Force sensitive toothbrush

A force-sensitive toothbrush incorporates a bistable mechanism into the toothbrush handle. The mechanism can alert a user to excessive brushing force by changing shape in response to brushing forces exceeding a predetermined threshold. The mechanism can also automatically return to its original state when the brushing forces are lowered back down below the predetermined level. In one aspect, the mechanism may include a force-sensitive region having a principal beam and a secondary notched hinge buckling support beam located within the handle between the bristles and the gripping portion of the toothbrush. In another aspect, the force-sensitive region includes a principal beam and a secondary un-notched buckling support beam. In another aspect, the force-sensitive region includes a principal beam and a secondary support beam with a toothed clutch. These mechanisms can advantageously be molded into an integral toothbrush body using an injection molding operation.

BACKGROUND

Excessive force applied to teeth and with a toothbrush during brushing may cause tooth erosion, receding gums, and other dental problems. There have been attempts to mitigate this effect with a force-sensitive toothbrush that can alert a user when excessive force is applied. However, the prior art solutions to this problem require multiple components and often result in bulky, unattractive, and more expensive toothbrushes. As such, there are no commercially available force-sensitive toothbrushes even though the problems resulting from excessive brushing force are generally known.

There remains a need for a cost effective and ergonomic force-sensitive toothbrush.

SUMMARY

A force-sensitive toothbrush incorporates a bistable mechanism into the toothbrush handle. The mechanism can alert a user to excessive brushing force by changing shape in response to brushing forces exceeding a predetermined threshold. The mechanism can also automatically return to its original state when the brushing forces are lowered back down below the predetermined level. In one aspect, the mechanism may include a force-sensitive region having a principal beam and a secondary notched hinge buckling support beam located within the handle between the bristles and the gripping portion of the toothbrush. In another aspect, the force-sensitive region includes a principal beam and a secondary un-notched buckling support beam. In another aspect, the force-sensitive region includes a principal beam and a secondary support beam with a toothed clutch. These mechanisms can advantageously be molded into an integral toothbrush body using an injection molding operation.

DETAILED DESCRIPTION

All documents mentioned herein are hereby incorporated in their entirety by reference. References to items in the singular should be understood to include items in the plural, and vice versa, unless explicitly stated otherwise or clear from the text. Grammatical conjunctions are intended to express any and all disjunctive and conjunctive combinations of conjoined clauses, sentences, words, and the like, unless otherwise stated or clear from the context. Thus the term “or” should generally be understood to mean “and/or” and so forth.

While the following description provides detailed embodiments for a force-sensitive toothbrush, it will be appreciated that the techniques disclosed herein may be suitably adapted to a variety of other personal care devices such as brushes, eyelash brushes, eyeliner applicators, oral irrigators, electric toothbrushes, and other oral care and personal care items.

FIG. 1Ais a side view of a force-sensitive toothbrush. The toothbrush1may include a head2and a force-sensitive region3that couples the head2to a handle region4. A handle7in the handle region4may include any suitable ergonomic, gripping features such as indents for fingers, soft grippable material, and the like, along with a thumb grip8. In use, a user grips the handle7and applies a force and moment to move the toothbrush about and balance a force of a number of bristles9on the head2against the user's teeth. A force is transmitted from the user's hand through the toothbrush1(including the force-sensitive region3that couples the handle7to the head2) to the teeth thereby closing a structural loop between the user's hand and mouth through the toothbrush1on one hand and the user's body on the other. If a force applied by the user to the bristles9is below a predetermined threshold, the force-sensitive region3acts like a dual-beam structure cantilever comprised of a principal beam6in tension and a secondary beam11in compression. Modest deflection of the beams may occur as is the case with any toothbrush.

In general, the principal beam6and the secondary beam11of the force-sensitive region3may form a bistable mechanism that changes from a first state to a second state in response to an applied force on the bristles9that exceeds a predetermined force, and then returns to the first state when the applied force is released. In the second state, the secondary beam11may have a shorter end-to-end length (i.e., straight-line length between two endpoints of the beam). In other embodiments—e.g., where the toothed clutch ofFIG. 3is swapped in position with the principal beam—the secondary beam11may have a greater end-to-end length in the second state. More generally, the secondary beam11may transition in a bistable manner between a first state and a second state having different end-to-end lengths. This change in length relative to the principal beam6changes the structural characteristics of the overall dual-beam structure in a bistable manner as discussed below.

The secondary beam11may be displaced apart from and substantially parallel to the principal beam6as shown. In order to facilitate a bistable operation, the principal beam6may be relatively resilient, and the secondary beam11may collapse or otherwise compress or yield in a predetermined manner under a predetermined load. The secondary beam11may for example buckle, bend, or otherwise accommodate a bistable change in end-to-end length relative to the principal beam6. This axial displacement of the secondary beam11provides a bistable mechanism of the force-sensitive region1when the secondary beam11bends, collapses, or otherwise response to a predetermined load on the bristles9of the toothbrush. A suitable bistable mechanism may be achieved in a variety of ways, with several specific embodiments described below by way of illustrative examples. The structure may advantageously be formed of as a single piece with integrally molded structural elements, thus avoiding the costs, reliability issues, and potential hazards associated with a multi-part assembly.

It will be understood that the predetermined load at which brushing is excessive may be subject to disagreement among dental professionals. The precise predetermined load at which bistable deflection occurs is thus not essential to this disclosure, except to note that the force-sensitive region3may be readily designed to yield under any particular predetermined load within the typical loads of ordinary brushing activity, which may be on the order of about two Newtons of normal brushing force. More generally, normal forces on the order of 0.5 to 2.5 Newtons may be observed during brushing, and the force-sensitive region3may be designed to yield at a predetermined load (such as 2.0 Newtons) within this range through suitable selections of material and dimensions for the principal beam and secondary beam. In some cases, and in particular for veterinary use, higher loads might be desired, and the mechanisms shown herein can be designed for higher forces also. Sizing of members to achieve desired state changes at predetermined loads can be performed by one skilled in the art of structural mechanics using energy methods, for example, and/or may be quantitatively determined and fine tuned with the use of finite element analysis software with buckling analysis capability such as ALGOR or ANSYS.

In one aspect, the secondary beam may buckle. The secondary beam11may curve slightly away from the principal beam6in overall shape, as shown by some representative dimensions inFIG. 1B; however, it will be noted that a line connecting the centers of hinges13a,13b, and13chas a slight inflection inward toward the principal beam6. In this configuration, as the force on the bristles9is increased, the compression force in a first element12aand a second element12bof the secondary beam11correspondingly increases. Hinges13a,13b, and13c, which may be elastic notched hinge elements or any other similar hinging mechanisms, may be formed such that straight lines connecting the centroids of their thinned regions point inward toward a center of the force-sensitive region3, even though the secondary beam11is overall concave and curved away from the principal beam. The hinges13a,13b, and13cmay, for example, be integral flexure hinges positioned at the ends and middle of the secondary beam11. Such hinges may be formed for example by partial cylindrical cuts with the end hinges13a,13cfacing towards the principal beam6and a center hinge13bfacing away from the principal beam6. These are commonly referred to as “hourglass hinges.”

Under sufficient load, the bending moment and axial force overcome the elastic resilience of the secondary beam11and the secondary beam11buckles upward (per the relative orientation of the centroids of the thinned regions, which provides an initial location of the central hinge13bcloser to the principal beam6than the end hinges13a,13c) such that the central hinge13bmoves inward until it contacts a side5of the principal beam6. This motion may occur quickly, as typical of buckling, with the resultant impact readily heard and felt by a user even though the range of motion might only be on the order of about one to two millimeters for the design shown, or less than one to five millimeters for typically-dimensioned toothbrushes. Thus, the force-sensitive region3may provide feedback to a user when excessive brushing force is applied (e.g., the predetermined load is exceeded) in the form of an audible click, a tactile click, and/or a change in angle of the force-sensitive region3relative to the handle7and the head2, with the feedback generated when the secondary beam suddenly changes shape and creates an impact with the principal beam6.

When the secondary beam11thus makes contact with the upper beam6it can buckle no further and together the principal beam6and the secondary beam11act as a single, resilient member that can transmit additional force without damaging the toothbrush. When the excessive brushing force is relaxed, the principal beam6can straighten and the secondary beam11can snap back to an unbuckled position, thus restoring the force-sensitive region to a first state.

The principal beam6may be about twice the thickness of the secondary beam11. In one aspect, the principal beam6may be fabricated of a material and at a thickness such that it will not buckle or deform beyond the elastic zone under typical brushing forces (including even excessive brushing forces that the toothbrush1is intended to mitigate). Illustrative dimensions are shown inFIG. 1B. The principal beam6and the secondary beam11may be relatively wide with respect to their thickness such that operation of the force-sensitive region3is not significantly affected by lateral or torsional brushing forces during use. It will also be observed from the design of the force-sensitive toothbrush1that a body of the toothbrush1generally, and the force-sensitive region3in particular, may be fabricated as a single, integral workpiece using, e.g., injection molding or any other suitable mass production or rapid prototyping technique with a variety of polymers (e.g., thermoplastics, elastomers, thermosets, etc.) and/or other materials.

FIG. 1Bis a close up side view of the force-sensitive region3of the toothbrush ofFIG. 1A.FIG. 1Cis an isometric view of the toothbrush ofFIG. 1A.

FIG. 2Ashows a force-sensitive toothbrush. The toothbrush may include a head region22having bristles29, a handle region24having a handle27and a thumb grip28for gripping by a user, and a force sensitive region23. The force sensitive region23may include a principal beam26having a side25and a secondary beam32having a first end33a, a center region33b, and a second end33c.

Similarly to the embodiment described above, as an applied force on the bristles29increases, a compression force in the secondary beam32also increases. Some bending moment is transmitted to first end33aand the second end33cof the secondary beam32as the principal beam26deflects downward. The bending moment imparts a slope to the structure at the end region33aof the secondary beam32. Under a predetermined force (e.g., an excessive brushing force), the bending moment and axial force on the secondary beam32overcome the elastic resilience of the secondary beam32and the secondary beam32bends and buckles upward such that the central region33bcontacts the side25of the principal beam26. This motion may occur quickly, with the resultant impact readily heard and felt by a user even though the range of motion is typically only on the order of about one to two millimeters for the design shown, or less than one to five millimeters for typically-dimensioned toothbrushes. In this manner, the force-sensitive region23may provide audible, tactile, and structural feedback as described above.

When the secondary beam32thus makes contact with the principal beam26, it can bend no further and together the principal beam26and the secondary beam32act as a single, resilient member that can transmit a force beyond the excessive brushing force without damaging the toothbrush. When the brushing force is relaxed, the principal beam26can straighten and the secondary beam32can elastically return to an unbuckled shape, thus restoring the force-sensitive region to a first state.

The principal beam26may be about twice the thickness of the secondary beam32. In one aspect, the principal beam26may be fabricated of a material and at a thickness such that it will not buckle or deform beyond the elastic zone under typical brushing forces (including even excessive brushing forces that the toothbrush1is intended to mitigate). The principal beam26and the secondary beam32may be relatively wide with respect to their thickness such that operation of the force-sensitive region23is not significantly affected by lateral or torsional brushing forces during use.

FIG. 2Bis a close up side view of the force-sensitive region of the toothbrush ofFIG. 2A.FIG. 2Cis an isometric view of the toothbrush ofFIG. 2A.

FIG. 3Ashows a force-sensitive toothbrush. The toothbrush41may include a head region42having bristles49, a handle region44having a handle47and a thumb grip48for gripping by a user, and a force-sensitive region43. The force sensitive region43may include a principal beam46and a secondary beam52with a mechanical slip clutch formed of a first toothed region53aand a second toothed region53b. While the depicted toothed clutch performs adequately, other engagement means and configurations will be apparent to those skilled in the art of clutch design, and may be suitably adapted for use in the force-sensitive region43contemplated herein.

The secondary beam52may be a straight beam, or the secondary beam52may be curved as desired for ergonomic or other reasons. At an end of the secondary beam52nearest to the handle27, the secondary beam52may have a number of teeth60in a saw tooth or similar configuration. It will be appreciated that this placement of the teeth60is not critical, and the teeth60may instead be placed at an opposing end nearest to the head region42, or in the middle, with two extending arms from each end. The angle and length of each tooth60may vary according to a degree of axial force the beam is to withstand before release. These teeth60may engage complementary teeth62that are rigidly coupled to the principal beam46, handle47, or other suitable location. Injection molding or similar fabrication techniques permit very close placement of the teeth60and complementary teeth62to within a fraction of a millimeter.

As the force on the bristles49is increased, the principal beam46may bend, and the compression force in the secondary beam52may increase. Thus, as the brushing force increases, the resulting compression in the secondary beam52may cause the teeth60to slip on the complementary teeth62to provide a tactile click and a physical displacement of the head region42of the toothbrush. When the brushing force is released, the principal beam46may elastically return to an unbent shape, and the teeth60,62may return to their initial positions. The action of the teeth slipping over each other creates a tactile sensation that the user may feel in addition to the feeling of suddenly greater compliance in the toothbrush handle. The sensation of suddenly greater compliance may also be achieved with the other bistable techniques described herein.

The principal beam46may be about two to three millimeters thick and the secondary beam52may be about one to two millimeters thick. More generally, the principal beam52may be any suitable thickness to permit normal brushing forces, and to resiliently bend in response to excessive brushing forces. The secondary beam52may be sufficiently thick to maintain the teeth60on the secondary beam52in frictional engagement with the complementary teeth62on the principal beam46.

It will be understood that the teeth60,62may include any number of teeth having any suitable angle to provide slip clutching as contemplated above. In addition, the teeth60,62may be asymmetrical, with a leading edge (that resists bending) having a first angle for release when excessive brushing force is applied, and a trailing edge (that resists return of the principal beam46to a first shape) having a second angle to permit elastic forces in the principal beam46to return to a straight shape notwithstanding the gripping forces of the trailing edges. These angles may be adapted to provide greater resistance to a transition from the first state to the second state than to a transition from the second state to the first state (e.g., returning to a state for normal use).

While the teeth62are illustrated in the plane of the drawing, it will be understood that the teeth62may be molded into any suitable angle relative to the axis of the toothbrush. For example, by orienting the teeth62orthogonally to the plane of the drawing, in-mouth forces from teeth, lips, and so-forth on the secondary beam52may be reduced in order to prevent interference with the load required to transition between states.

FIG. 4depicts angle change in a force-sensitive toothbrush as contemplated herein. As noted above, a force-sensitive region64may include a bistable, dual-beam structure having a first state in which a head66of a toothbrush68is in an ordinary orientation for use. With an application of sufficient normal force70to the head66—e.g., an excessive brushing force—the force-sensitive region64may change to a second state, such as using any of the techniques described above, in which the head66deflects by an angle72(relative to a handle73) to indicate to a user that excessive force has been applied. When the normal force70is reduced or removed, the force-sensitive region64may resiliently return to the first state with the head66once again oriented for use in brushing teeth.

During the transition from the first state to the second state, the force-sensitive region64may also provide tactile or audio feedback such as a clicking noise or feel using, e.g., the various bistable mechanisms described above. To accentuate the tactile or audible feedback, a sharp bump or other protrusion (not shown) can be included at the center of the secondary beam or the principal beam to create a higher-contact-pressure region along the corresponding surfaces when they touch.

FIG. 5shows a generalized, bistable, dual beam structure. The structure500is shown with a secondary beam502in a first state504and a second state506.

One way to view the bistable operation described in the embodiments above is as a sudden change in length of a secondary beam502relative to a principal beam508under a predetermined load. That is, whether slip clutching against the principal beam508, (reversibly) buckling against the principal beam508, or bending against the principal beam508, the secondary beam502shortens slightly and reversibly in end-to-end length under a compressive force that is created when the principal beam508yields to a brushing load. While the principal beam may also change somewhat in end-to-end length as it bends, the secondary beam502will generally change more in length, that is, change in length relative to the principal beam508, during a bistable transition. By changing from a first length510(corresponding to the first state described above) to a second length512(corresponding to a second state) slightly shorter than the first length510as generally depicted, the secondary beam502accommodates further bending of the principal beam508, accompanied by a change in an angle514of the force-sensitive region coupling the handle to the head. As noted above, this affect may be similarly achieved in certain embodiments where the beams are reversed and the second length512is slightly longer than the first length510. The change in angle514can be perceived by a user along with audible or tactile feedback created by the state change in the secondary beam502so that the user is aware that a load threshold for brushing force has been exceeded.

In some embodiments described above, a bistable transition may be achieved with a buckling of the secondary beam502. In general buckling should be understood to mean a sudden change in geometry of a structural member subjected to high compressive stress, typically with an eccentricity that introduces a moment to the buckling member. Usually this is accompanied by a rapid movement and change in shape. While more detailed and formal definitions exist, this contemplates an adequately wide range of deformations to accurately describe many of the embodiments described above. The term “buckling” as used herein is intended to include any such deformation. In particular, the bistable mechanism of the force-sensitive region may employ a controlled buckling, in which an anticipated buckling of the secondary beam is constrained by the rigid surface of an adjacent principal beam. Herein, the buckling is also preferably elastic, which means that when the load is released, the structure returns to its original shape.

In one aspect, a protrusion516may be included on the principal beam504or the secondary beam502that provides a high-impact stress point when the secondary beam502buckles into the primary beam508. This may generally enhance tactile or auditory feedback from the click that occurs upon the high-speed impact following the sudden movement of the secondary beam502as it buckles into the primary beam508. In general, the protrusion516may be positioned at or near the center of the beams502,508for maximum effect, although enhancement of tactile feedback may be obtained over a wide range of possible positions.

As used herein, a “sudden” movement is intended to refer to the rapid movement typical of buckling deformation, which in the context of the toothbrushes contemplated herein also corresponds to a movement of sufficient speed to provide auditory or tactile feedback upon contact of the “suddenly” moving part (e.g., a buckling or tooth-clutched beam) against a relatively fixed contact point. Thus “sudden” may in one aspect be understood to mean with sufficient acceleration to reach a velocity that provides auditory or tactile feedback within a predetermined range of motion, such as from a first state to a second state of the bistable elements contemplated herein. In the context of the entire device, “sudden” may also mean reaching a velocity that provides sufficient auditory or tactile feedback to alert a toothbrush user to reduce brushing force.

It will be noted thatFIG. 5abstracts away mechanical details of the secondary beam502. This figure is intentionally general in nature, and is not intended to illustrate specific dimensions, displacements, or bending patterns in either the principal beam504or the secondary beam502. The general nature of this figure is instead intended to suggest that a variety of other bistable mechanisms might also or instead be used in the force-sensitive region of a toothbrush, any of which may be equally suitable for fabrication as an integral, one-piece component using, e.g., injection molding or the like. Accordingly, while particular embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications in form and details may be made therein without departing from the spirit and scope of this disclosure and are intended to form a part of the invention as defined by the following claims, which are to be interpreted in the broadest sense allowable by law.