigh segment assembly 38 around the hip pivot pin 40 . the ball - screw 48 is inserted into the hip joint ball screw holder 46 with angular - contact bearings set 55 in a back - to - back arrangement ( see fig4 ). because this arrangement provides a stiff linkage between the ball screw 48 and the hip joint ball - nut assembly 42 , it is necessary to have an accurate alignment between the ball screw 48 and the hip joint ball - nut assembly 42 . the thigh segment assembly 38 is illustrated in an exploded perspective view in fig6 . the thigh segment assembly 38 makes the link between the prosthesis leg 32 ( fig1 ) and the horizontally movable support 30 . the thigh segment assembly 38 includes two parallel plates 56 and 58 interconnected by a spacer 60 and a bracket 62 configured and sized to mount the prosthesis leg thereto . two toller bearings 64 are provided to pivotally mount the thigh segment assembly 38 to the hip frame assembly 34 . a hip joint position sensor assembly 66 is located between the two plates 56 and 58 . the position measurement of the thigh segment assembly 38 is achieved via the hip joint position sensor assembly 66 illustrated in a perspective view in fig7 . angular position measurement of the thigh segment assembly 38 is supplied by rotational optical sensor disk 68 installed on the hip pivot pin 40 and read by an encoder module 70 . the hip joint axis sleeve 72 and hip joint sensor hub 74 receive the hip pivot pin 40 that pivotally mount the thigh segment assembly 38 to the hip frame assembly 34 . without limiting the present description , it has been found that the sensor model heds - 9040 - t00 e3 - 2048 - 1000 - ihub made by us digital is adequate to be used as the hip position sensor assembly 66 . turning now to fig8 to 11 of the appended drawings , the pelvic structure 29 , its vertically movable support 28 , its horizontally movable support 30 , its attached vertical and horizontal axis movement generator assemblies and the bumper structure will be described . as can be seen from fig9 , the vertically movable support 28 includes a generally triangular body defined by two triangular plates 76 and 78 , maintained at a predetermined spacing by spacers 80 ( only one shown ), and both a vertical plate 82 and a horizontal plate 84 . a vertical axis movement generator 86 is mounted to the vertical plate 82 and a horizontal axis movement generator 88 is mounted to the horizontal plate 84 . the vertical and horizontal axis movement generators 86 and 88 are identical . accordingly , for concision purposes , only the vertical axis movement generator 86 will be described hereinbelow with respect to fig1 . the vertical axis movement generator 86 includes a motor 94 to which is associated a ball screw 92 . a pair of linear slides 95 are mounted to the fixed portion of the motor 94 . a mobile unit 96 is slidably mounted to the pair of slides 95 via linear bearings 97 . the mobile unit 96 includes a carriage portion 98 and secondary portions 100 . both portions 98 and 100 being slidably mounted to the slides 95 via the linear bearings 97 . a ball nut 102 is mounted to the carriage portion 98 of the mobile unit 96 and is engaged by the ball screw 92 . accordingly , rotation of the ball screw 92 by the motor 94 causes a linear movement of the mobile unit 96 on the slides 95 . four springs 104 are provided between the carriage portion 98 and the secondary portions 100 of the mobile unit 96 . these springs 104 are used as a suspension between the carriage portion 98 and the secondary portions 100 . this suspension is interesting in the simulation of human locomotion because this type of mechanism provides the expected damping effects of the mobility of the vertical movable support 28 of the pelvic structure 29 , as will easily be understood by one skilled in the art . the four springs 104 are part of the series elastic actuators ( sea ) that are used to control the force applied on the corresponding vertical and horizontal movable supports 28 or 30 . these springs 104 allow the simulation of various persons weight and to separate the inertia of the actuator from the inertia of the vertical and horizontal movable supports 28 and 30 . in other words , the linear slides 95 and linear bearings 97 guide the movement and the actuation is provided by a combination of motor 94 , ball - screw 92 and ball - nut 102 . the vertical and horizontal axis movement generators 86 and 88 are controlled in position and force and use a special mechanism and sensors to perform this task as will be described hereinbelow . the position control loop utilizes position sensors 99 to get position feedback on both vertical and horizontal axes . without limiting the present disclosure , table 1 presents the technical information on linear optical sensors that have been found suitable to be used as position sensors 99 . force sensors are used to measure the force levels applied on the vertical and horizontal axes . those sensors measure the displacement between the carriage portion 98 and the secondary portions 100 of the mobile unit 96 for each axe . the secondary portions 100 being linked to the carriage portion 98 with springs 104 , the applied force is a function of the displacement between the two portions ( 98 , 100 ) and of the known strength of the springs 104 . force sensors advantageously require fine position measurement accuracy . therefore , magnetic stripe technology was selected . without limiting the present disclosure , table 2 presents the technical information on linear magnetic sensors that have been found adequate for this application . along with the linear magnetic sensors , an index sensor is used to determine the reference position . turning now to fig1 to 13 , the linear magnetic sensors will be described . fig1 illustrates , in a perspective view , the mobile unit 96 of the vertical axis movement generator 86 without the slides 95 and the motor 94 . a magnetic stripe 106 is attached to the carriage portion 98 and a linear magnetic sensor 108 is in close proximity to the magnetic stripe 106 and is designed to be rigidly connected to the secondary portions 100 . more specifically , as can be better seen from fig1 , the linear magnetic sensor 108 is secured to a bracket 101 itself mounted to a plate 103 that connects to the secondary portions 100 . therefore , relative displacement of the carriage portion 98 with respect to the secondary portions 100 is detected and measured by the linear magnetic sensor 108 . an optical index sensor 110 is also mounted to the carriage portion 98 . the optical index sensor 110 serves as a means to determine the absolute home position of the linear magnetic sensor 108 . as can be better seen from fig1 , the index sensor 110 includes a thin opaque mask 111 attached to the carriage 98 that moves between the emitter and the receptor of a photo sensor 113 attached to the plate 103 of the mobile unit 96 . for example , and without limiting the present disclosure , it has been found that a transmissive photomicrosensor made by omron under model number ee - sx1042 has been found suitable for the present application . the actuators used to move the mobile units of the vertical and horizontal axis movement generator 86 and 88 are series elastics actuators ( sea ). these actuators are mechanisms that allow to control position and force while eliminating undesired inertia of the drive system . since sea actuators are believed well known in the art they will only be briefly discussed herein . referring to fig1 , the present implementation of the sea consists of a motor 94 and a motor drive transmission ( ball - screw 92 and ball - nut 102 ) connected at the output of the motor 94 . an elastic element , in the form of the four springs 104 , is connected in series with the motor drive transmission , and this elastic element is positioned to alone support the full weight of any load connected at an output of the actuator . referring to fig1 , a position sensor , in the form of the linear magnetic sensor 108 positioned between the carriage 98 and the mobile unit 96 generates a signal proportional to the deflection of the elastic element and indicates the force applied by the elastic element to the output of the actuator . referring now to fig8 and 14 of the appended drawings , the bumper structure will be described . the bumper structure is so designed that each axis is completely independent . the bumper structure includes an upper vertical bumper assembly 112 , a lower vertical bumper assembly 114 , a front horizontal bumper assembly 116 , a back horizontal bumper assembly 118 , a back thigh bumper bracket 120 and a front thigh bumper bracket 122 . it is to be noted that even though only one of each bumper assembly 112 , 114 , 116 and 118 is illustrated in fig8 , two of each of these assemblies are present , one for each side of the simulator . the upper vertical bumper assembly 112 includes a bumper 112 a mounted to the triangle plate 76 of the vertically movable support 28 and a stop bracket 112 b , mounted to the vertical post 26 ( see fig1 ) and vertically aligned with the bumper 112 a to upwardly stop the course of the vertically movable support 28 . similarly , the lower vertical bumper assembly 114 includes a bumper 114 a mounted to the triangle plate 76 of the vertically movable support 28 and a stop bracket 114 b , mounted to the vertical post 26 and vertically aligned with the bumper 114 a to stop the course of the vertically movable support 28 at the lowers desired position . the front horizontal bumper assembly 116 includes a bumper 116 a and the back horizontal bumper assembly 118 includes a bumper 118 a where the both bumper 116 a and 118 a are positioned on the mobile unit of the horizontal axis movement generator 88 . the front and back horizontal bumpers assembly 116 , 118 share a common stop bracket screwed on the triangle plate 76 of the vertically movable support 28 providing the front stop bracket 116 b and the stop bracket 118 b . front and rear movement of the hip - thigh mechanism 33 is stopped by the contact of the bumpers 116 a , 118 a with the stop bracket portions 116 b and 118 b , respectively . referring to fig1 , the back thigh bumper bracket 120 includes a bumper 124 and a bracket 126 positioned to the hip frame assembly 34 . similarly , front thigh bumper bracket 122 includes a bumper 128 and a bracket 130 positioned to the hip frame assembly 34 . the thigh bumper brackets 120 and 122 limit the movement of the thigh segment assembly 38 . the bumpers were selected such that the system &# 39 ; s kinetic energy can be absorbed by the bumpers . all bumpers are the same , simply for standardization . the worst case condition that produces the highest kinetic energy level is when the system stands at the highest point and is let down in free - fall . the motor of the vertical axis movement generator 86 could also add to the total energy , but its contribution is negligible compared to the free - fall . both bumper 114 a of the lower vertical bumper assembly 114 b and the bumper 128 of the front thigh bumper bracket 122 shall be able to sustain the free - fall drop . the condition where the bumper 128 can be solicited is when the foot enters in contact with the floor before the said bumper 114 a hits its respective stop bracket 114 b . the total energy is calculated as follow : therefore , each bumper should be able to sustain about 1700 lb . in . miner &# 39 ; s gba - 5 bumpers or one gba - 9 meet this requirement . one skilled in the art will understand that the range of motion of the vertically movable support 28 can be adjusted by changing the position of respective stop brackets 112 b , 114 b , 116 b , 118 b , 120 and 122 or their corresponding bumpers 112 a , 114 a , 116 a and 118 a . from the kinetics standpoint , all joints provide enough force / torque to simulate the locomotion activities characterizing a human subject , which mass is corresponding to the mechanical simulator lower - limb linkage ( i . e ., about 72 . 5 kg in the illustrated embodiment ) by adequately mobilizing the vertically and horizontally movable supports 28 and 30 of the pelvic structure 29 , the hip - thigh mechanism 33 and the thigh segment assembly 38 . another aspect of the present invention is concerned with the simulation of human locomotion in stairs . in order to simplify the simulation approach , limit the number of subsystems required , minimize modifications to the actual platform design , and facilitate integration with the actual level - walking simulation capabilities of the platform , the implementation of a complete stance phase simulation with a modified swing phase using the treadmill was proposed over the use of an approach requiring the use of a stepmill - like device . in the proposed approach , the treadmill moving surface is used to simulate the step tread as well as the velocity corresponding to the horizontal progression speed of a normal human subject climbing or descending stairs . this approach allows to correctly simulate the pelvic , the hip and the knee joint mobility during both stairs ascent and descent tasks stance phase , while the swing phase needs to be modified to account for the limited motion range available on the platform and in order to generate coherent stance initial conditions . the swing phase trajectories modifications mostly affect the vertical and horizontal degrees - of - freedom and do not harm the overall simulation validity in a significant manner of this type of locomotion and more specifically the respective stance phase . the range of motion provided by the vertical , horizontal displacement of the pelvic structure 29 and the rotational displacement of the thigh segment assembly 38 , combined with the constant treadmill 24 movement , allows the simulation of the desired tasks : level walking , ascending and descending stairs . the trajectory of the vertical axis of the pelvic structure 29 has been modified ( as can be seen in fig1 and 16 ) for the stair ascent and descent to address the fact that the simulator &# 39 ; s 20 flat treadmill 24 approach doesn &# 39 ; t allow natural kinematics during those tasks . for example , at the end of the stance phase of a step during stair ascent , the pelvic structure 29 would normally continue going up until the next step , but due to the limited vertical freedom of movement on the simulator 20 , the body of the simulator 20 will go down during the swing phase and ensure that the foot is placed properly on the treadmill 24 for the next step . fig1 and 16 show an example of how the vertical axis motion of the pelvic structure 29 is modified for the stairs ascent . the graph of fig1 displays the modified displacement 142 during the stair ascent simulation whereas the fig1 displays the force level 144 required on the vertical axis to follow the desired trajectory . the trajectory displacement 142 and the exerted vertical force 144 represent the kinematics and the kinetics respectively of the vertical mobility of the pelvic bone of the human body . it is to be noted that the forces displayed in fig1 represent the vertical forces to be applied in order to precisely follow the given trajectory , with the assumption that there is no ground contact . this assumption provides force levels that are at least as high as with ground contact condition . it is obvious that the highest force peaks originate from the modification of the trajectory instead of the original gait motion itself ( high acceleration level at the end of the modified trajectory ). all three axes of the simulator 20 are driven by drive systems that allow following their respective trajectories while providing the required level of forces and accelerations . the range of motion was established directly from the trajectory to follow , and the required motor forces are computed from acceleration levels to reach and from the masses / inertias of the moving bodies . to select the different components of a drive system ( electric drive / motor / screw ), the motor torques and speeds are computed and compared with the capacity chart of the drive system . without limiting the present disclosure , we present here below an example of dimensions and specifications that could be used to build the simulator 20 . referring to fig2 , the following dimensions have been used : the distance between the hip joint 40 and the prosthesis knee axis was selected as 403 . 34 mm . table 3 position and force feedback sensors characteristics force feedback sensor position feedback sensor axis type model resolution type model resolution vertical linear siko 4 μm linear us digital 1 / 250 inch magnetic msk200 / 1 optic emi - 0 - 250 ( 0 . 1 mm ) mb200 lin - 250 - 16 - s2037 horizontal linear siko 4 μm linear us digital 1 / 250 inch magnetic msk200 / 1 optic emi - 0 - 250 ( 0 . 1 mm ) mb200 lin - 250 - 16 - s2037 hip n / a n / a n / a rotational us digital 1 / 2048 turn optic heds - 9040 - ( 0 . 18 °) t00 e3 - 2048 - 1000 - ihub the vertical and horizontal axes of the pelvic structure 29 are controlled in position and force ( see fig1 ). position control is conventional , and relatively straightforward . force control is utilized to eliminate the appearance of inertia induced by the drive system . in the case of the vertical axis of the pelvic structure 29 , the mass of the system is about 75 kg , but for the reason that the motor / ball screw system rotates when the mass moves vertically , the apparent mass when accelerations are induced would increase to about 85 kg ( apparent inertia ). the force control mechanism allows eliminating the additional apparent inertia of the drive system . this system also allows simulating weights different than the system &# 39 ; s weight by requesting the desired level of force on the force control loop . although the present invention has been described by way of particular embodiments and examples thereof , it should be noted that it will be apparent to persons skilled in the art that modifications may be applied to the present particular embodiment without departing from the scope of the present invention .
the present invention discloses locomotion simulator comprising a base having a surface movable along a base axis , a post mounted to the base a pelvic structure and a hip - thigh mechanism wherein coordinated displacement of the pelvic structure and pivoting of the thigh segment assembly simulates patterns of locomotion . the pelvic structure includes a first support movably mounted to the post , the first support allowing a displacement of the pelvic structure along a first pelvic axis generally perpendicular to the base axis and a second support movably mounted to the first support , the second support allowing a displacement of the pelvic structure along a second pelvic axis generally parallel to the base axis . as for the hip - thigh mechanism , it is mounted to the second support and includes a hip joint having a pivot axis generally perpendicular to the displacement of the second support and a thigh segment assembly pivotally so connected to the hip joint as to pivot in a plan defined by the first and second pelvic axes .