Patent Description:
Power toothbrushes typically provide either a sweeping motion of the brush head, in which the brush head rotates about its longitudinal axis, or a rotary motion, where bristle tufts arranged in a circular pattern rotate about an axis perpendicular to the toothbrush's longitudinal axis. Low cost power toothbrushes with brush heads moving in a sweeping motion typically use an eccentric rotary mass (ERM) motor to obtain a sweeping brush head motion.

Low cost power toothbrushes often exhibit a generally uncontrolled orbital sweeping motion which lacks efficacy. They also produce considerable handle and brush vibrations, which can be uncomfortable for the user. There are more efficient toothbrushes that produce good efficacy using a magnetic coil to drive a mechanical resonator and the brush motion. Such a system can be complex, requiring tuning and electronics such processers and MOSFETs to create the optimal AC signal to drive the coil. This results in higher manufacturing costs.

<CIT> discloses a toothbrush including a handle, a DC motor and a drive shaft with an eccentric portion extending from the motor. A first support plate and a second support plate are secured to the handle and support the drive shaft. A brushhead shaft is fixed between the support plates and a spring member is secured between a yoke member on the brushhead shaft and a sleeve which rotates on the drive shaft. The spring member is a compression spring, and when operated, it produces a sweeping motion of the brushhead shaft.

<CIT> describes a power toothbrush system that can be manufactured at low cost using an electric motor, with a resonance-seeking characteristic. In an embodiment described in this patent, as the RPM of the motor increases from zero following start-up, the drive signal frequency increases to a point near resonance, where the energy from the drive signal is transferred into the rotating motion of the driven assembly, producing an effective amplitude of a brush head sweeping motion.

A toothbrush which moves its brush head exclusively in a direction parallel to the bristle direction may provide good cleaning efficacy. This motion (which will be called "tapping" in the discussion below) heretofore has not been available in a low-cost electric toothbrush. According to aspects and embodiments described herein addressing such a need, the present disclosure is directed to a low-cost toothbrush with a simple-to-manufacture design that provides a tapping motion of the brush head.

According to the invention, there is provided a dental cleaning device according to claim <NUM>.

In the embodiments, the power supply may be a DC power supply. The DC power supply may be a battery, and the battery may be rechargeable or replaceable.

In an embodiment, the spring element may include a pair of torsion springs positioned on opposing sides of the driven member.

In the embodiments, the spring element may include a plastic element. The spring element may be a helical spring, a torsion bar or a leaf spring.

In an embodiment, a power toothbrush includes a frame; an eccentric mass rotary motor mounted on the frame; and a drive shaft mechanically coupled to the motor. A torsion spring is mounted to the drive shaft and to the frame in a configuration where it applies a force to the drive shaft in a direction perpendicular to the axis of the drive shaft. The torsion spring, drive shaft and frame form an assembly having a resonant frequency. A brush head is mounted on the drive shaft in an orientation in which the bristles on the brush head are parallel to the direction of force exerted by the torsion spring. A battery supplies DC power to the motor power sufficient to cause the motor to operate near the resonant frequency of the assembly. In this embodiment, while the motor is operating near the resonant frequency, the brush head moves in a substantially tapping motion.

Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the inventive subject matter.

The disclosed subject matter will become better understood through review of the following detailed description in conjunction with the figures. The detailed description and figures provide example embodiments of the invention described herein. Those skilled in the art will understand that the disclosed examples may be varied, modified, and altered without departing from the scope of the invention described herein.

Referring to <FIG>, a power toothbrush <NUM> has a brush head <NUM> mounted to a drive shaft <NUM> which extends outward from a housing <NUM>. The housing <NUM> is of a size and form that serves as a handle for a user. The brush head <NUM> may be replaceable. The toothbrush <NUM> has a longitudinal axis <NUM> through the drive shaft <NUM> and neck <NUM> of the brush head <NUM>. In a conventional power toothbrush, the drive shaft <NUM> rotates about the longitudinal axis <NUM>. This, in turn rotates the brush head <NUM> through an arc generally indicated by the arrows in <FIG>. This arc is perpendicular to the longitudinal axis <NUM>. Rotational movement through an arc perpendicular to the longitudinal axis of a power toothbrush is referred to herein as a sweeping motion. Referring to <FIG>, the embodiments described herein will provide a brush head motion in a generally up-and-down direction indicated by the two-headed arrow in <FIG>. This direction is generally perpendicular to the longitudinal axis <NUM> of the drive shaft <NUM>, and parallel to the length of the bristles <NUM> (see double-headed arrow <NUM> in <FIG>). Brush head motion in a direction generally perpendicular to the longitudinal axis and parallel to the length of the bristles is referred to herein as a tapping motion.

While conventional power toothbrushes provide a predominantly sweeping motion, it has been recognized that a predominantly tapping motion can be efficacious in cleaning teeth. A power toothbrush that provides this motion would be an effective alternative to the sweeping motion of commonly available power toothbrushes, and in some cases, may be more effective than a conventional sweeping movement. The embodiments described herein provide a power toothbrush with an effective alternative cleaning mechanism, i.e. a brush head moving predominantly in a tapping motion, which can be easily manufactured at relatively low cost.

Referring to <FIG>, in the illustrated embodiment an eccentric rotating mass motor (ERM) <NUM> is mounted to the interior of the housing <NUM>. ERM motors which have a size and form that fits within a housing <NUM> used as a toothbrush handle are commercially available. A DC power source <NUM> which provides a constant voltage to the motor <NUM> is connected to the ERM motor <NUM>. The power source <NUM> may be a battery that is replaceable or rechargeable. The battery <NUM> may be one which provides a battery voltage of about <NUM> to <NUM> volts , matching the specified operating voltage for the ERM motor <NUM>. If it is desired to vary the performance of the toothbrush to provided different performance levels to the user, or to accommodate voltage degradation as the battery discharges, the effective voltage can be changed through pulse width modulation.

Drive shaft <NUM> is mechanically coupled to the motor <NUM>, and extends outward from the housing <NUM> to engage with the brush head <NUM>. The ERM motor <NUM> provides a reciprocating force which is transferred via the drive shaft <NUM> to the brush head <NUM>. An example of a coupling mechanism between a drive shaft and a brush head which is capable of transferring such a force can be found in <CIT>.

A seal <NUM>, which may be, for example, a rubber seal, is on the end of the housing <NUM> to seal the opening where the drive shaft <NUM> exits the housing <NUM>, to prevent the egress of water or other fluids into the housing <NUM>.

A torsion spring <NUM> is mounted to the interior of the housing <NUM> and to the drive shaft <NUM> in a configuration where the torsion spring <NUM> acts on the drive shaft <NUM> in a direction perpendicular to the drive shaft's axis <NUM> and parallel to the length of the bristles <NUM> on the brush head <NUM>. In the illustrated embodiment, the housing <NUM> acts as a frame which is substantially stationary relative to the drive shaft axis <NUM>. In other embodiments, a separate frame which is stationary relative to the drive shaft <NUM> may be contained within the housing <NUM>, and in such an alternative embodiment, the torsion spring <NUM> would be mounted to the frame and the drive shaft <NUM>. A pair of torsion springs may be used, mounted on opposing sides of the drive shaft.

The torsion spring <NUM> may be metal or a plastic material. Low-cost plastics such as polyoxymethylene (POM) or a polyamide may be used. It may be formed as a torsion bar, a helical spring, a combination of leaf springs, a V-shaped leaf spring, or a spiral spring.

In an embodiment, the drive shaft <NUM>, torsion spring <NUM> and housing/frame <NUM> may be fabricated as a unitary piece from a plastic material (such as, for example, POM or PA), or may be separate pieces of metal or plastic which are assembled together.

In operation, the ERM motor <NUM> imparts a reciprocating motion to the drive shaft <NUM>, which transmits it to the brush head. The spring element <NUM>, acting in a direction perpendicular to the drive shaft axis <NUM> and parallel to the direction in which the bristles <NUM> extend, will urge the drive shaft <NUM> and brush head <NUM> into a translational movement and provide the stiffness needed to inhibit orbital movement. With the brush head <NUM> and spring element <NUM> positioned in orientations where the direction of the bristles <NUM> is parallel to the force exerted by the spring <NUM>, this results in a predominantly tapping motion of the brush head <NUM>. To minimize motion at the seal <NUM>, the torsion spring <NUM> of the illustrated embodiment is positioned near the seal <NUM>.

The motor, drive shaft <NUM>, brush head <NUM> and spring <NUM> combined form a mechanical resonant system. After powering on the motor <NUM>, its frequency will increase. As it nears the resonant frequency of the resonant system, the motor frequency will stabilize, and it will establish an equilibrium between the energy output of the motor <NUM> and the energy absorbed by the resonant system. At this point, the brush head <NUM> will move in a tapping motion with substantial amplitude, because the resonant system is absorbing the bulk of the energy from the motor <NUM>, and the torsion spring <NUM> is applying a force that results in a predominantly tapping motion of the brush head <NUM>. The voltage of the DC signal from the power source <NUM> will control to that point of stability, with a higher voltage nearing closer (or beyond) the resonant frequency. Reference is made to <CIT>, owned by assignee of the present invention, which describes a power toothbrush with a resonance-seeking characteristic. In an embodiment described in this patent, as the RPM of the motor increases from zero following start-up, the drive signal frequency increases to a point near resonance, where the energy from the drive signal is transferred into the rotating motion of the driven assembly, producing an effective amplitude of a brush head sweeping motion.

Changes to the resonant system will change its resonance characteristics, and therefore, the amount of energy it can absorb. For a given toothbrush, its resonance characteristics can change over time by, for example, a spring element gradually losing its stiffness over time or the effect of wear on other parts of the system. Resonance characteristics will also vary from one toothbrush to the next due to manufacturing tolerances. Also, aspects of how a user interacts with the toothbrush (for example, how tightly it is gripped or applied to the teeth) may affect the resonant system. Because the motor <NUM> output of the embodiment increases until is near the resonant frequency of the resonant system rather than increasing to a preset frequency, it does not require manufacturing tuning or adjustment to operate at optimal performance. Also because of this, relatively low cost materials and relatively large manufacturing tolerances can be used. The spring element <NUM> can be formed of a low cost plastic such as POM or PA, since the system will self-adjust to gradual stiffness changes over time. The drive shaft, housing and spring can be fabricated as a single plastic part, made of a common plastic such as POM or PA, with the resonance-seeking characteristic of the embodiment accommodating any stiffness changes over life of the product. In such an embodiment, the plastic construction can also provide for a motor attachment (clamping or adhesive) and housing interface.

In the illustrated embodiment, overshoot may be avoided. If, as a result of a change or variance in resonance characteristics, the system could not absorb the energy output of the motor <NUM>, the motor frequency would rise above the resonant frequency of the resonant system. This is called "overshoot". If overshoot were to occur, the motor frequency would continue to rise and would not decrease to the resonant frequency. This would have undesirable consequences, such as uncomfortable vibration of the toothbrush in the user's hand, , increased wear-and-tear on the components of the toothbrush, and a brush head motion that would be inefficient to the point of being ineffective.

In an embodiment, the drive shaft <NUM> has a characteristic such that it acts as a compliant element between the motor <NUM> and the brush head <NUM> and absorbs some of the motor output. This keeps the operating frequency of the motor <NUM> below the system resonant frequency, thus avoiding overshoot. The compliant element can, alternatively, be an additional part.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference numbers in the claims should not be construed as limiting the scope of the claims.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents cited and/or ordinary meanings of the defined terms.

While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the claims.

Claim 1:
A dental cleaning device (<NUM>) comprising: (i) a rotary motor (<NUM>) with an eccentric mass;
(ii) a driven member mechanically coupled to the motor;
(iii) a spring element mounted to the driven member and acting in a direction perpendicular to the axis of the driven member;
(iv) a frame (<NUM>) though which the driven member extends; and
(v) a power source (<NUM>);
wherein the driven member comprises:
- a drive shaft (<NUM>) coupled to the motor, and
- a brush head (<NUM>) coupled to the drive shaft;
wherein the spring element comprises a torsion spring (<NUM>) mounted between the drive shaft and the frame in an orientation where it applies a force to the drive shaft in a direction perpendicular to the axis of the motor;
wherein the brush head has bristles oriented in a direction parallel to the direction of the force exerted by the spring element;
wherein the motor, spring element and driven member forming an assembly having a resonant frequency;
wherein the power source supplying to the motor power sufficient to cause the motor to operate near the resonant frequency of the assembly;
wherein while the motor is operating near the resonant frequency of the assembly, the brush head moves in a predominantly tapping motion.