Drive train assembly for a personal care device

Abstract

According to an embodiment, a drivetrain assembly (1) for a personal care device (10) is provided. The drivetrain assembly (1) includes a shaft (4), a frame (4) including an opening in a surface (4a) of the frame (4) with a shaft (2) extending through the opening, and an abutment (3) provided in cooperation with the shaft (2). An engagement surface (3a) of the abutment (3) is configured to engage the surface (4a) of the frame (4) such that relative movement between the frame (4) and the shaft (2) in a given direction (d) beyond a threshold distance is inhibited.

Description

Technical Field

[0001] Embodiments of the present invention generally relate to motors for personal care devices, such as, for example, power toothbrushes, power shavers, and skin care devices.

Background Art

[0002] The drive train within a personal care device is an electromagnetic module that creates the necessary motion of the device. In a power toothbrush, the drive train creates the reciprocating motion of the brush head. The drive train includes a motor that includes a rotor and a stator, and a shaft (output shaft, drive shaft).

[0003] Personal care devices, such as power toothbrushes, are generally sensitive to drop events, i.e., being dropped by the user or falling from a countertop or similar high surface. A scenario that can particularly damage a personal care device is when the personal care device falls onto a ceramic floor (or similar hard surface) and the shaft of the drive train impacts directly onto the ceramic floor. In this case, the drop force applied to the shaft can be up to several kN, which can severely damage the personal care device.

[0004] As described above, the shaft is provided as part of the drive train, and the drive train of a personal care device is sensitive to drop forces such that the drive train may fail as a result of axial drops onto the shaft.

Summary of the Invention

Problems to be Solved by the Invention

[0005] It is desirable to provide a personal care device, such as a power toothbrush, with drop protection.

Means for Solving the Problems

[0006] According to an embodiment of the first aspect, a drive train assembly for a personal care device is provided, the drive train assembly including a shaft, a frame, and an abutment, the frame including an opening in a surface of the frame, the shaft extending through the opening, the abutment being provided in cooperation with the shaft, and an engagement surface of the abutment being configured to engage a surface of the frame such that relative movement between the frame and the shaft in a given direction beyond a threshold distance is inhibited.

[0007] Thus, according to an embodiment of the present invention, the abutment is provided to engage the frame of the drive train such that movement of the shaft relative to the frame is inhibited (hindered, blocked, or obstructed). That is, the abutment is provided at a position on the shaft that allows the shaft to move in a given direction to a specific position (threshold distance) at which the abutment engages the frame to prevent / inhibit further movement of the shaft. More specifically, the engagement surface of the abutment engages the surface of the frame through which the shaft extends.

[0008] Accordingly, the abutting portion provides a drop protection element that protects vulnerable elements of the drive train by changing the direction of the path of the force applied to the shaft, and changing the direction of the path of the force applied to the shaft moves the shaft away from the vulnerable / sensitive elements of the drive train in a given direction. Once the shaft moves a threshold distance, the path of the force is redirected through the frame by engagement of the abutting portion with the surface of the frame. Since the path of the force applied to the shaft is redirected away from the sensitive components of the drive train, there is a lower likelihood of component failure in the event that the personal care device is dropped. Thus, the threshold distance may be considered the distance that the shaft is allowed to move before the path of the force is redirected through the frame via the abutting portion. The threshold distance may be, for example, 0.2 mm (+ / - 0.05 mm). The path through the frame may be considered a robust path that bypasses the vulnerable components of the drive train.

[0009] As described above, the abutting portion abuts against the frame to prevent the shaft from moving beyond the threshold distance. More specifically, the engaging surface of the abutting portion abuts against the surface of the frame through which the shaft extends. The abutting portion may be considered an interfering element, stop, block, restraint, or obstructing body. The shaft may be considered an output shaft or a drive shaft. The shaft is disposed within the drive train assembly such that the shaft extends through an opening (hole, aperture, passage, slot) in the surface of the frame configured for the abutting portion to engage. The abutting portion is provided in cooperation with the shaft such that the abutting portion moves with the shaft, i.e., the abutting portion and the shaft move together, cooperate, or move as a unit.

[0010] The given direction may be along the longitudinal axis of the shaft, and thus, the shaft may move along the longitudinal axis relative to the frame over a threshold distance. The longitudinal axis of the shaft may be considered as the axial direction of the shaft. The movement of the shaft in the given direction may be caused by the application of a force to the shaft. For example, the force may be a dropping force caused by dropping the personal care device such that the shaft contacts a hard surface and moves the shaft in a given direction along the longitudinal axis of the shaft. The movement of the shaft need not be exclusively in the given direction, but it is movement in the given direction that exceeds a threshold distance that causes the engagement of the engaging surface of the abutting portion with the surface of the frame.

[0011] According to a preferred embodiment, the abutting portion is a collar, and the collar includes a body having an inner diameter corresponding to the diameter of the shaft, and an engaging portion that protrudes from the body and is configured to provide an engaging surface. If the abutting portion is a collar, the collar may be disposed on the shaft to provide cooperation between the shaft and the collar such that the shaft extends through the collar. That is, the collar includes an opening or core configured to receive the shaft. Accordingly, the inner diameter of the body of the collar may correspond to the diameter of the shaft such that the shaft receives the collar and the collar fits snugly on the shaft. Accordingly, the diameter of the shaft may be slightly smaller than the inner diameter of the body of the collar. Accordingly, the inner diameter of the body and the diameter of the shaft may be interdependent or complementary such that the inner diameter of the body may determine the diameter of the shaft or vice versa.

[0012] Different portions of the shaft may have different diameters. If this is the case, the inner diameter of the body of the collar may correspond to the diameter of the shaft at the location where the collar is disposed. The inner shape of the collar may correspond to the outer shape of the shaft at the location where the collar is disposed. That is, the shape of the cross-section of the shaft may match the shape of the opening of the cross-section of the collar. The collar may be considered a flanged collar, a sleeve, or a bearing. If the collar is considered a flanged collar, the flange may be the engaging portion.

[0013] The colored engaging portion extends from the body such that it is configured to engage with the surface of the frame. Thus, it is clear that the engaging portion protrudes beyond the opening in the surface, and thus the overall diameter or width of the color including the engaging portion is greater than the width of the opening. The engaging portion may be considered a protrusion or lip, or multiple protrusions or lips.

[0014] The abutting portion may be provided as a ring or washer, or any other component that can cooperate with the shaft and engage with the frame. The abutting portion may be formed as part of the shaft. For example, the shaft may extend beyond the opening in the frame and include one or more protrusions configured to engage with the surface of the frame to provide an engaging surface. Similarly, widening the width of the shaft may be presented to engage with the frame and provide the abutting portion and the engaging surface. If the abutting portion is provided as part of the shaft, the drive train may be assembled to position the shaft relative to the frame in front of the rotor assembly such that a small gap is provided between the surface of the frame through which the shaft extends and the engaging surface of the abutting portion.

[0015] Furthermore, the body of the color may have an outer diameter corresponding to the width of the opening. That is, the outer diameter of the body may correspond to the width of the opening such that the body can fit into the opening with little or no friction, i.e., such that the opening receives the body of the abutting portion. Thus, the outer diameter of the body may be slightly smaller than the width of the opening to allow a gap for the body to fit into the opening without engaging the edge of the opening. Thus, the outer diameter of the body and the width of the opening may be interdependent or complementary such that the outer diameter of the body may determine the width of the opening or vice versa.

[0016] Of course, it will be understood that the width of the opening relates to the size of the opening across the cross-section of the opening that receives the color. If the opening is provided as a circular opening, the width of the opening refers to the diameter of the opening. Receiving the body of the color in the opening may prevent lateral movement of the shaft within the opening in one or more directions, i.e., movement in (a plurality of) directions substantially perpendicular to a given direction. The shape of the opening may at least partially match the outer shape of the color such that the opening is configured to receive the body of the color.

[0017] The drive train assembly may include a motor including a rotor and a stator. The rotor may include a rotor surface, the stator may include a stator surface disposed on the opposite side of the rotor surface, and the threshold distance may be less than the distance between the stator surface and the rotor surface. The rotor and stator of the motor are separated by an air gap, and the distance between the stator surface and the rotor surface may define the air gap of the motor. The shaft may be attached or connected to the rotor such that movement of the shaft also causes movement of the rotor toward the stator and a reduction in the air gap. Thus, if the threshold distance is shorter than the distance between the rotor surface and the stator surface, movement of the shaft and rotor is suppressed by abutment before the rotor surface contacts the stator surface. Thus, engagement of the abutment and the frame may prevent the air gap of the motor from closing.

[0018] The threshold distance may preferably correspond to a predetermined force applied to the shaft in a given direction. That is, the threshold distance may correspond to or be equal to the distance that the shaft moves in the given direction when the predetermined force is applied to the shaft. Accordingly, the abutting portion may be provided at a position on the shaft that prevents movement of the shaft beyond a specific point in response to the force applied to the shaft. If a force smaller than the predetermined force is applied to the shaft, the distance that the shaft moves may be shorter than the threshold distance so that the abutting portion does not engage with the frame. If a force greater than the predetermined force is applied to the shaft, the shaft is prevented from moving further than the threshold distance by contact of the abutting portion with the surface of the frame.

[0019] The predetermined force may correspond to a force considered to be the safety limit of sensitive components within the drive train. That is, the predetermined force may be an acceptable force for the sensitive components of the drive train such that the likelihood of component failure due to the application of the predetermined force to the shaft is low. For forces applied to the shaft up to the predetermined force, the abutting portion does not engage with the surface of the frame, and the force path passes through components of the drive train such as the shaft and the motor. Accordingly, the predetermined force, and forces less than the predetermined force, may be forces that the components of the drive train can withstand without failure. For forces greater than the predetermined force, since the abutting portion engages with the frame, the force path is redirected away from the components of the drive train through the frame.

[0020] According to an embodiment of the present invention, the shaft and the abutting portion may be configured to move together between a primary position and a secondary position relative to the frame. The engagement surface of the abutting portion and the surface of the frame need not engage in the primary position, and the engagement surface of the abutting portion and the surface of the frame may engage in the secondary position. The threshold distance may correspond to or be equal to the distance between the engagement surface of the abutting portion and the surface of the frame in the primary position.

[0021] The primary position may be considered as the position of the shaft and the abutting portion during normal operation. At this position, a gap is provided between the engaging surface of the abutting portion and the surface of the frame. The secondary position may be considered as the position of the shaft when a predetermined force such as a dropping force is applied to the shaft. At the secondary position, the shaft and the abutting portion have moved in a given direction such that there is no gap between the engaging surface of the abutting portion and the surface of the frame, and the two surfaces are in contact. The engagement of the surfaces inhibits further movement of the shaft and the abutting portion.

[0022] Thus, when a force is applied to the shaft to move the shaft and the abutting portion in a given direction, the shaft and the abutting portion move from the primary position, and the distance between the engaging surface of the abutting portion and the surface of the frame decreases. When the force is increased to a predetermined force or more, the abutting portion and the shaft reach the secondary position. The distance between the engaging surface of the abutting portion and the surface of the frame in the primary position is the threshold distance. That is, the threshold distance is the distance that the engaging surface of the abutting portion moves between the primary position and the secondary position.

[0023] The abutting portion may preferably be fixed to the shaft. That is, the cooperation between the shaft and the abutting portion may be achieved by fixing the abutting portion to the shaft. The abutting portion may be fixed to the shaft by any suitable means, such as by laser welding. The position of the abutting portion on the shaft may be determined by the position of the shaft relative to the frame and the threshold distance. The threshold distance may be 0.2 mm or less.

[0024] According to an embodiment of the second aspect, a personal care device including the drive train assembly according to the above aspect of the present invention is provided. For example, the personal care device may be an oral care device such as an electric toothbrush, an electric shaver, or a skin care device such as a skin massager. Embodiments of the present invention may be applied to any personal device including a shaft on which a relatively significant force, such as a dropping force due to dropping of the device, is likely to act.

[0025] Accordingly, embodiments of the present invention extend to a drive train assembly and a personal device including the drive train assembly. The configuration of the first aspect is applied mutatis mutandis to the second aspect, and vice versa.

[0026] The present invention extends to a method aspect corresponding to the apparatus aspect.

[0027] In particular, according to an embodiment of the third aspect, a method of manufacturing a drive train assembly for a personal care device is provided, the method comprising elastically attaching a shaft to a frame of the drive train assembly such that the shaft extends through an opening in a surface of the frame; disposing an abutment in movable engagement (movable engagement) with the shaft at a first position on the shaft such that an engagement surface of the abutment engages a surface of the frame; applying a predetermined force to the shaft in a given direction along the longitudinal axis of the shaft such that the shaft moves relative to the frame in the given direction and the abutment moves to a second position on the shaft due to the engagement of the engagement surface of the abutment and the surface of the frame; releasing the predetermined force applied to the shaft such that the shaft moves in a direction opposite to the given direction and the abutment moves with the shaft such that the abutment remains at the second position on the shaft and the engagement surface of the abutment no longer engages the surface of the frame; and fixing the abutment to the shaft at the second position.

[0028] Accordingly, a drive train assembly according to an embodiment of the present invention may be manufactured using the above method. The manufacturing method enables a small predetermined distance with precision to be provided between the engagement surface of the abutment and the surface of the frame. This distance corresponds to (or is equal to) the distance by which the shaft moves when the predetermined force applied to the shaft is released, and this distance may be considered equal to the threshold distance described above. That distance depends on the force applied to the shaft and the elasticity of the shaft mounted within the frame.

[0029] In the manufacturing method, a predetermined force is applied to the shaft, which moves the abutting portion from a first position on the shaft to a second position on the shaft due to engagement with the surface of the frame. The shaft is elastically mounted within the frame such that when the predetermined force is no longer applied to the shaft, the shaft returns to a position (equal or similar) corresponding to the position the shaft was in before the force was applied. The movement of the shaft is movement relative to the frame.

[0030] The abutting portion is movably engaged with the shaft such that the two elements move together, provided that the movement of the abutting portion with the shaft due to engagement with the frame is not impeded. If the abutting portion engages the surface of the frame, the movable engagement of the shaft and the abutting portion allows the abutting portion to move along the shaft when a force is applied to the shaft in a given direction. That is, the abutting portion contacts the surface of the frame and does not at least completely pass through an opening in the surface of the frame, so that when the shaft moves relative to the frame in a given direction, the abutting portion moves along the shaft to a second position. Thus, when the abutting portion and the frame are engaged, it may be considered that the shaft moves relative to the abutting portion. The movement of the abutting portion from the first position to the second position is in a direction opposite to the given direction. This is because the shaft is moving in the given direction. The movable engagement of the abutting portion and the shaft means that when the force is released from the shaft and the shaft moves in a direction opposite to the given direction, the abutting portion moves with the shaft. This is because the movement of the abutting portion is not impeded by the frame, i.e., the abutting portion moves away from the frame with the shaft, so the abutting portion no longer engages the frame.

[0031] In other words, the engagement of the frame and the abutting portion prevents the abutting portion from moving with the shaft when a force is applied to the shaft and the shaft moves relative to the frame in a given direction. Conversely, after the force is released from the shaft, when the shaft returns to its starting position, the movement of the shaft is in a direction opposite to the given direction, and the abutting portion moves with the shaft. Since the shaft moves away from the frame, there is no impedance to the movement of the abutting portion together with the shaft. Therefore, due to the engagement of the shaft and the abutting portion, the abutting portion remains in the second position and moves with the shaft.

[0032] The distance between the first position and the second position of the abutting portion defines a threshold range of movement of the shaft relative to the frame. Once the abutting portion is fixed to the shaft, the abutting portion inhibits the shaft from moving in a given direction beyond the threshold distance when a force is applied to the end of the shaft.

[0033] The abutting portion may be a collar including a body having an inner diameter corresponding to the diameter of the shaft and an engaging portion protruding from the body and configured to provide an engaging surface. The collar may be arranged in movable engagement with the shaft by sliding the collar on the shaft. Thus, the shaft may receive the collar such that the shaft extends through the opening of the collar. To provide a movable engagement between the shaft and the abutting portion, the inner diameter of the body of the collar may be configured with the diameter of the shaft to provide a snug fit of the collar on the shaft. Thus, the inner diameter of the body may be slightly larger than the diameter of the shaft. Thus, the inner diameter of the body and the diameter of the shaft may be interdependent or complementary such that the inner diameter of the body may determine the diameter of the shaft or vice versa.

[0034] Furthermore, if the abutting portion is provided as a collar, the body may have an outer diameter corresponding to the width of the opening on the surface of the frame. The width of the opening may be considered, for example, as the diameter of the opening if the opening is provided as a hole. Therefore, the outer diameter of the collar body may correspond to the width of the opening on the surface of the frame such that the collar body may be received in the opening and an interference fit may be provided between the body and the opening. Therefore, the outer diameter of the collar body may be slightly smaller than the width of the opening on the surface of the frame. Thus, the outer diameter of the body and the width of the opening may be interdependent or complementary such that the outer diameter of the body may determine the width of the opening or vice versa.

[0035] Therefore, the collar body may extend through the opening on the surface of the frame and fit snugly into the opening, so that the lateral movement of the shaft within the opening may be suppressed by the collar body. Of course, since the engaging portion of the collar provides the engaging surface of the abutting portion that engages with the surface of the frame, it is clear that the engaging portion of the collar does not at least completely extend or pass through the opening of the frame. Therefore, the total diameter of the collar including the engaging portion may be considered to be larger than the width of the opening.

[0036] The abutting portion may be fixed to the shaft at the second position by any suitable means. For example, the abutting portion may be fixed to the shaft at the second position by laser welding.

[0037] The predetermined force may correspond to the force considered as the safety limit for the sensitive components within the drive train. That is, the predetermined force may be the force that the sensitive components can withstand without failure or malfunction. The predetermined force may be 50 N or less.

[0038] Therefore, it may be understood that embodiments of the present invention may provide means for preventing movement of the shaft relative to the frame beyond an acceptable distance. The engagement of the contact portion and the frame may, for example, redirect the path of the force applied to the shaft away from the sensitive components of the drive train in order to protect the sensitive components in the event of axial drop of the shaft. As discussed above, the manufacturing method according to embodiments of the present invention may enable the distance between the abutting portion and the frame to be set to an appropriate distance.

Brief Description of the Drawings

[0039] Embodiments of the present disclosure may take the form of various components and arrangements of components as well as various steps and arrangements of steps. Accordingly, the drawings are for the purpose of illustrating various embodiments and should not be construed as limiting the embodiments. In the figures, like reference numerals refer to like elements. Additionally, it should be noted that the figures may not be drawn to scale.

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Mode for Carrying Out the Invention

[0040] Embodiments of the present disclosure, as well as their various configurations and advantageous details, will be more fully described with reference to the non-limiting examples described and / or illustrated in the drawings and detailed in the following description. It should be noted that the configurations illustrated in the drawings are not necessarily drawn to scale, and the configuration of one embodiment may be used with other embodiments, even if not explicitly described herein, as will be recognized by those skilled in the art. Descriptions of well-known components and processing techniques may be omitted so as not to unnecessarily obscure the embodiments of the present disclosure. The examples used herein are merely intended to facilitate understanding of how embodiments of the present invention may be implemented and to further enable those skilled in the art to do the same. Accordingly, the examples herein should not be construed as limiting the scope of the embodiments of the present disclosure, which is defined only by the appended claims and the applicable law.

[0041] It is understood that embodiments of the present disclosure are not limited to the specific methodologies, protocols, devices, apparatus, materials, uses, etc. described herein, as these may vary. It should also be understood that the terms used herein are for the purpose of describing only specific embodiments and are not intended to limit the scope of the claimed embodiments. It should be noted that, as used in this specification and the appended claims, singular expressions include plural references unless the context clearly indicates otherwise.

[0042] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of the present disclosure belong. Preferred methods, devices, and materials are described, but any methods and materials similar or equivalent to those described herein may be used in the practice or testing of the embodiments.

[0043] As described above, it is desirable to provide a personal care device with drop protection. Means for reducing drop forces have been considered in the art, and such methods rely on reducing the axial stiffness of the drive train to limit the effects of axial drops, slow down impacts, and average out impact forces over time.

[0044] FIG. 1 graphically shows the relationship between drop force and reduction in axial stiffness. As can be seen from the drop model of FIG. 1, the drop force may be reduced by reducing the stiffness of the drive train. Thus, reducing the axial stiffness of the drive train in a device such as an electric toothbrush reduces the peak drop force but makes it more sustained. A lower drop force is less likely to cause internal damage to the electric toothbrush. In the simplified model of FIG. 1, stiffness can be seen as the (reciprocal) summation of the contact stiffness of the drive train (e.g., with the floor) and the internal stiffness.

[0045] FIGS. 2a - 2c show exemplary models of the impact force resulting from dropping a device onto a surface such as the floor. FIG. 2a shows a device of mass m dropping from a height h. The drive train has a stiffness of k_DT, the floor has a contact stiffness of k_floor, and the device has no velocity at this point. In FIG. 2b, the device is in contact with the floor. At this point, the two springs may be (reciprocally) summed into one spring k_total. At the instant just before contact, the velocity is at a maximum. In FIG. 2c, the deflection of the spring is at a maximum and the velocity is zero since all of the energy has been absorbed by the spring. The spring force scales (increases or decreases) with the square root of the total stiffness and the mass. Thus, reducing the stiffness of the device reduces the magnitude of the drop force.

[0046] Figures 3a and 3b show a power toothbrush 90 with reduced axial rigidity. In the power toothbrush 90 of FIGS. 3a and 3b, at least one spring 92 is provided to reduce the impact force (indicated by the arrow in FIG. 3b) and protect the vulnerable components 91 of the drive train. However, reducing the axial rigidity of the drive train has many drawbacks. First, the design complexity increases. This is because additional components and / or more complex components are required to achieve low rigidity in the axial direction while maintaining the main functions of the drive train. Second, when the rigidity decreases, the volume requirements of the device increase. This is because more space is required for the drive train elements to slide back.

[0047] An alternative strategy for reducing the effects of axial drops is to transmit the impact force to insensitive components within the drive train configuration. This can be achieved by closing the gap between the shaft hub and the frame of the drive train. Closing such a gap effectively redirects the force path away from the most vulnerable parts within the drive train. FIGS. 4a and 4b show a power toothbrush 90 including such a structure, with a gap provided between the shaft hub 94 and the frame 93 in FIG. 4a and a closed gap shown in FIG. 4b.

[0048] However, such an approach has many drawbacks. Due to the tolerances in the drive train, it is difficult to achieve in manufacturing the required gap size, which ideally should be as small as possible to limit the forces passing through the drive train. Larger gaps mean that higher forces are applied to the drive train before the gap is closed. Thus, higher forces are applied to the drive train and the elastic components of the drive train may be damaged.

[0049] Therefore, it is desirable to overcome the drawbacks of the above approaches and provide a drive train assembly with fall prevention.

[0050] FIG. 5 is a block diagram of a personal care device according to a general embodiment of an aspect of the present invention. The personal care device 10 includes a drive train assembly 1 according to an embodiment of the present invention. The personal care device 10 may be, for example, an oral care device such as an electric toothbrush, or may be a skin care device such as an electric shaver or a skin massager.

[0051] FIG. 6 shows an exemplary personal care device 10 in which the teachings of the present disclosure may be implemented. The personal care device of FIG. 6 is in the form of an electric toothbrush (powered toothbrush), but this is not limiting, and it will be understood that the teachings of the present disclosure may be implemented in other devices including a motor. For example, the present teachings may be applied to personal care devices such as tongue cleaners, shavers, hair clippers or trimmers, hair removal devices, or skin care devices. The personal care device 10 has an attachment structure 116 and a handle portion 112. The handle portion 112 has a motor 11. In one embodiment, the attachment structure 116 includes, or is, a replaceable attachment. That is, the attachment structure 116 may be removed from the personal care device 10 and exchanged for another attachment structure 116. The personal care device 10 preferably includes, or is, an electric toothbrush, and the attachment structure 116 may include a brush head 118. The handle 112 includes a drive train 1 and a drive shaft 2. The drive shaft 2 extends into the attachment structure 116 from the distal end of the handle 112 when the attachment structure 116 is attached to the handle 112.

[0052] The motor 11 may include a motor controller (i.e., control electronics), which may be any suitable controller, microcontroller, processor, power supply, and / or other electronics that provide power and control signals, or any combination thereof, for implementing various functions as further discussed herein. In an embodiment, the motor 11 may be configured to provide and control the operation or operations of the drive train 1 to generate mechanical stimulation. The mechanical stimulation may include vibrations or other movements at high frequencies, e.g., frequencies greater than 50 Hz, and, e.g., frequencies within the range of 250 - 300 Hz. The drive train 1 and the drive shaft 2 may be provided as part of a drive train assembly according to an embodiment of the present invention.

[0053] Still referring to FIG. 6, the distal end of the attachment 116 may include an operating component 120 configured according to the requirements of a particular use of the attachment 116. In the example of FIG. 6, the personal care device is an electric toothbrush, and the operating component 120 is a toothbrush head. However, it can be understood that the operating component may be different for different types of personal care devices. During operation, in response to the motor 11 operating to control the operation of the drive train 1 and the drive shaft 2 to generate mechanical stimulation, the attachment structure 116 performs a cleaning operation of the operating component 120.

[0054] Figures 7a and 7b show a configuration according to an embodiment of an aspect of the present invention. The personal care device 10 of Figures 7a and 7b includes a drive train assembly 1. The drive train assembly 1 includes a shaft 2, an abutment 3 (abattement), and a frame 4. The abutment 3 acts in cooperation with the shaft 2 so as to provide a gap 9 between an engagement surface 3a of the abutment 3 and a surface 4a (frame surface) of the frame 4. In this embodiment, the gap 9 corresponds to a threshold distance such that the shaft 2 may move in a given direction by the threshold distance in order to close the gap 9. That is, the shaft 2 and the abutment 3 may move towards the frame 4. When the gap 9 is closed, the abutment 3 engages with the frame 4, preventing further movement of the shaft 2 in a given direction. Accordingly, the force flow of the force applied to the shaft 2 that moves the shaft 2 in a given direction is directed away from the sensitive component 91 of the drive train through the frame 4.

[0055] Figure 7a shows an initial position of the shaft 2 and the abutment 3, which may be considered as the position during normal operation, i.e., the primary position. In Figure 7b, a force F is applied to the shaft 2, which moves the shaft 2 and the abutment 3 together in a predetermined direction, as a result of which the gap 9 is closed and the engagement surface 3a of the abutment 3 engages with the surface 4a of the frame 4 along which the shaft 2 extends. This position may be considered as the drop position, i.e., the secondary position, reflecting a drop event of the personal care device 10 including the drive train assembly 1.

[0056] The abutment 3 is a component that acts as a fall protector. The abutment 3 operates in cooperation with the drive train shaft (rotor) so as to effectively redirect the force flow away from the sensitive components inside the drive train and is configured to contact the drive train frame when the personal care device falls. Due to the configuration of the abutment, the shaft, and the frame, a very small gap may be provided between the abutment (fall protector) and the frame of the drive train (drive train frame).

[0057] Figure 8 shows a part of a drive train assembly according to an embodiment of an aspect of the present invention. The abutting portion 3 is provided in cooperation with the shaft 2. A gap 9 is provided between the engaging surface 3a of the abutting portion 3 and the surface 4a of the frame 4. The gap 9 corresponds to a threshold distance, and the shaft can move in a given direction D over the threshold distance before further movement is suppressed by the engagement between the abutting portion 3 and the frame 4.

[0058] In the embodiment shown in Figure 8, the abutting portion 3 is provided as a collar (ring) disposed on the shaft 2, although other configurations are possible. The body of the collar corresponds to the opening 4b of the frame 4 such that the body of the collar is at least partially received within the opening 4b. The collar further includes a lip, projection, or engaging portion that extends from the body of the collar and extends beyond the opening 4b of the frame 4. The engaging portion provides an engaging surface 3a configured to engage the surface 4a of the frame 4.

[0059] Figures 9 to 11 show individual components of a drive train assembly according to an embodiment of an aspect of the present invention. Specifically, Figure 9 shows a schematic view of a part of the shaft 2 according to an embodiment of an aspect of the present invention, Figure 10 shows a schematic view of a part of the frame 4 according to an embodiment of an aspect of the present invention, and Figure 11 shows a schematic view of the abutting portion 3 according to an embodiment of an aspect of the present invention. As shown in Figure 10, the frame 4 includes a frame opening 4b, which is an opening of the frame 4 through which the shaft 2 extends when the drive train assembly is configured. The frame 4 further includes a frame surface 4a. As shown in Figure 11, the abutting portion 3 includes a body 3b and an engaging portion 3c. The abutting portion 3 further includes an engaging surface 3a configured to engage or contact the frame surface 4a of the frame, and the engaging surface 3a is the surface of the engaging portion 3c. Thus, when the drive train components are assembled, the engaging surface 3a is disposed opposite (i.e., facing) the frame surface 4a. The components of Figures 9 to 11 may be the components of the drive train assembly shown in Figure 8.

[0060] Accordingly, embodiments of the present invention may utilize the existing (usually low) axial compliance in the drive train. The abutting portion is arranged as an adapter on the shaft at a position where a very small gap to the frame of the drive train is provided. As shown in FIG. 7(b), in the case of a drop event, the small gap may be closed. The distance between the abutting portion and the frame may be 0.2 mm or less. The air gap provided by embodiments of the present invention may be smaller than the air gaps provided in alternative devices known in the art, such as the air gap of FIG. 4. The air gaps in such devices known in the art are typically formed by two sub-assemblies that must be positioned relative to each other and include a plurality of elements. Due to assembly tolerances, it is difficult to achieve an air gap smaller than 0.5 mm. That is, if the nominal drive train design includes an air gap of 0.2 mm, there is a risk that a certain percentage of the manufactured devices will have a zero airgap (airgap closure). Airgap closure causes a large amount of friction between the drive train and the rotor, which leads to device defects.

[0061] A flowchart of a manufacturing method according to an embodiment of the present invention. First, in step S121, the shaft is elastically attached within the frame of the drive train assembly such that the shaft extends through an opening in the surface of the frame. In step S122, the abutting portion is disposed in a movable engagement (movable engagement) with the shaft at a first position on the shaft such that the engaging surface of the abutting portion engages the surface of the frame in this step. Next, in step 123, a predetermined force is applied to the shaft in a given direction along the longitudinal axis of the shaft such that the shaft moves relative to the frame and the abutting portion in a given direction. In step S124, the shaft moves relative to the frame in a direction opposite to the given direction such that the abutting portion remains at a second position on the shaft and the engaging surface of the abutting portion no longer engages the surface of the frame, and the given force applied to the shaft is released such that the abutting portion moves with the shaft. Finally, in step S125, the abutting portion is fixed to the shaft at the second position.

[0062] Figures 13a - 13d are a series of diagrams used to illustrate a method of manufacturing a portion of a drive train assembly according to an embodiment of an aspect of the present invention. By way of mere example, the method is described with reference to a portion of the drive train assembly shown in Figure 7. The drive train assembly shown in Figures 13a - 13d also includes a motor composed of a rotor 5 and a stator 6. The shaft 2 is connected to the rotor 5 such that movement of the shaft 2 (e.g., from the application of force to the shaft 2) also causes movement of the rotor 5. Similarly, movement of the rotor 5 (e.g., due to the operation of the motor) also causes movement of the shaft 2. The manufacture of these components of the drive train assembly is not described here.

[0063] As depicted in Fig. 13a, the abutting portion (fall protection device) 3 is movably engaged with the shaft 2 such that the abutting portion 3 may move along the shaft. In the embodiment shown in Figs. 13a to 13d, the abutting portion 3 is a collar that slides on the shaft 2. Due to the dimensions of the collar and the shaft 2, there is sufficient friction for the collar to grip the shaft 2, but it is possible to slide the collar on the shaft 2 without excessive friction that would prevent the collar from sliding along the shaft 2. Although the abutting portion is depicted as a collar, embodiments of the present invention are not limited to such a configuration. For example, the abutting portion may be a ring or washer, or any other component that may be movably engaged with the shaft and may engage with the frame.

[0064] As depicted in Fig. 13b, the abutting portion 3 is pressed against the frame 4 such that there is no space or gap between the abutting portion 3 and the surface 4a of the frame 4. That is, the abutting portion 3 is pressed against the frame 4 such that the engaging surface 3a of the abutting portion 3 contacts / engages with the surface 4a (frame surface) of the frame 4. This position may be considered the first position.

[0065] As shown in Fig. 13c, next, a predetermined preload force F is applied to the shaft 2 in a given direction (axial / longitudinal direction). Due to the compliance of the drive train, the shaft moves slightly rearward in the axial direction. That is, the shaft 2 moves slightly in the given direction. Since the abutting portion 3 engages with the surface 4a of the frame 4, the abutting portion 3 slides forward relative to the shaft. That is, the abutting portion 3 moves along the shaft in a direction opposite to the given direction.

[0066] Due to the compliance in the structure and engagement of the abutting portion 3 and the frame 4, the abutting portion 3 slides to a position corresponding to the applied force. This position may be considered the second position. As an example, the applied force F may be 50 N.

[0067] Next, as depicted in FIG. 13d, the axial force of the shaft 2 is released. Since the shaft 2 is elastically attached, when the force is released, the shaft 2 moves forward with respect to the frame 4. That is, the shaft 2 moves in a direction opposite to a given direction and returns to its starting position or a position close to its starting position. The contact portion 3 cooperates with the shaft 2 such that the contact portion 3 moves with the shaft 2 when the contact portion 3 moves in a direction opposite to a given direction. Accordingly, a small gap 9 is created between the contact portion (fall prevention tool) 3 and the frame 4. When the force is released due to the cooperation with the shaft 2, the contact portion 3 remains at the same position on the shaft 2. Thus, the contact portion 3 may be considered to remain in the second position.

[0068] Next, the contact portion 3 is fixed to a location on the shaft 2, i.e., a predetermined location on the shaft 2 at the second position, for example, by a laser weld portion 8. A small gap 9 that does not depend on assembly tolerances remains. The only factors affecting the gap are the compliance of the drive train and the preload gravity applied during step (3). As an example, a gap of 0.2 mm may occur between the contact portion 3 and the frame 4 when the force is released.

[0069] The rotor 5 includes a rotor surface 5a, and the stator 6 includes a stator surface 6a disposed on the side opposite to the rotor surface 5a. A distance is defined between the rotor surface 5a and the stator surface 6a. This distance may be longer than a threshold distance so that the movement of the shaft 2 with respect to the frame 4 is suppressed before the distance between the rotor surface 5a and the stator surface 6a becomes zero. That is, since the shaft 2 is attached to the rotor 5, the movement of the shaft 2 in a given direction moves the rotor 5 toward the stator 6, and the distance between the rotor surface 5a and the stator surface 6a decreases. Since the contact portion 3 prevents the shaft 2 from moving beyond the threshold distance, if the threshold distance (corresponding to the gap 9) is smaller than the distance between the rotor surface 5a and the stator surface 6a, the contact portion 3 prevents the rotor 5 from contacting the stator 6.

[0070] Accordingly, the method enables the abutting portion to be set and fixed at a position corresponding to a predetermined force and the resulting movement of the shaft. The force passing through the sensitive part of the drive train does not exceed the magnitude of the predetermined preload gravity F. That is, for example, when a force exceeding the predetermined force, such as a dropping force, is applied to the shaft, the abutting portion engages with the frame to prevent further movement of the shaft and redirect the force through the frame. Since the predetermined force may be relatively small compared to the maximum load limit of the sensitive component, a robust protection mechanism is created.

[0071] FIG. 14 shows a schematic view of a part of a drive train assembly according to an embodiment of an aspect of the present invention. The drive train assembly of FIG. 14 shows a configuration in which an abutting portion 3' is provided as an expansion of the shaft 2. More specifically, a part of the shaft 2 is wider than the opening of the frame 4 through which the shaft 2 extends such that the wider part of the shaft 2 provides the contact portion 3'. Thus, the wider part of the shaft 21 includes an engagement surface 3'a configured to engage with the surface 4a of the frame 4. A gap is provided between the engagement surface 3'a of the abutting portion 3' and the surface 4a of the frame 4. The gap corresponds to a threshold distance, and the shaft 2 can move in a given direction d over the threshold distance before further movement is suppressed by the engagement of the contact portion 3' and the frame 4. Since the abutting portion 3' is provided as a part of the shaft 2, the threshold distance is determined by the positioning of the shaft 2 relative to the frame 4. Thus, the shaft 2 may be positioned during the manufacturing process to provide the desired gap.

[0072] FIG. 15 shows a schematic view of a part of a drive train assembly according to an embodiment of an aspect of the present invention. The drive train assembly of FIG. 15 shows a configuration in which the abutting portion 3” is provided as a protrusion extending from the shaft 2. The protrusion protrudes from the surface of the shaft 2, so that the protrusion extends beyond the opening of the frame 4 through which the shaft 2 extends, and a wider portion of the shaft 2 provides the abutting portion 3”. Thus, each of the protrusions extending from the shaft 2 includes an engaging surface 3”a configured to engage with the surface 4a of the frame 4. Although two protrusions are shown in FIG. 15, the shaft 2 may include only one protrusion or more than two protrusions. A gap is provided between the engaging surface 3”a of each protrusion of the contact portion 3” and the surface 4a of the frame 4. The gap corresponds to a threshold distance, and the shaft 22 can move in a given direction over the threshold distance d before further movement is restricted by the engagement of the abutting portion 3” and the frame 4. Since the abutting portion 3” is provided as part of the shaft 2, the threshold distance is determined by the positioning of the shaft 2 relative to the frame 4. Thus, the shaft 2 may be positioned during the manufacturing process to provide the desired gap.

[0073] FIG. 16 shows a schematic view of a part of a drive train assembly according to an embodiment of an aspect of the present invention. The drive train assembly of FIG. 16 shows a configuration in which the abutting portion 3”’ is provided as a threaded collar, washer or nut configured to engage with the corresponding threaded portion 2a of the shaft 2. More specifically, a part 2a of the shaft 2 is threaded such that the threaded inner surface of the abutting portion 3”’ engages with the thread 2a of the shaft 2 and the abutting portion 3”’ may be screwed (rotated) to a desired position on the shaft 2. The abutting portion 3”’ is wider than the opening of the frame 4 through which the shaft 2 extends, and the abutting portion 3”’ includes an engaging surface 3”’a configured to engage with the surface 4a of the frame 4.

[0074] A gap is provided between the abutting portion 3”’a and the surface 4a of the frame 4. The gap corresponds to a threshold distance, and the shaft 2 can move in a given direction d over the threshold distance before further movement is inhibited by the engagement of the abutting portion 3”’ with the frame 4. Since the abutting portion 3”’ is screwed onto the shaft 2, the gap may be set and adjusted by screwing (rotating) the abutting portion 3”’ to a predetermined position. Thus, the shaft 2 may be positioned during the manufacturing process to ensure that the threaded portion 2a coincides with the opening of the frame 4, and the abutting portion 3”’ may be screwed onto the shaft 2 to a position where the distance between the abutting portion 3”’a and the surface 4a of the frame 4 corresponds to the desired gap. The gap may be adjusted by screwing the abutting portion 3”’ in or out to adjust the position of the abutting portion 3”’ on the shaft.

[0075] As may be appreciated from above, embodiments of the present invention may provide a drive train assembly and manufacturing method that includes fall protection. The drive train assembly and manufacturing method may be utilized in a personal care device such as an electric toothbrush. Embodiments of the present invention may overcome the disadvantages of the prior art discussed above.

[0076] Although only some exemplary embodiments have been described above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without substantially departing from the novel teachings and advantages of the embodiments of the present disclosure. The above-described embodiments of the present invention may advantageously be used independently of any other embodiment of the embodiments or in any realizable combination with one or more other embodiments of the embodiments.

[0077] Accordingly, all such modifications are intended to be included within the scope of embodiments of the present disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited functions, and are intended to cover not only structural equivalents but also equivalent structures.

[0078] In addition, reference numerals in parentheses in one or more claims shall not be construed to limit the claims. Words such as "comprising" and "comprises" do not exclude the presence of elements or steps other than those recited in any claim or the entire specification. A reference to an element in the singular does not exclude a reference to plural such elements and vice versa. One or more of the embodiments may be implemented by hardware including several distinct elements. In a claim of a device or apparatus listing several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used to advantage.

Claims

1. A drive train assembly for a personal care device, comprising: a shaft; a motor for driving the shaft; a frame for housing the motor; a contact portion fixed to the shaft and movable together with the shaft; the frame includes an opening in a distal surface of the frame facing an engagement surface proximal to the contact portion, and the shaft extends through the opening; the contact portion is provided to cooperate with the shaft such that a gap is formed between the engagement surface of the contact portion and the surface of the frame; the engagement surface of the contact portion is configured to engage the surface of the frame to close the gap such that relative movement between the frame and the shaft in a given direction along the longitudinal axis of the shaft exceeding a threshold distance corresponding to the gap is suppressed, and a force applied to the shaft to move the shaft in the given direction is redirected through the frame away from components inside the frame of the drive train assembly; A drive train assembly.

2. The contact portion is a collar, the collar comprising: a body having an inner diameter corresponding to the diameter of the shaft; an engagement portion protruding from the body and configured to provide the engagement surface; The drive train assembly according to claim 1.

3. The drive train assembly according to claim 2, wherein the body has an outer diameter corresponding to the width of the opening.

4. The motor includes a rotor and a stator, the rotor includes a rotor surface, the stator includes a stator surface disposed on the opposite side of the rotor surface, the threshold distance is less than the distance between the stator surface and the rotor surface; The drive train assembly according to any one of claims 1 to 3.

5. The drive train assembly according to any one of claims 1 to 4, wherein the threshold distance corresponds to a predetermined force applied to the shaft in the given direction.

6. The shaft and the contact portion are configured to move together between a primary position and a secondary position relative to the frame, the engagement surface of the contact portion and the surface of the frame do not engage in the primary position, the engagement surface of the contact portion and the surface of the frame engage in the secondary position. The threshold distance corresponds to the distance between the engagement surface of the contact portion at the primary position and the surface of the frame. The drive train assembly according to any one of claims 1 to 5. **Claim 7** The contact portion is fixed to the shaft. The drive train assembly according to any one of claims 1 to 6. **Claim 8** The threshold distance is less than 0.2 mm. The drive train assembly according to any one of claims 1 to 7. **Claim 9** A personal care device including the drive train assembly according to any one of claims 1 to 8. **Claim 10** A method of manufacturing a drive train assembly for a personal care device according to claim 1, comprising: Elastically attaching the shaft to the frame of the drive train assembly such that the shaft extends through an opening in the surface of the frame; Disposing the contact portion in movable engagement with the shaft at a first position on the shaft such that the engagement surface of the contact portion engages the surface of the frame; Applying a predetermined force to the shaft in a given direction along the longitudinal axis of the shaft such that the shaft moves relative to the frame in the given direction and the contact portion moves to a second position on the shaft due to the engagement of the engagement surface of the contact portion and the surface of the frame; Releasing the predetermined force applied to the shaft such that the shaft moves relative to the frame in a direction opposite to the given direction and the contact portion moves with the shaft, and the contact portion remains at the second position on the shaft and the engagement surface of the contact portion no longer engages the surface of the frame; Fixing the contact portion to the shaft at the second position. Method. **Claim 11** The contact portion is a collar, and the collar Comprises a body having an inner diameter corresponding to the diameter of the shaft; And an engagement portion protruding from the body and configured to provide the engagement surface. Disposing the contact portion in movable engagement with the shaft at a first position on the shaft by sliding the collar on the shaft. The method according to claim 10. **Claim 12** The method according to claim 11, wherein the body has an outer diameter corresponding to the width of the opening on the surface of the frame. **Claim 13** The method according to any one of claims 10 to 12, wherein the contact portion is fixed to the shaft at the second position by laser welding. **Claim 14** The method according to any one of claims 10 to 13, wherein the predetermined force is less than 50 N.

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