Movement limiting apparatus

Description

The present invention relates to a movement limiting apparatus and in particular to a movement limiting apparatus for wheeled apparatus such as a walking aid.

Walking aids are often used by those with limited mobility, such as the elderly, to provide support and increase stability whilst walking. Referring to Figure 1, a conventional walking aid 1 comprises a handlebar 3, a frame 5, two front wheels 7, and two back wheels 9.

The handlebar 3 forms three sides of a rectangle in the horizontal plane. The back of the walking aid 1 is defined as the open side of the rectangle. The handlebar is supported at approximately waist height by the frame 5. The frame 5 comprises two front legs 11, being a left front leg 11 and a right front leg 11, and two back legs 13, being a left back leg 13 and a right back leg 13.

Each of said front legs 11 connects a front wheel 7 to a respective corner of the handlebar 3. Each of said back legs 13 connects a back wheel 9 to a respective end of the handlebar 3. The front wheels 7 and the back wheels 9 contact the ground.

Each of said front wheels 7 is attached to its respective front leg 11 via a rotatable axle assembly 15. Therefore, the front wheels can swivel about an axis that is parallel to the front leg 11, and can be used to alter the direction of movement of the walking aid 1.

Each of said back wheels 9 comprises a rubber or synthetic rubber tyre and rim combination 15 and a plurality of spokes 17 connecting a hub (not shown) to and supporting the tyre and rim 15. The hub of the back wheel 9 is rotatably mounted on an axle 19 fixed to the back leg 13.

The frame 5 also comprises a plurality of supports 21 which together act to retain the legs 11, 13 in place. A first support 21 connects the left back leg 13 to the left

front leg 11. A second support 21 connects the left front leg 11 to the right front leg 11. A third support 21 connects the right front leg 11 to the right back leg 13. The first, second and third supports 21 are connected to the front legs 11 and back legs 13 approximately half way along the length of the legs. The supports 21 strengthen the frame 5.

A rectangle formed on the ground by lines connecting the front wheels 7 and back wheels 9 defines a base area of the walking aid 1. In the following description, the user is defined to be inside the walking aid 1 when both of the user's feet are inside the base area, and the user is defined to be outside the walking aid 1 when either or both of the user's feet are outside the base area.

The above-described walking aid 1 suffers from the disadvantage that there is a risk of the user slipping. This can occur when the user forgets to, or is physically unable to, step forwards when they have pushed the walking aid 1 forwards. This can cause the walking aid 1 to be pushed away from the user, resulting in the user falling forwards, and usually to the ground.

The user can also slip when the user supports themselves on the handlebar 3 of the walking aid 1 when they are outside the frame 5 of the walking aid 1. In such a position, it is unlikely that the user is able to exert only downwards force on the walking aid 1, and some horizontal force can unintentionally also be applied to the walking aid 1. This can cause the walking aid 1 to be pushed away from the user unexpectedly, potentially causing the user to fall. Unbalancing can occur also laterally, or in a backwards direction.

According to a first aspect of the present invention there is provided a movement limiting apparatus for forming part of a walking aid as claimed in claim 1.

According to a second aspect of the present invention there is provided a movement limiting apparatus for forming part of a walking aid as claimed in claim

2.

Such a movement limiting apparatus can ameliorate some of the above-mentioned disadvantages.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 illustrates a prior art walking aid;

Figure 2 illustrates a first embodied movement limiting apparatus according to the present invention, formed on a walking aid; Figure 3 illustrates a detailed view of part of the Figure 2 movement limiting apparatus;

Figure 4 illustrates a side view of part of the Figure 2 limiting apparatus;

Figure 5 illustrates a side view of part of the interior of the Figure 2 limiting apparatus; Figures 6A and 6B illustrate a plan view of the interior of part of the Figure 2 movement limiting apparatus in first and second positions respectively;

Figure 7 illustrates a second embodied movement limiting apparatus according to the present invention, formed on a walking aid;

Figure 8 illustrates a detailed view of part of the Figure 7 movement limiting apparatus;

Figure 9 illustrates a side view of the interior of part of the Figure 7 limiting apparatus;

Figure 10 is a schematic of the control circuitry of the Figure 7 movement limiting apparatus; Figure 11 illustrates a third embodied movement limiting apparatus according to the present invention, formed on a walking aid;

Figure 12 is a schematic diagram of a fourth embodied movement limiting apparatus, installed on a walking aid;

Figure 13 is an alternative view of the fourth embodied movement limiting apparatus, with the walking aid removed;

Figure 14 is a further alternative view of the fourth embodied movement limiting apparatus, with the walking aid removed; and

Figure 15 is a view of the fourth embodied movement limiting apparatus; and

- A -

Figure 16 is a sectional view of the control circuitry of the Figure 11 movement limiting apparatus.

In the Figures, reference numerals are re-used for like elements throughout unless otherwise stated.

Referring firstly to Figure 2, a walking aid 1 is formed with movement limiting apparatus. In this example, the walking aid 1 has the same structure as the conventional walking aid described above and shown in Figure 1.

The movement limiting apparatus comprises a left unit 23 formed on the left back leg 13 of the walking aid 1. The movement limiting apparatus further comprises a right unit 25 formed on the right back leg 13. Each of said left unit 23 and right unit 25 comprises a wheel disk 27, attached to the inside rim of the respective back wheel 9, a controlling unit 29 attached to the back leg 13 just above the level of the axle, a nylon rod 31 projecting from the controlling unit 29 and a stopping arm 33.

The right unit 25 will now be described in detail. The left unit 23 has a structure corresponding to the right unit 25.

Referring to Figure 3, the wheel disk 27 is securely attached to the inside face of the right back wheel 13, so that the wheel disk 27 rotates as the wheel rotates. The controlling unit 29 is attached to the right back leg 9 just above the axle.

The nylon rod 31 projects from the controlling unit 29 in a direction generally on a line connecting the right back wheel 9 to the left back wheel 9. The nylon rod 31 can be deflected in the horizontal plane by applying a force to it.

The stopping arm 33 also projects from the controlling unit 29, and is controllably moveable in a direction perpendicular to the plane of the wheel disk 27.

As shown in Figure 3, in a fully extended position, the end of the stopping arm 33 is in the plane of the wheel disk 27 but does not extend past the wheel disk 27 to the

spokes 17 of the right back wheel 9. In a withdrawn position (not shown), the end of the stopping arm 33 is separated from the plane of the wheel disk 27.

Referring now to Figure 4, the wheel disk 27 comprises a ring 35 centred on the axle, and a stopping spoke 37 extending from the centre of the wheel disk 27 to the ring. When the stopping arm 33 is in the fully extended position, the walking aid 1 can only move forward a maximum distance d equal to the circumference of the back wheel 9 minus a distance dependent on the width of the stopping spoke 37, before the stopping arm 33 contacts the stopping spoke 37 and prevents the back wheel 9 from rotating further. When the stopping arm 33 is in the withdrawn position, the right back wheel 9 can rotate freely. In this example, the circumference of the right back wheel 9 is 30cm, and the width of the stopping spoke 37 is lcm, which is equivalent to 2cm in terms of the circumference of the wheel 9.

Referring to Figures 5, 6A and 6B, the controlling unit 29 causes the position of the stopping arm 33 to be dependent upon the position of the nylon rods 31.

Referring in particular to Figure 5, the controlling unit 29 includes a housing 39 supporting a pivot 41. The pivot 41 is connected to the top inside wall and bottom inside wall of the housing 39. A cam 43 is mounted on the pivot 41, and is rotatable in the horizontal plane. The cam 43 forms an ellipse having a long axis and a short axis in the horizontal plane.

The nylon rod 31 has a first end fixed to the bottom surface of the cam 43, in line with the long axis. The nylon rod 31 passes through a first slot 45 in the housing 39. The first slot 45 allows movement of the nylon rod 31 around the pivot 41, from a pushed back position, where the nylon rod 31 lies generally on a line connecting the right back wheel 9 to the left back wheel 9, to a pushed forward position, where the nylon rod 31 lies generally on a line connecting the right back wheel 9 to the right front wheel 7.

A torsion spring 47 is mounted on the pivot 41. The torsion spring 47 has a first arm 49 attached to the top surface of the cam 43, and a second arm 51 attached to the top inside wall of the housing 39. The torsion spring 47 acts to keep the nylon rod 31 in the pushed back position when there is no force applied to the nylon rod 31.

The housing 39 of the controlling unit 29 has a second slot 53 in the side of the housing 39 closest to the right back wheel 9. The size of the second slot 53 is slightly larger than the cross section of the stopping arm 33. The stopping arm 33 passes through, the second slot 53 near a first end. An extension spring 55 connects a second end of the stopping arm 33 to the interior wall of the housing 39 opposite to the second slot 53. The second end of the stopping arm 33 butts against the cam 43. The stopping arm is supported for travel along its longitudinal axis and is prevented from movement in any other direction.

Referring in particular to Figure 6A, when the nylon rod 31 is in the pushed back position, the long axis of the cam 43 is parallel to the stopping arm 33. This forces the stopping arm 33 into the fully extended position. In this position, the stopping arm 33 enters the plane of the wheel disk 27.

Referring in particular to Figure 6B, when the nylon rod 31 is pushed forward, for example by the user exerting a displacing force on the nylon rod 31, the cam 43 is rotated such that the long axis is not longer parallel to the stopping arm 33. Therefore, the distance from the pivot 41 to the edge of the cam 43 in a direction parallel to the stopping arm 33 decreases. The extension spring 55 pulls the stopping arm 33 back to butt against the cam 43. In this position, the stopping arm 33 withdraws from the plane of the wheel disk 27. Thus, the wheel disk 27 is free to rotate unimpeded. It may be necessary to remove any forward force applied to the walking aid 1 before the stopping arm 33 would be retracted by the spring 55.

As described above, the position of the stopping arms 33 are determined by the position of the nylon rods 31. When the user is inside the walking aid 1, the users legs exert a force on the nylon rods 31 and push them forward. Thus, the nylon

rods 31 rotate in the horizontal plane. This causes the stopping arm 33 to be withdrawn from the wheel disk 27, and the walking aid 1 can be pushed forward. When the user is outside the walking aid 1, the nylon rods 31 are pushed back by the action of the tension spring 47. This causes the stopping arm 33 to be in the first extended position, and the wheel disk 27 can move forward a maximum distance d equal to the circumference of the back wheel 9 minus the width of the stopping spoke 37 (which in this example is 28cm) before the back wheel 9 is locked. Since the walking aid is only allowed to move forward a small distance until the user next is inside the walking aid, the chance of the user falling is reduced.

In this embodiment, the left unit 23 and the right unit 25 are independently controlled. Therefore, if only one of the users legs is inside the walking aid 1, one back wheel 9 is unlocked whilst the other back wheel 9 is locked. In other embodiments (not shown), a suitable link may be provided between the left unit 23 and the right unit 25, to ensure that both the back wheels 9 unlock only when both the users legs are inside the walking aid 1.

Referring to Figure 7, a second embodied movement limiting apparatus is formed on a walking aid 1. The walking aid 1 is similar to the conventional walking aid 1 described above and shown in Figure 1. The movement limiting apparatus comprises a left unit 61 formed on the left back leg 13 of the walking aid 1. The movement limiting apparatus further comprises a right unit 63 formed on the right back leg 13. Each of said left unit 61 and right unit 65 comprises a wheel disk 67, a sensor 69, a brake 71, a controlling unit 73, and a nylon rod 75.

The right unit 63 will now be described in detail. The left unit 61 has a structure corresponding to the structure of the right unit 63.

Referring to Figure 8, the wheel disk 67 is mounted on the inside face of the right back wheel 9. The wheel disk 67 is formed of a material having a high coefficient of friction, such as rubber. A plurality of small magnetic disks 77 is provided on the wheel disk 67. The magnetic disks 77 are equally spaced on the boundary of a circle that is centred on, and has a circumference smaller than, the wheel disk 67.

The controlling unit 73 is mounted on the respective back leg 13 of the walking aid 1. The sensor 69 and the brake 71 protrude from the face of the controlling unit 73 that is nearest to the right back wheel 9. The nylon rod 75 protrudes from the opposite face of the controlling unit 73, towards the inside of the frame 5.

The sensor 69 has an end that is held at a small distance from the circle defined by the magnetic disks 77. In this example, the sensor 69 is a Hall effect sensor. The distance between the sensor 69 and the magnetic disks 77 is dependent on the properties of the sensor 69 of the magnetic disks 77. A suitable distance could be of the order of lmm. In other embodiments, any suitable proximity arrangement can be used instead of the Hall effect sensor in combination with magnetic disks.

The brake 71 comprises a brake pad 79 attached to the end of a rod 80. The brake pad 79 is formed of a material with a high coefficient of friction, such as rubber. The brake pad 79 has a flat face that contacts the wheel disk 67 when the brake 71 is actuated.

Referring to Figure 9, the controlling unit 73 includes a housing 81. The housing 81 contains control circuitry 84. The control circuitry 84 is powered by a battery 86. The control circuitry 84 controls the operation of the brake 71.

The brake 71 passes through, a first slot in the housing 81. The brake 71 is supported so as to be moveable only along its longitudinal axis. The brake 71 is controlled by means of a pull-type solenoid 85 contained within the controlling unit 73. The axis of the solenoid 85 corresponds to the axis of the brake 71. The brake 71 has a second end that is attached to a slug 87 inside the solenoid 85. When there is no current flowing through the solenoid 85, the slug 87 is held partly outside of the solenoid 85 by means of a compression spring 89. In this position, the brake pad 79 is separated from the wheel disk 67. When a current passes through the solenoid 85, the magnetic field created forces the slug 87 to fully enter the solenoid 85, compressing the spring 89. In this position, the brake pad 79 contacts the wheel disk 67.

The nylon rod 75 is mounted on a pivot 91, and it can rotate in a horizontal plane around the pivot 91. The nylon rod 75 passes through a first slot in the housing 81. The first slot allows movement of the nylon rod 75 around the pivot 91, from a pushed back position, where the nylon rod 31 lies generally in a direction connecting the right back wheel 9 to the left back wheel 9, to a pushed forward position, where the nylon rod 75 lies generally in a direction connecting the right back wheel 9 to the right front wheel 7.

The pivot 91 is attached to the roof of the interior wall of the housing 81 of the controlling unit 73. A torsion spring 93 is wound around the pivot 91 between the housing and the nylon rod 75. A first arm 95 of the torsion spring 93 is fixed to the nylon rod 75. A second arm 97 of the torsion spring 93 is fixed to the housing 81. The torsion spring 93 acts to return the nylon rod 75 to a position parallel to a line connecting the left back wheel 9 to the right back wheel 9.

A switch 99 comprises a conducting panel 101 fixed to the end of the nylon rod 75 that is inside the controlling unit 73, and two conducting switch contacts 103 provided on a non conducting board 105. The non-conducting board 105 is fixed to the top inside wall of the housing 81, and protrudes downwards within the housing 81. The non-conducting board 105 is arranged such that, when the nylon rod 75 is pushed forward by the user, the conducting panel 101 contacts both switch contacts 103. Each of the switch contacts 103 is connected to the control circuitry 84.

The sensor 69 is fixed to the top interior wall of the controlling unit 73. The sensor passes through a third slot in the housing 81. The sensor 69 is also connected to the control circuitry 84.

Referring to Figure 10, the control circuitry 84 includes a controller 107. The controller 107 has a first input connected to the switch 99 of the nylon rod 75. The controller has a second input connected to an output of a counter 109. The counter 109 has a first input connected to an output of the wheel sensor 69. The controller

has an output connected to the input of a driver 111. The driver 111 has an output connected to the brake 71.

Each time the sensor 69 is aligned with one of the magnet disks 77 on the wheel disk 67, a spike in output voltage of the sensor 69 occurs. The counter 109 counts the spikes in the output voltage. The count of spikes in the output voltage is directly proportional to the angle through which the wheel disk 67 has been rotated, and thus is directly proportional to the distance that the walking aid 1 has been moved.

When the count of spikes is equal to a predetermined number, the controller 107 registers that a predetermined distance has been travelled by the walking aid 1. This causes the controller 107 to activate the driver 111. The driver 111 drives a current through the solenoid 85, thus actuating the brake 71.

When the user is inside the walking aid 1, a force is applied to the nylon rods 75, causing them to rotate. This causes the conducting panel 101 on the inside end of the nylon rod 75 to contact the switch contacts 103. Therefore, the switch 99 is turned on. When the switch 99 is turned on, the controller 107 controls the driver 111 to deactivate the solenoid 85 and thus release the brake 71. The controller 107 also controls the counter 109 to reset.

In this way, the movement limiting apparatus limits the amount of forward movement of the walking aid 1. The walking aid 1 is only able to move forward by the predetermined distance, until the user is again inside the walking aid 1.

Therefore, the chance of the user falling while using the walking aid 1 is greatly reduced.

Referring to Figure 11, a third embodied movement limiting device forms part of a walking aid 1. The walking aid 1 has a similar structure to the conventional walking aid 1 described above and shown in Figure 1. The movement limiting device comprises a controlling unit 121, a left movement sensor 123, a right movement

sensor 125, a left motor 127, a right motor 129, a left brake 131 and a right brake 133.

The controlling unit 121 is mounted on the handlebar 3. Therefore, the controlling unit 121 can be easily accessed by the user. The controlling unit 121 is connected to the left brake 131 by means of a first connecting lead 134.

The left brake 131 comprises a solenoid unit 137 and a brake pad 139. The solenoid unit 137 is mounted on the left back leg 13 of the walking aid 1. The solenoid unit 137 has a similar structure to the solenoid unit of the Figures 7 to 9 embodiment. Thus, the solenoid unit comprises a solenoid (not shown), a slug (not shown) and a compression spring (not shown). The slug is connected to the brake pad 133 by means of a rod 141.

The brake pad 139 is in the shape of an arc and is aligned with the top of the left back wheel 9. Therefore, the brake pad 139 can be arranged to contact the left tyre 15 over a substantial part of the outwardly facing area of the brake pad 139. If there is no current passing through the solenoid, the brake pad 139 is separated from the left tyre 15. If a current is driven through the solenoid, the brake pad 139 is arranged to contact the left tyre 15.

The controlling unit 121 is also connected to the right brake 133 by means of a second connecting lead 143. The right brake 133 has a structure corresponding to the structure of the left brake 131.

The left sensor 123 is connected to the controlling unit 121 by means of a third connecting lead 145. The left sensor 123 is mounted on the left back leg 13. In this example, the left sensor 123 is an ultrasonic proximity sensor. However, any suitable proximity sensor can be used, for example an active infrared sensor is suitable. The left sensor 123 faces the inside of the walking aid 1. Therefore, the left sensor 123 is operable to detect when the users leg enters the walking aid 1.

The left sensor 123 has a range that is between one third and one half the distance between the left back wheel 9 and the right back wheel 9. Therefore, if the user is walking forwards into the walking aid 1, the left sensor 123 detects when the user's left leg is inside the walking aid 1 but cannot detect when the user's right leg is inside the walking aid 1.

The right sensor 125 is connected to the controlling unit 121 by means of a fourth connecting lead 147. The right sensor 125 is mounted on the right back leg 13, and has a structure corresponding to the structure of the left sensor 123. The right sensor 125 has a similar range as the left sensor 123. Therefore, the right sensor 125 detects when the user's right leg is inside the walking aid 1 but cannot detect when the user's left leg is inside the walking aid 1.

The left motor 127 is mounted on the axle of the left back leg 13 and the left back wheel 9. The left motor 127 is connected to the controlling unit 121 by means of a fifth connecting lead (not shown).

The right motor 129 is mounted on the axle of the right back leg 13 and the right back wheel 9. The right motor 129 is connected to the controlling unit 121 by means of a sixth connecting lead (not shown). A power supply (not shown) is included at a suitable location on the walking aid 1.

The left and right motors 127, 129 are operable to drive the left and right back wheels 9 of the walking aid 1 respectively and therefore move the walking aid 1 forwards.

Referring to Figure 12, the controlling unit 121 comprises a controller 153, a timer 155, and a driver 157. A first input of the controller 153 is connected to a first output of the timer 155. A first output of the controller 153 is connected to an input of both the left and right motors 127, 129. A second output of the controller 153 is connected to an input of the driver 157. An output of the driver is connected to both the left and right brakes 131, 133. An output of the left sensor 123 is connected to a first input of an AND gate 159. An output of the right sensor 125 is

connected to a second input of the AND gate 159. An output of the AND gate 159 is connected to a second input of the controller 153.

The controller 153 controls the left and right motors 127, 129 to move the walking aid 1 forwards. In this example, the controller 153 controls the left back wheel 9 and the right back wheel 9 to move simultaneously.

The time that the left and right motors 127, 129 are driven for is directly proportional to the distance travelled by the walking aid 1. Therefore, the controller 153 can use the output of the timer 155 to calculate accurately the distance travelled by the walking aid 1. When the calculated distance is equal to a predetermined distance, the controller 153 controls the driver to drive a current through the solenoid and thus actuate the brake 131, 133. In this example, the predetermined distance is 30cm.

When the user's left and right legs are inside the walking aid 1, both the left sensor 123 and the right sensor 125 provide an output signal to the AND gate 159. The AND gate 159 provides an output signal to the controller 153 only when both of the user's legs are inside the walking aid 1.

When the controller 153 receives the output signal from the AND gate 159, it controls the left and right brakes 131, 133 to be released via the driver 157, so that the left back wheel 9 and right back wheel 9 of the walking aid 1 are free to rotate. The controller 153 then controls the motor to move the walking aid 1 forwards. At the same time, the controller 153 resets the timer 155, so that a predetermined forward movement can again be measured.

In this way, the movement limiting apparatus acts to allow only a predetermined amount of forward movement. Further movement is only allowed when both of the users legs are inside the walking aid 1.

In another embodiment, no brakes are provided to the wheels. Instead, the internal resistance of the undriven motors acts to impede further forward movement beyond the predetermined distance.

In yet another embodiment, only one motion sensor is provided on either the right back wheel 9 or the left back wheel 9. The motion sensor has a range approximately equal to the distance between the right back wheel 9 and the left back wheel 9, and can thus detect when either of the user's legs enters the walking aid 1.

In a further embodiment (not shown in the Figures), movement limiting apparatus for a walking aid is provided without an arrangement for sensing leg position. Instead, the presence of the user within the frame is inferred by other means. For instance, one or mote pressure sensitive transducers could be provided at the handlebar. The transducer(s) may be incorporated into hand grips for instance. Detection of a light pressure on the handlebar indicates that the user is supporting their weight on their feet.

By incorporating a transducer into each of left and right side hand grips, the transducers are able to allow the user's stance and balance to be inferred. If the pressure (weight) is approximately equal on the left and right sides, it can be inferred whether or not the user is balanced.

By incorporating two or four transducers on each hand grip, even more information about the user's balance and stance can be inferred.

When it is determined from the outputs of the transducers that the user is balanced, the brakes or other movement impeding means are controlled to be off. If a heavy pressure is detected or it is detected that the user's stance is wrong or that the user is unbalanced, it is inferred that the user needs the frame to support their weight, and the brakes are controlled to be on.

If no pressure is detected, it is inferred that the device is not in use, and the brakes are controlled to be on.

The transducer outputs can be used in addition to or alternatively to the sensing of one or both legs within the frame.

This aspect of the invention is considered to be inventive in its own right, and is severable as an inventive concept from the other embodiments. This invention may be implemented as a walking aid, or as an add-on for a walking aid.

A still further embodiment will now be described with reference to Figures 13 to 16. reference numerals are not re-used from Figure 12.

In Figure 13, a movement limiting apparatus 150 is shown mounted on a vertical leg 151 of a walking aid, which may for example take the form shown in Figure 11. No motorised driving is present in this embodiment.

The apparatus 150 includes an actuator 152, which in this example is a miniature servomotor. The actuator 152 is fixedly coupled to the leg 151 by a bracket (not shown)

A horizontal support tube (HST) 153 is freely rotatable about an axle 154, visible only in Figures 14 and 15. The axle 154 is fixedly attached to the leg 151 by the bracket that fixes the actuator 152 to the leg 151.

The HST 153 supports the other components of the apparatus 150. The actuator 152 drives a belt 155 which contacts a pulley 149 fixedly coupled to the HST 153. Accordingly, energising the actuator 152 causes rotation of the HST 153, and all the components fixed to it, about the axle 154.

At each end of the HST 153 is a braking arrangement. These braking arrangements ate mirror images of one another, so only one is described here. Each braking arrangement comprises a hard brake arrangement and a soft brake arrangement.

The soft brake is mounted on a carriage 160, which is rotatable about the axle 154 but which is not fixedly connected to the HST 153. The carriage 160 is mounted on the axle 154 by bearings 160a separate from bearings 153a used to mount the HST 153 onto the axle 154.

The soft brake comprises a rubber contact drum 156 which is fixed to one end of a torsion element 157, in this example in the form of a steel cable. The torsion element 157 extends parallel to axis of the HST 153 into a central part of the drum 156, and is immovably fixed thereto. The torsion element 157 then passes horizontally through bearings 158 where it is then bent through 90 degrees upwards and is received in a support bearing 159 attached to the carriage 160.

The hard brake comprises a hard brake bracket 161, which is fixedly connected to the HST 153 and to a hard brake pad 162. Thus, the hard brake pad 162 is in a fixed position relative to the HST 153.

The soft brake carriage 160 is biased away from the hard brake by a carriage hold- off spring 163, which is visible only in Figure 16. This spring 163 is a small coil spring in this example. The possible amount of rotation of the carriage 160 relative to the HST 153 is limited in both directions by a limit stop 165.

The apparatus 150 is supported adjacent a wheel 164 such that the actuator 152 can restrict movement of the wheel using the soft brake alone or using the soft brake and the hard brake together as follows. The wheel 164 is a 205 mm diameter wheel, and thus is the same size as wheels generally used on wheeled walkers, also known as walking aids.

The default position of the apparatus 150 is with both the hard brake and the soft brake operational, i.e. is a braking position. In this position, the hard brake pads 162 and the contact drum 156 are in contact with the rim of the wheel 164. To get to this position, the actuator 152 rotates the HST 153 via the belt and pulley arrangement until the hard brake is in contact with the wheel rim. The notched limit stops allow the soft brake carriage 160 to move in concert, against the effect of

the coil spring 163. The default position can also be termed the 'at rest' state or 'braked' state. In this state, rotation of the wheel is prevented by frictional contact between the soft and hard brake mechanisms and the wheel rim. The material of the hard brake pads 162 is chosen to exhibit properties that present a good compromise between grip and durability.

Upon energisation of the actuator 152, the pulley and belt causes the HST 153, and thus the braking arrangements, to rotate. After a small amount of rotation, the hard brake pads 162 move way from the wheel rim. The soft brake carriage 160, sprung against the inside of the hard brake flange, keeps the soft brake drum 156 in contact with the wheel rim.

At this stage, the soft brake is operational but the hard brake is not. The soft brake drum 156 contacts the wheel rim, and friction ensures that the drum 156 rotates as the wheel 164 rotates. Rotation of the drum 156 causes corresponding rotation of the torsion element 157. Because the torsion element 157 is bent through 90 degrees along its length, transmission of the rotation of the torsion element 157 along its length induces tensile, compressional and frictional forces within the torsion element 157. These forces within the torsion element 157 translate to resistance to rotation of the drum 156, and thus provides a limited braking effect. This state is particularly suitable for transiting downward inclines etc. The soft brake function avoids the need for an ABS-alike pulsed braking, which when used increases brake pad wear due to local surface abrasion and binding on impact. When the soft brake is operated and the wheel is rotated, the torsion element 157 generates heat. However, due to the design, the torsion element operates in free air, and heating of it is not seen to be a potential problem.

Upon further energisation of the actuator 152, the HST 153 rotates further until the carriage limit stop 165 engages with the corresponding cutout in the HST 153. At this stage, further rotation of the actuator 152, and thus the HST 153, rotates the carriage 160 and thus the soft brake away from the wheel rim until there is no contact between the drum 156 and the wheel 164. In this state, the mechanism is 'free' and the wheel 164 can rotate without additional resistance.

Upon energisation of the actuator 152 in the opposite sense, the HST 153 is rotated so that the soft brake firstly engages, followed by the hard brake.

Control of the actuator is effected electronically, for example as described above with reference to Figure 12. Advantageously, control is effected such that the apparatus 150 is left in the braked state when it is not being used. A positive (sprung) action may be added to the apparatus so as to bias it to the braked state, The actuator 152 is driven such that the transition times between 'braked', 'soft brake' and 'unbraked' are of the order of small fractions of a second.

Since the braking arrangements are located oppositely to one another, unwanted shear and torsional forces within the hub of wheel 164 are minimised. However, alternative arrangements, having fewer or greater numbers of braking arrangements, ate conceivable and are within the scope of this invention. Additionally, the number of hard braking units may be different to the number of soft braking units.

In general, the arrangement of Figures 13 to 16 allows for the implementation of an add-on braking mechanism suitable for use with a range of wheel sizes, sectional profiles and attachment methods, with minimal maintenance (if any) being required.

In all the above-described embodiments, the movement limiting apparatus has been added to the conventional walking aid of Figure 1. In other embodiments, the movement limiting apparatus can be formed on any suitable walking aid. The movement limiting apparatus may comprise a removable unit that can be easily installed on a walking aid. Alternatively, the movement limiting apparatus may be integrated with the walking aid.

In all the above-described embodiments, the movement limiting apparatus includes impeding means that are installed on the walking aid. However, in other embodiments, the movement limiting apparatus can be formed on a walking aid that includes pre-installed brakes, and use said pre-existing or pre-installed brakes to impede or prevent movement of the walking aid beyond a predetermined distance.

The above embodiments all relate to walking aids of the type in which a user stands and walks with the aid. The invention is applicable, in some embodiments, also to other wheeled apparatus, for instance wheelchairs and pushchairs. In such embodiments, the movement limiting apparatus can make operation easier for a person walking with the wheeled apparatus, for instance the person pushing someone in a wheelchair. This is particularly useful when travelling downhill, when even able-bodied users can have difficulty operating wheelchairs safely, but can be useful for less mobile operators in other situations aswell.

Although the present invention has been described with respect to the above embodiments, it should be apparent to those skilled in the art that modifications can be made without departing from the scope of the invention. For example, any suitable sensor can be used to detect when the user is inside the walking aid. In addition, any suitable brake or impeding means may be used to impede or prevent movement of the walking aid beyond a predetermined distance. Furthermore, the movement limiting apparatus may operable to allow movement of the walking aid in response to a stimulus other than an indication that the user is inside the walking aid, such as an indication that user is within a required distance of the walking aid.