Abstract:
A toothbrush provides a head with bristles, a neck and a handle. An eccentrically rotational weight is engaged for rotation with a motor, the weight disposed within the head. The motor is disposed within the handle. The head and neck are integrally formed with a natural resonance frequency of vibration approximately equal to the rotational speed of the motor and synchronized therewith.

Description:
INCORPORATION BY REFERENCE 
   Applicant(s) hereby incorporate herein by reference, any and all U.S. patents, U.S. patent applications, and other documents and printed matter cited or referred to in this application. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The field of the invention is hand held electric appliances and more particularly electric toothbrushes. 
   2. Description of Related Art 
   The benefits of electric toothbrushes are well known. One type of electric toothbrush utilizes an eccentrically moving weight coupling to motor&#39;s rotating shaft to cause a handle of the toothbrush to vibrate, the vibration of the handle being transmitted to the bristles of the brush via a neck coupling the bristle portion/head of the brush to the handle. The use of such devices is not always desirable however, at least in part because of the relatively large amount of vibration required in the handle in order to get an acceptable amount of vibration of the bristles, and the corresponding high energy usage and the uncomfortable degree of vibration transferred to the hand of a person using such a brush. Examples of such prior art toothbrushes can be found in U.S. Pat. Nos. 3,685,080, 5,421,726, 5,651,157, 5,706,542, 5,718,667, and 5,706,542. An eccentric weight, as the term is used herein, is a weight whose center of mass is not on the center of rotation of the weight. 
   Unfortunately, current toothbrushes are constructed in a manner that is cost prohibited. Moreover, such toothbrushes are unduly cumbersome because of their weight, and size, and/or because of a battery charger accessory. Thus, there is a continuing need for affordable electric toothbrushes that are not unduly cumbersome, are relatively inexpensive and do not use excessive energy. 
   The following art defines the present state of this field: 
   Giuliani et al., U.S. Pat. No. 5,189,751 describes a vibrating toothbrush, which includes a toothbrush body and a lever arm having toothbrush bristles at one end thereof. The lever arm is mounted for pivotal movement at a pivot member, which is in the vicinity of the other end of the lever arm. In one embodiment, a pair of permanent magnets are provided at the other end of the lever arm, positioned side-by-side with opposite polarities. An electromagnet is provided to the rear of the lever arm. The electromagnet includes an E-core having top, bottom and center legs with a coil wound around its center leg which receives an alternating current driving signal from an oscillator/battery section. The frequency of operation is in the range of 150-400 Hz. The action of the alternating current in the electromagnet causes the lever arm to move about the pivot member, first in one direction and then in an opposing direction to provide the desired vibrating effect. 
   Hahn, et al., U.S. Pat. No. 5,987,681 describes an electric toothbrush with a handle, a brush head and a shank, which connects the handle to the brush head. A rotary motor is arranged in the handle and drives an unbalanced mass. The unbalanced mass driven by the motor is supported on one side or on both sides in the shank close to the brush head and is driven via an extended drive shaft, preferably an intermediate shaft, by the motor. 
   McDougall, U.S. Pat. No. 6,421,866 describes an electric toothbrush having a balanced mass provided on a shaft extension that rotates freely about a longitudinal axis, inside a cavity in a brush head. The shaft extension and the brush head are flexibly coupled to a drive shaft and to a remote end of a shank respectively. When the shaft is rotated by an electric motor in a handle, of the toothbrush, an offset stub axle, effectively at a remote end of the shaft extension and fitted to a bearing in the brush head, causes the brush head to vibrate. The shank is not caused to vibrate to any extent. 
   Wolf, Susan, Hendrix, Ph.D., Suzanne (1998).  Automated Toothbrush Comparison Statistical Report . Clinical Research Associates, describes an evaluation of 6 toothbrushes that was performed using two populations to determine if toothbrushes with sonic or ultrasonic capabilities reduce dental plaque, more effectively than a manual or other automated toothbrushes. The Sensonic (Teledyne) and Sonicare (Optiva) toothbrushes claim sonic capabilities and the Ultrasonex (Sonex) claims ultrasonic capabilities. Control toothbrushes were the Interplak (Corsair) and Ultra Plaque Remover (Braun), which are automated toothbrushes not claiming sonic or ultrasonic capabilities, and the Advantage (Oral-B) manual toothbrush. Population one consisted of 24 non-handicapped subjects, while Population two consisted of 24 institutionalized handicapped subjects. Non-handicapped subjects were included to represent the majority of the population, while handicapped subjects were included because they have been reported as having frequent problems with heavy plaque in their oral cavities due to lack of manual dexterity necessary for effective tooth brushing. 
   Staff. (1998, July). CRA Status Report: Toothbrushes, Sonic &amp; Ultrasonic.  CRA Newsletter . P. 2-3, provides a comparison between sonic, ultrasonic, and manual toothbrushes. CRA laboratory &amp; clinical studies compared plaque removal capability, test subject preferences, durability, &amp; maintenance of 6 different toothbrushes over a 1¼ year period. 
   The prior art teaches vibrating toothbrushes, rotary bristle toothbrushes, and laterally oscillating toothbrushes. The prior art also includes electric toothbrushes in common use such as the Advantage by Oral-B, Interplak by Conair, Sensoic by Teledyne, Sonicare by Optiva, Ultra PR by Braun and Ultrasonex by Sonex. However, the prior art does not teach the matching of the natural frequency of vibration of the toothbrush itself with the purposely generated vibration frequency of the operational engine of the toothbrush. The present invention fulfills these needs so as to enable low energy usage, low energy loss in the handle of the device, improved vibratory action in the bristles and other benefits, and provides further related advantages as described in the following summary. 
   SUMMARY OF THE INVENTION 
   The present invention teaches certain benefits in construction and use which give rise to the objectives described below. 
   The present invention is directed to a toothbrush that utilizes a rotating eccentric weight positioned in or near the head of the toothbrush to cause movement of the head relative to a handle of the toothbrush, and methods relating to same. Positioning the weight in or near the head produces a toothbrush having numerous advantages over manual toothbrushes as well as powered toothbrushes. Such advantages include (a) use of a relatively low power motor; (b) lighter appliance weight; (c) reduced handle vibration; (d) longer battery life; (e) higher reliability; and/or (f) disposability. The phrase “near the head” is used herein to indicate that the weight is at least closer to the head than to the body/handle. 
   Disposable embodiments are possible as the use of a low power motor permits the toothbrush to operate for longer periods without recharging its batteries. This may result in having a single battery or set of batteries last as long as the bristles of the brush. The use of a lower power motor, a simple movement mechanism, non-rechargeable batteries, and non-replaceable bristles permits the total cost of the brush to be brought to a level where it is reasonable to dispose of the toothbrush after the bristles wear out and/or batteries are drained. Making the toothbrush disposable permits the batteries to be permanently sealed inside the toothbrush which in turn increases safety while reducing manufacturing costs. 
   A primary objective of the present invention is to provide an apparatus and method of use of such apparatus that provides advantages not taught by the prior art. 
   Another objective is to provide such an invention capable of maximizing the amount of vibration energy delivered to the head. 
   A further objective is to provide such an invention capable of improved operation with long battery life. 
   A still further objective is to provide such an invention capable of inexpensive production. 
   A still further objective is to provide such an invention capable of replacement of a brush head. 
   Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate the present invention. In such drawings: 
       FIG. 1  is a longitudinal sectional view of a first toothbrush embodying the invention; 
       FIG. 2  is a series of schematic representations of the motion of a weight positioned on a shaft within the head of the toothbrush of  FIG. 1  as viewed from one end of the shaft; 
       FIG. 3A  is a schematic representation of the motion of the head of the toothbrush of  FIG. 1  for embodiments where the motion is circular/orbital; 
       FIG. 3B  is a schematic representation of the motion of the head of the toothbrush of  FIG. 1  for embodiments where the motion is in the direction of the bristles of a brush of the invention; 
       FIG. 3C  is a schematic representation of the motion of the head of the toothbrush of  FIG. 1  for embodiments where the motion is lateral to the direction of the bristles of the brush of the invention; 
       FIG. 4  is a partial sectional view of a second toothbrush embodying the invention; 
       FIG. 5A  is a graph showing the effects of tuning on toothbrush head vibration amplitude; 
       FIG. 5B  is a graph showing the effects of tuning on toothbrush head velocity; 
       FIG. 6  is a plan view of a removable brush of the invention; 
       FIG. 7  is a plan view of a neck and head of the invention with the removable brush shown partially and also fully installed on the head; 
       FIG. 8  is a side elevational view of the neck and head of the invention showing the removable brush in the partially installed position; and 
       FIG. 9  is a side elevational view of the neck and head of the invention showing the removable brush in the fully installed position. 
       FIG. 10  is a schematic diagram showing an end view of the head in two extreme positions of its vibration. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The above described drawing figures illustrate the invention in at least one of its preferred embodiments, which is further defined in detail in the following description. Referring first to  FIG. 1 , toothbrush  1000  comprises body  1100 , bristles  1200 , motion assembly  1300 , power source(s)  1400 , and control assembly  1500 . Body  1100  comprises head  1110 , neck  1120 , and handle  1130 . Head  1110  is that portion of body  1100  to which bristles  1200  are mounted. Neck  1120  is that portion of body  1100  that couples head  1110  to handle  1130 . Handle  1130  is that portion of body  1100  that is adapted to be gripped by a hand of a persen using toothbrush  1000 . Body  1100  also comprises body cavity  1101  that is subdivided into cavities corresponding to head  1110 , neck  1120 , and handle  1130 . The sub-cavities of body cavity  1101  are head cavity  1111 , neck cavity  1121 , and handle cavity  1131 . Motion assembly  1300  comprises motor  1310 , motor spindle  1311 , coupler  1312 , flexible wire shaft  1320 , shaft bearing  1321 , weight  1330 , and weight well  1331 . Power source  1400  comprises two AAA batteries. Control assembly  1500  comprises the switches and circuitry used to control the movement of weight  1330  by controlling the use of motor  1310 . 
   Distance D 1  is the distance from the tip of toothbrush  1000  to the center of mass of weight  1330 . Distance D 2  is the distance from the center of mass of weight  1330  to motor  1310 . Distance D 3  is the total length of the head  1110  and neck  1120  portions of body  1100 . Distance D 4  is the length of handle  1130 . 
   Body  1100  is preferably formed as a plurality of molded plastic pieces, the pieces coupled together in a manner which hermetically seals the body cavity  1101 . Sealing the various components of motion assembly  1300  and power assembly  1400  within body cavity  1101  is contemplated to increase the life of motion assembly  1300  and power assembly  1400  by preventing dirt, water, or other substances from affecting these parts and also prevents any chemicals or parts from the components adversely affecting a user of toothbrush  1000 . 
   Head  1110  and handle  1130  preferably has a size and shape suitable for being used in a manner similar to common toothbrushes in use. The handle cavity  1131  is preferably sized and dimensioned to securely hold power source  1400 . Head cavity  1111  is preferably sized and shaped to position and permit proper operation of the weight  1330  and shaft  1320 , and to properly position the weight well  1331  and shaft bearing  1321  of motion assembly  1300 . 
   Neck  1120  is preferably sized and dimensioned to provide a desired overall length and flexibility and to contain neck cavity  1121 . Neck cavity  1121  is preferably sized and dimensioned to allow flexible wire shaft  1320  to extend from the motor  1310  to the shaft bearing  1321  without having flexible wire shaft  1320  contact the sidewalls of neck cavity  1121 . It is contemplated that the structure of neck  1120  may vary between embodiments, with the variance in structure resulting in different motions for head  1110  as weight  1330  rotates. 
   Looking at  FIGS. 3A-3C , it is known that structural shape, material type, and wall thickness variations of neck  1120  will result in motions of head  1110  that may be in the direction of the bristles  1200 , iateral to the bristles  1200 , circular, or some combination of these motions. In  FIG. 3A , the motion M 1  of head  1110  is circular/orbital in that head  1110  moves along a path that is at least somewhat similar to the circle shown having a radius M1R, where movement distance M1V is approximately equal to movement distance M1H. In  FIG. 3B , the motion M 2  of head  1110  is in line with bristles  1200  in that movement distance M2V is substantially larger than the horizontal movement distance M2H. In  FIG. 3C , the motion M 3  of head  1110  is horizontal in that horizontal movement distance M3H is substantially larger than the vertical movement distance M3V. 
   Bristles  1200  are preferably permanently mounted to head  1110 . It an alternate embodiment, however, the bristles  1200  may be removeably mounted to head  1110  for ease of replacement. Similarly, head  1110  and neck  1120  may be removeably coupled to each other and/or neck  1120  may be removeably coupled to body  1130 . 
   Motion assembly  1300  is used to convert energy from power source(s)  1400  to movement of head  1110 . In the preferred embodiment, the motor spindle  1311  is coupled to flexible wire shaft  1320  by a coupling  1312  such as a flexible tube, or universal joint or other joint capable of isolating the head  1110  and the motor  1310  so that when power is applied to motor  1310 , spindle  1311  and flexible wire shaft  1320  rotate together. Weight  1330  is mounted to flexible wire shaft  1320  such that flexible wire shaft  1320  does not pass through the center of gravity of weight  1330  as can be clearly seen in  FIGS. 1 and 2 .  FIG. 2  illustrates the motion of weight  1330  as flexible wire shaft  1320  rotates to cause the head to move as illustrated in  FIGS. 3A-3C . Because weight  1330  is off center with respect to tis rotation, it wobbles generating lateral thrusts. Weight well  1331  permits weight  1330  to rotate without contacting any of the side walls of head cavity  1111 . The lateral thrusts of weight  1330  are transferred to head  1110  via shaft bearing  1321 . Shaft bearing  1321  is preferably chosen to minimize the noise generated by the rotation of flexible wire shaft  1320  and weight  1330 . In summary, while fixed to shaft  1320 , weight  1330  is rotatably mounted within toothbrush  1000  as shaft  1320  is caused to rotate within the toothbrush  1000 . 
   For improved motion of head  1110 , distance D 1  is less than distance D 2 . Preferably, distance D 2  is at least 50 mm or 2 inches. Similarly, distance D 1  is preferably less than 12.5 mm or 0.5 inches. Preferably, the ratio of D 2  to D 1  is at least 4:1. Preferably, the distance between weight  1330  and shaft bearing  1321  is minimal to maximize the transfer of motion of weight  1330  to head  1110 . Shaft bearing  1321  may also be positioned between weight  1330  and motor  1310  in an alternate embodiment. 
   Preferably, shaft  1320  and coupling  1312  are flexible so as to isolate the lateral thrusts of the weight  1330  from the handle  1100 , motor  1310  and power source  1400 . The amount of flexibility in shaft  1320  and coupling  1312  may vary, although it is preferred that as shaft  1320  is made stiffer, coupling  1312  is made more flexible and vice-versa. 
   Power source  1400  is preferably battery cells such as AAA size batteries. However, alternative embodiments may use different types of batteries or capacitors as power source  1400 . It is preferred that the choice of power source be made such that the amount of time that power source  1400  is able to adequately power motor  1310  is at least 8 hours, and preferably at least 9-12 hours. If usage is about 2 minutes per day, the operational life of the toothbrush is approximately 8 months for an 8 hour battery life, and 9-12 month for a 9-12 hour life. 
   Control assembly  1500  may comprise a simple switch used to complete or break an electrical connection (not shown) between power source  1400  and motor  1310 . Such connections are well known in hand held flashlights. However, alternative embodiments may use more complex means of motor control. 
     FIG. 4  illustrates an alternate embodiment having an angled neck. As shown in  FIG. 4 , toothbrush  2000  comprises body  2100 , bristles  2200 , motion assembly  2300 , power source(s)  2400 , and control assembly  2500 . Body  2100  comprises head  2110 , neck  2120 , and handle  2130 . Head  2110  is the portion of body  2100  to which bristles  2200  are mounted. Neck  2120  is the portion of body  2100  that couples head  2110  to handle  2130 . Handle  2130  is the portion of body  2100  that is adapted to be gripped by the hand of a person using toothbrush  2000 . Body  2100  also comprises body cavity  2101  that is subdivided into cavities corresponding to head  2110 , neck  2120 , and handle  2130 . The only sub-cavity of body cavity  2101  shown is handle cavity  2131 . Motion assembly  2300  comprises motor  2310  and motor spindle  2311 , as well as a coupler, flexible wire shaft, shaft bearing, weight, and weight well which are similar to those shown in  FIG. 1 . Power source  2400  comprises two AAA batteries. Control assembly  2500  comprises the switches and circuitry used to control the use of motor  2310 . 
   The use of either toothbrush  1000  or  2000  can be described as using an electric toothbrush having an eccentric weight located within a head of the toothbrush to rotate and, while the weight is rotating, using the toothbrush to brush teeth. More specifically, causing an eccentric weight to rotate comprises electrically connecting an electric motor to a power source so as to cause a motor spindle to rotate, the motor spindle causing a shaft to rotate, the shaft causing the eccentric weight to rotate and transfer its lateral thrusts to the head  2110  of the toothbrush  2000  thereby causing brushing action against teeth and gums. 
   In the present invention rotational energy imparted to the off center mounted weight  1330  is converted to side thrusting forces, i.e., away from the longitudinal axis of the head  1110  and neck  1120 , which causes the head  1110  and bristles  1200  to move laterally as previously described. Important parameters that are associated with the type and magnitude of such lateral movements are the amount of the off center weight  1330 , the speed of rotation of the shaft  1320 , the flexibility of the shaft  1320  in conjunction with the separation distance between the weight  1330  and the bearing  1321  because this distance is proportional to the diameter of the circle swept by the weight  1330 ; these all being proportion to the magnitude of the side thrust forces created and thus the magnitude of head movement. Stiffness of the head  1110  and the neck  1120  is inversely proportional to head movement. 
   As stated, because the side thrust forces are generated in the head  1110 , it is primarily the head  1110  that tends to be moved, which is desirable, however, the shaft  1320  and neck  1120  are flexible in order to provide vibrational isolation between the handle  1130  and the head  1110 , some of the energy created by the spinning weight  1330  is necessarily transmitted to the handle  1130  and therefore lost relative to the total energy potentially available for head movement. This is clearly undesirable and is minimized by fashioning the neck  1120  and head  1110  in such a manner that its natural resonance frequency (primary harmonic) is nearly the same as the rotational frequency of the off center mounted weight  1330 . When this is true the weight  1330  on each one-half rotation away from the bristles  1200  tends to flex the head  1110  away from the tooth surface (not shown), and when, on the next one-half rotation when the weight  1330  moves toward the bristles  1200  it tends to pull the head  1110  toward the tooth surface and this movement of the head  1110  is augmented by the natural flexing of the head  1110  toward the tooth surface due to the elastic restoring action of the material of the head  1110  and neck  1120 . The natural flextural movement of the head  1110  and neck  1320  are synchronized with the movement of the weight  1330 . 
   The result of tuning, as defined above, is shown in  FIGS. 5A and 5B .  FIG. 5A  is a plot of the magnitude of head  1110  excursion on the y axis versus time plotted on the x axis. It should be noted that the cycle time is constant, i.e., 0.00343 seconds per revolution. This is the rotational speed of the motor used; 17,500 rpm. However, as shown, the magnitude of the excursion of the head  1110  varies with its tuned reflex frequency. The greatest excursions were obtained when the neck and head were tuned to 17,500 cycles per minute (cpm). Smaller excursions were obtained with neck and head tuned to 10,000 cpm and 8,000 cpm respectively. As stated above, the head and neck are tuned by adjustment of the neck length, material stiffness, wall thickness and other physical parameters. As shown in  FIG. 5B  the velocity of the head of the synchronously tuned neck and head is significantly greater than the mistuned units. It may be shown that the synchronously tuned unit develops at least four-times the cleaning energy then does the least well tuned unit. 
     FIGS. 6-9  teach a preferred embodiment of the invention wherein a removable brush  3000  is attached to the head  1110  via a sliding engagement. The removable brush  3000  has a first engagement element  3010 , preferably a slot on its underside, while head  1110  has a second engagement element  1333 , preferably a finger conforming to the slot, so that the elements  1333  and  3010  are preferably interlocking as is known in the art when the brush  3000  is slid onto the head  1110 . A tab  3020  of the brush  3000  is positioned for engaging a tab receiver  1125  on the neck  1120  for holding the brush  3000  in place. When worn out, the brush  3000  may be removed and replaced with a substitute of the same design by merely snapping the tab  3020  away from the tab receiver  1125  and sliding the worn brush  3000  off the head  1110 , and then installing a new brush  3000  by reversing the process of removal. 
     FIG. 10  shows graphically the preferred embodiment of the invention where the center of mass  1112  of the head  1110  is laterally offset from the drive shaft  1320 . In this case, the head  1110  is caused to flex about its longitudinal axis transferring elastic spring energy as it oscillates from side to side in synchronization with the rotating weight  1330 , as shown in the figure with the head  1110  shown in solid line in the extreme left side oscillation position, and numeral  1110 ′ shown in broken line in the extreme right side oscillation position. 
   While the invention has been described with reference to at least one preferred embodiment, it is to be clearly understood by those skilled in the art that the invention is not limited thereto. Rather, the scope of the invention is to be interpreted only in conjunction with the appended claims and it is made clear, here, that the inventor(s) believe that the claimed subject matter is the invention.