Cam device having backlash reversal suppression means

To prevent the generation of noise and/or vibration due to the backlash of the gear wheels in the cam device driven by a two mutually meshing gear wheels, a backlash reversal suppression means which suppresses an impulsive reversal of the backlash during transition from a rotational phase region in which the cam drives the cam follower to a rotational phase region in which the cam is driven by the cam follower is provided to operate only at a necessary portion.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a cam device, and more particularly, a cam 
device wherein a cam which biases a cam follower against an elastic 
biasing force applied thereto is driven to rotate about a rotation axis 
thereof by a gear train including at least two mutually meshing gear 
wheels. 
2. Description of the Prior Art 
A cam device in which a cam adapted to be driven to rotate about its 
rotation axis biases a cam follower against an elastic biasing force 
applied thereto is conventionally used at a lot of places. Further, in 
many applications, as in, for example, a rotary stencil printer which 
carries out stencil printing by rotationally driving a printing drum while 
moving a press roller in synchronization with the rotational phase of the 
printing drum so as to be forwarded against the printing drum in a first 
phase of rotation thereof and to be retracted from the printing drum in a 
second phase of rotation thereof, such a cam device is driven to rotate 
about its own rotation axis by a gear train which synchronizes the cam 
operation with other operating mechanisms. 
In more detail, as shown somewhat diagrammatically in FIG. 1, a rotary 
stencil printer has a printing drum 2 having a circumferential portion of 
a perforated construction for mounting a perforated stencil sheet and 
mounted to rotate about its rotation axis 1, and a press roller 3 for 
pressing a print sheet against the printing drum, and is adapted to 
operate such that the printing drum 2 is rotated about the rotation axis 
1, while print sheets are successively fed in between the printing drum 
and the press roller 3, with ink being pressedly supplied to the inside of 
the printing drum 2 by an ink supply means not shown in the figure, so 
that each of the print sheets is given a print image thereon by contact 
with the printing drum. In such a rotary stencil printer, since a raised 
base projection 4 is provided at a part of the circumference of the 
printing drum 2 for mounting a leading edge of the stencil sheet, the 
press roller 3 must be periodically retracted to be away from the printing 
drum 2 in synchronization with the rotation of the printing drum 2 at a 
phase region in which the raised base portion 4 traverses in front of the 
press roller, so as to avoid a collision of the press roller 3 with the 
raised base portion 4. Therefore, the press roller 3 is supported at one 
end of a pivot arm 7 held by a pivot shaft 6 at the other end thereof, 
wherein the pivot shaft 6 is mounted in a housing of the printer not shown 
in the figure to be pivotable about a pivot axis 5, and the pivot arm 7 is 
swung about the pivot axis 5 in synchronization with the rotation of the 
printing drum 2, such that the press roller 3 is forwarded to a position 
shown by a phantom line 3', where it contacts with the printing drum 2 
during a first phase of operation which excludes a second phase of 
operation, in which the raised base portion 4 traverses in front of the 
press roller 3, while in said second phase of operation the press roller 
is retracted to be away from the printing drum as shown by a solid line, 
though, in fact, shown in a broken line, because it is located behind a 
cam described hereinbelow. 
The above-mentioned reciprocating movement of the press roller 3 
synchronized with the rotation of the printing drum 2 is readily 
accomplished by employing a cam device adapted to be driven to rotate in 
synchronization with the rotation of the printing drum 2. An example of 
such a cam device is shown in FIG. 1. 
In FIG. 1, 10 is a cam adapted to be driven by a gear wheel 12 to rotate 
about a rotation axis 14 thereof integrally therewith. The gear wheel 12 
meshes with a gear wheel 16 and is driven thereby about the rotation axis 
14 in the anti-clockwise direction in the figure, while the gear wheel 12 
drives in turn a gear wheel 8 meshed therewith and integrally rotatable 
with the printing drum 2 about the central axis 1 so as thereby to 
rotationally drive the printing drum 2 about the central axis 1. The gear 
wheel 16 is adapted to be driven to rotate about its rotation axis 18 in 
the clockwise direction in the figure as indicated by an arrow by a 
driving source not shown in the figure. The unitary body of the cam 10 and 
the gear wheel 12 and the gear wheel 16 are rotationally supported to 
rotate about the rotation axes 14 and 18, respectively, by a support frame 
not shown in the figure. 
20 is a lever member supported by the pivot shaft 6 to swing about the 
pivot axis 5 integrally with the pivot arm 7 via the pivot shaft 6. A 
roller 24 is carried by the lever member 20 to be freely rotatable about 
its rotation axis 26. 28 is a tension coil spring having a lower end 
engaged to a support frame not shown in the figure and an upper end 
engaged with an end portion of the lever member 20, thereby applying a 
biasing elastic force to the lever member 20 so that it is elasticity 
biased about the pivot axis 5 in the anti-clockwise turning direction in 
the figure. When the roller 24 is not engaged with a convex portion 10a of 
the cam 10, the lever member 20 is turned in the anti-clockwise turning 
direction in the figure under the elastic biasing force of the tension 
coil spring 28, so as to press the press roller 3 against the 
circumferential surface of the printing drum 2. Although not shown in the 
figure, there is provided a press roller control means which acts at an 
arm portion 30 of the lever member 20 for retracting the press roller 3 to 
be away from the printing drum 2 regardless of the operation of the cam 
10. When the convex portion 10a engages the roller 24, the lever member 20 
is pivoted about the pivot axis 5 in the clockwise turning direction in 
the figure against the elastic biasing force of the tension coil spring 
28. 
In the condition shown in FIG. 1, the cam convex portion 10a is going to 
engage the roller 24, wherein the cam 10 is pushing the roller 24 in a 
direction of departing from the rotation axis 14 against the biasing force 
applied by the tension coil spring 28, so that the rotation of the gear 
wheel 12 is reacted against by a high resistance, while the gear wheel 16 
is driving the gear wheel 12 in the forward rotational direction. 
When the apex of the cam convex portion 10a passes over the roller 24 such 
that the cam device comes to the condition partly shown by a phantom line 
in the figure, the roller 24 in turn drives the cam 10 in the forward 
rotational direction under the elastic biasing force applied to the lever 
member 20 by the tension coil spring 28, so that the gear wheel 12 is 
driven in the forward rotational direction via the engagement of the 
roller 24 and the cam 10, while a braking is applied by the gear wheel 16 
rather than being driven thereby in the forward rotational direction. 
FIG. 2 is a partial view showing the details of the meshing relation 
between the gear wheels 12 and 16 in the condition where the cam 10 takes 
the position shown by the solid line in FIG. 1. In this condition, the 
gear wheel 16 is driving the gear wheel 12 in the forward rotational 
direction, so that the forwardly viewed front gear face 16f of the gear 
wheel 16 is in contact with the forwardly viewed rear gear face 12r of the 
gear wheel 12, with a backlash between the two gear wheels being generated 
between the forwardly viewed rear gear face 16r of the gear wheel 16 and 
the forwardly viewed front gear face 12f of the gear wheel 12. 
FIG. 3 is a view similar to FIG. 2, showing the meshing relation between 
the gear wheels 12 and 16 in the condition where the cam 10 takes the 
position partly shown by the phantom line in FIG. 1. In this condition, 
the gear wheel 12 is forwardly driven by the elastic biasing force of the 
tension coil spring 28, so that the gear wheel 16 brakes the forward 
rotation of the gear wheel 12. Therefore, the forwardly viewed rear gear 
face 16r of the gear wheel 16 is in contact with the forwardly viewed 
front gear face 12f of the gear wheel 12, with a backlash being generated 
between the forwardly viewed front gear face 16f of the gear wheel 16 and 
the forwardly viewed rear gear face 12r of the gear wheel 12. Thus, during 
a transition of the cam operation from the condition shown in the solid 
line to that shown in the phantom line in FIG. 1, i.e. when the contact 
point between the roller 24 and the cam convex portion 10a has passed 
somewhat over the apex point of the cam convex portion 10a to come to such 
a point where the magnitude of the driving torque transmitted from the 
roller 24 to the cam 10 reaches a critical value, the backlash between the 
gear wheels 12 and 16 changes from the condition shown in FIG. 2 to that 
shown in FIG. 3, said critical value being dependent upon the slope angle 
of the cam surface, etc. In this case, since a certain friction force is 
acting at the pivotal supports of the roller 24 and the lever member 20, 
the above-mentioned reversal of the backlash occurs catastrophically when 
the magnitude of the torque transmitted from the roller 24 to the cam 10 
has exceeded a certain relatively large value corresponding to the 
resistance at the frictionally contacting portions, so that the reversal 
of the backlash from the condition shown in FIG. 2 to that shown in FIG. 3 
occurs impulsively at an instant, at a relatively large torque, thereby 
generating a noise and/or a vibration. 
Thus, a cam device which has a cam and a cam follower shifted by the cam 
against an elastic biasing force operates to alternately repeat an idling 
phase region in which the cam does not operatively engage the cam follower 
so that cam follower is positioned at its return position by the elastic 
biasing force and a cam operating phase region in which the cam 
operatively engages the cam follower so that the cam follower is shifted 
from its return position against the elastic biasing force, and in many 
cases the cam operating phase region is divided into a first operating 
phase region in which the cam positively drives the cam follower against 
the elastic biasing force by the cam engaging the cam follower at an 
inclining slope portion thereof and a second operating phase region in 
which the cam is in turn positively driven by the cam follower under the 
elastic biasing force by the cam engaging the cam follower at a declining 
slope portion thereof, as in the above-mentioned example. In the cam 
device in which the cam operating phase region is divided into such first 
and second operating phase regions, when the cam is rotationally driven 
about its rotation axis via a gear train including at least two mutually 
meshing gear wheels as in the example of rotary stencil printer described 
above, it can happen that the backlash between the two mutually meshing 
gear wheels is impulsively reversed during a transition of the cam 
operation from the first operating phase region to the second operating 
phase region as described above, thereby generating a noise and/or a 
vibration. 
In order to accomplish a low friction, light meshing operation of the gear 
wheels by substantially completely canceling the backlash between the two 
meshing gears, the manufacturing precision of the gears and the 
manufacturing precision and the strength as well as rigidity of the gear 
support construction including bearing means must be substantially 
increased. Therefore, in view of a substantial increase of the 
manufacturing costs, in many applications it is not practical to try to 
avoid the generation of noise and/or vibration due to the backlash by 
canceling the backlash from the meshing of the gears. 
SUMMARY OF THE INVENTION 
The present invention deals with the above-mentioned problems in the cam 
device in which a cam rotationally driven about its rotation center by a 
gear train including two mutually meshing gear wheels shifts a cam 
follower against an elastic biasing force, and has its object in providing 
a cam device having a means for effectively decreasing the generation of 
noise and/or vibration due to the backlash without increasing the 
manufacturing costs of the cam device. 
In order to accomplish the above-mentioned object, the present invention 
proposes a cam device comprising a cam adapted to be driven to rotate 
about a rotation axis thereof, a cam follower adapted to be shifted by 
said cam against an elastic biasing force applied thereto, said cam being 
rotated via a gear train including at least two mutually meshing gear 
wheels so as to cyclically repeat a first phase of operation in which said 
cam positively drives said cam follower against said elastic biasing force 
and a second phase of operation in which said cam is positively driven by 
said cam follower under the application of said elastic biasing force, and 
a backlash reversal suppression means adapted to operate only in said 
second phase of operation so as to suppress a backlash in the mutual 
meshing of said gear wheels from being impulsively reversed during 
transition from said first phase of operation to said second phase of 
operation. 
As described above, in the cam device in which a cam rotationally driven 
about its rotation axis by a gear train including at least two mutually 
meshing gear wheels shifts a cam follower against an elastic biasing 
force, it is due to an impulsive reversal of the backlash during a 
transition of the cam device from the above-mentioned first rotational 
phase region to said second rotational phase region that a noise and/or a 
vibration is generated as caused by the backlash of the two mutually 
meshing gear wheels. Therefore, if there is provided a means which 
suppresses or dampens the reversal of the backlash only in the 
above-mentioned second rotational phase region, there should be no problem 
of noise and/or vibration even when the backlash is left free in the 
meshing of two gear wheels in the other rotational phase region which 
occupies the most part of the cam rotation. 
Therefore, if a very limited local backlash suppression means is provided 
as described above, a gear means for driving the cam device manufactured 
at a relatively low cost and having a relatively large backlash can 
operate lightly at a low friction as a whole without causing the problem 
of generation of noise and/or vibration due to the backlash. 
The above-mentioned backlash reversal suppression means may be a gear 
sector superposed on one of said two gear wheels to mesh with the other of 
said two gear wheels substantially only in said second phase region. It is 
conventionally know to superpose two gear wheels to be finely adjustable 
of the relative rotational position thereof so as to be operated as a 
unitary gear wheel for the purpose of decreasing the backlash. However, if 
such a backlash reduction measure is applied over the whole circumference 
of the gear wheel, the manufacturing precision of the gear wheels and the 
bearing as well as the precision, strength and rigidity of the 
construction for supporting the bearing for the two meshing gear wheels 
must also be increased in order to avoid an increase of the resistance of 
the meshing between the superposed gear wheels and a mating gear wheel. 
In contrast, if a gear sector is superposed on a gear wheel such as to 
cancel the backlash only in the above-mentioned second rotational phase 
region which occupies only a small part of the whole rotational phase of 
the gear, it is possible to accomplish a light operation of the gear 
train, without causing any substantial problem over the entire rotational 
phase thereof, without substantially increasing the manufacturing 
precision of the gear and the gear sector and the manufacturing precision, 
strength and rigidity of the supporting structure therefor. 
The above-mentioned backlash reversal suppression means may comprise a 
first member adapted to rotate integrally with one of said two gear wheels 
while presenting an arcuate surface coaxial with said one gear wheel, and 
a second member adapted to rotate integrally with the other of said two 
gear wheels while presenting an arcuate surface portion coaxial with said 
other gear wheel and a raised surface portion radially raised from an 
arcuate contour corresponding to said arcuate surface portion, said raised 
portion being elasticity pressed against said arcuate surface of said 
first member substantially only in said second phase of operation, thereby 
frictionally suppressing said two gear wheels from rotationally shifting 
relative to one another in said second phase of operation. 
Or the above-mentioned backlash reversal suppression means may comprise an 
elastic spring piece having a root portion supported by one of said two 
gear wheels and extending in a radial direction of said one gear wheel, 
and a spring engaging means provided at the other of said gear wheels, 
said spring piece and said spring engaging means being positioned with 
respect to rotational phases thereof such that said spring piece is so 
biased by an engagement with said spring engaging means substantially only 
in said second phase of operation that a force generated by the biasing of 
said spring piece biases a driven one of said two gear wheels in a 
backward rotational direction relative to a driving one of said two gear 
wheels. 
In either of these constructions, the backlash reversal suspension means 
operates to suppress a relative phase shifting from occurring between two 
mutually meshing gears in the direction to cause reversal of the backlash 
therebetween only in the above-mentioned second rotational phase region, 
by interfering in the mutual meshing of the gear wheels only at a very 
limited part of the whole rotational phase of the gear wheels, thereby 
suppressing the backlash between the two gear wheels from impulsively 
reversing under a condition that a torque for driving the cam is being 
transmitted between the two gear wheels, while doing nothing with the 
meshing of the two gear wheels in the other rotational phase region 
occupying the most part of the rotational phase of the gear wheels, not to 
interfere with a light low friction operation of the gear train having a 
relatively large backlash.

DESCRIPTION OF THE EMBODIMENTS 
In the following, referring to FIGS. 4 and the subsequent figures, the 
present invention will be described in detail with respect to some 
embodiments thereof. 
FIGS. 4 and 5 are somewhat diagrammatical side views showing a first 
embodiment of the cam device according to the present invention, each 
figure showing only the cam driving mechanism for reciprocating the press 
roller in synchronization with the rotation of the printing drum of the 
rotary stencil printer shown in FIG. 1, in which the first embodiment of 
the present invention is incorporated. In the below-mentioned embodiments, 
the portions corresponding to those shown in FIG. 1 and described with 
respect to FIG. 1 operate in the same manner as in FIG. 1, and therefore 
those corresponding portions are indicated by the same reference numerals 
as in FIG. 1, and further repetitive descriptions of the constructions and 
the operations of those portions will be omitted. 
In the first embodiment of the present invention shown in FIGS. 4 and 5, at 
a part of the gear wheel 16 substantially corresponding to a rotational 
phase region of the meshing of the gear wheels 12 and 16 in which there 
occurs a phenomenon that the roller 24 drives the cam 10 in the forward 
rotational direction by the biasing force applied thereto from the 
expansion coil spring 28, there is provided a gear sector 34 in a manner 
shown in more detail in FIG. 6. In the embodiment shown in FIG. 6, the 
gear sector 34 has a thickness of about a half of the thickness of the 
gear wheel 16 and is received in a sectoral indent 36 formed at a portion 
receiving the gear wheel 16, with an opening 38 aligned with a central 
axis of its pitch circle (not shown in the figure but inherent to a gear 
or gear wheel) being rotationally slidably engaged by a hub portion 40 of 
the gear wheel 16, so that the relative rotational phase between the gear 
wheel 16 and the gear sector 34 is finely adjusted and fastened by a screw 
46 having a head portion and a threaded shank portion passed through an 
arcuate through opening 42 formed in the gear sector 34 as centered at the 
pitch axis being once loosened and screwed at its threaded shank portion 
into a threaded opening 44 formed in the gear wheel 16. When such a gear 
sector 34 is mounted to the pertinent rotational phase portion of the gear 
wheel 16, in the operating condition of the cam device shown in FIG. 5, 
the meshing between the gear wheels 12 and 16 is held in the condition 
shown in FIG. 7 so that the backlash between the two gear wheels in this 
rotational phase region is canceled by the gear sector, whereby when the 
meshing between the gear wheels 12 and 16 transfers from the rotational 
phase region in which the cam positively drives the cam follower to the 
rotational phase position in which cam is in turn positively driven by the 
cam follower, the meshing condition of the gear wheels does not change 
from the condition shown in FIG. 2 to the condition shown in FIG. 3 but is 
changed to the condition shown in FIG. 7 which is substantially the same 
as the condition shown in FIG. 2. As will be apparent from FIG. 7, the 
gear sector 34 has gear teeth as substantially the same tooth shape as the 
gear wheel 16. 
When the operation of the cam device proceeds further from the condition 
shown in FIG. 5 so that the cam convex portion 10a comes to a rotational 
phase position where it is disengaged from the roller 24, the gear sector 
34 does no longer mesh with the gear wheels 12 and 16, so that the 
backlash in the meshing of the two gear wheels is released free. However, 
since at this time no substantial torque is transmitted between the two 
gear wheels in either rotational direction, there is no probability that 
there occurs an impulsive contact between the gear faces of the two gear 
wheels which would generate a noise and/or a vibration. 
Although the gear sector 34 may be provided on the side of the gear wheel 
12 in order to accomplish the same function of suppressing the 
above-mentioned impulsive reversal of the backlash, in a construction like 
the rotary stencil printer shown in FIG. 1 in which the gear wheel 12 
further meshes with the gear wheel 8 for driving the printing drum 2, it 
is desirable that the gear sector 34 is provided on the side of the gear 
wheel 16 as in the shown embodiment, so that a uniform meshing of the gear 
wheel 12 and the gear wheel 8 is not interfered. 
FIGS. 8 and 9 are somewhat diagrammatical side views showing a second 
embodiment of the cam device according to the present invention, wherein 
the cam operating condition shown in FIG. 8 corresponds to that shown in 
FIG. 4, and the cam operating condition shown in FIG. 9 corresponds to 
that shown in FIG. 5. In FIGS. 8 and 9, the portions corresponding to 
those shown in FIGS. 4 and 5 are designated by the same reference numerals 
as in FIGS. 4 and 5, and since the constructions and the operations 
indicated by the same reference numerals are the same as those in the 
first embodiment shown in FIGS. 4 and 5, further repetitive descriptions 
of those portions will be omitted. 
In the embodiment shown in FIGS. 8 and 9, the backlash reversal suppression 
means for suppressing an impulsive reversal of the backlash in the meshing 
of the gear wheels 12 and 16 which can occur during a transition from the 
first rotational phase region in which the cam 10 positively drives the 
roller 24 as shown in FIG. 8 to the second rotational phase region in 
which the cam 10 is positively driven by the roller 24 as shown in FIG. 9 
is constructed by a disk member 50 having a cylindrical surface 48 coaxial 
with the gear wheel 16 and adapted to rotate integrally with the gear 
wheel 16 and a generally disk shaped elastic member 58 having a 
cylindrical surface portion 52 coaxial with the gear wheel 12 and a convex 
surface portion 56 arcuately raised from the cylindrical contour 54 of the 
cylindrical surface portion 52 and adapted to rotate integrally with the 
gear wheel 12. 
The cylindrical surface 48 of the member 50 and the cylindrical surface 
portion 52 of the member 58 have each a diameter equal to or slightly 
smaller than the diameter of the pitch circle of the gear wheel 16 or 12, 
so that these two opposing surfaces do not substantially contact one 
another. However, the convex surface portion 56 provided to correspond to 
the rotational phase region in which the cam 10 is driven by the roller 24 
so as to oppose the cylindrical surface 48 of the member 50 in said 
rotational phase region is adapted to be radially compressed to follow the 
cylindrical surface 48 of the member 50 under an elastic deformation 
thereof, so that the two members are strongly frictionally engaged with 
one another, whereby the relative rotational phase between the gear wheels 
12 and 16 is maintained at the state thereof where the contact of the two 
members started, i.e. the condition shown in FIG. 2, or even when the 
meshing condition changes from the condition shown in FIG. 2 to the 
condition shown in FIG. 3, the change proceeds moderately, without any 
impulsive change of the backlash in the meshing of the gear wheels 12 and 
16 from the condition shown in FIG. 2 to the condition shown in FIG. 3, 
thereby definitely avoiding the generating of noise and/or vibration due 
to an impulsive change of the backlash. 
In the embodiment shown in FIGS. 8 and 9, the member 50 presents the 
cylindrical surface 48 extending over 360.degree., while the member 58 
presents the cylindrical surface 52 extending over the remaining 
circumference excluding the convex surface portion 56. However, in either 
of the members 50 and 58 the portions not engaging with the frictional 
contact of the convex surface portion 56 may be appropriately omitted, 
such that the member 50 provides only an arcuate surface at a portion to 
oppose the convex surface portion 56, while the member 58 provides only 
the convex surface portion 56 and an arcuate surface adjacent the leading 
end and the trailing end of the convex surface portion, as will be obvious 
in view of the object, the functions and the effects of the present 
invention. Therefore, it will be apparent for those of ordinary skill in 
the art that those modifications are within the scope of the present 
invention. Further, although the member 50 may be made of a rigid material 
such as a metal or the like, it will be apparent that the member 50 may 
also be made of an elastic material. Still further, the member 50 may be 
made of an elastic material at least at its peripheral portion, while the 
member 58 in turn may be made of a rigid material such a metal or the 
like. 
FIGS. 10 and 11 are somewhat diagrammatical side views showing a third 
embodiment of the cam device according to the present invention, wherein 
the operating condition shown in FIG. 10 corresponds to that shown in 
FIGS. 4 or 8, and the operating condition shown in FIG. 11 corresponds to 
that shown in FIGS. 5 or 9. In FIGS. 10 and 11, the portions corresponds 
to those of the first and second embodiments are designated by the 
corresponding reference numerals, and further repetitive descriptions of 
those common portions will be omitted. 
In the embodiment shown in FIGS. 10 and 11, the backlash reversal 
suppression means for suppressing an impulsive reversal of the backlash in 
the meshing between the gear wheels 12 and 16 during transition from the 
first rotational phase region in which the cam 10 positively drives the 
roller 24 shown in FIG. 10 to the second rotational phase region in which 
the cam 10 is in turn positively driven by the roller 24 as shown in FIG. 
11 comprises a spring piece 60 supported at its root end by the gear wheel 
12 to extend in the radial direction of the gear wheel 12 and a spring 
engaging means 62 provided at the gear wheel 16. When the operation of the 
cam device transfers from the condition shown in FIG. 10 to that shown in 
FIG. 11, the spring piece 60 engages the spring engaging means 62, and as 
the rotation of the two gear wheels proceeds, due to a difference between 
the mounting phases of the spring piece 60 and the spring engaging means 
62 and also due to a deviation of the position of contact between the 
spring piece and the spring engaging means from a middle point between the 
rotation centers 14 and 18 of the gear wheels 12 and 16 toward the side of 
the rotation center 18, the spring piece 50 is deformed to bend such that 
the spring force generated thereby biases the gear wheel 12 in the 
retarding direction relative to the gear wheel 16, thereby suppressing an 
impulsive reversal of the backlash from occurring. 
The spring piece 60 may be made of a leaf spring having a certain bending 
elasticity calculated to be required, while the spring engaging means 62 
may be a pin-shaped projection planted in the gear wheel 16 to project 
therefrom in the axial direction thereof. 
In the embodiment shown in FIGS. 10 and 11, the spring piece 60 is provided 
on the side of the gear wheel 12, while the spring engaging means 62 is 
provided on the side of the gear wheel 16. However, a variation is 
possible such that the spring piece 60 is provided on the side of the gear 
wheel 16, while the spring engaging portion 62 is provided on the side of 
the gear wheel 12. In this case, the spring piece 60 will engage the 
spring engaging means 62 at the front face thereof as viewed in the 
rotational direction of the gear wheel 12, with the direction of the 
bending of the spring piece 60 being reversal to the direction thereof 
shown in FIG. 11. 
It will be apparent that although the present invention has been described 
with respect to three kinds of embodiments in the above, the technical 
concept of providing a cam device immune to the generation of noise and/or 
vibration due to the backlash in spite of use of an economical driving 
gear train adapted to operate with a relatively large backlash by 
providing a backlash reversal suppression means which operates only in a 
necessary minimum rotational phase region of the whole rotational phase of 
the gear wheels such as to suppress an impulsive reversal of the backlash 
between the two mutually meshing gear wheels for rotationally driving the 
cam during the transition from the first rotational phase region in which 
the cam positively drives the cam follower to the second rotational phase 
region in which the cam is positively driven by the cam follower can be 
reduced to practice by various other constructions readily thought of by 
one of ordinary skill in the art based upon the embodiments herein 
disclosed.