Key-controlled safety switch

Abstract: A key-controlled safety switch assembly includes a box-like case (2) anchorable to a fixed part of a protection or barrier of a machine or installation and provided with one or more slots (5), an actuating key (3) anchorable to a moving part of the protection and insertable in any of the slots (5). The case (2) contains internally thereof a safety electric circuit (6) for selectively closing/opening a general relais or a safety switch of the machine or installation on insertion/extraction of actuating key (3), locking parts (9) for selectively locking the actuating key (3) in the inserted position in a slot (5) until the dangerous parts of the machine or installation are moving, a detecting device (13) for detecting the position of the key (3) to allow closing of the safety switch (6). The detecting device (13) is exclusively of the electronic type acting from distance, and the key (3) is shaped so as to enter freely in the slot (5) with a minimal predetermined clearance ( s ).

Description: Technical field The present invention relates to industrial safety and has in particular for object a key-controlled safety switch assembly, particularly adapted for use in strongly dirty and polluting environment. Background art The switches of the described type are normally employed to block cabinet doors or protection barriers for machines and industrial plants with dangerous moving parts, like saws, rotors, tools or blades, in which the access time to the area interested by such parts is shorter than the stopping time of the machine or plant. Such switches are essentially made of two distinct elements, namely a box-like case containing a series of electric contacts connected with the power supply circuit of the machine, for example with a control coil or relais, and a key-like element insertable in one or more slots of the case to commute the above-mentioned electric contacts. Preferably, the box-like case is anchored to the frame of the machine or plant, and the key-like element is fixed to the door or moving barrier in a position facing a slot of the box-like case. For security reasons, inside the case there are provided blocking parts acting on the key-like element to block it in its inserted position inside the case until the dangerous moving parts are completely stopped. To operate the blocking parts there is provided a special sensor which senses the stopping of the dangerous parts or a time switch which sends a signal after a time longer the time necessary for stopping said parts. When an operator wants to open the door or barrier, he must at first press a button placed on the electric control cabinet of the machine, so that the dangerous part of the machine begins to decelerate progressively. When the sensor detects the condition of "dangerous part stopped", it will automatically send an electric signal to the blocking part, thus unlocking the key and allowing the opening of the door or barrier. Examples of key-controlled safety switches the type over described are given in the United States patent No. 4, 904, 829, No. 5, 584, 378, No. 5777284 in the European applications No. 0 553 885, No. 0 817 227, No. 0 814 490, in the international applications WO No. 95/06323, 95/18457, 96/33504 and in the German applications No. 3309372 and 3710079. A drawback of these known switches is related to the operative environment. In fact, if they are applied to machines and installations working in particular dirty and polluting environments, like for example cement production plants, land movement machines, concrete mixing installations, tile production installations, machining equipment of stone materials, they are easily subject to damage and malfunction. In fact, the powder material dispersed in the environment can deposit on the actuating element or in the box-like case, thus creating on the same layers of adherent material of great consistency. Progressively, the thickness of such layers can increase and even reach some millimetres, and can involve the delicate sensing mechanisms of the keys provoking in short time their seizure and putting them out of use. In order to solve this problem a magnetic type recognition device has been provided which is described in the United States patent n. 5254879, essentially made of two components protected by respective cases, on one side a simple permanent magnet with functions of magnetic field generator, on the other an electric switch enclosed in an tubing (reed) which shuts when influenced by the field produced by the permanent magnet. Besides, to avoid altering operation of the switch approaching to the tubing a second magnet similar to the first one, a personalized decoding system of the analogic (radio waves, radar, etc.) or digital type (EPROM) has been associated to the magnetic recognition device. In an attempt to use the traditional key-controlled switches with mechanical recognition in very dirty and polluting environments, German patent No. 4209086 discloses a lip-gasket of rubber or similar material applied at the edge of the input slot of the actuating key-like element, so as to limit dust and dirt penetration. From the British patent No. 2052158 a key-controlled switch is known with a key-like actuating element provided with a permanent magnet and a tapered end portion. The permanent magnet has the function of moving a leaf member of insulating material interposed between two electric contacts contained in the case, which are subsequently closed by the tapered extremity of the actuating element. From the European patent application No. 0 837 485, there is known a key-controlled safety switch having all the characteristics belonging to the state of the art and indicated in the preamble of claim 1, and further having a recognition or decoding device of the key-like element which is both electronic and mechanical, similar to that of some anti theft systems for motor vehicles. In a preferred embodiment, the electronic recognition device is essentially constituted of a series of Hall effect sensors placed on a wall of the insertion slot and facing a series of correspondent permanent magnets fixed on the key-like element. The tension detected by the Hall-effect sensors with predetermined and characteristic values of every key. This switch has the inconvenience of presenting a great complexity and a comparatively high cost because of the presence of a key recognition system which is both mechanical and electronic. Additionally, the mechanical recognition system constitutes a drawback since it is subject to the risks of stratification of dirt and dust and to consequent seizures and/or break-downs. Furthermore, it is well known, for instance from US-A-5239202, that reed tubings and contacts may be employed as magnetically controlled switches. US-A-5541562 describes a key-controlled safety switch having all the characteristics indicated in the preamble of claim 1. Moreover, this switch comprises a case with only two slots placed at two opposite side thereof. The case is provided of three proximity digital sensors all placed between one side of the case and a locking member. The actuating element has two holes placed in two opposed extremity portions of the actuating element for receiving the locking member. A main drawback of this known switch resides in that it has only two slots, thus reducing the freedom of installation on plants requiring insertion of the actuating element across all four sides of the case. Moreover, the actuating member must have two holes in order to allow the insertion of the actuating element through either slots, thus increasing the overall length of the actuating member. Presentation of the invention A primary aim of the present invention is to eliminate the above drawbacks providing a key-controlled safety switch assembly which is particularly adapted for use in dirty and polluted environments, ensuring uninterrupted operation at least for a prolonged period of time. A particular aim is to provide a key-controlled safety switch assembly which can be easily cleaned so as to ensure its functionality and effectiveness by means of a periodic maintenance. A further particular aim is to provide a key-controlled safety switch assembly with great structural simplicity so as to be reliable and intrinsically safe. An other particular aim is to provide an extremely versatile switch assembly, flexible and of reduced cost. In accordance with one preferred aspect of the invention, there is provided a key-controlled switch assembly according to claim 1. Thanks to this particular configuration, the actuating key-like element can be freely inserted along different directions in corresponding slots also in dirty and polluting environments, avoiding seizures and technical malfunctions. Short description of the drawings Further characteristics and advantages of the invention will become apparent from the detailed description of a preferred but not exclusive embodiment of the key-controlled switch assembly according to the invention, illustrated by way of non-limitative example in the accompanying drawings wherein: the FIG. 1 is a general partially exploded perspective view of a key-controlled switch assembly according the invention; the FIG. 2 is a front view of a partial section taken along the axial plane II-II of the assembly of Fig. 1, in a first operative position; the FIG. 3 represents a side view of a partial section of the assembly of Fig. 2 taken along the axial plane III-III; the FIG. 4 represents a side view of the assembly of Fig. 3 in a first operational phase; the FIG. 5 represents a lateral sight of the assembly of Fig. 4 in a second operational phase. Detailed description of a preferred embodiment With reference to the cited figures, a key-controlled switch assembly according to the invention, globally designated with the reference numeral 1, comprises a box-like case 2, of substantially parallelepiped form with main axis V, and a key-like actuating element 3. The case 2 is preferably anchored to the frame of a machine or installation, with dangerous moving parts and not shown in the drawings, by means of screws 4. The case 2 has on a lateral wall and in vicinity of one extremity axial portion at least a through slot 5 for the insertion of the key-like actuating element 3. In the illustrated form, on all four sides of the case 2, there is provided a slot 5 to allow the insertion of the key-like actuating element 3 from all sides. The element 3 can be in this way fixed to the moving part of a protection or barrier of the machine or installation, also not represented on the drawings, in position facing one of the slots 5 of the case 2. The case 2 has internally thereof a safety electric circuit, globally designated with the reference numeral 6, having end connectors 7, 8 connected to a general relais of the machine or installation to control its starting or stopping on insertion and on extraction of the actuating element 3 in the slot 5. A locking part or electromagnetic bolt 9 is also placed in the case 2, comprising a substantially cylindrical armature 10 enclosed by an electromagnet coil 11, which armature extends out of the head of the coil 11 and can be inserted in a hole 12 placed in the straight portion 12' of the actuating element 3 when the latter is inserted in the slot 5, firmly locking it and preventing its extraction as long as the dangerous part of the machine is moving. Advantageously, the armature 10 has a prominence 10' projecting from the lower part of the winding 11 whose function will be explained hereinafter. Finally, in the case 2 there is placed a detecting device 13 adapted to detect the position of said actuating element 3 to allow activation of the electric bolt 9. In accordance with the invention, the detecting device 13 is of exclusively electronic type acting from a distance, and the key-like element 3 is shaped to enter freely in the slot 5 with a predetermined clearance s . The actuating element 3 has a straight end portion 12 with constant cross section, of similar form and of dimensions smaller than those of the slot 5, and substantially smooth lateral surfaces. Thus, on insertion of the portion 12' of the element 3, the clearance s will be distributed in substantially uniform manner along the entire periphery C of the cross section of the portion 12' of the element 3 and there will not be any mechanic interaction between the two elements of the switch assembly. The clearance s , equal to some millimetres, will allow an optimal operation also in strongly dirty and polluting environments as the stratifications on the actuating element will not cause a seizure for a period sufficient to carry out a scheduled maintenance and an accurate cleaning of the moving parts. In particular, the detecting device 13 is a magnetic proximity switch. In particular, the magnetic proximity switch is made of a tubing 13, denominated commonly reed, that contains electric contacts that are shut if in the vicinity of a magnetic flux. The tubing 13 is suitable to co-operate with a permanent magnet 14 fixed to the key-like actuating element 3, in an extremity portion of the latter so as to be close to the tubing 13 adjacent to the insertion slot 5. More precisely, a magnetic tubing 13 is placed close to every slot 5 of the body 2 and all tubings are connected in parallel through a first integrated circuit. Thus, inserting the actuating element 3 in an any of the four slots 5, a signal will be issued by the recognition device 13. Possibly, the detecting device 13, 14 can include a transponder or a radar transmitter/receiver, not illustrated in the drawings, so as to avoid decoding with the ordinary commerce means. The tubings 13 that constitute the detecting device are connected in parallel to the safety electric circuit 6, in particular to a first section 15 that comprises a first pair of electric contacts 16, 17 fixed on a second integrated circuit 15' perpendicular to the first. By means of a special integrated operator, also enclosed in the circuit 15', the two contacts 16, 17 can be closed in response to a signal produced by any of the tubings 13 of the detection device, on insertion of the actuating element 3 in the correspondent slot 5. The safety electric circuit 6 includes additionally a second pair of electric contacts 18, 19 connected to the first pair of electric contacts 16, 17 by a bridge 18' and placed in a covering 20 made of insulating material. From the covering 20 a button 21 leans out for commuting the state of the contacts 18, 19. As can be seen in the Fig. 3, when the electromagnet coil 11 is not excited the armature 10 is blocked in the hole 12 of the actuating element 3, the prominence 10' is at a distance from the button 21 of the covering and the contacts 18, 19 are normally closed. On the contrary, when the electromagnet is excited, as shown in the Figure 4, the armature 10 is disengaged from the hole 12 and the prominence 10' compresses the button 21 and causes the aperture of the contacts 18, 19. In use, when the machine or installation is in operation and the barrier or door is closed, the actuating element 3 is inserted completely in the slot 5 and remains locked inside it by the bolt 9. On the electric side, all the contacts 16, 17, 18, 19 are closed and the actuating relais of the machine or installation is excited, as shown in Figure 3. When the operator stops the machine or installation and all the dangerous parts are still, a sensor will send an electric signal to the coil 11 of the bolt 9 which will open the contacts 18, 19 and will free the actuating key-like element 3 from its engagement with the armature 10. The operator can thus open manually the door or barrier by pulling out the actuating element 3. As the latter is at a distance of some millimetres from the slot, the magnetic flux produced by the permanent magnet 14 will reduce its influence on the tubing 13, consequently opening its electric contacts and then opening also the contacts 16, 17 of the section 15 of the safety circuit. From the foregoing description, it is apparent that the key-controlled safety switch assembly according the invention reaches fully the objects set above and in particular its structural simplicity, reliability, flexibility and contained cost are underlined. The key-controlled safety switch assembly according the invention is subject to numerous modifications and variations, all of which are within the scope of the accompanying claims. All the details may furthermore be substituted with other equivalents without departing from the scope of the invention.

Claims: Key-controlled safety switch assembly, comprising a box-like case (2) anchorable to a fixed part of a protection or barrier of a machine or installation and provided with one or more slots (5), an actuating element (3) anchorable to a moving part of said protection and having a straight portion (12') insertable in any of said slots (5), said case (2) having at least four sides and containing internally thereof a safety electric circuit (6) for selectively closing/opening a general relais or a safety switch of said machine or installation on insertion/extraction of said actuating element (3), a locking member (10) adapted to be inserted in a hole (12) placed in said straight portion (12') to selectively lock said actuating element (3) in the inserted position in a slot (5) as long as the dangerous parts of the machine or installation are moving, a detecting device (13) which is exclusively of electronic type acting from distance and is adapted to detect the position of said actuating element (3) to allow closing of said safety electric circuit (6), said detecting device (13) comprising a permanent magnet (14) fixed to said actuating element (3), said detecting device (13) further comprising at least one recognition device (13) adapted to co-operate with said permanent magnet (14), characterized in that each recognition device (13) is associated with a respective side of said case (2), slots (5) being provided on the at least all four sides of the case (2), each slot (5) on one different side of the case (2), said at least one recognition device (13) being placed in proximity of each slot (5), each recognition device (13) being placed between the respective side to which it is associated and said locking member (9) in order to co-operate with said permanent magnet (14) fixed to said actuating element (3) inserted in any slot (5), said locking member (10) being placed centrally in the case (2), said actuating element (3) being shaped to freely enter in said slot (5) with a predetermined clearance ( s ). Key-controlled safety switch assembly according to claim 1, characterised in that said straight portion (12') of the actuating element (3) has a substantially constant cross section and smooth lateral surfaces so as to avoid any mechanical interference with said slot (5). Key-controlled safety switch assembly according to claim 1, characterised in that each recognition device (13) is a tubing with magnetic contacts. Key-controlled safety switch assembly according to claim 3, characterised in that all said tubings (13) are connected in parallel to said safety circuit (6). Key-controlled safety switch assembly according to claim 4, characterised in that said permanent magnet (14) is fixed to an extremity portion (12") of said actuating element (3), so as to be in proximity of said tubing (13) when said actuating element (3) is inserted in said slot (5). Key-controlled safety switch assembly according to claim 1, characterised in that said detecting device includes a trasponder. Key-controlled safety switch assembly according to claim 1, characterised in that said detecting device further includes a radar/trasmitter assembly. Key-controlled safety switch assembly according to claim 1, characterised in that said locking member (10) includes an electromagnetic bolt (9) having an armature (10) enclosed by an electromagnet (11). Key-controlled safety switch assembly according to claim 1, characterised in that said safety electric circuit (6) includes a first pair of electric contacts (16, 17) operatively connected to said detection device (13) and moving between an open position with said actuating element (3) completely extracted and a closed position with the straight portion (12') of said actuating element (3) completely inserted. Key-controlled safety switch assembly according to claim 9, characterised in that said safety electric circuit (6) includes a second couple of electric contacts (18, 19) series connected to said first pair of electric contacts (16, 17) by a bridge circuit (18'). Key-controlled safety switch assembly according to claim 10, characterised in that said second pair of electric contacts (18, 19) is normally closed when said electromagnet bolt (9) is not excited and when said actuating element (3) is blocked by said electromagnetic bolt (9). Key-controlled safety switch assembly according to claim 11, characterised in that the armature (10) of said electromagnetic bolt (9) has a prominence (10') adapted to interact with a commutation button (21) of said second couple of electric contacts (18, 19) when said electromagnetic bolt (9) is excited by an external control device.

Inventors: PIZZATO BERNARDO, PIZZATO GIUSEPPE, PIZZATO MARCO, PIZZATO, BERNARDO, PIZZATO, GIUSEPPE, PIZZATO, MARCO
Applicants: PIZZATO ELETTRICA SRL, PIZZATO ELETTRICA S.R.L.
Application year: 1999
Main classification: H01H27
IPC codes: H01H36, H01H27