Patent Application: US-82305410-A

Abstract:
the present invention relates to a ungrounded , reconfigurable , parallel mechanism based , force feedback exoskeleton device for the human ankle . the primary use for the device is aimed as a balance / proprioception trainer , while the exeskeleton device can also be employed to accommodate range of motion / strengthening exercises . this device is also used for metatarsophalangeal joint exercises .

Description:
the following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention , its application , or uses . as illustrated in fig1 , there is shown an ankle therapy and measurement exoskeleton device ( 1 ) according to an embodiment of the present invention , the device comprising ; a moving platform ( 2 ) which faces with the foot of the operator , a base platform ( 3 ) which faces with the leg of the operator , a connecting member ( 4 ) that connects the base platform ( 3 ) and the moving platform ( 2 ). the exoskeleton device ( 1 ) further comprises a joint member ( 5 ) which connects the connecting member ( 4 ) to the base platform ( 3 ). by the help of said joint member ( 5 ) the exoskeleton device ( 1 ) can support two different exercise types , namely rom / strengthening exercises and balance / proprioception exercises independently of each other . the joint member ( 5 ) can selectively be in different modes . in the preferred embodiment of the invention it switches between a universal joint and a revolute joint . in a preferred embodiment of the invention the connecting member ( 4 ) is connected to the moving platform ( 2 ) by using spherical joints . the ankle joint can be modeled as a spatial serial kinematic chain with two revolute joints ( rr ) namely an upper ankle joint and subtalar joint . the upper ankle joint supports the rotational dorsiflexion / plantarflexion motion whereas the subtalar joint supports the rotational supination / pronation motion . supination / pronation rotation is a complex motion that has both inversion / eversion and abduction / adduction components . the kinematic chain used in the preferred embodiment of the invention is the closed kinematic chain ( parallel mechanism ). said closed kinematic chain serves as an exoskeleton and it allows for and supports the natural movements of the human joints when the device ( 1 ) is worn by the operator . a closed kinematic chain offers the compact designs with high stiffness and has low effective inertia . the actuators of the closed kinematic chains can be grounded or placed on parts of the mechanism that experiences low accelerations . the closed kinematic chain used in this invention can be used as at least two different mechanisms by the help of the joint member ( 5 ). by the help of this fact , the device ( 1 ) gains a reconfigurable property . in the preferred embodiment of the invention it can be used as a 3ups ( universal , prismatic , spherical ) as shown in fig4 , and 3rps ( revolute , prismatic , spherical ) mechanisms as shown in fig3 , independently from each other . in a preferred embodiment of the invention , the joint member ( 5 ) is the reconfigurable joint which can selectively be used in unlocked or locked positions . in an unlocked position the reconfigurable joint ( 5 ) can freely rotate around two axes ( a , b )( see fig5 ). the first axis ( a ) is tangential to the base plate ( 3 ) while the second axis ( b ) is perpendicular to the base plate ( 3 ). when the joint ( 5 ) is unlocked , the series of revolute joints function as a universal joint rotating about desired said axes . when the second joint axis ( b ) is locked , the reconfigurable joint ( 5 ) is constrained to function as a revolute joint , that is free to rotate only around the first axis ( a ) ( see fig6 ). hence , the reconfigurable joint ( 5 ) allows a 3ups mechanism to be reconfigured into a 3rps mechanism , and vice versa . as shown in fig1 and 2 , the connecting member ( 4 ) basically comprises a drive unit ( 6 ) and a moving element ( 7 ). drive unit ( 6 ) can apply the necessary force onto moving element ( 7 ), so that the moving element ( 7 ) can move . in a preferred embodiment of the invention the drive unit ( 6 ) is an electric motor whereas the moving element ( 7 ) is at least one extensible link . in the case that the closed kinematic chain is used as a 3ups mechanism , the reconfigurable joint ( 5 ) is in an unlocked position , in other words it is free to rotate about desired axes ( a , b ), and behaves as a universal joint . furthermore , the leg of the operator behaves as a center links of the mechanism , in other words the operator ankle becomes a member of the mechanism . in a preferred embodiment of the invention , the mechanism is a symmetric 3ups mechanism as shown in fig4 , where the universal joint ( 5 ) and the spherical joints are spaced at 120 ° along the circumference of the base platform ( 3 ) and the moving platform ( 2 ). when worn by the user , the 3ups mechanism attached to the human ankle has two degrees of freedom ( dof ) corresponding to a coupled motion of the moving platform ( 2 ) with respect to the fixed base platform ( 3 ). the lengths of the extensible links ( 7 ) are actuated to control these dof . the moving platform ( 2 ) is a distance z from the base platform ( 3 ) and does not possess translational movement transverse to the vertical axis through the base ( 2 ). even when the operator is completely passive , the two dof 3ups mechanism has three actuated joints ; hence , is a redundant mechanism . this redundancy can be exploited to increase the effective workspace of the device ( 1 ), since singularity resolution becomes feasible in case the device ( 1 ) approaches singularities within the workspace . in the case that the closed kinematic chain is used as a 3rps mechanism , the reconfigurable joint ( 5 ) is in locked position , in other words the rotational motion of the joint ( 5 ) about second axis ( b ) is prevented . the reconfigurable joint ( 5 ) behaves as a revolute joint and its axes of rotation are oriented along the tangents of base platform ( 3 ). the base platform ( 3 ) is attached to the upper mid - calf of the leg through a passive revolute joint to allow for the internal / external rotations of the foot . in a preferred embodiment of the invention as shown in fig3 , the mechanism is a symmetric 3rps mechanism where the revolute joints ( 5 ) and the spherical joints are spaced at 120 ° along the circumference of the base platform ( 3 ) and the moving platform ( 2 ). the 3rps mechanism has three dof corresponding to the height z . the lengths of the extensible links ( 7 ) are actuated to control these dof . the moving platform ( 2 ) possesses limited translational movement transverse to the vertical axis through the base ( 3 ) and no singularities for limited values of revolute joint angles . when the closed kinematic chain is in the 3ups mode , the device ( 1 ) can be employed as a rom / strengthening exercise device whereas is in the 3rps mode it ( 1 ) can be employed as a balance / proprioception exercise device . couplings between the exoskeleton device ( 1 ) and the operator are designed to be elastic to ensure safety and to allow for small joint misalignments and modeling imperfections . elasticity allows for the relative motion of the human limb with respect to the device ( 1 ) when the kinematics of the device ( 1 ) is in conflict with the natural movement of the ankle . in one embodiment of the invention , the weight of the device ( 1 ) is distributed over the upper leg and the upper mid - calf by using tight straps around the knee . in another embodiment of the invention the weight of the device ( 1 ) can be distributed over the body by suspending the device ( 1 ) from the shoulder of the operator . the exoskeleton device ( 1 ) further comprises a control unit ( not shown in the figures ), and at least two sensors ( not shown in the figures ). one of the sensors measure the length of the connecting member ( 4 ) whereas the second sensor measures the axial rotation amount of the joint member ( 5 ). the measured data of the elements are processed by the control unit for calculating the configuration of the device ( 1 ) and estimating the forces acting on it ( 1 ). in particular , forward kinematics of the device ( 1 ) is used to calculate the configuration of moving platform ( 2 ), while the device ( 1 ) dynamics is used with a reaction torque observer implemented in software to estimate the forces acting on it ( 1 ). for estimating the ankle parameters , the link ( 7 ) lengths of the kinematic chain must be known along with the rotation axes of the revolute joints . determination of the bone lengths of the operator is relatively straightforward as x - ray images of the ankle can be studied to achieve reasonably accurate estimates . however , determination of the rotation axes is challenging since the motion of the ankle depends on the size and orientation of the foot bones , and the shape of articulated surfaces . only course estimates of joint axes can be obtained by studying the x - ray images . more accurate estimates of joint axes are desired to study the ankle motion and such estimates are made possible thanks to the data collected with the exoskeleton . given good estimations of the bone lengths , the axes of rotation of the revolute joints of the human ankle can be determined by instructing the operator to perform free rom movements and by collecting position data from the extensible links ( 7 ) and preferably three rotation sensors placed on the joint member ( 5 ). as the data becomes available , the configuration level forward kinematics of the 3ups mechanism is solved for the moving platform ( 2 ) configurations at each instant of time . once the foot configurations are recorded , the configuration level inverse kinematics of the two link rr manipulator with unknown the revolute joint axes ( representing the human ankle ) is solved for the axes of revolute joints and the amount of rotation around these axes . given the configuration and motion level forward and inverse kinematics of the coupled 3ups - rr system ( the exoskeleton coupled to the human ankle ) and the dynamic properties of the exoskeleton device ( 1 ) only , a robust position controller with a reaction torque observer can be implemented to characterize the dynamic properties of the ankle . in particular , by employing a robust position controller as that illustrated in fig7 , the exoskeleton device ( 1 ) can command the ankle trace a desired trajectory , while disturbance forces due to the unknown dynamics of the ankle can be estimated during this motion . in the controller implementation , forces due to the known dynamics of the exoskeleton device ( 1 ) is added to the system in a feed forward manner to ensure that the disturbance acting on the system is solely due to the unknown dynamics of the ankle . under such a control , the forces commanded by the controller are to counteract the unmodeled dynamics of the ankle . hence , the actuator forces can be mapped to the joint torques at the ankle and assuming that all other disturbances are comparatively small , these torques provide a close estimate of the actual joint torques provide a close estimate of the actual joint torques due to ankle dynamics . the exoskeleton device ( 1 ) can deliver passive , active , assistive and resistive exercise modes . virtual tunnels and force fields inside these tunnels can be implemented to enable safe practice with assistance or resistance . since the device ( 1 ) in 3ups configuration allows for all possible movements of the ankle within its full range , it is possible to use the device ( 1 ) for clinical measurements . firstly , the device can be used to determine range of motion of the patient . when the patient moves his / her ankle , the device can measure and log the time history of this movement ( the trajectory ). given the measured the time history of movements , it is possible to determine how fast the patient completes a movement , the amount of error involved with respect to a reference trajectory and how smooth / intermittent these movements are . since the kinematics of the device ( 1 ) is known , it is also possible to map the measured configuration changes to the rotations of the ankle joint . this capability allows for measurement of orientation , speed and smoothness of ankle joint movements . coordination and synergies of joint movements can also be detected from these measurements . as explained above , employing a robust position controller and commanding the exoskeleton device ( 1 ) to trace a desired trajectory , the disturbance forces due to the unknown dynamics of the ankle can be estimated during this motion . these forces can also be mapped to the joint torques at the ankle using ankle kinematics . this measurement technique can be used to determine maximum joint torques the patient can exert the impedance and the tone of the patent ankle , at any configuration of the ankle . in particular , if the gains of the robust position controller is set to stay at any reference configuration , and the patient is asked to apply maximum torque at his / her ankle joints , then the disturbance forces acting on the controller can be mapped to joint torques to estimate human ankle joint torques about the relevant axes . finally , given a pre - specified reference trajectory for the robust position controller , the joint torques can be estimated at each instant of time and the relation between the joint rotation and the joint torques can be used to estimate ankle impedance and / or tone . in another embodiment of the invention the ungrounded , wearable and reconfigurable ankle therapy and measurement exoskeleton device can be combined with the virtual reality games . the description of the invention is merely exemplary in nature and , thus , variations that do not depart from the gist of the invention are intended to be within the scope of the invention . such variations are not to be regarded as a departure from the spirit and scope of the invention . h . tropp and h . alaranta , sport injuries : basic principles of prevention and care , proprioception and coordination training in injury prevention . oxford , 1993 . d . hung , m . kennedy , a . rowland , j 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