GB2185068A - Releasable fastening - Google Patents

Abstract

A releasable fastening device for engaging or releasing a movable member 3 has a first member 10 for actuating the fastening and a second member 13 for limiting the movement of the movable member 3. A resilent means 27 is arranged between the two members 10 and 13 such that on actuation of the first member 10 to a new position, the second member 13 will take up a new position corresponding to the new position of the first member 10 when there is no external force acting on the second member 13. In an alternative embodiment, the first member takes the form of a pivoted lever 29 and includes a spring-loaded plunger 33 urged against a slot 34 formed on member 10. <IMAGE>

Description

SPECIFICATION Releasable fastening This invention relatesto releasable fastenings, and particularly to mechanisms incorporating means for engaging or releasing a movable member in circum- stances where the said member might be atone end ofitsrangeoftravelatwhich it pushes againstthe mechanism, making the operation ofthefastening rather difficult.

It is frequently the casethatsuch engaging or re- leasing involves the sliding ofatleastpartofone member in contact with another, and i n these circu mstances, if the members are atthe limitoftheirre- lative movement and there is a strong force being applied across the joint, then a considerable amount offriction has to be overcome before the members referred to can be moved. This can be alleviated by ) the use of lubricants or special materials, but where the cost of equipment incorporating such a joint has to be kept as low as possible and regular maintenance is unlikely, the problem needs to be overcome by other methods.One example of this problem is in hip guidance orthoses, where the wearer requires the hipjointto be rotatable firstly, when walking, over a limited range corresponding to the swing of his leg, and secondlyforthe leg to berotatablefor- wards by 900 or so when he wishes to sit down. It is easy to incorporate into the joint mechanism a sliding member which contains a stepped portion which in one position limits the forward rotation of the leg support member, but usually atthetimethe patient wishes to operate this to enable him to sit down,the leg member is being strongly urged forwardly against the stop.Wearers of such devices arefrequently not sufficiently strong to overcome the frictional forces which act in these circumstances, and the alternative, of supporting their body in a nearupright position whilst at the same time releasing both hip joints, is clearly in many cases ratherhazardous.

This invention consists of a releasable fastening comprising afirstmemberforactuatingthefasten- ing, a second member for limiting the movement of the device to be controlled by the fastening, resilient meansfixedtothefirstmemberandarrangedto urge the second member towards a position corresponding to the position ofthefirst memberand means for retaining the said first member in the desired position; whereby in the absence ofanycon- straintthe said two members will maintain a corresponding relationship but if the second member has been preventedfromfollowingthefirstmember by an external force or object, then the second member will take up the position corresponding to the new position of the first member as soon as the said force or object is removed.

The resilient means may interconnectthesaidtwo memberswhereby in the absence ofany constraint the said members will move together as a single rigid body which configuration will be resumed on the removal of any external force or object which has prevented the second member from following the first member.

The resilient means may conveniently comprise a coil spring whose distortion onn relative movement ofthe said two members creates a force urgingthe two members back into their original relationship.

Alternatively, the first member may take the form of a pivoted lever including a spring-loaded plunger urged against the second member,the position of the first member controlling the direction in which the plunger acts againstthesecond member. The lever may act as an over-centre mechanism so that it remains in the position in which it has been set whether or not the second member has been able to move undertheaction of the spring.

By way of example, the invention will now be des cribed and compared with a prior art equivalent with reference to the drawings, of which Figure 1 is a side elevation of part of a hip guidance orthosis including the left hip joint and the upperand lower orthosis members pivotally attached by said joint, Figure 2 is a section along the line Il-Il of Figure1, Figures3and 4are sections along the line Ill-Ill of Figure 2 illustrating respectively a prior art mechanism and a mechanism incorporating the present invention, and Figure5is a section, similarto Figure 3 but along a line having a position indicated by V-V on Figure 2, of an alternative embodiment ofthe invention.

With reference to Figures 1 and 2, an upper member 1 containing a recessforthe rigid attachment of the back rest and torso supports of a hip guidance orthosis is pivoted about an axis 2 to a lower member 3 to which a supportforthe left leg ofthe wearercan be rigidlyfixed.Theaxis2 is defined bya bolt4 passing through a hole in the upper member 1 into a threaded hole Sin a cover 6 on the outer side of the upper member,the lower member3being rotatable aboutthe bolt 4 in bearings 7 and 8.

Sothatthewearercan switch the hip joint from onemodetoanother,vizfromawalking mode in which the range of forward swing of the lower member 3 relative to the upper member 1 is limited, to a sitting mode in which the lower member can rotate forwards by up to 900 or so, there is provided a sliding switch 9, the position of which when in the sitting mode being indicated by dashed lines 9a.

The operation of the switch is more easily seen with reference to Figure 2 in conjunction with Figure 3, which illustrates a conventional arrangement.

The switch 9 consists of a plate 10 supporting a handle and is slidable along the top surface ofthe cover 6, being guided bythe engagement of a lip 11 against a step 12 in the upper member 1. The plate 10 is rigidly attached to a stop member 13 bytheengagementof a threaded bolt 14 in one oftwothreaded holes in the plate 10 (the other hole being used in the right hand switch), and the limits of sliding move mentoftheswitch are governed by the travel ofthe bolt 14 with i n a cavity 1 formed between the upper member 1 and the cover 6, and two studs 16 and 17 formed between the upper member 1 which also en close shafts for bolts 1 8 and 1 9 by means of which the cover6 is fastened to the upper member.A positive location ofthe switch at both limits oftravel is obtained by the engagement of a spring-loaded ball bearing 20 housed within the cover 6 with one oftwo dimples formed in the lower surface of the plate 10.

The stop member 13 includes a tapered portion 21 adjacent to a thicker portion 22, and is thus adapted to act as a limit to the relative rotation of the lower member3aboutthe bolt4bytheabutmentofthe stop member against eitheroftwo spigots 23 and 24 adjustably locked in threaded bores 25 and 26 formed in the lower member3. The lower member3 is shown in Figure 3 in an intermediate position, but with the switch 9 in the walking mode, and it can be seen that rotation of the lower member 3 is possible only between the positions corresponding to the positions of spigots shown by the dashed lines 23a and 24a in Figure 3.However, when the switch 9 is in the sitting mode (shown as 9a in Figure 3), the spigot 24 no longer engages with the thicker portion 22 of the stop member and the leg of the wearer is there fore free to rotate forwards.

The drawback with this, conventional, type of switch is that the wearerwill usually wish to engage the switch intothe sitting modewhen he is leaning forward, urging the spigot 24 hard against the portion 22 of the stop member. The force needed to overcomethefriction thus created causes problems for disabled people who need to support themselves atthe same time as they engage both the left and right switches.

This problem is overcome by a modification to the switch which is the subject of the present invention and is illustrated in Figure 4.

The construction ofthe orthosis is essentially the same as the conventional type described above - and the same references have been applied to Figure 4 wherethereis nochange-withthemajorchange thatthe bolt 14 is replaced pyx coil spring 27 screwed and glued into threaded holes in the plate 10 and the stop member 13 so thatthe said plate and member are no longer rigidly fixed to one another.

Thus, if the switch 9 is moved to the sitting mode with the wearer ofthe orthosis causing the spigot 24 to press hard against the stop member, the switch will initiallytake up the position illustrated in Figure 4, in which the original position ofthe plate 10 is shown by dashed lines 1 Oa and ofthe coil spring by dashed lines 27a.

In the position illustrated, the positive engage mentofthe ball bearing 20 (see Figure 2) in the plate 10 prevents the free return of the plate to its original position, but as soon as the wearer has, at his leisure, engaged both left and right hand switches, he is free to support or straighten himself whereupon the pres sure exerted onthestop member 13 by the spigot 24 is removed and the stop member moves underthe action of the spring 27 to the position shown by dashed lines 13b, ieinwhichtheswitch isfullyinthe sitting mode. In this mode, the position of the spring 27 is indicated by the dashed lines 27b.

When getting up from the sitting position in order to stand, wearer can pull the switch back into the standing mode, even though the spigot 24 is rearward ofthetapered portion 21,forexample in the position illustrated by dashed lines in Figure4.

Whereas in the conventional design the portions 21 and 22 would have prevented the free return of the spigot 24, by use of the present invention the spigot, on rotation ofthe lower member3, pushes the stop memberl3forwardsbyengagementwiththetap- ered portion 21 until the spigot reaches the position shown by dashed lines 24a in Figure 3, whereupon the stop member is sprung backto its standing mode position, limiting thereafter the rotation ofthe lower member 3 as described above.

One further refinement of the conventional embodiment is the addition, illustrated in Figure 4, of a spring loaded ball bearing 28which urges against the rear face of the switch 9 to reduce the ease of inadvertent lifting ofthe plate 10 out of its seating.

Such lifting is possible with the introduction of the present invention since the plate 10 is no longer rigidly engaged with the step 12 by its rigid fixing to the stop member 13.

In the alternative embodiment illustrated in Figure 5, the construction is similar to that shown in Figure3 exceptthatthe plate 10 is not directly fixed to a handle and includes a slot 34 in its upper surface. The switch is operated by a lever29 pivoted about a stud 30. The lever includes an axial bore 31 in its lower section which serves as a guide for a spring 32 and plunger33. The plunger is arranged to urge against one or other end of the slot 34, depending on the position oftheswitch, andthusgives a biastotheloca- tion of the plate 10. Because of the location of the stud 30 above the slot 34, the lever operates as an over-centre mechanism so that the switch will remain in its set position whatever the location ofthe plate 10.

In the position illustrated in Figure 5, the orthosis is in the walking mode, ie one in which the lower member 3 is prevented from free rotation by the abutment of the spigot 24 against the thick portion 22 of the stop member 13. The lever 29 however has been moved intothe position in which the plunger33 urges the plate 10 into the position (not shown) in which the lower member 3 is free to rotate but only when the pressure exerted by the spigot 24 on the stop member 13 is released will the plate 10 move.

Similarly, if the lever 29 is in the position shown by dashed lines 29a,the switch will be urged into, or remain in,thewalking mode.

Although described in connection with a clinical orthosis, itwill be obvious to those skilled in the art that the invention can be used in many other applications, especially where it is not convenient or possible to releasetheforces acting on a mechanical switch before the switch is actuated. The invention may, moreover, be applied to rotary as well as to sliding switches.

Claims (8)

1. A releasable fastening device comprising a firstmemberforactuatingthefastening,asecond member for limiting the movement ofa device to be controlled bythefastening, a second memberfor limiting the movement ofthe mechanism to be controlled by the fastening, resilient means fixed to the first member and arranged to urge the second member towards a position corresponding to the position ofthefirstmemberand meansforretaining the said first member in the desired position; whereby in the absence of any constraint the said two members will maintain a corresponding relationship but if the second member has been prevented from following the first member byan external force or object, then the second memberwill take up the position corresponding to the new position of the first member as soon astheforceorobject is removed.

2. A releasable fastening device according to claim 1 in which the resilient means interconnectthe twomemberswherebyintheabsenceofanycon- straintsthe members will move together as a single rigid body which configuration will be resumed on the removal of any external force or object which has prevented the second member from following the first member.

3. A releasable fastening device according to Claim 2 in which the resilient means is a coil spring whose distortion on relative movement of the first and second members creates a force urging the two members back into their original relationship.

4. A releasable fastening device according to claims 1, 2 or 3 in which the first member is provided with a spring loaded ball bearing to prevent the memberfrom lifting out of its seating.

5. A releasable fastening device according to claim 1 in which the first membertakestheform of a pivoted lever including a spring-loaded plunger urged against the second member.

6. A releasable fastening device according to claim Sin which the lever acts as an over-centre mechanism sothatthe level remainsinthe position in which it has been set whether or notthesecond member has been able to move-under the action of the spring.

7. Areleasablefastening device according to any one of the preceding claims in which the mechanism is a hip guidance orthosis.

8. A releasable fastening device substantially as described herein with reference to Figures 1 to 3 or to Figure 4 or to Figure 5.