JP4774741B2 - clock - Google Patents

Description

  The present invention relates to a high-precision gear, a method for manufacturing a high-precision gear, and a timepiece equipped with the high-precision gear.

  Conventionally, in a high-precision circular gear made of a fiber-reinforced thermoplastic material by injection molding with a tooth row engraved on the outer periphery, the gear is a web portion intermediate between the main spindle cylinder and the tooth row that determines the central axis thereof. Small through holes with a required diameter are provided at approximately equal intervals on a substantially concentric circle outside the position corresponding to the gate of the injection mold provided at equal intervals in a plurality of locations concentrically with the cylinder. It is known that the number of lines is increased to eliminate gear deformation (for example, see Patent Document 1).

  Further, in an injection molding method of an insert-containing resin gear having a resin layer that forms a dentition on the outer periphery of the insert, five points of molten resin are contained in the mold while the insert is supported at the cavity central portion of the injection mold. A gear manufacturing method is known in which the molten resin injected from the above pin gate and the distance between the pin gate and the insert is 0.5 mm or more is once applied to the insert and then fed into the outer teeth. (For example, refer to Patent Document 2).

  Furthermore, in a watch that receives a standard radio wave and corrects the time, the light detection sensor is fixed to the circuit board fixed to the wall of the upper case and the wall of the upper case, and the circuit is connected in parallel with the light emitting element. A light emitting device comprising a light emitting device attached to a substrate, the main body portion being disposed near or integrally with the inner wall of the lower case, and one end portion sandwiching the formation region of the third through hole of the first fourth wheel The other end of the through hole of the minute hand wheel, the through hole of the hour hand wheel, the through hole of the second third wheel, and the through hole of the second fourth wheel are overlapped with each other. There is known a watch provided with a light guide disposed so as to face a light receiving portion with a region where the light can be generated (see, for example, Patent Document 3).

Japanese Patent Laid-Open No. 10-34762 (page 3, FIG. 1) JP 2002-248649 A (page 3, FIG. 3) JP 2002-107465 A (pages 9 to 11, FIG. 3)

  In Patent Document 1, the required diameter of the mold cavity is approximately equal to the concentric circle outside the position corresponding to the gates of the injection molds provided at equal intervals in a plurality of concentric circles. It is possible to eliminate the deformation of the gear by providing a small cylinder and increasing the weld line at the time of injection molding, but in the case of opening a through-hole that transmits light like the above-mentioned Patent Document 3 in the gear By providing this through hole, it is assumed that the flow state of the molten resin changes, the gear is deformed during injection molding, and it is difficult to form a highly accurate tooth row.

  The through holes as described above are for detecting the rotational position of the gear accurately by light detection, and the position and shape of the through holes must be accurately controlled. There is a problem that it is difficult to accurately manage the position and shape of the through hole only by providing a cylinder.

  According to the above-mentioned Patent Document 2, while the insert is supported at the cavity central portion of the injection mold, molten resin is injected into the mold from five or more pin gates, and the distance between the pin gate and the insert is set. The molten resin injected as 0.5 mm or more is once applied to the insert and then fed to the teeth on the outer periphery so that the molten resin flows uniformly. This is a gear having a metal insert. Even if it is effective, it cannot be used for small gears that do not contain inserts. In addition, there is a problem that a sufficient effect cannot be found in the gear having the light detection through hole as described above.

  Further, according to the aforementioned Patent Document 3, in order to detect the rotational position of the gear, the third through hole of the first fourth wheel, the through hole of the minute hand wheel, the through hole of the hour wheel, The through hole of the third wheel and the through hole of the second fourth wheel are provided, but when these gears are injection-molded, the position and shape of the through holes are shifted, and accurate detection is possible. It has a problem that it cannot be done.

  In addition, in the production of gears by injection molding, it is conceivable that light may be transmitted depending on the material and color of the resin, and there is a problem of false detection when light from a light emitting element is transmitted at a place other than a through hole. It is done.

  SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems, and a high-precision gear having a high-precision detection hole and a tooth row, a method of manufacturing a gear that realizes the high-precision gear at low cost, and the gear It is to provide a watch equipped with.

The high-precision gear of the present invention is a gear made of synthetic resin molded by injection molding, and a plurality of detection holes for detecting the rotational position of the gear and a plurality of holes provided at substantially equal intervals in the rotational direction of the gear. And the detection hole is provided at substantially the center of the adjacent gate portions.
Here, the gate portion indicates the position of the gate through which the synthetic resin flows into the mold cavity when the gear is formed by injection molding.

  According to the present invention, the detection hole is opened between the adjacent gate portions. The molten synthetic resin flowing in from the adjacent gate portions merges between the two gate portions to form a weld line radially from the center of the gear. Since the deformation around the weld line is small due to the shrinkage of the synthetic resin after molding, the detection hole arranged in the middle of the adjacent gate portion is opened on or near the weld line. Deformation and displacement can be reduced.

  In addition, since a plurality of gate portions are provided at substantially equal intervals in the rotation direction of the gear, the peripheral area of the weld line with less shrinkage is increased, the area that is easily shrunk can be reduced, and the gear teeth are deformed. Can be reduced.

  Further, since the detection hole is opened in the vicinity of the weld line with small shrinkage, there is an effect that the influence on the deformation of the dentition due to the provision of the detection hole can be reduced.

  Further, the means for detecting the rotational position of the gear is light detection for detecting light transmitted through the detection hole, and is formed from a material having a light shielding rate of 80% or more at a predetermined thickness of the gear. Preferably it is.

  Although details will be described in an embodiment described later, the rotation position of the gear is detected by detecting that light is transmitted through the detection hole. Therefore, by setting the light shielding rate of the portion other than the detection hole of the gear to 80% or more, it is possible to prevent erroneous detection due to light transmission before or after the detection hole reaches the predetermined detection position. .

In addition, it is preferable that the gear is formed of a material having a light shielding rate of 80% or more at a predetermined thickness by kneading a pigment in a synthetic resin as a base material.
Here, as the pigment, for example, a black carbon pigment can be employed.

  Thus, by kneading a pigment having a high light-shielding property, it is not necessary to increase the thickness of the gear in order to improve the light-shielding property, and it is possible to provide a gear having a high light-shielding property even if it is thin. Further, there is no need to change the mold structure or the like in order to knead the pigment, and the moldability does not change.

Moreover, it is preferable that the gear is formed of a material having a light shielding rate of 80% or more at a predetermined thickness by kneading reinforcing fibers with a synthetic resin as a base material.
Here, as the reinforcing fiber, for example, glass fiber (GF), potassium titanate, carbon fiber (CF), glass beads and the like can be employed.

  In this way, the structural strength of the gear can be increased, and the above-mentioned reinforcing fiber has a light-shielding property in itself and is kneaded with a synthetic resin as a base material so that light is reinforced. Therefore, the light shielding property is improved, and erroneous detection of the rotational position of the gear can be reduced.

Moreover, it is preferable that the gear is molded from a crystalline resin having a light shielding rate of 80% or more at a predetermined thickness.
Here, the crystalline resin refers to a resin having a property that polymer chains are regularly arranged at a temperature equal to or lower than the melting point.

  The crystalline resin has a high density of the crystallized portion after being cured and becomes opaque, so that the light shielding property is improved, and erroneous detection of the rotational position detection of the gear can be reduced.

Furthermore, it is desirable that an irregular reflection layer for irregularly reflecting light is formed on at least one main surface of the gear.
The irregular reflection layer can be obtained, for example, by forming fine irregularities on the surface corresponding to the main surface of the gear of the mold cavity by means such as sandblasting.

  By forming the irregular reflection layer on the main surface (planar portion) constituting the gear, light for detection is diffusely reflected on the gear surface, and the amount of light transmitted through the gear can be reduced. This irregular reflection layer can be formed on one or both of the main surfaces of the gear, and if formed on both, the effect is still great.

  The high-precision gear manufacturing method of the present invention is a high-precision gear manufacturing method for molding the above-described high-precision gear by injection molding, and includes a plurality of gates for injecting the synthetic resin into a mold cavity. The plurality of gates are provided at substantially equal intervals in the rotation direction of the gear, and a molding shaft that forms a detection hole for detecting the rotation position of the gear is provided at a substantially center between the adjacent gate portions. And

  According to the present invention, by arranging the gate and the molding shaft in the mold cavity as described above, it is possible to mold a highly accurate gear with an inexpensive mold. Further, as described above, even when a pigment, reinforcing fiber, or the like is kneaded with a synthetic resin, a high-precision gear can be easily manufactured without changing the mold structure by setting a predetermined shrinkage rate. In addition, the irregular reflection layer can be easily formed on the main surface of the gear by forming irregularities on the inner surface of the mold cavity, and a low-cost high-precision gear can be provided.

  In the timepiece of the present invention, the high-precision gear manufactured by the above-described configuration and manufacturing method is a gear that drives any one of the hour hand, the minute hand, and the second hand for time display, and the detection provided on the gear. A light detection device for detecting light transmitted through the hole, and the predetermined rotation position of the gear is detected by the light detection device, so that the predetermined indication position of any of the hour hand, the minute hand, and the second hand is set; It is characterized by detecting.

  Here, for example, the timepiece described above receives a standard time radio signal, and detects the detection hole opened in the gear driving the hands by the light detection device when the hand position of the timepiece is adjusted to the standard time. A radio-controlled timepiece that derives the difference between the standard time radio signal and the hand and automatically corrects it to the correct time can be considered.

  According to such an invention, since the detection hole having a highly accurate position and shape can be detected by the light detection device, it is possible to accurately adjust the standard time radio wave and the watch pointer display. it can. In addition, since the gear teeth can be formed with high accuracy, a timepiece that maintains stable driving can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 are partial cross-sectional views of a timepiece according to an embodiment of the present invention, FIG. 3 is a graph showing a relationship between light detection and detection voltage of the timepiece according to the embodiment, and FIG. 4 is related to the embodiment. Sectional view and plan view of the third wheel, FIG. 5 is an explanatory view showing the relationship between the gear manufacturing method and the accuracy of the dentition according to the embodiment, FIG. 6 is an explanatory view of the detection hole, and FIG. FIG. 8 is an explanatory view of a detection hole according to the prior art.
(Embodiment)

1 and 2 show a rotational position detector of a timepiece according to an embodiment of the present invention.
FIG. 1 is a cross-sectional view showing a part of a train wheel including a first light detection device for detecting the hour / minute hand position of the present embodiment, and FIG. 2 is a wheel including a second light detection device for detecting a second hand position. It is sectional drawing which shows a part of row | line | column. A timepiece 1 according to this embodiment includes an hour step and a minute stepping motor that drive hour and minute hands as a time display unit (not shown), a wheel train that transmits the driving of the minute stepping motor to the hour and minute hands, and a second stepping motor that drives the second hand. A wheel train that transmits the driving of the second stepping motor to the second hand, a first machine casing 10 that supports these wheel trains, a second machine casing 20, and first and second light detection devices, , And a radio receiving device (not shown) and a control circuit.

  In FIG. 1, the train wheel structure of the timepiece is well known and will not be described in detail. However, a minute stepping motor (not shown) is a five-second step driving motor that rotates 180 degrees every five seconds. The fifth wheel 50 and the third wheel 30 are decelerated so that the number wheel 60 rotates once per hour. The second wheel is provided with a cylindrical shaft portion (not shown), and a minute hand is fixed to the shaft portion.

  The driving force from the center wheel & pinion 60 is transmitted to the hour wheel 70 through a minute wheel (not shown), and decelerated so that the hour wheel 70 makes one rotation in 12 hours. In the hour wheel 70, an hour hand is fixed to a cylinder portion (not shown).

  The second stepping motor rotates 180 degrees every second, decelerates so as to rotate once per minute via the second intermediate wheel 42, and drives the second wheel 40. In the second wheel 40, a second hand is fixed to a second hand shaft (not shown). The second wheel 40, the second wheel 60, and the hour wheel 70 rotate on the same axis, and the time is displayed by the hour hand, the minute hand, and the second hand.

  The hour wheel 70 has a detection hole 71, the second wheel 60 has a detection hole 61, the third wheel 30 has a detection hole 31, the fifth wheel 50 has a detection hole 51, and the second wheel 40 has a detection hole 41. Has been. When these detection holes 71, 61, 31, 51, and 41 all overlap, the light detection device converts the light transmitted through these detection holes into a voltage and detects it. The first machine casing 10 is provided with a through-hole 11 that transmits light whose center coincides with the optical axis 82.

  The first photodetecting device includes an LED (Light Emitting Diode) 80 as a light emitting unit, a phototransistor 90 as a light receiving unit, a light emitting / receiving control circuit (not shown), and a CPU (Central Processing Unit). The LED 80 is fixed to the first circuit board 85 by fixing means such as adhesion, and the phototransistor 90 is also fixed to the second circuit board 86 by adhesion means such as adhesion. The LED 80 and the phototransistor 90 are provided opposite to each other on the optical axis 82, and the detection holes described above overlap so that light emitted from the LED 80 is transmitted to the phototransistor 90 at a predetermined time.

  The LED 80 and the phototransistor 90 are applied with the same potential voltage (power supply voltage). In this embodiment, when the light emitted from the LED 80 is received by the phototransistor 90, the phototransistor 90 is initialized. When the potential is 80% of the voltage applied to the threshold voltage, the threshold voltage is set. When the power supply voltage is 1.5V, the threshold voltage is set to 1.2V. That is, when the phototransistor 90 detects a voltage exceeding 1.2 V, it is detected that all the detection holes 71, 61, 31, 51, 41 described above overlap.

  When these detection holes are overlapped, it indicates that the hour hand, the minute hand, and the second hand are all in a predetermined position. In the present embodiment, this means that all these hands are overlapped at the 12 o'clock position. That is, 0:00 is detected by the first photodetector. For detection in units of seconds, single light detection is performed in order to obtain more accuracy.

  In the present embodiment, the hour wheel 70, the second wheel 60, and the second wheel 40 are provided with structural strength because pointers such as an hour hand, a minute hand, and a second hand are attached, and are formed of metal. 30 and the fifth wheel & pinion 50 are formed of a synthetic resin.

Next, detection in units of seconds will be described.
FIG. 2 is a cross-sectional view showing a part of a train wheel including a second photodetection device that detects the second hand position. In FIG. 2, the second photodetecting device is composed of an LED 81 as a light emitting unit, a phototransistor 91 as a light receiving unit, a light emitting / receiving control circuit (not shown), and a CPU, like the first photodetecting device. Yes. The light emission / reception control circuit and the CPU are used in common with the first photodetection device. The LED 81 is fixed to the first circuit board 85 by fixing means such as adhesion, and the phototransistor 91 is also fixed to the second circuit board 86 by adhesion means such as adhesion.

  In this embodiment, a second stepping motor (not shown) different from the minute stepping motor is provided, and the second stepping motor rotates 180 degrees every second, and rotates once per minute via the second intermediate wheel 42. The second wheel 40 is decelerated in this manner to drive the second wheel 40, and a second detection wheel 44 for detecting the rotational position of the gear in units of one second is provided. The second detection wheel 44 has the same number of teeth as the second wheel 40 and interlocks with the second wheel 40.

  A detection hole 43 is opened in the second intermediate wheel 42, and a detection hole 45 is opened in the second detection wheel 44. Further, in the first machine casing 10 and the second machine casing 20 that pivotally support these wheel train components, the detection hole 12 and the detection hole 21 are respectively provided on the optical axis 83 that connects the LED 81 and the phototransistor 91. When the detection hole 43 and the detection hole 45 overlap each other at a predetermined time, the light emitted from the LED 81 is transmitted to the phototransistor 91, so that the second wheel 40 is in a predetermined position (in this embodiment, , The second hand is at the 0 second position).

  The timepiece 1 of the present invention receives a time standard radio signal transmitted from the Communications Research Laboratory (CRL) of the Ministry of Posts and Telecommunications, and corrects the time accurately and automatically. The predetermined position is accurately detected, and the deviation from the time standard signal is corrected. In this embodiment, the difference between the time standard signal and the time standard signal is detected when each hand is at the 0: 0: 0 position, and when the hands are behind the time standard signal, the stepping motor is fast-forwarded and advanced. Sometimes the stepping motor is stopped or reversely fed to display an accurate time that matches the time standard radio signal.

  Here, the timepiece 1 has a second stepping motor and a minute stepping motor (both not shown), and when there is a deviation within one minute, the second stepping motor is driven and there is a deviation of one minute or more. In the configuration, the minute stepping motor and the second stepping motor are driven to correct the display of the pointer accurately in a short time.

Subsequently, a method of light detection according to the present embodiment will be described.
FIG. 3 is a graph showing the relationship between the position of the detection hole 31 and the detection voltage according to the present embodiment. In FIG. 3, the third wheel 30 will be described as an example. This will be described with reference to FIG. In FIG. 3, the horizontal axis indicates the position (angle) of the detection hole 31 around the optical axis 82 of the LED 80, and the vertical axis indicates the detection voltage of the phototransistor 90. A straight line 95 indicates the relationship between the detection voltage and the position (opening interest rate) of the detection hole 31.

  Here, the design value of the third wheel & pinion 30 according to the present embodiment will be described. The detection hole 31 has a diameter of 0.4 mm, and the center distance from the center G is 1.2 mm. Therefore, the range of the detection hole 31 diameter from the center G is as follows. The angle (center angle) is 9.5 degrees. The third wheel & pinion 30 rotates 3.75 degrees in one step (every 5 seconds) of the minute stepping motor. In the detection hole 31, as an initial setting, the pointer is attached at the 12 o'clock position in a state where the optical axis 82 and the center g of the detection hole 31 coincide (indicated by (a) in the figure). At this time, the detection hole 31 is fully opened (aperture ratio 100%), the detection voltage shows a peak voltage of 1.5 V, and this voltage matches the power supply voltage.

  The detection voltage is generated after the third wheel 30 rotates (in the direction of the arrow in the figure) and the detection hole 31 begins to transmit the detection light (indicated by (b) in the figure), and the third wheel 30 rotates. As the aperture ratio of the detection hole 31 increases, the detection hole 31 rises, and at the position shown in FIG. When the aperture ratio of the detection hole 31 decreases through the center g optical axis 82 of the detection hole 31, the detection voltage decreases. When the threshold voltage exceeds 1.2 V, it is determined that the third wheel & pinion 30 indicates a predetermined position, that is, the hour hand and the minute hand indicate the 12 o'clock position (0 position).

  When the third wheel 30 further rotates and the detection hole 31 is deviated from the optical axis 82 by 1 degree (indicated by (d) in the figure), the detection voltage becomes smaller than the threshold value 1.2V and is detected outside the predetermined position. It is determined that there is a hole 31.

  As shown in FIG. 3, the range exceeding the threshold voltage of 1.2V is a range of ± 1 degree with respect to the optical axis 82, and if the center g of the detection hole 31 is within this ± 1 degree range, It indicates that there is no deviation from the setting. When the position exceeds ± 1 degree, the position is shifted from the initial setting by 5 seconds for one step of the third wheel & pinion 30.

  The rotation pitch of the third wheel 30 (one step of the minute stepping motor) is 3.75 degrees, the center angle of the detection hole 31 is 9.5 degrees, and ± 4.75 degrees with respect to the optical axis 82 When assigned, the rotation pitch of the third wheel & pinion 30 is designed to be a difference of an absolute value of 1 degree on one side and coincide with the threshold voltage range.

  Here, based on the design value of the detection hole 31 described above, the allowable range ± 1 degree of the center g of the detection hole corresponds to ± 0.02 mm in terms of the shape (radius) of the detection hole 31. Therefore, if the shape of the detection hole 31 is within a range of ± 0.02 mm in the circumferential direction passing through the center g with respect to the design value, the pointer position matches the zero position detection.

Next, from the relationship between the position of the detection hole 31 described in FIG. 3 and the detection voltage, the position accuracy and shape accuracy of the detection hole affect the detection accuracy. A method for manufacturing a precision gear will be described.
FIGS. 4A and 4B are a sectional view and a plan view showing an example of the high-precision gear according to the present embodiment, and illustrate the third wheel 30. 4A and 4B, the third wheel & pinion 30 includes a large-diameter gear portion 34, a pinion 32, and rotation support shafts 33A and 33B. The third wheel & pinion 30 is integrally molded by injection molding with a synthetic resin kneaded with a carbon pigment having a weight ratio of 1% (carbon pigment particle size: 100 nm) using polyoxymethylene (POM) as a base material.

  The gear portion 34 of the third wheel & pinion 30 molded with such a synthetic resin has a light shielding ratio of 80% or more in the thickness direction (in this embodiment, the thickness of the gear portion 34 is 0.12 mm) and is emitted from the LED 80. However, since the threshold voltage of 1.2 V is not exceeded in the phototransistor 90, the detection is canceled when the detection hole 31 does not reach the predetermined position. Since the threshold voltage is set to 80% of the power supply voltage, the light shielding rate of the gear unit 34 is set to 80% or more.

  On one main surface of the gear portion 34 (the upper surface in FIG. 4A), three concave portions 36 are formed on a substantially concentric circle at equal intervals of 120 degrees. The recess 36 is a place where a gate for injecting molten synthetic resin into the mold cavity is provided, and the bottom of the recess 36 has gate portions 37A, 37B, as traces when the gate is removed after injection molding. 37C remains. The depth of the recessed portion 36 is set so that the gate portions 37 </ b> A to 37 </ b> C do not protrude from the upper surface of the gear portion 34.

  A detection hole 31 is opened outside the middle between the gate portions 37B and 37C. The detection hole 31 is formed by a molding shaft (not shown) planted in the mold cavity. Further, a stepped portion 35 is formed in the central portion on the other main surface of the gear portion 34 (the lower surface in FIG. 4A). The step portion 35 is provided to increase the fluidity of the synthetic resin near the center of the third wheel 30 and to increase the structural strength of the gear portion.

The relationship between the detection hole 31 provided in the third wheel 30 and the gate portions 37A to 37C will be described in more detail. Here, the prior art will be described in comparison with the present embodiment.
FIG. 7 is a plan view showing the gear portion 34 of the third wheel & pinion 30 formed by the prior art. Here, in the prior art, the gate is provided only at one place, and the position is represented as the gate portion 37. The mold is provided with four ejectors 38 </ b> A to 38 </ b> D at substantially the same distance at a distance close to the distance from the center G of the gear portion 34 to the gate portion 37.

  The detection hole 31 is opened at a position 60 degrees clockwise from the position connecting the center G and the gate portion 37. The synthetic resin injected from the gate part 37 gradually flows away from the gate part 37 (in the direction of the arrow in the figure), and merges on the opposite side of the gate part 37 across the center G. This joining position is a weld line 39. The synthetic resin begins to cure and shrinks as the temperature drops.

  When the synthetic resin reaches a predetermined temperature (predetermined curing depth), the third wheel 30 is removed from the mold cavity by the ejectors 38A to 38D provided in the mold, and the third wheel 30 is completed. Here, the result of measuring the distance from the center G of the gear portion 34 to the tooth tip of the dentition is displayed as a point, and is displayed as a curve 134 connecting these points. This curve 134 connects the distance from the center G to the tooth tip of the dentition, and the difference from the distance to the tooth tip that should be a perfect circle is the deformation amount.

  In FIG. 7, the measured value is schematically represented by a curve 134 for easy understanding of the deformation amount. Here, the deformation amount in the vicinity of the extended line of the weld line 39 is small, and the deformation amount in the direction perpendicular to the weld line 39 is large. Further, the deformation amount of the peripheral tooth tip on the straight line connecting the center and the center G of the detection hole 31 is large.

  The measured value of the distance between the tooth tip and the center G is 6.4 μm when the diameter of the tooth tip of the third wheel 30 is 3.8 mm, and the difference between the maximum value and the minimum value is 6.4 μm. The variation was 5 μm when taken at 3σ. If there is such a deformation of the tooth tip, the driving force cannot be accurately transmitted to the fifth wheel 50, or a predetermined meshing relationship with the 50 pinion of the fifth wheel cannot be obtained and stopped. It is possible to end up.

Next, deformation of the detection hole 31 will be described.
FIG. 8 is an explanatory view schematically showing a part of the gear portion 34 of the third wheel & pinion 30 formed by the prior art. In FIG. 8, the detection hole 31 is opened at a position rotated by an angle θ from a straight line connecting the center G and the gate portion 37. In this embodiment, θ = 60 degrees. After the injection molding, when the synthetic resin contracts, as described above, the detection hole 31 expands in the circumferential direction because it contracts toward the weld line 39 (in the direction of arrow B). Moreover, it expands also in the center direction and becomes a shape like 31A shown in the figure.

The deformation amount in the circumferential direction passing through the center g of the deformed detection hole 31 is 0.03 mm larger on one side than the design value (indicated by the detection hole 31) in the experimentally measured value. As described above, the size of the detection hole must be controlled to 0.02 mm or less with respect to the design value. Therefore, according to the above-described prior art, the deformation amount of the detection hole 31 is large and it is difficult to detect the accurate position.
The third wheel & pinion 30 is rotated in the direction of arrow A (counterclockwise) by the minute stepping motor, but since the amount of deformation is large in the circumferential direction (rotation direction) as in 31A, the rotation position is detected by the light detection device. It cannot be done accurately.

Next, the third wheel & pinion 30 molded by the method according to the present embodiment will be described.
FIG. 5 is a plan view showing the gear portion 34 of the third wheel & pinion 30 formed by the manufacturing method of the present embodiment described above. In the present embodiment, gates are provided at three locations, and the positions are represented as gate portions 37A to 37C. The mold is provided with four ejectors 38A to 38D at positions close to the distance from the center G of the gear portion 34 to the gate portion at the positions shown in the figure.

  The detection hole 31 is opened at the center of the gate portions 37B and 37C (see FIG. 6). The synthetic resin injected from the gate portions 37A to 37C gradually flows away from the gate portion and joins at an intermediate position of the gate portion. This joining position is a weld line 39. In this embodiment, the weld line 39 is formed in the middle of the gate portions 37A and 37B, the gate portions 37B and 37C, and the gate portions 37C and 37A. After injection molding, the synthetic resin begins to cure and shrinks due to the temperature drop.

  When the synthetic resin reaches a predetermined temperature (predetermined curing depth), the third wheel 30 is removed from the mold cavity by the ejectors 38A to 38D provided in the mold, and the third wheel 30 is completed. Here, the result of measuring the distance from the center G of the gear portion 34 to the tooth tips of the dentition is displayed as points, and is displayed as a curve 134 connecting these points. This curve 134 connects the distance from the center G to the tooth tip of the dentition, and the difference from the distance to the tooth tip that should be a perfect circle is the deformation amount.

  In FIG. 5, the measured value is schematically represented by a curve 134 for easy understanding of the deformation amount. Here, the deformation amount is small in the vicinity of the extended line of the weld line 39, and the deformation amount at a position away from the weld line 39 is large. Further, since the deformation amount of the tooth tip on the straight line connecting the center g of the detection hole 31 and the center G of the gear portion 34 is set on the weld line 39, the deformation amount becomes small, and the periphery thereof is deformed. The amount is getting bigger.

  According to the present embodiment, when the tooth tip outer diameter of the third wheel & pinion 30 is set to 3.8 mm, the difference between the maximum value and the minimum value is 4. It was 3 μm, and when the variation was taken as 3σ, it was 3.2 μm. Therefore, the amount of deformation of the tooth tip is reduced by about 33% and the variation is reduced by about 36% as compared with the above-described prior art.

Next, deformation of the detection hole 31 will be described.
FIG. 6 is an explanatory view schematically showing a part of the gear portion 34 of the third wheel & pinion 30 molded according to the present embodiment. In FIG. 6, the detection hole 31 is opened at a position of an angle θ from the gate portions 37B and 37C. In this embodiment, θ = 60 degrees. After the injection molding, when the synthetic resin contracts, it contracts toward the weld line 39 (in the direction of arrow B) as described above, but a molding shaft for forming the detection hole 31 is implanted in the mold. Therefore, the contraction is restricted, and there is almost no deformation in the rotation direction (arrow A direction).

  The deformation amount in the circumferential direction passing through the center g of the deformed detection hole 31 is less than +0.01 mm on one side in the experimental value with respect to the design value (indicated by the detection hole 31) in the experimental measurement value. . As described above, the size of the detection hole must be controlled to 0.02 mm or less with respect to the design value. Therefore, according to the manufacturing method of this embodiment, since the deformation amount of the detection hole 31 is within the allowable range, it is indicated that accurate position detection can be performed.

  In the above-described embodiment, the third wheel & pinion 30 is described as an example. However, the present invention can be applied to other gears manufactured by injection molding a synthetic resin.

  In the above-described embodiment, the detection hole 31 is opened at the center (position of the angle θ = 60 degrees) between the gate portions 37B and 37C. However, the detection hole 31 does not necessarily have to be in the center, and the adjacent gates. The same effect can be obtained if it is opened in the approximate center of the part, for example, in the vicinity of the weld line 39.

  In the above-described embodiment (see FIGS. 4 and 5), three gates are provided. However, the number of weld lines is not limited to three but the number of weld lines increases, and the gear part 34 is deformed by contraction. Can be small.

  The third wheel & pinion 30 according to the above-described embodiment employs polyoxymethylene (POM) as a base material, and as the base material, polypropylene (PP), polyethylene sulfide (PPS), polybutylene terephthalate (PBT). ), Modified polyphenylenoxide (PPO), polycarbonate (PC), polyamide (PA), liquid crystal polymer (LCP), and the like can be employed.

  These base materials are materials called crystalline resins, and are synthetic resins having a property that polymer chains are regularly arranged at a temperature below the melting point, and the density of the crystallized portion after curing becomes high and opaque. Therefore, the light shielding property is enhanced and the structural strength is also high, so that it is suitable for fine high-precision gears.

  In the above-described embodiment, a black carbon pigment with a weight ratio of 1% is kneaded with polyoxymethylene (POM). However, the light-shielding pigment is not limited to the black carbon pigment, and has a light-shielding property, particularly an infrared wavelength. Any material can be used as long as it shields the light in the region.

  Furthermore, potassium titanate, carbon fiber (CF), glass fiber (GF), glass bead (GB), etc. can be employed as the reinforcing fiber to be kneaded into the substrate. In particular, the reinforcing fiber is characterized in that the effect of the structure of the gear and the manufacturing method according to the present embodiment greatly appears because flow anisotropy and shrinkage illegality are likely to appear due to fiber orientation during injection molding. In this embodiment, reinforcing fibers having a weight ratio of 30% with respect to the base material are kneaded, but the kneading amount of the reinforcing fibers is fluidity, shrinkage rate, structural strength, light shielding properties during injection molding. Can be appropriately selected.

  Further, as a means for enhancing the light shielding property of the gear portion 34, a light irregular reflection layer can be provided on at least one (front surface or back surface) of the gear portion 34. This irregular reflection layer can be obtained by forming small irregularities on the portion corresponding to the main surface of the gear portion 34 of the mold cavity by means such as sandblasting. If it does in this way, the amount which permeate | transmits the gear part 34 can be suppressed by irregularly reflecting the light inject | emitted from LED80 by a diffused reflection layer. Although the irregular reflection layer may be formed only on one of the main surfaces of the gear portion 34, the light shielding property can be further improved by forming the irregular reflection layer on both surfaces.

  Therefore, according to the above-described embodiment, the detection hole 31 is opened in the middle between the adjacent gate portions 37B and 37C, and the molten synthetic resin flowing in from the adjacent gate portions merges in the middle between both gate portions. Then, the weld line 39 is formed radially from the center G of the gear portion 34. Since the deformation around the weld line 39 is small due to the shrinkage of the synthetic resin after molding, the detection hole 31 arranged in the middle of the adjacent gate portion is opened on or near the weld line 39. , Deformation and misalignment can be reduced.

  In addition, since three gate portions are provided at equal intervals in the rotation direction of the gear portion 34, the peripheral area of the weld line 39 that is less contracted is increased, and the area that is easily contracted can be reduced, and the gear teeth can be reduced. There is an effect that the deformation of the row can be suppressed to be small.

  Further, since the detection hole 31 is opened in the vicinity of the weld line 39 with small shrinkage, there is an effect that the influence on the deformation of the dentition due to the provision of the detection hole 31 can be reduced.

  The rotation position of the third wheel & pinion 30 is detected by detecting that light is transmitted through the detection hole 31. Accordingly, by setting the light shielding rate to 80% or more in a predetermined thickness of the gear portion 34 other than the detection hole 31, light can be transmitted before or after the detection hole 31 reaches a predetermined detection position. Can prevent false detection.

  Further, as a means for improving the light shielding property of the gear portion 34, it is not necessary to increase the gear thickness in order to improve the light shielding property by kneading the base material with a black carbon pigment or the like having a high light shielding property. High gears can be provided. Further, it is not necessary to change the mold structure or the like by kneading the pigment, and the moldability does not change.

  Further, as another means for improving the light-shielding property, a method of kneading the above-mentioned reinforcing fiber to the base material is adopted, and thereby the structural strength of the gear can be increased, and the above-mentioned reinforcing fiber is In addition to being light-shielding, the light is irregularly reflected by the reinforcing fibers when kneaded into the synthetic resin, so that the light-shielding property is enhanced and erroneous detection of the rotational position of the gear can be reduced.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
For example, in the above-described embodiment, a material in which a polyoxymethylene (POM) is used as a base material and a black carbon pigment and a reinforcing fiber are kneaded as a light-shielding pigment is exemplified. Fibers and pigments can be used in appropriate combinations. In this case, the combination is preferably selected in the watch according to the place of use and purpose of use.

  Further, in this embodiment, an example in which one detection hole 31 is provided in a circular shape has been described. However, the number of the gate portions described in the above-described embodiment is not limited to a plurality of detection holes or a deformed shape. The same effect can be obtained by following the concept of the positional relationship with the gate portion.

  Although the timepiece of this embodiment has been described with reference to light detection of a radio-controlled timepiece, the present invention is not limited to a timepiece, and is applied to the case where the position, shape, and the like of components constituting the timepiece are detected by light detection. In addition, even if the detection hole has a function that requires another accurate position, it can be applied to the formation thereof.

  Therefore, according to the above-described embodiment, a high-precision gear having a high-precision detection hole and a tooth row, a gear manufacturing method that realizes the high-precision gear at a low cost, and a timepiece equipped with the gear are provided. be able to.

Sectional drawing which shows a part of train wheel including the 1st photon detection apparatus which concerns on embodiment of this invention. Sectional drawing which shows a part of train wheel including the 2nd photon detection apparatus which concerns on embodiment of this invention. The graph which shows the relationship between the position of the detection hole which concerns on embodiment of this invention, and a detection voltage. (A) is sectional drawing which shows the 3rd wheel which concerns on embodiment of this invention, (b) is a top view. The top view which shows the third wheel shape | molded by the manufacturing method which concerns on embodiment of this invention. Explanatory drawing which represented typically a part of gear part of the 3rd wheel & pinion which concerns on embodiment of this invention. The top view which shows the third wheel shape | molded by the prior art. Explanatory drawing which represented typically a part of gear part of the 3rd wheel shape | molded by the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Clock, 10 ... 1st machine casing, 20 ... 2nd machine casing, 30 ... 3rd wheel, 31 ... Detection hole, 34 ... Gear part, 37A-37C ... Gate part, 40 ... Second wheel, 50 ... Fifth wheel, 60 ... second wheel, 70 ... cylinder wheel, 80, 81 ... LED, 82,83 ... optical axis, 90,91 ... phototransistor.

Claims (1)

A gear made of synthetic resin formed by injection molding, wherein a detection hole and a plurality of gate portions provided at substantially equal intervals in a rotation direction of the gear are provided, and the detection holes are adjacent to the gates. A high-precision gear provided in the approximate center of the part,
A light detection device for detecting light transmitted through the detection hole ,
The high-precision gear is a gear for driving one of an hour hand, a minute hand, and a second hand for time display;
A timepiece that detects a predetermined indicated position of any of the hour hand, the minute hand, and the second hand by detecting a predetermined rotational position of the gear by the light detection device .

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