ENERGY HARVESTER FOR A WEARABLE AND/OR PORTABLE DEVICE

The invention relates to an energy harvester for a wearable and/or portable device, such as a wrist watch or a remote control for e.g. a (television) screen, the harvester comprising a mass that is arranged, e.g. suspended, to move, e.g. swing, back and forth between extreme positions and that is coupled, via a transmission, to an energy converter, such as a generator that converts kinetic energy into electrical power, and/or an energy storage, such as the main spring of a watch or a battery.

In GB 766,295, "The oscillatory weight of a watch self winding mechanism is carried by at least one flexible element attached to the watch movement. The weight 1, Fig. 1, is carried by a leaf spring 2 connected at 3 to the movement 4. Push and pull pawls 8, 7 are carried by an extension 6 of the weight 1 and are urged by a spring 9 into engagement with a ratchet 5 in the mainspring winding train. The pawl 8 drives the ratchet 5 as the weight 1 swings clockwise and the pawl 7 as the weight swings counter-clockwise. A detent 11 prevents reverse rotation of the ratchet 5 by urging it to a neutral central position."

US 2019/332061 relates to a monolithic component for a timepiece, in particular for a mechanical timepiece, comprising at least one rigid portion and an elastically flexible portion and designed to transmit the movement of an actuator of the timepiece to a driven part of the timepiece. The monolithic component comprises a rigid frame, a first rigid driving member, and a first elastically flexible structure connecting said frame to said first driving member. The first elastically flexible structure is configured in a manner such as to provide a displacement of said first driving member with at least two degrees of freedom, said displacement being caused as a result of the actuator coming into contact with said first driving member.

WO 2019/160404 relates to an energy harvester comprising a mass that is subject to environmental forces for bringing it into the status of a moving mass, and means linked to the mass for converting and storing of energy embodied in the moving mass, which means are arranged for subsequent release of said energy, wherein the mass is comprised in a frame, and wherein at least one elastic beam connects the mass to the frame to arrange that the mass is statically balanced, wherein the at least one elastic beam is a buckling beam which buckles when the moving mass departs a neutral position with reference to the frame in which the elastic beam is not buckled, and wherein the elastic beam in its buckled condition counteracts forces of gravity acting on the moving mass so as to substantially statically balance said moving mass in the frame.

WO 2021/002745 relates to a watch or timepiece comprising a wheel and a mass that drives the wheel, the mass being subjectable to environmental forces for bringing it into the status of a moving mass, wherein the mass is part of a system comprising a frame and at least a first elastic beam suspending the mass from the frame.

It is an object of the present invention to provide an improved energy harvester, in particular to increase its efficiency and/or reduce or avoid wasting energy.

To this end, the transmission ratio between the mass and the converter and/or storage is variable and, for at least one of the extreme positions, preferably for at least two, e.g. both, extreme positions, increases as the mass moves towards that position.

In an embodiment, the transmission ratio increases disproportionally when the mass moves towards one of the extreme position. I.e., both the first derivative and the second derivate of the transmission ratio are positive. Examples include exponential, hyperbolical, and sinusoidal increases.

Thus, input accelerations are converted to output power more efficiently. E.g., in a wearable or portable device, more of the kinetic energy provided by the person wearing or holding the device is harvested, e.g. to increase the amount of energy harvested and thus the autonomy of the device and/or to enable smaller dimensions of the harvester and potentially the wearable and/or portable device.

In the context of the present invention, the transmission ratio is the ratio between (the amount of) translation and/or rotation in the converter or storage and (the amount of) translation and/or rotation of the mass. E.g., in an automatic winding system of a wrist watch having a rotationally suspended inertial mass and a spiral main spring as an energy storage, a higher transmission ratio implies that the mainspring is rotated more (over more degrees) for the same rotational displacement of the mass. Further, the extreme positions of the mass are defined as the positions where the mass changes direction, swings back. The location of the extreme positions depends on the acceleration of the mass and thus will vary.

In an embodiment, at least one of the backward movement and the forward movement of the mass is limited, e.g. by means of stiffness increasing with the stroke of the mass. In another embodiment, the transmission ratio increases asymptotically, i.e. theoretically infinitely, practically e.g. up to 20, or up to 30, or even higher, when the mass moves towards one of the extreme positions.

Thus, in principle, the mass and transmission are configured such that, at least during normal or anticipated use, the mass will not hit an end stop, which enables highly efficient withdrawal of energy and/or avoids the waste of energy that inevitably results from hitting an end stop.

In another embodiment, in at least one position of the mass, between the extreme positions, e.g. in the middle between the extreme positions, the transmission has a mechanical advantage of zero or substantially zero, i.e. smaller than 0,5, preferably smaller than 0,2.

In another embodiment, the transmission has a mechanical advantage of zero or substantially zero over a range between the extreme positions.

Thus, the harvester will be more susceptible to lower accelerations and also harvest energy at smaller and/or more gradual movements of the person wearing or carrying the device.

In another embodiment, the energy harvester comprises a base, e.g. a frame or base plate, a ground, which e.g. is part of or attached to the frame or base, and at least one link, e.g. two or three links, suspending the mass from the ground. Two or more links provide more options to fine tune stiffness of the suspension and may facilitate micro-manufacture.

In a refinement, the at least one link is compliant, i.e. elastically flexible. In an embodiment, the mass and the at least one link, and optionally also the ground, are planar, i.e. extend in the same plane, and preferably monolithic, i.e. made from a single piece of material. Examples of suitable materials included silicon, beryllium copper, and steel. To increase the weight of the mass, an element, e.g. an insert, of a high density metal, such as gold, platinum of wolfram, can be attached to the part(s) defining the mass.

The mass, and in particular the combination of the mass and its resilient suspension, may have a natural frequency in a range from above 0 to 5 Hertz, preferably in a range from 0,1 to 4,5 Hertz. Thus, the natural frequency or 'eigenfrequency' corresponds to input frequencies of common human activity, in particular running, with dominant frequencies typically between 3 and 4,5 Hertz, and walking, with dominant frequencies typically between 0,5 and 1,5 Hertz.

The invention also relates to a watch movement comprising an automatic winding system comprising the energy harvester described above. In an embodiment, the mass is coupled to a ratchet wheel, which in turn is coupled to the energy converter and/or the energy storage. In another embodiment, the energy storage comprises a spiral spring, known in horology as main spring.

The invention also relates to a wristwatch comprising a movement as described above.

In an embodiment, the mass is suspended to swing between limits defined by one and five o'clock positions on the dial of the watch or between limits defined by seven and eleven o'clock on the watch.

Below, the invention will be explained further, which reference to the appended figures in which an embodiment of the invention is shown.

Figures 1A to 1C are top plan views of a first embodiment of an energy harvester according to the present invention, with its inertial mass in the neutral position (Fig. 1A) and in the two extreme positions (Figs. 1B and 1C) .

Figure 2 is an exploded rear view of a wrist watch comprising a movement equipped with an automatic winding system in accordance with the invention.

Figure 3 is a top plan view of the automatic winding system shown in Figure 2.

Figures 4A to 4C are enlarged views of the transmission in the automatic winding system shown in Figures 2 and 3.

Elements in different embodiments that are similar or identical or that perform a similar or identical function are referred to by the same reference number.

Figures 1A to 1C show a first embodiment of an energy harvester 1 according to the present invention, comprising a base, such as a base plate 2. A ratchet wheel 3 is rotatably mounted on the base plate by means of a shaft 4 that extends through the base plate and is connected to an energy converter and/or storage on the other side of the base plate. An inertial mass 5 is mounted to the base plate by means of a first pivot 6, which enables the inertial mass to swing back and forth between extreme positions, shown in Figures 1B and 1C. Further, an arm 7 is mounted to the base plate by means of a second pivot 8. The arm extends around the ratchet wheel and is provided with one or more teeth 9 to enable the arm to pull and rotate the spring-loaded ratchet wheel, e.g. in clockwise direction (CW). A pawl (not shown) is provided to prevent the ratchet wheel from rotating in the opposite direction, e.g. counter-clockwise (CCW).

The inertial mass is coupled to the arm by means of a link 10. In the example shown, the link is a rigid bar connected to the inertial mass by a third pivot 11 and coupled to the arm by a fourth pivot 12. In another example, the link is compliant and optionally monolithic with the mass and/or the arm.

Figure 1A shows the neutral position of the inertial mass. In this position, the pivot 6 of the inertial mass and both pivots 11, 12 of the link are on a straight line that extends between the pivot 8 of the arm and the rotational shaft 4 of the ratchet wheel 3. As a result, in the neutral position, the transmission ratio between the mass and the ratchet wheel is substantially zero, i.e. has practically no mechanical advantage and will start to move at the slightest acceleration of the device containing the energy harvester. Due to the configuration of the link, in particular its dimensions and the location of the pivots, the arm will rotate in the same direction, CW in the example shown, irrespective of the direction, CW or CCW, of the inertial mass and pulls the ratchet wheel to rotate in that same direction, CW. Also, as the inertial mass swings towards one of the extreme positions, shown in Figures 1B and 1C, the transmission ratio between the inertial mass and the ratchet wheel increases disproportionally, i.e. the number of degrees of rotation of the ratchet wheel increases with each degree of rotation of the inertial mass, in this example to such an extent that the inertial mass is decelerated to come to a full stop after a stroke or swing of less than 25 degrees, e.g. 20 degrees, and no end stops are required.

Figure 2 shows, in an exploded rear view, a wrist watch 20 comprising a movement 21 including a conventional main spring 22 and an automatic winding system 1 in accordance with the invention.

As also shown in Figure 3, the movement 1 comprises a base plate 2, a ratchet wheel 3 rotatably mounted on the base plate by means of a shaft 4 that extends through the base plate and that is connected to the main spring 22 housed in a barrel on the other side of the base plate or accommodated in an opening of the base plate. An inertial mass 5 is mounted to the base plate by means of flexures 23 and a ground 24, which ground is fastened, e.g. screwed, to the base plate. Examples of a suitable mass and suspension are described in WO 2019/160404.

Further, as shown in more detail in Figures 4A to 4C, an arm 7 is mounted to the base plate by means of a pivot 8, which, in this example, is formed by the shaft 4, i.e. the arm 7 is co-axial with the ratchet wheel 3. The arm is provided with one or more teeth 9 to enable the arm to pull the spring-loaded ratchet wheel in one rotational direction, e.g. clockwise (CW). A pawl mechanism 25 is provided to prevent the ratchet from rotating in the opposite direction, e.g. counter-clockwise (CCW).

The inertial mass is coupled to the arm by means of a link 10. In the example shown, the link is rigid and substantially S-shaped. It is connected to the inertial mass by a first hinge 11 and coupled to the arm by a second hinge 12. In another example, the link or at least the hinges are compliant and optionally monolithic with the mass and/or the arm.

Figure 4A shows the neutral position of the inertial mass. In this position, the hinges are straight. As the inertial mass swings towards one of the extreme positions, shown in Figures 4B and 4C, at least one of the hinges 11, 12 bends the transmission ratio between the inertial mass and the ratchet wheel increases disproportionally.

Thus, input accelerations are converted to output power more efficiently, i.c. more of the kinetic energy provided by the person wearing the watch is harvested. This can be employed to increase the autonomy of the watch and/or to design a smaller or thinner watch.

The invention is not limited to the described embodiments and can be varied within the scope of the claims.