Tremolo device for a guitar

A tremolo device for a guitar comprising a flat plate pivotably mounted about a fulcrum on the guitar, a bar secured to the flat plate, at least one tension spring for imparting rotational force to the flat plate and the bar in one rotating direction, against another rotating force derived from a tension of guitar strings, and a tremolo arm manually engageable with the flat plate to oscillate the flat plate and the bar to thereby produce a tremolo effect. The fulcrum is provided by at least two contacts between a pin-shaped member having a substantially half-spherical tip portion on a front end thereof and a concave member having a depression into which the pin-shaped member is inserted.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a tremolo device for a guitar, and more 
particularly, it relates to a device enabling a smoother handling thereof 
when the tremolo device is used. 
2. Description of the Related Art 
A guitar, for example, an electric guitar, equipped with a tremolo device 
which is manually moved to produce a tremolo effect on musical tones 
obtained by, for example, plucking the strings, is well-known and widely 
used. Known conventional tremolo devices include a synchronized device 
fitted to guitars made by the Fender Company (U.S. Pat. No. 2,741,146), a 
"Bigsby" device fitted to guitars made by the Gibson Company, and a 
"Vibramute" device fitted to guitars made by the Mosrite Company, and 
these tremolo devices have basically similar constructions. 
Namely, these devices are provided with springs having a tension almost the 
same as the total tension of the strings of the guitar, and while an 
equilibrium is maintained between the tension of the springs and the total 
tension of the strings, the tones of the strings of the guitar are raised 
or lowered by moving a rod member, i.e., a tremolo arm, upward and 
downward in relation to a guitar body, to thus rotate the tremolo device 
about one fulcrum on the guitar body and thereby vary the tension of the 
guitar strings. 
In one of the conventional tremolo devices mentioned above the fulcrum 
about which the tremolo device is rotated is provided by two contacts 
between a flat plate, which receives and anchors strings of the guitar, 
and two screws screwed into a guitar body. In this device, the flat plate 
has a knife-edge shaped front end which comes into contact with V-shaped 
grooves formed on the screws, to lower frictional resistance occurring 
when activating the tremolo device and to enable a smoother handling 
thereof. 
In such a tremolo device, however, a problem arise in that the knife-edge 
shaped front end of flat plate is linear engaged with the V-shaped grooves 
of screws, i.e., a smooth handling of the tremolo device can be realized 
only when a bottom of a groove of one screw is aligned with a bottom of a 
groove of the other screw; namely, a height of one V-shaped groove from a 
top surface of the guitar body must be equal to a height of the other 
V-shaped groove. Accordingly if the height of one V-shaped groove is not 
the same as the height of the other V-shaped groove after, for example, 
the heights of the strings of the guitar are adjusted, or after a thorough 
overhaul of the guitar, the frictional resistance occurring when using the 
tremolo device will be remarkably increased to thereby make the handling 
of the tremolo device uneven and difficult. 
SUMMARY OF THE INVENTION 
An object of the present invention is to solve the above-mentioned problem 
by providing a tremolo device for a guitar by which it is possible to 
realize a smooth handling of the device even if the height of one contact 
is not the same as the height of the other contact. 
The above object is achieved, according to the present invention, by 
providing a tremolo device for a guitar comprising: a base plate means 
able to receive and anchor strings of the guitar and including a flat 
plate pivotably mounted about a fulcrum on the guitar, and a bar secured 
to the flat plate, the bar extending from the flat plate into a guitar 
body; spring means including at least one tension spring, the tension 
spring having one end engaged with the guitar body and another end engaged 
with the bar, to thereby urge the base plate means in a direction of 
rotation opposite to a rotating force applied to the base plate means in 
an another direction of rotation due to a tension of the guitar strings; 
and a tremolo arm extending from and manually engageable with the base 
plate means to oscillate the base plate means and thereby vary a tension 
applied to the strings, whereby a tremolo effect is produced; the fulcrum 
being provided by at least two contacts between a pin-shaped member 
provided with a substantially half-spherical tip portion having a 
predetermined curvature, and a concave member able to come into contact 
with the pin-shaped member and having a depression in the form of a 
circular opening having a radius greater than that of the predetermined 
curvature of the half-spherical tip portion.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 2, reference numeral 1 designates a tremolo device 
for a guitar in accordance with the first embodiment of the present 
invention. As shown in FIG. 1, the tremolo device 1 includes a flat plate 
2 and a bar 3 secured to a lower surface 2a of the plate 2. The flat plate 
2 has a plurality of bridge members 4 and corresponding anchor members 5 
arranged thereon. 
Reference numeral 6 designates a tremolo arm. The tremolo arm 6 is screwed 
into the flat plate 2 and extends upward therefrom, and referential 
numeral 7 designates strings of the guitar, the extremity of each string 7 
being provided with an anchor element 8 seated on the anchor member 5. 
Each string 7 is then passed over the corresponding bridge member 4, and 
the other extremity of each string 7 is fixed to a tuning peg in a guitar 
head, not shown in the figures. 
The bar 3 is provided with recesses 3a at the lower extremity thereof, and 
one end of each of a plurality of tension springs 9 is engaged with a 
respective recess 3a. The other ends of the tension springs 9 are 
connected to a guitar body 10. Note, the plurality of tension springs 9 
may be replaced by one tension spring. The tension springs 9 impart a 
rotational force to the bar 3 and the flat plate 2 in a clockwise 
direction as seen in FIG. 2, against an another rotating force in the 
opposite direction, i.e., the counter-clockwise direction as seen in FIG. 
2, derived from the total tension of the strings 7. 
Reference numeral 11 designates a fulcrum about which the flat plate 2 is 
rotated. The tremolo arm 6 is manually engageable to oscillate the flat 
plate 2 and the bar 3 about this fulcrum 11, to thereby vary the tension 
of the guitar strings 7, and thus produce a tremolo effect while raising 
or lowering the tone of the guitar strings 7. 
To provide the fulcrum 11 of the tremolo device 1, two pin-shaped members 
12 are inserted in a front end of the flat plate 2 on one hand, and a 
receiving member 13 is arranged on the guitar body 10. As shown in detail 
in FIG. 3, each pin-shaped member 12 has a ball 14 embedded in a tip of 
the member 12, to form a half-spherical tip portion having a predetermined 
curvature. The ball 14 is made of rigid material such a steel. The 
receiving member 13 has two concave members 15 embedded in each side 
thereof, corresponding to two pin-shaped members 12, and each concave 
member 15 is provided with a half-spherical depression 16 into which the 
corresponding pin-shaped member 12 can be easily inserted. Namely, the 
concave member 15 is formed in such a manner that a circular opening of 
the depression 16 has a greater radius than the above predetermined 
curvature of the ball 14. Preferably, the concave member 15 is hardened 
by, for example, quenching process, to prevent abrasion of the concave 
member 15 by the pin-shaped member 12. Note that the receiving member 13 
is fixed to the guitar body 10 by screws 17. 
According to the above-described construction of the fulcrum of the tremolo 
device, it is possible to realize a smooth handling when activating the 
tremolo device, since a point of each pin-shaped member 12 comes into 
contact with each concave member 15, whereby frictional resistance 
occurring at the fulcrum 11 will be remarkably reduced in comparison with 
the conventional linear contact. Furthermore, even if the receiving member 
13 is mounted and inclined to a top surface of the guitar body 10, a 
smooth handling of the tremolo device 1 still can be realized, for the 
above reasons. 
FIG. 4 shows a second embodiment of the present invention. 
According to this embodiment, there are provided a pin-shaped member 22 and 
a concave member 25, corresponding to the above pin-shaped member 12 and 
the concave member 15, respectively. Namely, in this embodiment, the 
pin-shaped member 22 is not provided with the rigid ball 14 as shown in 
FIG. 3, but the member 22 itself is formed with a half-spherical tip 
portion 22a having a predetermined curvature. Also, the concave member 25 
is provided with a substantially conical-shaped depression 26 having a 
circular opening which has a greater radius than the curvature of tip 
portion 22a. 
FIG. 5 shows a third embodiment of the present invention, which provides a 
fulcrum different from those provided by the first and second embodiments. 
According to this embodiment, a pin-shaped member 32 comprises a rigid ball 
33 and a ball-receiving pin 34 provided with a conical-shaped depression 
34a into which the ball 33 is mounted, and a concave member 35 provided 
with a conical-shaped depression 36 into which the ball 33 is mounted. 
That is, the ball-receiving pin 34 is linked to the concave member 35 
through the intermediary of the ball 33. Note that a circular opening of 
the conical-shaped depression 36 has a greater diameter than that of the 
ball 33. Namely, the former has a greater radius than a curvature of tip 
of the pin shaped member 32. Although the pin-shaped member 32 comes into 
contact with the concave member 35 in a circular line in this embodiment, 
it is possible to realize a smooth handling when activating the tremolo 
device, due to the rotation of the ball 33. 
Although the pin-shaped member 12, 22 or 32 is attached to the flat plate 2 
and the concave member 15, 25 or 35 is mounted on the stable guitar body 
10 in the above embodiments, it will be understood by those skilled in the 
art that the pin-shaped member may be arranged on the guitar body and the 
concave member may be attached to the flat plate as a modification. 
FIGS. 6 and 7 show a fourth embodiment of the present invention. 
Note, in FIGS. 6 and 7, elements similar to those of the first embodiment 
shown in FIGS. 1 and 2 are indicated by the same reference numerals, and 
elements corresponding to those of the first embodiment are indicated by 
the same reference numerals suffixed with a prime. 
According to this embodiment, a bridge member 4' is separated from a flat 
plate 2' i.e., the member 4' is mounted on the guitar body 10. In 
addition, the member 4' has two concave members 15 embedded in each side 
thereof. Therefore, in this embodiment, the receiving member 13 of the 
first embodiment can be omitted, to thereby reduce the number of 
components of the tremolo device. Furthermore, according to this 
embodiment, by mounting the bridge member 4' supporting the strings 7 on 
the guitar body 10, the levels of the strings 7 from the guitar body 10 
will be constant even if the tremolo device is activated. Consequently, 
unexpected contact of the strings 7 with frets of a fingerboard (not 
shown), which often occurs with the conventional tremolo device when 
moving the tremolo arm upward, will be eliminated. Furthermore, even when 
playing the guitar while resting the hand on the bridge member 4', without 
a tremolo effect, the tuning of the guitar will not be affected, due to 
the stable mounting of the member 4'. 
It will be understood by those skilled in the art that the foregoing 
description is of preferred embodiments of the disclosed tremolo device, 
and that various changes and modifications may be made to the present 
invention without departing from the spirit thereof. For example, although 
the fulcrum in the previous embodiments is positioned on the guitar body, 
it may be located in a guitar hole into which the bar of the tremolo 
device extends to thereby enable a change of the feeling of handling of 
the tremolo arm as required by the player.