Electronic wrist watch

Abstract: An electronic wrist watch comprising an electrical power source (2) for driving time indicating means (10,11) characterised in that the electrical power source (2) is arranged to be electrically charged by an oscillatable weight (15) and converter means (16-21) for converting mechanical energy obtained from the oscillatable weight (15) into electrical energy for transmission to the electrical power source (2).

Description: The present invention relates to an electronic wrist watch. Electronic wrist watches normally employ batteries, and it has therefore been of great concern to extend the lifetime of the batteries. However, there is in practice a limit to the size of batteries which can be employed in a small wrist watch. As one means of solving this problem, an electronic wrist watch has been produced in which a solar battery is provided on a display face, for example, a dial, and either a secondary battery or a charging capacitor is charged by means of the solar battery so that a timepiece circuit is driven by the output of either the secondary battery or the capacitor, as shown in US-A-4,653,931. With this arrangement, however, since a black or blue solar battery is disposed on the dial, the range of possible designs of the watch is limited and therefore this arrangement is not suitable for those electronic watches which are bought largely for their design. In JP-A-52-27669 there is disclosed a wrist watch which has an electric cell which is charged by the energy generated by a rotating heavy weight. The charge so generated, however, is liable to be excessive if the watch is dropped and a strong impact load torque is applied to the weight. According, therefore, to the present invention, there is provided an electronic wrist watch comprising an electrical power source for driving time indicating means, an oscillatable weight, and converter means for converting mechanical energy obtained from the oscillatable weight into electrical energy for transmission to the electrical power source, the converter means comprising a permanent magnet rotor which is arranged to be driven by the oscillatable weight, rotation of the permanent magnet rotor inducing a voltage in a transducer coil connected to the electrical power source; characterised in that the converter means comprises an oscillatable weight wheel, which is connected with and oscillates with the oscillatable weight, a transmission wheel comprising a transmission wheel spindle which has a pinion which meshes with the oscillatable weight wheel, and a gear wheel which engages with the rotor, and the transmission wheel spindle and the gear wheel are connected by friction coupling, the arrangement being such that drive is transmitted from the transmission wheel spindle to the rotor only when the torque transmitted to the transmission wheel spindle from the oscillatable weight is weaker than the friction between the transmission wheel spindle and the gear wheel. The converter means preferably has a one-piece stator having a bore within which the permanent magnet rotor is disposed. The oscillatable weight is preferably pivotally supported at the central portion of the watch and has an outer peripheral portion which is disposed radially outwardly of and in substantially the same plane as the transducer coil. The electrical power source may be electrically connected to a timepiece coil of a stepping motor whose rotor drives the time indicating means by way of a time indication gear train, the timepiece coil being carried by a circuit board. Preferably, the time indication gear train, the timepiece coil, the transducer coil and the circuit board have no substantial overlap with each other when the watch is viewed in plan. The oscillatable weight may be disposed on the obverse side of an assembly constituted by the time indication gear train, the timepiece coil, the transducer coil and the circuit board. The circuit board may face a main plate which has at least one recess therein for accommodating a respective electrical component which is carried by the circuit board. The circuit board may be flexible and the flexible circuit board may be pressed against the main plate so as to be located thereon by a press plate formed from a metal sheet. The present invention, in its preferred form, enables an electronic wrist watch to be produced which is thin and has superior charging efficiency, and in which damage can be avoided even when an external impact is applied. The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 is a plan view of the obverse side of an electronic wrist watch according to the present invention; Figures 2, 2a and 3 are fragmentary sectional views of parts of the electronic wrist watch shown in Figure 1; Figures 4(a) and 4(b) are schematic diagrams of circuits which may be employed in the electronic wrist watch shown in Figure 1; Figure 5 is a plan view of a transmission wheel forming part of the watch shown in Figure 1; and Figure 6 is a sectional view of another embodiment of transmission wheel. On the upper surface of a plastics main plate 1 (Figure 1) are disposed a time indicating wheel train, a stepping motor, an accumulating means, a generator and a circuit board. The time indicating wheel train (Figures 1 and 2(a)) comprises an intermediate wheel 6, a second wheel 7, a third wheel 8, a centre wheel (not shown), a minute wheel 10 and an hour wheel (not shown) which are meshed in series and driven by a timepiece stepping motor comprising a timepiece coil block 3, a plate-shaped stator 4 and a permanent magnet rotor 5, with the intermediate wheel 6 being meshed with the rotor 5. A train wheel bridge 12 rotatably supports the obverse-side wheel train, i.e. from the rotor 5 to the third wheel 8, between the same and the main plate 1. The timepiece coil block 3 comprises a coil and a core which extends therethrough. The timepiece coil block 3 is arranged such that it is separated from the train wheel bridge 12 so as not to overlap it, thereby preventing an increase in the thickness of the train wheel section. The generator (Figures 1 and 2(a)), comprises an oscillatable or oscillating weight 15 which is pivotally supported through a bearing (not shown) by an oscillating weight bridge 13 disposed on the upper side of the train wheel bridge 12; an oscillating weight wheel 16 which is secured to the oscillating weight 15 in one unit; a transmission wheel 17 and a permanent magnet rotor 18 for generation which are meshed in series with the oscillating weight wheel 16 so as to be rotated; and a stator 19 for generation and a coil block 20 for generation which are disposed around the generation rotor 18. The transmission wheel 17 (Figure 2(a)) comprises a transmission wheel spindle 17a provided with a pinion 17d and a transmission gear wheel 17b which is connected to the spindle 17a by friction coupling as described below. The permanent magnet generation rotor 18 comprises a permanent magnet 18b, the rotor 18 being formed so as to be "flat", i.e. so as to have an appropriate ratio of the rotor diameter R d to the motor thickness, with a view to increasing the generation efficiency. According to experiments, it has been revealed that the charging efficiency is increased when the ratio of the rotor diameter R d to the rotor thickness is set at from 0.05 to 0.5, and preferably from 0.1 to 0.3. The rotor magnet is formed using a rare-earth magnet, for example Sm₂Co₁₇ or the like, which is light and has a high magnetic flux density, and the magnet is magnetized so as to have two magnetic poles. However, the number of magnetic poles of the rotor magnet may also be 6, 8 or the like. The transmission wheel 17 and the generation rotor are rotatably supported between the main plate 1 and the oscillating weight bridge 13, and the generation coil block 20 is disposed such that it is separated from the oscillating weight bridge 13 so as not to overlap it, thereby preventing increase in the thickness of the watch. As will be clear from Figure 1, the transmission wheel 17 and the generation rotor 18 which constitute in combination the generation wheel train are dispersedly disposed so as not to overlap the indicating wheel train 6-10. The timepiece coil block 3 and the generation coil block 20 are also dispersedly disposed at the outer periphery of the main plate 1 with a view to preventing increase in the thickness. In the generator, as the oscillating weight 15 oscillates, the rotor 18 is rotated with an increased speed through the oscillating weight wheel 16 and the transmission wheel 17, thus generating an induced voltage in the generation coil block 20. The induced voltage is stored in a capacitor 2 serving as an accumulating means through a circuit block, which will be described later. Since the oscillating weight 15 is readily oscillated by the natural swing of the arm occurring when the user is carrying the watch with him, satisfactory charging is available. According to experiments, it has been revealed that the speed increasing ratio from the oscillating weight 15 to the rotor 18 needs to be set within the range of from 30 to 200. It should be noted that the reason why the stator 19 is arranged in the form of a one-piece stator in the present embodiment is that, if the stator 19 is arranged in the form of a two-piece stator (as described in US-A-3,984,972), the force of attraction acting between the rotor and the stator increases and acts so as to brake the oscillation of the oscillating weight 15. A two-piece stator may, of course, be employed if it is set strictly. In the case of the above-described generator, if a strong impact load torque is applied to the oscillating weight 15, for example, when the watch is dropped, there is a risk that the wheel support portions of the power transmission section and the teeth of the wheels may be damaged. In other words, the generator may be inferior in terms of impact resistance. It may be desirable in order to improve the impact resistance to increase the strength of each individual part so that it can withstand impact force. However, an increase in the strength leads to an increase in the size of the structure, so that it becomes difficult to employ such a generator for a small-sized product such as a wrist watch. In the present invention, therefore, the section for transmitting the power from the oscillating weight 15 has at least one means which transmits the power by means of a slipping drive, so that, when a strong impact load torque is applied to the oscillating weight member 15b, for example, when the watch is dropped, the slipping drive slips, thus preventing the strong impact load torque from being transmitted to the power transmission section on the downstream side of said means. More specifically, the transmission wheel spindle 17a and the transmission gear wheel 17b of the transmission wheel 17 are coupled together by means of frictional force, as described above. The transmission gear wheel 17b (Figure 5) is resiliently attached to the transmission wheel spindle 17a through resilient arms 17c. The level of the transmission force required to prevent slipping between the parts of the slipping drive is set from the following relationship. Let us consider first a normal operation state. Since in this state the power must be transmitted without slip, the level of the said transmission force should be set so as to be higher than a load component applied by the magnetic force produced between the rotor 18 and the stator 19 and a mechanical load such as the friction occurring in the wheel train section 16, 17. Let us consider next an occasion on which an impact is applied to the watch. As the speed of rotation of the rotor 18 increases, the load applied by the magnetic force increases due to the electromagnetic induction; therefore, the level of the said transmission force should be set so as to be lower than the load applied by the magnetic force and the above-described mechanical load. To meet requirements in actual use, these values may be simply obtained on the following basis. The value of the lower limit of the said transmission force is set such that the lower limit value which is converted into torque on the basis of the gear ratio overcomes the unbalanced torque of the oscillating weight 15. For example, when the unbalanced torque of the oscillating weight 15 is W g cm and the numbers of teeth of the oscillating weight wheel 16 and the transmission wheel pinion 17d are Z₁ and Z₂, respectively, the said transmission force should be set so as to be greater than W (Z₂/Z₁), By doing so, when the watch is carried gently, only an acceleration of about lg is acting on the oscillating weight 15 and therefore there is no fear of slip. The higher limit value of the said transmission force should be set so as to be lower than the limit of mechanical strength at the pivot, teeth and so forth of each wheel. By virtue of the above-described arrangement, when the watch is carried in a normal state, the level of the said transmission force is higher than the torque of the oscillating weight 15 which is generated by the motion of the arm or the like. Therefore, the transmission gear wheel 17b transmits the oscillation of the oscillating weight member 15b to the rotor 18 as it is. However, when a strong impact is applied to the oscillating weight 15, for example, when the watch is dropped, the torque of the oscillator weight 15 exceeds the frictional force, so that the transmission gear wheel 17b slips and the oscillation of the oscillating weight 15 is not transmitted to the following wheels. It should be noted that the position of the friction clutch so provided may be set on another wheel. More specifically, a frictional engagement section may be provided in between the oscillating weight wheel 16 and the oscillating weight wheel spindle 21 and/or between the rotor pinion 18a and the rotor magnet 18b. The level of the frictional force in these cases depends on the gear ratio in each case. In the former case, the level of the frictional force needs to be higher than the unbalanced torque of the oscillating weight 15, whereas, in the latter case, the level of the frictional force may be further lowered by an amount corresponding to the gear ratio of the pinion provided on the rotor spindle 18a to the transmission gear wheel 17b. Further, the means for generating frictional force is not necessarily limited to the foregoing and it is possible to employ various other means, for example, a known cannon pinion method which is used as a slip mechanism for a minute wheel or a method which employs magnetic force from a magnet. In another embodiment (Figure 6) employing magnetic force, a transmission wheel 17 has a pinion 17e on a spindle 17f, which pinion is made of magnetic material, a magnet 17g and a gear wheel 17h. The magnet 17g is rigidly secured to the gear wheel 17h, but the gear wheel 17h is loosely engaged with the pinion 17e so that the former can rotate against the latter. The gear wheel 17h is secured to the pinion 17e by means of the force of attraction acting between the magnet 17g and the pinion 17e. When the force transmitted from the oscillating weight 15 is weaker than the said force of attraction, the rotation is transmitted, whereas, when the transmitted force is stronger than the force of attraction, the pinion 17e races. Since such a structure is applied to the generation rotor 18, the magnet 17g thereof also serves as the rotor magnet 18b. The accumulating means comprises a capacitor 2. As will be clear from Figures 1 and 3, the capacitor 2 has a lead plate 23 welded to a convex electrode portion 2a thereof. The capacitor 2 is installed in a recess provided in the main plate 1 in such a manner that the lead plate 23 is disposed at the obverse side, and the capacitor 2 is pressed and thereby retained by a ring-shaped capacitor holder 24 through an insulating plate 25. The capacitor holder 24 is rigidly secured to the main plate 1 by means of screws 26 and 27. In this arrangement, a pattern 28a of a circuit board 28 is clamped between the lead plate 23 and the main plate 1 so as to provide electrical connection with a negative electrode of the capacitor 2. The positive electrode of the capacitor 2 is electrically connected to a positive lead 39 which is in turn electrically connected to the circuit board pattern by bringing the positive lead 39 into resilient contact with the side of the capacitor 2. The circuit board 28 comprises a flexible board serving as a base on which an IC chip 30 (Figure 1), a diode 31, capacitors 32 for boosting, an auxiliary capacitor 33 and a crystal oscillator 34 are rigidly secured to the surface thereof which faces the main plate, these circuit elements being interconnected through electrode patterns (not shown). The circuit board 28 shown in Figure 3, is provided at one end portion 28b thereof with a pattern which is connected to a pattern on a coil lead board 20a provided on the generation coil block 20, the two patterns being pressed and thereby connected to each other by means of a screw. As shown in Figure 3, at the other end 28c of the circuit board 28, a pattern 28a which serves as a part for connection with the above-described capacitor 2 projects from the circuit board 28. A relief bore 28d (Figure 2) for the timepiece coil block 3 and the crystal oscillator 34 is provided in the intermediate portion of the circuit board 28, thereby preventing an increase in the thickness of the watch. A pattern which is connected to a pattern of a coil lead board 3a provided on the timepiece coil block 3 is formed at the periphery of the bore 28d, the two patterns being pressed and thereby connected to each other by means of a screw 36. The electronic parts which are rigidly secured to the circuit board 28, i.e. the IC chip 30, the diode 31, the capacitors 32 for boosting, the auxiliary capacitor 33 and the crystal oscillator 34, are accommodated within respective recesses formed in the plastics main plate 1, thereby protecting these parts and also preventing an increase in the thickness of the watch. Further, the circuit board 28 is dispersedly disposed so that it does not overlap either the indicating wheel train 6-10 or the generation wheel train 16, 17, thus preventing an increase in the thickness of the watch. A circuit press plate 29 which is made from a metal sheet is mounted on the obverse side of the circuit board 28. The circuit press plate 29 is disposed so as to be interposed between the circuit board 28 and the screws, i.e., the screws 35, 36, 26 and a screw 38 (Figure 1) for securing the coil block 3, the circuit press plate 29 being rigidly secured to the main plate 1 by this multiplicity of screws. The circuit press plate 29 has spring portions formed at some positions thereon for pressing the circuit board 28 at the peripheral portion of the main plate 1 so that the circuit board 28 will not be within the locus of the oscillating weight member 15. Further, a spring portion 29c (Figure 1) which presses a setting lever (not shown) for positioning a time indication adjusting stem 50 is formed in the vicinity of the screw 38. The circuit board 28 has a bore formed at a position which faces the spring portion 29c. Further, as best seen in Figure 2, the circuit press plate 29 is integrally provided with a spring portion 29d which presses the crystal oscillator 34 against the main plate and, as best seen in Figure 3, a spring portion 29e which is in contact with the casing to provide a ground connection. It should be noted that the reason why the spring portion 29e which serves as a ground lead is provided at the side of the watch is to prevent the spring portion 29e from being within the locus of the oscillating weight 15. In the foregoing, the time indicating wheel train, the stepping motor, the accumulating means, the generator and the circuit board have been successively described. The features of the general layout will next be explained. According to the layout in this embodiment, the time indicating wheel train 6, 7, 8, the generation wheel train 17, 18, the timepiece coil block 3 and the generation coil block 20, the capacitor 2 and the circuit board 28 are dispersedly disposed so that these elements do not overlap each other in plan view, and the electric elements 30-34 on the circuit board 28 are accommodated within the respective recesses formed in the main plate 1, thereby preventing an increase in the thickness of the watch. Further, the crystal oscillator 34 is disposed in what would otherwise be an unused space radially outwardly of the timepiece coil 3, thereby effectively utilizing the space and thus enabling the mechanical structure except for the oscillating weight 15 to be formed into a flat shape as a whole. The oscillating weight 15 has a peripheral thick-wall portion 15 c thereof provided at the outer peripheral portion of the main plate 1. The portion 15 c is disposed radially outwardly of the timepiece coil 3 so that, as shown in Figure 2(b), the portion 15 c is in the same plane as the timepiece coil 3 as viewed in section. Therefore, the clearance between the oscillating weight 15 and the oscillating weight bridge 13 can be minimized, so that it is possible to provide an electronic watch having an oscillating weight such that the watch is not inferior to conventional watches in terms of the overall thickness. In addition, since the heaviest portion 15 c of the oscillating weight member 15 b is disposed at the outermost peripheral portion of the watch, it is possible to provide an electronic wrist watch with a generator which has high generation efficiency. Generation circuits which may be employed in this embodiment are schematically shown in Figures 4(a) and 4(b). Figure 4(a) shows one example in which a full-wave rectifier circuit is employed. Diodes 41, 42, 43 and 44 for full-wave rectification are connected to a generator coil 40, and a capacitor 45 for accumulation is connected thereto. The reference numeral 46 denotes an auxiliary capacitor which has a smaller capacity than that of the capacitor 45. The auxiliary capacitor 46 is charged with the charge accumulated in the capacitor 45 and a watch circuit 47 is driven by the output of the auxiliary capacitor 46. As the oscillating weight 15 oscillates in one direction, a current flows as shown by the full line, whereas, as the oscillating weight 15 oscillates in the other direction,a current flows as shown by the chain line. Thus, the oscillation of the oscillating weight member in any direction can be utilized for charging. It should be noted that the reference numeral 48 denotes a limiter which is arranged such that, when the capacitor 45 is overcharged, the limiter 48 detects this overcharge state and shorts the ends of the coil to thereby prevent the capacitor 45 from being further charged. Figure 4(b) shows another example in which a half-wave rectifier circuit is employed. In the figure, the coil 40, the capacitor 45, the auxiliary capacitor 46, the watch circuit 47 and the limiter 48 are the same as those in Figure 4(a). In this embodiment, only one diode 49 is employed as a rectifier element. In this case, since the number of diodes employed is reduced, the resistance component is reduced correspondingly, so that it is possible to realize even more efficient charging. It should be noted that, to utilize the voltage accumulated in the capacitor 45 even more effectively, it is also possible to insert a booster circuit between the capacitor 45 and the auxiliary capacitor 46. A specific arrangement thereof is described in detail in US-A-4,730,287 of the present Applicants.

Claims: An electronic wrist watch comprising an electrical power source (2) for driving time indicating means (10,11), an oscillatable weight (15), and converter means (16-21) for converting mechanical energy obtained from the oscillatable weight (15) into electrical energy for transmission to the electrical power source (2), the converter means (16-21) comprising a permanent magnet rotor (18) which is arranged to be driven by the oscillatable weight (15), rotation of the permanent magnet rotor (18) inducing a voltage in a transducer coil (20) connected to the electrical power source (2); characterised in that the converter means (16-21) comprises an oscillatable weight wheel (16) which is connected with and oscillates with the oscillatable weight (15), a transmission wheel (17) comprising a transmission wheel spindle (17a) which has a pinion which meshes with the oscillatable weight wheel (16), and a gear wheel (17b) which engages with the rotor (18), and the transmission wheel spindle (17a) and the gear wheel (17b) are connected by friction coupling, the arrangement being such that drive is transmitted from the transmission wheel spindle (17a) to the rotor (18) only when the torque transmitted to the transmission wheel spindle (17a) from the oscillatable weight (15) is weaker than the friction between the transmission wheel spindle (17a) and the gear wheel (17b). An electronic wrist watch as claimed in claim 1 characterised in that the converter means (16-21) has a one-piece stator (19) having a bore within which the permanent magnet rotor (18) is disposed. An electronic wrist watch as claimed in claim 1 or 2, characterised in that the oscillatable weight (15) is pivotally supported at the central portion of the watch and has an outer peripheral portion (15c) which is disposed radially outwardly of and in substantially the same plane as the transducer coil (20). An electronic wrist watch as claimed in any preceding claim characterised in that the electrical power source (2) is electrically connected to a timepiece coil (3) of a stepping motor (3-5) whose rotor (5) drives the time indicating means (10,11) by way of a time indication gear train (6-8), the timepiece coil (3) being carried by a circuit board (28). An electronic wrist watch as claimed in claim 4 characterised in that the time indication gear train (6-8) the timepiece coil (3), the transducer coil (20), and the circuit board (28) have no substantial overlap with each other when the watch is viewed in plan. An electronic wrist watch as claimed in claim 5 characterised in that the oscillatable weight (15) is disposed on the obverse side of an assembly constituted by the time indication gear train (6-8), the timepiece coil (3), the transducer coil (20) and the circuit board (28). An electronic wrist watch as claimed in any of claims 4-6 characterised in that the circuit board (28) faces a main plate (1) which has at least one recess therein for accommodating a respective electrical component (3,30-34) which is carried by the circuit board (28). An electronic wrist watch as claimed in any of claims 4-7 characterised in that the circuit board (28) comprises a flexible circuit board. An electronic wrist watch as claimed in claim 8 characterised in that the flexible circuit board (28) is pressed against the main plate (1) so as to be located thereon by a press plate (29) formed from a metal sheet.

Inventors: NAGAO SHOICHI, NAGAO, SHOICHI
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1989
Main classification: G04C10
IPC codes: G04C10