Key-locked electromechanical safety switch

Abstract

 It is described a key-locked electromechanical safety switch comprising a control head (4) provided with a cam actuator (8), a pusher (9) for switching over electrical contacts (3) operated by the cam actuator (8), an operating key (7) insertable into a slot formed in the control head, and a tempering-preventing device (12) having at least one safety element (13) adapted to block rotation of the cam actuator (8).

Description

[0001] The present invention relates to a key-locked electromechanical safety switch of the type comprising a main body adapted to house electrical contacts, a control head provided with a cam actuator and integrally connected with the main body, a pusher, operated by the cam actuator, for switching over the electrical contacts, and an operating key insertable into a slot formed in the control head and adapted to set the cam actuator in rotation, said slot defining a fitting direction of the operating key in the control head.

[0002] It is known that in many application fields it is required the presence of devices intended for enabling activation of plants, machines, mechanical and electrical apparatuses, such as assembly lines, conveyors, machine tools, sliding surfaces, movable barriers or screens and control boards or, in any case, the presence of devices capable of accomplishing safety functions involving opening or closing of electrical contacts.

[0003] For example, the international rules impose that operation of the sliding protection barrier for some types of machines shall take place by means of an electromechanical key-locked switch fastened to the sliding barrier itself, which switch enables the feeding circuit to be cut off and the protected machine operation to be stopped in case of an incautious opening of the barrier.

[0004] The key-locked electromechanical switches are usually comprised of a main body or contact block adapted to house the electrical contacts and of a control head connected with the main body and provided with a cam actuator. Said actuator has a profile formed with appropriate projections and hollows capable of shifting a pusher acting on the electrical contacts, which emerges from the main body and is elastically pushed against the cam itself.

[0005] Formed in the control head is a slot into which a substantially flattened operating key is insertable, which key is adapted to set the cam actuator in rotation in either direction depending on whether it is moved to the inside of the slot or pulled out of the slot itself.

[0006] The known electromechanical switches briefly described above suffer from some limits and drawbacks from the point of view of safety, because they can be easily switched off in an illicit manner by individuals that are not in possession of the foreseen operating key.

[0007] In fact, by introducing a blade, a metal wire or a clip into the slot it is possible to cause rotation of the cam actuator and consequently produce switching over of the electrical contacts.

[0008] Therefore, it is substantially still unresolved the technical problem of making an electromechanical cam switch capable of ensuring an appropriate degree of safety against tampering actions carried out by illintentioned people.

[0009] Under this situation, the technical task underlying the present invention is to provide a key-locked electromechanical safety switch capable of substantially eliminating the above mentioned drawbacks.

[0010] Within the scope of this technical task it is an important object of the invention to provide an electromechanical switch that, without carrying out important modifications to the conformation of both the operating key and the main body as well as to the control head, as compared with the electromechanical switches of known type, greatly increases safety of same against tampering.

[0011] The technical task mentioned and the object specified are substantially achieved by a key-locked electromechanical safety switch which is characterized in that it comprises a tampering-preventing device disposed within said control head close to said slot, said tampering-preventing device having at least one safety element movable between a stop position adapted to block rotation of said cam actuator and a release position of said cam actuator, which is activated by the thrust action of said operating key on the safety element during insertion of the key into said slot.

[0012] The description of a preferred embodiment of a key-locked electromechanical safety switch according to the invention is now given hereinafter by way of non-limiting example, with reference to the accompanying drawings, in which:

• fig. 1 is a perspective view of a safety switch according to the invention;
• fig. 2 is a perspective view of some component parts of the switch shown in Fig. 1, and in particular the tampering-preventing device;
• Figs. 3, 4 and 5 show, in a plan and cross-sectional view respectively, successive operating positions of the switch in Fig. 1; and
• Fig. 6 is a perspective view of an alternative solution of the safety switch shown in fig. 1.

[0013] Referring to the drawings, the key-locked electromechanical safety switch in accordance with the invention is generally identified by reference numeral 1. It comprises a main body or contact block 2 adapted to house electrical contacts 3, in turn consisting of a normally closed contact and a normally opent contact, for example.

[0014] Integral with the main body 2 is a control head 4 formed with a slot 5 defining a fitting direction 6 for a special operating key 7. The control head 4 can be applied to the main body 2 according to positions differentiated from each other and rotated through 90° so that, depending on requirements, the best orientation of the slot 5, and therefore of the key-fitting direction, can be selected.

[0015] Disposed within the control head 4 is a cam actuator 8 having a profile formed with projections and hollows adapted to perform functions known in themselves.

[0016] More particularly, a pusher 9 elastically abuts against one portion of the cam actuator 8 profile, said pusher being adapted to switch over the position of the electrical contacts 3. Another portion of the cam actuator 8 profile is acted upon by the key 7 in order to set said actuator in rotation in either direction depending on whether the key is introduced into or drawn out of the slot 5.

[0017] The operating key 7 has a conventional shape typical of this kind of switches: that is, it comprises two longitudinal parallel portions 7a and two transverse stretches 7b delimiting a through cavity 10 which is adapted to house a corresponding first projection 8a of the cam 8 profile (see Fig. 5).

[0018] In addition, the key 7 has a recess 11 at the front which matches with a second projection 8b of the cam 8 in a first length of its insertion stroke into the slot 5.

[0019] In an original manner, the switch 1 comprises a tampering-preventing device 12 disposed within the control head 4, close to the slot 5.

[0020] The device 12 in turn comprises two safety elements 13 each consisting of a shaped plate-like body having one stop end 13a insertable into a corresponding stepped hollow 14 formed in the cam 8 profile at an appropriate position, and a second drive end 13b defined by a thrust edge emerging at the inside of slot 5 and inclined to the fitting direction 6 of the operating key 7.

[0021] Each safety element 13 is movable independently of the other safety element, transversely of the fitting direction 6, between a stop position (shown in Figs. 1 and 4), in which the first end 13a is inserted in the hollow 14 and holds the cam actuator 8 against rotation, and a release position (Fig. 5) activated by a thrust action exerted on the second end 13b of the key 7 introduced into the slot 5, in which the first end 13a is disengaged from hollow 14 thereby enabling rotation of the cam 8 itself.

[0022] More precisely, for each safety element 13 a spring 15 is provided which is adapted to elastically abut, by its first and 13a, against the stepped hollow 14. The operating key 7, by its sliding in contact with the thrust edge 13b, applies a compression load against the action of spring 15, thereby moving the safety element 13 to said release position. The degree of displacement of the safety element 13 is given by the operating key 7 thickness. This thickness must therefore have a gauged value higher than the stroke necessary for the safety element 13 to pass from the stop position of cam 8 to the release position of the latter.

[0023] In addition, the two safety elements 13 are such positioned in the control head 4 that their second drive ends 13b are spaced apart from each other to an extent corresponding to the distance between the longitudinal portions 7a of the operating key 7. This feature enables said key to simultaneously press on both the safety elements 13 when it is introduced into the slot 5, and therefore to jointly disengage the first stop ends 13a from the cam actuator hollow 14.

[0024] With reference to Fig. 6, in order to inhibit tampering of the switch by the introduction of clips, blades and the like, the alternative solution illustrated therein provides for the presence of at least one rib 16 arranged between the two adjacent projections 8a and 8b. The rib 16 is intended for engagement in an opening 17 formed in the front transverse stretch 7b of the operating key 7.

[0025] In addition, the external profile of the rib 16 extends continuously and flush with the perimetric external profiles of the projections 8a and 8b. In this way, the rib 16 counteracts the insertion of even a clip, thereby enabling operation of the cam actuator 8 only by means of the operating key 7 shown in Fig. 6.

[0026] Operation of a key-locked electromechanical safety switch described above mainly as regards structure, is as follows.

[0027] Introduction of the operating key 7 into the slot 5 first causes compression of both the safety elements 13 until disengagement of the first stop end 13a from the stepped hollow 14 of the cam actuator 8. Prosecution of the key insertion into the slot 5 brings the front recess 11 of said key into contact with the second projection 8b of the cam actuator 8. Subsequently, the key imparts an anti-clockwise rotation (with reference to the accompanying drawings) to the actuator itself which is no longer blocked, until the position shown in Fig. 5 is achieved, in which the first projection 8 is fitted into the through cavity 10 of the key. During rotation of the actuator 8, the pusher 9 is subjected to translation and causes switching over of the electrical contacts 3.

[0028] The operating key 7 being pulled out drags the cam actuator along in the opposite rotation direction, due to the action of the front transverse stretch 7b, and the pusher 9 brings the electrical contacts 3 back to their starting position as soon as the longitudinal portions 7a of the key stop pressing against the second ends 13b of elements 13.

[0029] The first ends 13a of elements 13, pushed by springs 15, therefore abut against the stepped hollow 14 of the cam actuator 8 which is in register therewith. In this manner, the cam actuator 8 is held against rotation again.

[0030] Should fraudulent attempts be made on the safety switch according to the invention, by means of a metal wire for example introduced into the slot for pressing against one safety element 13, the other safety element would in any case remain in the stop position thereby preventing rotation of the cam actuator.

[0031] Also in the case in which a paper clip is used, release of the cam actuator is impossible because the metal wire of said clip generally is not of a sufficient diameter (that is equal to or greater than the thickness of the special key), so as to move the safety elements to the release position. In addition, since hardly the width of a clip corresponds to the width of an operating key, that is the distance between the longitudinal portions of the key itself, it is impossible to exert the necessary thrust actions simultaneously on both the safety elements 13, which actions are necessary for the latter to be brought to the release position.

[0032] Finally, if the fraudulent action is put into practice by means of a mere blade that, introduced into the slot, were able to release both the safety elements, the initial rotation of the cam actuator would bring the projection 8a to obstruct the slot itself thereby preventing any body fitted thereinto from coming out.

[0033] Practically, the switch in accordance with the invention offers a high degree of safety against the most different tampering attempts and ensures to an appropriate degree that setting in operation of plants, machines, apparatuses is really enabled only by the authorized staff in possession of the special operating keys.

[0034] Many modifications and variations may be made to the invention, all of them falling within the scope of the inventive idea. In addition, all of the details may be replaced by technically equivalent elements.

[0035] In practically carrying out the invention the materials, shapes and sizes may be of any nature and magnitude in accordance with requirements.

Claims

1. A key-locked electromechanical safety switch comprising:

- a main body (2) adapted to house electrical contacts (3),

- a control head (4) provided with a cam actuator (8) and integrally connected with the main body,

- a pusher (9), operated by the cam actuator, for switching over the electrical contacts, and

- an operating key (7) insertable into a slot (5) formed in the control head (4) and adapted to set said cam actuator (8) in rotation, said slot (5) defining a fitting direction of the operating key (7) in the control head (4),

characterized in that it comprises a tampering-preventing device (12) disposed within said control head (4) close to said slot (5), said tampering-preventing device having at least one safety element (13) movable between a stop position adapted to block rotation of said cam actuator (8) and a release position of said cam actuator (8), activated by the thrust action of said operating key (7) on the safety element (13) during insertion of the key into said slot (5).

2. A switch according to claim 1, in which provision is made for two of said safety elements (13) which are independently active on said cam actuator (8) in said stop position, and jointly shiftable to said release position by means of said operating key (7).

3. A switch according to claim 1, in which said safety element (13) comprises a first stop end (13a) insertable, in said stop position, into a corresponding hollow (14) of the cam actuator, and a second drive end (13b) embodied by a thrust edge emerging at the inside of said slot (5) and inclined to said fitting direction of the operating key (7).

4. A switch according to claim 3, in which at least one spring (15) for each said safety element (13) is provided, which spring is adapted to elastically cause abutment of said first stop end (13a) on said hollow (14) of the cam actuator (8), and in which said operating key (7) applies a compression load on said thrust edge against the action of said spring (7).

5. A switch according to claim 1, in which said safety element (13) is movable transversely of said key-fitting direction according to a displacement given by the thickness of the key inserted in said slot (5), and in which said thickness is of a gauged value greater than the value of the stroke between said stop position and release position.

6. A switch according to claim 2, in which said operating key (7) comprises two longitudinal parallel portions (7b) and at least two transverse stretches (7b) delimiting a through cavity (10) which is adapted to house a profile projection (8a) of said cam actuator (8), and in which said two independent safety elements (13) have drive ends spaced apart from each other to an extent corresponding to the distance between said longitudinal portions (7a) of the key (7).

7. A switch according to claim 6, in which said key at its front transverse stretch (7b) is formed with an opening (17) in which a rib /16) is engaged which is provided at least between two adjacent projections (8a, 8b) in the profile of said cam actuator (8).

8. A switch according to claim 6, in which said rib (16) has an external profile extending continuously and flush with the profile of said adjacent projections (8a, 8b) of the cam actuator (8).

Drawing