Power plants – Pressure fluid source and motor – Unsafeness – unreadiness or disarray prevent manual change or...
Reexamination Certificate
2000-06-29
2002-05-28
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Unsafeness, unreadiness or disarray prevent manual change or...
Reexamination Certificate
active
06393837
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air tool such as an air grinder or the like with a safety device.
2. Description of the Related Art
Conventionally, an air grinder driving an abrasive member prevents over-speed by reducing the amount air consumption at low load and by increasing the amount of air at heavy load. Such control maintains a roughly constant speed at all values of load. For these purposes, an air grinder generally includes a speed adjusting apparatus capable of controlling the rotational speed at high and low load.
Referring now to
FIGS. 4
,
5
a
and
5
b
, a speed adjusting apparatus
30
in a main body casing
28
of a prior art air grinder includes a rotary member
31
having a flange portion near the center on a side surface of a cylinder. A speed adjusting valve body
36
includes a flange portion near the bottom of the side surface of the cylinder. A speed adjusting weight
32
, having a substantially L-shaped cross section as seen from the side is pivoted below rotary member
31
.
A valve seat
38
is interposed in an air passage
29
within the main body casing
28
. An air motor
40
is driven by air supplied through the air passage
29
. The rotary member
31
is directly connected to an output shaft
41
of the air motor
40
. Rotation of the air motor
40
is directly transferred to the rotary member
31
. The speed adjusting valve body
36
is fitted to the outside of the rotary member
31
. The speed adjusting valve body
36
is free to slide in an axial direction along the outer surface of the rotary member
31
. The speed adjusting valve body
36
and the valve seat
38
of the air passage
29
are positioned facing each other.
Spring receivers
39
,
39
protrude diametrically outward on both opposing side surfaces above the rotary member
31
. The respective spring receivers
39
and
39
are fitted into axially elongated holes pierced through opposing side surfaces of the rotary member
31
above the speed adjusting valve body
36
. A speed adjusting valve spring
37
is interposed between the spring receivers
39
,
39
and the flange portion of the speed adjusting valve body
36
. The speed adjusting valve body
36
is urged by the speed adjusting valve spring
37
in a direction away from the valve seat
38
.
The speed adjusting weights
32
and
32
, having an a substantially L-shaped cross section as seen from a side view, are each pivoted on a pin
34
. The speed adjusting weights
32
,
32
each includes a weight portion
33
and a lever portion
35
. As the rotational speed of rotary member
31
increases, the weight portions of the speed adjusting weights
32
,
32
are urged outward by centrifugal force about their pins
34
,
34
. This tilts the speed adjusting weights
32
,
32
, as shown in
FIG. 5
a
so that the lever portions
35
,
35
apply an upward force on the flange portion of the rotary member
31
.
In operation, at light load, the speed adjusting apparatus
30
assumes the configuration shown in
FIG. 5
a
. Centrifugal force on the weight portions
33
,
33
of the speed adjusting weight
32
,
32
due to the rotation of the air motor
40
, tilts the weight portions
33
,
33
outward around their respective pins
34
,
34
. The lever portions
35
,
35
, in contact with the flange portion of the speed adjusting valve body
36
, apply a force in an upward direction for urging the speed adjusting valve body
36
. This moves speed adjusting valve body closer to the valve seat
38
. When the thrust applied by the speed adjusting weights
32
,
32
exceeds the opposing force of the speed adjusting valve spring
37
, the speed adjusting valve body
36
is displaced upward, thereby decreasing the effective opening of the air passage through the valve seat
38
. As a result, the amount of air supplied through the air passage
29
is reduced, and the rotational speed is correspondingly reduced.
Referring now to
FIG. 5
b
, under heavy load on an abrasive member, such as a grindstone or the like (not shown), the rotational speed of the air motor
40
is reduced. As a result, the centrifugal force applied to the speed adjusting weight
32
is reduced. Accordingly, the thrust applied in the upward direction to speed adjusting valve body
36
is also reduced. Accordingly, the speed adjusting valve body
36
is pressed downward by the speed adjusting valve spring
37
to move the speed adjusting valve body away from the valve seat
38
. This increases the effective opening of the air passage thereof As a result, an amount of air supplied from the air passage
29
is increased, and the torque output of the air motor
40
is increased. As a result, slowing of the air motor
40
under heavy load is reduced. As mentioned above, the rotational speed of the air motor is automatically adjusted by the speed adjusting apparatus
30
.
However, if the speed adjusting apparatus
30
mentioned above does not operate normally for some reason, for example, because of foreign material in the speed adjusting apparatus
30
, a dangerous over-speed condition may result. In the conventional device, the only way to prevent this danger is to perform periodic inspections by dismantling the device.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide an air tool which overcomes the conventional disadvantages mentioned above.
It is a further object of the invention to provide an air tool having a safety device which automatically reduces the rotational rate and locks the air tool to inhibit normal use when rotation generated by an air motor of the air tool exceeds a predetermined rotational speed.
Then, in accordance with a first aspect of the present invention, there is provided an air tool with a safety device comprising: a main body casing
22
, an air passage
23
formed within the main body casing
22
, an air motor
26
rotated by air supplied from the air passage
23
, a valve seat
24
interposed in the air passage
23
, a safety valve body
4
arranged in such a manner as to change an effective opening of the passage by moving in a direction of moving close to and apart from the valve seat
24
, first urging means
6
for urging the safety valve body
4
in a direction of moving close to the valve seat
24
, a rotary member
2
rotating in interlocking with an output shaft
25
of the air motor
26
, a safety valve stopper
16
mounted to the rotary member
2
so as to be displaced outward in a diametrical direction due to a centrifugal force generated by a rotation of the rotary member
2
, and second urging means
20
for urging the safety valve stopper
16
in a direction inverse to a direction in which the centrifugal force is applied, wherein a lock mechanism for locking a motion of the safety valve body
4
in a steady operation state that the safety valve body
4
moves apart from the valve seat
24
against an urging force of the first urging means
6
so as to increase an effective opening of the passage, disengaging the lock so as to move the safety valve body
4
in a direction of moving close to the valve seat
24
by the first urging means
6
, thereby reducing the effective opening of the passage when a rotation rate of the output shaft
25
of the air motor
26
is increased to be over a predetermined rotation rate and the safety valve stopper
16
moves against the urging force of the second urging means
20
due to the centrifugal force, and again locking the motion of the safety valve body
4
in this state is provided between the safety valve body
4
and the safety valve stopper
16
.
In accordance with the air tool with the safety device described in the first aspect mentioned above, when the rotational speed of the output shaft
25
of the air motor
26
exceeds a predetermined speed of rotation, for example, 10 to 15% of a normal rotational speed, the safety valve stopper
16
locking the motion of the safety valve body
4
mentioned above moves against the urging force of the second urging means
20
due to the centrifugal force so as
Fuji Air Tools Co., Inc.
Leslie Michael
Look Edward K.
Morrison Law Firm
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