GB2127981A

GB2127981A - Invalid hoists

Info

Publication number: GB2127981A
Application number: GB08325364A
Authority: GB
Inventors: David Richard James
Original assignee: James Industries Ltd
Current assignee: James Industries Ltd
Priority date: 1982-09-29
Filing date: 1983-09-22
Publication date: 1984-04-18
Also published as: GB2127981B; NO833497L; JPS59131352A; FR2533436A1; SE8305184D0; NL8303255A; FR2533436B1; GB8325364D0; AU558720B2; DE3335404A1; DK440683A; DK440683D0; SE8305184L; AU1927083A; CH654198A5; JPS6136939B2

Abstract

An invalid hoist with a weighing facility comprises a mobile chassis (1) on which is an upright support column (2) is mounted. A lifting arm (3) projects from the column (2) and supports a patient support member (4) fixed at the outer end of the arm (3). Manual lifting mechanism within the column (2) is operable to raise or lower the arm (3) along a rectilinear path. The arm (3) comprises a short inner end stub portion (7), adjacent the column (2), and an outer end portion (8) to which the support member (4) is attached. A strain gauge load cell (9) is let into the arm (3) and is flange-bolted to the arm portions (7) and (8). Associated electronic detecting and indicating circuitry (U) mounted on the column (2) and connected to the strain gauge arrangement of the load cell (9) provides an indication of the weight of a patient when supported on the patient support member 4. <IMAGE>

Description

SPECIFICATION Invalid hoists This invention relates to invalid hoists as used in hospitals and elsewhere for the lifting of invalids and disabled persons generally.

There is an increasing requirement for invalid hoists to provide a weighing facility, as an alternative to a central weighing machine or providing a large number of weighing machines in hospital wards and bathrooms, for example. A hoist with a weighing facility, hereinafter referred to as "weighing hoist" thus has obvious advantages as it enables a patient to be weighed at the bedside or in the bathroom when already undressed, for example.

Several forms of hoists on which patients can be weighed are already known, but they all suffer from various disadvantages and in general can be considered as invalid hoists adapted to turn the hoists into patient weighing machines rather than hoists with a weighing facility. It is known to suspend a patient from the lifting arm of a hoist through a detachable weighing unit, but this has the disadvantage that the weighing unit has to be attached and detached when not in use (and may not be available when required) and only sling suspension of the patient can be employed. With such a weighing unit it is also difficult to achieve satisfactory accuracy.

Hoists adapted as weighing machines are known in which a weighing mechanism is built into the lifting arm adjacent a column of the hoist, but the weighing mechanism employs a parallelogram linkage arrangement with associated problems of pivot friction and wear, which particularly affects long term accuracy, and the mechanism is essentially sensitive to bending moments in the arm.

Thus the positioning of the patient being weighed with respect to the arm is important. Furthermore, the prior arrangements are not able to weigh a patient while seated on a support in the form of a so-called "bathing chair".

The object of the invention is to provide a weighing hoistwhich overcomes the foregoing disadvantages and which, moreover, can be designed so that different types of patient support means and/or different arm configurations can be used with the same basic hoist construction.

According to the invention an invalid hoist with a weighing facility comprises an upstanding support structure, a rigid cantilever lifting arm projecting from the support structure and supporting or adapted to support a patient support member at the outer end of the arm remote from the support structure, lifting mechanism operative to raise or lower the arm along a rectilinear path, a load cell which embodies a strain gauge or displacement transducer arrangement and which is let into the arm at an intermediate position therealong and arranged so as to be responsive to shear stresses in the arm resulting from weight loading thereof, and associated electronic detecting and indicating circuitry to provide an indication of the weight of a patient supported on or in the patient support member.

Preferably the support structure comprises an upright support column supported on a mobile chassis.

The load cell is preferably fitted into the arm adjacent the support structure, and the electronic circuitry if mounted on the arm is preferably disposed between the load cell and the support structure so that operation of the controls of the circuit does not affect the loading of the outer end of the arm and hence does not affect the signal obtained from the load cell. The load cell is preferably flange bolted between a short stub projecting from the support structure, providing an inner end portion of the arm, and a longer outer arm portion which supports the patient support member.

Such a flanged fitting of the load cell has several advantages. Firstly, the outer end portion of the arm can readily be changed for one of a different type but similar flange fixing, for example an arm which supports the patient on a legless bathing chair can be changed for one which suspends the patient in slings; secondly, the load cell can readily be changed for maintenance or repair purposes, and thirdly, a basic hosit can initially be supplied without the weighing facility and the purchaser has the opportunity of introducing this later purchase of a load cell. In the iatter case a different outer arm portion may initially be fitted, which is of increased length to compensate for the missing load cell, or the arm may be identical with the load cell replaced by a spacer block.

The load cell is preferably a metal block with a symmetrical lateral cut-out which leaves upper and lower webs interconnecting the two arm portions and which flex, under the shear loading of the arm, in the manner of a pivotless parallelogram. The deflection of this parallelogram may be sensed by a central limb of the load cell which extends across the cut-out therein, on the neutral axis of the arm, and to which strain gauges are attached. The strain gauge and circuit arrangements may be of known conventional form, desirably such as to provide a rapid response and good long-term stability with a reliable weighing accuracy of at least 0.045 kgm (0.10 Ibs).

The invention will now be further described with reference to the accompanying drawings which illustrate, diagrammatically and by way of example, a weighing hoist in accordance with the invention and a modification thereof.

In the drawings: Figure lisa side view of the hoist; Figure 2 is a detail thereof to a larger scale; Figure 3 is a corresponding partial plan view; Figure 4shows the modification in a similar plan view.

The hoist as shown in Figure 1 comprises a mobile chassis 1 with four corner castors la, an upstanding lifting column 2 mounted centrally at the rear of chassis 1, a lifting arm 3 projecting from the column 2, and a patient support member 4 of stretcher form fixed at the outer end of the arm 3. The column 2 is of telescopic type with a lower portion 5 fixed to the chassis 1 and an upper portion 6at the upper end of which the arm 3 is fixed. Manual lifting mechanism (not shown) within the column 2 has a winding handle which can be turend to extend or contract the column and thus raise or lower the arm 3 along a rectilinear path.

The arm 3 comprises a short inner end stub portion 7 which is secured to the column portion 6 and an outer end portion 8 to which the support member 4 is attached. A strain gauge load cell 9 is let into the arm 3, being flange bolted to the arm portions 7 and 8. As shown in the detail view of Figure 2, the load cell 9 is secured between flanges 10 and 11, respectively, on the arm protions 7 and 8.

The arm portion 7 consists of a plate 7a welded to the upper column portion 6 and to which the flange 10, also in the form of a plate, is secured by bolts 12 after the flange plate 10 has been secured to the load cell 9 by counter-sunk bolts 1 2a. The outer arm portion 8 is fixed to the outer side of the load cell 9 by bolts 13.

The load cell, which is illustrated in Figure 2 with a side cover removed, is of type specially developed so as to be sensitive to shear stress in the lifting arm but substantially insensitive to bending moments in the arm. The result is that the weighing device is effectively responsive only to the vertical weight loading of the arm, and hence the type of patient support member, and the positioning of the patient thereon, is relatively unimportant and does not affect the accuracy of weighing. The load cell 9 is a metal block with a machined lateral cut-out 14 which leaves thin upper and lower webs, 15 and 16 respectively, through which the arm portions 7 and 8 are interconnected. These webs flex under load so that the cut-out central portion of the block in effect acts as pivotless parallelogram.Athin central limb 17, which extends across the cut-out 14 on the neutral axis of the load cell 9, has a conventional strain gauged arrangement 18 cemented on the side thereof. The inner and outer portions 9a and 9b of the load cell block, on either side of the cut-out 14, are of adequate thickness so that tightening of the bolts 12a and 13 does not distort the block and affect the weighing accuracy.

An electronic unit control and digital indicating unit U, empioying detecting and indicating circuitry of conventional form, is mounted on the column 2 and connected to the strain guages 18 and fixed at a suitable position adjacent the arm 3 on the column portion 6. This unit U is self-contained with internal batteries and embodies an ON/OFF switch and various controls, such as a zeroing control to adjust zero without the patient on the support member 4, and as operation of the switch and controls does not load the outer end portion 8 of the arm 3 it does not affect the signals obtained from the load cell 9. The control unit embodies a timing circuit which is operative to switch off power to the strain guages after a pre-set interval when a steady weight-indicating reading has been obtained, thereby conserving battery power and thus prolonging battery life.

The hoist of Figures 1 to 3 has a short overall length of arm 3 with the stretcher support member 4 fixed at the end of arm 3. The stretcher frame is supported cantilever fashion on two down tubes 19 which are cranked in side view, as shown in Figure 1 and branching outwardly to provide an A-frame configuration in front view (not shown). Figure 4 shows for example how the arm portion 8 of Figures 1 to 3 can be replaced by a longer outer arm portion 20 having an attachment flange 21 identical in the fixing sense to the flange 11. Thus the same fixing screws 21 can be used and the arm portion 20, only an inner end section of which is shown in Figure 4, can be of any desired type.Thus, it can be designed to carry a patient support member in the form of a legless bathing chair, or have attachment means for patient support slings or for the sling support of a stretcher frame, these being known patient support arrangements which are employed with non-weighing hoists.

The basic hoist structure of Figure 4 is also different in respect of the lifting mechanism, the column 22 in this case being non-telescopic. Instead a carriage (not shown) movable along the hollow rectangular column 22 has the short inner end arm portion attached to it so as to project through a longitudinal slot 24 in the front side face of the column 22. This arm portion 23 has a flange 25, identical to the flange plate 10, for fixing to the load call 9. Thus in this case also the arm 3 undergoes rectilinear translating movement during raising and lowering of the arm.

The special form of the load cell 9 and its arrangement in the arm 3, as a result of which the cell is sensitive only to the shear stress in the arm and is substantially independent of bending moments therein, enables an outer arm portion 20 of any desired length and any patient support arrangement to be used. It will, of course, be appreciated that for stability the actual arm and support arrangments must always be suited to the configuration of the chassis 1,so that the suspended weight acts within the supported area defined by the castors 18.

Claims

1. An invalid hoist with a weighing facility comprising an upstanding support structure, a rigid cantilever lifting arm projecting from the support structure and supporting or adapted to support a patient support member at the outer end of the arm remote from the support structure, a lifting mechanism operative to raise or lower the arm, along a rectilinear path, a load cell which embodies a strain gauge or displacement transducer arrangement let into the arm at an intermediate position therealong and aranged so as to be repsonsive to shear stresses in the arm resulting from weight loading thereof, and associated electronic detecting and indicating circuitry operative to provide an indication of the weight of a patient supported on the patient support member.

2. An invalid hoist according to claim 1, wherein the support structure comprises an upright column supported on a mobile chassis.

3. An invalid hoist according to claim 1 or claim 2, wherein the electronic circuitry is mounted on the support structure or on the arm between the support structure and the load cell.

4. An invalid hoist according to any one of the preceding claims, wherein the load cell is fitted into the arm adjacent the support structure.

5. An invalid hoist according to claim 4, wherein the load cell is flange bolted between a short stub projecting from the support structure, which stub provides an inner end portion of the arm, and a longer outer arm portion which supports the patient support member.

6. An invalid hoist according to any one of the preceding claims, wherein the load cell is a rectangular metal block with a symmetrical lateral cut-out leaving upper and lower webs which interconnect portions of the arm between which the load cell is disposed and which flex under the shear loading of the arm in the manner of a pivotless parallelogram.

7. An invalid hoist according to claim 6, the load cell has a central limb which extends across the cut-out therein and which is disposed on the neutral axis of the arm, and said load cell embodies a strain gauge arrangement with strain gauges thereof attached to said central limb to sense the deflection of said parallelogram.

8. An invalid hoistwith a weighing facility, substantially as herein particularly described with reference to Figures 1 to 3, or Figure 4, of the accompanying drawings.