Patent Publication Number: US-4321699-A

Title: Wrist watch with alarm

Description:
CROSS-REFERENCE 
     This is a Continuation-in-part application of Ser. No. 833,148 filed Sept. 14, 1977, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a wrist watch with an alarm, which emits audible time sound produced by a vibrating plate to be vibrated by applying AC voltage to a piezoelectric element forming vibratory plate. 
     2. Prior Art 
     In conventional wrist watches of this type, alarm sound is produced inside a watch case where a diaphragm having a piezoelectric element is mounted. Such wrist watches are hermetically constructed for water-proofing or dust-proofing. Consequently, the alarm sound produced inside the watch case is barely audible, in most cases. 
     The wrist watch, as shown in FIG. 1 for example, discloses a solution to this problem. In FIG. 1 a reference numeral 1 represents a watch case on which a threaded back cover 2 is mounted with an O-ring 3 given pressure therewith. The back cover 2 has some holes 2a for passing sound, said holes being made on the bottom face of the back cover, and a disk diaphragm 4 fixed on the inner stepped portion. The diaphragm 4 consists of a base electrode 4a fixed at the periphery on the back cover 2, a piezoeletric element 4b attached to the inner side of the base electrode 4a and an electrode 4c formed on the inner side of the piezoelectric element 4b. The electrode 4c is connected to a circuit board 6 through a resilient lead 5. The circuit board 6 is mounted on a movement 7 which is housed inside the watch case 1. 
     In such a wrist watch as shown in FIG. 1, the piezoelectric element 4b is vibrated when voltage is applied between the base electrode 4a and the electrode 4c, and a vibration or alarm sound is produced at the center of the diaphragm 4. Said alarm sound is transmitted to the outside through the holes 2a. 
     In the wrist watch shown in FIG. 1, it is certain that the alarm sound produced therein can be transmitted to the outside with less resistance. However, the wrist watch cannot be kept hermetic or water-tight because of the holes 2a for sound passage, and neither water nor dust can be prevented from entering the watch. Furthermore, such holes are undesirable from the viewpoint of good appearance. 
     Thus, the wrist watch shown in FIG. 2 is designed to overcome the above disadvantages. This wrist watch includes a piezoelectric element 14b attached directly to a back cover 12 as a base, an electrode 14c formed on the other side of the piezoelectric element 14b, said electrode 14c being connected to a circuit board 16 mounted on a movement 17 through a lead 15. 
     In the wrist watch shown in FIG. 2, the back cover 12 itself is vibrated so as to produce alarm sound. Consequently, said alarm sound can be transmitted to the outside without any obstacle. It is, however, difficult to generate a sound of a high amplitude due to the back cover 1, which is commonly made of stainless steel having high rigidity, and therefore, sufficient alarm sound cannot be produced. 
     Furthermore, in prior art wrist watches vibrations may occur at the center of a diaphragm, and a high driving voltage is required for producing sound of a high amplitude. Such a low driving voltage as employed in these wrist watches would not be good enough, resulting in poor acoustic conversion efficiency. In addition, a plate-like diaphragm can be vibrated with small amplitude due to its high spring constant in vibrations, and has a high characteristic frequency, which is disadvantageous. A thinner diaphragm has been suggested for eliminating this drawback; however, this may result in cracking the piezoelectric element fixed on the base electrode and reducing the strength of the diaphragm itself unfavorably. 
     SUMMARY OF THE INVENTION 
     A primary object of the present invention is to provide a wrist watch with an alarm which permits emission of sufficient alarm sound with small power consumption by virtue of high acoustic conversion efficiency. 
     Another object of the present invention is to provide a wrist watch with an alarm which is good in appearance, highly water-proof and dust-proof, and capable of producing reliable and sufficient alarm sound. 
     Still another object of the present invention is to provide a wrist watch with an alarm where the exterior bottom housing vibrates by itself with the result of a compact and simple structure. 
     Yet another object of the present invention is to provide a wrist watch with an alarm where no sound outlet opening is needed allowing improved durability. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 show conventional wrist watches with an alarm. 
     FIG. 1 is a cross-sectional view in part of a wrist watch which is provided with some holes for passing sound on the back cover; and 
     FIG. 2 is a cross-sectional view in part of a wrist watch which has a piezoelectric element attached directly to the back cover. 
     FIGS. 3 through 5 show some embodiments of the present invention. 
     FIG. 3 is a cross-sectional view in part of a wrist watch as one embodiment, which has a vibratory plate fixed on a projection formed on the bottom housing; 
     FIG. 4 is a cross-sectional view of a fixing portion, as an example, where a vibratory plate is fixed on the back cover through a spacer; and 
     FIG. 5 is a cross-sectional view of a fixing portion as another example, where a vibratory plate is fixed at a point in contact with the bottom housing. 
     FIGS. 6A and 6B show still another embodiment of the present invention. 
     FIG. 6A being a plan view of a part of an alarm in a wrist watch; and 
     FIG. 6B being a vertical sectional view of the alarm taken diametrically. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 3, reference numeral 21 represents a watch case on which a threaded bottom housing 22 is mounted. An O-ring 23 is provided for water-proof and dust-proof use between the watch case 21 and the bottom housing 22, said O-ring being under pressure therebetween. The bottom housing 22 has a projection 22a formed at the center inwardly, and a vibratory plate 24 is fixed to the projection 22a. The vibratory plate 24 is attached by spot welding or screws. The vibratory plate 24 thus attached consists of a base electrode 24a fixed at the center of the projection 22a, a piezoelectric element 24b attached to the inner side of the base electrode 24a with adhesive or the like, leaving its central portion open, and an electrode 24c formed on the inner side of the piezoelectric element 24b, said electrode 24c being connected to a circuit board 26 through a resilient lead 25. This connection may be made by soldering a commonly used lead wire. The circuit board 26 is mounted on a movement 27 in a conventional manner, said movement being housed in the watch case 21. 
     In short, the plate 24 of the present invention comprises the piezoelectric element 24b, the base electrode sheet 24a provided at one side of the element 24b and the electrode 24c attached to the other side of the element 24b by evaporation, etc. The base electrode sheet 24a also works as a weight sheet for the relatively light weight piezoelectric element 24b so that the vibration of the vibratory plate 24 may be transmitted better to the exterior bottom housing 22. 
     With such an arrangement of the wrist watch shown in FIG. 3, ground potential is applied to the base electrode 24a through movement 27, watch case 21 and bottom housing 22, while driving potential is applied to the electrode 24c from the circuit board 26 through the resilient lead 23. As a result of alternate application of voltage between the base electrode 24a and the electrode 24c, the piezoelectric element 24b is oscillated. Such osillations are transmitted to the bottom housing 22 through the projection 22a, and audible time signals are produced from the bottom housing 22. 
     In other words, the base electrode sheet 24a is fixed to the inner face of the above-mentioned plaen of the exterior bottom housing 22 and is supported by the plane at a single point. Thus the vibration of the vibratory plate 24 with now considerably heavy weight is transmitted to the plane of the exterior bottom housing 22 to vibrate the plane to generate an alarm. 
     In the embodiment of FIG. 3, the projection 22a is formed on the bottom housing 22. It may be formed on the base electrode 24a, which is fixed on the bottom housing 22. 
     Furthermore, as illustrated in FIG. 4, a vibratory plate 24 may be fixed on a back cover 32 via a spacer 30. In FIG. 4 a reference numeral 34a represents a base electrode, 34b a piezoelectric element and 34c an electrode. 
     In addition, as illustrated in FIG. 5, a vibratory plate 44 may be fixed at a single point 40 by spot welding in contact with a back cover 42. In FIG. 5 a reference numeral 44a represents a base electrode, 44b a piezoelectric element and 44c an electrode. 
     In the embodiments shown in FIGS. 3 through 5, there is no description of the shape of these vibratory plates, which may be rectangular or in any other form. 
     In accordance with the teachings of the present invention, a vibratory plate is fixed at one point on the bottom housing of a wrist watch. This makes mounting work quite easy and assembling work simplier. Furthermore, the alarm sound can be produced efficiently even through a bottom housing of high rigidity by the effect of oscillations as if produced by a tuning fork controlled oscillator formed of the bottom housing and a vibratory plate integral therewith. Additionally, the piezoelectric elements may be damaged less frequently by handling such elements together with base electrodes having them attached thereto. 
     In FIGS. 6A and 6B reference numeral 54 represents a vibratory plate which consists of a piezoelectric element 54b, a base electrode 54a and an electrode 54c. The base electrode 54a is fixed on one side of the piezoelectric element 54b having a hole h at the center of the element like a disk, for example. The base electrode 54c is a disk which is larger in diameter than the piezoelectric element 54b, and has a projection p which extends in a direction opposite to the piezoelectric element 54b. The projection p is formed in alignment with the hole h on the piezoelectric element 54b so as to be spot welded on the bottom housing 52, to be described hereinafter. The electrode 54c, which is formed on the other side of the piezoelectric element 54b is a thin layer of silver evaporated thereon, for example, is connected to a lead wire 55 from a a power source (not shown). 
     The vibratory plate 54, thus constructed, has a plurality of slits which extend radially from the middle of the radius to the periphery in such a manner as to divide the vibratory plate 54 into like sections. Thus, the vibratory plate 54 has a plurality of fan-like sections separated from each other. 
     The projection p formed at the center of the vibratory plate 54 is fixed on the back cover 52. This is done by spot welding, for example, which applies a high energy to portions to be adhered for melting and bonding them. Two electrodes are required for spot welding, for which the hole h is provided on the piezoelectric element 54b for insertion. The vibratory plate 54 may also be fixed to the bottom housing 52 with an adhesive. 
     The vibratory plate 54 is vibrated by causing the piezoelectric element 54b to be strained periodically with AC voltage applied between the base electrode 54a and the electrode 54c holding the element therebetween. The vibratory plate 54 has a low intrinsic frequency of a high amplitude, retaining a large vibratory area which is divided into fan-shaped sections by radially extending the slits s. 
     As has been described heretofore, the present invention permits generation of vibrations of a high amplitude by means of a vibratory plate fixed at a single point on the inner side of the bottom housing of a wrist watch, said vibratory plate being divided into like sections by slits, with high acoustic efficiency obtained by small energy. This is very advantageous, particularly in electronic wrist watches where the power supply is quite small. In addition, fixing the vibratory plate at one point on the bottom housing prevents the plate from being damaged when any external force is imparted to the bottom housing, and makes it very easy to mount the plate thereon in the assembly of watch parts and elements. 
     It is preferable to produce an alarm sound whose pulse recurrence frequency is in a range of 1KHz to 4KHz, which would be most easy for users to hear. A vibrating system is naturally set for a resonance frequency between 1KHz and 4KHz.