DEVICE IN A SAFETY SWITCH

Abstract: The present invention relates to a device in a safety switch. The device (1) comprises a contact arm (2) and a latch (3) cooperating with the contact arm. The latch has an integrated spring portion (30). The invention also relates to a safety switch utilising the device. The safety switch comprises an operating handle (11) for manual switching on and off of the safety switch, the above-mentioned device (1) for closing and opening an electric circuit through the safety switch, a handle link (12) which connects the operating handle to the device for transferring a motion from the operating handle to the device, and a housing in which the parts included in the safety switch are arranged.

Description: DEVICE IN A SAFETY SWITCH Field of the Invention The present invention relates to safety switches and more specifically to a device in a safety switch accord¬ ing to the preamble to claim 1. Safety switches are used as short-circuit and over¬ load protection for single-phase or multiphase machinery, plants etc. and are frequently arranged in groups. Background of the Invention The inventive device in a safety switch consists of those parts that cooperate through a safety switch for maintaining and rapidly opening a connected (live) electric circuit when too much current flows in the cir¬ cuit which indicates some sort of short-circuit, over¬ load or leakage current. The device usually comprises a movable contact arm which, when the safety contact is first switched on, comes into engagement with a fixed contact and closes the electric circuit through the safety switch, and a locking and release mechanism com¬ prising a plurality of links and springs, which serves to lock the contact arm in a triggered, or switched-on, position and which is actuated to release the mechanism for opening the electric circuit. There are normally two members for actuating the locking and release mechanism, a solenoid reacting to a rapidly occurring short-circuit current by switching on the locking and release mecha¬ nism, and a bimetallic strip which is bent by generation of heat owing to a lower, longer current which is greater than a limiting value. The bimetallic strip acts on the locking and release mechanism through a link. Prior-art devices, such as the device in German Patent 3,516,217 or the device according to European Patent Publication 295 158, suffer above all from a basic drawback, viz. that they are made up of far too many com¬ ponents. This results in a high mass, which is a serious drawback. The relatively great mass of the prior-art devices gives, in combination with a high total friction between the many movable parts, a slow release of the locking and release mechanism. The speed is also reduced owing to the release of the mechanism occurring as a chain reaction between several components. In case of short-circuit, this causes a prolonged arc between the contact surface of the movable contact arm and the fixed contact, which in turn causes a great generation of heat in the safety switch. Therefore con¬ ventional safety switches burn unnecessarily quickly. This results, of course, in unnecessarily high operation expenses. Moreover, the risk increases that the connected machinery or plant is damaged dramatically with each moment that passes before the electric circuit is opened. Moreover, the mounting of the device will be compli¬ cated and time-consuming and the manufacture will be made more expensive. A particular drawback of prior-art devices is the small, loose springs that are used and that must be mounted together with the above-mentioned contact arm and links in the housing of the safety switch. Apart from their contributing to the above-mentioned drawback, they render automated mounting of the device in a safety switch considerably more difficult. Object of the Invention The object of the present invention is to provide a device in a safety switch, which has few components, has a small mass and permits automated mounting. Summary of the Invention The above-mentioned object is achieved by the in¬ ventive device being given the features stated in the accompanying claims. The main purpose of the spring integrated in the latch is to bias the latch and the contact arm in rela¬ tion to one another in various positions taken by the contact arm. This single and integrated spring eliminates a plurality of loose springs in conventional structures. This solution according to the invention reduces the weight and complexity of the device to a considerable extent, rationalises production and permits automated mounting of the device in a safety switch. Brief Description of the Drawings Figs 1-4 show a safety switch using the device according to the invention, the Figures illustrating various states of function. Fig. 5 shows a preferred embodiment of the inven¬ tive device. Fig. 6 shows from below a latch included in the device in Fig. 4. Fig. 7 is a side view of the latch in Fig. 6. Fig. 8 is a top plan view of the latch in Fig. 6. Fig. 9 shows a contact arm included in the device in Fig. 4. Fig. 10 shows a contact arm spring included in the device in Fig. 4. Fig. 11 shows an alternative embodiment of the latch included in the inventive device. Description of the Preferred Embodiment Fig. 1 shows a safety switch comprising a preferred embodiment of a device 1 according to the invention, said device having a movable contact arm 2 and a latch 3. Merely those parts which are included in the device 1 or which are necessary in order to explain the invention are shown. Through the safety switch, an electric circuit is made from, among other things, an incoming pole 4 ( illu- strated highly schematically), a bimetallic strip 5, a copper braid 6, the movable contact arm 2, a fixed con¬ tact 7, a solenoid 9 and an outgoing pole 10 (illustrat¬ ed highly schematically). The safety switch further com¬ prises an operating handle 11 for manual switching on/ switching off of the safety switch. The operating handle 11 is, via a handle link 12, connected to the device 1. The device 1 also comprises a contact arm spring 13, which is biased between the housing 14 of the safe¬ ty switch and contact arm 2. A clamp 15 connects the latch 3 to the bimetallic strip 5. The safety switch has two stable positions, switch- ed-on and switched-off. The positions are shown in Figs 1 and 3, respectively. From the switched-off position, the safety switch is switched on by moving the operating handle 11 in the direction of arrow A. This procedure will be described in more detail below. From the switch- ed-on position, the safety switch can be released, i.e. switched off, automatically in two ways. If a short-cir¬ cuit arises in the circuit in which the safety switch constitutes a link, a very great current arises imme¬ diately. This rapid and great change affects the sole- noid 9, such that its anchor is moved and displaces a forcing lever 17 (see Fig. 2), which in turn actuates the latch 3 such that the device 1 is released and takes its switched-off starting position. The second way arises as a slower procedure, in which a current which is above a permissible value arises in the electric circuit without affecting the solenoid. The too high current causes the bimetallic strip 5 to be hot and bend, thereby actuating the latch 3 via the clamp 15. The device 1 represents a unique new approach, which will be obvious from the following specification. The contact arm 2 and the latch 3 are rotatably arranged on a pivot pin 18, which in turn is mounted in the housing 14. One end 19 of the handle link 12 communicates with one end 20 of the contact arm 2 and one end 21 of the latch 3. In the starting position, Fig. 1, one end 19 of the handle link 12 is located, as is best seen in Fig. 5 in which the device 1 is shown in a view from the oppo¬ site side compared with the one shown in Figs 1-4, in a space which is defined by a first 22 and a second 23 engaging surface of the latch 3 and an engaging sur¬ face 24 of the contact arm 2. When the safety switch is switched on by means of the operating handle, the end 19 of the handle link 12 acts by a force on the contact arm 2 and the latch 3. The engaging surfaces 22-24 are so designed and angled and the link 12 performs such a move¬ ment that there is practically no power component forcing the ends 20, 21 of the contact arm 2 and the latch 3 apart. The friction between the link 12 and the contact arm 2 and the latch 3 contributes to this condition. How¬ ever, there is a risk that the contact arm 2 and the latch 3 separate from each other if the construction is subjected to vibrations. Among other things, for elimi¬ nating this risk, the device 1 according to the invention comprises a spring which forces one end 20 of the contact arm 2 and one end 21 of the latch 3 towards one another. The spring is integrated in the latch 3, i.e. it consti- tutes a spring portion 30 formed in one piece with the latch 3. In conventional devices serving the same purpose, a plurality of links and small, loose springs correspond to the latch 3 and its integrated spring 30. These links and springs make the mounting of the device complicated, give the mechanism an unnecessarily great mass and make the entire construction expensive. A preferred embodiment of the latch 3 and its spring portion 30 is shown in the Figures, especially in Figs 5-8. The spring portion 30 is below called latch spring 30. The latch spring 30 forms a tongue, whose first free end 31 is provided with a protrusion 33 which rests in a seat 34 formed in the contact arm 2. The other end 35, the base end or fixing end, of the latch spring 30 is positioned at one end 21 of the latch 3. During mounting in the housing 14, the contact arm 2 and the latch 3 are first joined in a simple operation in which the free end 31 of the latch spring 30 is placed in its seat 34 and the latch spring 30 is slightly biased by the latch 3 and the contact arm 2 being forced together and fixed by means of the pivot pin 18, which is moved into pivot pin seats which here consist of pivot pin holes 36a and 36b in the contact arm 2 and the latch 3, respectively. The pivot pin hole 36a in the contact arm 2 is elongate, see Figs 9 and 4. The reason for this will be explained below. Subsequently, this unit or package is mounted in the housing 14, a portion projecting from the package, in this case a portion of the pivot pin 18, being accommo¬ dated in a recess in the housing 14. The interconnection of the contact arm 2 and the latch 3 can be automated, but can also be carried out very quickly by hand. The package can advantageously be finally mounted, together with the remaining components of the safety switch, in the housing 14 in an automated operation. The latch 3 also comprises a clamp seat 40 for the clamp 15. In the preferred embodiment, the latch spring 30 is L-shaped, but has a curved transition portion 37 instead of the straight angle of the L. The pivot pin 18 is located essentially between the two ends 31, 35 of the latch spring 30. This means that the first and second ends 31, 35 of the latch spring 30 are so arranged that a clockwise turning moment arises when the contact arm 2 and the latch 3 are moved together, since the latch spring 30 is then forced essentially in the direction of arrow B by the contact arm 2 and is bent, mainly in the long leg 38. The turning moment forces the ends 20 and 21 towards one another. The latch spring 30 can be designed in various ways. For instance, the two ends of the spring portion can be positioned on the same side of the pivot pin 18, i.e. between the pivot pin 18 and one and the same end of the latch 3, as seen in the longitudinal direction of the latch 3, instead of being positioned on either side of the pivot pin, as in the embodiment described above. A further conceivable embodiment of the latch spring as shown in Fig. 11 has the spring fixed in both ends. This alternatively designed latch spring 60 comprises a clamp-shaped portion 61 and a protruding portion 62, resting in the seat of the contact arm, between the ends 63, 64. The latch spring 30 has a further function which is principally its main function. When the device 1 is released from the switched-on position, the latch 3 is caused to rotate in the direction of arrow C, see Fig. 5. The contact arm spring 13, like at this stage also the latch spring 30, strives to rotate with the contact arm 2 in the same direction, but owing to the handle link 12 retaining the contact arm 2, this cannot rotate. The end 21 of the latch 3 therefore is urged away from the end 20 of the contact arm. When the space between the ends 20 and 21 becomes greater than the diameter of the link 12, the inclination of the engaging surface 24 causes the end of the link 12 to be driven towards the pivot pin 18 and then the contact arm 2 can begin to rotate. The contact arm spring 13 drives the mechanism 1 to the switched-off position illustrated in Fig. 2. The operating handle 11 comprises a handle spring 25 which is tensioned during the manual switching-on of the switch. The handle spring thus acts as a return spring that returns the operating handle 11 to the starting position when the device 1 has been released. This results in the handle link 12 being moved back to the ends 20, 21 of the arm 2 and the latch 3. At this moment, the other function of the latch spring 30 will also come into the picture. The latch spring 30 keeps the ends 20, 21 together, thereby preventing the handle link 12 from leaving the space between the latch 3 and the contact arm 2. On the other hand, the handle spring 25 is sufficiently strong to pull the handle link 12 into the space defined by the engaging surfaces 22-24, which results in a transition from the switched-off posi¬ tion shown in Fig. 2 to the switched-off position shown in Fig. 3, where the operating handle 11 has returned to its starting position. The unique construction according to the invention having essentially two main components only, i.e. the contact arm 2 and the latch 3 and a spring 30 acting therebetween and constituting a portion of the latch 3, provides possibilities of designing the contact arm 2 in a completely new fashion. When the device 1 is released, the contact arm 2 moves very rapidly from the contact 7 to a stop lug 26. Then the contact arm 2 hits the stop lug 26 forcefully, which subjects the contact arm 2 to great stresses. It is therefore important that the con¬ tact arm 2 is designed so as to withstand high moments about the pivot pin 18. The stresses occurring on the contact arm 2 perpendicularly to the direction of motion thereof, however, are insignificant. The possibilities supplied by the integrated spring 30 in combination with the described force acting on the contact arm 2 have resulted in the illustrated, prefer¬ red embodiment of the contact arm 2. The contact arm 2 is flat, i.e. has a main extent in one plane, viz. in a plane perpendicular to the pivot pin, which in this case is the plane in which the contact arm 2 moves between the contact 7 and the stop lug 26. The flexural rigidity of the contact arm 2 is thus optimised and concentrated to the plane in which the great stresses arise. The most important advantage of the flat contact arm 2 is its greatly reduced weight in relation to the contact arms of the prior-art devices. A great advantage in terms of pro¬ duction is also achieved since the contact arm 2 can be made directly with a punch from a metal sheet. The flat shape of the contact arm 2 also simplifies the connection thereof with the latch 3. In the latch 3 there is formed a slit 39 which is centrally positioned in the latch 3. When moving the contact arm 2 and the latch 3 together, the contact arm 2 is simply moved into this slit 39 which guides the contact arm 2 and makes it easy to align the holes 36a and 36b, respectively, of the contact arm 2 and the latch 3 to pass the pivot pin 18 therethrough, as has been described above. The contact arm spring 13, which is shown on its own in Fig. 10, is fixed between the contact arm 2 and the housing 14. It has essentially three engag¬ ing portions, two at the ends 50, 51 of the contact arm spring 13 and one in the U-shaped central portion 52 of the spring 13. Each of the ends 50, 51 consists of a bent portion of the contact arm spring 13 and extends substan¬ tially perpendicularly to the plane of extension of the contact arm 2. The central portion 52 of the contact arm spring 13 rests in a seat 53 in the contact arm 2. The seat 53 is positioned between one end 20 of the contact arm 2 and the pivot pin hole 36a thereof. The ends 50, 51 of the contact arm spring rest in a seat 54 in the hous¬ ing 14. The contact arm spring 13 has two functions. When the mechanism is released, it causes the contact arm 2 to rotate about the pivot pin 18 such that its contact end moves from the contact 7 to the stop lug 26. The contact arm spring 13 is tensioned when the operating handle 11 is turned for switching on the safety switch. During the switching-on procedure, a point is reached when the con¬ tact end 8 of the contact arm 2 comes into engagement with the contact 7, see Fig. 4, where a portion of the latch 3 is broken away so as to uncover the contact arm 2 and its pivot pin hole 36a. From this position, the operating handle 11 is further turned a distance and dis¬ places the contact arm 2 in relation to the pivot pin 18. This displacement is made possible by the hole 36a in the contact arm 2 being elongate. The pivot pin 18 is now positioned approximately in the centre of the hole 36a. When the contact arm 2 is displaced, a new position in respect of the moments acting on the contact arm 2 arises. Instead of the pivot pin 18, the new point of engagement of the contact arm spring 13 is the engaging surface 24. This means that it is the contact arm spring 13 which produces the contact force by which the end of the contact arm 2 acts on the contact 7. By the contact arm spring 13 being connected to some other part merely at its ends 50, 51 and in its central portion 52, the contact arm spring 13 will, while being tensioned, pivot about its engaging portions or engaging points at the ends 50, 51 and in the central portion 52. The pivoting takes place above all about the ends 50, 51 engaging with the housing 14. This confers an important advantage when releasing the mechanism. Thanks to the contact arm spring 13 pivoting, during the initial stage of the releasing procedure, mainly about the ends 50, 51 and opening but to a small degree, it causes merely a very small fric¬ tional resistance which does not brake the movement of the contact arm 2 from the contact 7 to the stop lug 26 to any considerable extent. Also the mounting of the con¬ tact arm spring 13 thus contributes to the rapidity of the device. In order to further optimise the releasing rapidity of the device, the latch 3 and the contact arm 2 have been designed such that their masses are positioned as close as possible to the centre of rotation, i.e. the pivot pin 18. As a result, the moments of inertia are minimised. In the preferred embodiment of the invention, the latch 3 is made of plastic and is designed so as to be in ection-mouldable. The dimensions of the contact arm 2 and the latch 3 are minimised, as has also appeared from that stated above. As appreciated by a person skilled in the art, the illustrated preferred embodiment of the device consti¬ tutes merely an example and many modifications are con¬ ceivable within the scope of the invention as defined in the appended claims. As a possible modification, it may be mentioned that the contact end of the contact arm 2 can be extended in the plane perpendicular to the main extent of the contact arm 2. The aim is to increase the engaging surface of the contact arm 2 with the contact 7. Many different mate¬ rials are possible for the contact arm as well as the latch 3. The latch spring 30 can, of course, be designed in various ways and have various points of attachment, of which some examples have been stated above, and its con¬ nection with the contact arm 2 can be designed in diffe¬ rent ways. The device can be used in safety switches of diffe- rent kinds, such as safety switches having a different design of operating handle, short-circuit protection (solenoid) or thermal protection (bimetallic strip) or other parts for actuating the latch, compared with the forcing lever 17 and the clamp 15. The safety switch may also serve as short-circuit protection only.

Claims: CLAIMS 1. A device in a safety switch, said device (1) com- prising a contact arm (2), c h a r a c t e r i s e d in that said device further comprises a latch (3) cooperat¬ ing with said contact arm, that said latch has an inte¬ grated spring portion (30), and that the contact arm is substantially flat. 2. The device as claimed in claim 1, c h a r a c ¬ t e r i s e d in that the spring portion (30) engages with the contact arm, and that the spring portion is biased to force a first end ( 21 ) of the latch towards a first end (20) of the contact arm. 3. The device as claimed in claim 2, c h a r a c ¬ t e r i s e d in that the latch and the contact arm each have a pivot pin seat (36a and 36b, respectively), said pivot pin seats being adapted to receive a common pivot pin, about which the latch and the contact arm are pivot- able independently of each other, and that the spring portion is biased in such a manner that the first ends of the latch and the contact arm are forced towards each other by pivoting of the latch and the contact arm in opposite directions about the centre of the pivot pin seats. 4. The device as claimed in any one of claims 1-3, c h a r a c t e r i s e d in that the spring portion (30) forms a tongue (30) having a first free end (31) and a second fixed end (35), the first end engaging with the contact arm. 5. The device as claimed in claim 4, c h a r a c ¬ t e r i s e d in that the first and second ends of the tongue are positioned on either side of the centre of the pivot pin seats. 6. The device in a safety switch according to any one of the preceding claims, the safety switch compris¬ ing a housing and the contact arm being pivotable between a switched-on position and a switched-off position, c h a r a c t e r i s e d in that the device comprises a contact arm spring ( 13 ) having at least one first engag¬ ing portion which engages with the contact arm having a second engaging portion engaging with the housing, which acts on the contact arm and is adapted to perform a pivoting motion about the first engaging portion and also a pivoting motion about the second engaging portion when pivoting the contact arm between said positions. 7. The device in a safety switch according to any one of the preceding claims, c h a r a c t e r i s e d in that the latch and the contact arm are connectible in advance by means of a connecting member ( 18 ) so as to form a unit which in turn is mountable in a safety switch. 8. A safety switch comprising an operating handle (11) for manual switching on and switching off of the safety switch, a device (1) comprising a contact arm (2) for closing and opening an electric circuit through the safety switch, an operating handle link (12) connecting the operating handle with the device for transferring a motion from the operating handle to the device, and a housing in which said parts included in the safety switch are arranged, c h a r a c t e r i s e d in that the device further comprises a latch (3) cooperating with the contact arm, that the latch has an integrated spring portion (30), and that the contact arm is substantially flat.

Inventors: SJOESTEDT LENNART, SOEDERLUND PATRIK, SJOESTEDT, LENNART, SOEDERLUND, PATRIK
Applicants: ENPECE SIGMA AB, ENPECE SIGMA AKTIEBOLAG
Application year: 1996
Main classification: H01H71
IPC codes: H01H71