Mobility assistance device

Abstract

The invention relates to a mobility assistance device comprising a first self-balancing wheel mounted on a first wheel guide which defines a first curved path along which the first wheel guide and the first self-balancing wheel may move with respect to one another; a second self-balancing wheel mounted on a second wheel guide which defines a second curved path along which the second wheel guide and the second self-balancing wheel may move with respect to one another; a frame connecting the first wheel guide and the second wheel guide; a harness for receiving a user, the harness being provided on the frame; at least one control unit configured to control the first self-balancing wheel and / or second self-balancing wheel in accordance with an inverse pendulum principle. In a further aspect the invention relates to a method of using a mobility assistance device of the invention, the method comprising a step of propagating an intentional movement of a user by means of the device, while preventing falling, wherein the intentional movement is in particular a forward-backward rocking movement, a forward or backward displacement, a turning movement around a point and / or a turning movement in a partial circle.

Description

[0001] MOBILITY ASSISTANCE DEVICE

[0002] DESCRIPTION

[0003] The invention relates to a mobility assistance device comprising a first self-balancing wheel mounted on a first wheel guide which defines a first curved path along which the first wheel guide and the first self-balancing wheel may move with respect to one another; a second self-balancing wheel mounted on a second wheel guide which defines a second curved path along which the second wheel guide and the second self-balancing wheel may move with respect to one another; a frame connecting the first wheel guide and the second wheel guide; a harness for receiving a user, the harness being provided on the frame; at least one control unit configured to control the first self-balancing wheel and / or second self-balancing wheel in accordance with an inverse pendulum principle. In a further aspect the invention relates to a method of using a mobility assistance device of the invention, the method comprising a step of propagating an intentional movement of a user by means of the device, while preventing falling, wherein the intentional movement is in particular a forward-backward rocking movement, a forward or backward displacement, a turning movement around a point and / or a turning movement in a partial circle.

[0004] BACKGROUND AND PRIOR ART

[0005] Mobility assistance devices are commonly used to assist persons who due to disability, injury, age or illness cannot maintain a normal posture, gait or walking speed. Examples of traditional mobility assistance devices include walking sticks, crutches, wheelchairs, walkers or walking frames such as Zimmer frames and the like. These typically rely heavily on the user’s existing motor functions, for example in the upper body and specifically in the arms and hands, to drive them. In general, their use is restricted to adults or older children who already have sufficient strength and motor control to drive the device. Furthermore, they do not encourage normal walking patterns at normal speeds. These devices are particularly unsuitable for users where congenital or acquired neuromuscular diseases affect muscle strength, motor control, balance or posture in such a way that they are unable to stand and walk independently, who have generally weakened motor functions and for younger children, such as those with cerebral palsy, who cannot rely on their arms to drive a mobility assistance device.

[0006] Among users who require assistance with mobility, a large proportion are children with long-term or hereditary conditions. Other users include those who are elderly, frail, have suffered an injury or a stroke. There exists a large imbalance in the market which is mainly directed to such adult users or those who have experience in mobility before an injury took place. In the case of children, the special requirements of training them to improve their strength and balance are added to the general needs of all children to learn, explore and socialize as they grow. Regular and independent movements should ideally take place from early childhood in order to secure both physical and cognitive development opportunities in the long term. Furthermore, the needs and sizes of children tend to change quickly while they have generally reduced strength compared to older users. In particular in the case of cerebral palsy, depending on the severity of the condition, children may have lowered motor skills and strength but still enough for their movement intentions to be read and interpreted by an outside person. Around 1 - 4 out of every 1000 children are born with cerebral palsy.

[0007] To assist such persons with limited mobility in developing their muscle strength, motor control, balance and posture with a wide range of movement possibilities, a parent, therapist or assistant may partially lift them up and hold them straight by holding their waist or hips to prevent them from falling. At the same time, the arms and legs may be kept generally free such that the affected persons may develop better control and strength in their limbs. The assistant may observe and interpret the person’s movement to support intentional movements such as a deliberate squatting to the ground while suppressing unwanted movements such as falls or spastic movements. This requires a high degree of reliance on the assistant and does not allow such persons to become independent and interact with their peers at eye level.

[0008] Especially in the case of children and teenagers, this can significantly affect the development of the user in other areas such as social skills. The need for constant assistance by another person not only reduces the user’s sense of confidence but also limits their access to a variety of places and activities such as outdoor areas, schools, leisure facilities and the like. Often the child and / or the assistive device must be carried over a step or obstacle by the carer. The reliance on a carer, who is often a family member, may lead to overburdening the user’s family environment. Thus, by excessive reliance on others, the user not only does not develop physically but is also hindered from developing their own personality, interests and social relationships.

[0009] A similar issue can be seen in adult patients who inherit or develop mobility limitations, for example as a result of a stroke. In the case of adult patients, reliance on a therapist is even more difficult due to the larger weight of the adult and their need for independence and privacy. Adult patients recovering from strokes or accidents may also need to re-learn how to walk. Larger devices are usually required for assisting such patients under the guidance of a professional, wherein said devices are very limited in their functionality. For example, known devices may be configured to assist the patient only in walking in a straight line with the help of railings. For the patient to learn the more complex movements required in everyday life activities, they may still require the assistance of one or more further adults. This is very labor intensive.

[0010] Devices have therefore been developed to perform the role of the assistant and allow improved mobility for users with reduced muscle strength overall, reduced motor functions and a tendency to become quickly exhausted.

[0011] As an example, WO 2010 / 139936 A1 discloses a wheeled device comprising a load, wherein the load may itself be a battery driving the wheels. The device may stabilize the walking speed of a user due to the added inertia caused by the load. In use, if the user is pushing the device so that the device is in front of the user, then the device may produce a pulling force when the user slows down, and a pushing force when the user begins to accelerate. Depending on the position of the load, the effective weight of the user may be altered. It is important to highlight here that the device is still mainly driven and controlled by the user who is described as being a frail elderly person for example.

[0012] In a particular embodiment of WO 2010 / 139936 shown in Fig. 10, the device comprises a hinge extending from a distal end of the device, close to the wheels. The hinge comprises a load which functions as a counterweight to reduce the effective weight of the user. Although the user may hold the proximal end of the device with their hands, an alternative is the use of a belt or the like to attach the device to the user, leaving the hands free. The device may thus provide some relief and assistance to a frail user. In a further embodiment illustrated in Fig. 4, WO 2010 / 139936 A1 discloses a speed controller for the user to set a desired walking speed. The user must pay attention while walking to safely control the speed themselves. Apart from the need for user intervention in the control unit, the device still relies heavily on the user’s own balance and motor functions. The device cannot, for example, assist the user in turning - this must be done by overcoming the inertia caused by the load. If the user chooses to crouch down, for example to pick up an object from the floor, the angle at which the load is raised to would cause the device to stop supporting the user. The device also has no control system able to distinguish between crouching and falling and therefore is only suited to users with a reasonable degree of balance and good motor functions.

[0013] Devices have also been developed to both reduce the effective weight of the user and prevent falling for those with reduced motor skills. As an example, EP2859872B1 discloses a passive (not motorized) device equipped with a set of rods arranged in an A-shaped frame between which a hip-supporting belt is provided at a height corresponding to a standing position. The belt is connected by pneumatic or spring-loaded arms to the frame. The belt supports the user’s hips and replaces the assistant’s hands in the case of training a child to walk. The rods prevent the whole device from tipping forwards and provide a stable base, as well as preventing falling as the belt may be clipped directly onto the rods. The device is also equipped with a pair of parallel wheels arranged to follow the user from behind and a counterweight arranged behind the wheels on an arm extending from and pivoting about the wheel axis. The counterweight reduces the effective weight of the user, allowing those with weaker muscle tone to stand upright and walk. Due to the frame arrangement, this device provides a higher degree of safety to those with limited balance and mobility. The device also allows users, typically children with cerebral palsy, to interact with peers at eye level and take part in activities such as eating and playing due to the hands and feet being kept free.

[0014] Similarly to WO 2010 / 139936 A1 however, the angle of the arm carrying the counterweight of and its low height from the ground also limit the support provided by this device of EP2859872B1 . If the user were to squat, the counterweight would not provide enough support to lift them up again. An assisting adult would be required in case this occurred. When the belt is clipped to the rods, the user can no longer crouch or tiptoe as the height of their hips is effectively fixed within a narrow range. The device provides no active assistance for the user to move forwards, backwards or to turn left or right and therefore, despite its better safety, is limited in the range of movements it can support.

[0015] Furthermore, due to the lack of motorized support in the walking aid according to EP2859872B1 , the user must at least partially carry their own weight as well as that of the device. With their own weight being partially supported by the device, the ground reaction to the effective body weight of the user is lowered. This decreases the horizontal force of the foot against the ground. With an increased weight to be pulled by the user and a lowered grip on the ground, a risk of sliding occurs. The need to pull the weight of the device can also become a particular hindrance when moving over uneven ground or attempting to overcome minor obstacles. When walking uphill, the user needs assistance from another adult to maintain their walking speed and prevent exhaustion. When walking downhill, the user needs the adult’s assistance to safely come to a halt.

[0016] When children are using such a device, they must additionally be heavily supervised with frequent active intervention from an adult. The limited range of movement a child can make without help from an adult prevents the child from exploring their surroundings effectively such as lifting objects from the ground or reaching upwards. Therefore, there remains a heavy strain on others.

[0017] An issue with existing mobility assistance devices designed for children (such as that of EP2859872B1 ) is that they cannot be easily scaled up for use with teenagers or adults. Increasing the dimensions of known devices tends to result in a device that is too heavy, bulky and unwieldy for everyday use.

[0018] A further issue with the above-mentioned devices of the prior art is that in order to change their direction of walking or standing, the user must turn about a pivotal point of the device which is typically located behind or in front of the user. The user must thus walk in a partial circle in order to change the way their body is facing. This is quite strenuous and is moreover unnatural. Natural walking in healthy users allows users to turn about a spot which substantially coincides with the ground they are standing on. In other words, healthy users can usually turn about their own body. The devices of the prior art however require the user to make a much larger movement in order to face left, right or to look behind them. Where only large and bulky devices are available for supporting adults, the turning circle is made even larger, requiring a large amount of open space. Walking around the large turning circle can also be quite strenuous for the user.

[0019] To provide a greater degree of assistance to users, motorized devices have also been developed. An example is JP 2011115323 A which discloses a walking assistance robot for training a user, wherein the robot comprises a main body carried by a set of four wheels which follow the user from behind. An arm extends from the main body of the robot with an attachment belt for a user’s hips. The belt and the robot are fitted with a plethora of sensors configured to either support or assist the movement of a user to promote a normal gait. To do this, the positions and motions of virtually all of the user’s limbs are monitored and interpreted. The wheels of the robot are also motorized and controlled using feedback from the sensors. The robot is configured to move the arm and the user upwards when the sensors detect motions consistent with falling.

[0020] The size of the robot is however large, resulting in a very large turning circle which is not compatible with use in everyday environments. Furthermore, the robot is configured for supporting a user when training to walk only. Other movement types are not foreseen. Due to the size of the robot and the arrangement of the four wheels, it would be impossible for the user to overcome small obstacles on the ground, a threshold or set of stairs with the robot. It is therefore only suited for use in controlled environments such as hospitals or rehabilitation centers. Though it may relieve some of the burden on an assistant, significant supervision is still required.

[0021] It is indeed a drawback of the devices of the prior art in general, that their large size and their configuration leads to a large turning circle required for the user to turn about a spot. This results in the user requiring a large amount of personal space, making group interactions difficult. As an example, a school child using a large mobility assistance device to sit at a table with other children would need a large amount of space if they were to turn their whole body around and face another area of the classroom. The large turning circle required may mean that other children cannot be seated immediately next to said child and that close interaction between the children is not possible. This can limit the educational development of the children involved. The issue is further exacerbated in the case of adults where devices are generally much wider in order to provide stability for the adult. The presence of protruding components in the device such as the rods and weight of the device of EP2859872B1 or the large attachment belt of JP 2011115323A further increases the turning circle as another person may not stand too close to the user without risking conflict with the rods or weights. There is therefore a need for a mobility assistance device having a more compact turning circle for both adults and children.

[0022] JP 2011062474A refers to an assistance system designed to enhance the stability of a person who is intended to walk with its help. The wheels of the device are positioned behind the walking person in a V-shaped configuration, with the device being fastened around the users’ waist with a belt.

[0023] WO 2020060422A1 refers to a device intended to attach a hoverboard to a walker, allowing a mechanical walker to be cost-effectively and optionally converted into a motorized walker with the hoverboard serving as the drive mechanism. The hoverboard is mounted between the front and rear wheels of the walker, being attached to the rear legs of the walker with clamps.

[0024] KR 101981403B1 refers to a walking aid in the form of an exoskeleton robot to support natural walking movement. It consists of a rigid frame with four wheels, two of which are positioned to the sides of the used, and two behind the user. The user wears a harness, which is connected to the frame at three points using variable length modules. A sensor is provided to detect the walking movement and a controller that can adjust the length of the variable length modules. The device does not seem to support other natural movement patterns, other than walking.

[0025] In light of the teachings of the prior there is room for providing an improved mobility assistance device which can adequately support a variety of up / down movements such as standing, jumping and squatting as well as supporting turning movements. Regular and independent movements should ideally take place from early childhood in order to secure both physical and cognitive development opportunities in the long term. In particular, the devices of the prior art typically still require an assistant to lift the user in case of squatting down to the ground, to help them change direction and / or to overcome an obstacle. This means that if a building such as a museum, cinema, sports centre or the like must be accessed by overcoming even one or two steps, the user of the device is effectively excluded due to the burden of overcoming the steps with a heavy device. Thus, a great degree of independence cannot be provided.

[0026] Due to these difficulties, there exists a pressing need for improved mobility assistance devices which can support users, especially children with long-term conditions, in a wide range of activities without the need for close supervision or assistance. There is a lack of gait training devices and training devices specifically designed to improve users balance or posture and especially which are suitable to be used regularly in day-to-day environments. There is additionally a need for improved mobility assistance devices which enable interaction between users, active participation, and providing more joy in movement both indoors as well as outdoors, in particular by providing more independence, overcoming obstacles with ease, and an improved maneuverability on uneven ground and with a more compact turning circle. SUMMARY OF THE INVENTION

[0027] An objective of the present application was to overcome the disadvantages of the prior art and to provide an improved mobility assistance device which supports a wide range of postures and movements and is preferably adapted for use with adults and children.

[0028] The problem is solved by the features of the independent claims. Preferred embodiments of the present invention are provided by the dependent claims.

[0029] The invention relates to a mobility assistance device comprising: a first self-balancing wheel mounted on a first wheel guide which defines a first curved path along which the first wheel guide and the first self-balancing wheel may move with respect to one another; a second self-balancing wheel mounted on a second wheel guide which defines a second curved path along which the second wheel guide and the second self-balancing wheel may move with respect to one another; a frame connecting the first wheel guide and the second wheel guide; a harness for receiving a user, the harness being provided on the frame; one or more control units configured to control the first self-balancing wheel and / or second selfbalancing wheel in accordance with an inverse pendulum principle.

[0030] In the sense of the invention, a “mobility assistance device" is preferably a device for assisting a user in moving, positioning or maintaining a posture of their own body. The assistance may be for therapeutic or non-therapeutic purposes. In particular, the mobility assistance device may be configured for assisting a user in training their body to carry out a given movement or to maintain a given position. The training may concern co-ordination, spatial awareness, strength, stamina, posture, balance, endurance or any other skill. Such a training may occur in the context of physiotherapy, rehabilitation, elderly care or mobilization after a stroke or accident, to name a few examples. A mobility assistance device in the sense of the invention may preferably also be a device for assisting a user in moving, positioning or maintaining a posture of their own body for leisure reasons such as walking, hiking, dancing or performing a sporting activity. The device may serve to reduce exhaustion and increase stamina and / or endurance as well as to prevent accidents, e.g. by protecting the user against falls. A mobility assistance device in the sense of the invention need not be specifically designed for walking or for activities carried out while standing. Rather, the mobility assistance device may also be configured to support seated activities. For example, the mobility assistance device may serve as an improved alternative to any type of wheelchair or wheeled office chairs. Such a mobility assistance device may improve posture when a user is seated in such a chair whilst also enabling the user to swivel or move around a desk. This may be particularly beneficial for training good posture whilst providing relief to legs, arms or other muscle groups which a user typically uses repetitively to push or pull themselves to / from a desk in order to move in and / or an office chair. Such a mobility assistance device may be especially suited to preventing repetitive strain injury. Additionally or alternatively, the mobility assistance device may be configured for supporting a user’s special mobility needs. Such a mobility assistance device may be used as an alternative to a crutch, wheelchair or Zimmer frame. It may also be used to safely support a user’s movement or rest (e.g. seated activities) within their own home. In the sense of the invention, the vertical axis z may be defined as being in the direction of gravity. This is also referred to herein as an up-down direction or a vertical direction. The x axis may be defined as being in the direction in which a user walks. This is also referred herein as a forwardbackward direction. The y axis may be defined as a lateral direction which is orthogonal to the x and z axes. This is also referred to herein as a left-right direction or a sideways direction. These directions will be used below to explain the relationships between different components of the device and their functions.

[0031] In the sense of the invention, a “frame” is preferably a mechanical connection between different components which is configured to set a distance and / or relative positioning between said components. The frame may fix the distance between the first wheel guide and second wheel guide such that these are substantially parallel to one another. Alternatively, the frame may allow for a limited movement or “play” between the wheel guides, for example by means of a compressive or tensive element. The frame may limit the variation in a distance between the wheel guides to less than 50 mm, preferably less than 10 mm, more preferably less than 5 mm. The frame may also limit the variation in angular position between the wheel guides with respect to the y-axis to less than 2°, preferably less than 1 °. The frame may also limit the variation in angular position between the wheel guides with respect to the x-axis to less than 10°, preferably less than 2°, more preferably less than 1 °. Said angular position may in particular represent a camber angle of the self-balancing wheels.

[0032] In the sense of the invention, a “harness” is preferably any means for securing and / or supporting a user to a device. This may include a seat, a saddle, a belt, a set of straps, torso orthotics, a set of bandages, a rucksack-type arrangement, a wearable piece of clothing, an exoskeleton, a trunk orthosis, a torso orthosis or the like. The harness is preferably customized for the user, in particular where the harness comprises an orthosis. The harness may be movably or fixedly connected to the frame. The connection of the harness to the frame is preferably such that the harness is fixed thereto, can move or can move within constraints with respect to the frame.

[0033] In the sense of the invention, a “wheel guide” is preferably a mechanical element configured to direct and limit the movement of a centre of rotation of a wheel with respect to the frame and the harness being provided at the frame and vice versa. The wheel guide may be configured for example as a skid, rail, track or the like. Preferably the wheel guide mechanically limits a forward and backward movement of a respective wheel, such that the wheel reaches a forward stop and a backward stop. This can prevent excess tilting of the device, ensuring that the user does not fall or reach an uncomfortable position.

[0034] In the sense of the invention, a “curved path” is preferably a path along which a center of rotation (or other reference point) of a respective wheel may move. Preferably the curved path is provided mechanically in or on a respective wheel guide. The curved path is preferably limited, having a forward end point and a backward end point. Preferably the curved path comprises a central portion, the central portion preferably comprising at least 60 %, preferably at least 70 %, more preferably at least 80 % of the length of the curved path. The central portion of the curved path is preferably curved in a substantially vertical plane such that it is substantially concave when viewed from above and convex when viewed from below. In other words, when viewed from the side the curved path preferably open upwards, that is in a central region, especially at the midpoint of the wheel guide, the quadratic term of a function approximating the curved path is positive. The curved path or said central portion is not rectilinear. The curved path or said central portion may have a constant or gradually varying radius, as explained further herein. One or more extremes of the curved path may however be straight, angled, differently curved, or may otherwise diverge from the curved form of the central portion.

[0035] The curved path is thus preferably provided by the wheel guide, wherein a self-balancing wheel can preferably move on a curved path along the wheel guide or vice versa. For instance, the wheel guide can move relative to the self-balancing wheels, allowing for a forward and backward tilting movement of the frame and thus of the user, such as in a rocking motion, or when leaning forward.

[0036] A curvature in the sense of the invention is preferably a line of continuously changing tangent gradient, the tangent gradient preferably being positive on one side of the curve and negative on another side of the curve. Preferably the tangent gradient increases (or decreases) from one end of the curved path or central portion thereof to another. In other words, the rate of change of the gradient along the curve is preferably always either positive or negative, depending on the direction in which the curve is traced. Preferably the curved path curves away from the ground at its ends and is by default closest to the ground at a point between its ends. Preferably every point on the curved path or on the central portion thereof has a radius to a virtual origin, the virtual origin preferably always lying above the respective wheel guide, more preferably above the default height position of the harness. Preferably, a difference between the radii of two adjacent points (e.g. less than 5 mm away from one another) on the curved path or the central portion thereof is not more than 20 %. It is also possible for the curved path to comprise one or more rectilinear portions of continuously differing gradients. In such a case, a circular curve of best fit can preferably be drawn through the points of the curved path, such that the circular curve of best fit has a virtual origin above the respective wheel guide.

[0037] The curved path of the wheel guides preferably allows the device to rock in a forwards-backwards direction (x-z-plane) without necessarily driving the whole device forwards. Small changes in the user’s posture can thus be accommodated by the device, without forcing the user to move. When the user tilts their body forwards slightly, without pushing a foot against the ground in order to walk or run, the device can rock forwards. The wheel guides can move along the curved path with respect to stationary self-balancing wheels which remain in place on the ground directly under the user’s centre of gravity. The device can thus differentiate between an intention to lean forwards, e.g. to reach for an object on a low shelf, and the intention to walk forwards. The risk of the device “forcing” the user to walk forwards against their intention can thus be avoided.

[0038] In the sense of the invention, a “rocking” movement is preferably a movement about a real or virtual fulcrum, the movement occurring within a limited angular range which is preferably less than a full circle, The rocking movement may also be referred to as swinging or see-sawing about a real or virtual fulcrum. The fulcrum is preferably a lateral or y-axis or is substantially parallel to the y-axis. The fulcrum may be static or moving during the rocking movement.

[0039] In the sense of the invention, a “self-balancing wheel” preferably functions as a wheeled inverted pendulum system. An example of such a system is known from the Segway patent US6302230B1 .

[0040] In the present invention, each self-balancing wheel is preferably equipped with its own motor and its own set of sensors. One or more control units may centrally control both self-balancing wheels individually or together in accordance with the inverse pendulum principle. To do this, a central control unit may receive data from the set of sensors of each of the first and second self-balancing wheels. Preferably, the “one or more control units” comprise at least two control units, wherein each self-balancing wheel comprises its own control unit which drives the motor on the basis of sensed data from the set of sensors. Each self-balancing wheel is thus preferably capable of being controlled individually, independently of the other self-balancing wheel. A further (third or central) control unit may be provided to monitor and / or centrally control the individual controllers of the first and second self-balancing wheels. For example, a central control unit may monitor the positions of the self-balancing wheels with respect to one another and to maintain these within pre-determined parameters.

[0041] Each self-balancing wheel preferably comprises at least one sensor, at least one motor, and is preferably connected to at least one control unit preferably comprising a computing device.

[0042] Self-balancing wheels are preferably equipped with sensors and are connected to a control system maintaining the wheels’ upright position and stability autonomously. The self-balancing wheel can preferably comprise at least one sensor, preferably a gyroscopic sensor and / or an accelerometer, a microcontroller, and / or a motor. These components preferably work together to detect the wheels’ orientation and make real-time adjustments to keep it balanced.

[0043] The center of gravity of a weight carried by each self-balancing wheel can be theoretically modelled as an inverted pendulum. In a wheeled inverted pendulum system, the speed, acceleration and direction of rotation of a motorized wheel are preferably controlled such as to prevent a pendulum extending vertically upwards from the wheel axis against tilting, swinging down and falling. When the pendulum is in a vertical position above the wheel axis, the wheeled inverted pendulum system is balanced. This vertical position is referred to as an unstable equilibrium position. This becomes a target position which the system aims to return to in case of any deviation of the pendulum’s orientation.

[0044] A pendulum may begin tilting and falling ahead of or behind the wheel in an x-plane. The x-plane is preferably defined as spanning the x- and z-axes. The angle between the pendulum, the wheel’s center and the vertical position in the x-plane is preferably detected by the set of sensors. The wheel drives in the direction in which the pendulum is tilting and falling, to prevent the fall and to bring the orientation of the pendulum back towards the vertical position.

[0045] In this case, the weight of the pendulum may comprise at least partially the weight of the selfbalancing wheel itself, the weight of the frame, any counterweights placed on the frame, and the weight of the user. The user usually maintains contact with the ground separately from the wheels, wherein usually at least half of a user’s foot is on the ground such that the user can intentionally influence the orientation of all or part of the device. Furthermore, due to the contact with the ground, usually only a part of the user’s weight contributes to the weight of the hypothetical inverted pendulum.

[0046] Preferably the self-balancing wheels can be controlled independently of each other in accordance with an inverse pendulum principle. This is preferably achieved by providing each self-balancing wheel with its own control unit. As used herein the expression “independent regulation of each of the self-balancing wheels according to an inverse pendulum principle” preferably means that each self-balancing wheel functions as an independent wheeled inverted pendulum system. Additional overarching control methods and co-ordination between the wheels is hereby not excluded. Hence, the angular position of a falling pendulum in the x-plane is preferably detected by a set of sensors for each wheel and each wheel drives in the necessary direction and at the necessary speed to return the pendulum to the vertical position as described above.

[0047] Preferably the frame of the device is so configured that the angular position of the pendulum in the x-z-plane passing through each self-balancing wheel is varied when the user shifts their center of gravity forwards or backwards, i.e. in the x-z-plane. To achieve this, the harness may be configured on the frame such that a user’s centre of gravity is substantially raised above the centre of rotation of each self-balancing wheel. An angle 0 in the x-z-plane made by the user’s centre of gravity to the centre of rotation of each self-balancing wheel with respect to a vertical position may preferably be varied during use of the device. This variation in the angle 0 may be achieved by the user leaning forward in the harness and / or by the user pushing a foot against the ground, in order to move their body (and the device) forwards. Preferably the frame is so configured that the angle 0 formed by the user’s position may vary independently between one lateral side of the device and the other, such that the orientation of the pendulum in an x-z-plane passing through a first self-balancing wheel may be different to the angle 0 formed in another x-z-plane passing through the second selfbalancing wheel. Each self-balancing wheel may then be actuated independently of the other to return the pendulum to its vertical position. For example, when a user begins to move their body forwards, a positive angle 0 may be formed with respect to the vertical. The user’s centre of gravity may be slightly ahead of the centre of rotation of a self-balancing wheel. The respective selfbalancing wheel may be actuated by the controller to bring its centre of rotation back under the user’s centre of gravity, returning the angle 0 to zero. This may be done by the respective selfbalancing wheel moving forward, following the movement of the user. As the self-balancing wheel moves forward, its position with respect to its wheel guide may also change, depending on the user’s acceleration in the forwards direction. When the user begins to slow down, the whole device may tilt backwards slightly, providing the user with a slight backwards rocking (or “swinging” or “see-sawing”) motion. This can bring the user back to a slow walking or standing posture. The opposite may occur where the user leans backward in the harness and / or moves their body backwards by pushing against the ground, creating a negative angle 0 to the centre of rotation of the self-balancing wheel. In such a case, the self-balancing wheel may rotate in the opposite direction such that it moves backwards. The whole device may thus move backwards.

[0048] Preferably, the direction in which the user attempts to turn laterally effects a smaller (or a negative) deviation in the angle 0 of the frame member connected to the wheel positioned in the direction of the turn. A wheel on the other side of the user preferably detects a larger (or positive) angle 0 to balance out. The self-balancing wheel having the lower angle 0 preferably rotates more slowly in a forward direction or (if the angle 0 is negative) moves in a backward direction compared to the selfbalancing wheel with the larger angle 0. This causes the whole device to turn. Depending on the user’s movement, the device may change direction, follow a curve or rotate about the user’s body.

[0049] When two such self-balancing wheels are used in conjunction with one another, a turning action is preferably effected by a difference in speed or direction between the two wheels. The frame connecting the wheel guides preferably maintains the distance between the centers of rotation of the self-balancing wheels within a limited range. The centers of rotation of the self-balancing wheels may be kept approximately equidistant. This supports the device in turning about a single point.

[0050] Advantageously for the mobility device according to the invention, each self-balancing wheel may be provided as an off-the-shelf item. It may be preferable, as is typically the case with off-the-shelf self-balancing wheels, that each self-balancing wheel comprises its own set of sensors and its own processor housed within the wheel or within a wheel casing. Each wheel may also comprise a motor. Each processor may control the motor of the respective wheel according to the inverse pendulum principle, independently of the other wheel. The self-balancing wheels may alternatively be provided custom-designed, wherein either separate processors are provided for each wheel or a common processor allows for an independent regulation of each of the self-balancing wheels in accordance with an inverse pendulum principle. Additional or alternative processors may be used to provide the self-balancing wheels with some degree of dependence and / or to co-ordinate movement between them.

[0051] For the purposes of this application, a “control unit” preferably refers to any computing device having a processor, a processor chip, a microprocessor or a microcontroller to allow for an automatic control of the components of device, such as the self-balancing wheels and / or potential actuators for adjusting the position of a support wheel, a harness, a counterweight etc. The components of the control unit may be conventional or custom-configured for the particular implementation. Preferably the control unit comprises a processor, a memory and computer code (software / firmware) for controlling the components of the device.

[0052] The control unit may also comprise a programmable printed circuit board, microcontroller, or other device for receiving and processing data signals from the components of the device, such as from sensors with respect to the position of self-balancing wheels or other sensory information in relation to a position of the harness, the frame or portions thereof.

[0053] The control unit preferably further comprises a computer-usable or computer-readable medium, such as a hard disk, a random access memory (RAM), a read-only memory (ROM), a flash memory etc., on which a computer software or code is installed. The computer code or software to perform the control of the components of the device may be written in any programming language or modelbased development environment, such as but not limited to C / C++, C#, Objective-C, Java, Basic / VisualBasic, MATLAB, Python, Simulink, StateFlow, Lab View, or assembler.

[0054] The software, and any functional descriptions of the software by description of controlling particular components or aspects of the device described herein, are considered technical features due to a direct physical output on the device. Functional descriptions of software may therefore be considered as preferred and defining embodiments of the invention. The particular computer code employed is available to a skilled person and may be constructed accordingly using standard knowledge.

[0055] The term “one or more control units” or “at least one control unit” as used herein preferably refers to the presence of at least one computing device for controlling the movement of one or both of the self-balancing wheels. Although it is within the scope of the invention for a single control unit to be connected in a wired or wireless manner to both self-balancing wheels and to control both of these together or independently, it can be assumed in most embodiments of the invention that each selfbalancing wheel comprises a dedicated control unit. Thus, the term “one or more control units” is usually to be understood as referring to the preferred two control units: a first control unit for the first self-balancing wheel and a second control unit for the second self-balancing wheel. An overarching or “central” control unit may preferably also be referred to.

[0056] The term “control unit is configured to” perform a certain operational step, such as determining the relative positions of the self-balancing wheels and wheel guides and in response to the sensed data to suppress or propagate the movement of a user by adjusting the position of a counterweight, adjusting the speed and / or direction of the self-balancing wheels, may encompass a custom- designed or standard software installed on said control unit that initiates and regulates these operational steps.

[0057] Preferably, the one or more control units comprise one or more processors for regulating each of the self-balancing wheels based on the data from sensors provided in said wheels in accordance with an inverse pendulum principle. Preferably, the one or more control units may comprise a first processor for a first self-balancing wheel and a second processor for a second self-balancing wheel, wherein each of the first and second processors preferably receives data from the set of sensors pertaining to the respective wheel, uses the sensed data to determine a corrective action required to maintain stability of the device and commands one or more wheel-motors to make the corrective action.

[0058] As set out above, the wheel guides of the device comprise a curved path. This allows the device to support a forward-backward rocking motion. When rocking forwards or backwards, the frame of the device may tilt with respect to a default vertical position. This allows the user to adjust their vertical position, for example to reach for something at a low position by leaning forward and causing the frame to tilt forwards. The curved paths and / or wheel guides preferably limit the degree of said forward tilt, such that the user does not overexert themselves and does not fall. The user may then return to an upright position by leaning backwards which brings the frame back to its default vertical position. This advantageously allows the user to adjust their position whilst allowing the user’s hands to remain free. This maneuver also does not require a strong upper body with skilled arms and hands, making it especially suitable for stroke patients and elderly users. In particular, the user does not need to use their hands to control the device in contrast to known devices. By freeing the user’s hands, the user is free to take part in daily activities. This is especially important for allowing users to be integrated into society.

[0059] The forward-backward rocking motion also allows the self-balancing wheels to remain stationary during small forward-backward shifts in the user’s centre of gravity. This is because these may be compensated by the movement of the wheel guides along the curved paths, such that the position of the self-balancing wheels with respect to the user’s centre of gravity need not change until the end of the curved path is reached. A change in the user’s posture therefore need not even be detected by the self-balancing wheels (or sensors thereof), such that these are not actuated when not needed or desired. On the other hand, a forward shift of the user’s centre of gravity which is caused by the user’s attempt to walk would be detected by the self-balancing wheels as this movement - being mainly characterized by a forward translation rather than a tilt - cannot be compensated by the tilting of the device. The self-balancing wheels can be intuitively activated to help move the user forward at their pace, according to their intention.

[0060] The harness is preferably configured to be forward-facing. That is, the user may be secured to the harness with the frame substantially behind them. As the harness is provided on the frame which connects the first and second wheel guides, a forward-facing harness can position a user between and above the vertical wheel guides. The user may preferably be placed such that their centre of gravity is by default above a horizontal plane defined by the wheel guides (or the centres of rotation of the wheels) but neither ahead of nor behind the forward and backward extremes of said wheel guides. The harness and the user can thus be positioned relatively centrally and / or slightly to the rear of the device. In contrast to devices comprising large protrusions ahead of or behind the user, this can reduce the turning circle of the device. This arrangement also allows the device to turn substantially about the harness, mimicking a more natural movement by which the user turns substantially about their own body. This can improve the rehabilitation of injured or elderly patients. It also allows users to change the direction in which they are facing more quickly and with less effort, especially as the user does not need to walk in a large partial circle. Interaction with peers is further facilitated as the user can respond more quickly to social cues. Pivoting about a spot is indeed essential in smaller spaces such as supermarket aisles, within which a user may wish to maneuver themselves in order to carry out everyday tasks. In some sports activities or when the mobility assistance device is used as a desk chair in an office environment, pivoting is necessary for a quick and effective reaction to environmental cues. The small turning circle can thus widely expand the uses of the device.

[0061] A further advantage of using a harness is that it can secure the user to the device in a manner that is space-saving and compact, such that they can face their peers without a perceived physical “barrier”. This is in contrast to known devices, in which the plethora of sensors are arranged in and around a large inflexible carrying arm for receiving the user. Furthermore, the use of a harness allows the device to be simply adaptable to the growth of a child as harness straps may be loosened or tightened as appropriate. Harnesses are easily replaced, cleaned or adapted to changing requirements and due to their flexibility and variety can allow a wide range of unrestricted movement. This is especially important for children who often play with objects on the floor or crouch and / or crawl. For adult patients going through a physical rehabilitation program, support needs may also change such that harnesses with greater flexibility may be used as treatment progresses.

[0062] The connection of the harness to the frame also assists the user in remaining in an upright position with reduced fatigue. This is because the harness and frame may mechanically support the user such that their default position is an upright one. Due to the reduced strength, motor control, balance and posture control of children and those with weakened muscles, the support provided by the harness significantly reduces the burden on their muscles. This allows the user to stand or walk for much longer before exhaustion sets in. The user can thus take part in activities for longer, developing their experience of the world and improving their quality of life. As explained further herein, the harness and frame may be configured in a variety of manners to further support an up- down movement of the user, reducing muscle strain required for reaching downwards and getting back up.

[0063] The self-balancing wheels provide a further compact way to carry the frame including the harness in a forwards-backwards and left-right direction. As such, the device may assist the user not only by allowing them to remain upright for longer but by maintaining their balance regardless of the direction they walk in. The force required to move the device which includes the weight of the wheels, wheel guides, frame, harness (and user) is kept minimal since the user need only move the pendulum out of an unstable equilibrium position to make the device move. A small attempt at walking can thus be detected by the one or more control units. The sensitivity of the device can be set such that this movement is minimal where users have weakened muscle tone. For users suffering from involuntary movements such as spasms or jerks, the movement required to trigger the inverse pendulum control may also be raised, such that only intentional movements cause the device to react. The strength required to move forwards and backwards as well as to turn is thus reduced to an appropriate degree and kept safe by the device. As such, the active assistance of another person is no longer required, especially for turning, when maneuvering on uneven ground, or for overcoming small obstacles.

[0064] The inverse pendulum principle used to control the self-balancing wheels provides a simple alternative to the more complex motorized solutions of the prior art. Balance can thus be achieved without requiring a great number of sensors for the various limbs. The limbs can remain free and normal clothing can be worn. By using at least two self-balancing wheels, the size of the device may be reduced whilst maintaining a high degree of stability and at the same time exceeding in maneuverability. It is thus not necessary to increase the size of the device to four wheels which would lead to increasing the turning circle.

[0065] Furthermore, in the case of uneven ground - as is often found outdoors - using at least two selfbalancing wheels provide an advantage over the prior art as they react quickly and automatically to sudden shifts in the user’s center of gravity. As such, challenging terrains are also accommodated by the device. As the device does not require more than two self-balancing wheels, climbing stairs and overcoming obstacles and thresholds or the like is also eased. The presence of further wheels such as support wheels or self-balancing wheels on the device is however not excluded and may indeed be preferable in some embodiments. For example, the first self-balancing wheel may form part of a first group of self-balancing wheels provided to the right side of the harness while the second self-balancing wheel may form part of a second group of self-balancing wheels provided to the left side of the harness.

[0066] By providing the self-balancing on a curved path of the wheel guides, the front portions of the wheel guides may tend to point away from the ground. This can provide an increased ground clearance towards the front of the device, causing the device to be more adapted to overcoming obstacles. For example, a step at a doorway may, instead of colliding with a rectilinear portion of a device, meet the device at its curved wheel guides. The curved wheel guides can be smoothly passed over the step while the user places their feet onto the step, until the self-balancing wheels engage with a surface of the step and bring the device and the user over the step, as for example in case of a doorway. It is preferable that the harness is configured for the user to face away from the frame. As such, the wheels and frame follow the user from behind, allowing them more freedom to see ahead of them, to perform activities with their hands and feet and to interact with others without physical barriers.

[0067] In a further preferred embodiment of the invention, the harness is arranged pivotably with respect to the frame, wherein a shock absorber is preferably provided between the harness and the frame. The skilled person is aware of means for arranging the harness pivotably with respect to the proximal arm. Examples of such means may include a hinge. The hinge may enable pivoting about a single axis, preferably the y-axis. Alternatively, a ball joint may be used to enable pivoting about two or three axes. A pivotable connection between the harness and the frame allows the user to increase their range of unrestricted mobility as the angle of their hips or waist must not be kept constant with respect to the frame. More natural movement patterns may thus be achieved. By providing a shock absorber between the harness and the frame, for example a rubber, compressible hydraulic component, compressible pneumatic component or a compression, tension or torsion spring, a voluntary or involuntary backwards movement of the user’s torso would not be abruptly stopped by the proximal arm.

[0068] In a preferred embodiment of the invention, each of the first and second curved paths comprise a central portion. The central portion of a curved path is preferably a portion of its length which excludes one or more extremes. The central portion preferably comprises at least 60 %, more preferably at least 70 %, even more preferably at least 80 % of the length of the curved path. Each central portion preferably has a characteristic radius CR to a virtual fulcrum VF. The virtual fulcrum of a curved path is preferably an imaginary point representing the origin of a circle having the characteristic radius. The respective wheel guide may be considered to pivot about its virtual fulcrum, in particular to produce a forward-backward rocking motion. The virtual fulcrum is preferably above the respective wheel guide and may move with the device. This provides the device with improved stability as forwards and backwards tilting of the user and the device can be accommodated without the device tipping. A particularly high stability is provided where the virtual fulcrum VF is higher than the height of the device’s centre of gravity, in particular higher the centre of gravity of a system including the device and the user in the harness. As the weight of the system is largely influenced by the weight of the user, this can be approximated by referring to the centre of gravity of the user. As the centre of gravity of the user tends to fall within the harness, this can also be approximated by referring to the position of the harness, wherein the virtual fulcrum VF is preferably always above any possible vertical position of the harness.

[0069] In the case of a curved path having a circular curvature along its entire length or along a central portion thereof, the characteristic radius is preferably the radius of the circle. The curvature of the curved path or its central portion may however vary along its length. In such a case, the characteristic radius is preferably a mean radius of curvature.

[0070] In a preferred embodiment of the invention, the characteristic radius CR of the central portion of each of the first and second curved paths is identical. This may also apply to the whole first and second curved paths. By providing an identical characteristic radius CR, the wheel guides and the device as a whole may pivot about a single virtual fulcrum. The single virtual fulcrum may represent the origin of an imaginary sphere or ellipsoid, while the curved paths (or central portions thereof) may represent arcs of the imaginary sphere. This can provide an even rocking movement such that the user is not tilted left or right when their intention is to kneel or crouch.

[0071] In some preferred embodiments of the invention, it may be preferred for each of the first and second curved paths (or central portions thereof) to comprise different characteristic radii CR. This may result in a slight lateral tilt of the user alongside the forward-backward rocking movement. Such a tilt may be desirable where the user’s anatomy includes a pelvic or spinal tilt to be balanced out by the lateral tilt of the device. This can assist such users in maintaining a normal posture when carrying out a range of vertical and forward-backward movements.

[0072] In a preferred embodiment of the invention, one or more end portions of a wheel guide have a form different to that of a central portion of the same wheel guide. For example, one or more end portions of a wheel guide may be free of curvature. The wheel end portion may be configured to be substantially horizontal when the harness is in a default position. The wheel end portion may be configured to angled away from the ground. The one or more end portions may alternatively be curved or angled in an opposite direction to the curvature of the central portion. The same feature may be present at one or more end portions of the respective curved path. Such a feature may allow the user to sense that a self-balancing wheel has reached an end portion of the wheel guide such that the user may intuitively reduce the forward tilt of their body in order to slow the device down and / or to prevent tipping in a forward or backward direction.

[0073] In a further preferred embodiment of the invention, the harness is provided at a default height hi above the first wheel guide and second wheel guide. The harness being provided above the first wheel guide and second wheel guide preferably means that the harness is also provided between a vertical plane corresponding to the front extremes of the wheel guides and a vertical plane corresponding to the rear extremes of the wheel guides, in particular when these are in a default position. Providing the harness in such a position allows the harness to be particularly stable and to remain within a safe range of heights during the use of the device. When a user is strapped into the harness, the centre of gravity of the device is by default preferably approximately above a centre of the first and second wheel guides such that no rocking (in particular about the virtual fulcrum or about the y-axis) occurs. When the user shifts their body weight forwards or backwards, the centre of gravity of the device may be kept safely above the wheel guides which form the base of the device, such that the device does not easily tip. By placing the harness at the default height hi above the wheel guides, it is less likely that the whole device tips, such that the user loses the support of the device and may fall. This is explained further herein with respect to the figures which show preferable relative dimensions of the components to avoid tipping.

[0074] In the sense of the invention, the “default height” hi is preferably the height of the harness when the user is not applying any intentional force thereto. The default height of the harness may be its height without the user in it. The default height of the harness may alternatively correspond to its height when it is holding a user in a standing position, such that both feet of the user can touch the ground. Alternatively, such as where the device is generally to be used for sitting (e.g. as an ergonomic or therapeutic movable chair), the default height of the harness may correspond to its height when it is holding a user in a seated position, such that both feet of the user can touch the ground. The height of the harness may be measured from any reference point thereof to the ground, in particular from a point corresponding to the user’s hip to the ground. In a further preferred embodiment of the invention, the device is configured for use with children aged up to 3 years old. Where such a device is intended for standing or walking use, the default height of the harness is preferably at 33 - 64 cm from a ground level. Where such a device is intended for seated use, the default height of the harness is preferably between 15 - 26 cm from a ground level. The characteristic radius of each wheel guide is preferably at least 65 cm, more preferably 70 - 130 cm.

[0075] In a further preferred embodiment of the invention, the device is configured for use with children aged between 4 - 8 years old. Where such a device is intended for standing or walking use, the default height of the harness is preferably at 55 - 80 cm from a ground level. Where such a device is intended for seated use, the default height of the harness is preferably between 23 - 40 cm from a ground level. The characteristic radius of each wheel guide is preferably at least 81 cm, more preferably 90 - 170 cm.

[0076] In a further preferred embodiment of the invention, the device is configured for use with children aged between 9 - 14 years old. Where such a device is intended for standing or walking use, the default height of the harness is preferably at 70 - 96 cm from a ground level. Where such a device is intended for seated use, the default height of the harness is preferably between 36 - 48 cm from a ground level. The characteristic radius of each wheel guide is preferably at least 96 cm, more preferably 110 - 180 cm.

[0077] In a further preferred embodiment of the invention, the device is configured for use with teenagers or adults over the age of 14. Where such a device is intended for standing or walking use, the default height of the harness is preferably at 86 - 120 cm from a ground level. Where such a device is intended for seated use, the default height of the harness is preferably between 42 - 54 cm from a ground level. The characteristic radius of each wheel guide is preferably at least 120 cm, more preferably 110 - 200 cm, in particular 130 - 170 cm.

[0078] In a further preferred embodiment of the invention, the characteristic radii CR of the first and second curved paths (or the central portions thereof) are greater than the default height hi , in particular greater than a minimum distance between the first or second curved path and a centre of gravity of the user in the harness. It has been found that such curved paths provide improved stability against tipping. When the characteristic radius of a curved path is greater than the height of the centre of gravity of the user (which is usually located within the harness, between the hip height and the umbilicus, depending on age, gender and medical condition), the imaginary spherical arc (or the curved path) formed by the wheel guides can lie between the user’s centre of gravity and the ground for all possible rocking positions. The wheel guides can thus serve as a base to the system comprising the mobility assistance device and the user. As the user’s centre of gravity is always above the base during use, the device does not tip.

[0079] In a further preferred embodiment of the invention, each of the first and second self-balancing wheels is provided with one or more guide elements to support its movement along the curved path of the first or second wheel guide respectively. Such guide elements can ensure that the movement of the first self-balancing wheel is limited to the first curved path of the first wheel guide and cannot diverge from it. The same applies to the second self-balancing wheel. This can be done by configuring the guide elements to provide sufficient contact between each self-balancing wheel and its respective wheel guide.

[0080] In a further preferred embodiment of the invention, the one or more guide elements connect the first or second self-balancing wheel to the first or second curved path at a centre of rotation of each self-balancing wheel. In this case, it may be preferred that a guide element is provided both on an inner and an outer surface of each self-balancing wheel, in particular at its centre of rotation. This can prevent the self-balancing wheels from being separated from the wheel guides, particularly on uneven terrain. This arrangement is also space-saving as the self-balancing wheel may travel along the full length of the curved path.

[0081] In a further preferred embodiment of the invention, the one or more guide elements connect the first or second self-balancing wheel to the first or second curved path at a point other than its centre of rotation. For example, the first or second self-balancing wheel may be suspended from the first or second curved path, e.g. using a wheel case. This can increase the ground clearance of the device.

[0082] In a further preferred embodiment of the invention, the one or more guide elements connect the first or second self-balancing wheel to the first or second curved path at least at two separate points along the curved path, the at least two separate points preferably being at least 25 mm apart. By connecting the guide elements at least at two separate points along the curved path, a movement of the self-balancing wheel across the curved path is prevented. Movement of the wheel along the ground can thus not occur without respective movement of the wheel guide.

[0083] In a further preferred embodiment of the invention, the one or more guide elements connect the first or second self-balancing wheel to the first or second curved path at a tangent to the curved path. This may be the case where the two separate points of contact along the curved path are immediately adjacent to one another.

[0084] In a further preferred embodiment of the invention, the one or more guide elements preferably comprise a sleeve, a reel, a pulley, a scroll, a caster, a pair of clips, a pair of track-inserts, a pair of guide rollers or a pair of roller bearings. The use of guide rollers is particularly preferred due to the stability they provide to the wheels. These have also been found to be space saving, such that trip hazards and the risk of entanglement with items on the ground is reduced.

[0085] In a further preferred embodiment of the invention, the mobility assistance device comprises one or more contact, acceleration, position and / or tilt sensors and the one or more control units are configured to determine an angular tilt of the frame and / or the wheel guides about a virtual fulcrum VF based on sensed data. The virtual fulcrum VF may be the same for both wheel guides, in particular where these have the same characteristic radius. Alternatively, each wheel guide may have a different virtual fulcrum.

[0086] For example, the contact sensor may be provided on the wheel guides, in particular at an end of the curved path thereof. The contact sensor may detect that a self-balancing wheel, in particular a centre of rotation of the wheel or a wheel case, has reached the end of the curved path. Alternatively or additionally, contact sensors may be provided at intervals along the curved path. This enables the one or more control units to determine the position of the wheel with respect to the wheel guide. This can indicate the direction and angle of forward-backward tilt of the device, in particular of the frame. By determining the angular tilt of the frame and / or the wheel guides about the virtual fulcrum VF, the user’s intention - e.g. to move forwards or downwards may be interpreted by the one or more control units. The degree of angular tilt of the frame, optionally in combination with other factors such as the duration of the tilt, may be used to determine that the user’s intention is to crouch downwards. This may be carried out by allowing the harness to be lowered, while moving the wheels forward according to the inverse pendulum principle outlined above if the user attempts to crawl (pushing backwards with hands or feet against the ground). The angular tilt may also be electronically limited to prevent tipping of the device.

[0087] In a further preferred embodiment of the invention, the one or more control units are configured to determine whether the angular tilt of the frame and / or the wheel guides has reached or exceeded an allowable angular tilt. To do so, the one or more control units may comprise a suitable program for comparing the actual angular tilt of the device with a pre-stored allowable angular tilt. The program may also be configured to forecast an upcoming tilt movement of the device. Preferably, the angular tilt is determined in a forwards-backwards plane. It is advantageous to monitor this as the forwards-backwards tilt indicates the posture of the user in the harness, e.g. in such events like a slump. Movement of the device may be unsuitable for the user in this posture and may thus be slowed down or stopped. The forwards-backwards tilt may also indicate the stability of the device, and therefore the user. For example, an unallowable angular tilt may be one which is unstable or close to being unstable, such that there is an unacceptable risk of the device tipping over either forwards or backwards.

[0088] In the sense of the invention, the “allowable angular tilt” is preferably a range of angles in a particular plane, within which the device may safely be tilted. Insofar as the “allowable angular tilt” refers to the tilt in a forwards-backwards plane, it is preferably limited by a maximum forwards angular tilt and / or a maximum backwards angular tilt. The “allowable angular tilt” may also be a tilt in a left-right plane and may be limited by a maximum left tilt and / or a maximum right tilt. Preferably the “allowable angular tilt” is one in which the risk of the user falling is considered negligible. The “allowable angular tilt” may preferably be adjustable for a particular user. This may depend on various factors such as the type and default height hi of a harness being used by said user.

[0089] Preferably, if it is determined that the allowable angular tilt has been reached or exceeded, the one or more control units are configured to provide a signal to an actuator in order to prevent uncontrolled movement of the device, in particular to prevent the whole device from tipping and / or to prevent uncontrolled falling of the harness. Preventing uncontrolled falling of the harness may include preventing tipping of the device. While the curved paths or the wheel guides themselves may mechanically prevent tipping by limiting the possible positions of the self-balancing wheels, the one or more control units can add an additional layer of safety. This provides the user with additional protection from falling, especially when the device meets unexpected obstacles or unevenness in the ground which may cause unexpected tilting of the device beyond the tilting which is allowed by the curved paths themselves. The mental strain on a parent, companion or therapist for supervising the use of the device can thus be reduced. In a further preferred embodiment of the invention, if it is determined that the allowable angular tilt has been reached or exceeded, the actuator is configured to cut off power to the self-balancing wheels, to release one or more support wheels, to activate a brake, to adjust the position of a counterweight and / or to adjust the speed and / or direction of movement of the self-balancing wheels. By cutting off power to the self-balancing wheels, a continuous movement of the device may be stopped. This may prevent a user who is no longer intentionally controlling the device from driving into a wall or other obstacle. Preferably the device is so configured that cutting off power to the self-balancing wheels leaves the device in a stable position. This may be achieved by a weight distribution of the device, which may for example cause the self-balancing wheels to rest around the centre of each curved path. The weight distribution may also be such that a rear portion of the frame rests against the ground when the self-balancing wheels are stopped. Activating a brake may enable the self-balancing wheels to be stopped at a given position, in particular around the centre of the curved paths. This allows the device to be stopped safely such that the user is still upright with both feet touching the ground. Adjusting the position of a counterweight, e.g. to manipulate the centre of gravity of the system to above a central portion of the wheel guides, may also allow the device to stop in a safe position.

[0090] Adjusting the speed and / or direction of the self-balancing wheels may allow the device to return to the last safe position. For example, the device may retreat from an obstacle such as a ditch in the ground which has caused the maximum allowable angular tilt to be approached or reached. These approaches may of course be combined with one another to prevent the user from falling or landing in an unintended, uncomfortable position.

[0091] In a further preferred embodiment of the invention, the allowable angular tilt of the frame, first wheel guide and / or second wheel guide is limited by a maximum allowable forward angle, the maximum allowable forward angle being less than an angle at which the harness would reach a forward tipping point. This is because the user’s (and the system’s) centre of gravity coincides typically with a point in the harness. When the system’s centre of gravity begins to fall outside of its base, tipping can occur.

[0092] In the sense of the invention, a “forward tipping point” is preferably a position at which the centre of gravity of the device, the user, or a system comprising the device and the user is outside of the device’s base. This occurs when said centre of gravity coincides with a front extreme of the device’s base, in particular where the user tilts too far forwards. The device’s base is preferably a region spanning and including the wheels and wheel guides.

[0093] In a further preferred embodiment of the invention, the allowable angular tilt of the frame, first wheel guide and / or second wheel guide is limited by a maximum allowable left and / or right angle, the maximum allowable left and / or right angle being less than an angle at which the harness would reach a lateral tipping point. The mechanical and / or electronic safety mechanisms described herein may also be used to prevent lateral tipping.

[0094] In the sense of the invention, a “lateral tipping point” is preferably a position at which the centre of gravity of the device, the user, or a system comprising the device and the user is outside of the device’s base. This occurs in particular when said centre of gravity coincides with a left extreme or a right extreme of the device’s base, in particular where the user tilts too far sideways.

[0095] In a further preferred embodiment of the invention, the frame comprises a harness guide. This allows the harness to be moved in a controlled and limited manner with respect to the frame. This can advantageously increase user comfort as the user may take a variety of postures and positions while seated on or in the harness, without necessarily triggering the self-balancing wheels to move the device. Additionally, the harness guide can greatly increase the vertical range of movements of the user. For example, the harness guide may allow the user not only to rock forwards but also to kneel or crouch. By kneeling or crouching, the user may not necessarily bring their centre of gravity ahead of or behind a self-balancing wheel, such that the angle 0 may be kept substantially at zero. This allows the user to lower or raise their body without necessarily moving the device forwards or backwards, thus decoupling the forward and backwards movement from the up-down movement of the user.

[0096] In the sense of the invention, a “harness guide” is preferably a controlled means of varying the position of the harness with respect to the frame on which it is provided.

[0097] The harness guide preferably defines a path along which the harness may move in relation to the frame. By defining a path for the movement of the harness, said movement can occur in a controlled manner, in particular smooth without unwanted jerking. Preferably the path defined by the harness guide is substantially vertical. A substantially vertical path is one which is substantially vertical with respect to a default position of the device, e.g. with the user standing with both feet on the ground. The vertical path may of course be tilted if the device itself is also tilted. The user can thus raise and lower their body in a manner which is not only controlled but does not substantially move the centre of gravity of the user in a forwards-backwards direction. Thus the user can kneel, crouch, squat but also stand up from a low position, jump or reach up to grasp an object. This enables the user to practice a wide variety of physical movements and transitions from different positions, improving their muscle strength and motor skills whilst also aiding their everyday activities.

[0098] In a further preferred embodiment of the invention, the mobility assistance device comprises mechanical biasing means to return the harness towards a default height position hi when its height position is changed from the default height position. The default height position hi is preferably configured so that feet of the user can reach a ground surface between the first and second self-balancing wheels. At the default height position hi , the user may be sitting or standing, depending on the configuration and application of the device. By biasing the harness towards its default height position, a desired posture of the user (e.g. standing upright) can be promoted. The user can be supported in this posture, for example by providing an uplift force which reduces the strain on their muscles. The user can thus remain upright (or seated) for longer without exhaustion, whilst still enjoying flexibility of movement. The biasing also ensures that changes in the user’s vertical position only occur as a result of an intentional movement of the user, especially since the user must provide some effort, e.g. to overcome a threshold force, in order to move themselves against the bias. An unintentional slumping or falling to the ground can thus be prevented. At the same time, once the user has reached a low position, they are automatically raised back to the default height unless they exert sufficient force to indicate that it is their intention to remain at the lowered position. The device is thus both flexible and supportive.

[0099] In a further preferred embodiment of the invention, the harness guide additionally or alternatively defines a lateral path along which the harness may move with respect to the frame. The lateral harness guide may also comprise mechanical biasing means to return the harness to a default lateral position, said lateral position preferably being centred between the wheel guides. Such a lateral harness guide may allow the user a wider range of postures, e.g. leaning to one side or reaching for an object to the left or to the right. The user may thus move their centre of gravity slightly with respect to the device, without requiring the whole device to move with them.

[0100] In a further preferred embodiment of the invention, the mechanical biasing means comprise a counterweight, a parallelogram, a spring, an elastic material, a shock-absorbing material, a pneumatic cylinder, a hydraulic cylinder, a permanent magnet and / or an electromagnetic arrangement. The mechanical biasing means preferably comprises a compression spring for lifting the harness along a vertical harness guide of the frame, wherein the mechanical biasing means preferably further comprise a further second spring, the further second spring preferably being a tension spring for lowering the harness along a vertical harness guide of the frame. It is particularly preferable for the mechanical biasing means to comprise a combination of a compression spring and a tension spring due to the low cost and lack of power consumption of these components.

[0101] In a further preferred embodiment of the invention, the device comprises a counterweight, the counterweight preferably being provided on the frame or on one or both of the first and second wheel guides. The counterweight may form part of mechanical biasing means to return the harness to a default height position. The counterweight may however be integrated into the device regardless of the presence or absence of a harness guide and may provide various functions other than returning the harness to a default height position.

[0102] By applying a counterweight, the centre of gravity of the device may be shifted, such that the device tends to rest in a safe position, e.g. on a back portion thereof. When the user is not pushing a front portion of the device downwards, the counterweight may at least partially compensate the weight of the user and where necessary may provide an uplift force and raise the user to a default height position hi according to the lever or see-saw principle. The device may operate as a see-saw by allowing the user and the counterweight to rotate about a real or virtual fulcrum. The fulcrum of the see-saw is preferably a substantially horizontal axis passing laterally through or above the device. The fulcrum may in particular may in particular be a y-axis or substantially parallel to the y-axis. In some embodiments, the centres of rotation of the selfbalancing wheels act as a fulcrum. The fulcrum may alternatively be an axis running parallel to the centres of rotation of the self-balancing wheels.

[0103] In the sense of the invention, a “seesaw” is preferably a first-class lever supported at a single fulcrum provided between two (real or virtual) beam portions which may or may not be aligned with each other. The beam portions are each configured to carry a load. A first load may comprise the counterweight which may be provided on the frame or on one or both wheel guides by means of a distal arm having a length Li to the fulcrum. A second load may comprise the harness (and where applicable, the user in the harness) which may be provided on the frame by means of a proximal arm having a length l_2 to the fulcrum. I_2 is preferably larger than Li.

[0104] In the sense of the invention, a “compensation of the weight of the user” preferably means providing an upward force acting on the centre of gravity of the user in a direction opposite to their weight force. This upward force is often referred to as the uplift force.

[0105] The counterweight and see-saw preferably support the upward and downward movements of the user. This configuration allows the seesaw to lift the user up while allowing them to lower themselves down intuitively. The harness partially lifted by the counterweight notably allows the user’s hands to remain free and does not require a strong upper body with skilled arms and hands. In particular, the user does not need to use their hands to control the device in contrast to known devices. By freeing the user’s hands, the user is free to take part in daily activities. This is especially important for children who need to learn and socialize by playing.

[0106] The counterweight preferably operates passively, that is, it does not require an active lifting of the user. This also reduces the burden on either electrically, pneumatically, or hydraulically powered components of the device such that the device may be used wirelessly for longer, e.g. outdoors, before being charged. This further opens wider opportunities for users to travel and share experiences with others.

[0107] In a further preferred embodiment of the invention, the counterweight has a mass between 5 - 30kg preferably between 5 - 20 kg, more preferably between 8 - 12 kg, even more preferably around 10 kg. In the case of multiple counterweights, the total weight preferably corresponds to the aforementioned preferred values.

[0108] In a further preferred embodiment of the invention, the wheel guides are configured to extend behind the frame, in particular behind a harness guide. Preferably at least 10 %, in particular at least 20 % of a length of each wheel guide extends behind the frame. This extension behind the frame can itself represent a load. This load may act as a counterweight in a seesaw-like arrangement which may assist the user in rising from a lowered position.

[0109] In a further preferred embodiment of the invention, a rear portion of each of the first and second wheel guides which extends behind the frame is provided with a counterweight. Preferably the first wheel guide carries a first counterweight and the second wheel guide carries a second counterweight, the first and second counterweights preferably being of equal weight. The counterweights may together act as loads in a seesaw system. The counterweights may also shift the centre of gravity of the device towards its back such that when a user alights from the harness, the rear portions of the wheel guides rest on the ground. This can prevent a dangerous tipping of the device when the user alights as can be observed in many scooters. For users with limited mobility and potentially weak muscle tone, it is particularly advantageous that the device can be left without potentially falling on the user or on their carer. In a further preferred embodiment of the invention, the position of the counterweight along the wheel guides and / or frame is automatically or manually variable, such that Li may be varied. To this end the device may comprise an actuator for varying the position of the counterweight along a track. For instance, one or more control units may adjust the position of the counterweight, e.g. by sliding it along a dedicated track in the wheel guides by means of an actuator (electrical, pneumatic etc.), in accordance with a perceived intention of the user. For example, if sensors in the device detect that the user does not attempt to lift themselves up from a crouching position, the one or more control units may be configured to move the counterweight closer to the fulcrum to reduce the uplift force on the user, allowing them to continue to move according to their intention of remaining crouched. The counterweight may be moved further from the fulcrum to increase the moment applied to lift the user up if it is detected that they are reaching upwards, for example by tiptoeing or raising their arms.

[0110] The separation of the balance functions between the counterweight and the self-balancing wheels also allows for a greater modularity whereby different parts of the device may be replaced as the user’s needs develop. Preferably, any one or more of the harness, the counterweight, the selfbalancing wheels and any support wheels are configured to be removable and replaceable by an adult without the need for specialist tools. The replaceable parts may preferably be securable to the frame or to the seesaw by means of Allen keys for example. This further improves the modularity and longevity of the device. Preferably, the positions of the counterweight and / or any support wheels with respect to the frame are also manually adjustable by an adult without the need for specialist tools.

[0111] In a further preferred embodiment of the invention, the frame is connected to a central portion of the wheel guides, preferably at a point between 20 - 80 %, in particular between 30 - 70 % along a length of each wheel guide. In such an embodiment, it may be preferred for the fulcrum of the seesaw to pass through the points where the frame is connected to each wheel guide. Such an arrangement has been found to conveniently provide a length Li between one or more rear counterweights and a fulcrum which is shorter than a length l_2 between the harness (or the centre of gravity of a user therein) and the fulcrum. In such an embodiment, the user’s centre of gravity may be ahead of the wheel guides. However, the overall centre ofgravity of the system is preferably above the wheel guides.

[0112] In a further preferred embodiment of the invention, the frame is connected to a rear portion of the wheel guides, preferably at a point between 0 - 30 %, in particular 0 - 20 % of the length of each wheel guide. In such an embodiment, the centre of gravity of the user (and the system comprising the device and the user) is preferably above the wheel guides. This can protect the system against tipping whilst allowing the system to easily fall out of an unstable equilibrium when the user shifts their weight.

[0113] In a further preferred embodiment of the invention, one or more counterweights are also functional components of the system. Examples of functional components are mechanical or electronic components such as support wheels, replacement parts, shock absorbers, handles, components of guide elements such as pulleys, sensor packs, processors, memory units, batteries, cables and the like. In this manner, the counterweights may perform a hybrid function and the overall weight of the device need not be elevated. The mobility assistance device preferably comprises a portable power source, the portable power source preferably being positioned on the frame, preferably such as to serve as a counterweight to a weight of the user. The portable power source is particularly suitable for use as a counterweight as it is a relatively heavy component which can be positioned flexibly at a variety of positions on the device, including the frame and / or the wheel guides. The device may optionally comprise two portable power sources (e.g. one for each of a first and second self-balancing wheel), with each portable power source preferably being provided on a rear portion of each wheel guide. The portable power source preferably comprises a battery. The positioning of the portable power source is preferably selected not only to provide one or more of the benefits of a counterweight as described above, but also to reduce the length of cable required to connect the portable power source to a self-balancing wheel and / or to a control unit or other electronic component. Reducing the length of cable required can simplify the device, reducing trip hazards and reducing the risk of items becoming stuck in the device or the cable being caught on obstacles in the environment.

[0114] In a further preferred embodiment of the invention, a weight distribution of the mobility assistance device without the user is preferably such that the mobility assistance device tends to rest on a rear portion of each of the first and second wheel guides. This can prevent the device from tipping over a large angle when the user alights from the harness. Preferably the weight distribution of the device is such that a centre of gravity of the user in the harness is vertically above a central portion of the first and second wheel guides when the user is at a default height hi. This provides for a particular high stability against tipping, in particular against tipping forwards. Accidental falling of the user can be avoided.

[0115] In a further preferred embodiment of the invention, the mobility assistance device comprises at least one support wheel, the support wheel preferably being connected to the frame, the harness or to one or both wheel guides, in particular in a spring-loaded fashion, to prevent the device from uncontrolled movement during use. Such uncontrolled movement may include the whole device tipping over or the harness falling in an uncontrolled manner. The spring-loading may be achieved mechanically via an element of a compression spring, tension spring, torsion spring or pneumatically. The support wheel may be a wheel suspended by a telescopic spring-loaded rod from the proximal arm, also referred to here as the suspension, such that the wheel would reach the ground before the harness. The wheel and suspension would not cause the user to stop abruptly as in the case of rods seen in the prior art but would soften their landing. The length of the suspension and its position along the proximal arm may be configured to set a lowermost height position hmin for the user. The length of the suspension preferably corresponds to a user’s squat position, preferably between 5 - 40 cm, more preferably between 10 - 30 cm.

[0116] In a further preferred embodiment of the invention, the support wheel is positioned to allow the user to vary their height within a range corresponding to standing on tiptoes, walking, crouching and / or crawling. Advantageously, this allows the user a large degree of freedom and independence when using the device which only limits movements which are considered unsafe for the particular user. Preferably, the position of the support wheel is adjustable. This allows the device to grow with the user instead of being replaced. In a further preferred embodiment of the invention, the one or more control units are configured to monitor the position of the first and / or second wheel guide with respect to the first and / or second self-balancing wheel respectively. Alternatively or additionally, the one or more control units are configured to monitor the position of the first and / or second self-balancing wheel relative to the respective wheel guide. This enables the one or more control units to determine whether the device is being tilted and to which degree. Where both self-balancing wheels are at a non-central position along each respective curved path and where each self-balancing wheel is at the same distance along the length of its curved path, it can be concluded that the device is tilting. The distance along the length of the curved path, taken for example as a percentage of its total length, may be converted by the one or more control units to a tilt angle. The one or more control units may also detect that one of the first and second self-balancing wheels is slightly ahead of a central point of its curved path while the other of the first and second self-balancing wheels is slightly behind a central point of its curved path. Such an arrangement may indicate that the device is turning about a point. Other relative positions may indicate that the device is moving along a curve or in a straight line.

[0117] In response to monitored position data, the one or more control units are preferably configured to either suppress or propagate a movement of a user by adjusting the speed and / or direction of the self-balancing wheels, and / or adjusting a position of the harness to the frame. The one or more control units may comprise or have access to a program to this end. For example, the inventive device may comprise one or more infrared sensors detecting an upcoming obstacle such as a wall. The one or more control units may also determine that the device is moving forwards. The one or more control units may use this information to determine that the movement in the forward direction should be slowed down or stopped or that the device should be turned to avoid the obstacle. A greater degree of safety can hereby be achieved, in particular for users who require this additional assistance.

[0118] In a further preferred embodiment of the invention, the one or more control units are configured to interpret sensed data to determine whether a user’s movement is voluntary and to propagate only voluntary movements, wherein the degree of propagation and / or suppression of the user’s movement is preferably adjustable.

[0119] In a further preferred embodiment of the invention, the one or more control units are configured to interpret a force applied by the user and to command the motors and / or actuators to suppress or ignore a force falling below a threshold force and / or applied for less than a threshold duration, wherein the threshold force and / or duration correspond to an involuntary movement, one or more control units may thus be configured to filter out movements considered involuntary and not amplify these. This may be achieved by inputting data from various sensors to the one or more control units, for example data referring to conditions and positions of the user, movements of the frame, data from the wheel guides and / or data from the sensors of the self-balancing wheels. An algorithm may be used to interpret the sensed data, for example to filter and classify the sensed data. The one or more control units may be configured to send a command to one or more motors and / or actuators such as the motors of the self-balancing wheels, an actuator controlling the position of a counterweight, a stiffness in a pivotal connection between the harness and the frame and / or a stiffness of a suspension element to move in accordance with the user’s intention. Involuntary movements may be absorbed by the mechanical components of the device to avoid harsh stops. The one or more control units may advantageously only support the movements of the user which are considered to correspond with a particular intention so that the device moves the user further according to their intention. The user may rely less on their own muscle tone and exhaustion can be reduced.

[0120] The control unit preferably comprises adjustable threshold values including duration and force of a user’s movement corresponding to data from one or more sensors. Based on the user’s movements exceeding said thresholds, or remaining below said thresholds, the control unit preferably commands the motors and / or actuators to propagate, or suppress or ignore said movement.

[0121] In a further preferred embodiment of the invention, each of the first and second self-balancing wheels is negatively cambered, preferably such that each of the first and second self-balancing wheels defines a camber angle 0 of 5° - 20°, in particular about 10° to a ground surface. The frame and / or wheel guides may be configured to hold the first and second self-balancing wheels such that their camber angle is variable, in particular by up to 2°, more preferably by up to 1 °.

[0122] In the sense of the present invention, a “negative camber” is preferably a setting of the wheels of the device to be closer together in the y-direction at the top than at the bottom. The camber angle may be an angle of each self-balancing wheel about an x-axis. A “negative camber angle” 0 is preferably an angle between a center line passing from the top to the bottom of a wheel in the y-z- plane and the ground, wherein the angle faces the center of the device. Preferably the camber angle 0 is about 10°. This provides the device with a more stable shape having a wider base. Sideways tipping of the device is made virtually impossible by the cambering resulting in added safety in the case of uneven ground conditions and / or rough play with other children. In addition, the cambering significantly improves the maneuverability of the device, allowing the device to be easily turned about a single point.

[0123] In a further preferred embodiment of the invention, a portable power source is positioned on one of the first or second self-balancing wheels, wherein optionally a further portable power source is positioned on the other of the first or second self-balancing wheels. Positioning the portable power sources on respective self-balancing wheels can lead to the device being more compact with no or fewer cables. As each self-balancing wheel can be brought directly into contact with its own portable power source, no cable is needed to connect these components. The risk of cables coming loose, being entangled or trapped in surroundings can thus be eliminated. This improves the safety of the device.

[0124] In a further preferred embodiment of the invention, the mobility assistance device comprises an emergency stop button and an emergency stop relay for each of the first self-balancing wheel and second self-balancing wheel. This may cause the control device to stop any motorized movement and / or may cause a support wheel to drop to the ground. Preferably the emergency stop is located on an upper portion of the wheels or on an upper portion of the frame such as to be easily visible and accessible to a nearby adult. Depending on the needs and capabilities of the user, an emergency stop button may be provided on the harness or at such a point as to be operated by the user themselves.

[0125] In a further preferred embodiment of the invention, the frame further comprises a handle for guiding the mobility assistance device when not in use and / or to manually assist a user. As illustrated in the figures, the frame itself may be configured as a handle. This allows the user to take breaks from steering the device themselves such that they can also be assisted in their movement by a carer. The handle may also be used to carry the device to storage when not in use and conveniently does not need to add any weight to the device.

[0126] The device of the invention may be configured for use with adults, teenagers or children who need not have any special mobility requirements. The device may preferably be adapted for use in leisure activities for example in hiking. This may substantially reduce exhaustion even in a healthy adult and reduce the risk of falls.

[0127] In a preferred embodiment, the device is configured for non-therapeutic use. In particular, the device may be configured for use with healthy users, in particular healthy adults. For example, the device may be configured for extending the length of a continuous walk taken by a user before exhaustion is reached.

[0128] In a further preferred embodiment, the device may be configured for increasing the number of repetitive movements which a user may carry out before exhaustion. Such movements may include jumping, turning, touching the ground etc. The device may also be configured for assisting a user in making such movements, such that their attention and efforts may be directed to refining aspects of the movements, such as the position of the arms for shooting a basketball. This is particularly advantageous in sports and dance where users are usually trained with various degrees of support from a trainer or from a handrail, depending on their experience level. The device may especially reduce the burden on the trainer, such that a user may independently practice various movements for a long period of time to attain perfection.

[0129] In a further aspect, the invention relates to a method of using a mobility assistance device according to any embodiment of the invention.

[0130] A person skilled in the art understands that technical features and advantages that have been disclosed in regards to the mobility assistance device described herein, equally apply to the method of using such a device for assisting the movement of a user, and vice versa.

[0131] The method preferably comprises a step of propagating an intentional movement of a user by means of the device, while preventing falling, wherein the intentional movement is in particular a forward-backward rocking movement, a forward or backward displacement, a turning movement around a point and / or a turning movement in a partial circle.

[0132] In a preferred embodiment of the invention, the method of using the mobility assistance device comprises a step of propagating an intentional movement of a user for therapeutic purposes. The method may be a training or rehabilitation method. The method may also be for relieving exhaustion and preventing accidents. Preferably, the therapeutic method includes using the mobility assistance device to assist the user in moving, positioning or maintaining a posture of their own body in a safe and healthy manner. The device may be used by a user in an upright position. This can be achieved by the harness but preferably also involves the use of a vertical harness guide with mechanical biasing means which bring the user to a healthy upright position. In such a case, the device may assist the user in remaining standing for longer periods without exhaustion or risk of falling. This may allow the user to independently take part in everyday activities such as attending an event in standing position, standing at a queue, etc. The device may also be used to provide the user with relief from exhaustion during a walking or running activity. The user may thus safely walk for longer, in particular venturing further from their home. The support provided by the device may also allow the user’s attention to be directed to adjusting the movements of their body, improving their gait.

[0133] The device may also be used by a user in a seated position. In such a case, the device may assist the user in remaining seated for longer periods, e.g. without slumping forwards or leaning back. This can be achieved by the harness but preferably also involves the use of a vertical harness guide with mechanical biasing means which bring the user to a healthy seated position.

[0134] In a preferred embodiment of the invention, the method of using the mobility assistance device is a physiotherapeutic method. The device may perform one or more steps usually carried out by a physiotherapist, so that the user is sufficiently supported to safely train a muscle group or a skill. This can reduce the burden on physiotherapists which may not be widely available in all areas. The user may also use the mobility assistance device to carry out physiotherapeutic exercises in any place, such as at home, optionally with a telemedical assistance.

[0135] In a preferred embodiment of the invention, the method of using the mobility assistance device comprises a step of propagating an intentional movement of a user for non-therapeutic purposes.

[0136] As an example, the intentional movement of the user may be a walking movement and the user may be a healthy adult. In this manner, the device may allow the user to extend the period for which they may walk without exhaustion. This may be particularly useful in the context of long hikes, especially over uneven or uphill terrain. In such a context, the device may also serve to protect the user from slips and falls due to the inherent stability of the device.

[0137] As a further example, the intentional movement of the user may be a jumping movement and the user may be a healthy adult. In this manner, the device may allow the user to practice and improve their technique in carrying out the jumping movement for a longer period of time without exhaustion. This may be particularly useful for improving form in the context of basketball, volleyball, dance or gymnastics training. In some sports such as basketball or netball, it is essential that a user pivots about their own body. The mobility assistance device of the present invention may advantageously allow the user to play these games according to their rules, whilst at the same time reducing exhaustion and allowing the user to exercise specific muscle groups. For example, a netball player may catch the ball, pivot about themselves using the device and then shoot the ball into the net. In this process, the user’s attention may be focused on improving their shooting techniques rather than on the pivoting movement. This makes the device particularly suitable for training. In a further preferred embodiment of the invention, the method comprises using the device for a paralympic activity. The device may thus allow users to participate in a sport which requires them to support their own body weight in an upright or seated position.

[0138] In a further preferred embodiment of the invention, the method comprises using the device for a seated activity. In particular, the method includes supporting a user in carrying out a desk-based activity. In this context, the mobility assistance device can function as an improved ergonomic movable chair.

[0139] Terms such as substantially, approximately, about, etc. preferably describe a tolerance range of less than ± 20%, preferably less than ± 10%, especially preferably less than ± 5%, and especially less than ± 1 %, and include the exact value.

[0140] A person skilled in the art understands that technical features and advantages that have been disclosed in regards to the mobility assistance device described herein, equally apply to the method of using such a device for assisting the movement of a user, and vice versa.

[0141] DETAILED DESCRIPTION OF THE INVENTION AND EXAMPLES

[0142] It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the claims of the invention define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.

[0143] Without intending to be limiting, the invention will be explained in more detail with reference to exemplary embodiments and the following figures:

[0144] Brief description of the figures

[0145] Fig. 1 Schematic illustration of a side view of a mobility assistance device according to a preferred embodiment of the invention.

[0146] Fig. 2 Schematic illustration of a perspective view of the mobility assistance device of

[0147] Fig. 1.

[0148] Fig. 3 Schematic illustration of a side view of a mobility assistance device according to a further preferred embodiment of the invention, the illustration showing the radius of curvature of the curved path within a wheel guide.

[0149] Fig. 4 Schematic illustration of a curved path with a radius of curvature greater than the height of a system’s centre of gravity.

[0150] Fig. 5 Schematic illustration of a curved path with a radius of curvature equal to the height of a system’s centre of gravity.

[0151] Fig. 6 Schematic illustration of a curved path with a radius of curvature smaller than the height of a system’s centre of gravity.

[0152] Fig. 7 Schematic illustration of a rear view of a mobility assistance device according to the invention, illustrating a lateral tipping point. Fig. 8 Schematic illustration of a top view of a mobility assistance device according to a further preferred embodiment of the invention, wherein the self-balancing wheels are fitted with guide rollers.

[0153] Figs. 9 - 11 Schematic illustrations of a rear, perspective and side view respectively of the mobility assistance device of Fig. 8.

[0154] Fig. 12 Schematic illustration of a top view of a mobility assistance device according to a further preferred embodiment of the invention, wherein the self-balancing wheels are each fitted with a pair of upper and a pair of lower clips.

[0155] Fig. 13 Schematic illustration of a rear view of the mobility assistance device of Fig. 12.

[0156] Fig. 14 Schematic illustration of a perspective view of a mobility assistance device according to a further preferred embodiment of the invention, wherein the self-balancing wheels are each fitted to a wheel guide by means of a sleeve.

[0157] Fig. 15 Schematic illustration of a side view of the mobility assistance device of Fig. 14.

[0158] Fig. 16 Schematic illustration of a perspective view of a mobility assistance device according to a further preferred embodiment of the invention, wherein the self-balancing wheels are each fitted to a wheel guide by means of castors.

[0159] Fig. 17 - 18 Schematic illustrations of a side view and rear view of the mobility assistance device of Fig. 16.

[0160] Fig. 19 Schematic illustration of a perspective view of a mobility assistance device according to a further preferred embodiment of the invention, wherein the self-balancing wheels are each fitted to a wheel guide by means of guide rollers.

[0161] Fig. 20 Schematic illustration of a side view of the mobility assistance device of Fig. 19.

[0162] Fig. 21 Schematic illustration of a perspective view of a mobility assistance device according to a further preferred embodiment of the invention, in which the self-balancing wheels are each fitted to a wheel guide by means of inner and outer clips.

[0163] Fig. 22 Schematic illustration of a side view of a mobility assistance device according to a further preferred embodiment of the invention, wherein the mobility assistance device comprises front and rear support wheels.

[0164] Fig. 23 - 24 Schematic illustrations of a front and perspective view of the mobility assistance device of Fig. 22.

[0165] Fig. 25 Schematic illustration of a perspective view of a mobility assistance device according to a further preferred embodiment of the invention, wherein the wheel guides have a larger ground clearance and comprise retractable support wheels.

[0166] Fig. 26 Schematic illustration of a side view of a mobility assistance device according to a further preferred embodiment of the invention, wherein the wheel guides comprise a counterweight at their rear. Fig. 27 - 28 Schematic illustration of top and perspective view of the mobility assistance device of Fig. 26.

[0167] Fig. 29 Schematic illustration of a rear perspective view of a mobility assistance device according to a further preferred embodiment of the invention, wherein the harness guide element is supported at a default height by compressive and tensive mechanical biasing means within the vertical harness guide.

[0168] Fig. 30 Schematic illustration of a side view of a mobility assistance device, showing a forwards-backwards rocking motion.

[0169] Fig. 31 Schematic illustration of a side view of a mobility assistance device, showing a forwards-backwards drive.

[0170] Fig. 32 Schematic illustration of a mobility assistance device, showing the device turning about a point.

[0171] Fig. 33 Schematic illustration of a mobility assistance device according to a further preferred embodiment of the invention, showing preferred relative dimensions.

[0172] Detailed description of the figures

[0173] Fig. 1 shows schematically a mobility assistance device 100 according to a preferred embodiment of the invention. The device is shown from the right side and comprises a first self-balancing wheel 22 and a second self-balancing wheel (not shown). The first self-balancing wheel 22 is mounted on a first wheel guide 220. The first wheel guide 220 is itself curved such that is concave when viewed from above and convex when viewed from below. The first wheel guide 220 comprises a first curved path (not shown) along which the first self-balancing wheel 22 may move. The first selfbalancing wheel 22 is however trapped within the first wheel guide 220 such that it cannot exit the first curved path. The first self-balancing wheel 22 is provided with a wheel casing 48. The wheel casing protects the user of the device from coming into contact with the moving wheel and prevents objects from being trapped between the first self-balancing wheel 22 and the first wheel guide 220. The self-balancing wheel is provided with a set of sensors 46 and a dedicated control unit 36. To avoid the need for cables, the illustrated embodiment comprises a set of sensors 46 and a control unit 36 for each self-balancing wheel, the set of sensors 46 and the control unit 36 being provided within the respective wheel casing 48. Cables may otherwise be useful to connect the set of sensors 46 and the control unit 36 with each other and / or with a portable power source 66 such as a battery. In the shown embodiment, each self-balancing wheel 22, 24 comprises its own battery 66.

[0174] A frame 26 connects the first wheel guide 220 with a second wheel guide (not shown). The frame 26 is preferably made of a rigid material such as metal tubes or an aluminum profile. In this particular embodiment, the frame 26 is connected to a rear portion of each wheel guide, such that at least the rear portions of the wheel guides remain at a constant distance from one another.

[0175] The mobility assistance device further comprises a harness 16, in this case in the form of a seat with a back rest and a waist enclosure. The harness is connected to the frame 26 by a proximal arm 12. The proximal arm 12 is mounted on a substantially vertical portion of the frame 26 by means of a harness guide element 54. In this case, the harness guide element 54 connects to vertical rails of the frame 26 by means of rings. The vertical rails of the frame 26 form a vertical harness guide 16 which defines a path along which the harness 16 may move. A compression spring 56 constitutes a means for mechanically biasing the harness guide element 54 such that it (and therefore the harness 16) tends to remain at a default position along the vertical harness guide 160. The harness 16 is also mounted to the proximal arm 12 by means of a harness-arm coupling 52. The harness-arm coupling 52 comprises in this case a ball joint but may additionally or alternatively comprise a shock absorbing element. This can absorb minor movements of the user, in particular involuntary movements.

[0176] Fig. 2 shows a perspective view of the mobile assistance device 100 of Fig. 1 . More clearly visible are the first wheel guide 220 and the second wheel guide 240 having substantially the same radius of curvature and being substantially parallel to one another. In this embodiment, the first and second wheel guides 220 and 240 are solid profiles, the curved path along them being an imaginary path which follows their curvature in a longitudinal (or forwards-backwards) direction. The second self-balancing wheel 24 is mounted onto the second wheel guide 240 by means of guide elements 60. In this case, the guide elements 60 comprise a pair of clips per self-balancing wheel, the pair of clips being joined to the casing 48 of the second self-balancing wheel. The pair of clips ensures that the second self-balancing wheel moves along the second curved path without diverging from it. Although not shown, the wheel guides 220 and 240 comprise stops for limiting the movement of the first and second self-balancing wheels 22 and 24 to a central portion of the wheel guides. The central portion comprises 90% of the length of each wheel guide and excludes only the ends thereof.

[0177] Fig. 2 also shows more clearly the form of the frame 26 and the harness guide element 54 mounted thereon. As can be seen, the frame 26 comprises a substantially vertical portion. The harness guide element 54 is mounted to two parallel rails of the substantially vertical portion such that it can slide along a substantially vertical path. The compression spring 56 applies an upwards force to the harness guide element 54. When the harness guide element 54 is at a default position, the harness 16 is at a default height hi from the ground and a user seated therein is able to stand with both feet on the ground. At the default position, the upward and downward forces acting on the harness guide element 54 are preferably balanced. Said forces may comprise an upward force from the compression spring 56 and a downward force from the weight of the harness guide element 54, the proximal arm 12, the harness-arm coupling 52, the harness 16 and / or a user. As the harness 16 is lowered, e.g. by a change in the user’s posture, the upward force provided by the compression spring 56 preferably increases until a minimum height position hmin is reached. At the minimum height position hmin, the upward force provided by the compression spring 56 is preferably infinite. Additionally or alternatively, a closed end of the vertical harness guide 160 may prevent further downward movement of the harness along the vertical path provided. The frame 26 is also provided with an integral handle 64 at its top. The handle 64 preferably allows a carer to conveniently hold, push or carry the device 100.

[0178] Fig. 3 shows schematically a side view of a mobility assistance device 100 according to a further preferred embodiment of the invention. The curved path is shown as a curved dashed line. In this particular embodiment, the curved path shown has a constant radius R to a virtual fulcrum VF. The figure also shows schematically the location of a user’s centre of gravity 34. This is typically found between a person’s navel and hips and would be located within the harness 16. The overall centre of gravity of a system comprising both the mobility assistance device 100 and a user preferably approximately coincides with the user’s centre of gravity 34. A sector of a circle defined by the curved path and the virtual fulcrum is shown enclosed in dashed lines. A safe sector of the circle is shaded in a darker grey. This safe sector is delimited by a central portion of the curved path and the virtual fulcrum VF. In order to avoid tipping of the whole device 100, which would cause the user therein to fall, the user’s and the system’s centre of gravity remains preferably within the safe sector. This is best achieved where the radius R or the characteristic radius CR of each curved path is larger than the height of the standing user’s centre of gravity 34, especially preferably larger than the height of the user. This can provide a safe sector of sufficient breadth around the level of the user’s centre of gravity 34, such that the user may safely shift their weight to steer the device without risking falling.

[0179] Fig. 4 illustrates the form of the curved path without showing details of the mobility assistance device 100. The centre of gravity of the user 34 is shifted forwards slightly, causing the device 100 to rock forwards. This causes the wheel guides (and their curved paths) to rotate about the virtual fulcrum VF. A front edge of the wheel guide may coincide with a front of the curved path. This may represent a tipping point TP, such that when the centre of gravity of the user 34 falls directly above or ahead of the tipping point, tipping may occur. The location of the virtual fulcrum VF determines the distance of the user’s centre of gravity to the tipping point. This distance is shown by a rearfacing arrow. The virtual fulcrum however may fall significantly ahead of the front edge of the wheel guide without tipping, such that tipping would first occur at an extreme degree of rocking in a forward direction. Where the virtual fulcrum VF is at a sufficient distance from the curved path, the user may shift their weight and the device may rock over a broad range of angles before risking tipping. The radius of the curved path may however be limited in order to limit the size and weight of the mobility assistance device 100.

[0180] Fig. 5 illustrates a scenario where the virtual fulcrum of the curved path coincides with the centre of gravity of a user 34. In this scenario, as soon as the virtual fulcrum reaches a position directly above the front edge of the wheel guide, tipping may occur. The safe range of angles over which the device may rock is therefore more limited but covers the entire length of the curved path and the wheel guide. This preferably represents an edge case, i.e. the minimum recommended radius of the curved path.

[0181] Fig. 6 illustrates a scenario in which the virtual fulcrum of the curved path is lower than the user’s centre of gravity 34. The radius of curvature of the curved path is thus lower than the minimum distance of the user’s centre of gravity to the curved path. In such a case, the device has a more limited stability. The arrangement shown is in an unstable condition and will tip forwards. The tipping point TP is a point at which the user’s centre of gravity 34 falls ahead of the virtual fulcrum VF. This occurs before the user's centre of gravity 34 reaches a front edge of the wheel guide. A safe rocking is thus limited only to a smaller range of angles over a central portion of the wheel guide. Fig. 7 illustrates schematically a lateral stability of the mobility assistance device according to a preferred embodiment of the invention. The wheels may be in contact with the ground, in particular on uneven terrain, and may define a base for the system. Where the centre of gravity of the user 34 and of the whole system falls laterally outside the base, sideways tipping of the device may occur. The first and second self-balancing wheels shown here are negatively cambered at about 10°. This increases the breadth of the base and thus increases the breadth of a safe zone, within which the device may safely tilt sideways. The angle of the first and second self-balancing wheels which results from their position relative to the frame 26 thus increases the lateral stability of the device. Additional safety features such as support wheels may also be implemented to increase the forwards-backwards or lateral stability of the device.

[0182] Fig. 8 illustrates schematically a mobility assistance device 100 according to a further preferred embodiment of the invention. In this embodiment, each of the first and second wheel guides 220 and 240 comprises a set of parallel rails. The curvature of each parallel rail defines a curved path with a characteristic radius CR. The first and second self-balancing wheels are each mounted onto the respective wheel guide by means of guide elements 60 (shown here more specifically as guide rollers 62). The guide elements 60 comprise in this embodiment six guide rollers 62 per selfbalancing wheel. A centre of rotation of the first self-balancing wheel 22 is connected to an inner rail of the first wheel guide 220 by means of a guide roller 62 above the inner rail and a guide roller 62 below the inner rail. The first self-balancing wheel 22 is also connected to an outer rail of the first wheel guide 220 by means of a central guide roller 62 above the outer rail and two off-centre guide rollers below the outer rail. The guide rollers 62 are joined to the wheel casing 48. This arrangement has been found to be particularly lightweight, economic and stable.

[0183] Figs. 9 - 11 show further views of this embodiment. As can be seen in Fig. 11 , the wheel casing 48 is adapted to house a unit comprising the sensors 46 and the control unit 36. These are provided individually for each self-balancing wheel.

[0184] Figs. 12 - 13 show a further preferred embodiment of the mobility assistance device 100. The structure of the mobility assistance device of this embodiment mainly differs from Fig. 8 - 11 due to the form of the wheel guides 220, 240 and guide elements 60 used. In this embodiment, the wheel guides each comprise a curved profile with stops at its front and rear ends (not shown). The wheel casings 48 carrying the self-balancing wheels are each attached to their respective wheel guide 220, 240 by means of a pair of clips. Each clip encloses the respective wheel guide.

[0185] Figs. 14 - 15 show a further preferred embodiment of the mobility assistance device 100. In this embodiment, the wheel cases 48 are provided with slots configured to fit the curved profiles of the wheel guides 220 and 240. The wheel cases 48 are thus modified to form a sleeve enclosing the respective wheel guide. The sleeve may cover further guide elements 60 such as castors or guide rollers. This is a particularly safe solution as moving parts are enclosed and not accessible to a user or the environment. The risk of items being trapped or entangled with said parts is reduced.

[0186] Figs. 16 - 18 show a further preferred embodiment of the mobility assistance device 100. In this embodiment, each self-balancing wheel is suspended from a track in the respective wheel guide in the style of a caster. Unlike casters however, the self-balancing wheels are provided with drive means. The wheel guides 220 and 240 are closed from the top, preventing the user’s feet from accidentally entering any narrow cavities or gaps and becoming trapped. Guide elements are provided within the track in each wheel guide in order to limit the movement of the respective selfbalancing wheel to said track. The guide elements are conveniently enclosed by the wheel guides 220 and 240.

[0187] Figs. 19 - 20 shows a further preferred embodiment of the mobility assistance device 100. Each wheel guide 220 and 240 comprises a pair of parallel upper and lower guide rails. The guide rails are curved and have an identical characteristic radius OR. Each of the upper and lower guide rails comprises a groove. Each self-balancing wheel is mounted onto its respective wheel guide by means of guide rollers 62. These have a radius preferably not more than 20 % of the radius of each self-balancing wheel. A subset of the guide rollers 62 engages with a groove in an upper guide rail and a further subset of the guide wheels engages with a groove in the lower guide rail, such that the self-balancing wheel can only follow the path defined by the guide rails. As shown in the figure, the guide rollers 62 are arranged in a V-formation. By providing the self-balancing wheels on an outer side of the wheel guides 220 and 240, the user has more space to place their feet between said wheel guides.

[0188] Fig. 21 shows a further preferred embodiment of the mobility assistance device 100, wherein the wheel guides 220 and 240 each comprise a pair of guide rails. In this case, rather than upper and lower guide rails, the guide rails can be characterized as inner and outer guide rails. The selfbalancing wheel is positioned between the inner and outer guide rails and clipped onto these. The inner and outer guide rails join at their front and rear ends to limit the movement of the first and second self-balancing wheels 22, 24. These figures illustrate only a few examples of the many preferred arrangements for mounting the self-balancing wheels onto the wheel guides.

[0189] Fig. 22 shows a further preferred embodiment of the mobility assistance device 100, wherein the device comprises at least two, preferably four support wheels 38. A support wheel 38 is provided at a rear portion of the first wheel guide 220. A further support wheel 38 is also provided at a front portion of the first wheel guide 220. A lowermost point of each support wheel 38 is provided between the ground level and the level of a centre of rotation of the self-balancing wheel 22. In other words, the support wheel 38 is configured to reach a point within the so-called “ground clearance” of the device. Preferably the bottom of the support wheel 38 is at a height at least halfway up the ground clearance. The support wheel 38 is preferably provided with suspension such that its distance to the first wheel guide 220 can be reduced by application of pressure, especially when the support wheel 38 meets the ground. The support wheels 38 preferably meet the ground when the device tilts forward to a maximum allowable forward tilt angle or when the device tilts backwards to a maximum allowable backward tilt angle. The support wheels 38 can prevent a harsh stop or friction caused by the front of the device meeting an obstacle. Instead, these can assist the user of the device in overcoming the obstacle such as a step by providing the device with added stability when in contact with both the obstacle and the original ground level.

[0190] Figs. 23 and 24 show a front view and a perspective view of the mobility assistance device 100 of Fig. 22 having four support wheels 38. The support wheels 38 are provided at the front and rear of the first and second wheel guides 220, 240 respectively for an even weight distribution. Fig. 25 shows a perspective view of a further preferred embodiment of the mobility assistance device 100, wherein the support wheels 38 are configured to reach a ground level. These support wheels 38 are mounted on the first wheel guide 220 and second wheel guide 240 in a retractable manner in order to permit rocking of the device. They may provide some resistance to the forwardbacking rocking motion which the user must overcome in order to steer the device forwards or backwards. This may serve to filter out involuntary movements of the user.

[0191] In some preferred embodiments, the support wheels 38 are by default provided in a retracted position (as shown in Fig. 24), for example by means of a telescopic connection. The telescopic connection may bias the support wheels 38 towards the lowered position. Where certain conditions are detected, the support wheels 38 may be dropped to the ground as shown in Fig. 25, in order to stabilize the device. This may occur when the control unit 36 detects an abnormal or emergency condition, in particular where the forward / backward tilt of the device approaches, reaches or exceeds a maximum allowable forward / backward tilt angle. It may also occur where an emergency stop is used or brake is activated. The lowered support wheels 38 may prevent backwards-forwards rocking of the device, increasing stability so that the user may safely mount or alight.

[0192] Any number or arrangement of support wheels 38 may be combined with any number or arrangement of guide elements 60, as the above figures illustrate.

[0193] Figs. 26 - 28 show a further preferred embodiment of the mobility assistance device 100, wherein a counterweight 18 is provided at a rear end of each wheel guide 220 and 240. This can shift the centre of gravity of the device towards the rear such that especially when it is not in use, it tends to rest on the rear ends of the wheel guides 220 and 240. This can present a safe resting position. Especially where the device is being mounted or when a user is releasing themselves from the harness, this can prevent any large and sudden movement of the device as the system’s centre of gravity changes. The counterweight 18 may be so shaped that it does not substantially reduce the curved paths provided for the self-balancing wheels 22 and 24.

[0194] In the illustrated embodiment, the counterweight 18 is additionally used to configure the mobility assistance device 100 as a see-saw, with the centres of rotation of the self-balancing wheels 22 and 24 acting as the fulcrum of the see-saw. The frame 26 connects the wheel guides 220 and 240 with one another. Instead of being joined to a rear point of each wheel guide, the frame 26 is instead connected to a point around within the front half of each wheel guide 220, 240. This allows the harness 16 also to be provided above or in front of a front end of each wheel guide 220, 240. The harness 16 and the user can thus act as a load ahead of the fulcrum while the counterweights 18 act as another load behind the fulcrum. It may be preferable for the counterweights 18 to be portable power sources 66, in particular batteries.

[0195] Fig. 29 shows a further preferred embodiment of the mobility assistance device 100, wherein the harness guide element 54 is at a default position corresponding to a default height hi of the harness 16. A compressive spring 56 joins the harness guide element 54 to a lower end of a vertical harness guide 160 and functions as described above for Figs. 1 and 2. In this embodiment the harness guide element 54 is additionally suspended from an upper end of the vertical harness guide 160 by a tensive spring 58. When the harness guide element is raised above the default height position hi, the spring 58 provides a downward force on the harness 16 acting now as a compression spring instead to return it to a default height position hi , e.g. this is particularly the case when the user is jumping or standing on tip-toe.

[0196] Fig. 30 illustrates the influence of a shift in the centre of gravity of the user on the movement of the mobility assistance device 100. In the centre, Fig. 30 shows a default position of the device in which the user is in an unstable equilibrium over the self-balancing wheels. A vertical plane passing through the centres of rotation of the self-balancing wheels is represented by a dashed line. The centre of gravity of the user is directly above the centres of rotation of the self-balancing wheels 22 and 24. Thus the centre of gravity of the user forms an angle 0 of 0° to the vertical plane. This may be detected by the control unit 36, directly or indirectly using the data readings from the set of sensors 46. The self-balancing wheels 22 and 24 may remain stationary.

[0197] On the left, Fig. 30 illustrates the case where a user leans backwards within the harness 16, shifting their centre of gravity backwards. The user’s movement causes the frame 26 and therefore wheel guides 220 and 240 to rotate about their virtual fulcrum, while the self-balancing wheels remain stationary. This keeps the centre of gravity of the user in the same relative over the self-balancing wheels, keeping the angle 0 at zero. The device remains in an unstable equilibrium with the user in a new posture, leaning backwards.

[0198] On the right, Fig. 30 illustrates the case where the user leans forwards. The wheel guides 220 and 240 rotate again about their virtual fulcrum, while the self-balancing wheels may remain stationary. The angle 0 remains at zero and the device remains in an unstable equilibrium. As such, the user can shift their centre of gravity, in particular by changing their posture, at a stand-still, without causing the device to drive forwards or backwards.

[0199] Fig. 31 illustrates how the mobility assistance device 100 assists a user in walking forwards and backwards. In the centre of Fig. 31 , the unstable equilibrium position is shown, in which the user’s centre of gravity is directly above the centres of rotation of the self-balancing wheels. On the right, Fig. 31 shows a continuous forward shift of the user’s centre of gravity, as occurs when the user walks or attempts to walk forwards, e.g. by pushing backwards with one foot against the ground. The device is brought out of the unstable equilibrium by the user moving the centre of gravity such that it is ahead of the centres of rotation of the self-balancing wheels, raising the angle 0 above zero. To return angle 0 to zero, the self-balancing wheels move forwards in order to bring their centres of rotation back under the user’s centre of gravity. However, as the user’s centre of gravity is continuously shifting forwards, the self-balancing wheels continue to drive forwards. This assists the user as the harness 16, which supports the user’s upright posture and prevents fatigue, follows the user’s intended movement.

[0200] The opposite occurs when the user continuously shifts their weight backwards. This is illustrated in Fig. 31 on the left. The self-balancing wheels here continue to drive backwards until the user is still. At this point, the self-balancing wheels return their centres of rotation back under the user’s centre of gravity along the wheel guides to bring the system back into unstable equilibrium.

[0201] Fig. 32 illustrates how the mobility assistance device 100 rotates about a point. When the user intends to turn their body to the left, they tend to shift their right hip forwards and their left hip backwards. When such a rotary movement is initiated, the set of sensors 46 of the first (right hand) self-balancing wheel 22 detects a shift of the centre of rotation of the self-balancing wheel 22 along the wheel guide 220, forming a positive angle 0. At the same time, the set of sensors 46 of the second (left hand) self-balancing wheel 24 detect a shift of the centre of rotation of the selfbalancing wheel 24, along the wheel guide 240 but in the opposite direction, forming a negative angle 0, correspondingly. The self-balancing wheels act to bring both the respective angles 0 to zero. To do so, the first self-balancing wheel 22 drives forwards while the second self-balancing wheel 24 drives backwards at the same speed. The result of this is that the whole device turns about the user. A natural turning movement with a compact turning circle can thus be achieved.

[0202] Fig. 33 shows a mobility assistance device 100 according to a further preferred embodiment of the invention. The figure illustrates preferred forms and proportions of the device’s components. A ground level G is represented schematically by a horizontal line on which both the self-balancing wheels 22, 24 and a user’s feet rest. The self-balancing wheels 22 and 24 preferably have an identical wheel radius WR. The centres of rotation of the self-balancing wheels 22 and 24 are thus at a distance from the ground level equal to their wheel radius. A lowermost surface of the wheel guides 220 and 240 is separated from the ground G by a ground clearance GO. In some embodiments, the lowermost surface of the wheel guides 220 and 240 is approximately level with the centres of rotation of the self-balancing wheels, especially in embodiments of the wheel guides as inner and outer rails or as a track enclosed from the top, such that the ground clearance GO can be considered approximately equal to the wheel radius WR. However, the ground clearance GO is preferably slightly lower than the wheel radius WR. Preferably the ground clearance is 0.2-WR- 0.9-WR, more preferably 0.6-WR - 0.8-WR The ground clearance GO can be set to overcome obstacles such as steps. An upper surface of a step may be allowed to pass under the wheel guides, such that the user may step onto it, improving this physical skill. For this purpose, a ground clearance GO of 15 - 25 cm may be selected. The self-balancing wheels and wheel guides may be dimensioned accordingly.

[0203] The wheel radius WR may be selected according to the user, their walking speed, stride and the desired overall size and weight of the device. It is preferred that for children, in particular up to 12 years old, the wheel radius is between 10 - 15 cm. For children over 12 or for adults, the wheel radius is preferably 15 - 25 cm. The ground clearance may be set accordingly to be slightly lower than the wheel radius.

[0204] The dimensions of the device are preferably selected taking into account the user’s height hUSer. For children up to 12 years, user heights of around 80 - 160 cm are assumed. For adults or children over the age of 12 years, user heights of 140 - 220 cm are assumed. The centre of gravity of adults and children is usually between the umbilicus and the hip level. This may vary depending on age, gender and medical condition which may all be taken into account when dimensioning the device. For adults, the centre of gravity is usually around 56 % of the user’s height measured from the ground.

[0205] The default height of the harness is preferably such that when used by the user, the user may stand with both feet on the ground. The height of the user’s centre of gravity hi from the ground can be assumed to be at the level of the harness, in particular at a waist belt thereof. The characteristic radius OR of the curved paths of the wheel guides is preferably selected such that the virtual fulcrum VF is higher than the default height hi. In some embodiments, it is preferable for the virtual fulcrum VF to be higher than the height of the user huser. The characteristic radius is preferably selected accordingly, taking into account the wheel radius WR. The sum of the wheel radius WR and the characteristic radius CR of the curved path is preferably around 1.2-hUSer to 1.8-hUSer, especially preferably around 1 .5-hUSer. For devices intended to be used by children, a characteristic radius CR of around 1.5 m is preferred.

[0206] LIST OF REFERENCE SIGNS

[0207] 100 Mobility Assistance Device

[0208] 12 Proximal Arm

[0209] 16 Hamess

[0210] 160 Vertical Hamess Guide

[0211] 18 Counterweight

[0212] 22 First Self-Balancing Wheel

[0213] 24 Second Self-Balancing Wheel

[0214] 220 First Wheel Guide

[0215] 240 Second Wheel Guide

[0216] 26 Frame

[0217] 34 User’s Centre of Gravity

[0218] 36 Control Unit

[0219] 38 Support wheel

[0220] 46 Set of Sensors

[0221] 48 Wheel Casing

[0222] 52 Harness-Arm Coupling

[0223] 54 Harness Guide Element

[0224] 56 Compression Spring

[0225] 58 Tension Spring

[0226] 60 Wheel Guide Element

[0227] 62 Wheel Guide Roller

[0228] 64 Handle

[0229] 66 Portable power source

Claims

CLAIMS1 . A mobility assistance device (100) comprising: a first self-balancing wheel (22) mounted on a first wheel guide (220) which defines a first curved path along which the first wheel guide (220) and the first selfbalancing wheel (22) may move with respect to one another; a second self-balancing wheel (24) mounted on a second wheel guide (240) which defines a second curved path along which the second wheel guide (240) and the second self-balancing wheel (24) may move with respect to one another; a frame (26) connecting the first wheel guide (220) and the second wheel guide (240); a harness (16) for receiving a user (32), the harness being provided on the frame (26); one or more control units (36) configured to control the first self-balancing wheel (22) and / or second self-balancing wheel (24) in accordance with an inverse pendulum principle.

2. The mobility assistance device (100) of the previous claim wherein each of the first and second curved paths comprise a central portion, each central portion having a characteristic radius (CR) to a virtual fulcrum (VF), wherein preferably the characteristic radius (CR) of the central portion of each of the first and second curved paths is identical.

3. The mobility assistance device (100) of any of the previous claims wherein the harness (16) is provided at a default height (hi) above the first wheel guide (220) and second wheel guide (240) and wherein the characteristic radii (CR) of the first and second curved paths are greater than the default height (hi), in particular greater than a minimum distance between the first or second curved path and a centre of gravity of the user (32) in the harness (16).

4. The mobility assistance device (100) of any of the previous claims wherein each of the first (22) and second self-balancing wheels (24) is provided with one or more guide elements (60) to support its movement along the curved path of the first (220) or second wheel guide (240) respectively, wherein the one or more guide elements (60) connect the first (220) or second wheel guide (240) to the first or second curved path at least at two separate points along the curved path or at a tangent to the curved path, the at least two separate points preferably being at least 25 mm apart, the one or more guide elements (60) preferably comprising a sleeve, a reel, a pulley, a scroll, a caster, a pair of clips, a pair of track-inserts, a pair of guide rollers or a pair of roller bearings.

5. The mobility assistance device (100) of any of the previous claims wherein the mobility assistance device (100) comprises one or more contact, acceleration, position and / or tilt sensors and the control unit (36) is configured to determine an angular tilt of the frame (26) and / or the wheel guides (220, 240) about a virtual fulcrum (VF) based on sensed data.

6. The mobility assistance device (100) of the previous claim wherein the control unit (36) is configured to determine whether the angular tilt of the frame (26) and / or the wheel guides (220, 240) has reached or exceeded an allowable angular tilt and if it is determined that the allowable angular tilt has been reached or exceeded, to provide a signal to an actuator in order to prevent uncontrolled movement of the mobility assistance device (100), wherein preferably if it is determined that the allowable angular tilt has been reached or exceeded, the actuator is configured to cut off power to the self-balancing wheels (22, 24), to release one or more support wheels (38), to activate a brake, to adjust the position of a counterweight (18) and / or to adjust the speed and / or direction of movement of the self-balancing wheels (22, 24).

7. The mobility assistance device (100) of any of claims 5 - 6 wherein the allowable angular tilt of the first wheel guide (220) and second wheel guide (240) is limited by a maximum allowable forward angle, the maximum allowable forward angle being less than an angle at which the harness (16) would reach a forward tipping point.

8. The mobility assistance device (100) of any of the previous claims wherein the frame (26) comprises a harness guide (160) defining a path along which the harness (16) may move in relation to the frame (26), the path preferably being substantially vertical.

9. The mobility assistance device (100) of the previous claim wherein the mobility assistance device comprises mechanical biasing means to return the harness (16) towards a default height position (hi) when its height position is changed from the default height position, the default height position (hi) preferably being configured so that feet of the user (32) can reach a ground surface between the first and second self-balancing wheels (22, 24).

10. The mobility assistance device (100) of the previous claim wherein the mechanical biasing means comprise a counterweight, a parallelogram, a spring, an elastic material, a shock-absorbing material, a pneumatic cylinder, a hydraulic cylinder, a permanent magnet and / or an electromagnetic arrangement, the mechanical biasing means preferably comprising a compression spring (56) for lifting the harness (16) along a vertical harness guide (160) of the frame (26), wherein the mechanical biasing means preferably further comprise a further second spring, the further second spring preferably being a tension spring (58) for lowering the harness (16) along a vertical harness guide (160) of the frame (26).11 . The mobility assistance device (100) of any of the previous claimswherein the device comprises a counterweight (18), the counterweight (18) preferably being provided on the frame (26) or on one or both of the first and second wheel guides (220, 240), wherein preferably the mobility assistance device (100) comprises a portable power source, the portable power source (66) preferably being positioned on the frame (26), preferably such as to serve as a counterweight (18) to a weight of the user (32).

12. The mobility assistance device (100) of any of the previous claims wherein the mobility assistance device (100) comprises at least one support wheel (38), the support wheel preferably being connected to the frame (26), the harness (16) or to one or both wheel guides (220, 240), in particular in a spring-loaded fashion, to prevent the device (100) from uncontrolled movement during use.

13. The mobility assistance device (100) according to any of the previous claims Wherein at least one control unit of the one or more control units (36) is configured to interpret sensed data to determine whether a user’s movement is voluntary and to propagate only voluntary movements, wherein the degree of propagation and / or suppression of the user’s movement is preferably adjustable.

14. The mobility assistance device (100) according to any of the previous claims wherein each of the first and second self-balancing wheels (22, 24) is negatively cambered, preferably such that each of the first and second self-balancing wheels (22, 24) defines a camber angle 0 of 5° - 20°, in particular about 10° to a ground surface.

15. A method of using a mobility assistance device (100) according to any of the previous claims comprising a step of propagating an intentional movement of a user by means of the device, while preventing falling, wherein the intentional movement is in particular a forward-backward rocking movement, a forward or backward displacement, a turning movement around a point and / or a turning movement in a partial circle.

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