Conventionally, a timepiece with a wireless function such as a personal computer communication function, a cellular phone function, and a noncontact IC card function has been well known. As such a timepiece with a wireless function, a timepiece with a wireless function for receiving a long-wave standard radio wave (carrier wave) including time information and for correcting clock time based on the time information has been also widely known.
Similarly to other communication devices, the timepiece with a wireless function must be provided with an antenna for receiving a prescribed radio wave. Consequently, it is thought that a housing that is a chassis for storing the antenna that receives a radio wave is made of a nonconductive material such as a synthetic resin from a viewpoint of a function for receiving a radio wave, which is so-called receiving sensitivity.
However, the timepiece with a wireless function is a timepiece which requires the beauty and luxury as an ornament or an accessory unlike other communication devices. Consequently, it is required to adopt not a nonconductive material such as a synthetic resin but a conductive material, that is, a metal material as a material of the housing that is a chassis for storing the antenna that receives a radio wave.
The reason of the above requirement is that a housing made of a synthetic resin gives the cheap appearance and wearing sense to a user from a viewpoint of a texture, a color tone, and lightness in weight. On the other hand, a metal housing gives the luxury appearance and wearing sense to a user.
The demand to the metal housing is extremely remarkable for a wristwatch as a portable accessory of a user. However, in the case in which the antenna is stored in the conductive housing, that is, the metal housing, a magnetic flux generated around the antenna is absorbed in the metal housing that is a conductive material, thereby preventing a resonance phenomenon. Consequently, a receiving function for receiving the standard radio wave by the antenna is extremely degraded.
Therefore, a variety of proposals for improving receiving sensitivity has been carried out.
For instance, Patent document 1 (Japanese Patent Application Laid-Open Publication No. 2004-325315) discloses a radio controlled timepiece, in particular a radio controlled wristwatch, provided with a metal housing that is a metal chassis. More specifically, as shown in FIG. 34, a radio controlled wristwatch 100 is provided with a housing 102.
The vertical direction described in the present specification means the upward and downward direction in the cross sectional views of FIGS. 34 and 2 and so on. Consequently, the upper face is a face exposed outside in the state in which a user wears the wristwatch on the wrist, and the lower face is a face that faces the wrist in the same state.
The planar direction is a direction perpendicular to the vertical direction and means a horizontal direction in the cross sectional views of FIGS. 34 and 2 and so on. In some cases, the planar direction corresponds to a longitudinal direction of a band or a width direction of a band.
The housing 102 is provided with a watch case 104 that configures a metal frame, a rear cover 106 made of a metal mounted to the watch case 104 in such a manner that the rear cover 106 covers a lower opening section of the watch case 104 in a sealing state, and a windshield (glass) 108 mounted to the watch case in such a manner that the windshield 108 covers an upper opening section of the watch case in a sealing state.
The housing 102 contains a movement 110 that configures a clock drive section and a dial plate 112 made of a metal disposed on the movement 110.
An antenna 116 for receiving the standard radio wave is disposed under the lateral part of the movement 110.
A minute hand and an hour hand are mounted to a hand spindle that protrude from the movement 110 and that penetrate the dial plate 112 although this is not shown in the figure. The minute hand and the hour hand are located between the dial plate 112 and the windshield 108 to indicate time.
For the radio controlled wristwatch 100 in which a metal external packaging is adopted, the antenna 116 is shielded by the metal watch case 104, the metal rear cover 106, and the metal dial plate 112. Consequently, an external radio wave is blocked by the metal parts, thereby preventing a radio wave from being received by the antenna 116 disposed in the housing 102.
In particular, in the case in which the metal watch case 104, the metal rear cover 106, and the metal dial plate 112 are made into contact directly with each other, a loop is formed electromagnetically among the metal watch case 104, the metal rear cover 106, and the metal dial plate 112. The loop is closed electromagnetically, whereby an external radio wave is further hard to reach the antenna 116.
To avoid such a phenomenon, for the radio controlled wristwatch 100 disclosed in Patent document 1, the metal dial plate 112 is covered by an insulating film 114, and an insulating layer 118 is formed between the watch case 104 and the rear cover 106.
By the above configuration, a loop is not formed electromagnetically among the metal watch case 104, the metal rear cover 106, and the metal dial plate 112. Consequently, an external radio wave is hard to be shielded by the metal parts.    Patent document 1: Japanese Patent Application Laid-Open Publication No. 2004-325315    Patent document 2: Japanese Utility Model Application Laid-Open Publication No. 6-80192
However, for the radio controlled wristwatch 100 disclosed in Patent document 1 and depicted in FIG. 34 herein, the watch case 104 made of a metal is located close to the antenna 116 while surrounding the antenna 116 as a ring part made of a metal having a size almost equivalent to a vertical thickness of the radio controlled wristwatch 100.
As described above, the watch case 104 made of a metal extremely larger than other parts shields an external radio wave, thereby preventing a radio wave from being received by the antenna 116 disposed in the housing 102. Consequently, the antenna 116 cannot receive a radio wave sufficiently.
Moreover, in the case in which an external radio wave or a radio wave generated by the antenna 116 causes a magnetic field around the watch case 104 made of a metal to fluctuate periodically, a magnetic flux passing through the opening that vertically penetrates the watch case 104 also fluctuates. As a result, an eddy current is generated in a circumferential direction of the watch case 104 made of a metal due to an electromagnetic induction.
An eddy current generated as described above consumes the energy of a radio wave, thereby reducing the receiving sensitivity of a radio wave of the antenna 116 disposed in the housing 102.
In particular, an eddy current generated on the metal watch case 104 having a large cross section along a vertical direction (diagonal line section of the watch case 104 in FIG. 34) flows as a comparatively large inductive current. Therefore, the eddy current cancels a radio wave transmitted from the outside of the housing 102, thereby reducing the receiving sensitivity of the antenna 116. Consequently, the receiving sensitivity of the antenna 116 cannot be improved sufficiently.
Accordingly, the metal watch case 104 that is disposed around the antenna and that is a conductive part having the largest volume is separated into a plurality of parts, and the parts are insulated one from the other. It is thought that shielding of an external radio wave due to the watch case 104 can be reduced by the above configuration.
Moreover, by separating the watch case 104 into a plurality of parts, a small eddy current is generated for each separated part as compared with a large eddy current generated in the case of the watch case 104 of one body that is not separated into a plurality of parts. Consequently, it is thought that a reduction in the receiving sensitivity of the antenna 116 due to the eddy current can be suppressed.
As a result, even in the case in which the conductive watch case 104 made of a metal is used, it is thought that the receiving sensitivity of the antenna 116 can be improved.
Some radio controlled wristwatches provided with such a housing made of a metal are provided with a bezel as one of a plurality of parts separated from the watch case 104 made of a metal. The bezel is a ring member mainly disposed around the windshield on the upper side of the watch case. In some cases, the bezel is made of a metal from a viewpoint of a beauty, a luxury or the like.
Such a wristwatch provided with a bezel is disclosed in Patent document 2 (Japanese Utility Model Application Laid-Open Publication No. 6-80192). As shown in FIG. 35 herein, a wristwatch 200 is provided with a housing 202. The housing 202 is provided with a watch case 204 that configures a metal frame, a rear cover 206 made of a metal mounted to the watch case 204 in such a manner that the rear cover 206 covers a lower opening section of the watch case 204 in a sealing state, and a windshield (glass) 208 mounted to the watch case in such a manner that the windshield 208 covers an upper opening section of the watch case in a sealing state.
Moreover, the watch case 204 is provided with a watch case body 210 and a bezel 212 disposed above the watch case body 210. A waterproof packing 214 is disposed between the watch case body 210 and the bezel 212.
The housing 202 contains a movement 216 that configures a clock drive section and a dial plate 218 disposed on the movement 216.
A minute hand 222 and an hour hand 224 are mounted to a hand spindle 220 that protrude from the movement 216 and that penetrate the dial plate 218. The minute hand 222 and the hour hand 224 are located between the dial plate 218 and the windshield 208 to indicate time.
For the wristwatch 200 that adopts such a metal external packaging and that is provided with the watch case body 210 and the bezel 212 as one of parts separated from the watch case 204 made of a metal, in the case in which a rear cover 206 that functions as a ground on a human wrist side, the watch case body 210, and the bezel 212 are electrically insulated by the waterproof packing 214, a static electricity from the side of the windshield 208 is stored in the bezel 212 in some cases.
By the operation of a static electricity, as shown by the dashed lines in FIG. 35, the minute hand 222 is abutted to the windshield 208, and the minute hand 222 cannot be moved in some cases. In addition, a static electricity is transmitted to the movement 216 via the minute hand 222, thereby preventing the movement 216 from being operated.
To solve the above problem, in Patent document 2, a conductive paste 226 is disposed between the watch case body 210 and the bezel 212, thereby ensuring an electrical conduction between the watch case body 210 and the bezel 212. Consequently, a static electricity from the windshield 208 side is grounded to a human wrist via the bezel 212, the watch case body 210, and the rear cover 206.
However, Patent document 2 does not target a radio controlled wristwatch in which an antenna is stored in a housing. In addition, even in the case in which the configuration of Patent document 2 for ensuring an electrical conduction between the watch case body 210 and the bezel 212 by forming a conductive paste 226 between the watch case body 210 and the bezel 212 is applied to a radio controlled wristwatch, a loop is formed electromagnetically between the watch case body 210 and the bezel 212, and the loop is closed electromagnetically, whereby an external radio wave is hard to reach the antenna.
Moreover, an eddy current generated on the metal watch case 204 having a large cross section along a vertical direction (diagonal line sections of the watch case body 210 and the bezel 212 in FIG. 35) flows as a comparatively large inductive current. Therefore, the eddy current cancels a radio wave transmitted from the outside of the housing 202, thereby reducing the receiving sensitivity of the antenna. Consequently, the receiving sensitivity of the antenna cannot be improved sufficiently.
Some radio controlled wristwatches provided with such a housing made of a metal are provided with a dial ring as a lining part separated from the watch case or the bezel as one of a plurality of parts separated from the watch case 104 made of a metal. Chiefly, the dial ring is a ring member disposed between the windshield and the dial plate in the housing. The upper surface of the dial ring functions as a mounting face of the windshield, and an inclined surface extending downward from the upper surface to the dial plate functions as an index surface in which an index for indicating a functional display of a watch is arranged.
In some cases, the dial ring is also made of a metal from a viewpoint of a beauty, a luxury or the like.
However, in the case in which the dial ring made of a metal is used for the radio controlled wristwatch provided with a housing made of a metal as described above, the receiving sensitivity of the antenna is greatly reduced disadvantageously. For instance, even in the case in which an insulating later is disposed between a metal rear cover and a metal watch case as disclosed in Patent document 1, a reduction in the receiving sensitivity cannot be sufficiently improved.
The present invention was made in consideration of such conditions, and an object of the present invention is to provide a timepiece with a wireless function in which the metal watch case that is disposed around the antenna and that is a conductive part having the largest volume is separated into a plurality of parts, and the parts are insulated one from the other, whereby shielding of an external radio wave due to the watch case can be reduced. Moreover, by separating the watch case into a plurality of parts, a small eddy current is generated for each separated part as compared with a large eddy current generated in the case of the watch case of one body that is not separated into a plurality of parts, whereby a reduction in the receiving sensitivity of the antenna due to the eddy current can be suppressed for the timepiece with a wireless function. Furthermore, the timepiece with a wireless function has improved receiving sensitivity of the antenna and reliably receives a prescribed radio wave by the antenna even in the case in which a watch case or the like made of a conductive metal is used.