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(11) | EP 0 921 543 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Electric safety switch |
| (57) A switch (1) is described herein comprising a primary switch operator (2) and an
auxiliary switch operator (11) which are operatively and simultaneously opened and
closed by a push-button (7). The contacts of the switch operators (2,11) are set to
make the auxiliary switch operator (11) close and open in advance of the closure and
the opening of the primary switch operator (2). The switch (1) is fitted with locking
appendices and locking seats (16a, 16b) which operate an arrest of the push-button
(7) when the primary switch operator (2) remains welded in closure. This allows the
user immediately to detect the origin of the malfunction of the electrical circuit
(3). |
[0001] The present invention relates to an electric switch of the type comprising: at least one primary switch mechanism (2) comprising at least one primary movable contact (2a), at least a first primary fixed contact (2b) and at least a second primary fixed contact (2c) respectively connected to the opposite poles of the electrical circuit (3); first operating means (4) to bring selectively the primary switch operator (2) between an open condition and a closed condition of the electrical circuit (3); control means (7) for the selective activation of the first operating means (4); auxiliary switching means (11); second operating means (12) to bring the primary switching means (11) from a closed condition to an open condition of the electrical circuit (3) at least in a condition of non operation of the primary switch mechanism (2).
[0002] More in detail, the invention is applicable to switches, switch operators, shunt operators and the like employed for uses of all kinds.
[0003] As is well known, electric safety switches comprise a primary switch operator which opens and closes upon operation of control means which are essentially constituted by a push-button operated manually or in another manner by the user.
[0004] To the primary switch mechanism are associated auxiliary switching means able to ensure circuit opening in case the primary switch remains welded in a closed condition.
[0005] For the purposes of the present description, as the most pertinent example of the prior art, US patent 5,304,753 is hereby recalled.
[0006] With reference to the switch described in the aforementioned patent, said switch comprises a primary switch mechanism having a pair of primary movable contacts engaged on a first contact carrier. Said contact carrier can be translated along a sliding guide by the operation of the aforementioned push-button in opposition to a first return spring, to engage in closure said movable contacts on respective primary fixed contacts connected to a battery.
[0007] The auxiliary switching means present an auxiliary movable contact in bridging connection on the pair of primary movable contacts. Such auxiliary movable contact is engaged on a second contact carrier interposed between the push-button and the first cursor and able to translate along the sliding guide together with the first contact carrier itself.
[0008] Interposed between the first contact carrier and the second contact carrier is present a second return spring which tends to bias the second contact carrier away from the first contact carrier to cause the circuit to open by disengaging the auxiliary movable contact from the primary movable contacts.
[0009] Under normal operating conditions the second return spring remains compressed between the first and the second cursor as an effect of the action imparted by the first return spring, so that the auxiliary movable contact is maintained in closure on the primary movable contacts.
[0010] When the user presses the push-button, he/she pushes the second contact carrier and simultaneously the first contact carrier, thereby placing the primary movable contacts in closure onto the primary fixed contacts. In the moment wherein the user releases the push-button the primary spring pushes simultaneously both contact carriers thereby bringing the primary switch, and thus the entire circuit associated to the switch, back to an open condition.
[0011] However, as a consequence of the electrical discharges produced in the opening and closing phase, welding phenomena of the primary movable contacts on the primary fixed contacts may occur, with the result that in the moment wherein the user releases the control push-button, the return spring pushes the movement assembly without thereby obtaining any biasing effect.
[0012] In this circumstance, since the user no longer acts on the push-button, the auxiliary spring is no longer maintained compressed and is free to move the second contact carrier away from the first contact carrier thereby causing the disengagement of the auxiliary movable contact from the primary movable contacts and, consequently, the opening of the circuit.
[0013] As a consequence of the movement of the auxiliary movable contact away from the primary movable contact, expandable side portions of the second contact carrier interpose themselves between the auxiliary movable contact and the primary movable contacts themselves, in such a way as to prevent the electrical circuit from closing even after the push-button is operated anew.
[0014] A problem which can be encountered with safety switches of the type described above stems from the fact that the movable contact of the auxiliary switch operator is forced constantly to remain in the closed position throughout the duration of the life of the switch itself, since its opening switching takes place solely and exclusively as a result of the failure on the primary switch operator.
[0015] The static permanence of the auxiliary movable contact in the closed position can determine, in certain situations, the binding of the movable contact itself onto the primary movable contacts and, consequently, the lack of intervention by the auxiliary switch operator at the proper time.
[0016] Note that the disposition of the auxiliary movable contact in direct contact on the primary movable contacts favours the possibility of welding between therebetween, also as a consequence of the overheating which the primary movable contacts may undergo due to the discharges produced when opening and closing.
[0017] It should also be noted that with the use of the safety switches described above it is difficult for the user to verify immediately whether the cause of the inoperative condition of the electrical circuit resides in the failure of the switch itself. This is because it is possible to operate the push-button moving the second contact carrier, without thereby closing the circuit. In such cases the user has the impression that the safety switch is operating normally and he/she is led to formulate a series of erroneous hypotheses about the origin of the malfunction of the circuit with the deriving waste of time.
[0018] Object of the present invention is essentially to solve the problems of the prior art, proposing an electric safety switch of improved reliability. An additional object of the invention is to propose a safety switch that facilitates the immediate identification of the intervention of the auxiliary switch operator in opening.
[0019] This object and others besides, which will appear more clearly in the course of the present description, are essentially attained by an electric switch, characterised in that said auxiliary switching means comprise at least one auxiliary switch operator having at least a first auxiliary fixed contact connected to a pole of the circuit, at least a second auxiliary fixed contact connected with the first primary fixed contact and at least one auxiliary movable contact operatively connected with said second operating means.
[0020] Additional characteristics and advantages shall be made clearer by the detailed description of a preferred, but not exclusive, embodiment of an electric switch, according to the present invention. Such description shall be made hereafter with reference to the enclosed drawings, provided purely by way of non limiting indication, in which:
- Figure 1a shows the subject switch in perspective view in a resting phase wherein a primary switch operator and an auxiliary switch operator are open;
- Figure 1b shows the switch in top view in the same phase as Figure 1a;
- Figure 1c is a side view of the switch in the same phase as in Figures 1a and 1b and in an upside down position with respect to these Figures;
- Figure 2a shows the switch in perspective view in a transitory phase wherein the auxiliary switch operator is in a closed position and the primary switch operator is in an open position;
- Figure 2b shows the electric switch in top view in the same phase as in Figure 2a;
- Figure 2c is a side view of the electric switch in the same phase as in Figures 2a, 2b and in upside down position with respect to these Figures;
- Figure 3a shows the electric switch in perspective view in a phase wherein both switch operators are closed;
- Figure 3b shows the electric switch in top view in the same phase as in Figure 3a;
- Figure 3c is a side view of the electric switch in the same phase as in Figures 3a, 3b and in upside down position with respect thereto;
- Figure 4a shows the electric switch in perspective view in a locked situation wherein the primary switch operator remains closed and the auxiliary switch operator is open;
- Figure 4b shows the electric switch in top view in the same phase as in Figure 4a;
- Figure 4c is a side view of the electric switch in the same phase as in Figures 4a, 4b and in upside down position with respect thereto;
- Figure 5 is a diagram of the switch in the resting phase as per Figures 1a, 1b and 1c;
- Figure 6 is a diagram of the switch in the transitory phase as per Figures 2a, 2b and 2c;
- Figure 7 is a diagram of the switch in the closed situation as per Figures 3a, 3b and 3c;
- Figure 8 is a diagram of the electric switch in a return phase and in an operative condition wherein the primary switch operator is about to open the electric circuit whilst the auxiliary switch operator is still in the closed phase;
- Figure 9 is a diagram of the electric switch in the return phase and in an operative condition wherein the primary switch has opened the circuit and the auxiliary switch is about to open;
- Figure 10 is a diagram of the electric switch under welding condition of the primary switch operator, with the auxiliary switch operator still closed, but about to open;
- Figure 11 is a diagram of the electric switch under welding condition of the primary switch operator, with the auxiliary switch operator open;
- Figure 12 is a diagram of the electric switch in the locked condition as per Figures 4a, 4b and 4c.
[0021] With references to the aforementioned figures, the number 1 indicates in its entirety an electric safety switch, according to the present invention.
[0022] Electric switch 1 comprises at least one primary switch operator 2 which can be operatively associated to an electric circuit 3.
[0023] Preferably, the primary switch operator 2 comprises essentially at least one primary movable contact 2a operating in sliding relationship on at least a first primary fixed contact 2b and at least a second primary fixed contact 2c respectively connected to the opposite poles of the electrical circuit 3. A third primary fixed contact 2d can also be provided, which, in the embodiment shown, is essentially inactive for the purposes of the electrical connection and shall not therefore be further considered for the purposes of the present description.
[0024] To the primary switch operator 2 are associated first operating means 4 which serve to bring selectively the switch operator itself from an open condition wherein, as can be seen for instance in Figure 5, the primary movable contact 2a engages only the first primary fixed contact 2b, to a closed condition wherein the movable contact itself engages both the first and the second primary fixed contacts 2b, 2c, to determine the closure of the electrical circuit 3.
[0025] To this end, the first operating means 4 preferably comprise at least a first contact carrier 5 slidingly guided on a guide structure 6 (not visible in Figures 5-12) and carrying the primary movable contact 2a.
[0026] The first contact carrier 5 presents a first striker seat 5a acting in push-off relationship against control means 7, comprising for instance a push-button, a pedal or another organ which can be employed by a user to determine the selective activation of the operating means themselves.
[0027] In particular, the action by the user on the push-button or similar control means 7 determines the translation of the first contact carrier 5 along the guide structure 6 in contrast with at least a first spring 8, to bring the primary switch operator 2 from the open condition to the closed condition.
[0028] An arrest element 9 integral with the guide structure 6 serves to act on the contact carrier 5 to arrest its movement imparted by the control means 7 when the primary switch operator 2 reaches the closed condition.
[0029] A first pre-loading spring 10 acting between the primary movable contact 2a and the first cursor 5 ensures a suitable and constant support pressure of the movable contact itself on fixed contacts 2b, 2c.
[0030] By effect of the electrical discharges inevitably generated in the opening and closing phases of the primary switch operator 4, 5, following prolonged operation with repeated operations, welding phenomena of the movable contact 2a on the fixed contact 2b, 2c may arise.
[0031] In such a circumstance, the primary movable contact 2a can no longer be brought back to the opening condition, and the circuit 3 would remain in closure conditions even after the interruption by the user of the thrusting action on the control means 7.
[0032] This circumstance would cause dangerous situations, above all if the electrical circuit is used to supply power to a motor of a vehicle or of a machine of another kind.
[0033] To obviate this dangerous situation, the switch 1 is fitted with auxiliary switching means which, according to the present invention, preferably comprise at least an auxiliary switch operator 11 electrically connected in series to the primary switch operator 2. The auxiliary switch operator 11 also comprises an auxiliary movable contact 11a operating in sliding relationship on at least a first auxiliary fixed contact 11b connected to one of the poles of the electrical circuit 3, as well as a second auxiliary fixed contact 11c electrically connected with the first primary fixed contact 2b.
[0034] The enclosed Figures also show a third auxiliary fixed contact 11d, essentially inert for the purposes of the electrical contact and therefore not further considered in the course of the present description.
[0035] The auxiliary movable contact 11a is operatively connected to second operating means 12 set to bring the auxiliary switch operator 11 selectively from an open condition wherein the movable contact 11a is operatively engaged only with the auxiliary fixed contact 11b, to a closed condition wherein the movable contact itself is operatively in contact with both auxiliary fixed contacts 11b, 11c to cause the first primary fixed contact 2b to be electrically connected with the corresponding pole of the electrical circuit 3.
[0036] To this end, the second operating means 12 comprise a second contact carrier 13 slidingly guided on the guide structure 6 according to a direction parallel to the direction of sliding of the first contact carrier 5, and carrying the auxiliary movable contact 11a.
[0037] The second contact carrier 13 presents a second striker seat 13a which acts in push-off relationship against the control means 7 in such a way that, upon activation of the control means themselves, the cursor 13 is translated in contrast to the action of at least a second return spring 14 interposed between the first and the second cursor 5, 13, taking the auxiliary switch 11 from the open position to the closed position.
[0038] A second pre-loading spring 15 or equivalent elastic organs operatively interposed between the second contact carrier 13 and the auxiliary movable contact 11a ensure that a suitable and constant thrusting action is imparted thereby upon auxiliary fixed contacts 11b, 11c.
[0039] As the enclosed Figures show, the second contact carrier 13 is translated simultaneously to the first contact carrier 5 upon operation of the control means. However, the switch of the auxiliary switch operator 11 between the open and the closed condition occurs in advance with respect to the switch of the primary switch operator 2 between the corresponding open and closed conditions.
[0040] In this way, there is a guarantee that the closure of the auxiliary movable contact 11a on the auxiliary fixed contacts 11b, 11c takes place in the absence of current, in order to prevent the formation of discharges between the contacts of the auxiliary switch operator 11.
[0041] In this way there is a guarantee that the auxiliary switch operator 11 remains totally immune from risks of welding phenomena, which may instead occur on the primary switch operator 2.
[0042] To this end, primary movable contact 2a and auxiliary contact 11a are preferably to be set parallel according to a mutually offset position. As can clearly be seen in Figures 1c, 2c, 3c and 4c, also the primary fixed contacts 2b, 2c and the auxiliary fixed contacts 11b, 11c can be distributed along respective rows set parallel according to a mutually offset position, in such a manner as to cause the opening and closure of the auxiliary switch operator 11 to occur in advance with respect to the primary switch operator 2.
[0043] As can clearly be seen by comparing Figures 5 through 9, under normal operating conditions of the switch 1 the operation and return to resting position of the control means 7 determines the simultaneous movement of the first and of the second contact carriage 5, 13 and the subsequent selective switch in closure and in opening of the primary switch operator 2 and of the auxiliary switch operator 11.
[0044] When the primary movable contact 2a is welded onto the primary fixed contacts 2b, 2c, non-operation by the primary switch operator 2 prevents the first contact carrier 5 from being translated upon the action of the first return spring 8 when action by the user on the control means 7 is interrupted.
[0045] In this circumstance, the second return spring 14 determines the translation of the second contact carrier 13 with respect to the first contact carrier 5, thereby assuring the interruption of the electrical circuit 3 following the opening of the auxiliary switch operator 11.
[0046] According to the present invention, the safety switch 1 is further fitted with locking means 16 which intervene in case of non operation by the primary switch operator 2 to lock the second operating means 12 with the auxiliary switch operator in open condition, and to inhibit at the same time the further activation of the control means 7.
[0047] The locking means 16 comprise preferably one or more coupling appendices 16a extending from the second operating means 12, and more specifically from the second contact carrier 13, able to be operatively engaged in corresponding coupling seats 16b obtained in the first operating means, and more specifically in the first contact carrier 5. As can clearly be seen by comparing Figures 7, 10, 11 and 12, in case of non operation by the primary switch operator 2, the sliding engagement of the second operating means 12 with respect to the first operating means 4 causes the second contact carrier 13 to be brought, upon the action of the second return spring 14, from an operative position wherein the coupling appendices 15a are disengaged from the corresponding coupling seats, to a locking position wherein, as per Figure 12, the coupling appendices 16a are engaged in the corresponding seats 16b.
[0048] In this circumstance, the auxiliary switch operator 11 remains permanently locked in an open condition, and the second striker seat 13a borne by the second contact carrier 13 interferes with the operating means 7 thereby inhibiting their activation on the part of the user.
[0049] The engagement of the coupling appendices 16a in the corresponding coupling seats 16b is assured by elastic locking organs acting in thrust relationship on second operating means 12.
[0050] In a preferential embodiment, such elastic locking organs comprise the same pre-loading spring 15 operatively interposed between the auxiliary movable contact 11a and the second cursor 13.
[0052] The intervention of the locking means 16 determines, in addition to the disablement of the operation of the auxiliary switch operator 11, the locking of the control means in the rest position. In other words, the action of the user on the control means 7 produces no displacement thereof.
[0053] In this way, the user has the immediate perception of the failure situation on the safety switch, and is not led to seek in other points of the circuit the cause of the non-operation of the apparatus whereto the switch itself is associated.
[0054] It should also be noted that, differently from what can be found in the prior art, in the subject switch the auxiliary switch operator does not statically remain in a closed condition, but is subjected to the same opening and closing actions imposed on the primary switch operator.
[0055] In this way there is a guarantee that the auxiliary switch operator functions perfectly in the moment wherein it will have to intervene to open the circuit under a condition of malfunction of the primary switch operator.
[0056] It should further be noted that the use of sliding contacts both on the primary switch operator and on the auxiliary switch operator is an additional advantage for the purposes of the reliability of the system, deriving from the self-cleaning action which occurs on the contacts during the switching phases.
1. Electric safety switch comprising:
- at least a primary switch operator (2) comprising at least a primary movable contact (2a), at least a first primary fixed contact (2b) and at least a second primary fixed contact (2c) respectively connected to the opposite poles of the electrical circuit (3);
- first operating means (4) selectively to bring the primary switch operator (2) between an open condition and a closed condition of the electrical circuit (3);
- control means (7) for the selective activation of the first operating means (4);
- auxiliary switching means (11);
- second operating means (12) to bring the auxiliary switching means (11) from a closed condition to an open condition of the electrical circuit (3) at least in a condition of non operation by the primary switch operator (2).
2. Switch according to claim 1, characterised in that it further comprises locking means
(16) to lock the second operating means (12) with the auxiliary switch operator (11)
in open condition and inhibit the activation of the control means (7) when the condition
of non operation by the primary switch operator (2) arises.
3. Electric safety switch comprising:
- at least a primary switch operator (2) comprising at least a primary movable contact (2a), at least a first primary fixed contact (2b) and at least a second primary fixed contact (2c) respectively connected to the opposite poles of the electrical circuit (3);
- first operating means (4) selectively to bring the primary switch operator (2) between an open condition and a closed condition of the electrical circuit (3);
- control means (7) for the selective activation of the first operating means (4);
- auxiliary switching means (11);
- second operating means (12) to bring the auxiliary switching means (11) from a closed
condition to an open condition of the electrical circuit (3) at least in a condition
of non operation by the primary switch operator (2);
characterised in that it further comprises locking means (16) to lock the second operating
means (12) with the auxiliary switching means (11) in an open condition and to inhibit
the activation of the control means (7) when the condition of non operation by the
primary switch operator (2) arises.
4. Switch according to claim 2, characterised in that said auxiliary switching means
(11) comprise an auxiliary switch operator (11) having at least a first auxiliary
fixed contact (11a) connected to a pole of the electrical circuit, at least a second
auxiliary fixed contact (11c) connected with the first primary fixed contact (2b)
and at least one auxiliary movable contact (11a) operatively connected with said second
operating means (12).
5. Switch according to claim 1 or 3, characterised in that said primary movable contact
(2a) operates in a sliding relationship with respect to the primary fixed contacts
(2b, 2c).
6. Switch according to claim 1 or 4, characterised in that said auxiliary movable contact
(11a) operates in sliding relationship with respect to the auxiliary fixed contacts
(11b, 11c).
7. Switch according to claim 2 or 3, characterised in that said locking means (16) comprise
at least a first coupling appendix (16a) which extends from the second operating means
(12) and can be engaged in at least one corresponding coupling seat (16b) obtained
on the first operating means (4).
8. Switch according to claim 7, characterised in that said second operating means (12)
are slidingly engaged to the first operating means (4) and movable with respect thereto
between an operative position wherein the coupling appendix (16a) is disengaged from
the coupling seat (16b) and a locking position wherein the coupling appendix (16a)
is engaged in the coupling seat (16b).
9. Switch according to claim 2 or 3, characterised in that the locking means (7) present
at least a second striker seat (13a) obtained on said second operating means (12)
and acting in push-off relationship against the control means (7) to inhibit its operation
when the second operating means (12) are in the locked position.
10. Switch according to claim 7, characterised in that said locking means (16) further
comprise elastic locking organs (15) acting in thrust relationship upon the second
operating means (12) to insert the coupling appendix (16a) into the respective coupling
seat (16b).
11. Switch according to claim 1 or 3, characterised in that said first operating means
(4) comprise a first contact carrier (5) engaging the primary movable contact (2a)
and slidingly guided on a guide structure (6) to bring the primary switch operator
from the open condition to the closed condition in contrast to a first return spring
(8).
12. Switch according to claim 1 or 4, characterised in that said second operating means
(12) comprise a second cursor (13) engaging the auxiliary movable contact (11a) and
slidingly guided on a guide structure (6) to bring the auxiliary switch operator (11)
from the open condition to the closed condition in contrast to a second return spring
(14).
13. Switch according to claim 1 or 4, characterised in that the first and the second operating
means (4, 12) comprise respectively a first and a second striker seat (5a, 13a) acting
in push-off relationship against the control means (7) to bring respectively the primary
switch operator (2) and the auxiliary switch operator (11) from the respective open
conditions to the respective closed conditions upon activation of the control means
themselves.
14. Switch according to claim 1 or 4, characterised in that said primary (2) and auxiliary
(11) switch operators can be operated essentially simultaneously upon activation of
the control means (7), the switch of the auxiliary switch operator (11) between the
open condition and the closed condition occurring in advance with respect to the switch
of the primary switch operator (2) between the corresponding open and closed condition.
15. Device according to claim 1 or 4, characterised in that said primary movable contact
(2a) and said auxiliary movable contact (11a) are set parallel according to a mutually
offset position.
16. Device according to claim 1 or 4, characterised in that said primary fixed contacts
(2b, 2c) and said auxiliary fixed contacts (11b, 11c) are distributed according to
respective rows set parallel according to a mutually offset position.