Valves and valve actuation – Electrically actuated valve – Rotary electric actuator
Patent
1996-04-30
1998-11-17
McMahon, Marguerite
Valves and valve actuation
Electrically actuated valve
Rotary electric actuator
73168, F16K 3105
Patent
active
058365672
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELDS
The present invention relates to an apparatus for continuous detection of load in an electric valve actuator which is widely used in a nuclear power plant.
In power or petrochemical plants, a number of valves are used, and generally have electric valve actuators as drive means.
The electric valve actuator has a torque limit switch for detecting torque of more than a fixed value when a valve element bites foreign material to stop a drive source, thereby avoiding damage to the valve.
As torque detecting means in an electric valve actuator, an on/off switch which acts when torque of a motor reaches a predetermined value is generally used.
With respect to part of FIG. 1, a general load detecting apparatus in a conventional electric valve actuator will be described.
In FIG. 1, rotation of a motor 1 is reduced by helical gears 2 and 3, and is transmitted to a worm wheel 7 via a tubular worm 5 which is engaged with a worm shaft 4 integrally connected with the helical gear 3 so that the tubular worm 5 may rotate together with the tubular shaft 4. In a central bore of the worm wheel 7, a tubular stem nut 6 is engaged via a spline so that the nut 6 may rotate together with the worm wheel 7. A valve stem 8 is meshed in an internal thread bore of the stem nut 6. The valve stem 8 is therefore elevated and lowered by rotation of the motor 1.
The tubular worm 5 is meshed with an axial spline 9 in a worm shaft 4. The tubular worm 5 is axially movable on the worm shaft 4, and is rotatable together with the worm shaft 4.
On the front surface of the tubular worm 5, a compression spring 10 in which a plurality of belleville springs are reversely overlapped is directly or indirectly engaged. When the tubular worm 5 moves on the worm shaft 4 forward and backward depending on direction and size of torque of the motor 1. the compression spring 10 is compressed depending on the amount of mounted Torque of the motor 1 can be found by detecting deformation amount by a torque switch 11. Therefore, if the motor 1 turns on and off by the torque switch 11 when it reaches to a predetermined torque, overload can be prevented.
PROBLEMS TO BE SOLVED BY THE INVENTION
However, it is impossible to detect torque of motor continuously by an on/off switch type torque detecting means as above.
In the meantime, in the workplace there is a strong need to confirm stability of the operation at any time without disassembling an electric actuator. To comply with such need, it is necessary to detect torque continuously. Furthermore, to carry out sensitive valve control and to check stability of a torque switch at any time, it is necessary to detect torque continuously.
However, a predetermined tone is normally applied to the compression spring 10, to reduce its size and thus, there is an extreme nonlinear relationship between torque of the motor 1 and movement of the compression spring 10. So, even if means for detecting continuous quantity, such as a potentiometer, is used instead of the torque switch 11, it is impossible to detect torque of a motor continuously.
Instead of the tubular worm 5, the stem nut 6 is axially displaced as screw-feeding type, and by compressing the compression spring based on the movement, torque of motor can be detected. However, it is still impossible to detect torque of a motor continuously.
Patent Laid-Open Pub. No.64-58889 discloses an apparatus for continuously detecting thrust of a valve stem applied by torque of a motor. In this device, a strain gauge is directly attached on the outer circumferential surface of the valve stem, and axial elongation and shrinkage of the valve stem itself opposing torque can be detected. However, the diameter of the valve stem cannot be reduced less than a predetermined length. Accordingly, axial elongation and shrinkage of the valve stem which opposes torque becomes smaller, and the invention as disclosed in Patent Laid-Open Pub. No.64-58889 involves a low detecting rate by a strain gauge, thereby making high sensitive detection impossible. In the invention as disclos
McMahon Marguerite
Nippon Gear Co.,Ltd.
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