Timed electromechanical safety switch

Abstract: A timed safety switch, particularly for accident-prevention doors of machines and apparatus, includes an enclosure (2) which can be anchored to the machine and internally accommodates a series of fixed electrical contacts (3) and of moving electrical contacts (3'), devices (4, 5) for locking the door which includes a safety key (4) which can be anchored to the door and can be inserted in a slot (7) of the enclosure (2), delay devices (11) which can move between an active position and an inactive position and are suitable to anticipate or delay the operation of the locking devices (4, 5) with respect to the actuation of the switch, clearance-providing devices (8) which can move to allow the insertion/extraction of the key (4) through the slot (7) only when the delay devices (11) are in their inactive position, so as to prevent accidental actuations of the switch when the door is open. The delay devices, the locking devices and the clearance-providing devices are of a mechanical type in order to ensure maximum reliability and safety.

Description: The present invention relates to a timed safety switch of the type which can be applied to the doors of protective housings of moving parts of automatic machines and automatic apparatus in general. These switches are adapted to automatically interrupt the electrical power supply of the machine whenever attempts are made to open the door and are adapted to lock the door for a time which is long enough to protect the operator from the risks related to the residual kinetic energy of any moving parts of the machine which are protected by the housing. Conventional safety switches of the above cited type essentially include a casing enclosing a series of fixed electrical contacts which interact with other contacts which can move between a closed position and an open position, a means for opening and closing the contacts and a means for the timed mechanical locking of the door. In a conventional type of safety switch, the locking means is essentially mechanical and includes a threaded pin which engages the enclosure and has one end which is fixed to an actuation knob and the opposite end which protrudes by a certain extent toward the outside of the enclosure for insertion in a suitable seat of the door in order to selectively lock its opening. The threaded pin also controls the opening and closure of the electrical contacts according to a preset timing sequence. This conventional switch is usually applied to the body of a machine compartment in order to interact with the closure door. The door can be either of the sliding or hinged type. In the latter case, the switch is usually applied so that the pin can interact selectively with a hole which is formed radially on one of the rotation hinges of the door. A drawback of this conventional switch is that it does not always ensure high reliability and a sufficient degree of accident-prevention safety. While installation on sliding doors is very simple and the switch ensures a good degree of safety, installation on hinged doors is difficult, because in order to comply with safety standards, the switch must be applied proximate to the hinges of the door in order to interact with them. The installation in other positions in fact does not ensure the selective actuation of the switch only when the door is closed. Accordingly, the switch can be easily damaged by incorrect maneuvers for opening the door. In order to obviate this drawback, this conventional switch must be applied so as to interact with the side of the door which lies opposite to the hinge side, but even this construction has the significant drawback that it allows to actuate the switch even when the door is not perfectly closed and therefore the switch, on its own, does not ensure a sufficient degree of accident-prevention safety. In order to achieve higher safety, it is known to install two switches arranged in series on each individual door, one on the hinge side and one on the opposite side. This solution is of course expensive and rather complicated in practical use. Accordingly, conventional timed safety switches with an essentially mechanical locking system can be installed effectively only on sliding doors. Other timed safety switches with electronic, electromagnetic, electropneumatic or thermal locking devices are known; despite being suitable for their intended use, they do not ensure the reliability of mechanical switches, especially in heavy-duty conditions. It is in fact well-known that mechanical-type actuations are considered safer than the corresponding electronic actuations in the field of accident-prevention safety. Furthermore, these conventional switches require devices for supplying power to the timer circuit and external sensors suitable to detect the complete stop of the parts of the machine and are therefore rather complicated and expensive. DE-A-392 3663 discloses a safety switching unit comprising a combination of features as defined in the pre-characterizing portion of the appended claim 1. An aim of the invention is to eliminate the above drawbacks, providing a timed safety switch which is simple and reliable and ensures maximum accident-prevention safety. According to the invention, this aim is achieved by a timed safety switch according to claim 1. Some preferred but not exclusive embodiments of a switch according to the invention are described in detail hereinafter, and the switch is illustrated with the aid of the accompanying drawings, wherein: Fig. 1 is a perspective view of the switch according to the invention; Fig. 2 is a sectional side view of a first embodiment of the switch of Figure 1, in a first operating position; Fig. 3 is a sectional side view of the switch of Figure 1, in a second operating position; Fig. 4 is a sectional side view of the switch of Figure 1, in a third operating position; Fig. 5 is a sectional side view of a second embodiment of the switch according to the invention; Fig. 6 is a sectional side view of a third embodiment of the switch according to the invention. With reference to the above figures, the timed safety switch according to the invention, generally designated by the reference numeral 1, essentially includes an enclosure 2 which can be anchored to the main body of a machine or apparatus and internally accommodates a series of fixed electrical contacts 3 and moving electrical contacts 3'. According to the invention, the switch comprises a door locking means including a safety key 4 which can be rigidly coupled to the door. The switch also comprises, inside the enclosure, a locking pin 5 which can be coupled to an actuation means for the actuation of the electrical contacts 3 by virtue of a delay means which are suitable to anticipate or delay the coupling of the pin 5 with the shank 6, so as to delay the release/locking of the door with respect to the opening/closure of the electrical contacts 3. A consent means allows the insertion/extraction of the safety key 4, through a slot 7 formed on the enclosure 2, only when the delay means is in the inactive position. In particular, the consent means is constituted by a rotating cam 8 with at least one tooth 9 along the outer profile for engaging the key 4 and a peripheral groove 10 which is adapted to engage the locking pin 5. According to the invention, the delay means is exclusively mechanical. In a first preferred embodiment, the delay means includes a threaded pin 11 having longitudinal ends rigidly coupled to the shank 6 and to the locking pin 5 respectively. The delay means is operatively coupled to a control means for the axial translatory motion of the threaded pin 11 between an active position and an inactive position. The control means comprises a female thread which is formed centrally in a first gear 12 which is rotatably coupled to the enclosure 2 and in which the threaded pin 11 engages. The first gear is coupled to a second gear 13 which can be actuated manually from the outside of the enclosure. The actuation of the gear assembly, formed by the two gears 12 and 13, causes the axial translatory motion of the threaded pin 11, which in turn produces, at different times, the axial translatory motion of the locking pin 5 between an extended position for locking the cam 8 and a retracted position in which the cam can rotate freely, and produces the translatory motion of the shank 6 between an open position and a closed position of the contacts 3. More specifically, these translatory motions of the locking pin 5 and of the shank 6, respectively, occur in a preset timing sequence which depends on the length of the threaded pin 11, on the pitch thereof, and on the speed with which the user manually operates the second gear 13. The enclosure 2 of the switch can be constituted by a main body 14 which is coupled to a head 15, which is removable and can be orientated in multiple positions in order to facilitate the installation of the switch and in which there is the slot 7 for the insertion of the safety key 4. In the embodiment shown in Figure 5, the threaded pin 11 is installed transversely with respect to the locking pin 5 and to the shank 6 and has an outer portion which screws onto a ring 16 which is rotatably rigidly coupled to the enclosure 2, can be accessed from outside and forms the control means. The innermost end of the threaded pin 11 is rigidly coupled to a tang 17 which forms two surfaces 18 and 19 which are substantially shaped like inclined planes, are mutually staggered and are adapted to interact respectively with the shank 6 and with the locking pin 5 in order to promote their respective translatory motions. In the third embodiment shown in Figure 6, the delay means is constituted by a rod 20 which is slidingly mounted on the enclosure 2 and lies substantially transversely to the locking pin 5 and to the shank 6. The rod 20 is elastically biased by a spring 21 and is provided with a button 22 at its outer end and with a portion 23 at its inner end. The portion 23 forms two inclined surfaces 24 and 25 which are mutually staggered and interact respectively with the locking pin 5 and with the shank 6 to promote their respective translatory motions. Furthermore, in the intermediate portion of the rod there is a rack 26 which engages a delay gear 27 which has a transmission ratio which is preset according to the intended delay action. In the active position of the locking pin 5, the rod 20 is substantially retracted inside the enclosure 2 and is kept therein in a stable position by removable retainers 28; the release of the retainers causes the protrusion of the rod from the enclosure with a slow movement which is delayed by the rotational actuation of the gears 27. The timed safety switch according to the invention fully achieves the intended aim, and in particular attention is drawn to its high reliability and precision in operation, ensured by its purely mechanical actuation systems. The switch according to the invention can be reset only in absolutely safe conditions, when the safety key is correctly inserted in the appropriately provided slot and therefore when the protective door of the machine in which it is installed is properly closed. The safety switch according to the invention is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept expressed in the accompanying claims.

Claims: Timed safety switch, particularly for accident-prevention doors of machines and apparatus, comprising an enclosure (2) which can be anchored to the body of the machine or apparatus and internally accommodates a series of fixed electrical contacts (3) and of moving electrical contacts (3'), a means (4, 5) for locking said door, said means being accessible from the outside and being operatively coupled to a means (6) for actuating said electric switch, a delay means (11) for anticipating or delaying the operation of the locking means (4, 5) with respect to the actuation of said switch, said delay means (11) being movable between an active position and an inactive position, said locking means (4, 5) comprising a safety key (4), which can be anchored to said door and can be inserted in a slot (7) of said enclosure (2), a consent means (8) which can move between: a non-blocking position for said key (4) to allow the insertion/extraction of said key (4) through said slot (7) when said delay means (11) is in its inactive position; and a blocking position for said key to block the insertion/extraction of said key (4) through said slot (7) when said delay means (11) is in its active position, characterized in that said locking means (4, 5) comprises a movable locking pin (5) which is connected to said delay means (11) and interacts with said consent means (8), and said consent means comprises a rotating cam (8) with at least one tooth (9) along the outer profile for engaging said key (4) and at least one seat (10) which is adapted to selectively accept said locking pin (5). Switch according to claim 1, characterized in that said delay means is of a purely mechanical type and comprises a threaded pin (11) which interacts with said locking pin (5) and with said actuation means (6) according to a preset timing sequence. Switch according to claim 1, characterized in that said delay means (11) is operatively coupled to a control means (12, 13) which can be accessed from the outside of said enclosure (2) and is suitable to promote the axial translatory motion of said threaded pin (11) between an active position and an inactive position. Switch according to claim 1, characterized in that said threaded pin (11) is operatively connected to a longitudinal shank (6) which forms said actuation means and acts on said contacts (3) in order to shift them between an open position and a closed position. Switch according to claim 1, characterized in that said control means comprises a first gear (12) which is rotatably rigidly coupled to said enclosure (2) and has a central female thread in which said threaded pin (11) engages, said first gear (12) being coupled to a second gear (13) which can be actuated from the outside of the enclosure (2). Switch according to claim 1, characterized in that said threaded pin (11) is substantially arranged parallel and coaxially to said shank (6) and to said locking pin (5). Switch according to claim 1, characterized in that said threaded pin (11) is arranged substantially transversely to said locking pin and has an outer portion, which engages a threaded ring (16) which is rotationally rigidly coupled to said enclosure (2) and can be actuated from the outside, and an inner end which is rigidly coupled to a tang (17) interposed between said shank (6) and said locking pin (5). Switch according to claim 7, characterized in that said tang (17) has two inclined surfaces (18, 19) which are mutually staggered and interact respectively with said shank (6) and with said locking pin (5) to promote their respective axial translatory motions according to a preset timing sequence. Switch according to one or more of the preceding claims, characterized in that in said threaded pin (11), the thread pitch and the length of its threaded part are preset according to a selected actuation delay. Switch according to claim 1, characterized in that said delay means comprises a rod (20) which is slidingly mounted on the enclosure (2) and is interposed transversely between said locking pin (5) and said shank (6). Switch according to claim 10, characterized in that said rod (20) is elastically biased by a spring (21) and is provided, at its outer end, with an actuation button (22); said rod having an internal end portion (23) which forms two inclined surfaces (24, 25) which are mutually staggered and interact respectively with the locking pin (5) and with the shank (6) to promote their respective translatory motions. Switch according to claim 10, characterized in that the intermediate portion of said rod (20) has a rack (26) which engages a delay gear (27) which is accommodated inside said enclosure and has a preset transmission ratio. Switch according to claim 1, characterized in that it has a disengageable retention means (28) which is adapted to keep said rod (20) elastically retracted toward the inside of said enclosure (2). Switch according to one or more of the preceding claims, characterized in that said enclosure (2) comprises a substantially box-like main body (14) which is coupled to a detachable and orientatable head (15) in which there is said slot (7) for the passage of said safety key (4).

Inventors: PIZZATO BERNARDO, PIZZATO, BERNARDO
Applicants: PIZZATO ELETTRICA SRL, PIZZATO ELETTRICA S.R.L.
Application year: 1997
Main classification: H01H27
IPC codes: H01H27