Patent Application
20110211427
This application claims priority from European Patent Application No. 10154767.7 filed Feb. 26, 2010, the entire disclosure of which is incorporated herein by reference.
The invention concerns a striking mechanism for a watch provided with an active damper counter-spring. The mechanism includes at least one hammer arranged to strike at least one gong secured to a gong-carrier at determined times. Said hammer is held away from the gong by said damper counter-spring in an idle mode. A drive spring for the hammer of the mechanism can be configured in the form of a resilient strip or beam. This drive spring can be wound to drive said hammer against the gong to provide an acoustic signal, for example, of a programmed time period.
Within the field of watchmaking, a striking mechanism can be combined with a conventional watch movement to act as a minute repeater or to indicate a programmed alarm time. This type of striking mechanism generally includes at least one gong made of metallic material, such as steel, bronze, precious metal, metallic glass, sapphire or quartz. The gong may describe, for example, at least one portion of a circle around the watch movement inside the watch frame. The gong is secured by at least one end thereof to a gong-carrier, which is in turn secured to a watch plate. A strike-hammer is rotatably mounted on the plate, for example, in proximity to the gong-carrier so as to strike the gong and cause it to vibrate. The sound produced when the gong is struck by the hammer is within the audible frequency range of 1 kHz to 20 kHz. This indicates a well defined time, a programmed alarm or a minute repeater to the person wearing the watch.
As shown in EP Patent No 1 574 917, the striking mechanism of a watch may include two gongs each secured via one end thereof to the same gong-carrier, which is in turn secured to a plate. Each gong may be struck by a respective hammer. To achieve this, each hammer is driven by its own drive spring, which must have been pre-wound, so as to drive the hammer against the gong to indicate a minute repeater or an alarm time. Two damper counter-springs are each provided to push back and hold the two hammers away from the gongs in an idle mode. The damper counter-springs also slow down the fall of each hammer before it strikes the respective gong and then push the hammer back into the idle position. Eccentrics are also provided for adjusting the operation of the counter-springs to prevent each hammer from rebounding against the respective gong.
One drawback of this type of striking mechanism structure with counter-springs is that there is a significant loss of kinetic energy when the hammer strikes the respective gong, which reduces the acoustic level of the striking work. This energy loss is largely due to the slowing down imposed by each counter-spring on the path of the hammer when it strikes the gong. Moreover, even if the pre-winding of the drive springs is increased, this involves adapting the counter-springs via their eccentric, also to prevent any rebound, which is another drawback of this type of striking mechanism.
EP Patent No. 2 048 548, which mainly discloses a hammer of a watch striking mechanism may also be cited. This hammer includes two parts hinged to each other and a resilient member secured to one of the hinged parts. When the hammer is in a stable position, the resilient spring member holds the two parts of the hammer, whereas when the hammer is in the striking position, the two parts move away from each other, returned by the resilient spring member. With this arrangement, it is possible to reduce the kinetic energy that the hammer loses against a damper member. However, this type of hammer arrangement complicates the fabrication of the striking mechanism to prevent the hammer losing energy when it strikes the gong, which is a drawback. Undesirable rebounds of the hammer against the gong may also occur during the strike, which is another drawback.
It is thus an object of the invention to overcome the drawbacks of the aforementioned state of the art by providing a watch striking mechanism, which includes means for increasing the acoustic level of the sound produced by at least one gong struck by at least one hammer, and prevents the hammer from rebounding and losing energy during the strike.
The invention therefore concerns a watch striking mechanism, which includes:
wherein it includes means for actuating the damper counter-spring in a strike mode with a time lag after the hammer strikes the gong, so that after the hammer has struck the gong, the counter-spring pushes said hammer towards an idle position, said means for actuating the damper counter-spring in the strike mode including a stop member arranged on the path of the drive spring.
Specific embodiments of the watch striking mechanism are defined in the dependent claims 2 to 11.
One advantage of the striking mechanism according to this invention lies in the fact that it includes a damper counter-spring which is considered “active”, i.e. when the hammer strikes the gong it does not immediately act to push said hammer back towards the idle position. Once the hammer strikes the gong, the counter-spring can be actuated with a time lag via the drive spring abutting a stop member combined with the counter-spring.
Advantageously, the drive spring can take the form of a resilient metal strip or beam secured to the watch plate and with a free end for pushing a stud or shaft of the rotating hammer when the hammer strikes the gong. The hammer is driven in rotation by the drive spring to strike the gong while preserving all the strike energy and without being braked by the counter-spring. This thus ensures an increase in the acoustic level produced when the gong is struck by the hammer. The drive spring may also be braked by contact with the stop member combined with the counter-spring after said hammer has struck the gong. Once the hammer has struck the gong, the counter-spring pushes the hammer towards its idle position to prevent the hammer from rebounding against the gong. In the idle mode, the hammer shaft is kept confined between the free end of the drive spring and one end of the counter-spring.
The objects, advantages and features of the watch striking mechanism with an active damper counter-spring will appear more clearly in the following description, particularly with reference to the drawings, in which:
In the following description, all those parts of the watch striking mechanism combined with the watch movement, which are well known in this technical field, will be only briefly described. The emphasis is mainly placed on the arrangement of the spring elements of the striking mechanism, including the active damper counter-spring. As a result of the various spring elements of said striking mechanism, the hammer loses less energy when it strikes the gong, and there is improved security against any rebounding of the hammer against the gong.
Striking mechanism 1 further includes a damper counter-spring 5 for holding hammer 2 away from the gong in an idle mode, and a drive spring 3 for the hammer. Drive spring 3 can be wound by a lever 11, explained below, to drive hammer 2 against the gong in a gong striking mode to produce an acoustic sound. Damping counter-spring 5 is defined as active, since it acts on the hammer to return it to the idle position just after the hammer strikes the gong to prevent any loss of energy by the hammer when it is in action. This also increases the quality of the sound produced.
As can be seen in
The free end 3a of the beam of drive spring 3 may be arranged in an idle mode at a slight distance from hammer shaft 6 (not shown). However, since stop member 10 is combined with counter-spring 5, the first end 5a of said counter-spring is actively driven with hammer shaft 6 by stop member 10 against the free end 3a of the drive spring in the idle mode. The hammer is thus held at a distance by damper counter-spring 5 abutting against hammer shaft 6, which projects from plate 15 on the side of the spring elements.
Damper counter-spring 5 is formed by a substantially rectilinear lever rotatably mounted about a perpendicular axis 8 to watch plate 15. A first end 5a of the lever of counter-spring 5 thus abuts against hammer shaft 6 to hold it at away from the gong in the idle mode. A second end 5b of this lever of counter-spring 5 is arranged on an opposite side of the first end 5a relative to axis of rotation 8. An eccentric part 4 can be rotatably mounted on plate 15 to act as a rotational stop member for the lever of counter-spring 5.
The first end 5a of metal counter-spring 5 can bend slightly in the strike mode just after the hammer strikes the gong via the force applied by drive spring 3 when it is in action, as explained below with reference to
It is to be noted that, in theory, eccentric part 4 is not used in this embodiment to act as a support point for the lever of counter-spring 5 so that the latter pushes the hammer towards its idle position after the strike. The eccentric part could even be omitted from the striking mechanism. Eccentric part 4 is formed of a wheel which may be in contact with one surface of second end 5b. This wheel of eccentric part 4 is mounted off-centre on a rotating pin arranged in a bore in plate 15. The freedom of rotation of counter-spring 5 during the operation in which the hammer strikes the gong can thus be adjusted by rotating this eccentric part 4.
In the embodiment of
A second eccentric part 14 may also be rotatably mounted on counter-spring 5 for adjusting the position of stop member 10 on counter-spring 5. This eccentric part 14 includes a pin inserted in a bore of equivalent diameter made on an intermediate portion of counter-spring 5 between axis of rotation 8 and the second end 5b of the counter-spring. Above the pin, the second eccentric part 14 has an off-centre portion placed in another through opening 24 of particular shape at one end 10b of a second branch of stop member 10. This off-centre portion is in contact with an inner surface of the other through opening 24 of the stop member. When the second eccentric part 14 is rotated, this allows the free end of the first lever branch 12 of stop member 10 to be moved further away from or closer to the gong. In these conditions, the intermediate part of the pre-wound drive spring 3 comes into contact more or less quickly with the free end of first lever branch 12 of stop member 10 when the hammer strikes the gong. This also has the effect of adjusting the delay in action of counter-spring 5 after the hammer first strikes the gong.
The hammer, actuated by the drive spring at work, is quickly propelled against the gong before the drive spring actuates the counter-spring, via contact on stop member 10, to push the hammer back to its idle position. The time lag before counter-spring 5 acts may be around 2 ms depending upon the configuration of the spring elements and the hammer, and the materials of which they are formed.
In this embodiment, the first and second lever branches of stop member 10 are arranged substantially opposite each other, with a pierced part between the two branches. The rotation of the free end of first branch 12 and the second branch occurs on the same side relative to axis of rotation 8 of stop member 10 and counter-spring 5. On the path of drive spring 3 when the hammer strikes the gong, the intermediate part of the spring comes into contact with the free end of the first lever branch 12 of stop member 10. The second lever branch of stop member 10 is normally provided for driving counter-spring 5 so that the first end 5a thereof comes into contact with hammer shaft 6 in the idle mode. After contact with stop member 10 during a strike operation, the remaining movement of drive spring 3 can be estimated at between 0.03 and 0.06 mm. This second lever branch 12 of stop member 10 also brakes the drive spring 3 when it is in action, while activating damper counter-spring 5 to clamp and return hammer shaft 6 to the idle position. This operation is carried out with a time lag relative to the strike of the hammer against the gong.
In an embodiment that is not shown, the base of the first lever branch 12 of stop member 10 can be located at end 10b of the stop member, where the second eccentric part 14 is arranged. This gives a pierced part between the two branches of the stop member arranged in reverse fashion to the embodiment shown in
As shown in
Depending upon the material that forms the gong, an initial adjustment has to be carried out by second eccentric part 14 to prevent any rebound when the hammer strikes the gong. For a gold gong compared to a steel gong, the impact portion of the hammer can be arranged further away from the gong. However, because of stop member 10, drive spring 3 can be pre-wound more or less strongly with any type of gong material once the initial adjustment has been carried out.
Various positions of the different spring elements will now be described, before, during and after the strike of the hammer against the gong with reference to
In
To improve further the quality of the sound of gong 21 when it is struck by hammer 2, the hammer may be made of a hard material, such as cobalt-tungsten carbide (WCCo), or a ceramic or diamond material. At least the portion 2a of hammer 2 that impacts gong 21 should be made of this hard material. Further, the material of said hammer 2 may also have a high density. This increases the energy when the hammer strikes the gong for a given strike speed of the hammer. Damper counter-spring 5 does not cause any loss of energy when the hammer strikes given that it acts after a time lag to return the hammer to the idle position. This counter-spring 5 may also be made of hard metal or steel, like stop member 10, whereas drive spring 3 may be made of conventional spring steel.
Gong 21 can be made in the form of at least one portion of a circle or rectangle. The gong may also be, for example a metal wire of circular or rectangular transverse section, which is generally made of steel or precious metal or metallic glass. This portion of a circle or rectangle conventionally surrounds a part of the watch movement (not shown).
Following the idle mode, drive spring 3 is pre-wound at the start of the striking mode as shown in part in
In
In
Once the hammer has struck said gong, counter-spring 5 is actuated by drive spring 3 in contact with stop member 10, as shown in
From the description that has just been given, several variants of the watch striking mechanism with an active counter-spring can be devised by those skilled in the art without departing from the scope of the invention defined by the claims. The stop member and the counter-spring may form a single piece. Other means may be provided for actuating the counter-spring with a time lag after the hammer strikes the gong. A trigger device may force the counter-spring into a withdrawn position when the drive spring is being pre-wound. This trigger device may release the counter-spring as soon as the hammer first strikes the gong so that the counter-spring pushes the hammer towards the idle position without rebounding against the gong. The hammer may be mounted on the plate to strike the gong along a rectilinear path rather than a rotating path. Several gongs of different lengths may be provided, secured to or integral with the same gong-carrier mounted on the plate or on a portion of the watch case. Each gong can be struck by a respective hammer, where each hammer is driven by its own drive spring. A damper counter-spring combined with a stop member must thus be provided for each hammer.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10154767.7 | Feb 2010 | EP | regional |
