Arm mechanism of a pushbutton type tuner

Arm mechanism of a pushbutton type tuner, in which a setting plate is rotatably mounted on an arm, which setting plate has an arc shaped contacting part on the extremity side of the arm; at the periphery of the setting plate is disposed an approximately U-shaped plate spring having an open end on the base side of the arm, which plate spring is fixed to the arm on the extremity side of the arm; on the inner side of the plate spring is formed a tightening part against the contacting part of the setting plate; and a pair of tightening protrusions are disposed on the tightening part, interposing the center line of the arm therebetween, in contact with the contacting part of the setting plate, whereby both the tightening protrusions are comprised between 50.degree. and 70.degree., measuring from the center line of the arm with respect to the center of rotation of the setting plate.

BACKGROUND OF THE INVENTION 
This invention relates to an arm mechanism of a pushbutton type tuner. 
A pushbutton type tuner is a tuner, in which one among several 
predetermined frequencies is selected by inserting a core linked with a 
memory slide to a corresponding position in a tuning coil, whereby 
displacement of the memory slide is adjusted by adequately varying the 
angular position of a setting plate mounted on an arm so as to press the 
memory slide, which setting plate is fixed after adjustment. 
In such a pushbutton type tuner, in order to fix the setting plate to an 
arm at a desired angular position, heretofore a structure as indicated in 
FIG. 1 has been utilized. In this structure, on the upper surface of an 
arm 1 a setting plate 3 is mounted rotatably by using a setting pin 2 
having a frange at its upper end. A boss 4 having a circular periphery is 
formed in one body on the lower surface of the setting plate 3. The 
periphery of this boss 4 is surrounded by a plate spring 5 having an 
approximately U-shape. By pressing this plate spring 5 on both the sides 
by using a pushbutton, the periphery of the boss 4 is tightly grasped by 
the plate spring 5 so that the setting plate 3 fixed to the arm at a 
desired angular position cannot rotate around the setting pin 2. 
In such an arm mechanism, since the setting plate 3 is pressed laterally 
from right and left by the plate spring 5, the overall thickness of the 
arm mechanism may be reduced and thus contributes considerably to 
miniaturization and thinning of the pushbutton type tuner. However, 
utilization of such an arm mechanism in a pushbutton type tuner has given 
rise to following inconveniences. 
That is, since the setting plate 3 should be mounted rotatably with respect 
to the setting pin 2, certain space rests necessarily between the setting 
pin 2 and the wall of the hole formed for it in the setting plate 3. 
Consequently this space has given rise to some shakiness and it has been 
feared that the position of the setting plate with respect to the arm when 
the setting plate rotated was different from that observed when it rested. 
If the position of the center of the setting plate is not well fixed, it 
is difficult to position exactly the setting plate in accordance with the 
frequency to be selected. Displacement of the center provokes displacement 
in frequency and thus lowers considerably the quality of the tuner. 
In order to remove these inconveniences, it can be supposed to eliminate 
the shakiness by pressing the setting plate 3 always in one direction, for 
example toward the base side of the arm 1, so that the setting pin 2 and 
the wall of the hole in the setting plate 3 is in contact always at a well 
defined position, when the setting plate 3 is pressed by the plate spring. 
However, it has been extremely difficult to press the setting plate 3 only 
in one direction by using one plate spring 5 while fixing it with a high 
reliability so that the setting plate 3 once fixed never rotates. 
Specifically, in order to press the setting plate 3 only in one direction, 
contact position of the setting plate 3 with the plate spring can be 
disposed only in the pressing direction and contact area is 
correspondingly reduced. Therefore, even if shakiness is prevented, the 
small contact area gives rise to a disadvantage that the setting plate is 
inadvertently rotated. Of course, when pressing force exerted by the plate 
spring 5 is extremely strong, even if the setting plate is pressed only in 
one direction, it can be fixed with a high reliability. However, since 
pressing force by such a plate spring 5 is based on the force required at 
the moment when a pushbutton surmounts two tapered parts disposed at the 
base part of the plate spring, the pressing force caused by the plate 
spring is limited by the fact that the mounting operation of the 
pushbutton should be effected smoothly. The pressing force has, therefore, 
not been able to be increased imprudently. 
OBJECT OF THE INVENTION 
An object of this invention is to provide a new arm mechanism of the 
pushbutton type tuner, in which the setting plate is fixed with a high 
reliability by the plate spring by using effectively pressing force 
exerted by the plate spring and at the same time the center of the setting 
plate is always at a same position so that there is no fear that any 
displacement in frequency is provoked. 
SUMMARY OF THE INVENTION 
In order to achieve this object, the arm mechanism of the pushbutton type 
tuner according to this invention is characterized in that an arc shaped 
contacting part is disposed at the forward periphery of the setting plate, 
that a pair of tightening protrusions are disposed at the inner side of 
the approximately U-shaped plate spring, interposing the center line of an 
arm on which the setting plate is rotatably mounted, in contact with the 
contacting part, and that the tightening protrusions are comprised between 
50.degree. and 70.degree. measuring from the center line of the arm with 
respect to the center of rotation of the setting plate. By this way, when 
the setting plate is tightened by the plate spring, fixing force exerted 
on the setting plate by the tightening protrusions is increased by a 
factor of one to three with respect to the force exerted on the setting 
plate by the pushbutton in order to prevent displacement of the setting 
plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
This invention will be explained more concretely referring to an embodiment 
shown in FIG. 2 and the followings. 
In the figures the referring numeral 20 denotes an arm. On this arm 20 a 
setting plate 22 is mounted rotatably. That is, a setting pin 21 is fixed 
to the arm 20 and the setting plate 22 is engaged rotatably with this 
setting pin 21. The setting plate 22 is shaped in an arc form on the 
extremity side of the arm 20 and this arc shaped part forms a contacting 
part 22a in contact with the plate spring, which will be explained later. 
On the other hand, a pressing protrusion 23 is fixed upwardly at the 
extremity of the setting plate 22 on the base side of the arm 20 and this 
pressing protrusion 23 is engaged with a V-shaped notch of the memory 
slide. 
On the lower surface of the setting plate 22, a guiding protrusion 25, 
whose periphery is arc shaped, is formed in one body on the pushbutton 
side with respect to the setting pin 21. In the arm 20 an approximately 
V-shaped guiding aperture 24 corresponding to the guiding protrusion 25 is 
formed on the pushbutton side with respect to the setting pin 21. The 
above-mentioned guiding protrusion 25 is inserted movably into this 
guiding aperture 24. This guiding aperture 24 is symmetric with respect to 
the center line of the arm 20 passing through the center of the setting 
pin 21 and its outer edge is tapered so that the whole aperture has a 
V-shape pointing the base side of the arm 20. These two tapered parts are 
in contact with the arc shaped periphery of the above-mentioned guiding 
protrusion 25. 
On the upper surface of the arm 20 an approximately U-shaped plate spring 
26 is disposed so as to surround the setting plate 22. This plate spring 
26 is fixed at its extremity at the extremity of the arm 20 and its two 
branches, right and left, extend toward the base side of the arm, forming 
a U-shape, so as to hold the setting plate 22 between them. An arc shaped 
tightening part 27 is formed against the arc shaped contacting part 22a of 
the setting plate 22 at the inner edge on the extremity side of the arm. 
On this tightening part 27 a pair of tightening protrusions 27a are 
disposed, interposing the center line of the arm 20. These tightening 
protrusions 27a are so formed that the center of each protrusion is 
between 50.degree. and 70.degree. , measuring from the center line of the 
arm 20 with respect to the center of the setting pin 21. 
Furthermore, the base part of the arm 20 and the extremity of the right and 
left branches of the plate spring 26 extending to the base part of the arm 
20 are engaged with a pushbutton 28. When this pushbutton 28 is mounted on 
the arm, it presses the extremity of the right and left branches of the 
plate spring 26 toward the center line and reduces the distance between 
them. When the pushbutton is extracted half-way, the pressing force 
exerted on the plate spring 26 is removed and it becomes possible to 
enlarge the distance between the two branches. For this purpose, a pair of 
protrusions 29, right and left, are disposed at the inner side of the 
pushbutton 28. On each branch of the plate spring a release part, where 
the distance between the outer edge and the corresponding edge of the 
other branch is smaller than the other parts, a tapered part 31 adjacent 
to the release part 30, and a thrust part 32, where the distance between 
the outer edge and the corresponding edge of the other branch is greater 
than the other parts, are formed as a cam plate at the base part of the 
plate spring 26 corresponding to the protrusions 29 of the pushbutton 28. 
The working of the arm mechanism according to this invention, which is 
constructed as indicated above, will be explained hereinbelow. 
For setting frequencies to be selected by using the pushbuttons for given 
pushbuttons and arms belonging to them, the tuning shaft is beforehand 
rotated manually, and the core linked with the shaft is displaced to a 
determined position in the tuning coil. On the other hand a pushbutton 
corresponding to a frequency to be selected is pushed in. By this way, the 
memory slide 40 linked with the core is displaced laterally and stopped at 
a position corresponding to the frequency to be set. At this situation the 
pushbutton 28 mounted on the base part of the arm 20 and that of the plate 
spring 26 is extructed half-way so that the protrusions 29 are located at 
the release parts 30 of the plate spring 26. At this moment the pressing 
force exerted on the plate spring 26 by the pushbutton is released, and 
this gives rise to clearance between the tightening protrusions 27a of the 
plate spring 26 and the contacting part 22a of the setting plate so that 
the setting plate 22 can rotate freely around the setting pin 21. 
At this situation, when the pushbutton 28 and the arm 20 are pushed into 
the tuner, the pressing protrusion 23 of the setting plate 22 comes into 
contact with the V-shaped notch 41 of the memory slide 40, and guided by 
one of the slopes, reaches the vertex of the V-shaped notch 41. In this 
case, since the position of the vertex of the V-shaped notch 41 is 
determined by the position of the memory slide 40 corresponding to the 
core in the tuning coil, the setting plate 22 rotates around the setting 
pin 21 so that the pressing protrusion 23 is located at the vertex of the 
V-shaped notch 41. 
By this way, when the arm 20 is pushed into the tuner and the pressing 
protrusion 23 is engaged with the V-shaped notch 41 of the memory slide 
40, the setting plate 22 is pulled by the V-shaped notch 41 and tends to 
move toward the base side of the arm 20. At this moment the guiding 
protrusion 25 disposed on the lower surface of the setting plate 22 comes 
into contact with the V-shaped edge of the guiding aperture 24 formed in 
the arm 20 and moves along the edge toward the base side of the arm 20. 
Consequently, even if there is some clearance between the setting plate 22 
and the setting pin 21 and even if the setting plate is movable, the 
guiding protrusion 25 of the setting plate 22 pulled by the memory slide 
40 comes into contact with the deepest part of the V-shaped guiding 
aperture 24 of the arm 20. In this case, since the V-shaped guiding 
operture 24 is symmetric with respect to the center line of the arm and 
since the periphery of the guiding protrusion 25 engaged with the aperture 
is circular, the center of the setting plate 22 is always on the center 
line of the guiding aperture 24, that is, on the center line of the arm 
20. 
By this way, the rotation angle of the setting plate 22 is determined and 
its center is in position. After that, the pushbutton 28 disposed at the 
base side of the arm is further pushed in. Since the memory slide 40 
prevents forward movement of the arm 20, the pushbutton 28 slides on the 
arm and thus the pushbutton 28 is mounted completely. At this moment the 
protrusions 29 disposed on the pushbutton 28 advance from the release part 
30 of the plate spring 26 over the tapered part 31 to the thrust part 32 
and the base part of the plate spring 26 are pressed laterally toward the 
center line by the right and left protrusions 29 of the pushbutton 26. As 
the consequence, the distance between the right and left branches of the 
plate spring 26 becomes smaller. The tightening protrusions 27a disposed 
on the plate spring 26 are pressed against the arc shaped contacting part 
22a formed on the front part of the setting plate 22 and fixed the setting 
plate 22 on the arm 20. 
Thereafter, when the pushbutton 28 is pushed in the tuner, since the 
pressing protrusion 23 of the setting plate 22 fixed to the arm is in 
contact with the V-shaped notch 41 and pushes it, the memory slide 40 is 
displaced. The position of the core which is linked with the memory slide 
40 and inserted in the coil is thus determined. 
According to this invention, the tightening protrusions 27a disposed on the 
plate spring 26 are comprised between 50.degree. and 70.degree. , 
measuring from the center line of the arm 20 with respect to the center of 
rotation of the setting plate 22. Consequently, if the force exerted on 
the setting plate 22 by the tightening protrusions 27a is decomposed into 
the components in the axial and lateral directions of the arm, the ratio 
of the former to the latter is comprised between 1.2 and 2.7. This means 
that the force for fixing the setting plate 22 is always greater than the 
force for pushing it toward the base part of the arm 20 and preventing its 
displacement, and further that nevertheless the force for preventing the 
displacement of the setting plate 22 also rest sufficiently. Consequently 
it is possible to divide usefully the force exerted on the plate spring 26 
by pushing the pushbutton 28 into the fixing force and the force for 
preventing the displacement of the setting plate 22 and thus, since the 
force of the plate spring 26 can be effectively utilized, it is not 
necessary to increase excessively the force exerted by the pushbutton. 
Consequently, after the release of the engagement of the setting plate 22 
with the memory slide 40, the setting plate 22 is pressed so that the 
guiding protrusion 25 rests always on the center line of the guiding 
aperture 24. Owing to the force exerted by the plate spring for preventing 
the displacement of the setting plate 22, the guiding protrusion 25 never 
diverts from the center line of the arm 20. Consequently there is no fear 
that any displacement in frequency is provoked. At the same time, since 
the setting plate 22 is fixed by a pressing force which is great with 
respect to the force for preventing the displacement of the setting plate 
22, it is not feared that the angular position of the setting plate 22 
changes. With this respect displacement in frequency is also prevented. 
This invention is not limited to the embodiment illustrated in the drawing. 
The guiding protrusion 25 may not be disposed on the lower surface of the 
setting plate 22 and the V-shaped guiding aperture 24 need not necessarily 
be formed in the arm 20. That is, according to this invention, since the 
tightening protrusions 27a disposed on the plate spring 26 push the 
setting plate 22 toward the base part of the arm 20, even if there is some 
clearance between the setting plate 22 and the setting pin 21, the setting 
plate 22 is pressed always in one well defined direction, and even without 
V-shaped guiding aperture 24 shown in the embodiment, positioning of the 
setting plate 22 is effected effectively. 
As indicated in the above embodiments, the arm mechanism according to this 
invention is characterized in that the tightening protrusions disposed on 
the plate spring, which push the setting plate, are comprised between 
50.degree. and 70.degree. , interposing the center line of the arm 
therebetween, measuring from the center line of the arm with respect to 
the center of rotation of the setting plate. Owing to this fact, according 
to this invention, the force exerted on the plate spring by the pushbutton 
is divided usefully into the force for fixing the setting plate and the 
force for preventing its displacement, it is not necessary to increase 
excessively the force exerted by the plate spring and thus shakiness of 
the setting plate is removed. Therefore displacement in frequency of the 
tuner is also eliminated. Furthermore, since it is not necessary to 
increase excessively the force exerted by the plate spring, it is possible 
to mount and dismount the pushbutton giving rise to the pressing force 
exerted on the plate spring with a relatively small force. It is another 
advantage that frequency setting for each arm can be effected more easily.