WO2018192861A1

WO2018192861A1 - Gait training apparatus

Info

Publication number: WO2018192861A1
Application number: PCT/EP2018/059584
Authority: WO
Inventors: Gary Cripps; Richard Powell; Jeremy Greenwood; Hester CORNE; Alexander Morrison; Andrew FAIRGRIEVE; Paul King
Original assignee: Jaguar Land Rover Limited
Priority date: 2017-04-21
Filing date: 2018-04-13
Publication date: 2018-10-25

Abstract

The present disclosure relates to a releasable footplate assembly (6-1) for a gait training unit (5-1, 5-2). The releasable footplate assembly (6-1) includes a movable footplate (7-1) having fastening means (15) for fastening a user's foot (3-1, 3-2) to the movable footplate (7-1). A footplate carrier (12) having retaining means (10-1) is provided to generate a retaining force to retain the movable footplate (7-1). The retaining means (10-1) is controllable to adjust the retaining force. The retaining force may, for example, be controlled in dependence on a position and/or orientation of the releasable footplate assembly (6-1). In an alternative arrangement, the processor (41) may be configured to control the retaining means (10-1) to release the movable footplate (7-1) if an applied force is greater than a release force threshold (FT1). The processor (41) may be configured to adjust the release force threshold (FT1). The present disclosure also relates to a control unit (40) for controlling a releasable footplate assembly (6-1); and a gait training apparatus (1) comprising at least one releasable footplate assembly (6-1).

Description

GAIT TRAINING APPARATUS

TECHNICAL FIELD

The present disclosure relates to a gait training apparatus. In particular, but not exclusively, the present disclosure relates to a releasable footplate assembly for a gait training device. The present disclosure also relates to a gait training apparatus for training a user to modify their gait; and to a control unit for controlling a releasable footplate assembly.

BACKGROUND

The movement pattern of an individual's limbs during locomotion over a fixed surface, for example as they walk or run, is referred to as gait. A gait cycle (or locomotor cycle) is the movement pattern of the lower limbs. The gait cycle is made up of an alternating stance phase and swing phase. The stance phase is composed of the following phases: heel strike, heel strike to foot flat, foot flat to midstance, and midstance to toe off. The swing phase is composed of the following phases: early swing, midswing and late swing. The gait cycle starts when one foot makes contact with the ground and ends when that same foot contacts the ground again.

It is appropriate to train certain individuals to modify or correct their gait to improve their gait characteristics. By way of example, individuals having cerebral palsy may have lower levels of coordination which affects their gait. Specialist practitioners, such as physiotherapists, may work with individuals to modify their gait. However, this process is time-consuming and may not be available to all individuals due to the expense involved. Gait training devices are known. Current gait training devices typically force a user's feet and/or lower limbs in a predefined gait pattern that is calculated from basic measurements such as limb length. The predefined gait pattern is used to force the user's feet and limbs to mimic a walking movement and is repeated over extended periods so that the patient learns a normalised gait pattern. The user has to follow this pattern regardless of their abilities, such as muscle strength or joint freedom. This forceful process masks any ability that the user has which results in the training regime not being tuned to the user. This may cause the user discomfort as the new pattern is a step change from their existing gait.

At least in certain embodiments, the invention seeks to overcome or ameliorate at least some of the problems associated with existing gait training apparatus and methods.

SUMMARY OF THE INVENTION Aspects of the present invention relate to a releasable footplate assembly; a gait training unit; a gait training apparatus; and a control unit for controlling a releasable footplate assembly as claimed in the appended claims. According to an aspect of the present invention there is provided a releasable footplate assembly for a gait training unit, the releasable footplate assembly comprising:

a movable footplate having fastening means for fastening a user's foot to the movable footplate; and

a footplate carrier having retaining means for generating a retaining force to retain the movable footplate;

wherein the retaining means is controllable to adjust the retaining force. The releasable footplate assembly has particular application in a gait training unit to train a user to change their gait when walking. The retaining force may be increased when the user is required to apply a high load to the gait training unit; and may be reduced when the user is required to apply a low load to the gait training unit. Thus, it will be understood that the releasable footplate assembly may be controlled in dependence on the expected operating loads. At least in certain embodiments, the risk of injury to the user of the gait training unit may be reduced by adjusting the retaining force. For example, the retaining force may be controlled in dependence on a planned movement of the movable footplate.

The releasable footplate assembly may comprise a control unit for controlling the retaining means to adjust the retaining force. The control unit may comprise a processor and a memory device. The memory device may comprise a non-transient computer-readable medium for storing data.

The fastening means may comprise one or more strap having a releasable fastener. The releasable fastener may, for example, comprise a hook and loop fastener, an over-centre locking mechanism or a buckle. The footplate carrier may comprise a platform or other support member. The retaining means is operative to generate the retaining force to retain the movable footplate. At least in certain embodiments, the movable footplate is fixedly mounted to the footplate carrier when said retaining force is applied. The processor may be configured to determine a position and/or an orientation of the movable footplate. The retaining force may be adjusted in dependence on the determined position and/or orientation of the movable footplate. The processor may be configured to control the retaining means to adjust the retaining force in dependence on the determined position and/or orientation of the movable footplate relative to a predetermined trajectory. The predetermined trajectory may, for example, comprise a target gait trajectory. The retaining means comprises a footplate retention device.

The retaining means may comprise one or more electromagnet for generating a magnetic retaining force. For example, one or more electromagnetic coils may be disposed in the movable footplate. The processor may be configured to control the supply of electrical current to the one or more electromagnet to adjust the retaining force. By controlling the supply of electrical current, the processor may control the strength of the magnetic field generated by the one or more electromagnet.

The movable footplate may comprise one or more coupling elements which are attracted to the one or more electromagnet. The one or more coupling elements may, for example, comprise a permanent magnet or a ferromagnetic material. The one or more coupling member may be in the form of an insert in said footplate.

Alternatively, the retaining means may comprise one or more mechanical retention device. The one or more mechanical retention device may comprise a latching mechanism for generating the retaining force. The latching mechanism may comprise spring biasing means for applying a spring biasing force to one or more latching member, the spring biasing means being adjustable to change the spring biasing force. An actuator may be provided to adjust the spring biasing means. The spring biasing means may, for example, comprise a torsion spring. The actuator may be operable to adjust the tension in said torsion spring. The actuator may, for example, comprise an electric torque generating machine. The processor may be configured to control the actuator to adjust the spring biasing means.

The releasable footplate assembly may comprise force measurement means for measuring an applied force. The force measurement means may comprise: means for sensing the force applied along one axis, two axes or three axes; and/or means for sensing the force applied about one axis, two axes or three axes. The force measurement means may, for example, comprise a load cell comprising a strain gauge or a shear stress gauge. Other types of load cell that may be used include: hydraulic (or hydrostatic), pneumatic, piezo-electric and vibrating wire load cells. The retaining means may be configured to release the movable footplate if the applied force measured by the force measurement means is greater than a release force threshold. The release force threshold may be fixed or may be variable. According to a further aspect of the present invention there is provided a gait training apparatus comprising at least one releasable footplate assembly as described herein.

The movable footplate may be movable to follow a target gait trajectory. The processor may be configured to control the retaining means to adjust the retaining force in dependence on the determined position and/or orientation of the movable footplate relative to said target gait trajectory.

The gait training apparatus may comprise one or more actuator for controlling the movement and/or orientation of said footplate. The one or more actuator may be operable to control an activation force required to move the movable footplate in dependence on a determined position of the movable footplate relative to the target gait trajectory.

According to a further aspect of the present invention there is provided a control unit for controlling the releasable footplate assembly as described herein, the control unit comprising a processor and a memory device, the processor being configured to control the retaining means to adjust the retaining force. The memory device may comprise a non-transient computer-readable medium for storing data. The control unit may comprise one or more communication input for receiving data. The processor may be configured to read data from the non-transient computer-readable medium.

The processor is configured to determine a position and/or an orientation of the movable footplate; and to adjust the retaining force in dependence on the determined position and/or orientation of the movable footplate. The processor may be configured to adjust the retaining force in dependence on the determined position and/or orientation of the movable footplate relative to a predetermined trajectory.

According to a further aspect of the present invention there is provided a releasable footplate assembly for a gait training unit, the releasable footplate assembly comprising:

a movable footplate having fastening means for fastening a user's foot to the movable footplate; and a footplate carrier having retaining means for retaining the movable footplate;

force measurement means for measuring an applied force; and

a control unit for controlling the retaining means, the control unit comprising a processor and a memory device, the processor being configured to control the retaining means to release the movable footplate if the applied force measured by the force measurement means is greater than a release force threshold. The memory device may comprise a non-transient computer-readable medium for storing data.

The processor may be configured to adjust the release force threshold. The processor may be configured to determine the position and/or orientation of the movable footplate and to adjust the release force threshold in dependence on the determined position and/or orientation of the movable footplate. The processor may be configured to adjust the release force threshold in dependence on the determined position and/or orientation of the movable footplate relative to a predetermined trajectory.

The force measurement means may comprise means for sensing the force applied along one axis, two axes or three axes; and/or means for sensing the force applied about one axis, two axes or three axes. The force measurement means may, for example, comprise a load cell comprising a strain gauge or a shear stress gauge. Other types of load cell that may be used include: hydraulic (or hydrostatic), pneumatic, piezo-electric and vibrating wire load cells.

The retaining means may be controllable to adjust the retaining force. The control unit may be configured to control said retaining means to adjust the retaining force.

According to a further aspect of the present invention there is provided a gait training apparatus comprising at least one footplate described herein.

The movable footplate may be movable along a predetermined trajectory. The processor may be configured to adjust the release force threshold in dependence on a determined position and/or orientation of the movable footplate relative to said predetermined trajectory. The predetermined trajectory may comprise a target gait trajectory.

The gait training apparatus may comprise one or more actuator for controlling the movement and/or orientation of said footplate, the one or more actuator being operable to control an activation force required to move the movable footplate. According an aspect of the present invention there is provided a gait training unit comprising: a movable footplate;

one or more actuator for controlling the movement and/or orientation of said footplate;

a control unit comprising a processor and a memory;

wherein the processor is configured to control said one or more actuator to control an activation force required to move the footplate in dependence on a determined position of the footplate relative to a movement corridor defined in dependence on a target gait trajectory.

The target gait trajectory defines a gait trajectory for a gait cycle. The target gait trajectory may, for example, represent a corrective gait pattern. The movement corridor defines a permissible deviation (stray) in dependence on the target gait trajectory. The permissible deviation can be uniform throughout the gait cycle. When a user starts using the gait training unit, the permissible deviation may be relatively large. However, the permissible deviation may be decreased over time. The effect of reducing the permissible deviation is to narrow the movement corridor. Conversely, increasing the permissible deviation broadens the movement corridor. It will be understood that the permissible deviation may be modified during one or more sections of the gait cycle; or throughout the complete gait cycle. The permissible deviation may vary for different sections of the gait cycle. For example, the permissible deviation may be smaller in sections of the gait cycle deemed to be more important, such as the toe off and early swing sections of the gait cycle. The one or more actuator may be controlled so as to vary the activation force required to move the footplate, for example varying the magnitude and/or the direction of the activation force in dependence on the determined position of the footplate.

By controlling the footplate in dependence on a movement corridor, the gait training unit may be configured to correct the user's gait only when it deviates from the target gait trajectory outside of the defined permissible deviation. The target gait trajectory defines the target position of the footplate (and by extension the target position of the user's foot) as the user walks. At least in certain embodiments, the gait training unit is more comfortable for the user as the movement corridor may be tuned to the user rather than a calculated pattern.

At least in certain embodiments, the target gait trajectory is tailored for a particular user. The target gait trajectory may, for example, be generated in dependence on one or more measured gait parameter for a particular user. The target gait trajectory may be refined over time to progressively develop the user's gait. Alternatively, or in addition, the definition of the movement corridor may be refined. By way of example, the extent of the movement corridor may be reduced as the user's gait corresponds more closely to the target gait trajectory. The activation force is the force that a user must apply to move the footplate. The processor is configured to control the activation force depending on the determined position of the footplate. By way of example, if the footplate is following the target gait trajectory, the activation force required to move the footplate may be lower than if the footplate is not following the target gait trajectory. By controlling the activation force, the gait training unit provides feedback to the user and can teach the user the target gait trajectory. The movement corridor may be based on a target gait trajectory defined by a medical practitioner or physiotherapist. The movement corridor may be predefined. Alternatively, the movement corridor may change dynamically, for example to reflect changes in a user's centre of gravity and/or in dependence on a measured force applied to the footplate. The movement corridor comprises a spatial volume for controlling movement of the footplate during a gait cycle. The movement corridor may be defined in two or three dimensions with reference to the target gait trajectory. The target gait trajectory may correspond to a centreline of the movement corridor. In particular, the target gait trajectory may correspond to a centreline of the movement corridor in a transverse direction.

The processor may be configured to control said one or more actuator to vary the activation force in proportion to a distance between a determined position of the footplate and a target position. The position of the footplate may be determined in dependence on a predefined reference point. The distance may be measured in a plane extending perpendicular to a direction in which the user is walking.

The processor may be configured to control said one or more actuator to reduce the activation force when the footplate is inside the movement corridor and to increase the activation force when the footplate is outside the movement corridor.

The control unit may be operable in an assistance mode and/or a resistance mode. The control unit may be operable to select either said assistance mode or said resistance mode.

When operating in said assistance mode, the processor may be configured to control said one or more actuator to apply an assistive force to reduce the activation force required to move the footplate. The assistive force may bias the footplate in a longitudinal direction and/or a vertical direction and/or a transverse direction. The assistive force may bias the footplate towards the target gait trajectory; and/or along the target gait trajectory. The processor may be configured to control said one or more actuator to control the assistive force in dependence on the position of the footplate relative to the target gait trajectory. The processor may be configured to control a direction and/or magnitude of the assistive force based on the position of the footplate. The direction and/or magnitude of the assistive force may be varied.

When operating in said resistance mode, the processor may be configured to control said one or more actuator to apply a resistive force to increase the activation force required to move the footplate. The processor may be configured to control said one or more actuator to control the resistive force in dependence on the position of the footplate relative to the target gait trajectory. The processor may be configured to control a direction and/or magnitude of the resistive force based on the position of the footplate. The direction and/or magnitude of the resistive force may be varied.

The target gait trajectory may be defined by a first position loop and a second position loop. The first position loop may be defined by a target trajectory for a first reference point on the footplate; and the second position loop defining a target trajectory for a second reference point on the footplate. By way of example, the first position loop may correspond to a toe position loop and the second position loop may correspond to a heel position loop. The first and second position loop may also define a target footplate orientation.

The processor may be configured to control said one or more actuator to control an activation torque required to pivot the footplate about one or more axis. The activation torque is the torque that a user must apply to pivot the footplate. The direction and/or magnitude of the activation torque may be varied. The activation torque may be modified in dependence on a determined footplate orientation and a target footplate orientation. The activation torque may be modified in proportion to the angular offset between the determined footplate orientation and the target footplate orientation. The changes in the activation torque may be directly proportional to the angular offset between the determined footplate orientation and the target footplate orientation. When operating in said assistance mode, the processor may be configured to control said one or more actuator to apply an assistive torque to reduce the activation torque required to pivot the footplate. When operating in said resistance mode, the processor may be configured to control said one or more actuator to apply a resistive torque to increase the activation torque required to pivot the footplate. According to a further aspect of the present invention there is provided a gait training unit comprising:

a movable footplate;

a control unit comprising a processor and a memory;

wherein the processor is configured to control said one or more actuator to control an activation torque required to pivot the footplate about one or more axis in dependence on a determined footplate orientation and a target footplate orientation. The activation torque may be modified in proportion to the angular offset between the determined footplate orientation and the target footplate orientation. The changes in the activation torque may be directly proportional to the angular offset between the determined footplate orientation and the target footplate orientation. The one or more actuator may be controlled so as to vary the activation torque required to pivot the footplate, for example varying the magnitude and/or the direction of the activation torque.

The control unit is operable in an assistance mode and/or a resistance mode. When operating in said assistance mode, the processor may be configured to control said one or more actuator to apply an assistive torque to reduce the activation torque required to pivot the footplate. When operating in said resistance mode, the processor may be configured to control said one or more actuator to apply a resistive torque to increase the activation torque required to pivot the footplate.

The gait training unit may comprise force sensing means for measuring a force applied to the footplate by a user. The force sensing means may be configured to output one or more force measurement signal to the control unit. The processor may be configured to control said one or more actuator in dependence on said one or more force measurement signal received from the force sensing means. The force sensing means may comprise one or more force sensors for measuring an applied force along one or more axis. The gait training unit may comprise acceleration sensing for measuring acceleration along one or more axis; and/or about one or more axis.

The processor may be configured to determine the position and/or orientation of the footplate. The processor may be configured to determine the position and/or orientation of the footplate in dependence on an operating condition of said one or more actuator. One or more position sensor may be associated with said one or more actuator. For example, one or more angular position sensor may be provided for monitoring the position of said one or more actuator. The processor may be configured to determine the position of the footplate in dependence on the data received from said one or more position sensor. Alternatively, or in addition, the processor may be configured to determine the position and/or orientation of the footplate in dependence on data received from acceleration sensing means.

The one or more actuator may comprise one or more of the following:

a first displacement actuator for controlling longitudinal movement of the footplate; a second displacement actuator for controlling transverse movement of the footplate; and

a third displacement actuator for controlling vertical movement of the footplate; Alternatively, or in addition, the one or more actuator may comprise one or more of the following:

a first pivot actuator for controlling pivoting of the footplate about a transverse axis; a second pivot actuator for controlling pivoting of the footplate about a vertical axis; and

a third pivot actuator for controlling pivoting of the footplate about a longitudinal axis.

The target gait trajectory may comprise a target position of the footplate. The target position may be defined in one, two or three dimensions. Alternatively, or in addition, the target gait trajectory may comprise a target orientation of the footplate. The target orientation may be defined by one axis, two axes or 3 axes.

The movement corridor may be generated in dependence on a combination of a reference gait trajectory and a measured gait trajectory of a user.

The movement corridor may be predefined. Alternatively, the movement corridor may be determined dynamically, for example in dependence on one or more gait parameter of a user. The control unit may be operable in a learning mode to measure one or more gait parameter of a user for generating the target gait trajectory. When operating in said learning mode, the processor may be configured to track the movement and/or orientation of the footplate to measure said one or more gait parameter.

The processor may be configured to control said one or more actuator to define a virtual surface S1 for measuring said one or more gait parameter. The virtual surface S1 may be level (horizontal), and/or inclined. Alternatively, the virtual surface S1 may have a stepped profile. For example, the virtual surface S1 they comprise an upward step; and/or a downwards step.

The processor may be configured to generate the target gait trajectory by combining a reference gait trajectory and the measured gait trajectory. The gait training unit described herein could be used independently, for example to alternate between training of the left and right legs of the user. For example, the gait training unit could be used in conjunction with a moving walkway to simulate walking. However, at least in certain embodiments, two of said gait training units are used in conjunction with each other to perform simultaneous gait training on the left and right legs of the user.

According to a further aspect of the present invention there is provided a gait training apparatus comprising first and second gait training units as described herein.

The first gait training unit may comprise a first footplate; and the second gait training unit may comprise a second footplate. The processor may be configured to control said one or more actuator to control an activation force required to move the first footplate and/or the second footplate. The one or more actuator may be controlled so as to vary the activation force required to move the footplate, for example varying the magnitude and/or the direction of the activation force. A first movement corridor may be defined for the first gait training unit; and a second movement corridor may be defined for the second gait training unit. The activation force may be controlled in dependence on a determined position of the first and second footplates relative to each other. By controlling the activation force applied to said first footplate and/or the second footplate, the first gait training unit may ensure that the first and second gait training units remain synchronised with each other. An assistive force may be applied to one of the first and second foot plates; and/or a resistive force may be applied to the other of said first and second foot plates. The assistive force and/or the resistive force may be controlled to synchronise the first and second foot plates with each other. The assistive force may be applied along one axis, two axes or three axes. The resistive force may be applied along one axis, two axes or three axes.

The processor described herein may be in communication with a non-transient computer- readable medium for storing data. The movement corridor(s) may be stored in said non- transient computer-readable medium.

According to a further aspect of the present invention there is provided a control unit for controlling a gait training apparatus as described herein, the control unit comprising:

a processor, a non-transient computer-readable medium for storing data, the processor being configured to access a movement profile stored in the non-transient computer-readable medium. The movement profile may comprise a movement corridor for a user. The movement corridor may define a target gait trajectory for the user. The control unit may be configured to control one or more actuator to control an activation force required to move one or more footplate of the gait training apparatus in dependence on a determined position of the one or more footplate relative to the one or more stored movement corridor. The one or more actuator may be controlled so as to vary the activation force required to move the footplate, for example varying the magnitude and/or the direction of the activation force.

According to an aspect of the present invention there is provided a control unit for controlling a gait training unit having a moveable footplate and one or more actuator for controlling movement of the footplate; the control unit comprising a processor and a memory device, a user profile being stored on said memory device and defining a range of motion of one or more joint of the user, the processor being configured to:

identify a planned footplate position and/or a planned footplate orientation in dependence on a target gait trajectory;

generate a virtual kinematic model in dependence on the user profile; and determine one or more virtual joint angle when the virtual kinematic model is re- configured in dependence on the planned footplate position and/or the planned footplate orientation;

wherein, if the one or more virtual joint angle is outside the range of motion defined for a corresponding joint in the user profile, the processor is configured to output a control signal to control said one or more actuator to control movement of the footplate to the planned footplate position and/or the planned footplate orientation. It will be understood that the control unit implements a watchdog control strategy which, at least in certain embodiments, helps to ensure that the footplate is not moved to a position and/or orientation which may result in injury to the user. The one or more actuator may control the force and/or the torque required to move the footplate. The footplate may translate and/or rotate. The processor may be configured to control the one or more actuator to control the force required to translate the footplate; and/or the torque required to rotate the footplate. The one or more actuator may control movement of the footplate by reducing, limiting, restricting, or preventing movement of the footplate. The control unit is configured to model the virtual joint angles of the virtual kinematic model required to comply with the planned footplate position and/or the planned footplate orientation. If the virtual joint angles are outside of the one or more range of motion defined in said user profile, the control unit determines that the planned movement of the footplate would not be safe for the user. The control unit is configured to control any such planned movement before it is implemented. Thus, the control unit models each planned footplate position and/or orientation change to determine if they are permissible. The processor may be configured to enable movement of the footplate to the planned footplate position and/or the planned footplate orientation provided the virtual joint angle is inside the range of motion. The processor may be configured to output one or more control signal to control said one or more actuator.

The range of motion may be defined for each joint in the lower limb of the user. For example, the range of motion may be defined for a hip joint and/or a knee joint and/or an ankle joint. The range of motion defines the movement of the joint full flexion to full extension. It may also be referred to as joint movement, full flexion and full extension. The range of motion may be defined by first and second angular end positions. The first angular end position may correspond to full flexion; and the second angular end position may correspond to full extension. The user profile may be defined for a particular user. The user profile may, for example, define the dimensions of the user's limbs, particularly their lower limbs. The user profile may, for example, define an upper leg (thigh) length; and a lower leg (shank) length. The range of motion of each joint may be defined for a particular user. For example, the range of motion of the hip, the knee and the ankle may be defined for each user. The user profile may thereby make allowances for different joint flexibility, for example to allow for variations in muscle elasticity and/or previous injuries. If the one or more virtual joint angle is outside the range of motion defined for the corresponding joint in the user profile, the control signal may control said one or more actuator to limit halt movement of the footplate. If the one or more virtual joint angle is outside the range of motion defined for the corresponding joint in the user profile, the control signal may be configured to control said one or more actuator to move the footplate to a default position and/or a default orientation. The default position and/or the default orientation may be predefined. The default position and/or the default orientation may be a neutral position, for example to enable the user to stand in an upright position.

The processor may be configured to determine a current footplate position and/or a current footplate orientation. For example, the processor may monitor operation of said one or more actuator to determine current footplate position and/or the current footplate orientation. Alternatively, or in addition, one or more position sensor may be provided for determining current footplate position and/or the current footplate orientation. Alternatively, or in addition, one or more accelerometer may be provided for determining current footplate position and/or the current footplate orientation. Other techniques, such as image processing, may be used to determine current footplate position and/or the current footplate orientation.

The processor may be configured to determine the change in the virtual joint angle in said virtual kinematic model as the footplate moves from the current footplate position and/or the current footplate orientation to the planned footplate position and/or the planned footplate orientation.

The planned footplate position and/or the planned footplate orientation may be determined in dependence on the target gait trajectory. The target gait trajectory may define the position and/or orientation of the footplate during a gait cycle. The planned footplate position and/or the planned footplate orientation may correspond to the footplate position and/or the footplate orientation defined at a location on said target gait trajectory ahead of the current position. The target gait trajectory may be predefined. The target gait trajectory may be defined by one or more continuous loop composed of a plurality of discrete points. The discrete points may each define a target position and a target orientation for the footplate throughout the gait cycle. The planned footplate position and/or the planned footplate orientation may correspond to the footplate position and/or the footplate orientation defined at a discrete point ahead of the current discrete point (i.e. ahead of the discrete point corresponding to the current position of the footplate). For example, the planned footplate position and/or the planned footplate orientation may correspond to the footplate position and/or the footplate orientation defined at the next discrete point in said one or more loop. Alternatively, the planned footplate position and/or the planned footplate orientation may correspond to the footplate position and/or the footplate orientation defined at a predetermined interval along the target gait cycle.

The processor may be configured to determine a virtual reaction force and/or a virtual reaction torque generated when the virtual kinematic model is re-configured in dependence on the planned footplate position and/or the planned orientation. If the virtual reaction force is greater than a reaction force threshold and/or the virtual reaction torque is greater than a reaction torque threshold, the processor may be configured to output a control signal to control said one or more actuator to control movement of the footplate to the planned footplate position and/or the planned footplate orientation. The reaction force threshold and/or the reaction torque threshold may be stored in said user profile. The reaction force threshold and/or the reaction torque threshold may be defined for a particular user.

The processor may be configured to determine the virtual reaction force and/or the virtual reaction torque in said virtual kinematic model as the footplate moves from current footplate position and/or the current footplate orientation to the planned footplate position and/or the planned footplate orientation.

According to a further aspect of the present invention there is provided a control unit for controlling a gait training unit having a moveable footplate and one or more actuator for controlling movement of the footplate; the control unit comprising a processor and a memory device, a user profile being stored on said memory device and defining a reaction force threshold and/or a reaction torque threshold, the processor being configured to:

generate a virtual kinematic model in dependence on the user profile; and determine a virtual reaction force and/or a virtual reaction torque generated when the virtual kinematic model is re-configured in dependence on the planned footplate position and/or the planned footplate orientation;

wherein, if the virtual reaction force is greater than the reaction force threshold and/or the virtual reaction torque is greater than the reaction torque threshold, the processor may be configured to output a control signal to control said one or more actuator to control movement of the footplate to the planned footplate position and/or the planned footplate orientation. The processor may be configured to determine the virtual reaction force and/or the virtual reaction torque that may be generated if the footplate is moved to the planned footplate position and/or the planned footplate orientation. By modelling the virtual reaction force and/or the virtual reaction to work before the footplate is moved, the processor may determine if implementing the move may injure the user. If the processor determines that moving the footplate to the planned footplate position and/or the planned footplate orientation is likely to result in a reaction force or a reaction torque greater than the corresponding threshold, the movement of the footplate to the planned footplate position and/or the planned footplate orientation is controlled. The processor may be configured to enable movement of the footplate to the planned footplate position and/or the planned footplate orientation if the virtual reaction force is less than the reaction force threshold and/or the virtual reaction torque is less than the reaction torque threshold. The one or more actuator may control the force and/or the torque required to move the footplate. The movement of the footplate may comprise translation and/or rotation. The processor may be configured to control the one or more actuator to control the force required to translate the footplate; and/or the torque required to rotate the footplate. The one or more actuator may control movement of the footplate by reducing, limiting, restricting, or preventing movement of the footplate.

If the virtual reaction force is greater than the reaction force threshold and/or the virtual reaction torque is greater than the reaction torque threshold, the control signal may be configured to control said one or more actuator to halt movement of the footplate. If the virtual reaction force is greater than the reaction force threshold and/or the virtual reaction torque is greater than the reaction torque threshold, the control signal is configured to control said one or more actuator to move the footplate to a default position and/or a default orientation. The memory device may comprise a non-transient computer-readable medium for storing data. The memory device may comprise a non-transient computer-readable medium for storing data. The control unit may comprise one or more communication input for receiving data. The processor may be configured to read data from the non-transient computer- readable medium. The processor may be configured to read the user profile from said non- transient computer-readable medium. According to a further aspect of the present invention there is provided a gait training unit comprising a control unit as described herein.

According to a still further aspect of the present invention there is provided a gait training apparatus comprising first and second gait training units as described herein.

According to a further aspect of the present invention there is provided a method of controlling a gait training unit having a moveable footplate; the method comprising:

identifying a planned footplate position and/or a planned footplate orientation in dependence on a target gait trajectory;

generating a virtual kinematic model representing a user; and

determining one or more virtual joint angle when the virtual kinematic model is reconfigured in dependence on the planned footplate position and/or the planned footplate orientation;

wherein, if the one or more virtual joint angle is outside a range of motion defined for a corresponding joint, controlling movement of the footplate to the planned footplate position and/or the planned footplate orientation. The method may comprise enabling movement of the footplate to the planned footplate position and/or the planned footplate orientation if the virtual joint angle is inside the range of motion defined for the corresponding joint in the user profile. The method may comprise controlling the force and/or the torque required to move the footplate. The movement of the footplate may comprise translation and/or rotation. The method may comprise controlling the force required to translate the footplate; and/or the torque required to rotate the footplate. The method may comprise controlling movement of the footplate by reducing, limiting, restricting, or preventing movement of the footplate.

The method may comprise halting movement of the footplate if the one or more virtual joint angle is outside the range of motion defined for the corresponding joint in the user profile. The method may comprise moving the footplate to a default position and/or a default orientation if the one or more virtual joint angle is outside the range of motion defined for the corresponding joint in the user profile.

The method may comprise determining a virtual reaction force and/or a virtual reaction torque generated when the virtual kinematic model is re-configured in dependence on the planned footplate position and/or the planned footplate orientation. The method may comprise controlling movement of the footplate to the planned footplate position and/or the planned footplate orientation if the virtual reaction force is greater than a reaction force threshold or the virtual reaction torque is greater than a reaction torque threshold.

According to a further aspect of the present invention there is provided method of controlling a gait training unit having a moveable footplate;

generating a virtual kinematic model representing a user; and

determining a virtual reaction force and/or a virtual reaction torque generated when the virtual kinematic model is re-configured in dependence on the planned footplate position and/or the planned footplate orientation;

wherein, if the virtual reaction force is greater than a reaction force threshold or the virtual reaction torque is greater than a reaction torque threshold, controlling movement of the footplate to the planned footplate position and/or the planned footplate orientation. The method may comprise enabling movement of the footplate to the planned footplate position and/or the planned footplate orientation if the virtual reaction force is less than the reaction force threshold and/or the virtual reaction torque is less than the reaction torque threshold.

The method may comprise halting movement of the footplate if the virtual reaction force is greater than the reaction force threshold or the virtual reaction torque is greater than the reaction torque threshold.

The method may comprise moving the footplate to a default position and/or a default orientation if the virtual reaction force is greater than the reaction force threshold or the virtual reaction torque is greater than the reaction torque threshold.

The planned footplate position and/or the planned footplate orientation may correspond to the footplate position and/or the footplate orientation defined at a position along the target gait trajectory ahead of the current position. The footplate position and/or the footplate orientation may be known, for example corresponding to a predefined point. Alternatively, the footplate position and/or the footplate orientation may be determined dynamically, for example by determining the position and/or the orientation at a known interval along the target gait trajectory. According to a further aspect of the present invention there is provided a non-transient computer-readable medium having a set of instructions stored therein. When executed, the instructions cause a processor to perform the method(s) described herein. Any control unit or controller described herein may suitably comprise a computational device having one or more electronic processors. The system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term "controller" or "control unit" will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a controller or control unit, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. The control unit or controller may be implemented in software run on one or more processors. One or more other control unit or controller may be implemented in software run on one or more processors, optionally the same one or more processors as the controller. Other suitable arrangements may also be used.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying Figures, in which:

Figure 1 shows a perspective view of a gait training apparatus in accordance with an aspect of the present invention;

Figure 2 shows a schematic representation of one of the footplates of gait training apparatus shown in Figure 1 ;

Figure 3 shows a schematic representation of the electronic control unit for the gait training apparatus shown in Figure 1 ; Figure 4 illustrates a movement corridor for controlling the activation force required to move the footplate during a gait cycle;

Figure 5 shows a side elevation of heel and toe position loops used to generate the movement corridor shown in Figure 4;

Figure 6 shows a schematic representation of a virtual kinematic model used to implement a watchdog control function in the gait training apparatus;

Figures 7 is a first block diagram showing the operation of the watchdog control function;

Figure 8 is a second block diagram showing the incorporation of the watchdog control function into the control of the gait training apparatus; and

Figure 9 is a modified arrangement of the releasable footplate assembly incorporating a mechanical coupling.

DETAILED DESCRIPTION

A gait training apparatus 1 in accordance with an aspect of the present invention will now be described with reference to the accompanying Figures. At least in certain embodiments, the gait training apparatus 1 is operative progressively to train the gait of a user 2 to more closely resemble a target gait. The gait training apparatus 1 guides the movement of the user's right and left feet 3-1 , 3-2 to train the movements of their right and left legs 4-1 , 4-2. The gait training apparatus 1 has particular application as part of a physiotherapy treatment, for example as part of a treatment for cerebral palsy. The gait training apparatus 1 is described herein with reference to a virtual reference frame comprising a longitudinal axis X, a transverse axis Y and a vertical axis Z. As shown in Figure 1 , the gait training apparatus 1 comprises first and second gait training units 5-1 , 5-2. The first gait training unit 5-1 comprises a first releasable footplate assembly 6-1 ; and the second gait training unit 5-2 comprises a second releasable footplate assembly (not shown). The first releasable footplate assembly 6-1 comprises a first footplate 7-1 (shown in detail in Figure 2 and Figure 9); and the second releasable footplate assembly comprises a second footplate (not shown). A user 2 stands on the gait training apparatus 1 such that their right foot 3-1 and the left foot 3-2 are supported by said first and second footplates 7-1 respectively. The user 2 is also supported in a harness (not shown) suspended from a support frame (not shown). As described herein, the first and second gait training units 5-1 , 5-2 are configured to control the movement of the first and second footplates 7-1 to guide the user's right and left feet 3-1 , 3-2 and legs 4-1 , 4-2 as they perform a walking and/or stepping action. The first and second gait training units 5-1 , 5-2 have the same configuration and, for the sake of brevity, only the first gait training unit 5-1 is described herein in detail.

The first gait training unit 5-1 is operative to control the movement and orientation of the first footplate 7-1 . The orientation of the first footplate 7-1 is described herein with reference to a local virtual reference frame comprising a first longitudinal axis X1 ; a first transverse axis Y1 ; a first vertical axis Z1 . As shown in Figure 2, the first footplate 7-1 comprises fastening means 15 for releasably fastening the user's right foot 3-1 to the first footplate 7-1 . In the present embodiment the fastening means 15 comprises one or more strap having a releasable fastener, such as a hook and loop fastener, an over-centre locking mechanism or a buckle. In use, the user 2 moves their right foot 3-1 to apply a force to said first footplate 7- 1 .

The first footplate 7-1 comprises first force sensing means 8 for detecting the force applied to the first footplate 7-1 by the user 2. The first force sensing means 8 in the present embodiment comprises a first load sensor operative to measure forces (positive and negative) in the first vertical axis Z1 . The first force sensing means 8 may be arranged to also measure forces in the first longitudinal axis X1 and/or the first transverse axis Y1 and/or the first vertical axis Z1 . The first force sensing means 8 may comprise a load cell incorporating a strain gauge or a shear stress gauge. Other types of load cell that may be used include hydraulic (or hydrostatic), pneumatic, piezo-electric and vibrating wire load cells. The first footplate 7-1 also comprises first acceleration sensing means 9 for measuring acceleration of the first footplate 7-1 to facilitate tracking. The first acceleration sensing means 9 comprises at least one accelerometer. The at least one accelerometer may measure acceleration along said first longitudinal axis X1 ; and/or said first transverse axis Y1 ; and/or said first vertical axis Z1 . The first acceleration sensing means 9 may also measure acceleration about said first longitudinal axis X1 ; and/or said first transverse axis Y1 ; and/or said first vertical axis Z1 . As shown in Figure 2, the first gait training unit 5-1 comprises a first retaining means 10-1 for retaining the first footplate 7-1 on a footplate carrier 12. The first retaining means 10-1 is operable to release the first footplate 7-1 such that the first footplate 7-1 is disengaged from the footplate carrier 12 to protect the user 2 from injury. In the present embodiment the first retaining means 10-1 comprises an electromagnetic coupling 1 1 arranged to releasably mount the first footplate 7-1 to a footplate carrier 12. The electromagnetic coupling 1 1 comprises an electromagnetic coil 13 which can be energised to create a magnetic field. The first footplate 7-1 comprises a coupling element 14 which is attracted by the magnetic field to fixedly couple the first footplate 7-1 to the footplate carrier 12 when the electromagnetic coil 13 is energised. The coupling element 14 may, for example, comprise a ferromagnetic insert disposed in said first footplate 7-1 . In order to release the first footplate 7-1 , the electromagnetic coil 13 is de-energised. It will be understood that more than one electromagnetic coil 13 may be provided. The operation of the first retaining means 10-1 is described in more detail herein.

The first footplate 7-1 is pivotally mounted to an upper end of a first support arm 20. In the present embodiment, the first footplate 7-1 is pivotable about the first transverse axis Y1 and the first vertical axis Z1 . The first support arm 20 is pivotally mounted to a first carriage 21 which is movable along a first track 22 in a longitudinal direction. A first actuator 23 is provided to controllably adjust an incline angle of the first support arm 20. The first actuator 23 is operable to controllably adjust a vertical position of the first footplate 7-1 . The first actuator 23 in the present embodiment comprises a first electric motor 24 for rotating a threaded member 25 to drive a first pivot arm 26. The first electric motor 24 is reversible to enable the incline angle of the first support arm 20 to be adjusted to raise and lower the first footplate 7-1 . A second actuator 28 is provided on the first carriage 21 to adjust the pivot angle of the first footplate 7-1 . The second actuator 28 comprises a second electric motor 29 connected to a continuous belt 30. The continuous belt 30 may, for example, comprise a toothed belt or a chain. The second electric motor 29 is operable to drive the continuous belt 30 to adjust a footplate pitch angle (i.e. to adjust the pivot angle of the first footplate 7-1 about the first transverse axis Y1 ). The second electric motor 29 is reversible to enable the footplate pitch angle to be increased or decreased. The first footplate 7-1 is shown in a horizontal position in Figure 1 substantially parallel to the longitudinal axis X. The first footplate 7-1 is pivotable about the first vertical axis Z1 to adjust a footplate rotation angle. The footplate rotation angle is not actively controlled in the present embodiment, but a separate actuator may be provided to control the footplate rotation angle. Alternatively, or in addition, the first footplate 7-1 may be pivotable about the longitudinal axis X1 to adjust a footplate roll angle. A third actuator 31 is provided to displace the first carriage 21 in a longitudinal direction. The third actuator is operable controllably to adjust a longitudinal position of the first footplate 7-1 . The third actuator 31 may, for example, comprise a third electric motor 32 for driving a worm drive disposed in the first track 22. The present embodiment has been described herein as comprising electric motors for actuating the first gait training unit 5-1 . In a variant, pneumatic or hydraulic actuators may be used in the first gait training unit 5-1 . As shown in Figure 3, the gait training apparatus 1 comprises an electronic control unit (ECU) 40 for controlling operation of the first and second gait training units 5-1 , 5-2. As shown schematically in Figure 2, the ECU 40 comprises an electronic processor 41 , a memory 42 and a human machine interface (HMI) 43. The first, second and third actuators 23, 28, 31 are controlled by the electronic processor 41 . In particular, the electronic processor 41 is configured to output first, second and third actuator control signals S1 , S2, S3 for controlling operation of said first, second and third actuators 23, 28, 31 . The ECU 40 is configured to control the first and second gait training units 5-1 , 5-2 such that the trajectory of the first and second footplates 7-1 represents a target (corrective) trajectory for the user 2. The same control strategy may be used to control the first and second footplates 7-1 . Alternatively, different control strategies may be applied for the first and second footplates 7- 1 , for example to accommodate an asymmetric gait. The operation of the ECU 40 to control the first gait training unit 5-1 will now be described. A first movement corridor (illustrated by the reference numeral 50 in Figure 4) for a gait cycle is stored in the memory 42. The first movement corridor 50 defines a continuous (i.e. looped) three-dimensional volume within which the first footplate 7-1 is movable during the gait cycle. Unlike prior art arrangements, the first footplate 7-1 is not rigidly constrained to follow a predefined trajectory. Rather, the first footplate 7-1 is movable within the first movement corridor 50 during the gait cycle. As described in more detail herein, the first gait training unit 5-1 is configured to facilitate movement of the first footplate 7-1 inside the first movement corridor 50; and to hinder or restrict movement of the first footplate 7-1 outside the first movement corridor 50. The gait cycle is tailored to suit a particular user 2 and may, for example, be stored in a user profile in said memory 42.

The first movement corridor 50 in the present embodiment is defined with reference to a first toe position loop 52-1 and a first heel position loop 53-1 , as shown in Figures 1 and 5. The first toe position loop 52-1 defines a target trajectory for the front of the first footplate 7-1 ; and the first heel position loop 53-1 defines a target trajectory for the rear of the first footplate 7-1 . As shown in Figures 1 and 2, the first toe position loop 52-1 and the first heel position loop 53-1 differ from each other. By defining the relative position and profile of the first toe position loop 52-1 and the first heel position loop 53-1 , the position and orientation of the first footplate 7-1 may be defined throughout the gait cycle. The first toe position loop 52- 1 and the first heel position loop 53-1 may thereby define a target position and a target orientation of the first footplate 7-1 . The target position of the first footplate 7-1 in the gait cycle is referred to herein as a first target gait trajectory 54 and is defined in three dimensions by said first toe position loop 52-1 and said first heel position loop 53-1 . The first toe position loop 52-1 is subdivided into a series of discrete first toe points 55-n; and the first heel position loop 53-1 is subdivided into a series of discrete first heel points 56-n. The first toe points 55-n are each paired with a corresponding one of said first heel points 56-n. The relative position of the discrete points 55-n, 56-n in each pairing define a discrete target position and orientation of the first footplate 7-1 . By referencing these pairings, the electronic processor 41 determines a target position and orientation of the first footplate 7-1 . The electronic processor 41 interpolates between the discrete first toe points 55-n and the first heel points 56-n in order to determine the first target gait trajectory 54 of the first footplate 7- 1 throughout the gait cycle. The distribution and/or number of discrete first toe points 55-n and first heel points 56-n can be modified to provide the required resolution.

The first movement corridor 50 is defined as a first permissible longitudinal deviation ΔΧ1 , a first permissible transverse deviation ΔΥ1 and a first permissible vertical deviation ΔΖ1 for said first toe position loop 52-1 and said first heel position loop 53-1 . The magnitude of the first permissible longitudinal deviation ΔΧ1 , the first permissible transverse deviation ΔΥ1 and the first permissible vertical deviation ΔΖ1 could be constant. Alternatively, the magnitude of the first permissible longitudinal deviation ΔΧ1 and/or the first permissible transverse deviation ΔΥ1 and/or the first permissible vertical deviation ΔΖ1 may be modified along said first toe position loop 52-1 and/or along said first heel position loop 53-1 . One or more of said permissible deviations may be reduced in portions of the target gait trajectory where the position and/or orientation of the first footplate 7-1 is deemed more important. For example, the permissible deviations may be reduced in the portion of the first toe position loop 52-1 and the first heel position loop 53-1 corresponding to toe off and early swing in the gait cycle. These changes can help to encourage the user 2 to raise their right foot 3-1 and avoid toe drag during the initial portion of the swing phase. It will be understood that the first permissible longitudinal deviation ΔΧ1 , the first permissible transverse deviation ΔΥ1 and the first permissible vertical deviation ΔΖ1 may be modified independently of each other. In the above example, the first permissible vertical deviation ΔΖ1 may be reduced without any corresponding changes in the first permissible transverse deviation ΔΥ1 . In a still further refinement, the first permissible longitudinal deviation ΔΧ1 , the first permissible transverse deviation ΔΥ1 and the first permissible vertical deviation ΔΖ1 may be different on said first toe position loop 52-1 and said first heel position loop 53-1 . In a further development, one or more of the first permissible longitudinal deviation ΔΧ1 , the first permissible transverse deviation ΔΥ1 and the first permissible vertical deviation ΔΖ1 may be modified dynamically, for example in dependence on a detected gait parameter of a user. For example, one or more of said permissible deviations may be modified in dependence on a change in the centre of gravity of a user. The first target gait trajectory 54 comprises a stance phase (when the foot is in contact with the ground), and a swing phase (when the foot is lifted and moved forwards). The stance phase and the swing phase are reflected in the first toe position loop 52-1 and the first heel position loop 53-1 . As shown in Figure 1 , the first toe position loop 52-1 comprises a first toe position stance section 57 and a first toe position swing section 58; and the first heel position loop 53-1 comprises a first heel position stance section 59 and a first heel position swing section 60. The first toe position stance section 57 and the first heel position stance section 59 represent the stance phase when the right foot 3-1 is in contact with a virtual surface VS1 . The first toe position swing section 58 and the first heel position swing section 60 represent the swing phase when the right foot 3-1 is lifted and moving forwards relative to the virtual surface VS1 . The virtual surface VS1 is elevated above the upper surface of the first track 22 in the present embodiment to enable different training functions, for example to simulate a level (horizontal) virtual surface VS1 and an inclined (positive or negative gradient) virtual surface VS1 . In the arrangement illustrated in Figure 1 , the first toe position stance section 57 and the first heel position stance section 59 extend parallel to the longitudinal axis X to represent a level virtual surface VS1 . It will be understood that the first movement corridor 50 may be modified such that the first toe position stance section 57 and the first heel position stance section 59 are inclined at an acute angle relative to the longitudinal axis X to represent an inclined virtual surface VS1 . Alternatively, the first toe position stance section 57 and the first heel position stance section 59 may have a stepped profile to represent a stepped virtual surface VS1 , for example comprising one or more steps. It will be understood that the remainder of the first movement corridor 50 would be modified to define appropriate target gait trajectories for these revised scenarios. It will be appreciated that the first target gait trajectory 54 is modified for each of the different virtual surfaces VS1 described herein.

The electronic processor 41 is configured to determine the position and orientation of the first footplate 7-1 with reference to the operating state of the first, second and third actuators 23, 28, 31 ; and the data received from the first acceleration sensing means 9. One or more position sensors may optionally be provided to enable the electronic processor 41 to track the position and/or orientation of the first footplate 7-1 . For example, one or more position sensor may be provided to measure the longitudinal position of the first carriage 21 and/or an angular orientation of the first support arm 20 and/or an angular orientation of the first footplate 7-1 . The electronic processor 41 controls the first, second and third actuators 23, 28, 31 to provide a first activation force F1 required to move the first footplate 7-1 in dependence on the determined position of the first footplate 7-1 in relation to the first movement corridor 50. The first activation force F1 corresponds to a lower force threshold for displacing the first footplate 7-1 . When the first footplate 7-1 is determined to be inside the first movement corridor 50, the electronic processor 41 is configured to control said first and third actuators 23, 31 to reduce the first activation force F1 required to move the first footplate 7-1 . When the first footplate 7-1 is determined to be outside the first movement corridor 50, the electronic processor 41 is configured to control said first and third actuators 23, 31 to increase the first activation force F1 required to move the first footplate 7-1 . The increased resistance to movement of the first footplate 7-1 encourages the user 2 to guide the first footplate 7-1 within the first movement corridor.

The electronic processor 41 controls the second actuator 28 to a first activation torque T1 required to rotate the first footplate 7-1 about the transverse axis Y1 in dependence on the target footplate orientation. As described herein, the target footplate orientation is defined by the first toe position loop 52-1 and the first heel position loop 53-1 . The first activation torque T1 corresponds to a lower torque threshold for rotating the first footplate 7-1 about the transverse axis Y1 . The first activation torque T1 may, for example, be directly proportional to an angular offset between the determined angular orientation of the first footplate 7-1 and the target footplate orientation. The target footplate orientation changes in dependence on the position of the first footplate 7-1 in said gait cycle. Thus, the electronic processor 41 controls the second actuator 28 to modify the first activation torque T1 in dependence on the determined position and orientation of the first footplate 7-1 . Alternatively, or in addition, the first activation force F1 may be modified in dependence on the determined angular offset between the first footplate 7-1 and the target footplate orientation. The first activation force F1 may be directly proportional to the determined angular offset such that the force required to move the first footplate 7-1 increases the greater the determined angular offset. A permissible angular deviation Δα1 may be defined for said target footplate orientation. The first activation torque T1 may be varied depending on whether the determined orientation of the first footplate 7-1 is inside or outside the permissible angular deviation Δα1 . The permissible angular deviation may be constant or may change in dependence on the position of the first footplate 7-1 in said gait cycle. For example, the permissible angular deviation Δα1 may be smaller in portions of the gait cycle in which the angular orientation of the first footplate 7-1 is deemed to be important, for example at heel strike, toe off or early swing. The ECU 40 in the present embodiment is operable in an assistance mode to apply an assistive force to the first footplate 7-1 ; and a resistance mode to apply a resistive force to the first footplate 7-1 . The assistance mode may be activated to teach the user 2 the first target gait trajectory 54. When the assistance mode is engaged, the electronic processor 41 controls the first, second and third actuators 23, 28, 31 to apply an assistive force and/or an assistive torque to the first footplate 7-1 which guides the first footplate 7-1 . The electronic processor 41 may, for example, control one or more of the first and second actuators 23, 28 to apply an assistive force and/or an assistive torque to bias the first footplate 7-1 towards the first target gait trajectory 54. The resistance mode is activated to improve muscle strength and/or conditioning of the user 2, for example to improve stamina. When the resistance mode is engaged, the electronic processor 41 controls the first, second and third actuators 23, 28, 31 to apply a resistive force and/or a resistive torque to the first footplate 7- 1 . The resistive force and/or the resistive torque increase the first activation force F1 required to displace and/or rotate the first footplate 7-1 thereby increasing the physical workload of the user 2. The resistive force increases the minimum force required to displace the first footplate 7-1 when the determined position of the first footplate 7-1 is inside the first movement corridor 50. The first activation force F1 required to displace the first footplate 7-1 when the determined position is outside the first movement corridor 50 is also increased so that the user 2 is encouraged to move the first footplate 7-1 within the first movement corridor.

The electronic processor 41 is configured to control said first, second and third actuators 23, 28, 31 to vary the first activation force F1 in direct proportion to a distance (offset) between the first target gait trajectory 54 and a known reference point on the first footplate 7-1 . In the present embodiment, the distance is measured along the X axis, the Y axis and the Z axis. In alternative embodiments, the distance may be measured along one of said axes, or along two of said axes (for example in a transverse plane defined by the X axis and the Y axis). When the distance is less than or equal to a minimum threshold, the electronic processor 41 may control said first, second and third actuators 23, 28, 31 to minimise the first activation force F1 and potentially even to apply an assistive force to the first footplate 7-1 . As the distance between the first target gait trajectory 54 and the first footplate 7-1 increases, the electronic processor 41 is configured to control the first, second and third actuators to increase the first activation force F1 required to move the first footplate 7-1 . The first activation force F1 may increase in direct proportion to the distance between the first footplate 7-1 and the first target gait trajectory 54. If the electronic processor 41 determines that the first footplate 7-1 is outside the first movement corridor 50, the first, second and third actuators 23, 28, 31 are controlled to apply a biasing force to bias the first footplate 7-1 towards the first target gait trajectory 54. The first movement corridor 50 thereby defines a threshold around the target gait trajectory The ECU 40 is also operable in a learning mode to measure one or more gait parameter of the user 2. The one or more gait parameter may be stored in the memory 42 in a user profile associated with a particular user. In the learning mode, the electronic processor 41 is configured to control the first, second and third actuators 23, 28, 31 to minimise the activation force F1 required to move the first footplate 7-1 . The electronic processor 41 may control said first, second and third actuators 23, 28, 31 to apply an assistive force to compensate for the mass and/or mechanical losses in the first gait training unit 5-1 . The measured gait parameter(s) may thereby more closely reflect the natural gait of the user 2. In the present embodiment, the ECU 40 is configured to generate a first measured toe position loop and a first measured heel position loop when operating in said learning mode. The first measured toe position loop and the first measured heel position loop together generate a measured gait trajectory. The measured gait trajectory may be used to generate the first target gait trajectory 54 described herein. For example, the measured gait trajectory may be combined with a reference gait trajectory to generate the first target gait trajectory 54. A blending algorithm may be applied to combine the measured gait trajectory and a reference gait trajectory. Alternatively, or in addition, the measured gait trajectory may be manipulated by an operator having suitable experience or qualifications. The measured gait trajectory may thereby be manipulated to generate the first target gait trajectory 54. The HMI 43 may be used to manipulate the measured gait trajectory, for example to modify the first toe position loop 52-1 and/or the first heel position loop 53-1 .

The first retaining means 10-1 is operable to release the first footplate 7-1 in the event that the force detected by the first force sensing means 8 exceeds a first release force threshold FT1 (shown schematically in Figure 2). The first release force threshold FT1 may be fixed (for example a predefined first release force threshold FT1 ) and the first footplate 7-1 released in the event that the force detected by the first force sensing means 8 exceeds the first release force threshold FT1 . However, a potential disadvantage of this arrangement is that the direction and magnitude of the force applied by the user to the first footplate 7-1 is dependent on the position of the first footplate 7-1 in the gait cycle. By way of example, the user 2 applies an upwards force (+ve) at toe off and a downwards force (-ve) at heel strike. Thus, at certain positions within the gait cycle, the force detected by the first force sensing means 8 will be higher than at other positions in the gait cycle and/or the direction in which the force is applied may be reversed. Rather than define a fixed first release force threshold FT1 , the electronic processor 41 is configured to modify the first release force threshold FT1 in dependence on the determined position of said first footplate 7-1 in the gait cycle. For example, the direction and/or magnitude of the release force threshold the FT1 may be defined for each set of first toe points 55-n and first heel points 56-n. Alternatively, the first release force threshold FT1 may be calculated dynamically. For example, the first release force threshold FT1 may be inversely proportional to the activation force F1 required to move the first footplate 7-1 . The first release force threshold FT1 comprises magnitude and optionally also direction. The first release force threshold FT1 may comprise a force vector. The electronic processor 41 may also modify the first release force threshold FT1 in dependence on the determined orientation of said first footplate 7-1 , for example about said first longitudinal axis X1 (roll) and/or said first transverse axis Y1 (pitch) and/or said first vertical axis Z1 (rotation). Thus, the first release force threshold F1 may comprise a turning force (torque) about one or more of said reference axis.

It will be understood that the first release force threshold FT1 is adjusted dynamically in dependence on the position of the first footplate 7-1 in said gait cycle. In use, the electronic processor 41 monitors the force detected by the first force sensing means 8 and compares this to the first release force threshold FT1 determined in dependence on the position of the first footplate 7-1 in the gait cycle. If the detected force exceeds the first release force threshold FT1 , the electronic processor 41 is configured to de-energise the electromagnetic coil 13 to release the first footplate 7-1 from the footplate carrier 12. Furthermore, if the detected force exceeds the first release force threshold FT1 , the electronic processor 41 controls the first and second gait training units 5-1 , 5-2 to control further movement. The electronic processor 41 may, for example, control the first, second and third actuators 23, 28, 31 to halt movement of the footplate carrier 12.

A further aspect of the gait training apparatus 1 is the implementation of a watchdog control function to protect the user 2 from injury by ensuring that their legs are moved within a permissible (safe) range of motion. The watchdog control function ensures that the first and second gait training units 5-1 , 5-2 do not move to a position which may be potentially unsafe for the user 2. The watchdog control function implemented in the present embodiment performs a check to determine whether a planned movement is a valid movement, i.e. a movement that is within the physical ability of the user 2. Only if the watchdog control function determines that the planned movement is a valid movement are the first, second and third actuators 23, 28, 31 controlled to implement the planned movement. The watchdog control function may provide an additional level of refinement by allowing the range of movements to be predefined for a particular user 2. Thus, at least in certain embodiments, the watchdog control function can account for different physical capabilities. The implementation of the watchdog control function will now be described with reference to Figures 6, 7 and 8. The electronic processor 41 is configured to create a virtual kinematic model 70 of the lower limbs of the user 2, as shown in Figure 6. The virtual kinematic model 70 comprises right and left leg models 71 -1 , 71 -2 corresponding to the right and left legs of the user 2. The right and left leg models 71 -1 , 71 -2 each comprise an upper leg (thigh) 72, a lower leg (shank) 73 and a foot 74. The right and left leg models 71 -1 , 71 -2 have substantially the same configuration but, for the sake of brevity, the description of the virtual kinematic model 70 will focus on the right leg model 71 -1 . The right leg model 71 -1 comprises a hip joint 75 having three degrees of freedom (3DOF); a knee joint 76 having one degree of freedom (1 DOF); and an ankle joint 77 having three degrees of freedom (3DOF). A hip joint angle 0h defines the orientation of the hip joint 75; a knee joint angle 0k defines the orientation of the knee joint 76; and an ankle joint angle 0a defines the orientation of the angle joint 77. A range of motion is defined for each joint to define the angular movement of the joint from full flexion to full extension. The range of motion may also be referred to as joint movement, full flexion and full extension. The range of motion for each joint may, for example, comprise first and second angular end positions (corresponding to full flexion and full extension). The ECU 40 could contain standardised angular movement ranges. However, the angular movement ranges in the present embodiment are customised for each user 2 so as more closely to match the abilities of the user 2. The right leg model 71 -1 also defines an upper leg length (Uhigh) ; and a lower leg length (L_Shank). The upper leg length (Uhigh) and the lower leg length (Lshank) are preferably measured for a particular user 2 and input using the HMI 43. To account for variations in length, the upper leg length (Uhigh) and the lower leg length (L_Shank) may be defined for the left and right legs of the user 2. Similarly, the hip joint range 0h; the knee joint range 0k; and the ankle joint range 0a may be specified for the left and right legs of the user 2 to account for different movement ranges. The range of movement of each joint may be referenced independently (i.e. without any cross-referencing). Alternatively, the angular movement ranges may be interrelated. For example, the angular movement ranges may vary depending on the relative position/orientation of the upper leg 72 and the lower leg 73, or indeed the relative position/orientation of the right and left legs 71 -1 , 71 -2.

As described herein, the electronic processor 41 is configured to determine the position and orientation of the first footplate 7-1 with reference to the operating state of the first, second and third actuators 23, 28, 31 ; and the data received from the first acceleration sensing means 9. The electronic processor 41 applies a reverse kinematic model to determine the position and orientation of the limbs of the virtual kinematic model 70 in dependence on the known position and orientation of the first footplate 7-1 . In particular, the electronic processor 41 determines the angular orientation of the hip joint 75, the knee joint 76 and the ankle joint 77 of the virtual kinematic model 70. The reverse kinematics model may receive additional data in order to refine the determination of the right and left legs of the user 2. In the present example, the user 2 wears first and second upper leg accelerometers 78-1 , 78-2 to measure the acceleration of their right and left upper legs respectively; and first and second lower leg accelerometers 79-1 , 79-2 to measure the acceleration of their right and left lower legs respectively. The data received from the first and second upper leg accelerometers 78-1 , 78- 2; and the first and second lower leg accelerometers 78-1 , 78-2 is output to the electronic processor 41 for incorporation into the inverse kinematics model. Alternatively, or in addition, the position and/or movement of the right and the left legs of the user 2 may be tracked, for example by processing image data to track one or more location markers attached to the user 2.

The electronic processor 41 is configured to implement the watchdog control function to test the validity of planned movements of the first and second footplates 7-1 in order to prevent the apparatus from moving the gait training units in such a way as may expose the user 2 to a risk of injury. The watchdog control function will now be described with reference to a first block diagram 100 shown in Figure 7. The gait training apparatus 1 is activated and the watchdog control function starts (BLOCK 105). The electronic processor 41 determines the current position and orientation of the right and left leg models 71 -1 , 71 -2 and the next planned position of the right and left legs 4-1 , 4-2 of the user 2 (BLOCK 1 10). Alternatively, or in addition, the electronic processor 41 may determine the required activation force F1 and/or the required activation torque T1 required to move (to translate and/or rotate) the first and second footplates 7-1 from their respective current positions to the next planned positions. If the required activation force F1 and/or the required activation torque T1 are outside predefined limits, the electronic processor 41 determines that the planned change in position of the first and second footplates 7-1 is not safe and may inhibit movement of the first and second footplates 7-1 . The virtual kinematic model 70 is used to calculate the knee joint angle 0k and the ankle joint angle 0a required to transition from the current position to the next planned position of the right and left legs of the user 2 (BLOCK 1 15). The electronic processor 41 performs a check to determine if the required knee joint angle 0k is outside the predefined knee joint range; or if the required ankle joint angle 0a is outside the predefined ankle joint range (BLOCK 120). If the required knee joint angle 0k is outside the predefined knee joint range or the and the required ankle joint angle 0a is outside the ankle joint range, the electronic processor 41 determines that the planned change in position of the first and second footplates 7-1 is not safe (BLOCK 125). If the electronic processor 41 determines that the planned change in position represents a potential safety risk, the gait training apparatus 1 is controlled to control performance of the planned movement, for example by inhibiting movement of the first and second footplates 7-1 (BLOCK 130). If the required knee joint angle 0k is within the predefined knee joint range and the required ankle joint angle 0a is within the predefined ankle joint range, the electronic processor 41 uses the virtual kinematics model 70 to calculate the force that will be applied to the ankle, hip and knee from the current to the next planned position (BLOCK 135). The electronic processor 41 then performs a check to determine if the calculated force is within predefined limits (BLOCK 140). If the calculated force on one or more of the joints is outside the predefined limits, the electronic processor 41 determines that the planned change in position of the first and second footplates 7-1 is not safe (BLOCK 125). The gait training apparatus 1 is controlled to control performance of the planned movement, for example by inhibiting movement of the first and second footplates 7-1 (BLOCK 130). If the calculated force applied to each of the joints is inside the predefined limits, the electronic processor 41 determines that the planned change in position of the first and second footplates 7-1 is safe (BLOCK 145).

The operation of the electronic processor 41 to implement the watchdog control function in conjunction with other safety checks will now be described with reference to a second block diagram 200 in Figure 8. The gait training apparatus 1 is activated (BLOCK 205) and the electronic processor 41 starts a timer. A time check is performed to determine if a predefined time period t1 has elapsed since the timer started (BLOCK 210). The predefined time period t1 is measured in milliseconds. The predefined time period t1 may, for example, be 50 milliseconds. The electronic processor 41 performs a loop function until the predefined time period t1 has elapsed. When the electronic processor 41 determines that the predefined time period t1 has elapsed, the watchdog control function is implemented (BLOCK 215). The outcome of the watchdog control function is logged by the electronic processor 41 . One or more additional safety check may then be performed (BLOCK 220). The electronic processor 41 then checks if a potential safety risk was identified by the watchdog control function or the one or more safety check (BLOCK 225). If the electronic processor 41 determines that the planned change in position represents a potential safety risk, the gait training apparatus 1 is controlled to control performance of the planned movement (BLOCK 230). The electronic processor 41 may limit, restrict, inhibit or halt movement of the first and second footplates 7-1 . For example, the electronic processor 41 may bring the first and second footplates 7-1 to rest. If the watchdog control function and the one or more safety check do not identify a safety risk, the electronic processor 41 controls the first, second and third actuators 23, 28, 31 to perform the planned movement and the process is repeated. As long as no safety concerns are identified, the normal process is followed and the watchdog control function moves onto the next pair of current and planned points. If the electronic processor 41 determines that the planned change in position does not represent a potential safety risk, the gait training apparatus 1 is controlled to reset the timer and the process is repeated (BLOCK 235).

The watchdog control function is implemented on the assumption that incorrect/corrupt data has progressed through all previous detection mechanisms. The virtual kinematic model 70 is constructed based on the measurements of the legs and natural knee, ankle and hip movement for a given user 2. At a specified time interval (in the range of milliseconds) the machine will compare the current (known) position and the next planned position. The watchdog control function applies an algorithm which models movement, current position and force information and compares this to the next planned position and force information. The watchdog control function determines if the planned movement is valid. If the planned position is deemed safe, then the gait training apparatus 1 continues operate move and the watchdog control function checks the next planned movement. This process is repeated prior to performance of any planned movement. If the planned position is deemed to be invalid (i.e. potentially unsafe), the gait training apparatus 1 is stopped and the first and second footplates 7-1 brought to a halt.

The watchdog control function can be configured in conjunction with the learning mode described herein. For example, the learning mode may be used to measure a permissible range of movement for the right and left legs of a particular user 2. The learning mode can be used to determine the knee joint range and the ankle joint range, for example. Similarly, a hip joint range could be determined whilst operating in said learning mode. It will be understood that the data generated during the learning mode may be modified for use by the watchdog control function. The measured angular range may, for example, be reduced prior to implementation in the watchdog control function. As outlined above, the first and second gait training units 5-1 , 5-2 have the same configuration. The components and operation of the second gait training unit 5-2 corresponds to those described herein in respect of the first gait training unit 5-1 . The ECU 40 is operative to control both the first and second gait training units 5-1 , 5-2. In particular, the first and second gait training units 5-1 , 5-2 are controlled to guide the right foot 3-1 and the left foot 3-2 of the user 2. The operation of the gait training apparatus 1 to train a user 2 will now be described. A user profile associated with the user 2 is read from the memory 42 by the electronic processor 41 . The user profile defines one or more gait parameter for the user 2, including the first target gait trajectory 54. The user 2 puts on the harness and stands on the first and second gait training units 5-1 , 5-2. The harness is provided as a precaution and is not intended to support the weight of the user 2 in normal use. Rather, the user 2 supports their own weight by standing on the first and second footplates 7-1 . The right foot 3-1 and the left foot 3-2 are fastened to the first and second footplates 7-1 using the fastening means 15. In use, the right foot 3-1 and the first footplate 7-1 move in unison; and the left foot 3-2 and the second footplate 7-1 move in unison. The ECU 40 is controlled to select the first target gait trajectory 54 stored in the memory 42. The ECU 40 determines the position of the first and second footplates 7-1 in dependence on an operating state of each of the first, second and third actuators 23, 28, 31 . A calibration step may optionally be performed to determine the spatial location of the first and second footplates 7-1 . As described herein, the ECU 40 is operable in an assistance mode and a resistance mode. An operator controls the ECU 40 to select said assistance mode or said resistance mode. In the present example, the assistance mode is selected such that the electronic processor 41 controls the first, second and third actuators 23, 28, 31 to apply an assistive force to the first and second footplates 7-1 . A prompt or notification is output to the user 2 via the HMI 43 to indicate that the gait training apparatus 1 is ready to commence operation. The user 2 starts to walk whilst supported on the gait training apparatus 1 . The electronic processor 41 controls the first, second and third actuators 23, 28, 31 in dependence on the force measurement signals received from the first force sensing means 8. The electronic processor 41 analyses the force measurement signals to determine the direction and magnitude of the force applied by the user 2. The electronic processor 41 controls said first, second and third actuators to apply an assistive force to the first and second footplates 7-1 . The direction and magnitude of the assistive force is dependent on the direction and magnitude of the force applied by the user 2 to said first and second footplates 7-1 . The electronic processor 41 continues to monitor the position of the first and second footplates 7-1 . If the first footplate 7-1 is determined to move outside the first movement corridor 50, the first, second and third actuators 23, 28, 31 are controlled to generate an assistive force to bias the first footplate towards the first movement corridor 50 a similar control strategy is applied in respect of the second footplate. The same control strategy is applied to control the movement of the second footplate. The ECU 40 may be controlled to adjust the magnitude of the assistive forces applied by the first, second and third actuators 23, 28, 31 to the first and second footplates 7-1 . The ECU 40 is operable in a resistance mode to increase the physical workload on the user 2, for example to provide strength training for the user 2. Once the user is familiar with the required motion, the operator may control the ECU 40 to select the resistance mode. When the resistance mode is active, the electronic processor 41 is configured to reduce the assistance provided by said first, second and third actuators 23, 28, 31 , or to apply a resistive force to resist movement of said first and second footplates 7-1 . Again, the electronic processor 41 analyses the force measurement signals to determine the direction and magnitude of the force applied by the user 2. The ECU 40 may be controlled to adjust the magnitude of the resistive forces applied by the first, second and third actuators 23, 28, 31 to the first and second footplates 7-1 . The same control strategy is applied to both the first and second footplates 7-1 .

The first target gait trajectory 54 has been described herein as being defined with reference to a first toe position loop 52-1 and a first heel position loop 53-1 . In a variant, a single continuous gait loop may define the target gait trajectory. The continuous gait loop could, for example, define a trajectory for a reference point on the first footplate 7-1 . If required, a target footplate orientation may be defined around said continuous gait loop. For example, the continuous gait loop may be defined by a plurality of discrete points each having a matrix defining a corresponding target orientation in one, two or three dimensions. Thus, the target footplate position may be defined independently of the target footplate orientation.

In the embodiment described herein, the electronic processor 41 is configured to modify the first release force threshold FT1 in dependence on the determined position of the first footplate 7-1 in the gait cycle. In a modified arrangement, the strength of the magnetic coupling between the footplate carrier 12 and the coupling element 14 is modified in dependence on the determined position of the first footplate 7-1 in the gait cycle. In this arrangement the electronic processor 41 is configured to control the current supplied to the electromagnetic coil 13 to modify the strength of the magnetic field. The electronic processor 41 may thereby modify a retaining force with which the first footplate 7-1 is coupled to the footplate carrier 12. If the force applied to the first footplate 7-1 overcomes the retaining force, the first footplate 7-1 is released, thereby mitigating the risk of injury to the user 2. The electronic processor 41 is configured to detect the release of the first footplate 7-1 , for example by detecting a change in the current in the electromagnetic coil 13. If the electronic processor 41 detects that the first footplate 7-1 has been released, the electromagnetic coil 13 is de-energised to avoid the first footplate 7-1 unexpectedly reattaching to the footplate carrier 12. By changing the retaining force, it is not necessary to measure the force applied to the first footplate 7-1 and the first force sensing means 8 may be omitted. The first retaining means 10-1 has been described herein as comprising an electromagnetic coupling 1 1 . As shown in Figure 9, the first retaining means 10-1 could comprise a mechanical coupling 80 which is adjustable to vary a retaining force for mounting the first footplate 7-1 . The mechanical coupling 80 comprises one or more latching member 81 arranged to releasably engage the first footplate 7-1 . A spring biasing means 82, for example in the form of a torsion spring, may be provided to bias the one or more latching member into a latched position. The tension in said spring biasing means may be adjusted to change the retaining force with which the first footplate 7-1 is mounted. A control actuator 83, such as a servo motor, may be provided to control the tension in said spring biasing means 82. The electronic processor 41 may be configured to control said control actuator 83 in dependence on the determined position of the first footplate 7-1 in said gait cycle. Other forms of mechanical coupling may be used to mount the first footplate 7-1 to the footplate carrier 12.

The third actuator 31 is operative to apply torque to the first footplate 7-1 about said first transverse axis Y1 . The first gait training unit 5-1 described herein may be modified to incorporate additional actuators for applying torque to the first footplate 7-1 about said first longitudinal axis X1 and/or said first vertical axis Z1 . The electronic processor 41 may be configured to control said additional actuators to apply an assistive torque and/or a resistive torque to the first footplate 7-1 . By providing an actuator to control movement about the first longitudinal axis X1 , the electronic processor 41 may control a rolling movement of the first footplate 7-1 to control pronation of the user's right and left feet 3-1 , 3-2. For example, an actuator configured to control rotation about the first longitudinal axis X1 may reduce over pronation or under pronation. These modifications can also be incorporated into the second gait training unit 5-2.

In a modified arrangement, the watchdog control function implemented by the electronic processor 41 may be configured to test planned movements to ensure that acceleration and/or deceleration of the first and second footplates 7-1 does not exceed predefined acceleration thresholds. The acceleration threshold may be defined as a discrete value which must not be exceeded. Alternatively, an acceleration threshold may be defined in respect of each of the X, Y and Z axes. It will be understood that the acceleration threshold(s) may vary depending on the position and/or orientation of the first and second footplates 7-1 in said gait cycle. Alternatively, or in addition, the watchdog control function may be configured to test planned movements to ensure that the movement speed of the first and second footplates 7-1 does not exceed predefined speed thresholds. The speed thresholds may be defined as a discrete speed value which must not be exceeded. Alternatively, a speed threshold may be defined in respect of each of the X, Y and Z axes. It will be understood that the speed threshold(s) may vary depending on the position and/or orientation of the first and second footplates 7-1 in said gait cycle.

It will be appreciated that various modifications may be made to the embodiment(s) described herein without departing from the scope of the appended claims.

Claims

CLAIMS:

1 . A releasable footplate assembly for a gait training unit, the releasable footplate assembly comprising:

wherein the retaining means is controllable to adjust the retaining force.

2. A releasable footplate assembly as claimed in claim 1 comprising a control unit for controlling the retaining means to adjust the retaining force, the control unit comprising a processor and a memory device.

3. A releasable footplate assembly as claimed in claim 2, wherein the processor is configured to determine a position and/or an orientation of the movable footplate and to adjust the retaining force in dependence on the determined position and/or orientation of the movable footplate.

4. A gait training apparatus as claimed in claim 3, wherein the processor is configured to control the retaining means to adjust the retaining force in dependence on the determined position and/or orientation of the movable footplate relative to a predetermined trajectory.

5. A gait training apparatus as claimed in claim 4, wherein the predetermined trajectory comprises a target gait trajectory.

6. A releasable footplate assembly as claimed in any one of the preceding claims, wherein the retaining means comprises one or more electromagnet for generating a magnetic retaining force.

7. A releasable footplate assembly as claimed in claim 6 when dependent directly or indirectly on claim 2, wherein the processor is configured to control the supply of electrical current to the one or more electromagnet to adjust the retaining force.

8. A releasable footplate assembly as claimed in any one of claims 1 to 5, wherein the retaining means comprises one or more mechanical retention device.

9. A releasable footplate assembly as claimed in claim 8, wherein the one or more mechanical retention device comprises a latching mechanism for generating the retaining force.

10. A releasable footplate assembly as claimed in claim 9, wherein the latching mechanism comprises spring biasing means for applying a spring biasing force to one or more latching member, the spring biasing means being adjustable to change the spring biasing force.

1 1 . A releasable footplate assembly as claimed in claim 10 when dependent directly or indirectly on claim 2, wherein the processor is configured to control an actuator to adjust the spring biasing means.

12. A releasable footplate assembly as claimed in any one of the preceding claims comprising force measurement means for measuring an applied force.

13. A releasable footplate assembly as claimed in claim 12, wherein the force measurement means comprises:

means for sensing the force applied along one axis, two axes or three axes; and/or means for sensing the force applied about one axis, two axes or three axes.

14. A releasable footplate assembly as claimed in any one of claims 1 1 , 12 or 13, wherein the retaining means is configured to release the movable footplate if the applied force measured by the force measurement means is greater than a release force threshold.

15. A gait training apparatus comprising at least one releasable footplate assembly as claimed in any one of the preceding claims.

16. A gait training apparatus as claimed in claim 15, wherein the movable footplate is movable to follow a target gait trajectory, the processor being configured to control the retaining means to adjust the retaining force in dependence on the determined position and/or orientation of the movable footplate relative to said target gait trajectory.

17. A gait training apparatus as claimed in claim 15 or claim 16 comprising one or more actuator for controlling the movement and/or orientation of said footplate, the one or more actuator being operable to control an activation force required to move the movable footplate in dependence on a determined position of the movable footplate relative to the target gait trajectory.

18. A control unit for controlling the releasable footplate assembly claimed in claim 1 , the control unit comprising a processor and a memory device, the processor being configured to control the retaining means to adjust the retaining force.

19. A control unit as claimed in claim 18, wherein the processor is configured to determine a position and/or an orientation of the movable footplate; and to adjust the retaining force in dependence on the determined position and/or orientation of the movable footplate.

20. A control unit as claimed in claim 19, wherein the processor is configured to adjust the retaining force in dependence on the determined position and/or orientation of the movable footplate relative to a predetermined trajectory.

21 . A releasable footplate assembly for a gait training unit, the releasable footplate assembly comprising:

a footplate carrier having retaining means for retaining the movable footplate;

force measurement means for measuring an applied force; and

a control unit for controlling the retaining means, the control unit comprising a processor and a memory device, the processor being configured to control the retaining means to release the movable footplate if the applied force measured by the force measurement means is greater than a release force threshold.

22. A releasable footplate assembly as claimed in claim 21 , wherein the processor is configured to adjust the release force threshold.

23. A releasable footplate assembly as claimed in claim 22, wherein the processor is configured to determine the position and/or orientation of the movable footplate and to adjust the release force threshold in dependence on the determined position and/or orientation of the movable footplate.

24. A releasable footplate assembly as claimed in claim 23, wherein the processor is configured to adjust the release force threshold in dependence on the determined position and/or orientation of the movable footplate relative to a predetermined trajectory.

25. A releasable footplate assembly as claimed in any one of claims 21 to 24, wherein the force measurement means comprises:

26. A releasable footplate assembly as claimed in any one of claims 21 to 25, wherein the retaining means is controllable to adjust the retaining force.

27. A gait training apparatus comprising at least one releasable footplate assembly as claimed in any one of claims 21 to 26.

28. A gait training apparatus as claimed in claim 27, wherein the movable footplate is movable along a predetermined trajectory, the processor being configured to adjust the release force threshold in dependence on a determined position and/or orientation of the movable footplate relative to said predetermined trajectory.

29. A gait training apparatus as claimed in claim 28, wherein the predetermined trajectory comprises a target gait trajectory.

30. A gait training apparatus as claimed in any one of claims 26 to 29 comprising one or more actuator for controlling the movement and/or orientation of said footplate, the one or more actuator being operable to control an activation force required to move the movable footplate.

31 . A gait training unit comprising:

a movable footplate;

a control unit comprising a processor and a memory;

32. A gait training unit as claimed in claim 31 , wherein the processor is configured to control said one or more actuator to control the activation force in proportion to a distance between a determined footplate position and a target footplate position.

33. A gait training unit as claimed in claim 32, wherein the processor is configured to control said one or more actuator to reduce the activation force when the footplate is inside the movement corridor and to increase the activation force when the footplate is outside the movement corridor.

34. A gait training unit as claimed in any one of claims 31 to 33, wherein the control unit is operable in an assistance mode and/or a resistance mode.

35. A gait training unit as claimed in claim 34, wherein, when operating in said assistance mode, the processor is configured to control said one or more actuator to apply an assistive force to reduce the activation force required to move the footplate.

36. A gait training unit as claimed in claim 35, wherein the assistive force biases the footplate in a longitudinal direction and/or a vertical direction and/or a transverse direction.

37. A gait training unit as claimed in claim 35 or claim 36, wherein the processor is configured to control said one or more actuator to control the assistive force in dependence on the position of the footplate relative to the movement corridor.

38. A gait training unit as claimed in any one of claims 34 to 37, wherein, when operating in said resistance mode, the processor is configured to control said one or more actuator to apply a resistive force to increase the activation force required to move the footplate.

39. A gait training unit as claimed in claim 38, wherein the processor is configured to control said one or more actuator to control the resistive force in dependence on the position of the footplate relative to the movement corridor.

40. A gait training unit as claimed in any one of claims 30 to 39, wherein the target gait trajectory is defined by a first position loop and a second position loop; the first position loop defining a target trajectory for a first reference point on the footplate; and the second position loop defining a target trajectory for a second reference point on the footplate.

41 . A gait training unit as claimed in any one of the preceding claims, wherein the processor is configured to control said one or more actuator to control an activation torque (T1 ) required to pivot the footplate about one or more axis in dependence on a determined footplate orientation and a target footplate orientation.

42. A gait training unit as claimed in claims 40 and 41 , wherein said first and second position loops define the target footplate orientation.

43. A gait training unit as claimed in claim 41 or claim 42 when dependent directly or indirectly on claim 34, wherein, when operating in said resistance mode, the processor is configured to control said one or more actuator to apply a resistive torque to increase the activation torque required to pivot the footplate.

44. A gait training unit comprising:

a movable footplate;

a control unit comprising a processor and a memory;

wherein the processor is configured to control said one or more actuator to control an activation torque required to pivot the footplate about one or more axis in dependence on a determined footplate orientation and a target footplate orientation.

45. A gait training unit as claimed in claim 44, wherein the target footplate orientation is defined by a first position loop and a second position loop; the first position loop defining a target trajectory for a first reference point on the footplate; and the second position loop defining a target trajectory for a second reference point on the footplate.

46. A gait training unit as claimed in claim 44 or claim 45, wherein the control unit is operable in an assistance mode and/or a resistance mode.

47. A gait training unit as claimed in claim 46, wherein, when operating in said assistance mode, the processor is configured to control said one or more actuator to control the assistive torque in dependence on the orientation of the footplate relative to said predetermined orientation frame.

48. A gait training unit as claimed in any one of claims 45 to 47, wherein, when operating in said resistance mode, the processor is configured to control said one or more actuator to apply a resistive torque to increase the activation torque required to pivot the footplate.

49. A gait training unit as claimed in any one of claims 30 to 48 comprising force sensing means for measuring a force applied to the footplate by a user, the force sensing means being configured to output one or more force measurement signal to the control unit.

50. A gait training unit as claimed in claim 49, wherein the processor is configured to control said one or more actuator in dependence on said one or more force measurement signal received from the force sensing means.

51 . A gait training unit as claimed in claim 49 or claim 50, wherein the force sensing means comprises one or more force sensors for measuring an applied force along one or more axis.

52. A gait training unit as claimed in any one of claims 30 to 51 , wherein the processor is configured to determine the position and/or orientation of the footplate.

53. A gait training unit as claimed in claim 52, wherein the processor is configured to determine the position and/or orientation of the footplate in dependence on an operating condition of said one or more actuator.

54. A gait training unit as claimed in any one of claims 30 to 53, wherein the one or more actuator comprises one or more of the following:

a third displacement actuator for controlling vertical movement of the footplate;

55. A gait training unit as claimed in any one of claims 30 to 54, wherein the one or more actuator comprises one or more of the following:

a first pivot actuator for controlling pivoting of the footplate about a transverse axis; a second pivot actuator for controlling pivoting of the footplate about a vertical axis; and a third pivot actuator for controlling pivoting of the footplate about a longitudinal axis.

56. A gait training unit as claimed in any one of claims 30 to 55, wherein the target gait trajectory comprises a target position of the footplate; and/or a target orientation of the footplate.

57. A gait training unit as claimed in any one claims 30 to 56, wherein the movement corridor is generated in dependence on a combination of a reference gait trajectory and a measured gait trajectory of a user.

58. A gait training unit as claimed in any one of claims 30 to 57, wherein the movement corridor is predefined.

59. A gait training unit as claimed in any one of claims 30 to 58, wherein the control unit is operable in a learning mode to measure one or more gait parameters of a user for generating the target gait trajectory.

60. A gait training unit as claimed in claim 59, wherein, when operating in said learning mode, the processor is configured to track the movement and/or orientation of the footplate to measure said one or more gait parameter.

61 . A gait training unit as claimed in claim 60, wherein the processor is configured to control said one or more actuator to define a virtual surface for measuring said one or more gait parameter.

62. A gait training unit as claimed in any one of claims 59 to 61 , wherein the processor is configured to generate the target gait trajectory by combining a reference gait trajectory and the measured gait trajectory.

63. A gait training apparatus comprising first and second gait training units as claimed in any one of claims 30 to 62.

64. A gait training apparatus as claimed in claim 63, wherein the first gait training unit comprises a first footplate; and the second gait training unit comprises a second footplate; the processor being configured to control said one or more actuator to control an activation force required to move the first footplate and/or the second footplate in dependence on a determined position of the first and second footplates relative to each other.

65. A control unit for controlling a gait training apparatus as claimed in claim 63 or claim 64, the control unit comprising:

a processor, a non-transient computer-readable medium for storing data, the processor being configured to access a movement profile stored in the non-transient computer-readable medium.

66. A control unit as claimed in claim 65, wherein the movement profile comprises a movement corridor for a user, the movement corridor defining a target gait trajectory for the user.

67. A control unit for controlling a gait training unit having a moveable footplate and one or more actuator for controlling movement of the footplate; the control unit comprising a processor and a memory device, a user profile being stored on said memory device and defining a range of motion of one or more joint of the user, the processor being configured to:

generate a virtual kinematic model in dependence on the user profile; and determine one or more virtual joint angle when the virtual kinematic model is reconfigured in dependence on the planned footplate position and/or the planned footplate orientation;

wherein, if the one or more virtual joint angle is outside the range of motion defined for a corresponding joint in the user profile, the processor is configured to output a control signal to control said one or more actuator to control movement of the footplate to the planned footplate position and/or the planned footplate orientation.

68. A control unit as claimed in claim 67, wherein the processor is configured to enable movement of the footplate to the planned footplate position and/or the planned footplate orientation if the virtual joint angle is inside the range of motion defined for the corresponding joint in the user profile.

69. A control unit as claimed in claim 67 or claim 68, wherein, if the one or more virtual joint angle is outside the range of motion defined for the corresponding joint in the user profile, the control signal controls said one or more actuator to halt movement of the footplate.

70. A control unit as claimed in claim 67 or claim 68, wherein, if the one or more virtual joint angle is outside the range of motion defined for the corresponding joint in the user profile, the control signal is configured to control said one or more actuator to move the footplate to a default position and/or a default orientation.

71 . A control unit as claimed in any one of claims 67 to 70, wherein the processor is configured to determine a virtual reaction force and/or a virtual reaction torque generated when the virtual kinematic model is re-configured in dependence on the planned footplate position and/or the planned footplate orientation.

72. A control unit as claimed in claim 71 , wherein, if the virtual reaction force is greater than a reaction force threshold or the virtual reaction torque is greater than a reaction torque threshold, the processor is configured to output a control signal to control said one or more actuator to control movement of the footplate to the planned footplate position and/or the planned footplate orientation.

73. A control unit for controlling a gait training unit having a moveable footplate and one or more actuator for controlling movement of the footplate; the control unit comprising a processor and a memory device, a user profile being stored on said memory device and defining a reaction force threshold and/or a reaction torque threshold, the processor being configured to:

wherein, if the virtual reaction force is greater than the reaction force threshold and/or the virtual reaction torque is greater than the reaction torque threshold, the processor is configured to output a control signal to control said one or more actuator to control movement of the footplate to the planned footplate position and/or the planned footplate orientation.

74. A control unit as claimed in any claim 72 or claim 73, wherein the processor is configured to enable movement of the footplate to the planned footplate position and/or the planned footplate orientation if the virtual reaction force is less than the reaction force threshold and/or the virtual reaction torque is less than the reaction torque threshold.

75. A control unit as claimed in any one of claims 72, 73 or 74, wherein, if the virtual reaction force is greater than the reaction force threshold or the virtual reaction torque is greater than the reaction torque threshold, the control signal is configured to control said one or more actuator to halt movement of the footplate.

76. A control unit as claimed in any one of claims 72, 73 or 74, wherein, if the virtual reaction force is greater than the reaction force threshold or the virtual reaction torque is greater than the reaction torque threshold, the control signal is configured to control said one or more actuator to move the footplate to a default position and/or a default orientation.

77. A control unit as claimed in any one of claims 67 to 76, wherein the planned footplate position and/or the planned footplate orientation are defined at a position along the target gait trajectory ahead of the current position.

78. A control unit as claimed in any one of claims 67 to 77, wherein the memory device comprises a non-transient computer-readable medium for storing data.

79. A gait training unit comprising a control unit as claimed in any one of claims 67 to 78.

80. A gait training apparatus comprising first and second gait training units as claimed in claim 79.

81 . A method of controlling a gait training unit having a moveable footplate; the method comprising:

generating a virtual kinematic model representing a user; and

determining one or more virtual joint angle when the virtual kinematic model is re- configured in dependence on the planned footplate position and/or the planned footplate orientation; wherein, if the one or more virtual joint angle is outside a range of motion defined for a corresponding joint, controlling movement of the footplate to the planned footplate position and/or the planned footplate orientation.

82. A method as claimed in claim 81 comprising enabling movement of the footplate to the planned footplate position and/or the planned footplate orientation if the virtual joint angle is inside the range of motion defined for the corresponding joint in the user profile.

83. A method as claimed in claim 81 or claim 82 comprising halting movement of the footplate if the one or more virtual joint angle is outside the range of motion defined for the corresponding joint in the user profile.

84. A method as claimed in any one of claim 81 or claim 82 comprising moving the footplate to a default position and/or a default orientation if the one or more virtual joint angle is outside the range of motion defined for the corresponding joint in the user profile.

85. A method as claimed in any one of claims 81 to 84 comprising determining a virtual reaction force and/or a virtual reaction torque generated when the virtual kinematic model is re-configured in dependence on the planned footplate position and/or the planned footplate orientation.

86. A method as claimed in claim 85 comprising controlling movement of the footplate to the planned footplate position and/or the planned footplate orientation if the virtual reaction force is greater than a reaction force threshold or the virtual reaction torque is greater than a reaction torque threshold.

87. A method of controlling a gait training unit having a moveable footplate;

generating a virtual kinematic model representing a user; and

wherein, if the virtual reaction force is greater than a reaction force threshold or the virtual reaction torque is greater than a reaction torque threshold, controlling movement of the footplate to the planned footplate position and/or the planned footplate orientation.

88. A method as claimed in claim 86 or claim 87 comprising enabling movement of the footplate to the planned footplate position and/or the planned footplate orientation if the virtual reaction force is less than the reaction force threshold and/or the virtual reaction torque is less than the reaction torque threshold.

89. A method as claimed in any one of claims 86 , 87 or 88 comprising halting movement of the footplate if the virtual reaction force is greater than the reaction force threshold or the virtual reaction torque is greater than the reaction torque threshold.

90. A method as claimed in any one of claims 86, 87 or 88 comprising moving the footplate to a default position and/or a default orientation if the virtual reaction force is greater than the reaction force threshold or the virtual reaction torque is greater than the reaction torque threshold.

91 . A method as claimed in any one of claims 81 to 90, wherein the planned footplate position and/or the planned footplate orientation are defined at a position along the target gait trajectory ahead of the current position.

92. A non-transient computer-readable medium having a set of instructions stored therein which, when executed, cause a processor to perform the method claimed in any one of claims 81 to 91 .