Timepiece movement

Abstract: A timepiece movement comprising at least two rotors (4,7) which are respectively arranged to drive respective shafts (1 a ,2 a ) each of which is adapted to support a respective timepiece hand, the shafts (1 a ,2 a ) being concentrically mounted, characterised in that adjacent shafts (1 a ,2 a ) are rotatably supported by a tube (3) which is disposed therebetween and is fixed in fixed structure (11), whereby each shaft (1 a ,2 a ) is unaffected by the rotation of the other.

Description: The present invention relates to a timepiece movement, e.g. for use in an electronic timepiece. A timepiece movement is known in which two rotors are respectively arranged to drive respective shafts each of which is adapted to support a respective timepiece hand, the shafts being concentrically mounted. In the known construction, adjacent shafts are in contact with each other so that one of them is liable to be affected by the rotation of the other. For example, if one of the shafts is a seconds hand shaft which is driven by a stepping motor, the adjacent shaft being a continuously driven minutes hand shaft, the rotation of the minutes shaft is liable to cause swinging or vibration of the seconds hand when the latter should be stationary. In US-A-4,623,261 there is disclosed a timepiece movement comprising at least two rotors which are respectively arranged to drive respective shafts each of which is adapted to support a respective timepiece hand, the shafts being concentrically mounted, adjacent shafts being rotatably supported by a support tube which is disposed therebetween and is fixed in fixed structure. In US-A-4,623,261, however, the support tube is fixed to an intermediate bridge, whereas the rotors are rotatably mounted in a plate and a main bridge, while gearing between each rotor and its respective shaft is rotatably mounted in the intermediate bridge and in a further bridge. Consequently, the construction shown in US-A-4,623,261 involves the use of three bridges and of the said plate. In EP-A-148 414 a timepiece is disclosed having a fixed structure which provides prevents rotation of one drive means affecting the other. However, the timepiece involves the use of one base in which the fixed structure is mounted and at least two further bridges disclosed either side of the fixed structure to support the rotors and respective gear train. Hence, the timepiece in this document is not of a minimum thickness. According, therefore, to the present invention, there is provided a timepiece movement as claimed in claim 1 appended hereto. Each shaft may be constituted by a shaft portion of a gear forming part of the respective gearing. One of the shafts may be constituted by a seconds hand shaft which is arranged to be driven by the rotor of a step motor. The invention also comprises a timepiece, e.g. an electronic timepiece, provided with such a timepiece movement. In the case of the present invention, therefore, the hands of the timepiece can be operated accurately without irregularities, and swinging or vibration of a hand attached to a shaft which is currently not driven is prevented. At the same time, the drive force of one of the shafts is not transmitted to the other shaft or shafts since the shafts are not in direct contact with each other. Thus, when one of the shafts is driven while the other is at a standstill, the drive force of the driven shaft is not transmitted to the other shaft or shafts so that the hand attached to the stationary shaft does not swing or vibrate and the hand attached to the driven shaft runs smoothly without being affected by a load from the stationary shaft. The invention is iillustrated, merely by way of example, in the accompanying drawings, in which: Figure 1 is a sectional view of a movement of an electronic timepiece having two rotors in accordance with the present invention, and Figure 2 is a sectional view of a known movement of an electronic timepiece having two rotors. In Figure 1 there is shown a timepiece movement according to the present invention comprising a first hand gear 1 which is driven by a first rotor 4 as a drive source through drive transmitting gears 5 and 6, and a second hand gear 2 which is driven by a second rotor 7 as another drive source through drive transmitting gears 8 and 9. The first hand gear 1 has a central shaft 1 a which acts as its rotational axis and the second hand gear 2 has a shaft portion 2 a which acts as its rotational axis. A guide tube 3 is driven into and fixed in a bottom plate 11. The rotational shaft 1 a of the first hand gear 1 is rotatably mounted in the guide tube 3 so as to be supported by the inner surface of the guide tube 3. The shaft portion 2 a of the second hand gear 2 is rotatably mounted on the guide tube 3 so as to be supported by the outer surface of the guide tube 3. The guide tube 3 prevents the hand gears 1 and 2 from coming into direct contact with each other. The rotors 4 and 7 and the drive transmitting wheels 5, 6, 8, 9 are supported by the bottom plate 11 and by a gear train bridge 10 leaving rotational clearances. On the other hand, the first hand gear 1 is supported by the gear train bridge 10 and by the guide tube 3 which is driven into the bottom plate 11 leaving rotational clearances. Moreover, the second hand gear 2 is supported and guided by the guide tube 3 and is supported by a spring provided on a dial 12 so as to leave rotational clearances. Thus, by inserting the fixed guide tube 3 between the central shaft 1 a of the first hand gear 1 and the shaft portion 2 a of the second hand gear 2. a driven hand is not affected by a stationary hand so that the former is not subjected to an unstable load from the latter and the hand attached to the former runs smoothly without irregularities. Likewise, since the stationary hand gear is not affected by the driven hand gear, the hand attached thereto does not vibrate. Consequently, as indicated above, since the hand gears 1, 2 are held out of direct contact with each other by the guide tube 3, the driven hand runs smoothly without irregularities and the shaking or vibration of the stationary hand is prevented. The shaft 1 a may support a seconds hand (not shown), the first rotor 4 being the rotor of a stepping motor, e.g. of an electronic watch. The shaft portion 2 a , which is concentric with the shaft 1 a . may support a minutes hand (not shown). Moreover, a further shaft (not shown) for supporting an hour hand, may be disposed concentrically about the shaft portion 2 a and may be separated therefrom by a further fixed guide tube (not shown). In contrast, in the known construction shown in Figure 2, there is provided second gearing for transmitting drive to a second hand gear 14 from a second rotor 15, the second gearing comprising a second drive transmitting gear 16, and first gearing for transmitting drive to a first hand gear 13 from a first rotor 17, the first gearing comprising a first drive transmitting gear 18. The second hand gear 14 has a tube 14 which acts as its rotational axis, and the first hand gear 13 has a shaft 13 a which acts as its rotational axis. The shaft 13 a of the first hand gear is rotatably mounted in the tube 14 a of the second hand gear 14 so as to be guided by the inner surface of the tube 14 a . In the case of the structure shown in Figure 2, when the first hand gear 13 is driven by the first rotor 17, the second hand gear 14 tends, through slightly, to rotate resulting in swinging movement or vibration of a hand (not shown) attached to the second hand gear 14 since the shaft 13 a of the first hand gear 13 comes into direct contact with the tube 14 a of the second hand gear 14.

Claims: A timepiece movement comprising at least two rotors (4, 7) which are respectively arranged to drive respective shafts (1a, 2a) of first hand gear (1) and second hand gear (2) each of which is adapted to support a respective timepiece hand, the shafts being concentrically mounted, adjacent shafts (1a, 2a) being rotatably supported by a support tube (3) which is disposed therebetween and is fixed in a fixed structure, characterised in that the said fixed structure is a bottom plate (11) which is spaced from a gear train bridge (10), each of the rotors (4, 7) being rotatably supported by the bottom plate (11) and by the gear train bridge (10), each of the rotors (4, 7) being drivingly connected to the respective hand gear (1, 2) by way of transmitting gearing (1, 5, 6; 8, 9) which are rotatably supported by the bottom plate (11) and by the gear train bridge (10), the first hand gear (1) is rotatably supported by the support tube (3) and the gear train bridge (10), and the second hand gear (2) is rotatably disposed on the bottom plate (11) opposite from the first hand gear (1) whereby each shaft (la, 2a) is unaffected by the rotation of the other. A timepiece movement as claimed in claim 1 characterised in that one of the shafts (1a, 2a) is constituted by a seconds hand shaft (1a) which is arranged to be driven by the rotor (4) of a step motor. A timepiece having a timepiece movement characterised in that the timepiece movement is a movement as claimed in either claim 1 or 2.

Inventors: SATO MAMORU, WATANABE MAMORU, SATO, MAMORU, WATANABE, MAMORU
Applicants: SEIKO INSTR INC, SEIKO INSTRUMENTS INC.
Application year: 1988
Main classification: G04C3
IPC codes: G04B31, G04B33, G04C3, G04B13