TECHNICAL FIELD

The present disclosure relates to stator design in watches. More specifically, but not exclusively, the present disclosure relates to a differentiate stator design for second hand, minute hand and hour hand of the watch.

BACKGROUND

A watch uses a two-phase motor/ two-phase stepper motor for rotating hands of the watch. The two-phase stepper motor comprises of a stator (stationary part) and a rotor (rotating part). The stator, being an electromagnet, is connected to a coil carrying current. The coil magnetizes the stator when a current is passed through the coil. As a property of the electromagnet, a north pole and a south pole are created in the stator. The rotor, being a permanent magnet, tries to align its north pole with south pole of the stator and its south pole with north pole of the stator. When excitation is changed (e.g., by supplying reverse polarity current), polarity of the stator is changed, thus, changing position of the rotor. The change in excitation thus causes rotation of the rotor. Thus, the two-phase stepper motor allows bidirectional movement of the hands, i.e., clockwise rotation and counter-clockwise rotation. In the present trend, each hand of the watch is controlled by an independent two-phase stepper motor, thus allowing independent movement of the hands. For example, a second hand is controlled by a first two-phase stepper motor, a minute hand is controlled by a second two- phase stepper motor and an hour hand is controlled by a third two-phase stepper motor.

Commonly, structure of the second hand, the minute hand and the hour hand, are different. For example, a second hand is thin compared to the minute hand and the hour hand. As a result, detent torque required by the minute hand and the hour hand should be more than detent torque required by the second hand. Detent torque may be defined as amount of torque required to firmly hold the hands in a fixed position. Even under gravity stress and magnetic stress conditions, the hands should be in the fixed position. In an instance, consider the minute hand and the hour hand have similar structure, and the second watch is thinner than the minute hand and the hour hand. Thus, the minute hand and the hour hand may require more detent torque compared to detent torque required by the second hand. The stator parameters affect the detent torque of the rotor. Tn conventional watches, a stator of a motor used to control the second hand is similar to a stator of a motor used to control the minute hand and the hour hand. Thus, the detent torque is same for the second hand, the minute hand and the hour hand. If the detent torque is set according to requirements of the second hand, the minute hand and the hour hand may not be positioned properly due to lack of detent torque. If the detent torque is set according to requirements of the minute hand and the hour hand, then the second hand may require more power to rotate. As a result, in conventional watches, there is an imbalance between positioning the hands of the watch and power consumption.

Further, the stepper motor used to control the second hand will be in continuous rotation for every second and draws continuous current from the battery. The minute and Hour hand motors draws current at a frequent interval, say minute hand motor will move every 20 seconds once and hour hand will move every 4 minutes once since all the three hands are independent to each other. A Complementary Metal Oxide Semiconductor (CMOS) Integrated Circuit (IC) associated with an electronic circuit board provides pulses to the coil of the motor. Since the pulses are supplied to the coil for every second it significantly reduces life of the battery. A constraint in the stepper motor of the watch is, the battery size cannot be increased as the battery has to be installed within the watch and the current watches have constraints in increasing size. Hence, in the existing stepper motors of a watch, charge in the battery reduces soon, thus reducing the battery life.

The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY

In an embodiment, the present disclosure discloses a watch assembly comprising a plurality of micromotors for controlling hands of a watch assembly. Each of the plurality of micromotors comprises a rotor, a stator comprising a circular hollow for pro visioning the rotor and one or more coils for energizing the stator. The one or more coils are wound on respective coil cores and mounted on the respective stator. Each stator of the corresponding micromotor comprises a pair of notches present on a circumference of the circular hollow, indicating north pole and south pole formed on the stator. Position of the pair of notches on the circumference and dimension of the pair of notches are determined based on a detent torque required to control the corresponding hands of the watch assembly and power consumed by the corresponding micromotor. Further, the stator comprises at least one outer notch present around the circular hollow at a pre-defined notch angle and pre-defined wall margin from the pair of notches. The notch angle is the angle measured between a longitudinal axis passing through the centre of the pair of notches and a longitudinal axis passing through the centre of the at least one outer notch . The wall margin is the distance between the at least one outer notch and the circumference of the circular hollow and the position, the dimension of the pair of notches, the wall margin and the notch angle determines an amount of mutual flux distribution between the one or more coil windings and the rotor.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS

The novel features and characteristic of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

Figure 1A and Figure 1B shows a diagram of a movement assembly, in accordance with some embodiments of the present disclosure;

Figure 2 shows a diagram of a notched stator of a micromotor, in accordance with some embodiments of the present disclosure; Figure 3A and Figure 3B shows stator notches, in accordance with some embodiments of the present disclosure;

Figure 4 shows a diagram of a stator structure of a motor used in the watch assembly, for controlling a second hand of the watch assembly, in accordance with some embodiments of the present disclosure;

Figure 5 shows a diagram of a stator structure of a m otor used in the watch assembly, for controlling a minute hand and an hour hand of the watch assembly, in accordance with some embodiments of the present disclosure; Figure 6 shows a diagram of a coil assembly of the micromotor, in accordance with some embodiments of the present disclosure; and

Figure 7 shows a diagram of a magnet for a micromotor, in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus preceded by "comprises... a" does not, without more constraints, preclude the existence of other elements or additional elements in the system or apparatus.

In the following detailed description of the embodiments of the disclosure, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense. Embodiments of the present disclosure relate to differentiated stator notch structure for hands of a watch assembly. Stator design of each hand of the watch assembly is different from the other. Each stator may comprise a pair of imier notches present on a circumference of the circular hollow, indicating north pole and south pole formed on the stator. Position of the pair of notches on the circumference and dimension of the pair of notches are determined based on a detent torque required to control the corresponding hands of the watch assembly and power consumed by the corresponding micromotor. Stator comprises at least one outer notch present around the circular hollow at a pre-defined notch angle and pre-defined wall margin from the pair of notches. Position, the dimension of the pair of notches, the wall margin and the notch angle determines amount of mutual flux distribution between one or more coil windings and rotor.

Figure 1 A shows a diagram of a movement assembly 100. The watch assembly 100 comprises a plurality of motors and gears required for operating a watch. Figure IB shows a step motor in the watch assembly. The micromotor comprises a rotor, a stator and a coil assembly. The stator comprises a circular hollow for provisioning the rotor. Coil windings are wound on a coil core to form the coil assembly. The coil assembly energizes the stator and is mounted on the stator. In an embodiment, a first micromotor, a second micromotor and a third micromotor drives a second hand, a minute hand and an hour hand of the watch assembly respectively. Thus, each stator of the corresponding micromotor may have a specific design and structure according to detent torque required to drive respective hands.

Figure 2 shows a diagram of a stator 200 of a step motor (not shown). In an exemplary embodiment, the stator 200 is an electromagnet and made of Ni alloy. A person skilled in the art will appreciate that the stator may be made using any other suitable alloys and the present disclosure does not limit the aspects to stators made only of Ni alloy. The stator 200 comprises the circular hollow 201 for provisioning a rotor (not shown). The stator 200 is notched and comprises a first inner notch 202a and a second notch 202b on the circumference of the circular hollow 201. The first inner notch 202a and the second inner notch 202b may be collectively referred as a pair of inner notches 202. Further, the stator 200 comprises a first outer notch 203a and a second outer notch 203b. The first outer notch 203a and the second outer notch 203b may be collectively referred as at least one outer notch 203. The pair of inner notches 202 and the at least one outer notch 203 may be collectively referred as stator notches. The polarity of current energizing the stator 200 defines the poles created on the stator 200. Based on the poles created on the stator 200, the rotor tries to align its poles opposite to that of the stator 200, thereby resulting in rotation of the rotor. The pair of inner notches 202 indicate the north pole and south pole formed on the stator 200. In an embodiment, the pair of inner notches 202 are provided in opposite sides of the circular hollow, thus isolating/ separating the north pole and the south pole of the stator 200. Thus, the separation of the poles allows better rotation of the rotor. The Stator 200 is energised by the current supplied through the coil assembly. The stator 200 may receive divided pulses from the Complementary Metal Oxide Semiconductor Integrated Circuit (CMOS IC). The stator 200 being an electromagnet gets energized and the north pole and the south pole is created in the stator 200 based on the polarity of the pulses received by the coil assembly. In an embodiment, polarity of the pulses is reversed every cycle to reverse the north and south pole in the stator 200. A person of ordinary skill will appreciate that polarity is changed by driving reverse current through the coil. The rotor may be a permanent magnet having a north pole and a south pole. The rotor north pole is attracted by the south pole of the stator 200 and the rotor south pole is attracted by the north pole of the stator 200. The changing north and south pole in the stator 200 cases the rotor to rotate in clockwise or anti-clockwise direction. In an exemplary' embodiment, the stator 200 may be made of Fe- Ni 80 Nickel alloy.

In an embodiment, position and dimension of the pair of inner notches 202 play a major role in defining detent torque of the rotor and current consumption of the step motor. The detent torque may be referred as positioning torque or cogging torque. The detent torque should be set high enough to hold the rotor firmly in its home position i.e., to withstand the hand against the gravity when the movement is kept in stop position. If the detent torque is set too high, the rotor draws high current to release the hand from its home position and if the detent torque is set too low the rotor may not have the stability in holding the hands of the watch assembly 100. Therefore, the stator notch is designed in a way that it does not affect the detent torque of the rotor and the current consumption of the step motor.

Figure 3A shows stator notches, in accordance with some embodiments of the present disclosure. The positions of the stator notches are defined in a manner to create an angle between pair of inner notches 202 and the at least one outer notch 203. At least one outer notch 203 is present around the circular hollow 201 at a pre-defined notch angle and pre-defined wall margin (D) from the pair of inner notches 202. The notch angle is the angle measured between a longitudinal axis passing through the centre of the pair of inner notches 202 and a longitudinal axis passing through the centre of the at least one outer notch 203. The wall margin (D) is the distance between the at least one outer notch 203 and the circumference of the circular hollow 201.

In an embodiment, the notch angle is maintained at 55° to have a higher mutual flux distribution between coil assembly flux and the magnet (rotor) flux. Mutual flux is defined as a combination of rotor flux produced by the magnet and the flux produced by the coil. When the notch angle is maintained at 55° the flux distribution in the stator will become even, thus resulting in better / higher mutual flux creation between coil and magnet - i.e., notch angle of 55°will result in reducing the losses of flux distribution. The pair of inner notches 202 and the at least one outer notch 203 comprises a notch depth or notch radius, as shown in Figure 3B. In an embodiment, the notch radius of the pair of inner notches is 0.133 mm, resulting in reduction of the motor starting torque, which in turn reduces the motor current and result in high battery life. When the Notch radius is set large, the energy required by the motor to make the rotor to release from the home position will be more. When the Notch radius is less the amount of energy spent to release the rotor will also be less, therefore resulting in lower current drawn by the step motor. In an embodiment, the circular hollow 201 provisions a rotor 300 (as shown in Figure 3A). Diameter of the circular hollow 201 is defined as 2.00 mm to maintain the air gap as 0.30 mm per side. Maintaining a good air gap of 0.30 mm helps to reduce the motor current. Air gap is defined as the distance between the stator circular hollow and magnet outer diameter (OD). When the air gap is more, the motor losses will also be more, resulting in higher current. Thus, the airgap is maintained close enough to have better current control.

Figure 4 shows a diagram of a stator 200 structure of the micromotor used in the watch assembly 100, for controlling the second hand of the watch assembly 100. The stator 200 comprises an outer notch 401 , a left inner notch 402 and a right inner notch 403. The left inner notch 402 and the right inner notch 403 along with the current flowing through the coil assembly are responsible for rotation for the second hand in either clockwise direction or counter-clockwise direction depending on configuration of the left inner notch 402 and the right inner notch 403. For example, when a coil (not shown) energizes stator 200 such that the outer notch 401 and the left inner notch 402 are magnetized, the second hand may rotate in clockwise direction. Likewise, when the coil (not shown) energizes stator 200 such that the outer notch 401 and the right inner notch 403 are magnetized, the second hand may rotate in counter-clockwise direction. In an exemplary embodiment, the left inner notch 402 and the right inner notch 403 are designed such that notch radius is equal to 0.176mm. In an embodiment, the notch radius may be in the range of 0.172mm to 0.180mm. The notch radius of 0.176mm may provide the detent torque of 52μΝm. The detent torque of 52μΝm may retain the second hand in a fixed position. Also, the detent torque may enable optimum power consumption by the second hand. For example, the detent torque of minute hand (MH) / hour hand (HH) is 110μΝm due to stator notch radius definition of 0.225mm. Therefore, the motor will draw current more than the second hand (SH). The step motor parameters like stator material, notch radius, notch angle, rotor magnet, coil parameters define the optimum power output of stepper motor. In an embodiment, the notch radius may be determined based on one or more features related to structure of the second hand. Based on the specifications of the hands the notch radius is determined. For example, the unbalance value of SH is 15 mg.mm for which the notch radius is 0.176mm and the unbalance value for MH is 60 mg.mm where the notch radius is 0.225mm. Further, the detent torque may withstand second hand unbalance of 15mg.mm. The second-hand unbalance of 15mg.mm may be low enough to draw a current of 0.4μΑ. Thus, battery life may be extended by drawing less current.

Figure 5 shows a diagram of a stator 200 structure of the micromotor used in the watch assembly 100, for controlling the minute hand or the hour hand of the watch assembly 100. In an embodiment, Figure 5 is applicable in instances where design and structure of the minute hand is similar to that of the hour hand. In an embodiment, the individual micromotors may be used to control the minute hand and the hour hand. However, structure of the stator 200 used in respective motors of the minute hand and the hour hand is as shown in Figure 5. The stator 200 comprises an outer notch 501, a left inner notch 502 and a right inner notch 503. The left inner notch 502 and the right inner notch 503 along with the current flowing through the coil assembly are responsible for rotation for the minute and the hour hand in either clockwise direction or counter-clockwise direction depending on configuration of the left inner notch 502 and the right inner notch 503. In an exemplary embodiment, the left inner notch 502 and the right inner notch 503 are designed such that notch radius is equal to 0.225mm. In an embodiment, the notch radius may be in the range of 0.221mm to 0.299mm. The notch radius of the stator 200 used in controlling the second hand is more than the notch radius of stator 200 used in controlling the minute hand/ hour hand. The increase in the notch radius of the stator 200 accounts to a detent torque of 110 μΝm. The detent torque of 110 μΝm may keep the minute hand and the hour hand in a fixed position. Also, the said detent torque may enable optimum power consumption by the minute hand and the hour hand. As the minute hand and the hour hand may be thicker compared to the second hand, an optimum detent torque has to be maintained such that minimum power is consumed while keeping the hands position firmly. Thus, the notch radius of 0.225mm provides an optimum detent torque of 110 μΝm. In an embodiment, the notch radius may be determined based on one or more features related to structure of the minute hand and the hour hand. Further, the detent torque may withstand minute hand and hour hand unbalance of 60 mg.mm. The minute hand and hour hand unbalance of 60 mg.mm may be low enough to draw a current of 6.1 μΑ. Thus, battery life may be extended by drawing less current.

In an embodiment, the notch radius of the stator 200 used for controlling the second hand is lesser compared notch radius of the stator used for controlling the minute hand/ hour hand. The minute / hour hand micromotor withstands larger hand unbalance since profile of the minute/hour hand is bigger compared to the second hand. Correspondingly the weight and moment of inertia of the minute hand and the hour hand is higher than the second hand. Thus, the notch radius of the pair of inner notches corresponding to the stator of minute / hour hand micromotor is designed slightly higher than the notch radius of pair of inner notches corresponding to the second hand micromotor, which gives higher power to drive the hands and also maintain a better current consumption leading to have a good battery life. In an embodiment, the stator notch may be different for the minute hand and the hour hand. In an embodiment, except with the change in the stator the other motor components like the rotor and parameters of the coil assembly may be maintained common across second, minute and hour hand micromotors.

In an embodiment, coil assembly of minute hand stator, hour hand stator and second- hand stator may be similar. For example, the coil parameters for the stator 200 may be coil resistance of 940Ω, coil resistivity of 40Ω/ηι, coil wire diameter of 22μ, number of turns of the coil may be 4400, coil length may be 4.40mm, coil height may be 2.050mm, coil width may be 2.350mm, and coil material may be copper. In an embodiment, rotor of minute hand micromotor, hour hand micromotor and second hand micromotor may be similar. For example, the rotor parameters may be rotor magnet outer diameter of 1.40mm, rotor magnet inner diameter of 0.30mm, rotor magnet thickness of 0.45mm, magnetic Gauss value of 320G. In an embodiment, the minute hand stator, hour hand stator and second hand stator may have common parameters for the at least one outer notch 203.

In an embodiment, the wall margin of the stator 200 has to be precisely maintained between 80μm - 100μm to create two poles in the stator 200. Decreasing the wall margin beyond 80μm may result in improper directional rotation of the rotor. In the present disclosure, the wall margin is maintained at 90μm which is a resultant of the diameter of the circular hollow 201. The positioning control of the rotor is taken care by the definition of notch angle and wall margin. In a embodiment, the values of the hand unbalance, and current consumed may be based on the one or more features of the second hand, minute hand and hour hand and the values may vary based on the one or more features. For example, the one or more features may be pulse width, frequency of the motor pulses, current consumption, and driving torque. In an embodiment, the hand unbalance may vary between 25mg.mm to 60mg.mm. In an embodiment, the pulse width may vary between 2.5ms to 6.0ms. In an embodiment, the frequency of motor pulses may be 64Hz. In an embodiment, the current consumption may vary between 3.50 μΑ to 7.5 μΑ. In an embodiment, the driving torque may vary between 38 μΝm to 50 μΝm.

In an embodiment, the rotor parameters and coil parameters may vary based on application of the motor and the one or more features of the second hand, minute hand and the hour hand. Figure 6 shows a diagram of a coil assembly 600 of the micro step motor, in accordance with some embodiments of the present disclosure. The coil assembly 600 is used to energize the stator 200. In a conventional stepper motor for different applications, the coil wire will be wound on the stator. But in the watch stepper motor the coil assembly 600 will be wound separately on the component called coil core and the coil assembly 600 will be mounted on to the stator. The above said construction will be exclusively used in watch time piece stepper motors due to the limitations set in the time pieces (e.g.: thickness, overall size (OD) etc.,).

In an embodiment, coil resistance plays a major role in stepper motor for defining the motor current and anti-magnetic resistance. If the coil resistance is increased, the motor current decreases and vice versa based on the equation as below: I = V/R.

I = coil current;

V= voltage induced due to current flowing in the coil;

R= coil resistance.

The key parameters for forming the resistance value are coil diameter, number of turns and coil resistivity. In the proposed disclosure, the coil resistance is increased from 1.5ΚΩ to 2.10ΚΩ. The wire diameter turns of the coil winding and coil resistivity is maintained at 18.5μ, 8100 turns and 64Ω/m respectively.

The present disclosure discloses a coil length L of 11mm, unlike conventional coils having coil length of 6mm to 8mm. The increase in L increases inductance of the coil assembly 600. The increase in inductance helps in storing more charge in the coil assembly 600. Further, the coil assembly 600 has a tolerance of 20μm. Thus, the coil assembly 600 having a L of 11mm and tolerance of 20μm draws less current from the battery, thereby increasing the battery life.

In an embodiment, variation in the notch angle varies the amount of mutual flux distribution between the coil assembly and the rotor 300. Further, the amount of mutual flux distribution also depends on structure and dimensions of the permanent magnet used as the rotor 300. Figure 7 shows a diagram of a magnet 502 for a micromotor, in accordance with some embodiments of the present disclosure . Figure 7 shows a rotor pinion 701 attached to the magnet 702. The magnet 702 may have an outer diameter of 1.40mm, a thickness of 0.45mm and an inner diameter of 0.30 mm. Further, volume of the magnet 702 is increased to 0.7 mm ³ to produce higher magnetic flux between the magnet 702 and the coil 400 and results in higher anti-magnetic resistance≤ 18.8 Oesterd (Oe).

The micromotor of the present disclosure, has been subjected to tests including high temperature test, low temperature test, thermal cycle test, humidity test, medium shock test, vibration tests, drop test, Izod impact test and anti-magnetic tests. Table 1 provides data of tests performed on the step motor.

Table 1

Detent torque of 52μΝm corresponds to second hand detent torque of micro motor. In an embodiment, the present disclosure discloses optimizing battery life of the stepper motor. The disclosed s tepper motor may perform be tter than the existing stepper mo tors of a watch in terms of battery life, running torque, and resistance to external magnetic fields.

In an embodiment, the proposed stepper motor helps extend battery life up to 30 months. Also, the proposed stepper motor provides a highest torque of <7μΝm. In an embodiment, the present disclosure discloses stator design to achieve optimum detent torque for second hand, minute hand and hour hand of the watch.

The terms "an embodiment", "embodiment", "embodiments", "the embodiment", "the embodiments", "one or more embodiments", "some embodiments", and "one embodiment" mean "one or more (but not all) embodiments of the invention(s)" unless expressly specified otherwise.

The terms "in cluding", "comprising", '¾aving" and variations thereof mean "including but not limited to", unless expressly specified otherwise. The enumerated listing of items does not imply that any or all of the items are mutually exclusive, unless expressly specified otherwise. The terms "a", "an" and "the" mean "one or more", unless expressly specified otherwise.

A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary a variety of optional components are described to illustrate the wide variety of possible embodiments of the invention. When a single device or article is described herein, it will be readily apparent that more than one device/article (whether or not they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be readily apparent that a single device/article may be used in place of the more than one device or article or a different number of devices/articles may be used instead of the shown number of devices or programs. The functionality and/or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality/features. Thus, other embodiments of the invention need not include the device itself. Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this description. REFERRAL NUMERALS: