CLOCKWORK MECHANISM WITH CAM

Description

[0001] The present invention relates to a cam-driven clock mechanism. The present invention relates in particular to a cam-driven chronograph mechanism in which the kinematic chain driving the cam comprises a pair of non-circular moving parts with conjugate profiles in direct contact with each other and configured to allow optimal reading of the information transmitted by the cam.

[0002] Cams are commonly used in watchmaking, for example, to measure and / or store time information that is read by a feeler pressed against the cam's profile. Typically, the feeler is attached to one end of a lever, the other end of which is configured to actuate, for example, a display mechanism or a striking mechanism, depending on the information read from the cam. Such cam mechanisms are used, for example, in calendars, repeaters or striking mechanisms, chronographs, etc. Document CH 90 116 A describes a particular application of a cam in a watch mechanism for a 24-hour timepiece in which the change of the hour markers from 1 to 12 or 13 to 24 is controlled by means of a cam and a pair of follower feelers in continuous contact with the cam. The cam is rotated one step every twelve hours.

[0003] In some applications, the information transmitted by the cam resides in the value of the cam's diameter, for example, the height of a step located opposite the feeler. If the cam has several steps, each step can correspond, for example, to a discrete value of time information, such as a number of fractions of a second measured by a chronograph mechanism, the number of hours, quarter-hours, and / or minutes to chime, the day of the week to display, etc. The feeler is then preferably brought into contact with the cam profile at the user's request or at times determined by the timekeeping mechanism.

[0004] In other applications, the information transmitted by the cam consists of a jump in the cam profile passing over the probe; that is, a very short segment with a significant variation in the cam's radius. The probe is then, for example, in continuous contact with the cam profile during its rotation, and each detected jump triggers, for example, an increment in the date display or the activation of an alarm.

[0005] Regardless of the application, the transition between a cam profile jump and the feeler is a critical moment because it corresponds to a phase between two states of the watch mechanism. Positioning errors of the cam, particularly a profile jump, relative to the feeler, due for example to manufacturing tolerances of the parts and varying operating clearances, can lead to errors in reading the information on the cam and / or a time lag in the displayed information.

[0006] In the case of snail cams, that is, cams comprising one or more arms, each with several steps, it is known to use an additional mechanical device called a "surprise" to prevent errors if a reading is requested while a jump between the highest and lowest steps is close to the reading point. This safety device is fixed to the snail cam and extends the highest step if a reading is requested at that moment. One drawback of this solution is its relatively large size. The surprise increases the thickness of the cam and therefore occupies vertical space, for example, in a watch case. Furthermore, operating the surprise requires additional parts. In addition, adjustments, for example by filing, are often necessary on the "beak" of the feeler to ensure accurate readings on the snail cam steps.

[0007] Furthermore, non-circular clutches exist that allow for varying the angular velocity during a revolution of a moving part driven at a constant speed. Document EP 3 070 536 A1 describes, for example, a date display whose display disc is driven by a non-circular gear that drives a pin-and-pinion gear which meshes with a toothed section of the display disc. The non-circular gear is configured for a slower angular rotation of the pin-and-pinion gear in the dead zone than in the active zone, i.e., the angular zone that causes a change in the display. The aim is to allow for a rapid change in the position of the display disc and to minimize the time interval during which the pin-and-pinion gear does not reliably lock the display disc.

[0008] One aim of the present invention is to propose a clockwork mechanism with a cam, in particular a chronograph mechanism, exhibiting high reliability in reading information on a cam while being relatively compact and simple to manufacture.

[0009] This goal is achieved using the clockwork mechanism as claimed in claim 1 and a clockwork part according to claim 10.

[0010] This purpose and other advantages are achieved in particular by a chronograph mechanism comprising a kinematic chain including a first moving part fixed in rotation about a first axis of rotation and a second moving part fixed in rotation about a second axis of rotation, the first moving part being engaged with the second moving part at a point of contact, the first moving part being configured to be driven directly or indirectly by a driving element and to directly drive the second moving part, a cam for measuring and / or storing time information corresponding to minutes, seconds or fractions of a second, the cam comprising a variable diameter profile with at least one step and at least one jump, the cam being driven directly or indirectly by the second moving part, and a probe for reading the measured and / or stored time information by pressing against the cam profile when the cam is immobilized,the first and second moving parts being non-circular moving parts with conjugate profiles, and the kinematic chain being configured such that the ratio between a first distance measured between the first axis of rotation and the point of contact and a second distance measured between the second axis of rotation and the point of contact is greater when at least one step is opposite the probe than when part of at least one step is opposite the probe. Preferably, the kinematic chain is configured such that the ratio between a first distance measured between the first axis of rotation and the point of contact and a second distance measured between the second axis of rotation and the point of contact is greater when at least one step is opposite the probe than when the midpoint of at least one step is opposite the probe.

[0011] The use of non-circular moving parts for the cam drive allows for modulation of the cam's rotational movement, ensuring that the cam's angular pitch is larger when a jump in the cam profile passes the feeler than when a step, or at least part of a step, passes the feeler. In this way, the transition between two states of the timekeeping mechanism is rapid, thus preventing errors in reading and representing the information transmitted by the cam.

[0012] The first mobile and / or the second mobile has, for example, an ellipse-shaped and / or polygasteroid-shaped profile.

[0013] The first mobile and the second mobile are configured, for example, so that the second mobile completes a full rotation around the second axis of rotation when the first mobile completes a full rotation around the first axis of rotation.

[0014] According to other forms of execution, the first mobile and the second mobile are configured such that the second mobile makes an integer number of complete revolutions around the second axis of rotation when the first mobile makes a complete revolution around the first axis of rotation, or such that the second mobile makes a complete revolution around the second axis of rotation when the first mobile makes an integer number of complete revolutions around the first axis of rotation.

[0015] Preferably, the cam comprises an integer number of steps and the same integer number of jumps, each jump being separated from the next jump along the profile by a step, the first movable and the second movable being configured so that the ratio between the first distance and the second distance is always greater when any of the jumps is opposite the feeler than when any of the steps is opposite the feeler.

[0016] The stated purpose and other advantages are also achieved by a timepiece comprising a watch movement and such a chronograph mechanism.

[0017] The present invention will be better understood upon reading the detailed description illustrated by the figures, where: There figure 1 illustrates a cam in the form of a spiral comprising a single arm with ten rungs; The figure 2 illustrates a non-circular gear according to one embodiment of the invention; The figure 3 illustrates the modulation of the angular pitch obtained using the gear of the figure 3 ; There figure 4 illustrates a clockwork mechanism according to one embodiment of the invention; The figure 5 illustrates a clockwork mechanism according to another embodiment of the invention.

[0018] There figure 1 illustrates by way of example a cam 1 in the form of a snail whose peripheral profile includes ten steps 11 and ten jumps 12, each step 11 being separated from the next step 11 by a jump 12. Such a cam in a clock mechanism allows for example to measure and / or store time information which can take ten distinct discrete values, for example a digit from zero to nine corresponding to a fraction of time: minutes, seconds, fraction of a second, or any other time information.

[0019] The reading of the information is carried out in a known manner, for example, using a probe (not shown in the figures) pressed against the profile of the snail 1. The value of the information is determined by the height of the step 11 at the reading point, i.e., at the radius of the snail 1 opposite the probe. The display of the read value is then carried out in a similarly known manner, for example, using a pointer, a disc associated with a window, or a striking mechanism. The probe is, for example, fixed to one end of a lever whose axis of rotation is fixed relative to the axis of rotation 10 of the cam 1, while the other end of the lever is linked to the information display mechanism, which is configured to display the value read on the cam by the probe.

[0020] According to the invention, the cam 1 is driven in rotation about its axis 10 by a kinematic chain comprising at least two non-circular moving parts meshed with each other. An example of non-circular moving parts according to the invention is illustrated in the figure 2 According to this embodiment, the non-circular moving parts are two elliptical gears 2, 3 whose pitch profiles are conjugate, such that they remain constantly meshed with each other as they rotate about their respective axes of rotation 20, 30. Depending on the embodiment, the teeth are either directed at the center of rotation or normal to the pitch. In the illustrated embodiment, the pitch profiles of the two elliptical gears 2, 3 are configured such that the average transmission ratio is 1, with the driven elliptical gear 3 completing exactly one full revolution when the driving elliptical gear 2 completes one full revolution.

[0021] Since the gears 2 and 3 are non-circular, their respective radii R1 and R2 at the point of contact 4—that is, the distance measured between their respective axes of rotation 20 and 30 and the point of contact 4 corresponding to the point of contact of the primitive trajectories of the gears 2 and 3—vary according to their angular position. As the ratio between the angular velocities of two interlocking moving parts is inversely proportional to the ratio between their radii at the point of contact, the ratio between the angular velocities of the elliptical gears 2 and 3 also varies according to their angular position. As schematically illustrated in the figure 3 for non-circular mobiles 2, 3 illustrated in the figure 2 , this ratio varies periodically and passes through a maximum α1 and a minimum α2 at each turn of the elliptical gears 2, 3.

[0022] Other embodiments are possible within the scope of the invention. For example, it is possible to consider a non-circular gear system with a gear ratio other than 1 and / or with gears of a more complex shape than an ellipse, for example, star-shaped, as explained later. The number of absolute or relative maxima or minima of the ratio of the angular velocities per revolution of either gear may then differ from 1.

[0023] The elliptical gears 2 and 3 are, for example, driven by a mechanical watch movement. They then rotate step by step, and the ratio between the angular pitches of the elliptical gears 2 and 3 also varies in a similar way. The driving elliptical gear 2 is, for example, driven directly or indirectly by a watch movement at a constant rotational speed, i.e., with a constant angular pitch. Consequently, the angular pitch of the driven elliptical gear 3 varies to reach a maximum angular pitch α1 and a minimum angular pitch α2 at each complete revolution.

[0024] However, it is possible to drive the non-circular gear of the invention by other means and / or at a different rate, for example by a continuous and / or non-constant movement.

[0025] According to the invention, the kinematic chain driving the cam 1 and comprising two non-circular moving parts is configured so that the angular pitch of the cam is greater when a step passes opposite the feeler than when a more central part of a step is opposite the feeler. In other words, the kinematic chain driving the cam 1 and comprising the two non-circular moving parts is configured so that the angular velocity of the cam is greater when the position of the cam corresponds to a transition phase between two states of the clockwork mechanism than when the position of the cam corresponds to another moment of such a phase.

[0026] In the case of a non-circular gear such as the one illustrated in the figure 2 driving a cam 1 such as the one illustrated in the figure 1 For example, cam 1 is driven by driven wheel 3 through a reduction gear (not shown) with a 1:10 ratio configured such that elliptical gears 2 and 3 are in an angular position corresponding to the maximum angular pitch α1 whenever a jump 12 of cam 1 is opposite or near the feeler, and elliptical gears 2 and 3 are in an angular position corresponding to the minimum angular pitch α2 whenever the center of a step 11 is opposite or near the feeler. In this way, the rotation of the snail 1 is slowed when the central parts of the steps 11 are opposite the feeler and accelerated when the jumps 12 pass opposite the feeler.

[0027] Other configurations of the non-circular gears and / or the cam are possible within the scope of the invention. For example, the profiles of the non-circular gears can be chosen so that the average transmission ratio is not 1. Furthermore, the cam can take any shape suitable for transmitting discrete time information and may, for example, consist of a single jump and a single step, or several arms each having one or more jumps and steps, etc. It is also conceivable within the scope of the invention to combine several non-circular gears in a gear train to generate output angular velocity variations adapted to snail gears with step sizes that are not constant, or to generate output rotation with a constant angular velocity while some intermediate gears rotate at variable angular velocities.

[0028] According to a first example, the clockwork mechanism of the invention is a chronograph mechanism with a digital display configured to allow the counting and display of time information to the tenth of a second, part of whose kinematic chain is schematically illustrated in the figure 4 The digital display of measured time is achieved, for example, in a known manner using a display mechanism (not shown) comprising discs bearing numerals to be displayed through apertures. The numerals include, for example, a tenth-of-a-second digit, a second digit, a ten-of-a-second digit, etc. In some embodiments, the display mechanism is, for example, a combination of both, including a numeral display for tenths of a second, seconds, and tens of a second, and a hand display, for example, retrograde, for minutes and / or hours.

[0029] The chronograph mechanism is preferably designed to be integrated into a timepiece, for example, a wristwatch, and is configured to be driven by a power source, such as the movement of the timepiece and / or a dedicated power source. For clarity, the power source is not shown in the figures. The power source is, for example, a mechanical movement with a frequency of 5 Hz, thus completing one step every tenth of a second. When the chronograph is activated, a chronograph wheel 5 of the chronograph mechanism is driven in rotation by the power source, for example, via a clutch wheel (not shown) and / or by restarting the power source.

[0030] The chronograph movement further includes a cam 1, for example for measuring and storing the units digit of seconds, and a cam 9, for example for measuring and storing tenths of a second. These cams 1 and 9 are rotated by the movement of the chronograph wheel 5 during timing via the kinematic chain 5, 6, 7, 2, 3 of the chronograph mechanism. When timing is stopped, cams 1 and 9 are immobilized, and the information concerning the measured seconds digit and the measured tenths of a second digit during timing is then read from the profile of each cam 1 and 9 by a respective feeler and displayed, for example, by a specific display mechanism on a dedicated part of the wristwatch dial. The cams 1 and 9 are, for example, snail cams like the one illustrated in the figure 1 that is to say, snails each comprising ten steps 11 separated by ten jumps 12, each step corresponding to a value from zero to nine. During timing, the seconds snail 1 rotates one turn every ten seconds, while the tenths of a second snail 9 completes one turn per second.

[0031] The kinematic chain of the chronograph mechanism includes the chronograph wheel 5, which drives a multiplying gear train comprising, for example, two moving parts 6 and 7, which in turn drive the tenth-of-a-second snail 9. During timing, the chronograph wheel 5 makes, for example, one revolution per minute. The multiplying gear train 6 and 7 is configured so that the tenth-of-a-second snail 9 makes one revolution per second. Since the watch movement's frequency is 5 Hz, the tenth-of-a-second snail 9 thus makes ten 36° steps per complete revolution. The angular position of the tenth-of-a-second snail 9 on its axis is preferably determined so that, at each step, the midpoint of a segment of the tenth-of-a-second snail 9 is positioned opposite the corresponding feeler.

[0032] According to the invention, the seconds snail 1 is driven by non-circular moving parts, for example, by two elliptical gears 2 and 3 with conjugate profiles, to complete one revolution every ten seconds during timing. The driving elliptical gear 2 is, for example, rotationally fixed to the tenth-of-a-second snail 9 and drives the driven elliptical gear 3 at the same frequency, i.e., one revolution per second. The driven elliptical gear 3 then drives the seconds snail 1 via a reduction gear having a transmission ratio of 1:10, comprising, for example, a pinion 4 coaxial with and fixed to the driven elliptical gear 3 and a wheel 13 driven by the pinion 4, coaxial with and fixed to the seconds cam 1.

[0033] Since the non-circular moving parts 2 and 3 of the chronograph mechanism are elliptical, the angular pitch of the driven elliptical gear 3 passes through a maximum and a minimum at each revolution, as illustrated in the figure 3 The seconds snail 1, driven by the elliptical wheel 3 via the reduction gear 4, 13 having a transmission ratio of 1:10, has an angular velocity, and therefore an angular pitch, that passes through ten maxima and ten minima with each revolution. According to the invention, the seconds snail 1 is oriented on its axis such that the angular pitch is at its maximum when a jump of the tenth-of-a-second snail 1 is opposite or at least in the immediate vicinity of the tenth-of-a-second feeler, and the angular pitch is at its minimum when the midpoint of a step 11 of the seconds snail 1 is opposite or at least in the immediate vicinity of the seconds feeler.

[0034] Since the seconds snail 1 is configured to complete one revolution in ten seconds, and the watch movement's frequency is 5 Hz, the seconds snail 1 takes ten steps per second, or one hundred steps per revolution. The average angular pitch is therefore theoretically 3.6°. According to the invention, it has been calculated that with elliptical wheels 2, 3 measuring, for example, 4 mm x 2.2 mm, the maximum pitch of the tenth-of-a-second snail is 21.98°. By positioning the snail so that the angular pitch is maximum when a jump 12 passes opposite or is at least in the immediate vicinity of the tenth-of-a-second feeler, it is possible to prevent a reading of the measured time from being taken on a jump 12 or on the end of a step, despite possible positioning errors due to the manufacturing precision of the moving parts of the kinematic chain, which can lead to positioning errors of a few degrees.The person skilled in the art will understand that the angular position of the cam 1 relative to the angular position of the non-elliptical gear will be determined as a function of the angular position of the probe relative to the axis 10 of the cam.

[0035] For readability, only cams 9 and 1, which measure and store the units digit of measured seconds and tenths of a second, are shown. However, chronograph movements preferably include a third cam for measuring and storing the tens digit of measured seconds. This third cam might have, for example, six increments and six jumps, and complete one revolution per minute. The tens cam is driven, for example, by a reduction gear driven by the seconds wheel 13 or by another moving part of the chronograph movement. The tens cam is also driven, for example, via a non-circular gear.

[0036] There figure 5 This illustrates another embodiment of a chronograph movement according to the invention. According to this alternative embodiment, the kinematic chain comprises a 6, 8 speed-increasing gear for driving the tenth-of-a-second snail 9, and a 6, 2', 3' speed-increasing gear for driving the seconds snail 1. In this embodiment, the 6, 2', 3' kinematic chain driving the seconds snail 1 comprises a first non-circular moving part 2' in the form of a five-armed polygasteroid moving part and a second non-circular moving part 3' with a conjugate profile in the form of a ten-armed polygasteroid moving part. The average transmission ratio between the two non-linear moving parts is therefore 1:2, with the driven polygasteroid moving part 3' completing one full rotation while the driving polygasteroid moving part 2' completes two.

[0037] The seconds snail 1 is rotationally fixed to the driven polygasteroid 3', which completes one revolution every ten seconds, with a step every tenth of a second. During timing, the angular velocity of the driving polygasteroid 2' is preferably constant, while the angular velocity of the driven polygasteroid 3' passes through ten maxima and ten minima with each complete revolution. The angular position of the seconds snail 1 relative to the angular positions of the polygasteroid 2' and 3' is then chosen so that the angular step is at its maximum when a jump of the seconds snail 1 is opposite the seconds feeler, and the angular step is at its minimum when the midpoint of a step 11 of the seconds snail 1 is opposite the seconds feeler.

[0038] According to yet another embodiment, which is not part of the invention, the clockwork mechanism is a repeater or striking mechanism. In a known manner, one or more cams with an appropriate number of steps are used to determine the hours, quarter-hours, and / or minutes to be struck on demand and / or at the passing of the specified hour.

[0039] One or more cams of the repeater or striking mechanism are driven by a kinematic chain similar to those described above, comprising at least one first non-circular moving part driven directly or indirectly by a watch movement, meshing with a second non-circular moving part whose profile is conjugate to that of the first non-circular moving part. The cam(s) driven by this kinematic chain are then arranged angularly so that the angular velocity of the cam is maximum when a step in its profile passes opposite the corresponding feeler, and the angular velocity is minimum when the midpoint of a step is opposite the feeler. Preferably, the number of maxima and minima of the angular velocity, or of the angular step per complete revolution of the cam, corresponds to the number of steps and jumps in the profile.In this way, the reading of the time for an on-demand ringing and / or the time accuracy of the ringing can be optimized without the use of a surprise mechanism.

[0040] According to another embodiment, which is not part of the invention, the clockwork mechanism is a date mechanism. In a known manner, the date mechanism includes, for example, a single-jump cam for incrementing the date display and / or a cam comprising several jumps and several increments corresponding, for example, to the months of the year and / or the days of the week.

[0041] One or more of these cams are driven by a kinematic chain comprising at least one first non-circular driving element meshing with a second non-circular driven element, which in turn drives one or more cams. The cam(s) are preferably arranged on the kinematic chain so that their angular velocity is at its maximum at the moment of the date change, that is, when a jump in their profile passes opposite the corresponding feeler, for example, a follower configured to increment a date display. The cam, for example, a single-jump, single-step cam, is driven by the watch movement via the kinematic chain of the date mechanism of the invention.The cam, for example, completes one revolution in twenty-four hours and is accelerated when the time displayed by the timepiece, for example a wristwatch, approaches midnight, so that the change in the date display occurs as quickly as possible and as close as possible to midnight.

Claims

1. Chronograph mechanism comprising: - a kinematic chain comprising a first mobile (2, 2') fixed in rotation about a first axis of rotation (20, 20') and a second mobile (3, 3') fixed in rotation about a second axis of rotation (30, 30'), the first mobile (2, 2') being in engagement with the second mobile (3, 3') at a point of contact (4), the first mobile (2, 2') being configured to be driven directly or indirectly by a drive member and to drive the second mobile (3, 3') directly, - a cam (1) for measuring and / or storing time information corresponding to minutes, seconds or fractions of a second, the cam (1) comprising a profile of variable diameter with at least one step (11) and at least one jump (12), the cam (1) being directly or indirectly driven by the second mobile (3, 3'), and - a feeler to read the measured and / or stored time information by bearing against the profile of the cam (1) when the cam (1) is immobilised, characterised in that the first mobile (2, 2') and the second mobile (3, 3') are non-circular mobiles with conjugate profiles, and in that the kinematic chain is configured so that the ratio (R1 / R2) between a first distance (R1) measured between the first axis of rotation (20, 20') and the point of contact (4) and a second distance (R2) measured between the second axis of rotation (30, 30') and the point of contact (4) is greater when the at least one jump (12) is facing the feeler than when a part of the at least one step (11) is facing the feeler.

2. Chronograph mechanism as claimed in the preceding claim, wherein the kinematic chain is configured so that the ratio (R1 / R2) between a first distance (R1) measured between the first axis of rotation (20, 20') and the point of contact (4) and a second distance (R2) measured between the second axis of rotation (30, 30') and the point of contact (4) is greater when the at least one jump (12) is facing the feeler than when the middle of the at least one step (11) is facing the feeler.

3. Chronograph mechanism as claimed in one of the preceding claims, wherein the first mobile (2, 2') and / or the second mobile (3, 3') has a profile in the form of an ellipse.

4. Chronograph mechanism as claimed in one of the preceding claims, wherein the second mobile (3, 3') and / or the first mobile (2, 2') has a profile in the shape of a polygasteroid.

5. Chronograph mechanism as claimed in one of the preceding claims, wherein the first mobile (2, 2') and the second mobile (3, 3') are configured so that the second mobile (3, 3') effects one complete turn about the second axis of rotation (30, 30') when the first mobile (2, 2') effects one complete turn about the first axis of rotation (20, 20').

6. Chronograph mechanism as claimed in one of claims 1 to 4, wherein the first mobile (2, 2') and the second mobile (3, 3') are configured so that the second mobile (3, 3') effects an integer number of complete turns about the second axis of rotation (30, 30') when the first mobile (2, 2') effects one complete turn about the first axis of rotation (20, 20').

7. Chronograph mechanism as claimed in one of claims 1 to 4, wherein the first mobile (2, 2') and the second mobile (3, 3') are configured so that the second mobile (3, 3') effects one complete turn about the second axis of rotation (30, 30') when the first mobile (2, 2') effects an integer number of complete turns about the first axis of rotation (20, 20').

8. Chronograph mechanism as claimed in one of the preceding claims, wherein the cam comprises an integer number of steps (11) and the same integer number of jumps (12), each jump (12) being separated from the next jump along the profile by a step (11), the first mobile and the second mobile being configured so that the ratio between the first distance (R1) and the second distance (R2) is always greater when any of the jumps (12) is facing the feeler than when any of the steps (11) is facing the feeler.

9. Timepiece comprising a watch movement and a chronograph mechanism as claimed in one of the preceding claims, the chronograph mechanism being configured to be driven by the watch movement.