Electromagnetic relay equipped with bi-stable safety test push-button

Abstract: There is described an electromagnetic relay comprising a cover (1) containing a bi-stable test push-button (16), that realizes a temporary and a fixed contact positions; the test push-button (16) is equipped with retainer means (2⊘) to obtain the fixed position by pushing and simultaneously rotating it; and the cover (1) is equipped with means (34) to house the push-button (16) preventing its release in case of fixed closure. Moreover, the cover (39) can be equipped with a slider (4⊘) comprising means (46) to allow temporary pushing and means (42, 44) to allow permanently pushing the push-button (48) into its contact position.

Description: The present invention refers to an electromagnetic relay equipped with bi-stable safety test push-button. Various types of relay are known in the art, these relays being equipped both with Light Emitting Diodes (LED) indicating the active and inactive status of the relay itself, and with test push-buttons: by pressing these push-buttons, a user is able to close circuit contacts to detect its operation. Currently known test push-buttons are of two types: the first type, so-called "mono-stable", allows, by pressing it, to close the circuit for the test, but, once released, returns into its rest position, opening the circuit again. The second type of known push-button is the so-called "bi-stable" one (a type of bi-stable push-button is manufactured by Relpol) and is configured in such a way as to assume a circuit closing position both temporarily, after having pressed it, and permanently, that is by displacing it into a fixed position. This possibility, however, poses some problems, above all linked to plant and people safety: first of all, if the push-button is forgotten into its fixed actuation position, the circuit remains closed even when it should not be (that is, at the end of testing) and could damage plants or machines controlled thereby. Moreover, given the current configuration of known push-buttons, their fixed actuation can be simply and quickly carried out, even casually and by untrained people or by people that have no intention to carry out tests: all these generate risks that can be easily thought of. EP 408544 discloses a relay having a housing supporting a magnet system, an armature and a test pin. In order that the test pin can be locked in the operating position only by an authorised person, and is thus clearly visible, irrespective of whether the relay is in the test position or in normal operation, an operating device, separated from the relay, is provided to operate the test pin which operating device can be inserted into the relay and, in its operating position, in which it holds the test pin in its operating position, can be locked with the relay and which can be separated from the relay again only by exercising force. DE 8908125 discloses a device for switching on and off electric apparatuses including a relay, an armature operable by means of a coil and a control cam. An attachment carrying an electric switch is arranged in a circuit associated to the coil and is operable by means of the control cam. EP 534572 discloses a bistable electrical relay comprising a first contact, a movably mounted, essentially rigid arm coupled thereto and provided with a first connecting point, and a second contact coupled to an immovably mounted further arm which is provided with a second connecting point. To operate the contacts, electromagnetic drive means are provided which act on the movable arm via spring means for producing contact force. To keep the contacts closed, the drive means are provided with permanent magnets, while further spring means act on the movable arm to keep the contacts open. US 3,733,568 describes a push button relay, in which the closing of the relay contacts is independent of the magnetic circuit of the relay, includes a coil, a magnetizable armature, one end of which normally exerts a force upon a movable contact carrying member to move its contacts out of contact with the stationary contacts of the relay, and a manually operable push button which, when depressed, contacts the armature to overcome the contact opening force exerted by the armature upon the movable contacts, and urges the contact carrying member and its contacts toward the stationary contacts. US 4,378,543 describes a spring biased reciprocable latch-reset member provided for a relay of the type including an armature mounted on a support block for pivotal movement about an axis, a coil for displacing the armature from a first position to a second position when the coil is energized, a spring biasing the armature from the second position to the first position when the coil is de-energized, and an electrical contact controlled by the position of the armature. Object of the present invention is solving the above prior art problems, providing an electromagnetic relay equipped with a bi-stable test push-button that allows realizing the two working positions in a simple, but simultaneously efficient way, and above all a safe way, since inadvertent and undesired actuations are practically prevented. The above and other objects and advantages of the invention, as will appear from the following description, are obtained by means of an electromagnetic relay equipped with bi-stable safety test push-button as disclosed in Claim 1. Preferred embodiments and non-trivial variations of the present invention are disclosed in Claims 2 to 7. The present invention will be better described by some preferred embodiments thereof, provided as a non-limiting example, with reference to the enclosed drawings, in which: Figure 1 is a simplified side view of a relay equipped with an embodiment of a bi-stable push-button according to the present invention, in its rest position; Figure 2 is a side view similar to Fig. 1, but that shows the push-button actuated by a temporary pressure; Figure 3 is a side view similar to Fig. 1, but that shows the push-button actuated as closed in a fixed position; Figure 4 is a bottom view of the cover of the embodiment of the electromagnetic relay of the present invention shown in Fig. 1; Figure 5 is a side sectional view of the cover shown in Fig. 4; Figure 6 is a top view of the cover shown in Fig. 4; Figure 7 is a side view of the test push-button that can be used in the embodiment of the relay shown in Fig. 1; Figure 8 is a front, partially sectioned view of the test push-button in Fig. 7; Figure 9 is a top view of the test push-button in Fig. 7; With reference to the Figures, the electromagnetic relay of the present invention is composed of a cover 1, usually made of transparent plastic material, and of a body 3 including a support base 5 and a set of known electric components, that will not be described hereinbelow, apart from the major ones that have some relevance to the present invention. The base 5 of the relay body 3 is equipped with a set of lamellar terminals 7, 7', 7" for the adequate connections, some of these terminals 7, 7' being equipped with enlarged internal ends 9, 9' in turn equipped with contacts 11, 11'. Between the two pairs of terminals 7, 7', and therefore of contacts 11, 11', a contact member 13 is placed (commonly realized as small copper blades) that in turn is equipped with two contacts 14, 14' on its two sides, and that can assume two different contact positions, in which the two different pairs of contacts 11, 11' will be contacted. The two operating positions of the contact member 13 are controlled by energizing or de-energizing a coil 15, that attracts or releases the contact member 13 itself, that is supported by a support 15' and is taken back to its rest position by a resilient member 15". All operations that have been briefly described above are well known in the field of electromagnetic relays. The operation for these relays is commonly controlled by means of push-buttons that allow manually and mechanically operating the contact member 13 so that it is able, by striking and pushing the tongue 17, to make it assume, like in the case shown in Fig. 2 and 3, the operating position where lower contacts 11' are connected. Test push-buttons can be actuated by pushing and then releasing them, thereby recreating the two operating conditions respectively shown in Fig. 1 and in Fig. 2 and 3, or they can be taken to the position shown in Fig. 2 and 3 and left there to subject the relay to longer contact tests. In this case, the position reached is the one shown in Fig. 3. The push-button 16 used in the relays of the present invention is of this second type, and is therefore called "bi-stable", because it can assume both test positions, that is the temporary and the permanent one. The push-button 16 of the present invention, however, is different from the known ones because, in order to actuate it, a set of specific operations are necessary, that make a casual actuation as well as an actuation carried out in any undesired way, impossible. For this purpose, the push-button 16 is realized, in a first embodiment thereof, as best shown in Figures 7 to 9. In these Figures, the push-button 16 is composed of a small elongated cylinder 18, at one end of which a projection 20 is obtained so that the push-button 16 gets the shape of a key. Moreover, the small cylinder 18 is equipped with a tooth 21 whose function is preventing the cylinder from coming out of the relay in its rest position. At the opposite end of the small cylinder 18, the push-button is equipped with an elongated head 22 shaped as an arrow with a bit 24 on one side and a seat 26 for screwdrivers with normal or star bit. In order to efficiently actuate the push-button 16, the relay of the present invention must further be equipped with a suitable cover 1, that is best shown in Figures 4 to 6. In these Figures, the cover 1 is shaped in order to have a housing 28 for the push-button 16 in its rest position, and an hole 30 with a keyway 32. The hole allows inserting the small cylinder 18 of the push-button 16 inside a cylindric housing 34, also shaped in order to receive the cylinder 18 with the key projection 20 into the seat 32. Finally, a plurality of holes 36 with varying diameters are provided, said holes being adapted to contain corresponding projections of the front plate 33 of the relay that will be placed on the upper side of the cover 1. The cover 1 is finally equipped with a special safety feature, composed of a retainer tooth 38 made of plastic material, that can be easily broken down and detached from the cover 1 if one wishes to actuate the push-button 16 in its permanent test contact position. Otherwise, this retainer tooth 38 does not allow operating the push-button 16 by rotating it, only allowing it to be operated by pressing and releasing it as typical of mono-stable push-buttons. The operation of this first embodiment of the electromagnetic relay of the present invention will now be described, with particular reference to Fig. 1 to 3. The push-button 16 in Fig. 1 finds itself in a rest position, where a connection occurs between lower contacts 11 of the terminals 7 and upper contacts 14 of the contact member 13. From this position, by a finger pressure, the upper contacts 11' of the terminals 7 can be brought into connection with the lower contacts 14' of the contact member 13, as better shown in Fig. 2. Upon releasing the finger pressure, the push-button 16 will go back to the position in Fig. 1: it will therefore operate as mono-stable push-button. If one wishes to operate the push-button 16 as bi-stable, it will be firstly be necessary to break down and detach the retainer tooth 38 from the cover 1 and then, by acting through a suitable screwdriver, to push and simultaneously rotate (in a counterclockwise and upward direction with respect to the drawings) the push-button 16: in this way, this pushing actuates the connection between contacts 11' and 14' as shown in Fig. 2, and the rotation frees the projection 2⊘ from the keyway into the cylindric housing 34, so that, into the final contact position shown in Fig. 3, the projection 20 abuts against the cylindric housing 34 and keeps the push-button 16 into the connection position in Fig. 3. If one wishes to take back the push-button 16 to its rest position in Fig. 1, it will suffice to push with a finger the push-button 16 by rotating it and to snap-take it back into the adequate housings 28 and 34 provided on the cover 1.

Claims: Electromagnetic relay comprising: a body (3) equipped with a base (5) containing an energising coil (15) adapted to connect contacts (11, 11') of terminals (7, 7') to contacts (14, 14') of contact members (13); a cover (1) adapted to be inserted onto said body (3), said cover (1) being equipped with means (34) to house a test push-button (16) preventing the release thereof during the fixed closure step of the contacts (11', 14'); the test push-button (16) is of the bi-stable type, and is adapted to realise a fixed closing position of the contacts (11', 14') and a temporary closing position of the contacts (11', 14'), said test push-button (16) being equipped with retainer means (20) to perform the fixed closure position by pushing and simultaneously rotating said push-button (16), characterised in that said cover (1) is equipped with second retainer means (38) to prevent the undesired actuation, in the fixed closure, of said test push-button (16) while allowing to control said push-button (16) in the temporary closing position. Electromagnetic relay according to Claim 1, characterised in that said test push-button (16) is composed of a key with a small cylinder (18) and said retainer means (20) of said test push-button (16) are composed of a projection (20) from said small cylinder (18), said test push-button (16) being further equipped with an elongated head (22) with a seat (26) for a screwdriver and said cover (1) is equipped with a cylindric housing (34) containing a seat (32) for said projection (20). Electromagnetic relay according to Claim 1 or 2, characterised in that said retainer means (38) of said cover (1) are composed of a retainer tooth (38). Electromagnetic relay according to Claim 3, characterised in that said retainer tooth (38) is able to be broken down and detached from said cover (1). Electromagnetic relay according to Claim 3 or 4, characterised in that said retainer tooth (38) is made of plastic material. Electromagnetic relay according to claim 3, characterised in that said cylinder (18) is equipped with a further tooth (21) for preventing said cylinder (18) from coming out of said relay in its rest position. Electromagnetic relay according to any of the preceding claims, wherein said cover (1) is provided with a plurality of holes (36) having varying diameters, said holes (36) being adapted to contain corresponding projections of a front plate (33) of said relay arranged on the upper side of said cover (1).

Inventors: GIORDANINO PIERO, GIORDANINO, PIERO
Applicants: FINDER SPA, FINDER S.P.A.
Application year: 1997
Main classification: H01H50
IPC codes: H01H50