GB2162492A

GB2162492A - Spiral cam lift

Info

Publication number: GB2162492A
Application number: GB08418753A
Authority: GB
Inventors: Bernard Underwood
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-07-23
Filing date: 1984-07-23
Publication date: 1986-02-05
Also published as: GB2162492B; GB8418753D0

Abstract

The invention provides a lifting device comprising a plate rotatably driveable about an axis and comprising a spirally formed rib (7) extending across the surface of said plate, a bearing member (8) is associated with a lift member (11), said bearing member being adapted for rolling contact with a horizontal surface of said rib (7) whereby rotation of the plate (6) causes the bearing member (8), and hence the lifting member (11) to move upwardly or downwardly. This arrangement may be conveniently applied to invalids' chairs. <IMAGE>

Description

SPECIFICATION Spiral plate lift The present invention relates to a spiral plate lift.

There are many methods of lifting weights available to the Engineer. These include hydraulic jacks, screw jacks and worm drive lifting devices but these have the disadvantage that they are expensive to manufacture, have several moving parts and without periodic lubrication and maintenance are subject to a high friction and hence wear.

The present invention seeks to provide, therefore,a lifting device which will maintain its position even when all power is removed, which is cheap and simple to manufacture and can be relied upon to operate satisfactorily for long periods without maintenance and lubrication.

According to the present invention, therefore, there is provided in one aspect, a lifting device comprising a plate rotatably driveable about an axis and comprising a spirally formed rib extending across a surface of said plate, and a bearing associated with a lift member, said bearing member being adapted for rolling contact with the surface of said rib with an axis extending generally parallel to the said plate axis, the arrangement being such that rotation of the plate causes the bearing member and hence the lifting member, to move toward or away from the plate axis. It will be appreciated that if at a given point on the spiral plate a tangent is formed on the rib per se, and a tangent is also formed with a true circle passing through the same point, the angle 8 so formed will dictate the power required to move the bearing away from the plate axis under load.Thus, if the angle a is large, relatively more power will be required to drive the plate and force the bearing member to lift the lifting member. However, of course, such a movement would take place relatively quickly.

In the present invention, however, it is preferred that the angle 8 is relatively small so that a small motive power means, such as an electric motor, can be provided to lift large weights. To this end a small electric motor may be operatively connected to the plate via a gear box, the power of the motor and the reduction of the gear box being suitably matched to the speed and intended load.

In one preferred embodiment the plate may be provided with ribs on both sides of the plate, said ribs being provided in mirror image. Two bearing members are then provided, one to ride in each rib section, said bearing members being preferably conjoined by a Ushape lifting member. This increases the strength of the assembly and also prevents unwanted lateral movement of the bearing member relative to the plate.

In an alternative, the plate may be provided on one surface with the ribbed arrangement as hereinbefore described, and on the other side with a plane surface. A U-shape lifting member as just described is also provided, but instead of the bearing on the planar surface rotating on an axis parallel to the axis of the plate, it rotates perpendicularly, whereby the bearing member rolls in contact with the plane surface thereby ensuring that the bearing member riding in the rib spiral cannot actually displace.

In order to provide a generally fail-safe device it is generally desirable that the moment applied to the bearing member acts along a line which also passes through the axis of the plate. Thus, in a particularly preferred embodiment where the device is set in the generally vertical direction, the bearing should be as near as possible to a line extending vertically through the axis of the plate.

Where the lift is direct, i.e. where the object to be lifted for example is positioned immediately above the lifting device, the bearing may be positioned without difficulty along said vertical line. However, because of the excellent mechanical advantage to be gained from the present device it is often desirable to pivot the lifting member towards one end thereof eccentrically. Accordingly, the axis of the bearing member will describe an arc dependent upon the relative distances between the pivot of the lifting member and the position of the bearing member relative thereto. In such circumstances the arc described by the bearing member should be as near to the common line as possible.

It will be appreciated that where the angle O is comparatively small and where the bearing member is in contact with the spiral plate in a position between the axis thereof and the point of lift, failure of the motor would merely serve to lock the device in a position which it has reached immediately before the failure. Of course, where the angle 8 is large this will not happen and the device will gradually return to its lowest point, or load the gear chain between the plate and the source of motive power.

This spiral plate lifting device is particularly suited to low power uses such as domestic use. For a domestic use, of course, it is desirable that devices should be cheap, safe to use, and free of the possibility of lubricant leaks. Thus, the spiral lifting plate according to the present invention is particularly suited to use in chairs which assist the semi-disabled to stand up and/or sit down comfortably.

Such chairs are well known and generally comprise a chair frame made up in the form of an easy chair; said frame being pivotable about a forward axis and being driven by a suitable motor means from an at rest position to an operative position in which the disabled person may readily stand up. Generally these chairs are operated by an electric motor and a control device is provided which causes the electric motor to rotate in the desired direction of rotation. Thus, the semi-disabled person may rest in the chair while it moves from its operative to its at rest position and vice versa.

Various drives have been utilised to achieve this end; worm drives among them. According, therefore, to a second feature of the present invention there is provided an invalid's chair pivotable between a normal sitting position and an operative position, and driven by an electric motor and a lifting gear assembly, characterised in that the lifting gear is a spiral plate lifting device as just described.

If the angle 8 as hereinbefore described is comparatively small, as stated above, the device may be stopped at, and will remain at, any predetermined position between the said sitting and operative positions. Thus, by use of the present invention a chair may be positioned in any desired position within the range available for any desired length of time without the possibility of the mechanism re-adjusting itself gently to the normal sitting position.

One aspect of the invention will now be described by way of illustration only with reference to the accompany drawings wherein Fig. 1 shows in diagrammatic form a lifting device in accordance with the present invention, and Fig. 2 shows in side elevation and in diagrammatic form, the lifting device applied to a chair frame.

The lifting device of the present invention is provided with a base plate or frame (1) extending generally horizontally across a surface on which the device is to be supported.

Upstanding from the base plate (1) is a plate support (2) terminating in its uppermost end with a main support bearing (3).

The base plate (1) also supports a pivot post (5) extending upwardly from the base plate (1) and terminating at a position substantially above the top of the support (2).

A steel plate (6) of a generally circular configuration is provided on its one face with a spiral rib (7) extending from the outermost periphery of the plate (6) to a position immediately adjacent the bearing (3). The bearing (3) supports the plate (6) for rotation about a main axis.

A motor (4) provided with a suitable gear box is provided adjacent the spiral plate, the main drive from the gear by also passing through the bearing (3) and being so fixed, as by a flange, to the remote face of the plate (6) as to drive the same at a predetermined speed.

A bearing member (8) is journalled for rotation to an angle bracket affixed to an arm (9) which extends generally across the plate (6). The arm (9) is pivoted at its one end to pivot (10) which is supported on the post (5).

The pivot (10) is set at a convenient point on the post (5) such that the arc described by the axis of the bearing (8) is as near to a vertical line extending upwardly through the support (2) as possible. The remote end (11) of the arm (9) operatively connects with the device to be lifted.

In operation, rotation of the plate (6) in a clockwise direction as shown in Fig. 1 causes the bearing member (8) and hence the end (11) of arm (9) to move downwardly to a point where the bearing (8) is adjacent the bearing (3), at which point a limit switch may be interposed to cut off the motor. Similarly rotation in the anti-clockwise direction will have the opposite effect. Again a limit switch may be positioned near the periphery of the plate (6) at a suitable position within the ribbed members to stop the rotation of the plate at a suitable point.

The ribs (7) may be formed merely by welding onto the plate (6). However, in a preferred form the plate (6) is cast with the ribs already in situ.

With reference to Fig. 2 a chair frame (12) is provided in standard form. The chair frame comprises a pair of generally parallel trapezoidal members held in spaced relation-ship by crossbeams in accordance with general procedure. A pivotable frame (13) is pivoted towards the right hand side of the Fig. 2 and comprises members extending generally parallel to the horizontal members of the frame (12) and terminating in an upstanding seat back (14) angled thereto. It will be appreciated that the member (13) is pivotable about the forward end thereof through an arc. The lifting device as just described in Fig. 1 is position below the frame (12); the post (5) having been displaced by the frame (12). The cross member between the trapezoidal sections of the frame (12) supports the pivot (10) to which the arm (9) is attached.The end (11) of the arm (9) is attached to the end of the frame remote from the pivots at a point (15).

It will be appreciated that rotation of the plate (6) in Fig. 1 in the anticlockwise direction will drive the member (13) through an upward arc and subsequent rotation in the clockwise direction will have the opposite effect.

This device as described with reference to Fig. 2 was compared with an equivalent worm drive arranged according to the prior art. It was found that whereas the device in accordance with the present invention could move the heaviest individual through the arc described by the member (13) utilising a one twelfth horsepower electric motor to deliver 65 Ib/ins, the same motor and gear box when applied to a worm drive, which of course is more expensive to produce, caused the motor to labour and undoubtedly repeated use would have caused the motor to fail.

Accordingly, the present invention relates to a lifting device comprising a spiral plate lifting arrangement and to the arrangement when applied to an invalid's chair. The invention also embraces a method of imparting a lifting force which comprises moving a bearing member up a spiral path.

The spiral plate device has been described as operating generally vertically as a lifting device. It will be appreciated that it can operate at any angle, for example horizontally, because the bearing member can ride on the "underside" of the ribs and hence drive the arm in both directions. Thus, the device can be used to control the opening and shutting of large doors etc.

Claims

1. A lifting device comprising a plate rotatably driveable about an axis and comprising a spirally formed rib extending across a surface of said plate, and a bearing member associated with said lift member, said bearing member being adapted for rolling contact with said surface of said rib with an axis extending generally parallel to said plate axis, the arrangement being such that the rotation of the plate causes the bearing member and hence the lifting member to move toward or away from the plate axis.

2. A device according to Claim 1 wherein the plate is formed with ribs on each side thereof, and wherein a second bearing member is applied to the second set of so formed ribs.

3. A device according to Claim 2 wherein the bearing members are conjoined in a Ushaped configuration.

4. A device according to Claim 1 wherein an additional bearing member is provided, said bearing member being adapted to rotate perpendicularly against a plane surface of the plate.

5. A device according to any preceeding Claim wherein the axis of the bearing member describes an arc during the lifting sequence.

6. A lifting device substantially as hereinbefore set forth with reference to, and/or as illustrated in, the accompanying drawings.

7. An invalid's chair comprising an upholstered seat, said seat at least being driven upwardly or downwardly by a lifting device in accordance with any one of Claims 1 to 6.