The invention relates to an energy harvester compris ing a mass that is subject to environmental forces for bring ing 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.

Such an automatic harvester is known from

W02013/ 062406 in the name of Technische Universiteit Delft.

It is an object of the invention to simplify the con struction known from W02013/ 062406 and to make it in particu lar suitable for application as part of a wristwatch, or other wearable device which needs an energy source.

Wristwatches and in general other devices that are intended to be worn by a user, are subject to large motional excursions with low acceleration which makes it hard to har vest energy from these motions and bring this energy to use in the wristwatch or other device that is worn by the user. It is therefore another object of the invention to provide an energy harvester with improved capability to collect and store such motional energy that is characteristic for human motion, i.e. large motional excursions with low acceleration.

The energy harvester of the invention is embodied with the features of one or more of the appended claims.

As a first aspect of the invention 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. The word 'substantial ly' in the previous sentence expresses that intended and unin tended inaccuracies regarding the design of the elastic beam that counteracts the forces of gravity acting on the moving mass are comprised within the scope of the invention. From an engineering point of view inaccuracies up to a maximum of 10% of the nominal counteracting force required for perfect static balancing are allowable, without departing from the scope of the invention. The static balancing of the moving mass is very suitable to enable that the mass can assume a semicontinuous movement with a limited cycle, which is inflicted by a low ac celeration movement to which the frame is subjected. This lim ited cycle movement of the moving mass is then available for harvesting and storing of energy which is derived from the said low acceleration movement of the frame.

It is possible to keep the design of the energy har vester relatively simple by providing that the mass is con nected with a hinge to the frame, and that the at least one elastic beam is a single spring element that urges the mass towards its neutral position in the frame.

In another embodiment the mass is connected to the frame with at least one elastic supporting element with posi tive stiffness in relation to movement of the mass with refer ence to the frame, wherein the energy harvester is further equipped with one or more elastic beams that are capable to buckle when the moving mass leaves its neutral position in the frame and that provide negative stiffness in relation to move ment of the mass with reference to the frame, wherein the said positive stiffness of the at least one elastic supporting ele ment is compensated by the negative stiffness of the one or more elastic beams so as to provide a zero stiffness behavior to the moving mass in the frame. This construction is also very suitable to embody the energy harvester in an entirely compliant design.

Suitably the means linked to the mass for converting and storing of energy that is embodied in the moving mass, comprises a system selected from the group comprising a re- verser gear, a gear clutch system, a ratchet system linked to a spring which can be wound by the ratchet system for storing of energy, and a system for converting motional energy into electrical energy equipped with a battery for storing and re lease of said electrical energy.

The energy harvester of the invention preferably forms part of an automatically winding watch, such as a wrist- watch in particular. The invention will hereinafter be further elucidated with reference to the drawing of an exemplary embodiment of an apparatus according to the invention that is not limiting as to the appended claims.

In the drawing:

-figure 1 shows an embodiment of a fully compliant balanced energy harvester according to the invention, wherein the mass is in a neutral position in the frame;

-figure 2 shows the embodiment of figure 1 wherein the moving mass is moved out of the neutral position in the frame;

-figure 3 shows the embodiment of figure 1 embodied with a ratchet system;

-figure 4 shows another embodiment of a balanced en ergy harvester according to the invention, wherein the mass is connected to the frame with a hinge and the mass is in a neu tral position in the frame;

-figure 5 shows the embodiment of figure 4 wherein the moving mass is moved out of the neutral position in the frame; and

-figure 6 shows the embodiment of figure 1 embodied with an electrical system.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

Turning first to the simplest embodiment of the ener gy harvester of the invention shown in figure 4 and figure 5, the energy harvester according to this embodiment comprises a mass 1 that is subject to environmental forces for bringing it into the status of a moving mass. The energy harvester of the invention has means 4, 5, 6 linked to the mass 1 for convert ing and storing of energy embodied in the moving mass 1, which means 4, 5, 6 are arranged for subsequent release of said en ergy. The mass 1 is comprised in a frame 3a, 3b, and at least one elastic beam 2 connects the mass 1 to the frame 3a to ar range that the mass 1 can be statically balanced. It further shows that the mass is also connected with a hinge zl to the frame 3b. The at least one elastic beam 2 is in this embodi ment embodied as a single spring element that urges the mass 1 towards its neutral position in the frame 3a, 3b, and provides the just mentioned static balancing of the mass 1 against the forces of gravity. This neutral position is shown in figure 4.

Said means 4, 5, 6 for converting, storing, and re lease of energy embodied in the moving mass 1 comprises a flexure 5 that transfers motion from the moving mass 1 towards a ratchet wheel 4 when the moving mass 1 makes an upward move ment from a position as shown in figure 5 towards the neutral position shown in figure 4. The ratchet wheel 4 in turn may drive a coil spring or similar (not shown) to store the energy for later release and use. Another flexure 6 is further used to hold the ratchet wheel 4 in place when the moving mass 1 moves downward to an eventual position as shown in figure 5. Figure 5 also shows that the at least one elastic beam 2 that is embodied as a single spring, is a buckling beam which buck les when the moving mass 1 departs the neutral position with reference to the frame 3a, 3b in which the elastic beam 2 is not buckled as shown in figure 4. Figure 5 in turn shows the elastic beam 2 in its buckled condition wherein the elastic beam 2 counteracts forces of gravity acting on the moving mass 1 so as to statically balance said moving mass 1 in the frame 3a, 3b.

Turning now to figure 1 and figure 2 a more compli cated embodiment of the energy harvester of the invention is shown, in which the mass 1 is connected to the frame 3 with an elastic supporting element 2b with positive stiffness in rela tion to movement of the mass 1 with reference to the frame 3, and that the energy harvester is further equipped with one or more other elastic beams 2a, 2c, 2d that are capable to buckle when the moving mass 1 leaves its neutral position in the frame 3 which is shown in figure 1. The elastic beams 2a, 2c, 2d are arranged to provide negative stiffness in relation to movement of the mass 1 with reference to the frame 3, and the positive stiffness of the earlier mentioned elastic supporting element 2b is compensated by the negative stiffness of the one or more elastic beams 2a, 2c, 2d so as to provide a zero stiffness behavior to the moving mass 1 for its movement in the frame 3.

Figure 2 shows a situation wherein the moving mass 1 is moved out of the neutral position shown in figure 1, and wherein the elastic beams 2a, 2c, 2d are buckled, thus coun teracting the forces of gravity acting on the moving mass 1 and statically balancing this moving mass 1. The moving mass 1 is therefore both statically balanced and provided with a zero stiffness behavior due to the compensating stiffnesses of the elastic supporting element 2b and the elastic beams 2a, 2c,

2d. The embodiment of figure 1 and figure 2 is particularly suitable for realization as a completely compliant design.

In a way similar to the embodiment of figure 4 and figure 5, the embodiment of figure 1 and figure 2 can also be provided with a ratchet wheel 4 that is linked to the moving mass 1 and to a coil spring or similar for storing of energy harvested from the moving mass 1, and to be released for later use. This feature is shown in figure 3. Also an embodiment is feasible wherein the means for converting and storing of ener gy comprise a reverser gear or a gear clutch system. Figure 6 in turn shows an embodiment in which the moving mass 1 is pro vided with an element 6 that activates a piezoelectric system 4 that is mounted on the fixed world 5 for convergence of mo tion energy into electrical energy.

The different embodiments of the energy harvester of the invention can be suitably applied in a device worn by a user, in particular in the form of a watch or wristwatch to provide same with an automatic winding capability.

Although the invention has been discussed in the foregoing with reference to some exemplary embodiments of the energy harvester of the invention, the invention is not re stricted to these particular embodiments which can be varied in many ways without departing from the invention. The dis cussed exemplary embodiments shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiments are merely intended to explain the wording of the appended claims without intent to limit the claims to the said exemplary embodiments. The scope of protec tion of the invention shall therefore be construed in accord ance with the appended claims only, wherein a possible ambigu ity in the wording of the claims shall be resolved using these exemplary embodiments.