MOBILITY ASSISTANCE

Description

TECHNICAL FIELD

[0001] The present invention relates to devices for movement of incapacitated individuals and, more particularly to mobile devices which may transport a user from one location to another.BACKGROUND

[0002] Mobility aids in the form of hoists which allow a carer to lift and lower an incapacitated person, are well known. These devices are particularly used both in hospitals and in domestic situations for transfer of a person from, for example, a wheelchair onto a bed and vice versa.

[0003] Hoists range in complexity from a relatively simple frames mounted on castors and fitted with a ram-driven lifting arm, such as for example shown in www.dolphinlifts.co.uk / Suas_Hoists.html, to highly complex motor driven devices such as shown in http: / / www.activemedicalsupplies.com.au / Products / Multilift5 50MotorisedPatientLifter.aspx

[0004] While the simpler devices are relatively light weight and may even allow of disassembly for transport, a problem with castor mounted devices is the difficulty of manoeuvring them on any other than a hard smooth surface. Thus, on carpet where the generally small castors sink into the pile, moving the lifter in any direction can be very difficult and, especially when trying to move such a device laterally from a previous straight ahead movement, may even lead to the tipping over of the device.

[0005] The highly sophisticated devices such as that of Activemedical Supplies referenced above are very heavy, expensive and really only suitable for hospital or other health establishment use and are clearly not portable.

[0006] The rams used to raise and lower the articulated lifting arms of hoists are generally capable of exerting a force of 1300N, both in extension and in retraction. A safety issue arises if the carer is distracted, or there is a malfunction in the switching system during the lowering of a user when the ram is retracting, since the lifting arm may deliver a crushing force to the user's head and shoulders.

[0007] Typically hoists are constructed with a forward directed fork extending from a rear cross member and spaced apart sufficient for stability and moving the hoist through doorways. It is a common feature of known hoists to provide for a spreading or splaying of the two members of the fork to allow a wheelchair to move between them so as to bring the user directly under the end of the lifting arm. Splaying of the fork is typically achieved by manually pumping a pneumatic cylinder or manipulating a lever to activate a spreading mechanism. In both arrangements this can be very difficult, particularly so when the hoist is positioned on deep pile carpet.

[0008] It is an object of the present invention to address or at least ameliorate some of the above disadvantages or provide a useful alternative.

[0009] Documents EP1269960A2, EP0555198A1, WO90 / 01916A1, DE29823115U1, US2010 / 132114A1 and JPH10286290A all disclose a mobility aid assembly.

[0010] However, none of these documents discloses a mobility aid assembly wherein the lower end of the actuator disengages from its mounting at the lifting arm when the lifting arm may expose the user to a dangerous crushing force.Notes

[0011] The term "comprising" (and grammatical variations thereof) is used in this specification in the inclusive sense of "having" or "including", and not in the exclusive sense of "consisting only of".

[0012] The above discussion of the prior art in the Background of the invention, is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country.SUMMARY OF INVENTION

[0013] An object of the present invention is a mobility aid assembly for lifting and lowering a disabled user as recited in claim 1. Another object of the present invention is a method of assisting realignment of wheels of the mobility aid assembly as recited in claim 8. Another object of the present invention is a method of control of the mobility aid as recited in claim 9.

[0014] Accordingly in one broad form of the invention there is provided a mobility aid assembly for lifting and lowering a user; the assembly including an articulated lifting arm releasably mounted to a base structure; a first portion of the lifting arm operable between a lowered position and a raised position by a linear actuator; a first end of the linear actuator pivotally connected to the first portion of the lifting arm and, wherein a second end of the linear actuator is releasably mounted so as to avoid injury to the user if the linear actuator moves the first portion of the lifting arm to an excessively lowered position in which the first portion of the lifting impinges on the user.

[0015] Preferably the second end of the linear actuator is provided with a mounting boss; the boss provided with a first connecting element for releasable connection to a complementary second connecting element provided on a second, fixed upright portion of the lifting arm.

[0016] Preferably the mounting boss comprises a body provided with a transverse slot; the complementary connecting element comprising a transverse support pin located on the second, fixed upright portion of the lifting arm; the slot slidingly engaging with the transverse support pin when the assembly is in use.

[0017] Preferably the mounting boss disengages from the second connecting element when an upward force acting on the first portion of the lifting arm exceeds the combined weight of the first portion of the lifting arm and that of the linear actuator.

[0018] Preferably the base structure comprises a hollow body provided at each outer end with a drive wheel; each drive wheel driven by respective electric motor modules located within the hollow body.

[0019] Preferably each electric motor module includes a gear train to reduce the RPM of the electric motor to a predetermined RPM of the drive wheel.

[0020] Preferably each electric motor is controllable for synchronized rotation of the wheels for forward and rearward movement of the assembly and for contra-rotation of the wheels for rotation of the assembly about a vertical axis.

[0021] Preferably the assembly further includes a forwardly directed fork; the fork comprising two fork elements extending from the base structure; each outer end of a fork element provided with a swivelling castor; each castor provided with a locking system for locking the direction of movement of the castor at a desired angle relative to a horizontal centerline of the assembly.

[0022] Preferably each of the fork elements is releasably mounted to the base structure; each of the fork elements arranged for rotation about a respective vertical axis at the base structure; each fork element rotatable between a first direction parallel to the centerline of the assembly and a second splayed direction wherein the separation between the outer ends of the fork elements is greater than the separation of the vertical axes at the base structure.

[0023] Preferably the fork elements move from the first direction parallel to the centreline to the splayed direction if the castor at each outer end of the fork element is locked at a "toed out" angle relative a centerline of the respective fork element and the assembly is driven in a forward direction; the fork elements returning to the first direction when the assembly is driven in a rearward direction with the castors locked in the "toed out" angle.

[0024] Preferably the articulated lifting arm is provided with connector elements at a lower end of the second, fixed upright portion of the lifting arm; the connector elements including tabs provided with forwardly directed slots; the tabs inserted through slots in the upper surface of the support structure for connecting the lifting arm to the base structure; the forwardly directed slots of the connector elements engaging with a transverse pin mounted within the hollow body of the base structure.

[0025] Preferably a rear surface at the lower end of the second, fixed upright portion of the lifting arm is provided with a securing plate; the securing plate extending to below a lower edge of the second, fixed upright portion of the lifting arm and provided with apertures for engagement with pins projecting from a rear surface of the support structure.

[0026] Preferably one of the projecting pins is provided with an internally threaded hole; the internally threaded hole adapted to receive an externally threaded shaft of a securing knob for locking the lifting arm in position on the base structure.

[0027] In a further broad form of the invention there is provided components for assembly into a transportable disability aid; the components comprising a base structure, an articulated lifting arm assembly and two fork elements; the lifting arm assembly including a first portion operable between a raised position and a lowered position; characterized in that a second end of a linear actuator of the lifting arm assembly is adapted for releasable connection to a second, fixed upright portion of the lifting arm assembly so as to avoid injury to a user if the linear actuator moves the first portion of the lifting arm to an excessively lowered position.

[0028] Preferably the base structure is provided at each outer end with a driven wheel; each wheel driven by an electric motor module.

[0029] Preferably the articulated lifting arm assembly includes the first portion pivotally connected to the second, fixed upright portion and a linear actuator pivotally connected to the first portion of the articulated lifting arm at a first end of the linear actuator.

[0030] Preferably the lifting arm assembly the second end of the linear actuator is disconnected from a connecting element located on the second, fixed upright portion of the articulated lifting arm.

[0031] Preferably each of the two fork elements is rotatably and releasably mountable to the base structure at inner ends of the fork element; the fork elements rotatable about respective vertical axes between a parallel position and a splayed position wherein separation between outer ends of the fork elements is greater than the separation of the vertical axes.

[0032] Preferably the outer end of each fork element is provided with a swivelling castor; each swivelling castor provided with a locking mechanism for locking the direction of the castor at a desired angle.

[0033] In a further broad form of the invention there is provided a method of changing disposition of fork elements of a fork of a disability aid assembly from a first position in which the fork elements are parallel to a horizontal centerline of the disability aid assembly and a second position in which outer ends of the fork elements are more widely separated than inner ends of the fork elements; the method including the steps of: providing swivelling castors at the outer ends of the fork elements with locking mechanisms, locking each castor at an angle in which the direction of the castor is "toed out" relative to a centerline of the fork element, moving the disability aid assembly in a forward direction to drive the fork elements from the first position into the second position, moving the disability aid assembly in a rearward direction to drive the fork element from the second position into the first position, and wherein

[0034] In yet a further broad form of the invention there is provided a method of avoiding injury to a user of a disability aid assembly if a first articulated portion of a lifting arm of the assembly is lowered by a linear actuator of the assembly to a point at which the first articulated portion is driven into contact with the user by retraction of the linear actuator; the method including the step of providing a lower end the linear actuator with a releasable mounting, and wherein a force acting on the user by an end of the articulated portion of the lifting arm cannot exceed a combined weight of the articulated portion of the lifting arm and the linear actuator.BRIEF DESCRIPTION OF DRAWINGS

[0035] Embodiments of the present invention will now be described with reference to the accompanying drawings wherein: Figure 1 is a perspective view of a mobility aid assembly according to a preferred embodiment of the invention, Figure 2 is a further perspective view of the assembly of Figure 1 with a lifting arm of the assembly in a lowered position, Figure 3 is a side elevation view of a crush avoidance system of the assembly, Figures 4 and 4A are perspective views of the assembly showing details of the mounting arrangement of crush avoidance system of Figure 3, Figures 5 and 5A are a perspective views of the assembly showing a preferred way of mounting the lifting arm to a base structure of the assembly, Figure 6 is a perspective view of the assembly of Figure 1 showing a splayed positions of the fork elements of the assembly. Figure 7 is an exploded view of the assembly of Figures 1 to 6 indicating the components disassembled for transportation. Figure 8 illustrates an electronic block diagram of drive and control circuitry suitable to give effect to operation of the assembly illustrated in Figure 6. Figure 9 is a perspective view of an alternative wheel structure which can be utilised with the assembly of Figure 6. Figure 10 is a perspective view of the entire assembly in accordance with a further preferred embodiment. DESCRIPTION OF EMBODIMENTS

[0036] With reference to Figure 1, a mobility aid assembly 10 according to the invention, for lifting and lowering a disabled user (not shown), includes an articulated lifting arm 12 releasably mounted to a base structure 14 and a fork 16 extending from the base structure. A hanger 48 is suspended from the end of the lifting arm for attachment of slings or seating (not shown) for lifting a user.

[0037] A first portion 18 of the lifting arm 12 is pivotally attached to a second or fixed, upright portion 20, and is operable between a raised position (as shown in Figure 1 and a lowered position as shown in Figure 2 by a linear actuator 22.

[0038] Again with reference to Figure 1, the outer end 24 of the piston rod 26 of the linear actuator 22 is pivotally connected to the first portion 18 of the lifting arm 12, while its lower end 28 of the linear actuator 22, is releasably mounted to the second or fixed, upright portion 20 of the lifting arm 12.

[0039] Figures 4 and 4A shows a preferred arrangement for the mounting of the lower end 28 of the linear actuator. The second or lower end 28 of the linear actuator 22 is provided with a mounting boss 30 to providing a first connecting element for releasable connection to a complementary second connecting element provided on the second or fixed, upright portion 20 of the lifting arm 12. The mounting boss 30 comprises a body provided with a transverse slot 32 while the complementary connecting element comprises a transverse support pin 34 mounted between side plates 36 and 38 forming the second or fixed, upright portion 20 of the lifting arm. The slot 32 slidingly engages with the transverse support pin 34 (as in Figure 1) when the assembly 10 is in use for lifting and lowering a user.

[0040] The releasable mounting of the second or lower end 28 of the linear actuator 22 provides a novel and inventive crush avoidance safety feature which prevents injury to the user if the linear actuator moves the first portion 18 of the lifting arm to an excessively lowered position as shown in Figure 3, in which the first portion of the lifting may expose the user 40 to a dangerous crushing force. This may happen for example through inattention by a carer or through a malfunction of the control system.

[0041] In this situation in which the linear actuator 22 continues to retract and lower the second portion 18 of the lifting arm 12 when a user 40 is already resting on some support, such as a wheel chair or bed 42 for example, the end 44 of the arm will likely come into contact with the user. However, when the resulting upward force then acting on the end 44 of the first portion 18 of the lifting arm 12 exceeds the combined weight of the first portion 18 and that of the linear actuator 22, the downward force is disengaged by the lower end 28 of the actuator disengaging from its mounting. Thus the force of contact with the user in such a potentially injurious incident cannot exceed the combine weight of these components.

[0042] With reference again to Figure 1, the base structure 14 of the assembly comprises a hollow body 50 provided at each outer end with a drive wheel 52 and 54. Preferably the hollow body is formed of two length of channel section, one forming a base portion 56 and the other a cover portion 58.

[0043] Each drive wheel 52 and 54 is driven by a respective electric motor and gear train module (not shown) located within the hollow body 50. Preferably the gear trains are formed as a series of gear wheels and toothed belts to reduce the RPM of the electric motors to a predetermined RPM of the drive wheels. A rechargeable battery bank and electronic control module are also accommodated within the hollow body 50 of the base structure 14. Preferably the assembly's drive wheels and linear actuator are activated via a short range wired or wireless remote control.

[0044] The electric motors driving the wheels 52 and 54 are controllable for synchronized rotation of the wheels for forward and rearward movement of the assembly 10. They are also capable of contra-rotating the wheels for rotation of the assembly about a vertical axis. For safety reasons, the contra-rotation of the wheels can only be engaged when the assembly 10 is stationary. To prevent excessive swinging motion being imparted to a suspended user, the electronic control of the electric motors includes soft start and stop functionality.

[0045] With reference now to Figures 5 and 5A, the articulated lifting arm 12 is mounted at the centre of the base structure 14. The second or fixed, upright portion 20 of the lifting arm 12, is provided with connector elements 60 formed at the lower end of the side plates 36 and 38 which include tabs 62 and 64 provided with forwardly directed slots 65. These tabs 62 and 64 are inserted through slots 66,68 in the upper surface of the cover portion 58 of the hollow body of the support structure to allow the forwardly directed slots 65 of the connector elements 62 and 64 to engage with a transverse plate (not shown) mounted within the hollow body.

[0046] The rear surface 70 at the lower end of the second or fixed, upright portion 20 of the lifting arm 12 is provided with a securing plate 72, which extends below its lower edge and is provided with apertures 74 for engagement with pins 76 projecting from a rear surface 78 of the support structure 14. The centre one of the projecting pins is provided with an externally threaded shaft adapted to receive an internally threaded securing knob 80 for locking the lifting arm in position on the base structure.

[0047] In one preferred arrangement, the electric motor of the linear actuator 22, may be provided with an extension mechanism (not shown) by means of which the motor shaft and gear drive of the actuator may be manually rotated. This allows the linear actuator to be urged into extension or retraction in the emergency situation of a power loss in the system.

[0048] With reference now again to Figures 1 and 6 the fork 16 of the assembly 10 comprises of two fork elements 82 and 84 extending from the base structure 14. Each outer end 86 and 88 of fork elements 82 and 84 is provided with a swivelling castor 90 and 92 respectively, which incorporate a locking system for locking the direction of movement of the castor at a desired angle relative to a longitudinal axis of its respective fork element.

[0049] Each of the fork elements 82 and 84 is releasably and pivotally mounted to the base structure 14 and is arranged for rotation about a respective vertical axis 94 and 96, at the underside of the base structure 14. This allows each fork element to be rotatable between a first direction in which each fork element is parallel to the centerline 98 of the assembly (as shown in Figure 1), and a second splayed direction wherein the separation between the outer ends 86 and 88 of the fork elements is greater than the separation of the vertical axes 94 and 96 at the base structure 14. The degree of movement of the fork elements between the parallel and splayed positions is controlled by stops (not shown) at the base structure 14.

[0050] Locking elements (not shown) provided for each fork element provide for locking the fork elements in either the parallel or splayed position.

[0051] To change the fork elements 82 and 84 from the parallel to the splayed position, the locking elements of the fork elements are unlocked. Each castor 90 and 92 is then manually rotated into an outward (or "toed out") facing direction as shown in Figure 6, and locked at a suitable angle. The assembly is then driven in a forward direction for a short distance which causes the fork elements to spread outwardly due to the tracking of the castors 90 and 92. Reversing the assembly with the castors still rotated in the outward direction forces the fork elements back into the parallel position.

[0052] Alternatively, locking the castors into an inward pointing direction and driving the assembly in reverse, will rotate the fork elements from the parallel position into the splayed position, and it follows that with the castors in this position, forward movement of the assembly will return the splayed fork elements to the parallel position.

[0053] Figure 8 illustrates an electronic block diagram of drive and control circuitry suitable to give effect to operation of the assembly illustrated in Figure 6.

[0054] In a preferred form, a handheld controller unit 111 incorporates discrete push buttons for the following operations: up, down, forward, back, left, right and an emergency stop.

[0055] Figure 9 is a perspective view of an alternative wheel structure which can be utilised with the assembly of Figure 6.

[0056] In this arrangement, separate control units 104, 105 and 106 are provided for the left wheel motor assembly and the right wheel motor assembly and for the lifter.

[0057] In preferred forms, the battery units may be switched 107 between series and parallel operation. In parallel operation, they drive the wheel assembly. In series operation, they drive the linear actuator of the lifter.

[0058] In this arrangement, ferrules 101 are mounted for rotation about the periphery 102 of a wheel 103. The rotation of the ferrules is about an axis in the plane of the wheel thereby assisting realignment of the wheel on various surfaces including dense carpet and the like.

[0059] With reference to Figure 10, there is illustrated a further preferred embodiment wherein like components are numbered as for the embodiment shown in Figure 6.

[0060] In this instance, the drive wheels 52, 54 are replaced with the alternative wheel structure of Figure 9. In addition, in a preferred form the lead wheels 90, 92 are also replaced with the alternative wheel structure of Figure 9. In preferred forms, the wheels are aligned such that their axes of rotation are normally aligned at 45 degrees to the longitudinal axis 98 of the assembly 10.In a more particular preferred form their axes intersect at a common intersection point 110.

[0061] In a further particular preferred form the drive wheels 52,54 are affixed to the trailing ends of the legs 82,84. In this instance the drive motors may be located within the legs 82,84.

[0062] Similarly the lead wheels 90, 92 may be driven wheels with their respective drive motors preferably located within the legs 82,84.

[0063] In a further particular form the wheels may be mounted in pairs at the leading and trailing edges of the legs 82,84.INDUSTRIAL APPLICABILITY

[0064] The construction of the disability aid assembly of the invention allows for simple and rapid disassembly of the components for packing into suitable luggage for transport. Thus as shown in Figure 7 the components of the assembly 10 when disassembled, comprise the base structure 14, the lifting arm 12 folded as shown, the two fork elements 82 and 84 and the hanger 48.

[0065] Careful choice of materials and components such as the electric motors, gear trains, wheels and castors etc. allows for an all up weight of around 20Kg making the device ideal for travel and use in hotel rooms for example.

Claims

1. A mobility aid assembly (10) for lifting and lowering a disabled user; said assembly including an articulated lifting arm (12) releasably mounted to a base structure (14) and a fork (16) extending from the base structure (14); said assembly (10) further including a hanger (48) suspended from the end of the lifting arm (12) for attachment of slings or seating for lifting a user; said articulated lifting arm (12) has a first portion (18) which is pivotally attached to a second or fixed, upright portion (20) of the lifting arm (12); said articulated lifting arm (12) being operable between a raised position and a lowered position by a linear actuator (22) which includes a first or outer end (24) pivotally connected to the first portion (18) and a second or lower end (28) having a first connecting element; and wherein said base structure (14) of the assembly comprises a hollow body (50) provided at each outer end with a drive wheel (52, 54); each drive wheel (52, 54) driven by a respective electric motor; wherein ferrules (101) are mounted for rotation about the periphery (102) of each wheel; wherein the rotation of the ferrules (101) is about an axis in the plane of the wheel thereby assisting realignment of the wheel on various surfaces including dense carpet and the like; characterized in that the linear actuator (22) is releasably mounted to the second or fixed, upright portion (20) at the second or lower end (28) via the first connecting element which in use is releasably connected to a complementary second connecting element provided on the second or fixed, upright portion (20) thereby providing a crush avoidance safety feature which prevents injury to the user if the linear actuator (22) moves the first portion (18) of the lifting arm (12) to an excessively lowered position in which the first portion (18) of the lifting arm (12) impinges on the user; wherein the crush avoidance safety feature involves the first connecting element disengaging from the complementary second connecting element when an upward force acting on the first portion (18) of the lifting arm (12) exceeds the combined weight of the first portion (18) of the lifting arm (12) and that of the linear actuator (22).

2. The assembly (10) of claim 1, wherein the first connecting element includes a mounting boss (30) having a transverse slot (32) whilst the complementary second connecting element is a transverse support pin (34), the transverse slot (32) slidingly engages with the transverse support pin (34) when the mobility aid assembly is in use for lifting and lowering the user.

3. The assembly (10) of either claim 1 or 2, wherein said each drive wheel (52, 54) is driven by a respective electric motor located within a respective electric motor module located within the hollow body (50).

4. The assembly (10) of claim 3, wherein said each respective electric motor module includes a gear train to reduce the RPM of the electric motor to a predetermined RPM of the drive wheel (52, 54).

5. The assembly (10) of any one of the preceding claims, wherein each electric motor is controllable for synchronized rotation of the wheels (52, 54) for forward and rearward movement of the assembly (10) and for contra-rotation of the wheels (52,54) for rotation of the assembly (10) about a vertical axis.

6. The assembly (10) of any one of the preceding claims, wherein the fork (16) comprises two fork elements (82, 84) extending from the base structure (14); each outer end (86, 88) of a fork element provided with a swivelling castor (90, 92); each castor (90, 92) provided with a locking system for locking the direction of movement of the castor (90, 92) at a desired angle relative to a horizontal centerline of the assembly (10).

7. The assembly (10) of claim 6, wherein each of the fork elements (82, 84) is releasably mounted to the base structure (14); each of the fork elements (82, 84) arranged for rotation about a respective vertical axis at the base structure (14); each fork element (82, 84) rotatable between a first direction parallel to the centerline of the assembly (10) and a second splayed direction wherein the separation between the outer ends (86, 88) of the fork elements (82, 84) is greater than the separation of the vertical axes at the base structure (14).

8. A method of assisting realignment of wheels of a mobility aid assembly (10); the mobility aid assembly (10) for lifting and lowering a disabled user; said assembly (10) including an articulated lifting arm (12) releasably mounted to a base structure (14) and a fork (16) extending from the base structure (14); said assembly (10) further including a hanger (48) suspended from the end of the lifting arm (12) for attachment of slings or seating for lifting a user; said articulated lifting arm (12) has a first portion (18) which is pivotally attached to a second or fixed, upright portion (20) of the lifting arm (12); said articulated lifting arm (12) being operable between a raised position and a lowered position by a linear actuator (22) which includes a first or outer end (24) pivotally connected to the first portion (18) and a second or lower end (28) having a first connecting element; characterized in that the linear actuator (22) is releasably mounted to the second or fixed, upright portion (20) at the second or lower end (28) via the first connecting element which in use is releasably connected to a complementary second connecting element provided on the second or fixed, upright portion (20) thereby providing a crush avoidance safety feature which prevents injury to the user if the linear actuator (22) moves the first portion (18) of the lifting arm (12) to an excessively lowered position in which the first portion (18) of the lifting arm (12) impinges on the user; wherein the crush avoidance safety feature involves the first connecting element disengaging from the complementary second connecting element when an upward force acting on the first portion (18) of the lifting arm (12) exceeds the combined weight of the first portion (18) of the lifting arm (12) and that of the linear actuator (22), and wherein said base structure (14) of the assembly comprises a hollow body (50) provided at each outer end with a drive wheel (52, 54); each drive wheel (52, 54) driven by a respective electric motor; said method comprising orienting ferrules (101) with respect to the drive wheels (52, 54) wherein ferrules (101) are mounted for rotation about the periphery (102) of each wheel; wherein the rotation of the ferrules (101) is about an axis in the plane of the wheel thereby assisting realignment of the wheel on various surfaces including dense carpet and the like.

9. A method of control of a mobility aid, said mobility aid including an articulated lifting arm (12) releasably mounted to a base structure (14) and a fork (16) extending from the base structure (14); said method comprising providing drive wheels (52, 54) at each outer end of the base structure (14) of the mobility aid whereby realignment of the wheels of the mobility aid is assisted by incorporation of ferrules (101) mounted for rotation about an axis that lies in the plane of the drive wheels (52, 54) and is tangential to the circumference of the wheels; characterized in that a linear actuator (22) operating a lifting arm (12) of the mobility aid is releasably mounted at a second or lower end (28) of the linear actuator (22) thereby providing a crush avoidance safety feature which prevents injury to the user if the linear actuator (22) moves a first portion (18) of the lifting arm (12) to an excessively lowered position in which the first portion (18) of the lifting arm (12) impinges on the user, and wherein a first connecting element disengages from a second connecting element when an upward force acting on the first portion (18) of the lifting arm (12) exceeds the combined weight of the first portion (18) of the lifting arm (12) and that of the linear actuator (22).

10. The method of either claim 8 or 9, wherein the first connecting element includes a mounting boss (30) having a transverse slot (32) whilst the second connecting element is a transverse support pin (34), the transverse slot (32) slidingly engages with the transverse support pin (34) when the mobility aid assembly is in use for lifting and lowering the user.

11. The method of any one of claims 8 to 10, wherein the drive wheels (52, 54) are driven by respective electric motors located within the base structure (14) of the mobility aid.

12. The method of any one of claims 8 to 11, wherein each electric motor is controllable for synchronized rotation of the wheels (52, 54) for forward and rearward movement of the assembly and for contra-rotation of the wheels (52, 54) for rotation of the assembly about a vertical axis.

13. The method of any one of claims 8 to 12, wherein the fork (16) comprises two fork elements (82, 84) extending from the base structure (14); each outer end (86, 88) of a fork element (82, 84) provided with a swivelling castor (90, 92); each castor (90, 92) provided with a locking system for locking the direction of movement of the castor (90, 92) at a desired angle relative to a horizontal centerline of the assembly.

14. The method of any one of claims 8 to 13, wherein each of the fork elements (82, 84) is releasably mounted to the base structure (14); each of the fork elements (82, 84) arranged for rotation about a respective vertical axis at the base structure (14); each fork element (82, 84) rotatable between a first direction parallel to the centerline of the assembly and a second splayed direction wherein the separation between the outer ends (86, 88) of the fork elements (82, 84) is greater than the separation of the vertical axes at the base structure (14).