Retrograde display mechanism

Abstract

Retrograde display mechanism (1) for a timepiece comprising a pinion (2) for driving a display unit (3) in a retrograde motion when the pinion (2) is rotated only in one direction of rotation, the pinion (2) and the display unit (3) each comprising a two-stage toothing, a first stage of the pinion (2) teeth cooperating exclusively with a first stage of the display unit (3) teeth and a second stage of the pinion (2) teeth cooperating exclusively with a second stage of the display unit (3) teeth, the first stage of the pinion (2) teeth enabling the display unit (3) to be driven in a first direction and comprising at least one truncation (21) allowing the display unit (3) to return in a second direction opposite to the first direction,The second stage of the pinion's teeth (2) comprising at least one stop tooth (20) cooperating with a first tooth (30) of the second stage of the display wheel's teeth (3) to stop the display wheel (2) during its return. A date display for a timepiece comprising such a mechanism and a method for manufacturing such a mechanism.

Description

[0001] The present invention relates to a retrograde display mechanism for a timepiece. In particular, the present invention relates to a retrograde display mechanism for displaying the days of the week in a calendar.

[0002] Retrograde display mechanisms for timepieces are generally made using a snail cam and a rake. The cam is often fixed in rotation to a star wheel, which is driven step by step and held in position between each step by a jumper. The rake is held against the cam by a return spring and meshes with a display pinion, on the axis of which the indicator is usually mounted. A disadvantage of such display mechanisms is that the larger the display angle, the more difficult it is to achieve a precise reading. To improve display accuracy, the cam must be enlarged, which increases the overall size of the mechanism.

[0003] Some retrograde display mechanisms use a truncated toothed gear train, where the star wheel is rotationally fixed to a truncated pinion that drives a display wheel on the axle of which the indicator is mounted. The truncated teeth of the pinion cause the display wheel to disengage during one of the star wheel's steps and return to its starting position under the elastic force of a balance spring or return rack. A disadvantage of such a solution is that it generally requires an external stop on the mechanism's wheels to prevent the display wheel from returning to its starting position. This can create inaccuracies when displaying the first indication and / or requires the stop to be adjustable. Such a mechanism is therefore complex and delicate to manufacture and / or adjust to ensure accurate display from the very first indication.

[0004] Patent CH 681 761 B5 describes a retrograde display mechanism with truncated teeth whose stop function is performed by the teeth of the wheels, but the shape of the truncated teeth prevents its machining by traditional cutting, which does not allow its manufacture with maximum precision.

[0005] One aim of the present invention is to provide a retrograde display mechanism of simple construction and allowing for accurate display.

[0006] Another objective of the present invention is to provide a compact retrograde display mechanism.

[0007] Another objective of the present invention is to propose a retrograde display mechanism that can be machined using known processes and that allows for high precision.

[0008] These goals and other advantages are achieved by a retrograde display mechanism for a timepiece comprising a pinion for driving a display wheel in a retrograde motion when the pinion is turned only in one direction of rotation, the pinion and the display wheel each comprising a two-stage toothing, a first stage of the pinion teeth cooperating exclusively with a first stage of the display wheel teeth and a second stage of the pinion teeth cooperating exclusively with a second stage of the display wheel teeth, the first stage of the pinion teeth enabling the display wheel to be driven in a first direction and comprising at least one truncation allowing the display wheel to return in a second direction opposite to the first direction,the second stage of the pinion's teeth comprising at least one stop tooth cooperating with a first tooth of the second stage of the display mechanism's teeth to stop the display mechanism during its return.

[0009] The use of two-stage gears, the first stage of which is essentially dedicated to driving the display unit forward and the second stage is essentially dedicated to stopping the return movement of the display unit, allows for the realization of a simple retrograde display mechanism, easily made by partially machining the teeth of the display unit and the pinion driving it, and allowing for precise display.

[0010] At least one truncation of the first stage of the pinion teeth corresponds, for example, to a truncation of two teeth.

[0011] Preferably, the second stage of the display mobile's toothing includes only the first tooth, so that it certainly cannot block the return movement of the display mobile before the first tooth comes into contact with at least one stop tooth.

[0012] Preferably, the thrust tooth extends along a radial plane of the pinion passing through the truncation.

[0013] Preferably, the pinion includes a truncation of the second stage of its teeth, close to at least one stop tooth to allow direct contact of at least one stop tooth and the first tooth when returning the display element.

[0014] The display unit is, for example, a toothed sector.

[0015] The retrograde display mechanism is, for example, a display of the day of the week.

[0016] The goals mentioned above and other advantages are also achieved by a date display for a timepiece comprising such a retrograde display mechanism.

[0017] The goals mentioned above and other advantages are also achieved by a method of manufacturing such a retrograde display mechanism, comprising supplying a single-toothed pinion, partially milling the teeth of the pinion over a first height to create at least one truncation and at least one stop tooth, the first height corresponding to the height of the first stage of the pinion teeth, supplying a single-toothed display mobile; and milling over a second height of the teeth of the display mobile except for one tooth to create the first tooth, the second height corresponding to the second stage of the teeth of the display mobile.

[0018] Preferably, the partial milling of the pinion teeth includes milling on the first height of a tooth of the pinion teeth and the complete milling of a tooth adjacent to the previous one to create at least one truncation of the first stage of the pinion teeth and to create at least one stop tooth and a corresponding truncation of the second stage of the pinion teeth.

[0019] The invention will be better understood upon reading the description below, illustrated by the figures where: there figure 1 illustrates a retrograde display mechanism according to one embodiment of the invention; the figure 2 is a detail of the mechanism of the figure 1 .

[0020] With reference to the figures, the retrograde display mechanism 1 comprises a pinion 2 meshing with a display wheel 3 for driving an indicator (not shown) to display information, for example, the day of the week, on a watch dial. The indicator is, for example, a hand moving along a scale on the dial, or a disc on which information is inscribed to be displayed successively through an aperture in the dial. In the embodiment illustrated by way of example, the display wheel 3 is a toothed sector mounted for rotation on an axis. The indicator is preferably fixed in rotation to the display wheel 3, for example, attached to the rotation axis of the display wheel 3. Other arrangements of the indicator and methods of direct or indirect drive of the indicator by the display wheel are, however, possible within the scope of the invention.

[0021] The pinion 2 and the display arm 3 are configured so that the rotation of the pinion 2 in only one direction, corresponding to the forward direction of the retrograde display mechanism 1, causes the display arm 3 to move in a retrograde motion. In forward motion, the display arm 3 thus meshes with the pinion 2, which drives it in a first direction until the indicator reaches its last position on the scale or until the indicator displays the last piece of information in the series to be displayed. The display arm 3 then disengages from the pinion 2 and quickly, almost instantaneously, returns in the opposite direction to its initial position under the effect of an elastic restoring force, without the pinion 2 rotating in the opposite direction.According to the illustrated embodiment, the elastic return force is developed by a return spring 50, via a return rack 5 which meshes with a return pinion 6 that is rotationally fixed to the display unit 3. The return rack 5 and the return spring 50 also serve to tension the retrograde display mechanism 1 in order to counteract the effects of possible gear backlash. Other types of return devices are, however, conceivable within the scope of the invention, for example, a spiral or any other device adapted to the nature of the display unit.

[0022] According to the illustrated embodiment, the pinion 2 is rotationally fixed to a star 4, for example, a seven-pointed star. The position of the star 4 is indexed and maintained between each step in a known manner by a jumper 40 comprising a spring 41. The star 4 is, for example, driven step by step by a drive mechanism (not shown) and thus causes the display wheel 3 and the indicator to advance step by step. The retrograde display mechanism 1 is, for example, a day-of-the-week display mechanism for the date, and the drive mechanism includes a 24-hour wheel actuating a rocker at each revolution to advance the star one step per day. However, any other suitable mechanism for advancing the star one step at predetermined times and / or on demand is conceivable within the scope of the invention.

[0023] With reference to the figure 2 The star 4 and pinion 2 are intended to be driven in normal operation in the direction of rotation indicated by the arc-shaped arrow, i.e., counterclockwise as shown in the figure. Pinion 2 and display unit 3 each have two-stage teeth: a first stage of pinion 2's teeth, corresponding to a lower stage in the figures, cooperating exclusively with a first stage of the display unit 3's teeth, and a second stage of pinion 2's teeth, corresponding to an upper stage in the figures, cooperating exclusively with a second stage of the display unit 3's teeth.The first stage of the teeth of the display unit 3 and the first stage of the teeth of the pinion 2 preferably extend over the same first height of their respective teeth, and the second stage of the teeth of the display unit 3 and the second stage of the teeth of the moving pinion 2 preferably extend over the same second height of their respective teeth. Preferably, the first and second heights each correspond essentially to half the height of the teeth of the display unit 3 and the pinion 2, but other proportions between the first and second stages are possible within the scope of the invention.

[0024] The first stage of the gear teeth of pinion 2 is configured to allow the display unit 3 to be driven in a first direction by pinion 2, the first direction corresponding to the forward movement of the indicator. According to the invention, the first stage of the gear teeth of pinion 2 includes a truncation 21 allowing the first stage of the gear teeth of the display unit 3 to disengage and return the latter to its initial position in the opposite direction. According to the embodiment illustrated by way of example, the gear formed by the first stage of the gear teeth of pinion 2 and the first stage of the gear teeth of the display unit 3 advances two teeth with each step of the star 4, and the truncation 21 of the first stage of the gear teeth of pinion 2 is a truncation of two teeth allowing the free passage of the teeth of the first stage of the gear teeth of the display unit.Other truncation lengths of the first stage of the pinion teeth are however possible within the framework of the invention depending on the rate of movement of the retrograde display mechanism and / or the configuration of the display unit.

[0025] The second stage of the gear teeth of pinion 2 includes a stop tooth 20 configured to cooperate with a first tooth 30 of the second stage of the gear teeth of the display unit 30 to limit the return movement of the display unit 3. The stop tooth 20 preferably extends along a virtual radial plane (not shown) of the pinion 2 passing through the truncation 21 of the first stage of the gear teeth of pinion 2, such that when the stop tooth 20 is aligned with the display unit 3, at least a portion of the truncation 21 is also aligned with it. The stop tooth 20 and the first tooth 30 are configured so that, during its return movement, the display unit 3 is stopped in its initial position.The initial position of the display arm 3 typically corresponds to the position of the retrograde display mechanism 1 in which the indicator displays the first piece of information in the series to be displayed, for example, the position in which the indicator displays the first day of the week or month, or the first month of the year. The second stage of the pinion 2's teeth preferably includes a truncation 22 adjacent to the stop tooth 20 to allow the first tooth 30 of the second stage of the display arm 3's teeth to cooperate firmly with the stop tooth 20 without being hindered or stopped by a tooth adjacent to the stop tooth 20.The stop tooth 20 and the truncation 22 of the second stage of the teeth of the pinion 2 are together arranged on the same sector of the pinion 2 as the truncation 21 of the first stage, so that the stop tooth 20 and the two truncations 21, 22 are simultaneously opposite the display moving part 3 following the last step of a retrograde display cycle.

[0026] The second stage of the display mobile 3's teeth is configured to allow the return movement of the display mobile 3 until the first tooth 30 butts against the stop tooth 20 of the pinion 2. Preferably, the second stage of the display mobile 3's teeth does not include any teeth except for the first tooth 30, thus allowing free passage of the display mobile's teeth in the truncation 21 of the first stage of the pinion 2's teeth and under the stop tooth 20, until the first tooth 30 stops against the stop tooth 20.

[0027] THE figures 1 et 2 The diagram illustrates the retrograde display unit 1 in the initial position of a retrograde display cycle, when the indicator displays the first piece of information in the series to be displayed, for example, the first day of the week. The pinion 2 is held in position by the jumper 40 acting on the star wheel 4 after the last step of the previous retrograde display cycle and the return of the display unit 3. The first tooth 30 is then bearing against the stop tooth 20. In this initial position, the first stage of the teeth of the display unit 3 and the first stage of the teeth of the pinion 2 do not mesh due to the truncation 21 of the first stage of the teeth of the pinion 2, which is located opposite the display unit 3 and extends to below the stop tooth 20.

[0028] At the next step of the star 4 in the direction of the arc-shaped arrow, pinion 2 advances two teeth. During its movement, the stop tooth 20 of pinion 2 cooperates with the first tooth 30 of the display unit 3 to push the display unit 3 forward, so that the teeth of the first stage of the display unit 3 mesh with the teeth of the first stage of the gear teeth of pinion 2 following the truncation 21. The step-by-step advance of the retrograde display mechanism 1 thus continues in the same direction, advancing two teeth at each step, causing the successive display and skipping of information to be displayed. During the last step of the retrograde display cycle, the truncation 21 of pinion 2 is aligned with the display unit 3, which then disengages from pinion 2.Under the effect of the elastic restoring force, exerted for example by the return spring 50 via the return rake 5, the display unit 3 returns in the opposite direction to its initial position, the teeth of the first stage of the teeth of the display unit 3 passing freely in the truncation 21 of the first stage of the teeth of the pinion 2 and under the stop tooth 20. The return movement is stopped when the first tooth 30 of the display unit 3, after passing freely in the truncation 22 of the second stage of the teeth of the pinion 2, abuts against the stop tooth 20. The retrograde display cycle then resumes at the next step of the star 4, as explained above.

[0029] According to the illustrated embodiment, the retrograde display mechanism 1 is configured such that the display arm 3 completes one retrograde display cycle per full revolution of the pinion 2. However, within the scope of the invention, it is conceivable that the display arm 3 completes more than one retrograde display cycle per revolution, the number of steps per cycle being variable, for example, for the retrograde display of the date over a full year. The pinion teeth then comprise as many truncations and corresponding stop teeth as there are retrograde display cycles to be completed during one full revolution of the pinion.

[0030] It is also conceivable within the framework of the invention that the pinion, and consequently the display unit and the display itself, are driven continuously rather than step-by-step. The truncation(s) are then dimensioned according to the rotational speed of the pinion to allow the first tooth to engage unimpeded against the stop tooth during the return of the display unit, despite the advance of the pinion.

[0031] The two-stage teeth of the pinion 2 and the display mobile 3 according to the invention can be manufactured using traditional cutting processes allowing very high machining accuracy to be achieved.

[0032] Pinion 2, for example, is preferably made from a single-toothed pinion in which one tooth is truncated over its entire height and a tooth adjacent to the previous one is truncated, for example by milling, only on the first height corresponding to the first stage of the teeth, thus creating the truncation 21 of two teeth in the first stage of the teeth as well as the stop tooth 20 and the truncation 22 of a single tooth in the second stage of the teeth of pinion 2.

[0033] The display mobile 3 can be made from a single-toothed mobile whose teeth are milled on the second height corresponding to the second stage of the teeth, with the exception of the first tooth 30.

[0034] According to the illustrated embodiment, the display mobile 3 is a toothed sector for driving an indicator in the form, for example, of a needle or a sector of a disk, fixed in rotation to the display mobile 3. Other display mobiles are however conceivable within the framework of the invention, for example a toothed wheel mounted in rotation or a display mobile mounted in translation, for example a rack, driven by the pinion in a linear retrograde movement.

Claims

1. Retrograde display mechanism (1) for a timepiece comprising a pinion (2) for driving a display unit (3) in a retrograde motion when the pinion (2) is rotated only in one direction of rotation, the pinion (2) and the display unit (3) each comprising a two-stage toothing, a first stage of the pinion (2) teeth cooperating exclusively with a first stage of the display unit (3) teeth and a second stage of the pinion (2) teeth cooperating exclusively with a second stage of the display unit (3) teeth, the first stage of the pinion (2) teeth enabling the display unit (3) to be driven in a first direction and comprising at least one truncation (21) enabling the display unit (3) to return in a second direction opposite to the first direction,the second stage of the pinion teeth (2) comprising at least one stop tooth (20) cooperating with a first tooth (30) of the second stage of the display moving part's teeth (3) to stop the display moving part (2) during its return.

2. Mechanism (1) according to the preceding claim, the truncation (21) of the first stage of the teeth of the pinion (2) corresponding to a truncation of two teeth.

3. Mechanism (1) according to any one of the preceding claims, the second stage of the toothing of the display mobile (3) comprising only the first tooth (30).

4. Mechanism (1) according to any one of the preceding claims, the thrust tooth (20) extending along a radial plane of the pinion (2) passing through the truncation (21).

5. Mechanism (1) according to any one of the preceding claims, the pinion comprising a truncation (22) of the second stage of its teeth, close to at least one stop tooth (20) to allow direct contact of at least one stop tooth (20) and the first tooth (30) during the return of the display member (3).

6. Mechanism (1) according to any one of the preceding claims, the display moving part being a toothed sector.

7. Mechanism (1) according to one of the preceding claims, for displaying the day of the week.

8. Date display for a timepiece comprising a mechanism according to one of the preceding claims.

9. Method of manufacturing a mechanism (1) according to any one of claims 1 to 5, comprising: - supplying a single-toothed pinion (2); - partially milling the teeth of the pinion (2) over a first height to create at least one truncation (21) and at least one stop tooth (20), the first height corresponding to the height of the first stage of the teeth of the pinion (2); - supplying a single-toothed display unit (3); and - milling over a second height of the teeth of the display unit (3) except for one tooth of the teeth to create the first tooth (30), the second height corresponding to the second stage of the teeth of the display unit (3).

10. Method according to the preceding claim, the partial milling of the teeth of the pinion (2) comprising milling on the first height of a tooth of the teeth of the pinion (2) and the complete milling of a tooth adjacent to the previous one to create at least one truncation (21) of the first stage of the teeth of the pinion (2) and to create at least one stop tooth (20) and a corresponding truncation (22) of the second stage of the teeth of the pinion (2).

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