GB2064831A - Electronic time keeping device - Google Patents

Abstract

An electronic time keeping device has a step motor (4) including a rotor (11), a stator (8), and winding (10) provided in unitary fashion by means of motor case plates (6, 7). The hand (25) of the smallest unit of time (minutes hand) is mounted on the shaft (13) of the step motor (4) which is a 60 pole motor receiving one pulse per minute. Gear train (21, 22, 23, 24) driving the hour hand (26), and the electronic parts are accommodated in a depressed portion (7a) of the upper plate (7). The electronic parts are on a circuit board (15). Stator teeth (8a, b) are formed integrally with the plates (6, 7). A number of arrangements are described, and the hand on the rotor shaft may be a seconds hand. <IMAGE>

Description

SPECIFICATION Electronic time keeping device The present invention relates to an electronic time keeping device which displays the time of day by moving its hands with a step motor.

The electronic time keeping devices of this kind generally use a step motor with a small number of poles, for example, six poles or twelve poles, to make their size adequately small and are so constructed that the rotor, stator and coil of the step motor are directly fixed on the ground plate and the driving force of the step motor shaft transmitted to the second hand or the minute hand which is the minimum unit of time via a mechanical transfer means such as a gear-series mechanism and to the hour hand to drive it by way of another gear-series mechanism.The state of the art is such that the structure outlined above comprises many parts for mounting the pulse motor and the gears and a complicated composition because it uses a ground plate to fasten and support the pulse motor and the gears and a pivotal receptacle plate for pivotally supporting the shafts, thereby making it necessary to align the pivots (or bearings) on the ground plate with those on the receptacle plate when they are assembled and thus leading to high manufacturing cost and low productivity because of the onerous assembly work.

Further, the fact that the component parts such as cogwheels are tiny and thin makes the structure so delicate that it still has insufficient strength against an external shock and poor reliability. It should therefore be maintained carefully.

Accordingly, an object of the invention is to provide an electronic time keeping device which is small in size, light in weight, and low in cost, reduced in the number of parts, simplified in maintenance, and high in reliability.

To achieve the above object, there is provided an electronic time keeping device having a step motor rotatively driven by a reference clock pulse and hands for pointing time of which the rotation is controlled by the step motor, in which said step motor is packed in unit by a case covering a rotor, a stator and a coil, with a depressed portion.

With such construction, the number of parts is remarkably reduced, the assembling work is considerably improved, the maintenance is simplified, the reliability of the device is improved, the manufacturing cost is reduced, the gear-mechanism is minimized and made thin as a whole. Therefore, satisfactorily improved time keeping devices may be provided.

Other objects and features of the invention will be apparent from the following description taken in connection with the accompanying drawings, in which: Figure 1 shows a longitudinal sectional view of an electronic time keeping device according to the invention; Figure 2 shows perspectively a cross section of a major part of the pulse motor shown in Figure 1; Figure 3 shows an exploded view of a major part of the electronic time keeping device shown in Figure 1; Figure 4 shows perspectively a cross section of another embodiment of the time keeping device according to the invention; Figure 5 shows perspectively a cross section of a major part of still another embodiment of the time keeping device according to the invention; Figure 6 shows a cross sectional view of the movement of the time keeping device according to the invention;; Figures 7(a), 7fob), 7(c) show perspective views of other embodiments of the pulse motor; Figure 8 shows an exploded view of a major portion of the electronic time keeping device accord ing to the invention; Figure 9 shows a cross sectional view of a part of yet another embodiment of the time keeping device according to the invention; Figure 10 shows a cross sectional view of a further embodiment of the time keeping device according to the invention; Figure 11 shows a front view of the time keeping device which is another embodiment of the invention; Figure 12 shows a cross sectional view of the time keeping device shown in Figure 11; and Figure 13 shows perspectively an exploded view of the movement of the time keeping device shown in Figure 11.

The preferred embodiments of the electronic time-keeping device will be described in detail with reference to the accompanying drawings.

Figure 1 to Figure 3 show one of the preferred embodiments of the present invention as employed in an electronic wrist watch using a 60-pole, 60-step pulse motor. Figure 1 gives a cross section of the above electronic wrist watch, where reference numeral 1 denotes an outer casing of the wrist watch with a glass cover 2 fit in its front side opening and a back lid 3 screwed tight into its rear side opening.

Inside the outer casing 1 is located a 60-pole, 60-step pulse motor 4 so that it lies on an insulating base 5 as shown. A circular lower case 6 with an upright peripheral wall 6a on its perimeter is placed under a circular upper case 7 with a round concave or depressed portion 7a at its central part so that the two members form a casement of the pulse motor. A number of stator segments 8a, ... are placed vertically at certain intervals along the inner circumference of the annular coil space next inside of the peripheral wall 6a on the lower case 6. Similarly, a number of stator segments 8b,. . are placed vertically at certain intervals along the same circumference on the lower face of the upper case 7 as the stator segments 8a, . ..

are placed along so that the stator segments 8a,..

and the stator segments 8b, ... are located alternately to form the stator 8 as a whole. An insulating ring 9 is provided around the outer perimeter of the stator 8. The stator coil 10 made of copper wire is wound in the space between the insulating ring 9 and the circular wall 6a of the lower case 6. An annular rotor 11 is located between the stator 8 and the peripheral wall of the concave portion 7a of the upper case 7 so that the rotor 11 is encased by the bottom disc 6 and the top disk 7. The perimeter of the rotor 11 is divided into 60 equal parts which are given magnetic poles that are north and south alternately. The rotor 11 is mounted on a rotor support 12 fitted to perpendicular to the pulse motor shaft 13 at the center of the motor 4 as shown.The motor shaft 13 extends from the center of the lower case 6 through the center of the concave portion 7a of the upper plate 7 and penetrates a circuit board 15 to be mentioned later, extending upwardly. This shaft is seated on a pivot 14 at the center of the lower case 6 so as to rotate freely. The circuit board 15 which is round and has the same diameter as the upper case 7 is superimposed on the upper case 7 so as to cover the hollow over the concave portion 7a in the pulse motor. Thus, the circuit board 15 is so located that it forms a lamination with the pulse motor. The circuit board 15 has the printed circuit to perform the time keeping functions one of which is to drive the pulse motor 4.A LSl circuit 16 for driving the pulse motor 4, a crystal oscillator (not shown) and other electronic components are mounted on that surface of the circuit board 15 which faces the concave portion 7a of the upper case 7. Further, the bearings to hold the shaft of the pulse motor and that of the gears are located on the circuit 15. That is, a bearing 17 is placed at its center and a bearing 18 is provided near the bearing 17. The bearing 19 is located on the bottom of the concave portion 7a of the upper case 7 so as to make it opposite to the bearing 18. There is a gear 20 in the space between the concave portion 7a of the upper case 7 and the circuit board 15 laid on it.The gear 20 consists of a 1st gear 22 to mesh with a gear 21 formed on the middle of the motor shaft 13, a 2nd gear 23 formed together with the 1 sot gear 22 and 3rd gear (the hour hand gear) 24 to mesh with the 2nd gear 23. The axis of the 1 st gear 22 and the gear 23 is in parallel with the motor shaft 13. The shaft of the 1 st gear 22 and the 2nd gear 23 is pivoted free to rotate at the bearing 18 on the circuit board 15 and at the bearing 19.on the concave portion 7a. The motor shaft 13 extending through the circuit board 15 is inserted into the shaft of the 3rd gear 24 but kept free from it to rotate and the 3rd gear is held free to rotate by the bearing 17 on the circuit board 15. That is, the bearing 17 supports the motor shaft 13 and the 3rd gear 24, and the bearing 18 supports the 1 sot gear 22 and the 2nd gear 23.The minute hand 25 is mounted on the upper end of the motor shaft 13 extending beyond the circuit board 15. The hour hand 26 is mounted on the upper end of the shaft of the 3rd gear 24. In the figure, 27 denotes a dial disc with time numerals and others placed over the circuit board 15,28 denotes a button battery placed in the insulating base 5,29 denotes the lid of the battery space put into the back lid 3, and 30 denotes a flexible lead to connect the battery 28 to the circuit board 15.

The pulse motor 4 shown in perspectively and in cross section has the stator 8 of which the segments 8a, ... and the segments 8b,... alternatingly turn their magnetic polarities as the direction of the current flow through the coil 10 alters. The rotor 21 comprises 60 equal portions but alternately different in their magnetic polarities. Thus, pulse signals applied from the drive circuit on the circuit board 25 will rotate the pulse motor 4 stepwise at the rate of one step per minute. The motor shaft 13 makes one revolution in 60 minutes with 60 steps. The motor shaft acting as the shaft of the minute hand directly rotates the minute hand to point the time in minutes.

The gear series 20 is to transmit the rotation of the pulse motor 4 to the hour hand 26. The motion is transmitted from the gear 21 on the motor shaft 13 through the 1 sot gear 22 and the 2nd gear 23 to the 3rd gear 24 which rotates the hour hand 26 by 5 steps for each hourto indicate the time in hours.

Figure 3 shows an exploded oblique view of the pulse motor 4 and the circuit board 15. The circuit board 15 with the bearings 17 and 18 in it is superimposed on the pulse motor 4 to make a lamination. The bearings 17 and 18 in the circuit board 15 make possible to eliminate the need of at least eitherthe ground plate or the pivotal receptacle plate that are traditionally used to provide the bearing forthe motor shaft and gear shafts because they can support these shafts.That is, in consideration of the proximity between the pulse motor 4 and the gear series 20 in terms of location as well as function, the circuit board 15 is superimposed on the pulse motor 4 to form a lamination and the circuit board 15 is provided with the bearings 17 and 18 for the motor shaft 13 and the shafts of the gear series in order to make it play the same role as the ground plate or the pivotal receptacle plate. Since circuit board 15 does not pose any restriction in assembly rotative to the location of other components, it may be aligned with respect to the bearings 17 and 18 as the datum (so as to establish correct position of the motor shaft 13 and the gear shafts). Thus the circuit board 15 can be positioned easily and correctly when it is mounted because no other constraints exist except the positioning of the shafts leaving a wider tolerance for it.Further, in this embodiment, the combination ofthe concave portion 7a and the circuit board 15 makes it possible to eliminate the need of the ground plate and the pivotal receptacle plate because the motor shaft 13 penetrates the concave portion 7a of the upper case 7 and the bearing 19 is located in it so as to make it function as the ground plate or the pivotal receptacle plate. The use of the 60-pole, 60-step pulse motor 4 with its motor shaft 13 which directly moves the minute hand on it provides stable time keeping function with high reliability and also makes it possible to eliminate the minute hand portion of the gear series contributing to simplification and miniaturization of the device. Since the pulse motor 4 is provided with the concave portion 7a in the upper case, the gear series 20 and the electronic components of the circuit board 15 can be accommodated in the concave portion as part of the pulse motor, thereby helping design a timepiece even smaller in thickness. In this case, the gear series 20 may be made compact around the motor shaft 13 of the pulse motor 4 and the shafts of the gear series may be pivoted on the upper case 7 of the pulse motor 4.

Figure 4 shows another embodiment where the pulse motor has a concave portion at its center.

There is a channel 35 containing the exciting coil 34 on the periphery of a motor case 33 to cover the rotor 31. Stators 36a and 36b incorporated in the motor case 33 are so placed that they confront the magnet3la ofthe rotor 31.

Figure 5 shews still another embodiment of the pulse motor in which the stator is composed of two parts, one on top of the other, facing a magnet 40a of a rotor 40. Each of the two parts of the stator containing the exciting coils 42a and 42b has a U-shaped cross section made of metal with its edges alternately extending like a sawteeth and bent so as to have the tips on one edge come close to those on the other. The number of the tips referred to as 41 a1, 41a2, 41by and 41 b2 is 15 each. The stators 41a1, 41 a2, 41 b1 and 41 b2 are located alternately and they are 6 degrees apart from each other.

Figure 6 shows that the concave portion of the pulse motor may be different in shape, position and size depending upon the components to be placed in it. Thus, the bottom disc 6 may have a concave portion 6c to place the battery 28 in it. It is also possible to have a concave portion 50a in the area other than the center and the periphery of the motor case as shown in Figure 7(a), to have a concave portion 50b in the area covering the center and the periphery of the motor case as shown in Figure 7(b), and to have a small concave portion 50c between the center and the periphery of the motor case as shown in Figure 7(c).

Figure 8 illustrates another improved embodiment where a motor case 51 has a convex part 52 to engage with a concave part 53a of a circuit board 53 and the concave part 54a of a dial disc 54, thereby permitting easy alignment when they are assembled.

Figure 9 shows another embodiment of the present invention where a concave portion 56a is provided in the upper part of a pulse motor 56 located below a dial disc 55 so as to place a gear series 57 in the concave portion and the other concave portion 56b is provided in the lowest part of the pulse motor so that electronic components 57a and 57b on the circuit board 57 are housed in said concave portion when the circuit board 57 is attached to the bottom of the pulse motor 56 to complete the assembly.

Figure 10 shows another embodiment when the circuit board is located beneath the pulse motor. A circuit board 62 on which an LSI package 60 and a crystal oscillator 61 are mounted is placed below a pulse motor 58 with a spacer 59 between the two. It is so designed that a large battery, e.g. lithium battery, 63 is attached to the bottom of a circuit board 62.

Figures 11 and 13 illustrate a preferred embodiment of the present invention where the time of day is indicated by the hands of a wrist watch and also by an optical display such as liquid crystal display or electrochronic display. Figure 11 shows a front view of an electronic wrist watch to which this invention is applied.

Figure 12 gives a cross section of the electronic wristwatch and Figure 13 is an exploded oblique view of the electronic wrist watch except for the gears of the internal. The following description will refer to Figures 11 to 13 in which reference numeral 100 denotes the casing of the watch whose front end is fitted with a watch glass 101 and whose rear end is fitted with a screwed back lid 103. In the casing 100 is provided a 60-pole, 60-step pulse motor 104 under which a plastic member to form the space for a battery 105 is located. The shape of the pulse motor 104 is the same as a pulse motor 4 shown in Figure 1.

The detailed description of the pulse motor is omitted here. A circuit board 107 is fitted with an LSI 109 which operates the pulse motor 104 and the liquid crystal display 108 to be explained later, the crystal oscillator (not shown) and other electronic components. Output signals to drive the liquid crystal produced by the LSI 109 are transmitted via a flexible wiring sheet 110 and a conductive elastic connector 111 to the liquid crystal display 108, which comprises a front base sheet 112 of transparent glass with an electrode (not shown) formed on it and a rear base sheet 113 of transparent glass with an electrode on it. The front base sheet 112 is laid on a spacer 114, which is placed on the rear base sheet 113, and liquid crystal is sealed inside the space between the sheets 112 and 113.The front base sheet 112 has opaque coating on its surface except for the date and day of a week display area 11 2a, an AM display area 11 2b and a PM display area 11 2c so that it can serve as the dial disc. The rear base sheet 113 has a reflector (not shown) on its bottom and a clearance hole in it, through which a bearing 115 is located with a spacer 116 at its end to prevent it from touching the liquid crystal and deteriorating the liquid crystal. The liquid crystal display 108 has a clearance hole at its center penetrating the front base sheet 112, a spacer 117 and the rear base sheet 113. A bearing 118 is inserted in the clearance hole so as to allow the hour hand gear shaft 119 to rotate easily.The foregoing design of an electronic wrist watch enables its thickness to be small enough despite the use of the pointers as well as the optical display because it eliminates the need of the ground plate, pivotal receptacle plate and the like that are generally employed in the conventional electronic watches since the liquid crystal display 108 fitted with the bearings 115 and 118 is superposed on the pulse motor 104 with a concave portion to form a lamination so that the gear series and the circuit board 104 are lodged in the concave portion. The gear series may well be positioned to fit the gear shafts with the bearings embedded in the liquid crystal display 108. Thus, the assembly of the component parts has been made so simple that all that has to be done is to position the gear series, the circuit board 104 and the flexible wiring sheet 110 on the pulse motor 104 as required, and place the liquid crystal display 108 followed by mounting of the hour hand and the minute hand.

Although the shaft of the pulse motor is fitted with the minute hand to directly rotate it in all the foregoing embodiments, the present invention may be applied to a three-hand electronic watch by placing its second hand directly on the motor shaft.

Further, the present invention may widelyqbe applied to variously electronic time pieces including portable clocks in additicn to electronic wrist watches.

Claims (4)

1. An electronic time keeping device having a step motor rotatively driven by a reference clock pulse and hands for pointing time of which the rotation is controlled by the step motor, in which said step motor is packed in unit by a case covering a rotor, a stator and a coil, with a depressed portion.

2. An electronic time keeping device having a step motor rotatively driven by a reference clock pulse and hands for pointing time of which the rotation is controlled by the step motor, in which said step motor is packed in unit by a case covering a rotor, a stator and a coil and the packed step motor has substantially the same diameter as that of an opening of a movement containing portion of a clock case.

3. An electronic time keeping device having a step motor rotatively driven by a reference clock pulse and hands for pointing time of which the rotation is controlled by the step motor, in which said step motor is packed in unit by a case covering a rotor, a stator and a coil and the packed step motor is layered on a circuit board with an electronic part arranged thereon to supply the reference clock signal in superposed manner.

4. An electronic time keeping device, substantially as hereinbefore described with reference to the accompanying drawings.