|
(11) | EP 0 192 475 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
|
|
|
|
|||||||||||||||||||||||||||
| (54) | Automatic closing activator |
| (57) @ A temperature actuated traction device comprises an element (30) of a heat responsive
memory material, to respective ends of which are connected two relatively movable
parts (13, 16). One part (13) is connected to a load which is to be displaced relatively
to the other part (16) to cause a change in shape of the ductile element (30) when
cold. Heating means is provided to cause heating of the element (30) to restore it
to its original shape whereby a restoring force is applied to the displaced load,
and a spring (20) is provided to allow yielding of the other part (16) under traction
applied to the load when the element (30) is hot. |
[0001] THIS INVENTION is concerned with a traction device of elongated form which is cheap to manufacture and reliable in operation. The device is particularly, although not exclusively, suited to closing doors automatically follcwing a short delay after they have been opened. For example, it is convenient to have the doors of refrigerated-cubicles provided with self-closing doors so that they do not remain open longer than is necessary.
[0002] The traction device of the invention is also usable in other applications, such as providing a door-opening mechanism where there is a demand for a strong traction force to be applied over a short distance.
[0003] Traction devices providing a strong force over a short distance are either electrically, hydraulically or mechanically operated. Devices using an electric motor to provide traction are relatively expensive. The same is true of hydraulically-operated devices, as close-fitting moving parts and pressure seals are necessary. Mechanical devices, using springs or gravity, are cheap to install but have the disadvantage that they represent an additional load which has to be overcome at times when traction is not required.
[0004] An object of this invention is to provide a traction device operated by temperature and which provides a negligible resistance to movement of the load when the traction device is not operated.
[0005] In accordance with the present invention there is provided a temperature-operated traction device which comprises an elongated element made from a heat-responsive memory material of the type defined below, heating means operable to heat the element to restore it to its original shape, two relatively movable parts attached to respective ends of the element and the first of which is connected to a load which is to be displaced in the direction of traction when the element is heated, and a spring which yields resiliently to allow the load to move in the direction opposite to that in which traction is exerted if the element is hot.
[0006] Recent developments in metal alloys have created materials which, when cold, are remarkably ductile and can have their shape altered easily from an "original" shape by applying a small traction force. However, when such a material is heated above a certain temperature, it reassumes its original shape and, in so doing, is capable of exerting a very much greater force than that required to alter its shape when cold. Such a material is referred to throughout this specification as being "a heat-responsive memory material of the type defined". Examples of such materials are to be found in United States Patent Specification numbers 4,412,8-72 and 4,405,387 hereby inserted by way of reference, and as a product commercially available in the United States of America under the Trade Mark NITONOL.
[0007] In the preferred embodiment of the invention the element is of elongated form, such as a wire or a ribbon, and the load applied when the element is cold causes it to extend from its original length as its ductility is relatively high. On heating the element, the ductility falls and the element shrinks back to its original shape.
[0008] In a second embodiment of the invention the element is formed as an "L"-shape and the force applied by the load when the element is cold and ductile, causes the element to bend so that the included angle of the "L" is increased. When the element is heated, it loses ductility and re-assumes its former shape. The reduction in the angle of the "L" which occurs, exerts traction on the load.
[0009] Suitably the element is heated by an electrical current passed through it when traction is required. The advantage of heating the element this way is that the magnitude of the current can be precisely controlled to provide the requisite heating, and timing circuits are readily available to ensure that a required delay is incurred before the device exerts any traction. Also some loads have a non-linear characteristic and require more traction to be exerted to give them initial movement than is necessary to sustain .their movement. An electrical current control circuit is readily devisable by a competent electrical engineer to provide the current with characteristics which cause the element to have the desired traction characteristics.
[0010] Conveniently a second spring is provided to keep the element, which may be a wire or a strip, taut, irrespective of the spacing between the two parts connected to its opposite ends.
[0011] The invention will now be described in more detail, by way of examples, with reference to the accompanying drawings, in which:-
FIGURE 1 is a diagrammatic perspective view of a refrigeration cubicle having an opening closed by a door which is restored to its closed position automatically by a traction device after it has been open a predetermined time;
FIGURE 2 shows the traction device of figure 1 in a partially broken away plan view;
FIGURE 3 is a side view of the partially broken away traction device of figure 2;
FIGURE 4 is a block circuit diagram of an electrical circuit used to operate the device; and,
FIGURE 5 shows diagrammatically principal operative parts of a second form of traction device, in full outline when a heat-responsive memory element is in its original shape, and in broken outline when the element is in its altered shape.
[0012] Figure 1 shows a refrigerated cubicle 1 having an opening 2 closed by a door 3 turning on hinges 4 and having a handle 5. The door 3 opens outwardly and a traction device 6 is mounted on the cubicle 1 immediately above the door 3. A flexible tie 7 extends from one end of the device 6 into a door-closing mechanism 8 having an arm 9 which bears at its end on the door 3 to close it when the traction device 6 is operated. The mechanism 8 can be of any suitable design. In one arrangement (not shown) it contains a pulley having an upright axis and around which the free end of the tie 7 is wound. The pulley is integral with an axle and the arm 9 so that when the device 6 is operated, the tension in the tie 7 rotates the pulley and turns the end of the arm in contact with the door in the door-closing direction. A spring (not shown) retains the end of the arm in contact with the door.
[0013] Figures 2 and 3 show the construction of the traction device 6 in detail. It comprises an elongated, shallow, rectangular box 10 bolted to the cubicle 1 and containing two axially aligned slideways 11 and 1,2 respectively. The slideway 11 contains a slide 13 having an apertured angle bracket 14 welded to it and provided with an anchorage 15 to enable the tie 7 to be secured to it.
[0014] The slideway 12 contains a slide 16 having an upturned apertured lug 17 equipped at one side with a collar 18 locating one end of a coil compression spring 20. The other end of the spring 20 locates on a second, similar collar 21 attached to an apertured angle piece 23 which is welded to the floor of the slideway 12.
[0015] The spring 20 urges the slide 16 against an end stop 24. Adjacent the stop 24, the slide 16 has welded to it a second angle bracket 25 having an aperture which is aligned with the apertures in the lug 17, the angle piece 23 and the angle bracket 14.
[0016] A wire 30 made from said heat-responsive memory material of the type defined, extends parallel to the slideways 11 and 12, and passes through the aforesaid apertures. The wire 30 extends at one end through an insulating ferrule 31 in the angle bracket 25 and at the other end through a second insulating ferrule 32 in the angle bracket 14. The portions of the wire 25 projecting from the remote ends of the ferrules 31 and 32 have electrical connectors 34 and 35 crimped to them to enable an electrical heating current to be passed through the wire when the traction device is to be operated.
[0017] The box 10 is provided between the two slideways 11 and 12 with a block 38 which locates one end of a relatively weak compression spring 39. The other end of the spring 39 is attached to the slide 13 to bias it continuously away from the slide 16 so as to keep the wire 30 taut. The spring 39 is not strictly necessary, but ensures that the wire does not contact uninsulated parts of the box 10 should it slacken.
[0018] A microswitch 40 having a contact 47 in a circuit-closed condition is provided beside the slide 12 and carries a cantilever spring 41 which allows the microswitch 40 to assume a contact-open condition and break the circuit if the lug 17 is moved towards the angle piece 23 from the position shown.
[0019] A second microswitch is provided with a cantilever spring 51 which allows a contact 52 to assume a circuit-closed condition if the slide 13 moves to the left of the position illustrated. As long as the wire 30 is in its fully-shrunk state, the cantilever spring is engaged so that the microswitch contact 52 is in its circuit-open condition.
[0020] Figure 4 shows in block form a control circuit used with the device. Power is provided at 43 to contacts 50 and 47 which are connected electrically in series. If contact 50 is closed, the closure of contact 47 will allow current to flow to a time delay circuit 44 having a contact 48 which closes after a predetermined period to supply current to a current waveform generator 45. The generator 45 supplies an electrical current having required characteristics to cause the wire 30 to heat at a predetermined rate to a predetermined temperature sufficient to cause the wire 30 to shrink and exert traction on the tie 7.
[0021] The operation of the traction device to close the door 3 when open will first be described. As the door 3 is open, the wire 30 is in its extended condition and the slide 13 is spaced from the microswitch 56 so that the contact 50 is closed. This causes a heating current to flow via the closed contact 47, time delay contact 43 and the currant waveform generator 45 to the wire 30, heating it to its shrinkage temperature. The end of the wire 30 attached to the slide 16 may be regarded as being fixed if the door is free to close. The heating of the wire causes it to shrink to its original length, drawing the slide 13 towards the slide 36 so that traction is exerted on the flexible tie 7. This causes the mechanism 8 to operate to close the door 3. When the door is closed, the slide 13 engages the cantilever spring 51 causing the contact 50 of the microswitch 56 to de-energise the power supply circuit.
[0022] Should the wire 30 continue to shrink a small amount after the door 3 has completely closed, this final shrinkage is accommodated by movement of the slide 16 towards the angle bracket 23 and compression of the spring 20. However as the power circuit is now interrupted, the wire 30 cools and becomes more ductile. The spring 20 is then able to extend the wire 30 slightly, to bring the slide 16 against the end ' stop 24 and cause the cantilever 41 to re-close the contact 47 of the microswitch 40.
[0023] If the door is now opened after the wire 30 has cooled, the tensile loading on the tie 7 causes the cold wire 30 to extend easily as it has a low ductility when cold, and thus offers a negligible resistance to door opening. Opening of the door is accompanied by movement of the slide 13 to the left in figures 2 and 3, so that the cantilever spring 54 associated with the microswitch 56 operates to close the power circuit to the time-delay circuit 44. This closes the contact 48 after a predetermined period, so that the wire is again heated and door-closing re-occures'as described above.
[0024] It can happen that the closure of the door is obstructed. In thi case, slide 13 cannot move and the shrinkage of the wire 30 causes the slide 16 to move against the compression of the spring 20. The lug 17 then operates the microswitch 40 to open the contact 47 so that the power circuit to the wire 30 is interrupted before the components of the traction device or the object obstructing closure of the dcor can be subjected to a damaging force.
[0025] It can also happen that the door 3 is momentarily partially opened and then reclosed manually. In this event the cold wire is extended and then left slack. However the action of the spring 39 is to move the slide 13 in a direction which keeps the wire 30 taut and this causes the contact 50 of the microswitch 56 to close. This initiates operation of the time delay circuit 44 so that its contact 48 closes after a time delay and the wire is heat shrunk back to its "normal" length, despite the door being closed. The contact 50 is then moved by the slide 13 to its open-circuit condition shown in figure 4.
[0026] A third condition can arise if the door 3 is opened immediately after it has been closed, or an attempt is made to open it fully when the traction device is actually closing the door. In this case, the hot wire 30, no longer being ductile, cannot extend and, instead, the pull of the tie 7 is applied through the hot wire to the slide 16 which slides to compress the spring 20. The microswitch 40 is then operated so that its contact 47 interrupts the current circuit to the wire 30 which then cools and once again becomes ductile. This allows the spring 20 to extend the wire 30 until the contact of the microswitch 40 is again closed and the wire can be heated to shrink and return the door to its closed position.
[0027] In place of the wire 30, a flat strip of the material can be used. This enables a shallower box 10 to be used. Also the springs 20 and 39 can be located in other positions from those indicated in the drawings. Finally, although the invention has been specifically described with reference to a device for closing a door, it can be used to open a door or other form of closure, or to do any other form of work in which a high tractive force, with suitable safety features, .is required to perform work over a relatively short stroke.
[0028] Figure 5 shows a traction device in which component parts having the same functions as those already described are similarly referenced but in the hundred series. For convenience the electronic circuitry is omitted as it is the same as that already described. Also omitted are the details of the electrical switches corresponding to switches 41 and 56 of the earlier described embodiment, although the positions of these switches are shown at 141 and 156.
[0029] The traction device of Figure 5 comprises a tubular socket piece 60 having adjacent the mouth of the socket a pair of oppositely extending wings 138. The socket piece 60 contains a stiff tension spring 120 attached at one end to the base of the socket and at the other end to a stem 61 of a T-shaped element 130. The head of the element 130 provides two arms 62 each extending parallel to one of the wings 138. Two tension coil springs 139 respectively extend between each arm 62 and the wing 138 alongside it.
[0030] The free ends of the arms 62 are apertured to provide anchorages 63 for a Y-shaped flexible tie 107 connected to a load as described in the earlier embodiment. Each arm 62 may be consi.dered as forming with the stem 61 an L-shaped member.
[0031] The element 130 is made from the heat-responsive memory material of the type defined. It is therefore ductile and easily bent when cold. However when hot the element loses ductility and will exert considerable force in attempting to re-assume the shape shown in full outline, if bent from that shape to the shape shown in broken outline when cold.
[0032] The application of the tensile loading to the tie 107 causes the arms 62 of the element 130 to bend to the position shown in broken outline in which the element 130 assumes a y-shape. To restore the shape of the element 130 to a T-shape, it is heated. Its ductility then reduces also so that as its arms 62 return to the position shown in full outline, they exert traction on the load.
1. A temperature-operated traction device comprising an elongated element made from
a heat-responsive memory material of the type defined, heating means operable to heat
the element to restore it to its original shape, two relatively movable parts attached
to respective ends of the element and the first of which is adapted to be connected
to a load which is to be displaced in the direction of traction when the element is
heated, and a spring which yields resiliently to allow the load to move in the direction
opposite to that in which traction is exerted if the element is hot.
2. A device as claimed in claim 1, in which the heating means comprises an electrical
circuit arranged to pass an electrical heating current through the element after said
two parts have been moved apart.
3. A device as claimed in claim 2, including a time-delay which responds to said two
parts being moved apart by delaying operation of said heating means until a predetermined
period has elapsed.
4. A device as claimed in any one of the preceding claims, in which the two parts
comprise slides movable along respective tracks extending parallel to the e.lement.
5. A device as claimed in any one of the preceding claims, including a second spring
acting on the first part to maintain the element taut in all positions of said parts.
6. A device as claimed in any one of the preceding claims, including a first electrical
contact which prevents operation of the heating means unless the second of said parts
is at a position it occupies when the element is cold.
7. A device as claimed in claim 6, including a second electrical contact which prevents
operation of the heating means when said parts are at relative positions corresponding
to the element being fully shrunk.
8. A device as claimed in any one of the preceding claims, in which the element is
of extended length and shrinks in length when heated to apply traction to the load.
9. A device as claimed in claim 8, in which the element comprises a wire.
10. A device as claimed in any one of claims 1 to 7, in which the element is of angular
shape and the application of force by the load bends the element so that its angle
is varied, and the application of heat to the element restores the angle to its original
shape thereby applying traction to the load.