Electric toothbrush

An electric toothbrush includes a stem member on which a replaceable toothbrush is mounted. The stem member is made of synthetic resin and has a cavity for accommodating a DC motor and a vibration shaft connected to the DC motor. One end of the cavity is opened for inserting the DC motor and the vibration shaft together, and the other end thereof is closed. A free end of the vibration shaft is rotatably supported at the closed end of the cavity. The cavity has a cone-shaped wall so that the DC motor is firmly held in the cavity by a rigid contact between a shoulder portion of the DC motor and the cone-shaped wall.

BACKGROUND

Electric or powered toothbrushes that are currently available in the market have a number of constructing parts. Such parts are, for example: a body for holding a battery and an electric circuit board; a DC motor; an eccentric shaft connected to the DC motor; and a stem for holding the eccentric shaft and the DC motor. In the motor receiving cavity, detent protrusions are provided for securing the DC motor within the cavity. However, because the stem is typically formed from a synthetic resin, it is difficult to form the cavity through a single injection molding process. Also, the vibration of the eccentric shaft is transmitted through the motor and the stem to the bristle rather than directly to the stem, which results in a reduction in power and the production of excessive noise. Furthermore, the motor is located close to the tooth cleaning elements, which requires a small sized motor and results in low vibration power. Finally, the weight balance of the existing electric toothbrushes is difficult to adjust because the location of the motor is limited. Thus, a need exists for an electric toothbrush that addresses the above-noted issues in the existing devices of this type.

BRIEF SUMMARY

The present invention may be directed, in one aspect, to an electric toothbrush including a stem member on which a replaceable toothbrush is mounted. The stem member is made of synthetic resin and has a cavity for accommodating a DC motor and a vibration shaft connected to the DC motor. One end of the cavity is opened for inserting the DC motor and the vibration shaft together, and the other end thereof is closed. A free end of the vibration shaft is rotatably supported at the closed end of the cavity. The cavity has a cone-shaped wall so that the DC motor is firmly held in the cavity by a rigid contact between a shoulder portion of the DC motor and the cone-shaped wall.

In one aspect, the invention may be an electric toothbrush comprising: an elongated body portion having a cylindrical room which accommodates a battery and an electric circuit board, said elongated body portion having a first end and a second end; a stem member made of a synthetic resin and having an elongated cavity with a closed end and an open end, in which the open end of the stem member is connected to the first end of the elongated body portion, said elongated cavity having a cone-shaped wall extending from the open end towards the closed end of the elongated cavity such that the size of the opening of the cone-shaped wall close to the open end is wide and is gradually narrowed towards a middle point of the elongated cavity which is located between the closed end and the open end, said elongated cavity further having a recessed hole formed at the closed end such that an axis of the recessed hole is in alignment with an axis of the cone-shaped wall; a replaceable brushbrush mounted on the stem member; a DC motor inserted in the elongated cavity from the open end and firmly held in the elongated cavity by a rigid contact between a shoulder portion and/or side surface of the DC motor and the cone-shaped wall; and a vibration shaft having one end connected to the DC motor and another end formed with an axial shaft portion which is rotatably inserted into the recessed hole, said vibration shaft having an eccentric shaft whose gravity center is located at a position deviated from an axis of the DC motor, wherein a first distance between the gravity center of the eccentric shaft and the axial shaft portion is less than a second distance between the shoulder portion of the DC motor and the gravity center.

In another aspect, the invention may be an electric toothbrush comprising: an elongated body portion having an interior cavity which accommodates a battery and an electric circuit board, said elongated body portion having a first end and a second end; a stem member configured to receive a replaceable brush removeably mounted thereon, the stem member having an elongated cavity with a closed end and an open end, the open end being connected to the first end of the elongated body portion, said elongated cavity defined by an interior wall at least a portion of which tapers from the open end towards the closed end, said elongated cavity further having a recessed hole formed at the closed end; a vibration shaft having an end formed with an axial shaft portion which is rotatably inserted into the recessed hole at a first contact point, said vibration shaft having an eccentric shaft with a gravity center; a DC motor disposed at least partially in the elongated cavity and connected to another end of the vibration shaft opposite the axial shaft portion, wherein a shoulder portion and/or a side surface of the DC motor contacts the interior wall of the elongated cavity at a second contact point, wherein the gravity center of the eccentric shaft is offset from an axis of the DC motor; and wherein a first distance between a gravity center of the eccentric shaft and the first contact point is less than a second distance between the gravity center and the second contact point.

In yet another aspect, the invention may be an electric toothbrush comprising: an elongated body portion having an interior cavity which accommodates a battery and an electric circuit board; a stem member having an elongated cavity with a closed end and an open end, the open end being adjacent to the elongated body portion, said elongated cavity having a cone-shaped wall extending from the open end towards the closed end of the elongated cavity such that a cross-sectional area of the elongated cavity gradually decreases from the open end towards a middle point of the elongated cavity which is located between the closed end and the open end, said elongated cavity further having a recessed hole formed at the closed end, wherein the stem member is configured to receive a replaceable brush removeably mounted thereon; a DC motor positioned in the elongated cavity and such that a shoulder portion and/or a side surface of the DC motor is in contact with the cone-shaped wall; and a vibration shaft having one end connected to the DC motor and another end formed with an axial shaft portion which is rotatably inserted into the recessed hole, said vibration shaft having an eccentric shaft with a gravity center, wherein a first distance between the gravity center of the eccentric shaft and the axial shaft portion is less than a second distance between the shoulder portion of the DC motor and the gravity center.

According to a preferred embodiment, the vibration shaft comprises an extension shaft and the eccentric shaft which are connected in alignment with each other such that the extension shaft is located between the DC motor and the eccentric shaft.

According to a preferred embodiment, the cone-shaped wall is formed by a wall surrounding all around the DC motor.

According to a preferred embodiment, the cone-shaped wall is formed by a plurality of ribs forming wall segments surrounding intermittently around the DC motor.

According to a preferred embodiment, an upper portion of the elongated body portion is bent with respect to a lower portion thereof.

According to a preferred embodiment, said elongated cavity has a receiving corner at a narrowed end of the cone-shaped wall.

According to a preferred embodiment, a third distance between the first end of the elongated body portion and the should portion of the DC motor is less than the second distance.

According to a preferred embodiment, the cone-shaped wall is formed by a curved wall which is curved from the open end towards the closed end.

According to a preferred embodiment, the cone-shaped wall is formed by an upright wall portion and a slanted wall portion.

DETAILED DESCRIPTION

Referring toFIG. 1, an electric toothbrush1according to a preferred embodiment of the present invention is shown.

Referring toFIG. 2A, an exploded view of the electric toothbrush1is shown. Electric toothbrush1includes an elongated body portion10, a chassis20, a rechargeable battery44, an elongated circuit board50, a DC motor60having a cylindrical body, a vibration shaft70and a stem arrangement80. A replaceable brush (not shown) is to be mounted on the stem arrangement80. The replaceable brush covers the stem arrangement80completely or partially.

The body portion10is capable of being gripped or grasped by a user and has a recess11at its bottom end for receiving therein a projection of a battery charger. The body portion10has an interior cavity, which may be for example, cylindrical, for accommodating the chassis20, the rechargeable battery44, and circuit board50.

The stem arrangement80includes a bottom support member81, a packing ring82, a stem member83, a top support member84and a top ring85. The stem member83has an elongated cavity86for receiving the vibration shaft70and the DC motor60.

Referring toFIG. 2B, the vibration shaft70includes an extension shaft72made of synthetic resin and an eccentric shaft73made of metal. The extension shaft72may be integrally formed by a material called POM (polyoxymethylene) manufactured by, for example, POLYPLASTICS CO., LTD. JAPAN. The grade of the material POM may be NW-02 or grades, such as M90-44.

As shown inFIG. 2B, the extension shaft72of the vibration shaft70includes a collar portion74provided close to a bottom end, a resilient shaft portion75and a connecting portion76which are integrally formed by POM in the exemplified embodiment. The bottom end face of the extension shaft72is formed with a recess to be engaged with a shaft of the DC motor60. DC motor60has two wires62aand62bextending from a bottom face thereof for electric connection with the circuit board50.

The eccentric shaft73of the vibration shaft70includes an eccentric portion77and an axial shaft portion78. The bottom end of the eccentric portion77is firmly connected to the connecting portion76by molding and the upper end of the eccentric portion77is provided with the axial shaft portion78.

When the vibration shaft70rotates about its axis by the DC motor60, the eccentric portion77generates a high frequency vibration which is transmitted to the stem arrangement80and to the brush (not shown). The resilient shaft portion75has a flexibility to receive the high frequency vibration of the eccentric portion77.

Referring toFIG. 2C, the stem member83may also be formed by POM. A recessed hole87is formed at the end of the elongated cavity86. The recessed hole87slidably receives the axial shaft portion78. The elongated cavity86accommodates therein the vibration shaft70and the DC motor60. The vibration shaft70is freely rotated in the elongated cavity86. The recessed hole87serves as a bearing for freely holding the axial shaft portion78. The vibration shaft70freely rotates inside the elongated cavity86even under high frequency vibration.

Since the recessed hole87serves as the bearing, it is not necessary to provide a separate bearing arrangement for rotatably holding the axial shaft portion78.

A portion2D indicated inFIG. 2Cis shown in an enlarged scale inFIG. 2D.

Referring toFIG. 2D, a lower end portion of the stem member83is shown in detail. The elongated cavity86has an open end at the lower end of the stem member83so that the two wires62aand62bof DC motor60extends through the open end of the elongated cavity and through an opening formed in the chassis20, and terminates at electrodes52aand52bformed on the circuit board50, as shown inFIG. 2C.

Referring back toFIG. 2D, the elongated cavity86has a cone-shaped wall88and a receiving corner89at the end of the cone-shaped wall88. The cone-shaped wall88is widest at the open end of the elongated cavity86, and is gradually narrowed towards a middle point of the elongated cavity, such as at the receiving corner89. The inner diameter of the cone-shaped wall88at the receiving corner89is about the same or slightly smaller than the outer diameter of the DC motor60. The inner diameter of the cone-shaped wall88at the open end of the elongated cavity86is between 105% and 145% of, such as for example but not limited to 132% of, the outer diameter of the DC motor60. The cone-shaped wall88is formed with a wall surrounding all around the DC motor60without any intermittence. Also, the cone-shaped wall is straight from the open end to the receiving corner89. According to a variation, the cone-shaped wall88may have a step portion or a slanted step portion90at which the inner diameter of the cylindrical cavity86is widened abruptly.

The DC motor60together with the vibration shaft70is inserted into the elongated cavity86from the open end, and forcibly pushed in until the upper side edge, i.e., a shoulder portion, of the DC motor60is fittingly held at the end of the cone-shaped wall88such that the shoulder portion and/or side surface, such as upper side surface, of the DC motor60makes a rigid contact with the cone-shaped wall. The top surface of the DC motor60may abut against the receiving corner89. If necessary, a bonding agent may be applied between the shoulder portion and the cone-shaped wall, or between the top surface of the DC motor60and the receiving corner89. When the shoulder portion and/or side surface of the DC motor60is firmly held in the cone-shaped wall88, the axial shaft portion78is slidably inserted into the recessed hole87. It is apparent from the above that an axis of the recessed hole87is in alignment with an axis of the cone-shaped wall88.

As shown inFIG. 2C, a vibration generator defined by the DC motor60and vibration shaft70is positioned inside the stem member83such that the axial direction of the DC motor60is in alignment with the axial direction of the vibration shaft70, and that the vibration generator is held in the elongated cavity86at two contact points CP1and CP2. Contact point CP1is a point anywhere in the axial shaft portion78and, more specifically, a point where the axial shaft portion78contacts the recessed hole87, and contact point CP2is at a point where the shoulder portion of the DC motor60contacts the cone-shaped wall88.

A distance D1between contact point CP1and a gravity center G of eccentric shaft73is smaller than a distance D2between contact point CP2and the gravity center G of eccentric shaft73(D1<D2). This arrangement enables the location of the eccentric shaft73to be relatively close to the contact point CP1, i.e., close to a position where the bristle of the toothbrush is located. Thus, the vibration generated by the eccentric shaft73can be effectively transmitted through axial shaft portion78and recessed hole87to the bristle of the toothbrush. According to a preferred embodiment of the invention, distance D2is 10 mm or greater, such as 21.3 mm. Furthermore, DC motor60is located within a lower side of the stem member83, i.e., a side of a lower half-length (a side away from the bristle of the toothbrush) of full length of the stem member83. This arrangement provides an appropriate weight balance of the stem member83loaded with the vibration generator, and eventually an appropriate weight balance of the electric toothbrush1. Also, this arrangement gives a freedom to select a larger size of DC motor60, in comparison to a case where the DC motor is located in a side of an upper-half length of full length of the stem member83. In order to provide a sufficient distance between eccentric shaft73and DC motor60, the extension shaft72is provided. In a modification, it is possible to connect DC motor60directly to the eccentric shaft73without using any extension shaft72.

Furthermore, the elongated cavity86is widest at the open end and is gradually narrowed towards the receiving corner89and thereafter the diameter is narrowed at the receiving corner89and keeps a constant width or further narrowed towards the closed end until reaching the recessed hole87. Thus, the molding of the stem member83with the elongated cavity86gradually narrowed towards the closed end can be easily formed by an injection molding.

Furthermore, DC motor60can be held in a position without using any screws, but only by a single push and the resulting friction fit. Accordingly, the assembly of the stem member83loaded with the vibration generator is simple and can be done very easily.

Referring again toFIG. 2A, after placing the rechargeable battery44and the circuit board50at proper positions in the chassis20, the ends of the two wires62aand62bare soldered to electrodes52aand52b, respectively, of the circuit board50. Then, the chassis20carrying the battery44and circuit board50is inserted into the body portion10. During the insertion, stem member83is also partly inserted into the body portion10together with the bottom support member81, packing ring82, top support member84and top ring85, as shown inFIG. 2C. Accordingly the stem member83and the body portion10are firmly held together in a watertight manner.

It is to be noted that stem member83and body portion10can be formed integrally. In this case a bottom end of the body portion10where the recess11is formed should be opened to allow the insertion of an assembly of the vibration shaft70, DC motor60, and chassis20mounted with battery44and circuit board50. After the assembly is inserted from the bottom open end, the open end should be tightly closed by a cap member.

Referring toFIG. 2D, the most top position of the contact point between the body portion10and the stem member83is a contact point CP3. In other words, contact point CP3corresponds to an upper end of the elongated body portion10. According to a preferred embodiment, DC motor60intersects with a level of the contact point CP3. In other words, the length of DC motor60is longer than a distance D3between contact points CP2and CP3. In some arrangements, it is possible to make the length of DC motor60shorter than a distance between contact points CP2and CP3. Furthermore the distances are so selected that D3is less than D2(D3<D2), as apparent fromFIG. 2C. This arrangement has an advantage of producing an appropriate vibration of the stem member83.

Referring toFIGS. 3A and 3B, a first modification of the cone-shaped wall is shown. The cone-shaped wall is defined by a plurality of, such as four ribs92a,92b,92cand92d, located in the cylindrical cavity86extending parallel to each other from the receiving corner89to the open end of the elongated cavity86. The four ribs92a,92b,92cand92dare spaced equidistantly from each other along the circumference of the open end of the elongated cavity86. The free end surfaces of the four ribs define wall segments surrounding intermittently around the DC motor, as best shown inFIG. 3B.

The number of ribs can be two or greater. Also, the ribs may extend from the receiving corner89to an intermediate place somewhere between the receiving corner89to the open end of the elongated cavity86, such as to the slanted step portion90(seeFIG. 2D).

Referring toFIG. 3C, a second modification of the cone-shaped wall is shown. The cone-shaped wall88is formed by an upright wall portion (88a), and a slanted wall portion88b. At upright wall portion88a, the inner diameter of the wall is constant, i.e., nearly equal to the diameter of the DC motor60. At slanted wall portion88b, the inner diameter of the wall increases from the end of the upright wall portion88atowards the open end of the elongated cavity86.

Referring toFIG. 3D, a third modification of the cone-shaped wall is shown. The cone-shaped wall88cis curved from the open end to the closed end. Preferably, the curvature becomes great towards the open end.

Referring toFIG. 4, a modification of the body portion10is shown which is bent at neck portion thereof. The body portion10has an upper portion bent with respect to a lower portion thereof. Therefore, an axis A1of the upper portion of body portion10is inclined with respect to an axis A2of the lower portion thereof. Even in such an arrangement, since the DC motor60is not located in the body portion10, but in the stem member83, it is not necessary to provide any flexible shaft that is bent between the DC motor60and the eccentric shaft73. Therefore, a freedom of designing the body portion10is increased.

Furthermore, according to one embodiment of the present invention, the DC motor60which is described as having a cylindrical body can be arranged to have a cone-shaped body such that the wide side of the cone-shaped body is located close to the open end of the elongated cavity86and the narrow side of the cone-shaped body is located close to the closed end of the elongated cavity86. In this case, the outer wall of the cone-shaped body is more upright, i.e., less inclined with respect to the axis of the DC motor, than the cone shaped wall88.