Machine element or mechanism – Mechanical movements – Reciprocating or oscillating to or from alternating rotary
Reexamination Certificate
2000-01-19
2002-09-10
Lee, Kevin (Department: 3753)
Machine element or mechanism
Mechanical movements
Reciprocating or oscillating to or from alternating rotary
C074S002000, C074S424820, C251S129110, C251S069000
Reexamination Certificate
active
06446519
ABSTRACT:
RELATED APPLICATIONS
This application claims the benefit of European patent application No. 99101497.8 filed Jan. 27, 1999, hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates generally to electrically powered actuators for actuating control mechanisms as valves, chokes or other control mechanisms used in particular for sub-sea oil or gas production systems. Of course such an actuator could also be used in any terrestrial remote or inaccessible location.
U.S. Pat. No. 5,195,721 discloses a fail-safe valve actuator which moves a closure member of the valve between two positions. A separate spring member is arranged for urging the second drive part in a direction to move a closure member to a second position wherein an electrically powered member prevents a first drive part from rotating in an opposite direction and thus holds the closure member in its first position. In response to the loss of the supply of electrical power to the rotating prevention member, the closure member is moved by the spring member to its other position. The rotation preventing means comprises a number of sleeves, gears and pinions and also an electric motor connected by the sleeves, gears and pinions to the drive parts.
For releasing the rotation preventing means, a disc is lifted by a compressed spring and by de-energizing a solenoid, a threaded member is no longer in engagement with a groove in one of the sleeves and a wrapped spring is correspondingly no longer tightened around the sleeves, so that one of the sleeves may be rotated with respect to the other whereby the two driving parts can move relative to one another.
Accordingly, the valve actuator of U.S. Pat. No. 5,195,721 is of a quite complicated construction with a plurality of parts wherein a separate spring must be provided for forcing the rotatable part back in position and whereby the rotation preventing means uses the electric motor in its turned-off mode to create a torque and transmit same to the actuating member to prevent any rotation thereof.
SUMMARY OF THE INVENTION
For actuating the control mechanism, an actuating member of the actuator is axially moved and in one position, the control mechanism is, for example, switched on and in another position of the actuating member is switched off. Such actuators are arranged within a housing to protect the device against outer influences at the corresponding terrestrial or aquatic location. Within the housing, an electric motor is arranged for rotating a first rotatable part and a second rotatable part both in engagement with one another. The two rotatable parts form a reversible drive for axially moving the actuating member in a feed direction to the control mechanism for operating it. In its operating position the actuating member is locked by a rotation prevention member and for unlocking the actuating member, a release is provided that permits an axial movement of the actuating member in a direction opposite to the feed direction.
It is, therefore, an object of the invention to provide an actuator of simple construction reliably preventing rotation of the actuating member without loading the electric motor with a torque for preventing such rotation.
This object is solved by an actuator of know construction characterised in that the force acting on the actuating member is externally applied by the control mechanism and the rotation prevention member is arranged between the second rotatable part and the housing to rotationally fix the rotatable part to the housing to prevent rotation in the second direction.
As the force acting on the actuating member is externally applied by the control mechanism, no additional spring or other device arranged within the actuator is needed. Correspondingly, the construction of the actuator is simplified. To hold the actuating member in position where the control mechanism is actuated, it is no longer necessary to use the electric motor and a torque supplied by it in case it is switched-off, but instead the rotation prevention member is supported by the housing to provide a torque in opposite direction to the torque supplied by the force of the control mechanism acting on the actuating member.
A simple embodiment of the reversible drive comprises an internally threaded screw nut as the first rotatable part and an externally threaded screw stem as the second rotatable part.
To lower friction between screw and stem, the screw nut and screw stem may form a ball screwing device with balls therebetween. In such a case it is also possible to use a high speed, low torque motor as the electric motor.
The housing of the actuator can be such that the electric motor is arranged within the housing and in particular at one end thereof opposite to the control mechanism. In such a way the actuator is compact and can be easily handled.
For fixing the electric motor in a simple manner within the housing, it may be fixed to a sleeve-like head member with a longitudinal boring which itself is fixed to the housing. Besides the rotational force transmitting member, a gear box may be arranged between the transmitting member and the electric motor.
A rotational force transmitting member of simple construction is a sleeve in which one end of the ball screw stem is inserted wherein the other end of the ball screw stem extends from the ball screw nut in direction to the actuating member.
As the rotational force transmitting member connects the ball screw nut and the electric motor, the sleeve may be rotationally fixed to the ball screw nut to transmit any rotation of the motor to the nut. The connection between the sleeve and the ball screw nut may be in any way that allows a rigid attachment.
The sleeve may have a closed end at which it is connected to the electric motor or the gear box. It may further have an open end portion protruding from the head member in which the ball screw nut is inserted.
To prevent rotation of the sleeve with respect to the head member in a simple way at least in that direction used for moving the actuating member in direction to the control mechanism, the sleeve may be rotatable with respect to the head member in one direction and rotatably fixed to the head member in the other direction.
This may be realised by a rotation prevention member arranged between the end portion of the sleeve and an end portion of the head member.
A rotation prevention member of simple construction is realized by end portions of the sleeve and the head member of same outer diameter with a wrapped spring as the rotation prevention member arranged at least partially on both of these end portions. This wrapped spring has no influence in case the sleeve is rotated in one direction but tightens in case it is rotated in the other direction.
For rotatably supporting and holding the sleeve in position, radial and/or thrust bearings may be arranged between the end portion of the sleeve and an inner wall of the housing.
To prevent a direct contact of sleeve and housing, a sleeve-like bushing may be arranged between these bearings and the inner wall of the housing wherein this bushing is at least rotationally fixed to the housing. It may further also be fixed to the housing in axial direction, that means in longitudinal direction of the housing or the ball screw stem.
To also rotatably support that part of the ball screw stem protruding from the ball screw nut in direction to the actuating member, a sleeve-like extension member may be fixed with respect to the housing with a boring in which that part of the ball screw stem is rotatably supported.
In one embodiment of the invention, the extension member is fixed to the bushing and may axially extend therefrom in direction to the actuating member.
According to another embodiment of the invention, a further sleeve-like end member may be arranged between the extension member and the actuating member wherein the end member is rotatably supported within the housing and the rotation prevention member is arranged between the end member and the extension member.
A rotation prevention member of simple co
Conley & Rose & Tayon P.C.
Cooper Cameron Corporation
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