ELECTROMECHANICAL TIMEPIECE MOVEMENT COMPRISING A DEVICE FOR DETECTION OF THE ANGULAR POSITION OF A WHEEL

Abstract

The electromechanical timepiece movement comprises a stepping motor, a wheel driven in rotation by the motor, a pinion meshing with the wheel and a device for detecting the angular position of the wheel, the detection device making it possible to determine the passage of a reference half-axis of the wheel through a reference angle defined by the wheel and the pinion and comprising for such purpose an electronic circuit capable of detecting an additional localised resistive torque when the wheel is driven in a stepping motion. The localised resistive torque is achieved by a resilient element integral with the wheel and one portion of which is at least partially superposed on a given hollow of the toothing of said wheel. The movable component has a toothing which is at least partially situated at the level of the resilient element, such that the toothing moves and presses against the resilient element when it penetrates inside said given hollow.

Claims

1. An electromechanical timepiece movement comprising a stepping motor, a wheel driven in rotation by said motor, a movable component meshing with said wheel and a device for detecting the angular position of the wheel, said detection device making it possible to determine the passage of a reference half-axis of said wheel through a reference angle defined by said wheel and the movable component and comprising for such purpose an electronic circuit capable of detecting an additional resistive torque that occurs momentarily when the wheel and movable component are driven in a stepping motion by the motor; wherein said additional resistive torque is generated by a resilient element integral with the wheel and arranged to extend, in projection into a general plane of said wheel in which said toothing thereof is located, at least inside one given hollow between two adjacent teeth of said toothing, said resilient element being elastically deformable in a radial direction of the wheel substantially as far as the bottom of said given hollow; and wherein said movable component has a toothing which is at least partially situated at the level of said resilient element, such that said toothing moves and presses against the resilient element when said toothing penetrates said given hollow.

2. The electromechanical timepiece movement according to claim 1, wherein said resilient element is configured to penetrate, in projection in said general plane, inside one and/or the other of the two hollows adjacent to said given hollow to a lesser extent than inside said given hollow, or preferably, not to penetrate inside said two adjacent hollows.

3. The electromechanical timepiece movement according to claim 1, wherein the resilient element is arranged on a plate of said wheel, which contains said wheel toothing on the periphery thereof, said resilient element having a portion superposed on said given hollow of said toothing.

4. The electromechanical timepiece movement according to claim 3, wherein the resilient element is formed by a wire spring attached to the wheel at at least one of the two ends thereof.

5. The electromechanical timepiece movement according to claim 4, wherein the wire spring has a bent portion protruding from the main curvature thereof, said bent portion being superposed on said given hollow of said toothing of said wheel.

6. The electromechanical timepiece movement according to claim 1, wherein said movable component is a pinion or another wheel forming with said wheel a gear train of the timepiece movement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The invention will be described below with reference to the annexed drawings, given by way of non-limiting example, and in which:

[0016] FIG. 1 is a block diagram of the electromechanical movement according to the invention.

[0017] FIG. 2A is a top view of a wheel and a pinion of a gear train of the movement of FIG. 1, wherein the wheel is provided with a spring that belongs to the device for detecting the angular position of the wheel; FIG. 2B is a similar view to that of FIG. 2A but with a particular angular position of the wheel in which an additional resistive toque is generated by the spring.

[0018] FIG. 3 is a partial enlargement of FIG. 2A.

[0019] FIG. 4 is a partial cross-section along the line IV-IV of FIG. 2B.

[0020] FIGS. 5A to 5C are schematic views of the torque curves provided by the stepping motor for three different variants.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring to the Figures, there will be described below an embodiment of an electromechanical timepiece movement 2 comprising a stepping motor 4, a gear train 6 coupled to the motor and driving an analogue display 8. In a conventional manner, the movement also includes a power supply circuit 10 for the motor, a control logic circuit 12 which provides the power supply circuit with signals for shaping pulses applied to the motor, a clock circuit 14 defining a time base, particularly for logic circuit 12, and a central processing unit 18, which manages the various functions of the timepiece movement. Finally, the timepiece movement also includes a circuit 16 for detection of the load defined by the gear train and the analogue display, respectively of the motor torque supplied with each step to drive said load. This detection circuit forms part of a device for detecting the angular position of a wheel according to the invention. It is connected to the power supply circuit (connection A) and/or directly to the stepping motor (connection B) and/or also to the control logic circuit (in particular via the central processing unit).

[0022] Detection circuit 16 may be arranged in various ways known to those skilled in the art, in particular as in the aforementioned prior art. In the case where it is arranged that three different pulses can be provided with three different respective energies, load detection then consists in determining which of these three different pulses is required to effect a particular step. In another case, which provides real time management of the pulses as a function of load, load detection may occur in various ways, by analysing one or more parameters of the three physical parameters involved in the energy of an electrical pulse, i.e. time, the voltage applied and the current supplied. Load detection may be linked to a value of these parameters, for example the pulse length, peak current, or selected voltage, if applicable. In more sophisticated detection modes, it is possible to use several or these values or information derived therefrom. Finally, those skilled in the art also know detection means that analyse an induced voltage/an induced current in a motor coil after an electrical pulse has been supplied (using a switch between the power supply circuit and the detection circuit). Such an induced signal can, in particular, determine whether the step was properly taken, but an analysis of the signal can also provide information as to the resistive torque applied to the motor.

[0023] Gear train 6 includes a wheel 22 having a toothing 23 and driven in rotation by the motor, and a pinion 24 having a toothing 25 and meshing with the wheel. This pinion forms, in a non-limiting manner, a movable component meshing with toothing 23 of wheel 22. An additional localised resistive torque is achieved by a resilient element 26 integral with wheel 22. This resilient element is formed by a wire spring which is arranged on the wheel plate and whose end 29 is attached to the plate. At a free end of the wire spring there is a bent portion 30, which is superposed on a given hollow 32 of toothing 23 between two adjacent teeth 34 and 35 of the toothing. It will be noted that, in the advantageous variant represented in the Figures, bent portion 30 is curved so that it is not superposed on the two hollows 36 and 37 which are adjacent to hollow 32. In another variant, the wire spring is attached at both ends, the bent portion being located approximately midway along the length of the wire spring. The bent portion advantageously protrudes from the main curvature of the wire spring, to be superposed on toothing 23 in a very localised manner. However, this advantageous variant is not limiting, since the resilient element does not necessarily have such a bent portion. Thus, for example, in a variant, only the tip of the free end of the spring is superposed on the wheel toothing. Finally, toothing 25 of pinion 24 is at least partially on the wire spring, as represented in the cross-sectional view of FIG. 3, so that the toothing presses against the resilient element, i.e. against the bent portion of the wire spring here, when it penetrates inside given hollow 32.

[0024] More generally, it is arranged that the resilient element is arranged to extend, in projection in a general plane 40 of wheel 22 in which its toothing 23 is located, into a given hollow; this resilient element is elastically deformable in a radial direction of the wheel substantially as far as the bottom of the given hollow (i.e. at least sufficiently to allow the pinion toothing to penetrate the hollow, without risk of blocking the meshing of the pinion with the wheel). Advantageously, the resilient element is configured to penetrate, in projection into said general plane, to a lesser extent inside one and/or the other of the two hollows adjacent to the given hollow than into said given hollow. Preferably, as in the variant set out above, it is arranged that the resilient element is made and attached to the wheel so that it does not penetrate, in projection into said general plane, inside the two adjacent hollows.

[0025] The device for detecting the angular position of wheel 22 can thus determine the passage of a reference half-axis 42 of the wheel through a reference direction 44, corresponding to a reference angle α.sub.REF, defined by said wheel and the movable component. Half-axis 42 is defined by the middle of hollow 32, respectively by the portion of bent part 30 of the wire spring which is superposed on said selected hollow. Reference angle α.sub.REF, corresponds, in the case of a movable component forming a wheel or a pinion, to the angular position of a straight line 44 passing through the centre of wheel 22 and the centre of said movable component. The detection device according to the invention thus comprises a ‘hard point’ located in only one hollow of the wheel toothing, and for said detection, it includes an electronic circuit capable of detecting an additional resistive torque that occurs momentarily when wheel 22 and pinion 24 are driven in a stepping motion by motor 4.

[0026] FIGS. 5A, 5B and 5C respectively represent three curves 48A, 48B and 48C indicating the torque provided by the motor when gear train 6 is driven in a stepping motion, with the passage of one tooth of pinion 24 into hollow 32 of the toothing of wheel 22 and thus through the hard point generated by wire spring 28, which is superposed only on this given hollow. These three curves are a schematic representation of the resistive torque that the motor has to overcome during a series of pulses which are represented as joined, whereas in normal operation the pulses are separated by rest periods of the stepping motor.

[0027] FIG. 5A corresponds to a particular situation for a toothing 23 with sixty teeth and a wheel effecting sixty steps per revolution. In this case, the additional resistive torque generated by the wire spring occurs for only one motor step, such that the angular position of the wheel is determined immediately upon the detection, for a step N, of a peak 50A in the torque supplied by the motor. It will be noted however, that it is also possible, depending on the relative position of the toothings that mesh during the motor rest periods, for the effect of the additional resistive torque to be felt over two consecutive steps. This is notably the case if a motor rest position corresponds to a situation where bent portion 30 is pressed by a tooth of toothing 25. In that case, it is therefore necessary to define which of the two consecutive steps is the one that defines the angular reference position.

[0028] FIG. 5B corresponds to a variant wherein toothing 23 also has sixty teeth, but the wheel completes one revolution every thirty steps. The resistive torque increase peak 50B occurs over a shorter duration than a standard pulse length. As there is generally no practical advantage in knowing a reference position with a precision greater than that defined by one motor step, it will be noted that bent portion 30 of the wire spring could, in another variant, extend over two consecutive hollows, in particular if, advantageously, the meshing relationship of the two toothings is precisely controlled so that the two consecutive hollows are penetrated in the same step. However, preferably, a variant embodiment will be retained with the wire spring superposed on only one hollow. Thus, the relative position of the toothings during motor rest periods is less critical. The motor and the gear trains will preferably be mounted so that the passage of given hollow 32 occurs during only one step made by the motor.

[0029] FIG. 5C corresponds to a variant wherein toothing 23 has thirty teeth and the wheel makes sixty steps per revolution. In this case, the additional resistive torque is felt over several consecutive steps, with torque peak 50C extending over at least two steps and generally over three steps. Analysing the power supply signal generating the electrical pulses concerned by the several consecutive steps generally makes it possible to define the step in which the reistive torque passes through a maximum and therefore to determine the step corresponding to the reference position of wheel 22. However, in the case where the additional resistive torque acts over several consecutive steps of the motor, there are several ways to define which is the reference step. For example, it can be arranged to be the first step with a resistive torque above a predetermined threshold, or the last step of a series of steps which all have a resistive torque above said threshold. It is understood that it is also possible to choose a step situated in the middle of such a series of steps, or the step that follows such a series, i.e. the first step with a torque lower than a given threshold after a series of steps in which the resistive torque was above the threshold.

[0030] The detection device according to the invention is compact. It has the advantage, in terms of construction, that the entire detection device (with the exception of the electronic part which is incorporated in the electronic circuit of the timepiece movement) is placed on the wheel concerned. Indeed, all that is required is one resilient element integral with the wheel in question. It can easily be attached to the wheel so that it covers only one hollow.