GB2155887A - Invalid hoists - Google Patents

Abstract

An invalid hoist comprises a base structure 1 in the form of a mobile chassis, an upstanding column structure 2 supported on the chassis 1 and a lifting arm 8 which projects from the column 2. The arm 8 is fixed to a traveller 10 movable along the column 2 under the control of a lifting mechanism 12 incorporating a winch drum 18 on which is wound a flexible tape connected to the traveller 10. An operating handle 27 is mounted on a spindle 15 disposed coaxially of the drum 18. Turning the handle 27 in the raising direction turns the drum 18 to wind on the tape and thus raise the traveller 10, and on release of the handle 27 the drum is braked to retain the traveller in the raised position. Turning the handle 27 in the opposite lowering direction releases the braking action to allow the traveller to fall under gravity in a controlled manner. <IMAGE>

Description

SPECIFICATION Invalid hoists This invention relates to invalid hoists of the type comprising a base structure supporting an upstanding column structure, a lifting arm projecting from the column and moveable along a path guided thereby during lifting and lowering movement, and a lifting mechanism to effect the lifting movement.

Hoists are known with a hollow column from which the lifting arm projects, the arm being fixed to a traveller within the column and controlled by the lifting mechanism. Such known hoists employ a screw-and-nut lifting mechanism, with the screw thereof extending longitudinally of the column, or a chain-and-sprocket drive for the traveller within the column. In both cases the lifting mechanism suffers from wear and corrosion problems, particularly when used in humid conditions as in a hospital bathroom, and with a chain drive such corrosion can result in jamming of the chain within the column.

A hoist with a chain-and-sprocket drive can also be noisy in operation as a result of the moving chain engaging a chain guide which is normally fitted on the column. This noise is also a considerable disadvantage, particularly when the hoist is used in a hospital ward during the night.

The main object of the invention is to provide an invalid hoist with a lifting mechanism which overcomes the main disadvantages of the prior screwand-nut and chain-and-sprocket mechanisms. A further object is to provide such a hoist wherein the mechanism does not impose a direct downward drive to the traveller, and with which a "free fall" condition of the arm can occur in the event that operation of the mechanism in the lowering direction is continued if lowering movement of the arm is obstructed, for example by engagement with the rim of a bath tub.

According to one aspect of the invention a hoist of the foregoing type includes a lifting mechanism in the form of a winch mounted on the column and comprising a drum on which is mounted a flexible cord or tape connected to a traveller movable along a path guided by the column, and operating means by which the drum can be turned in one direction to wind on the cord or tape and thus raise the lifting arm and by which turning of the drum in the other direction can be controlled to pay out the cord or tape and thus effect lowering movement of the arm in a controller manner under gravity, the arrangement being such that with the operative means not operative to turn or control turning of the drum the latter is braked to hold the arm in a height-adjusted position.

According to another aspect of the invention of the hoist has a lifting mechanism in the form of a winch mounted at the top of the column and comprising a drum on which is wound a flexible lifting cord or tape coupled to a traveller to which the projecting lifting arm is fixed, the mechanism further comprising a rotatably mounted handle which can be turned in one direction to wind the tape on to the drum and in the opposite direction to pay out the tape to allow controlled lower movement of the arm under gravity, the lifting mechanism incorporating means which operate to prevent unwinding movement of the winch drum in the event that lowering movement of the arm under gravity is obstructed and the handle continues to be turned in said opposite or arm-lowering direction, whereby a free fall condition cannot occur when the obstruction is removed, and further means which brake the drum to hold the arm against lowering movement under gravity except when the operating handle is turned in said opposite direction.

Preferably the handle is mounted on a spindle disposed coaxially of the drum and it may have a screw-and-nut connection with said spindle so that relative movement of the handle in said one direction results in axial movement of the handle on the spindle which movement engages a friction clutch providing a drive connection through a first ratchet device operative only when the friction clutch is engaged and which then operates between the spindle and a housing of the mechanism so as to allow drum rotation in the raising direction and provide a brake action in the lowering direction.

The friction clutch may provide a drive connection through said first ratchet device and a second ratchet device disposed in series in the drive sense between the handle and the drum so that the tape is wound on to the drum when the handle is turned in said one direction when the first ratchet device free-wheels, with the second ratchet device comprising an input member fixed to the spindle and an output member fixed to the drum, to provide a drive when the handle is turned in said one direction to raise the arm of the hoist and a freewheeling condition in the event that the handle is turned in the opposite or lowering direction with the arm obstructed.Thus in this obstructed condition the second ratchet device free-wheels and the drum may be provided with frictional restraint sufficient to ensure that it remains stationary and hence the tape does not become slack so that a free-fall condition of the arm does not occur if the obstruction of the latter is removed.

The handle may be mounted on the spindle through a torque-limiting clutch or connection which limits the torque which can be applied to the drum in the lifting direction. This is a safety feature which prevents damage to the hoist when the arm reaches the upper end of its lifting range and which also prevents the application of an excessive lifting force should upward movement of the arm be obstructed.

Thus there is provided a lifting mechanism which does not apply a positive downward force to the arm during lowering movement and which can apply only a maximum lifting force thereto, thereby avoiding the possible dangers of continued turning of the operating handle if arm movement is obstructed in either direction which might otherwise result in the hoist being tipped over, obstructing equipment such as a bath being damaged or the mechanism being overloaded.

The lifting mechanism is preferably a sealed unit which bolts to the top of the column of the hoist and thus is not subject to corrosion in humid conditions such as apply in hospital bathrooms, for example. The sealing arrangements may include resilient annular seals, such as 0 rings, positioned between the ends of the drum and a housing of the mechanism in which the drum is rotatably supported. These seals may then engage the drum to provide said frictional restraint which prevents a free-fall condition resulting if downward movement of the arm is obstructed.

When using the preferred direct drive between the operating handle and the tape drum, so that the drum turns at the same speed as the handle, the end of the tape remote from the drum is preferably anchored with the tape looped around a pulley on the traveller. This provides a mechanical advantage which enables a reasonably sized drum to be employed in a compact lifting mechanism with an acceptable rate of lifting movement for a reasonable lifting force applied to the handle. The lifting tape wound on the drum is preferably a woven textile web, for example of nylon or polyester material.

The invention will now be further described with regard to the accompnaying drawings which illustrate by way of example, a preferred embodiment of invalid hoist in accordance with the invention. In the drawings: Figure 7 is a side view of the hoist; Figure 2 is a plan view thereof with a lifting mechanism and associated components removed; Figure 3 is a detail front view of an upper portion of the hoist; and Figure 4 is a cross-sectional view on the line iv-iv in Figure 3.

The hoist comprises a mobile U-shaped chassis 1 with an upstanding column 2 of general conventional form. Thus the chassis 1 has rectangularsection steel side members 3 with fixed axis front support wheels 4 and rear support castors 5. The side members 3 are inter-connected adjuacent the rear ends by a rectangular-section steel cross member 6 on which the column 2 is centrally mounted.The column 2 is slightly backwardly inclined and the side members 3 are connected to the cross members 6 through rectangular lateral stubs 7 which engage as a telescopic fit within the cross member 6 to allow for width adjustment of the chassis 1.A A lifting arm 8 projects forwardly from the column 2 over the chassis 1, this arm projecting through a slot 9 in the front side of the rectangular-section column 2 within which it is rig idly fixed to a wheeled traveller arrangement is well known and hence is not illustrated or described in detail.

For control of raising and lowering movement of the arm 8 the invention provides a lifting mechanism 12 in the form of a sealed unit with a housing 13 detachably secured to the upper end of the column 2 by bolts such as 14. A spindle 15 is rotata bly supported in the housing 13 by a front end ball bearing 16 and a rear ball bearing 17, this spindle having a reduced diameter end section 15a which projects generally horizontally from the rear side of the housing 13. A tape drum 18 is supported on the forward end of the spindle 15 so as to be rotatable thereon and a lifting tape 19 in the form of a woven nylon web is wound on to the drum 18. The tape 19 has end loops whereby the inner end of the tape is secured to the drum by means of a dowel 20 extending between the drum flanges 22 and 23 and the outer end is anchored by means of a dowel pin 24.The tape 19 is looped around a freely rotatable pulley 25 on the traveller 10 (see Figure 3) so that rotation of the drum in the clockwise direction as viewed from the rear of the hoist winds on the tape 19 to raise the lifting arm 8. Rotation of the drum 18 in the opposite direction pays out the tape 19 thus allowing the arm 8 to fall in a controlled manner under gravity.

A sleeve 26 mounted on the projecting end 15a of the spindle supports a two-armed operating handle or crank 27 which thus turns about the drum axis, the handle 27 being supported through a torque-limiting connection in the form of a crimped spring "tolerance" ring 28. This provides a connection which has a positive feel during normal hoist operation but which slips before an excessive lifting force can be applied through the tape 19 in the event that upward movement of the arm is obstructed or the traveller 10 reaches the upper end of its travel within the column 2.

The sleeve 26 has a screw-and-nut connection with the spindle section 15a through a screw thread at 29, a small degree of axial lost motion of the sleeve 26 being limited on the one hand by a thrust washer 30 fixed to the projecting end of the spindle by a screw 32 and, on the other hand, by a friction clutch brake and first ratchet device arrangement 33. A ratchet plate 34 rotatably mounted on the spindle 15 through a bearing bush 35 is disposed between the inner end of the sleeve 26 and a flange 36 on the spindle 15 with intervening friction discs 37 and 38. The ratchet disc 34 engages a fixed pawl 39 in the housing 13 which prevents rotation in the unwinding direction of the drum 18 and permits ratchet rotation in the winding direction thereof.

The drive between the spindle 15 and the drum 18 is provided by a second ratchet device 40 so that the two ratchet devices are disposed in series in the drive sense between the handle 27 and the drum 18. The ratchet device 40 comprises a hub 42 mounted on and secured to the spindle 15 by a dowel 43 and a pawl 44 fixed to the other and overhanging flange 23 of the drum 18. This ratchet device provides a positive drive between the spin dle 15 and the drum 18 in the raising direction, ie a direction which winds on the tape 19, but allows the drum 18 to free-wheel on the spindle 15 in the opposite direction.

The operation of the illustrated mechanism will now be described. Turning the handle 17 in the clockwise direction results in axial movement of the sleeve 26 along the screw thread 29 and towards the flange 36, thereby clamping the friction discs 37 and 38 to provide a direct drive from the handle 27 to the spindle 15 in the raising direction.

As will be appreciated the one-way ratchet device 34,39 prevents the spindle turning in the lowering direction unless the handle 27 is turned in the anticlockwise direction by the operator.

Turning the handle 27 in the anti-clockwise lowering direction produces initial axial movement of the sleeve 26 which frees the clutch discs 37 and 38, thus allowing the spindle 15 and drum 18 to turn in the direction to pay out the tape 19 with lowering movement of the arm 8 under gravity.

This movement is accomplished in a controlled manner corresponding to the same speed of drum rotation as that at which the handle 27 is turned because as soon as the drum 18 catches up with the handle 27 the clutch discs 37,38 lock up and the first ratchet device 36,39 becomes operative.

Thus the clutch/brake and first ratchet arrangement 33 ensure controlled lowering movement in response to turning of the handle 29.

The unit is sealed by an 0 ring 46 between the housing 13 and the drum flange 22, an 0 ring 47 between the housing 13 and the drum flange 23, an 0 ring between the housing 13 and the spindle flange 36 and a lip-type seal 49 between the housing 13 and the sleeve 26.

On release of the handle 27 the seal 49 applies sufficient frictional restraint to the sleeve 26 for the clutch/brake and ratchet arrangement 33 to be operative and thus hold the hoist arm 8 in any adjusted height position. The seals 46 and 47 apply sufficient frictional restraint to the drum 18 to prevent the latter turning if the handle 27 is turned in the lowering direction whilst lowering movement of the arm 8 is for any reason obstructed. Thus in such an obstructed arm conditon the spindle 15 turns freely with the handle 27 which now abuts the thrust washer 30 and the second ratchet device 42,44 free-wheels with the drum 18 stationary.

Hence the tape 19 remains taut and a free-fall condition does not result when the arm obstruction is removed.

Claims (14)

1. A hoist comprising a base structure supporting an upstanding column structure, a lifting arm projecting from the column and movable along a path guidable thereby during a lifting and lowering movement of the arm, wherein the hoist includes a lifting mechanism to effect the lifting movement in the form of a winch mounted on the column and comprising a drum on which is wound a flexible cord or tape connected to a traveller movable along a path guided by the column, and operating means by which the drum can be turned in one direction to wind on the cord or tape and thus raise the lifting arm and by which turning of the drum in the other direction can be controlled to pay out the cord or tape and thus effect lowering movement of the arm in a controlled manner under gravity, the arrangement being such that with the operating means not operative to turn or control turning of the drum the latter is braked to hold the arm in a height-adjusted position.

2. A hoist according to claim 1, wherein said operating means are manually actuated and comprise a rotataby mounted winding handle.

3. A hoist of the type set forther having a lifting mechanism in the form of a winch mounted at the top of the column and comprising a drum on which is wound a flexible lifting cord or tape coupled to a traveller to which the projecting lifting arm is fixed, the mechanism further comprising a rotatably mounted handle which can be turned in one direction to wind the tape on to the drum and in the opposite direction to pay out the tape to allow controlled lowering movement of the arm under gravity, the lifting mechanism incorporating means which operate to prevent unwinding movement of the winch drum in the event that lowering movement of the arm under gravity is obstructed and the handle continues to be turned in said opposite or arm-lowering direction, whereby a freefall condition cannot occur when the obstruction is removed, and further means which brake the drum to hold the arm against lowering movement under gravity except when the operating handle is turned in said opposite direction.

4. A hoist according to claim 2 or claim 3, wherein said handle is mounted on a spindle disposed coaxially of the drum.

5. A hoist according to claim 4, wherein said handle has a screw-and-nut connection with said spindle so that relative movement of the handle in said one direction results in axial movement of the handle on the spindle, which movement engages a friction clutch providing a drive connection between the handle and the drum through a first ratchet device only when the friction clutch is engaged with the ratchet device operating between the spindle and a housing of the mechanism so as to allow drum rotation in the raising direction and to provide a braking action in the lowering direction.

6. A hoist according to claim 5, wherein said friction clutch provides a drive connection through said first ratchet device and a second ratchet device disposed in series in the drive sense between the handle and the drum so that the tape is wound on to the drum when the handle is turned in said one direction when the first ratchet device freewheels, with the second ratchet device comprising an input member fixed to the spindle and an output member fixed to the drum, to provide a drive when the handle is turned in one direction to raise the arm of the hoist and a free-wheeling condition in the event that the handle is turned in the opposite or lowering direction with the arm obstructed.

7. A hoist according to claim 6, wherein said drum is provided with frictional restrain sufficient to ensure that it remains stationary and hence that the tape does not become slack in an obstructed condition of the arm when said second ratchet device free wheels.

8. A hoist according to any one of claims 4 to 7, wherein said handle is mounted on said spindle through a torque limiting clutch or connection which limits the torque which can be applied to the drum in the arm raising direction.

9. A hoist according to any one of the preceding claims, wherein said lifting mechanism is a sealed unit which is secured by bolts to the top of the column.

10. A hoist according to claim 9, wherein sealing arrangements include resilient annular seals such as '0' rings, which are positioned between the ends of the drum and a housing of the mechanism in which the drum is rotatably supported.

11. A hoist according to claims 7 and 10, wherein said resilient annular seals engage the drum to provide said frictional restraint thereof.

12. A hoist according to any one of the preceding claims, wherein one end of the tape remote from the drum is anchored and the tape is looped around a freely rotatable pulley on said traveller.

13. A hoist according to any one of the preceding claims, wherein the lifting tape which is wound on the drum is a woven textile web, for example of nylon or polyester material.

14. An invalid hoist constructed and arranged substantially as hereinbefore particularly described with reference to the accompanying drawings.