Eccentric-and-oscillator engagement structure

The invention is directed to a device for converting a circular motion into a reciprocating motion, which provides for improved guiding of a drive pin arranged on an eccentric within a slide slot of a drive member. The slide slot is bounded by at least two flexurally elastic portions whose respective first end is not deflectable by the drive pin, whilst the area towards the respective second end is deflectable. The two portions extend parallel to each other in opposite directions.

This invention relates to a device for converting the rotary motion of an 
eccentric driven by a motor shaft into a reciprocating motion parallel to 
a first direction (y-y') according to the prior-art portion of patent 
claim 1. 
Such devices for converting the rotary motion of an eccentric into a 
reciprocating motion are employed in numerous appliances, in particular in 
electrically powered small appliances. Customary applications include the 
generation of reciprocation of a cutter assembly in a shaver or the 
translational motion of the toothbrush of a dental cleansing device. In 
such arrangements, the converter device is directly or indirectly 
connected to an implement such as a cutter assembly or a toothbrush 
attachment. 
From JP 4-82586 (82586/92) a device according to the prior-art portion of 
patent claim 1 is known. This device includes a rigid plate acting as 
drive member which is in engagement with the eccentric in that a drive pin 
arranged on the eccentric engages a slide slot provided on the drive 
member. 
The slide slot is formed by two parallel, yet relatively spaced, arms of a 
fork having their respective first ends secured to the drive member while 
their respective second ends point in a direction away from the rigid 
plate. In this device, the first and second ends of the fork arms lie 
opposite each other, forming a slide slot open on one end. The facing 
surfaces of the fork arms provide the boundary surface of the slide slot 
along which the drive pin rolls. With the eccentric rotating, the pressure 
which the drive pin exerts on the first fork arm causes the drive member 
to be deflected in a first direction y, and following the reversal of 
motion related to the direction y, the drive pin urges the second fork 
arm--and thus the drive member--into the opposite direction y', thus 
resulting in the reciprocating motion of the drive member parallel to a 
first axis y-y'. Thus, the circular motion of the eccentric is transmitted 
by the rolling motion of the pin along the boundary surfaces of the slide 
slot and converted into a translational motion. 
The fork arms of this converter device are at such a relative distance as 
to receive the drive pin between them with a predetermined amount of bias 
or clamping force. To this effect, the fork arms carry flexurally elastic 
portions--referred to as spring and cushioning means in JA 4-82586--whose 
ends are connected to the rigid plate and to the free end of the fork 
arms. The clamping force acts at its highest level when the drive pin is 
between the two first ends of the fork arms, it is at its lowest when the 
pin is between the two second ends of the fork arms. 
The bias exerted by the fork arms on the drive pin is intended to prevent 
clatter of the rotating drive pin between the fork arms, which clatter 
tends to occur after prolonged periods of use when the drive pin 
disengages from and impinges again on the boundary surface. On the one 
hand, such clatter is considered a disturbance by the user of the 
appliance, while on the other hand it conveys the impression that the 
appliance has a defect. The greater the relative spacing between the fork 
arms, that is, the longer the distance to be traveled by the drive pin 
until it impinges on the boundary surface, the louder the clatter. 
The amount of clamping force or bias exerted by the fork arms is limited by 
the greatly increased power level necessary in the presence of an 
excessive bias. A significantly increased bias, that is, a narrow relative 
distance of the fork arms, causes an extraordinary increase in power loss 
due to increased friction of the drive pin between the fork arms, as is 
the case in particular when the drive pin approaches first the ends of the 
fork arms and is enclosed therebetween. 
It will become apparent from the foregoing that the clamping force 
progressively increasing greatly along the slide slot from the second ends 
to the first ends of the fork arms, that is, the non-uniform pattern of 
the bias exerted on the drive pin by the fork arms, has a particularly 
adverse effect because the relative distance of the fork arms is not at 
random conformable to the drive pin because the disproportionately large 
clamping action between the first ends of the fork arms results in an 
excessive power loss. 
The spring or cushioning means proposed in JP 4-82856 with the aim to 
reduce clatter of the drive pin between the fork arms are only a temporary 
remedy, because the basic problem of lack of adaptation possibilities of 
the fork arms to the drive pin is not solved. Moreover, it is anticipated 
that these additional means which involve greatly increased assembly work 
become plastically deformed after prolonged use, thus failing to eliminate 
clatter lastingly. 
The present specification is directed to an embodiment of the device for 
converting the rotary motion of an eccentric into a reciprocating motion, 
in which the slide slot is arranged on the drive member, while the drive 
pin is arranged on the eccentric. It will be understood, however, that the 
same considerations apply also to an embodiment of the present invention 
in which the slide slot is provided on the eccentric and the drive pin is 
provided on the drive member. 
It is an object of the present invention to improve upon a converter device 
of the type described in the foregoing by simple constructional means such 
that clatter is reliably avoided, while at the same time friction losses 
should be kept at a minimum. 
The present invention relates to a converter device in which the circular 
motion is converted into a translational motion by a drive pin engaging a 
slide slot. The slide slot may be provided on the eccentric and the drive 
pin on the drive member, or alternatively, the drive pin may be arranged 
on the eccentric and the slide slot on the drive member. The embodiments 
described in the following refer to the latter alternative. 
Contrary to the prior-art devices in which the slide slot is bounded by 
rigid members, in the solution of the present invention at least two 
flexurally elastic portions assuming the function of the fork arms against 
which the drive pin engages as the eccentric rotates are deflected by the 
drive pin at least in sections. A first end of each flexurally elastic 
portion is not deflectable, yet the deflectability of each flexurally 
elastic portion increases progressively towards its other second end. Each 
flexurally elastic portion has its first end connected with the drive 
member, while its second end projects freely. The flexurally elastic 
portions are preferably arranged in such a manner that their flexural 
rigidity increases in the acceleration area of the drive pin, that is, its 
deflectability decreases. 
With the eccentric rotating, the drive pin acts on a respective one of the 
two flexurally elastic portions, nearly canceling out the bias of the 
flexurally elastic portion by deflecting it at least in sections from its 
original position. Because the two flexurally elastic portions are 
arranged in such a fashion that a rigid first and a deflectable second end 
of the flexurally elastic portions lie opposite each other at the ends of 
the slide slot, the two flexurally elastic portions exert a greatly evened 
out, preferably nearly uniform clamping force or bias on the drive pin 
along the full longitudinal extent of the slide slot. 
This arrangement of the flexurally elastic portions enables the motor power 
to be significantly reduced while the bias is maintained unchanged, 
because the maximum clamping force to be overcome in the prior-art devices 
between the two first ends of the fork arms results in an undesirably high 
power loss. The present invention makes it possible to minimize the 
distance between the flexurally elastic portion and the drive pin with the 
eccentric rotating, such that clatter which becomes the louder the greater 
the distance between drive pin and boundary surface, is nearly completely 
eliminated. This results in a significant improvement of the converter 
device because the motor is dimensioned to lower power and/or clatter is 
avoided. 
Each of the flexurally elastic portions has a first end thereof preferably 
secured to a cutout of the drive member by suitable fastening means as, 
for example, screws, or is integrally formed thereon, so that the second 
end of the respective portion projects freely into the cutout. The first 
ends of the flexurally elastic portions are each arranged at opposite ends 
of the cutout in the drive member, and the flexurally elastic portions 
extend in an opposed parallel relationship at a predetermined relative 
distance which, as described in the foregoing, is conformed to the 
diameter of the drive pin such that both portions engage against the drive 
pin with such a bias that the frictional forces occurring between the 
drive pin and the flexurally elastic portions are evened out to the 
maximum possible extent along the full length of the slide slot, in 
addition to being configured such as to enable the eccentric to be 
operated at a low power level. Apart from affording the advantage of 
enabling an overall lower bias to be selected as compared with prior-art 
devices, this arrangement has the advantage that the flexurally elastic 
portions engage against the drive pin more closely, thereby eliminating 
clatter. 
The cutout into which the flexurally elastic portions extend may be 
provided at any desired location of the usually plate-shaped drive member. 
Depending on the design requirements of the individual appliance, the 
cutout may be provided at the end or in the center of the drive member, 
for example. Particularly in cases where the flexurally elastic portions 
are provided at the end, it is an obvious solution to arrange the two 
flexurally elastic portions so as to define a slide slot open on one end 
which facilitates the assembly of drive pin and drive member. 
The flexurally elastic portions are either configured as a separate 
component secured to the drive member during the assembly operation, or 
they are integrally formed with the drive member preferably in cases where 
the drive member is made of a plastics material. The drive member and the 
flexurally elastic portions may be manufactured from the same material, 
where applicable, in one single operation. The flexurally elastic portions 
may be made of any material of sufficient flexural elasticity, preferably, 
however, of metal or plastics. The flexurally elastic portions may be of a 
leaf- or rod-shaped configuration, depending on the design requirements of 
the appliance. 
The drive member effecting the reversal of motion is required to include at 
least one rigid component for transmitting the motion. This rigid 
component is conventionally configured in the shape of a plate on which 
are arranged the flexurally elastic portions and, where applicable, an 
output means for an implement as, for example, an inner cutter of a shaver 
or a toothbrush attachment, and a mounting means for the drive member on 
the housing of the individual appliance in which the converter device is 
utilized. If required by the stability of the converter device, the rigid 
component of the drive member may also be configured as a frame structure. 
In the event of the rigid component of the drive member being a frame 
structure (drive frame), the flexurally elastic portions may be arranged 
on a drive arm secured to the drive frame. 
In a further embodiment, the flexurally elastic portions are provided in 
the plane of the drive member, the plate-shaped configuration of the drive 
member or drive arm being thus maintained. 
In another embodiment, the flexurally elastic portions extend away from or 
towards the drive member or drive arm at right angles thereto. In this 
arrangement, for example, the first flexurally elastic portion has its 
first end formed on the drive member, while its second end extends away 
from the drive member. Extending parallel to the first flexurally elastic 
portion is a rigid wall member on whose free end, that is, the end remote 
from the drive member, the first end of the second flexurally elastic 
portion is formed. The second flexurally elastic portion is in parallel 
arrangement immediately opposite the first flexurally elastic portion, 
with the free second end of this second flexurally elastic portion 
pointing in the direction of the drive member. This provides between the 
first and the second flexurally elastic portion a slide slot having one 
end open and adapted for engagement with the drive pin. 
The solution of the present invention which comprises the step of limiting 
the slide slot by at least two flexurally elastic portions affords ease of 
implementation because the flexurally elastic portions can be either 
integrally formed on the drive member or simply mounted as by plug or 
screwed connections, for example. The provision of additional components 
such as cushioning or damping means is obviated. The assembly of drive 
member and eccentric is also easy because the drive pin can be introduced 
into the slide slot without particular effort. The flexurally elastic 
portions allow a production with sufficient tolerance because the bias 
predetermined by the relative distance of the flexurally elastic portions 
is variable within the scope of the manufacturing tolerances, and minor 
fluctuations in the relative distance of the two flexurally elastic 
portions, as for example, manufacturing tolerances, accordingly have no 
effect on the serviceability of the converter device. 
In a particularly preferred embodiment, the drive member is a component 
part of an oscillator, in particular an oscillator having two elastic legs 
between which at least one rigid basic member configured in plate shape or 
as a frame structure is arranged, with the drive member being connected 
with the basic member. The drive member may be secured to the basic member 
by fastening means, or alternatively, it may be integrally formed on the 
basic member. The elastic legs of the oscillator configured, for example, 
as film hinges, serve the function of supporting and securing the 
oscillator on the housing of the individual appliance. The drive member 
may be provided at any desired location on the oscillator, centrally or at 
the end, depending on the design requirements of the appliance. Thus, for 
example, the drive member may be arranged so that one end thereof is 
arranged at one end of the basic member outside the elastic legs in the 
manner of a drive arm of the oscillator. 
In a particularly preferred improved embodiment of the present invention, 
clatter is avoided or reduced after prolonged use particularly by 
providing spring means 80, 82 for supporting the flexurally elastic 
portions. The spring means are preferably arranged in the areas of maximum 
deflection between the flexurally elastic portions and the drive member. 
Where necessary, it is readily possible according to the present invention 
to couple several drive members to each other, for example, when it is 
desired to operate a multi-part oscillator whose various parts are 
deflected in opposite directions. Thus, for example, it is envisaged that 
several drive pins arranged on various serially-connected eccentric disks 
may be rotated within respective slide slots in mating arrangement with 
the drive pins.

For the subsequent explanation of the converter arrangement of the present 
invention, reference will first be made to FIG. 1. FIG. 1 illustrates a 
device 2 for converting the rotary motion A of an eccentric 6 driven by a 
motor shaft 4 into a reciprocating motion parallel to a first direction 
y-y'. Mounted on the eccentric disk 6 in an extension of the motor shaft 
is a drive pin 8 projecting into a slide slot 12 formed in the drive 
member 10. 
The drive member 10 is a plate of plastics or metal, for example, which 
includes a cutout 14 and has one end thereof formed on the rigid basic 
member 16 of an oscillator 18 in the manner of a drive arm. The oscillator 
is suspended by means of the film hinge 20. Such an oscillator 18 is 
conventionally part of a small appliance powered by an electric motor as, 
for example, a shaver or a dental cleansing device. 
Further formed on the drive member are two flexurally elastic portions 22 
and 24. The first portion 22 has its first end 26 formed on the drive 
member, while its second free end 28 extends into the cutout 14. On the 
opposite side of the cutout 14, the first end 30 of the second portion 24 
is formed on the drive member 10. The second end 32 of this portion 24 
provides the boundary for the cutout 14. The two flexurally elastic 
portions 22 and 24 extend parallel to each other in opposite directions, 
so that the first end of the one portion lies opposite the second end of 
the other portion. Thus, the first end 26 of the portion 22 lies opposite 
the second end 32 of the second portion 24, while the first end 30 of the 
second portion 24 lies opposite the second end 28 of the first portion 22. 
Arranging the flexurally elastic portions 22 and 24 in this manner 
provides a slide slot 12 having one end open through which the drive pin 8 
is insertable for assembly. 
The facing surfaces of the two portions 22 and 24 are referred to as 
boundary surfaces 34, and the space bounded by the boundary surfaces 34 is 
referred to as the slide slot 12. The relative distance of the two 
portions 22 and 24 is smaller than the diameter of the drive pin 8, 
causing the drive pin to be clampingly engaged by the flexurally elastic 
portions 22 and 24 with a predetermined bias. The length of the slide slot 
12 in the direction of its longitudinal axis x--x is at least double the 
relative distance of the drive pin 8 to the axis of the motor shaft 4. 
This thus ensures that the drive pin is guided in the slide slot 12 by the 
portions 22 and 24 in any position of the eccentric. 
The drive pin 8 describes a circular motion which the drive member follows 
in that the drive pin 8, which rolls along the boundary surfaces 34, 
exerts pressure on the drive member, whereby this circular motion is 
converted into a translational, reciprocating motion. Apart from the 
translational motion of the drive member, the portions 22 and 24 are 
deflected at least in sections by the circular motion of the drive pin. 
The circular motion of the drive pin 8 counteracts the bias exerted on it 
by the flexurally elastic portions. This bias is canceled out at least in 
part by the drive pin deflecting the flexurally elastic portions 22 and 24 
from their original positions at least in sections. 
Owing to the configuration of the slide slot 12 of the present invention, 
it is possible to minimize and to even out largely the bias exerted by the 
flexurally elastic portions 22 and 24 on the drive pin 8, and thus the 
friction between the pin and the flexurally elastic member, through the 
entire slide travel, that is, through the entire circular path of the 
drive pin 8. Apart from minimizing the bias, it is thereby accomplished 
that the flexurally elastic portions 22 and 24 engage against the drive 
pin more closely so that clatter is avoided. 
Further embodiments of the converter device of the present invention will 
be presented in the following. Like reference numerals identify like 
parts. 
FIG. 2 illustrates a second embodiment of the converter device of the 
present invention. The drive member is made integrally with the rigid 
basic member 40 of an oscillator 42, the basic member being configured as 
a frame structure. The oscillator is movably carried in an appliance by 
means of two film hinges 44. An output means 46 for an implement is 
provided on the frame structure on the surface facing away from the 
eccentric. 
In the surface of the frame structure opposite the eccentric 6, a cutout 14 
has been provided for the integrally formed drive member. Extending into 
the cutout 14 from opposite ends are two parallel, relatively spaced 
flexurally elastic portions 22 and 24. The respective second ends of these 
portions extend freely into the cutout 14 and are deflectable by the drive 
pin 8. In the embodiment shown, the two portions 22 and 24 form a closed 
slide slot 12 on the boundary surfaces of which the drive pin 8 rolls as 
it travels along its circular path. 
The embodiment illustrated in FIG. 2 affords particularly great ease of 
manufacture and assembly. Its components and space requirements are 
restricted to a minimum. 
FIG. 3 shows a further embodiment of the converter device of the present 
invention in which the flexurally elastic portions 22, 24 extend away from 
the surface of the drive member 10. The first portion 22 has its first end 
26 anchored to the drive member 10 and extends at right angles thereto so 
that the second end 28 projects freely. In relatively spaced parallel 
arrangement thereto is a rigid wall member 50 which is equally anchored 
to, and extends away from, the drive member 10. Secured to the freely 
projecting end of this rigid wall member 50 is the first end 30 of the 
second flexurally elastic portion 24. The second portion 24 extends 
between the rigid wall member 50 and the first flexurally elastic portion 
22 towards the drive member 10. The second end 32 of the second portion 24 
terminates, however, short of the drive member 10 in a freely projecting 
fashion. As in the embodiments of the present invention previously 
described, the slide slot 12 is formed by the portions 22 and 24 as a 
slide slot 12 having one end open. The drive pin 8 extends between the two 
flexurally elastic portions 22 and 24 and is guided within the slide slot 
12 by the two portions 22 and 24 on the boundary surfaces 34 as it travels 
along its circular path which the drive member converts into a 
reciprocating motion. 
The rigid wall member 50 and the second flexurally elastic portion 24 may 
be made of different materials (metal and plastics, various plastics 
materials or metals), or alternatively, they may be made of like material, 
yet of different thickness, for example. 
In order to simplify the insertion of the drive pin, the flexurally elastic 
portions 22 and 24 include each a chamfered guide surface 52 at the open 
end of the slide slot. 
FIG. 4 shows a shaver 54 with a housing 56 in which an oscillator 60 is 
movably carried by means of film hinges 58. The oscillator 60 includes a 
frame structure 62 providing a rigid basic member on which an output means 
64 is formed. The shaver 54 has an inner cutter 66 mounted on the output 
means 64. The shaver 54 further includes an electric motor 68 having a 
motor shaft 70 on which an eccentric disk 72 is provided carrying a drive 
pin 74 aligned parallel to the axis of the motor shaft 70. 
The eccentric 72 and the oscillator 60 are in relative engagement by means 
of the drive pin 74 engaging with a flexurally elastic member provided in 
a drive arm 76 formed on the frame structure 62 of the oscillator 60. The 
arrangement of drive pin and flexurally elastic member is as shown in FIG. 
1. The drive arm 76 is disposed outside the film hinges 58 because the 
motor and thus also the eccentric are arranged off-center in the shaver 
housing. As becomes apparent from FIG. 3, the possibility also exists to 
arrange the flexurally elastic member centrally on the basic member of the 
oscillator if the motor is mounted at center in the shaver housing.