Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-04-20
2001-02-06
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C318S759000, C318S376000, C251S077000, C251S129130
Reexamination Certificate
active
06184604
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a brake mechanism for suppressing the operation speed of an operation end such as a valve or damper provided with a return spring, and a powered actuator having this brake mechanism.
As a conventional powered actuator, a spring return type actuator having a valve or damper as the operation end is used. In this spring return type actuator, the rotation force of a drive motor is transmitted to the operation end through a reduction mechanism to increase the torque, thereby opening/closing the valve or damper constituting the operation end. The valve or damper is provided with a return spring. When power is not supplied to the drive motor because of a power failure or the like, the valve or damper is forcibly fully closed or opened with the force (restoration force) of the return spring. During the return operation of fully closing or opening the valve or damper forcibly, a braking force (brake torque) is effected to moderate impact generated during the full-closing or full-opening operation. An example of the braking method during this return operation includes the following and the like.
I. Inertia braking method employing weight
II. Governor method utilizing friction
III. Impeller method utilizing air resistance
I. Inertia Braking Method Employing Weight
With this method, as shown in
FIG. 16A
, a brake mechanism
1
having a disk
1
-
1
is rotationally connected midway along a power transmission line connected to an operation end. Weights
1
-
2
A and
1
-
2
B are arranged on the disk
1
-
1
and are connected to the rotation center through springs
1
-
3
A and
1
-
3
B. This increases the moment of inertia during the return operation and suppresses an increase in operation speed of the operation end. In this case, the moment of inertia can be changed by a centrifugal force, i.e., the rotation speed, and it is estimated that a brake torque T
B
be substantially constant with respect to a rotation speed N, as shown in FIG.
16
B. Accordingly, the operation speed (return speed) of the operation end from the start of return to the end of return will show the characteristics as shown in FIG.
16
C.
The characteristics shown in
FIG. 16C
are expressed by:
d&ohgr;/dt
=(
TS−TB
)/
J
The moment J of inertia increases in proportion to the second power of the speed, and the brake torque T
B
is constant regardless of the rotation speed.
II. Governor Method Utilizing Friction
With this method, as shown in
FIG. 17A
, a brake mechanism
2
having a case
2
-
1
is rotationally connected midway along a power transmission line connected to an operation end. Drums
2
-
2
A and
2
-
2
B are arranged in the case
2
-
1
and are connected to the rotation center through springs
2
-
3
A and
2
-
3
B. During the return operation, the drums
2
-
2
A and
2
-
2
B are pulled in the radially outward direction by a centrifugal force to generate friction between them and the case
2
-
1
, thereby suppressing an increase in operation speed of the operation end. In this case, it is estimated that a brake torque T
B
increase from a rotation speed N
0
, with which the drums
2
-
2
A and
2
-
2
B start to cause friction with the case
2
-
1
, in substantially proportional to a rotation speed N, as shown in FIG.
17
B. Accordingly, the return speed of the operation end from the start of return to the end of return will show the characteristics as shown in FIG.
17
C.
The characteristics shown in
FIG. 17C
are expressed by:
d&ohgr;/dt
=(
TS−TB
)/
J
The brake torque T
B
is constant when the rotation speed is equal to or smaller than a predetermined value, and is variable when the rotation speed exceeds the predetermined value.
III. Impeller Method Utilizing Air Resistance
With this method, as shown in
FIG. 18A
, a brake mechanism
3
having an impeller
3
-
1
is rotationally connected midway along a power transmission line connected to an operation end. During the return operation, the impeller
3
-
1
rotates to generate a braking force caused by an air resistance, thereby suppressing an increase in operation speed of the operation end. In this case, it is estimated that a brake torque T
B
increase in substantially proportional to a rotation speed N, as shown in FIG.
18
B. Accordingly, the return speed of the operation end from the start of return to the end of return will show the characteristics as shown in FIG.
18
C.
The characteristics shown in
FIG. 18C
are expressed by:
d&ohgr;/dt
=(
TS−TB
)/
J
The brake torque T
B
can be changed in accordance with the rotation speed.
According to the conventional spring return type actuators of this type, however, since a braking force proportional to the rotation speed N cannot be obtained in the inertia braking method I, a stable operation speed cannot be obtained in the return operation of an operation end. Since the portion for generating the braking force causes friction in the governor method II, performance degradation occurs due to the friction. Since a braking force with respect to a shape is limited in the impeller method III, a large braking force cannot be obtained, and a large shape is required to obtain a large braking force. In any method, the structure is complicated to change the return time of the operation end.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a brake mechanism and a powered actuator, capable of obtaining a stable braking force proportional to a rotation speed.
It is another object of the present invention to provide a brake mechanism and a powered actuator, capable of obtaining a large braking force in a compact structure.
It is still another object of the present invention to provide a brake mechanism and a powered actuator, capable of changing the return time of an operation end.
In order to achieve the above objects of the present invention, there is provided a brake mechanism comprising a rotation transmitting mechanism for transmitting at least a rotation force in a first rotational direction supplied from a drive source, the rotation transmitting mechanism being imparted with a returning tendency in a second rotational direction opposite to the first rotational direction, a motor structure having an output shaft rotatably connected to the rotation transmitting mechanism, and braking means for generating a torque in the first rotational direction to the output shaft which, upon being disconnected from the drive source, rotates to return in the second rotational direction through the rotation transmitting mechanism in accordance with the returning tendency, thereby suppressing a returning rotation speed of the rotation transmitting mechanism.
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Patent Abstracts of Japan, vol. 013, No. 267, Jun. 20, 1989.
Patent Abstracts of Japan, vo. 006, No. 081, May 19, 1982.
Miyazaki Takumi
Takano Tomohiro
Blakely & Sokoloff, Taylor & Zafman
Dougherty Thomas M.
Waks Joseph
Yamatake - Honeywell Co., Ltd.
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