CH712433A2 - Electromechanical watch movement comprising a device for detecting the angular position of a wheel. - Google Patents

Abstract

The electromechanical watch movement comprises a stepper motor, a wheel (22) driven in rotation by this motor, a pinion (24) meshing with this wheel and a device for detecting the angular position of the wheel, this device for detection for determining the passage of a reference half-axis (42) of this wheel by a reference angle (α REF) defined by this wheel and the pinion and comprising for this purpose an electronic circuit capable of detecting a resistive torque additional localization when driving the wheel step by step. The localized resistive torque is formed by an elastic element (28) integral with the wheel and a part of which is superimposed at least on a given hollow of the toothing (23) of this wheel. The moving component has a toothing (25) which is located at least partially at the level of the elastic element so that this toothing comes to press against this elastic element when it enters said given hollow.

Description

Description

Field of the Invention [0001] The present invention relates to a watch movement of the electromechanical type comprising a stepper motor arranged to be able to drive a gear train, formed at least of a first wheel and a pinion or a second wheel meshing with the first wheel, this clock movement further comprising a device for determining the angular position of the first wheel.

BACKGROUND OF THE INVENTION Several devices for detecting the angular position of a wheel driven by a clockwork motor have been proposed. Several documents relate to the arrangement of optical devices comprising a light source and a light sensor, the watch movement being arranged to vary in a controlled manner the reception of light by the sensor according to the angular position of the wheel considered. Other documents propose the arrangement of capacitive sensors or inductive sensors. Some documents propose to arrange magnetic elements and at least one Hall sensor. All of these devices are relatively expensive and complex. In addition, they often generate a relatively large footprint and / or require particular machining parts of the watch movement, including the wheel tray considered.

In order to reduce the cost, the complexity and the size of the device for detecting the angular position of a wheel, it has been proposed to introduce a 'hard point' in a gear of the gear train comprising the wheel considered, such a 'hard point' of adding a load, respectively an additional resistive torque for the motor driving the gear train in a localized way to a restricted angular range of the wheel. The detection of this additional resistive torque by appropriate detection means, in particular by a determination of the torque necessary to perform a motor pitch, makes it possible to detect the passage of a reference axis of the wheel considered by a certain reference angle relative to the axis of rotation of this wheel.

A first device without additional external sensor is disclosed in the document CH 640 098, which provides for arranging a ferromagnetic element on the wheel plate close to the toothing and a fixed magnet at the periphery of this wheel. During the rotation of the wheel, when the ferromagnetic element approaches the magnet, the latter attracts it in the direction of rotation and thus the energy required to effect a motor pitch decreases. By cons, once the angular position of the magnet exceeded, the magnet exerts a force in the opposite direction to the rotation, which causes an increase in the energy required to perform a step. A circuit for detecting the energy of the electrical pulse supplied by the motor at each step makes it possible to determine for which step the ferromagnetic element was substantially facing the magnet. This system has various disadvantages. First, it uses a magnet, which can impact other elements of the watch movement. In addition, the magnetic force on the wheel may have an axial component that generates a torque on the wheel shaft and increases the friction in the bearings. Then, the arrangement of the magnet at the periphery of the wheel requires a certain space to clear in the movement, which is not always easy. Finally, the magnet acts on the ferromagnetic element over a relatively large angular distance corresponding to several motor steps. The detection of the position of the reference axis of the wheel, defined by the ferromagnetic element, therefore requires analyzing the behavior of the motor on several steps. It is proposed here for this purpose to analyze the current curve for each pulse and to determine the evolution of certain specific parameters of this curve which are dependent on the torque supplied to perform the corresponding step.

A second device without additional external sensor is disclosed in US 6,414,908. This document teaches to arrange a 'hard point' generating in a localized way a high load for the stepper motor on one or more not when driving the wheel. The detection of this charge is carried out in a given example by measuring the duration of the pulses of the motor. Specifically, it is intended here to provide normal pulses with a first energy to perform step-by-step advance of the gear train. A sensing device is used to determine whether the rotor has made a step after a normal pulse has been supplied. If this is not the case, it is intended in this embodiment to provide a first catch-up pulse with a second energy higher than the first energy. In usual operation, without the arrangement of a hard point, the drive of the gear train is provided by the normal pulses and the first catching pulses. On the other hand, the resistive torque generated by the arrangement of the hard point requires a second catch-up pulse with a third energy higher than the second energy. Thus, a non-rotation detection after having provided a first catch-up pulse is caused by the hard point, which thus makes it possible to determine the position of a reference axis of a wheel by the sole determination of the steps having necessitated a second catch-up pulse. By way of example, for a substantially constant electric power supplied to the motor, the various pulses are distinguished by their respective respective durations.

Document US Pat. No. 6,414,908 describes in detail the detection of the passage of a needle by the "12 o'clock" position on the basis of the recording of the steps which necessitated the application of a second catch-up pulse, but it gives almost no teaching as to the practical realization of a hard point. To generate an additional resistive torque, only two examples are briefly indicated. The first variant proposes to modify the profile of the toothing locally. For the second variant, it is only indicated that the additional resistive torque is generated by a cam. This second variant is vague and the person skilled in the art here receives almost no practical teaching. Regarding the first variant, it is not devoid of interest, but no concrete example is given. It should be noted, however, that the implementation of this first variant poses certain technical problems. First, making a wheel with non-uniform toothing complicates its manufacture. Then, given the manufacturing tolerances, it is not easy to guarantee a hard point with a resistive torque whose value is within a certain given range. Finally, some gearing is usually necessary to ensure proper meshing. Creating a hard point by locally varying the profile of the toothing can easily have the consequence of blocking the rotation of the motor and thus the drive of the gear train associated with this engine. SUMMARY OF THE INVENTION [0007] An object of the present invention is to provide an electromechanical watch movement with a device for detecting the angular position of a wheel which is relatively simple to produce and which makes it possible to accurately detect the passage of a reference half-axis of this wheel by a given reference angle.

Another object is to provide such a detection device that works without requiring complex processing of an electrical signal in connection with the power supply of the stepper motor designed to drive the wheel.

Another object is to provide a detection device of the aforementioned type which is relatively compact.

For this purpose, the electromechanical watch movement according to the invention comprises a wheel driven in rotation by a stepper motor and a device for detecting the angular position of this wheel which is capable of detecting an additional resistive torque. intervening momentarily during the step-by-step training of the wheel. It is characterized in that said additional resistive torque is generated by an elastic element integral with the wheel and arranged so as to extend, in projection in a general plane of the wheel in which is located its toothing, in a given hollow between two adjacent teeth of this toothing. Then, the watch movement is arranged so that the wheel meshes with a movable component having a toothing which is situated at least partially at the level of the elastic element, so that this toothing comes to press against the elastic element when one of its teeth penetrate into said given hollow.

In an advantageous embodiment, the elastic element is configured so that it penetrates, in projection in the general plane of the wheel, to a lesser extent in one and / or the other of the two troughs. adjacent to the aforementioned hollow or, preferably, not to enter these two adjacent depressions.

Thanks to the characteristics of the detection device of the invention, the additional resistive torque can be limited to the passage of a tooth of the movable component in a single given cavity of the toothing of the wheel. It is thus very localized and can be detected in some cases on a single step of the engine. This simplifies the processing of the torque-dependent electrical signal provided by the stepper motor associated with the wheel and makes it possible to accurately determine a reference angular position of a reference half-axis of the wheel which passes through the center. of the given hollow of the teeth of the wheel and corresponds to a reference pitch of the motor.

According to an advantageous variant, the elastic element is a wire spring of small dimensions and fixed on the wheel plate. Such a wire spring is very compact and its attachment can be easily achieved by various fastening means, in particular by welding, taking care to precisely arrange a portion of its free end in superposition of the aforementioned hollow.

BRIEF DESCRIPTION OF THE DRAWINGS [0014] The invention will be described below with the aid of the accompanying drawings, given by way of non-limiting examples, in which: FIG. 1 is a block diagram of the electromechanical movement according to the invention; fig. 2A is a top view of a wheel and pinion of a gear train of the movement of FIG. 1, the wheel being provided with a spring which belongs to the device for detecting the angular position of this wheel, FIG. 2B is a view similar to that of FIG. 2A but with a particular angular position of the wheel for which an additional resistive torque is generated by the spring; fig. 3 is a partial enlargement of FIG. 2A; fig. 4 is a partial cross section along the line IV-IV of FIG. 2B; figs. 5A to 5C schematically show torque curves provided by the stepper motor for three different variants.

DETAILED DESCRIPTION OF THE INVENTION [0015] Referring to the figures, an embodiment of an electromechanical watch movement 2 comprising a stepping motor 4, a gear train 6 coupled to the motor will be described below. and driving an analog display 8. Typically, the movement further comprises a power supply circuit 10 of the motor, a canceled logic circuit 12 which supplies in particular to the power supply circuit the signals for the formation of the pulses applied to the motor, a circuit clock 14 defining a time base in particular for the logic circuit 12 and a central processing unit 18 which manages the various functions of the watch movement. Finally, the watch movement also comprises a load detection circuit 16 defined by the gear train and the analog display, respectively of the engine torque supplied at each step to drive this load. This detection circuit is part of a device for detecting the angular position of a wheel according to the invention. It is connected to the supply circuit (link A) and / or directly to the stepper motor (link B) and / or to the control logic circuit (in particular via the central processing unit).

The detection circuit 16 may be arranged in various ways known to those skilled in the art, particularly as in the prior art mentioned above. In a case where it is planned to be able to provide three different pulses with three different energies respectively, the detection of the load then consists in determining which of these three different pulses is necessary to perform a certain step. In another case where real-time charge-based pulse management is provided, charge detection can be done in a variety of ways by analyzing one or more of the three physical parameters involved in the energy of a electrical pulse, namely the time, the applied voltage and the current supplied. The detection of the load can be related to a value of these parameters, for example the duration of the pulse, the peak current, the selected voltage if necessary. In more sophisticated detection modes, more than one of these values or information derived from these parameters can be used. Finally, a person skilled in the art also knows detection means that analyze an induced voltage / induced current in a motor coil after providing an electrical pulse (using a switch between the power supply circuit and the power supply circuit). detection). Such an induced signal makes it possible in particular to determine whether the step has been carried out, but an analysis of this signal can also give information on the resistive torque applied to the motor.

The gear train 6 comprises a wheel 22, having a toothing 23 and rotated by the motor, and a pinion 24 having a toothing 25 and meshing with this wheel. This pinion forms a non-limiting manner a movable component meshing with the toothing 23 of the wheel 22. An additional localized resistive torque is produced by an elastic element 26 integral with the wheel 22. This elastic element is formed by a wire spring which is arranged on the wheel plate and one end 29 of which is fixed to this plate. The wire spring has at a free end a bent portion 30 which is superimposed on a given recess 32 of the toothing 23 between two adjacent teeth 34 and 35 of this toothing. Note that in the advantageous embodiment shown in the figures, the bent portion 30 is folded so as not to be superimposed on the two recesses 36 and 37 which are adjacent to the recess 32. In another variant, the wire spring is fixed to its two ends, the bent portion being located approximately in the middle of the length of this spring wire. The bent portion advantageously protrudes from the main curvature of the wire spring, so as to be superimposed on the toothing 23 in a very localized manner. However, this advantageous variant is not limiting, the elastic element does not necessarily have such a bent part. Thus, for example, in a variant, only the end of the free end of the spring is superimposed on the toothing of the wheel. Finally, the toothing 25 of the pinion 24 is located at least partially at the wire spring, as shown in the section of FIG. 3, so that this toothing is pressed against the elastic element, namely here against the bent portion of the wire spring, when it enters the given recess 32.

More generally, it is provided that the elastic element is arranged to extend, in projection in a general plane 40 of the wheel 22 in which is located its toothing 23, in a given recess, this elastic element being elastically deformable in a radial direction of the wheel substantially to the bottom of the given hollow (that is to say at least sufficiently to allow penetration of the hollow by the toothing of the pinion, without risk of blocking the meshing of this pinion with the wheel). Advantageously, the elastic element is configured to penetrate, in projection in said general plane, in one and / or the other of the two hollows adjacent to the hollow given to a lesser extent than in this given hollow. Preferably, as in the variant described above, it is provided that the elastic element is made and fixed to the wheel so as not to penetrate, in projection in said general plane, in the two adjacent hollows.

The device for detecting the angular position of the wheel 22 thus makes it possible to determine the passage of a reference half-axis 42 of this wheel by a reference direction 44, corresponding to a reference angle REREF, defined by this wheel and the moving component. The half-axis 42 is defined by the middle of the hollow 32, respectively by the portion of the curved portion 30 of the wire spring which is superimposed on this selected hollow. The reference angle aREF corresponds, in the case of a mobile component forming a wheel or a pinion, to the angular position of a straight line 44 passing through the center of the wheel 22 and the center of this mobile component. The detection device according to the invention thus comprises a 'hard point' located at a single hollow of the toothing of a wheel and comprises for its detection an electronic circuit capable of detecting an additional resistive torque occurring momentarily. during stepwise driving of the wheel 22 and the pinion 24 by the motor 4.

In figs. 5A, 5B and 5C are shown respectively three curves 48A, 48B and 48C indicating the torque provided by the motor during a step-by-step drive of the gear train 6 with the passage of a tooth of the pinion 24 in the 32 of the teeth of the wheel 22 and therefore by the hard point generated by the wire spring 28 which is superimposed only on

Claims (6)

this given hollow. These three curves are a schematic representation of the resistive torque to be overcome by the motor during a succession of pulses shown bumped, while in normal operation the pulses are separated by periods of rest of the stepper motor. FIG. 5A corresponds to a particular situation for a toothing 23 with sixty teeth and a wheel performing sixty steps per revolution. In this case, the additional resistive torque due to the wire spring intervenes for a single pitch of the motor, so that the angular position of the wheel is determined upon detection, for a pitch N, of a peak 50A in the torque supplied by the engine. It will be noted, however, that it is also possible, depending on the relative position of the teeth that mesh during periods of rest of the engine, that the additional resistive torque is felt on two consecutive steps. This is particularly the case if a rest position of the engine corresponds to a situation where the curved portion 30 is pressed by a tooth of the toothing 25. In this case, it is therefore necessary to define which of the two consecutive steps is the one which defines the angular position of reference. FIG. 5B corresponds to a variant where the toothing 23 also has sixty teeth but the wheel makes a turn every thirty paces. The peak 50B of increase of the resistive torque occurs for a shorter duration than the duration of a standard pulse. Since it is generally not practical to know a reference position with a precision greater than that defined by a motor pitch, it will be noted that the curved portion 30 of the wire spring could, in another variant, extend over two recesses. consecutive, particularly if advantageously the meshing relationship of the two teeth is precisely controlled so that the two consecutive recesses are penetrated during the same step. However, preferably, it will retain an alternative embodiment with the wire spring superimposed on a single recess. Thus, the relative position of the teeth during periods of rest of the engine is less critical. The motor and the gear train will preferably be mounted so that the passage of the given recess 32 occurs during a single step performed by the motor. FIG. 5C corresponds to a variant where the toothing 23 has thirty teeth and the wheel performs sixty paces per revolution. In this case, the additional resistive torque is felt on several consecutive steps, the torque peak 50C extending at least two steps and generally three steps. An analysis of the supply signal generating the electrical pulses concerned by the several consecutive steps may generally make it possible to define a step for which the resistive torque passes through a maximum and thus to determine a pitch corresponding to the reference position of the wheel 22. However, in the case where the additional resistive torque acts on several consecutive steps of the motor, it is possible to define in several ways what is the reference pitch. It can for example be provided that this is the first step having a resistive torque above a predetermined threshold or the last step of a series of steps all having a resistive torque above this threshold. It will be understood that it is still possible to choose a step situated in the middle of such a series of steps or the step that follows such a series, that is to say the first step corresponding to a torque lower than a given threshold after a series of steps for which the resistive torque was above this threshold. The detection device according to the invention is compact. It has the advantage, at the constructive level, of embedding the entire detection device (with the exception of the electronic part which is incorporated in the electronic circuit of the watch movement) on the wheel concerned. Indeed, only an elastic element integral with the wheel in question is required. It can easily be fixed on this wheel so as to cover only one hollow. claims 1. An electromechanical clock movement comprising a stepper motor (4), a wheel (22) rotated by this motor, a movable component (24) meshing with this wheel and a device for detecting the angular position of the wheel, this detection device for determining the passage of a reference half-axis (42) of this wheel by a reference angle (cxref) defined by this wheel and the mobile component and comprising for this purpose an electronic circuit ( 16) capable of detecting an additional resistive torque occurring momentarily during stepwise driving of the wheel and moving component by the motor; characterized in that said additional resistive torque is generated by an elastic element (28) integral with the wheel and arranged to extend, in projection in a general plane (40) of this wheel in which is located its toothing (23). ), at least in a given recess (32) between two adjacent teeth (34, 35) of this toothing, this elastic element being elastically deformable in a radial direction of the wheel substantially to the bottom of said given hollow; and in that said movable component has a toothing (25) which is located at least partially at said elastic member so that this toothing comes to press against the elastic member when it enters said given hollow. 2. Electromechanical watch movement according to claim 1, characterized in that said elastic element is configured so as to penetrate, in projection in said general plane, in one and / or the other of the two adjacent hollows (35, 37). hollow audit given to a lesser extent than in this given hollow or preferably not to enter these two adjacent hollows. 3. Electromechanical watch movement according to claim 1 or 2, characterized in that the elastic element is arranged on a plate of said wheel which has at its periphery said toothing of the wheel, this elastic element having a portion superimposed on said given hollow of this toothing. 4. electromechanical watch movement according to claim 3, characterized in that the elastic element is formed by a wire spring (28) fixed to the wheel at least one (29) of its two ends. 5. electromechanical watch movement according to claim 4, characterized in that the wire spring has a bent portion (30) projecting from its main curvature, this bent portion being superimposed on said given recess of said toothing of said wheel. 6. Electromechanical watch movement according to any one of the preceding claims, characterized in that said movable component is a pinion or other wheel forming with said wheel a gear train of the watch movement.