Motors: spring – weight – or animal powered – Spring – With winding means
Reexamination Certificate
2000-08-11
2002-08-13
Herrmann, Allan D. (Department: 3682)
Motors: spring, weight, or animal powered
Spring
With winding means
C074S398000, C074S405000, C074S425000, C185S038000, C185S043000, C192S048910, C192S069620, C192S09300C, C251S069000
Reexamination Certificate
active
06431317
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to electrically powered fail-safe actuators for use in a variety of rotary control devices, such as valves and dampers.
2. Description of Related Art
Electric actuators can be used in industrial applications to control full clockwise and counterclockwise positioning, and usually strive for the following characteristics:
high torque per volume;
reliability;
improved control of the speed of the device; and
reduced energy consumption.
Current technology aimed at providing an actuator with these features is described below. All current technology lacks critical features as outlined below that are provided by the instant invention and described in this application.
Fail-safe operation in an actuator is activated when power loss or other external failure condition causes the actuator, without benefit of external electric power, to move the valve to a pre-determined position. To achieve adequate torque, this requirement on an actuator usually necessitates an increase in volume, thus reducing the torque/volume ratio. Fail-safe actuation has been approached in several ways. Some approaches involve an energy storage means such as a spring that is used to move the valve or damper to a certain position when a prespecified condition or set of conditions occurs. U.S. Pat. No. RE30,135 discloses an electric fail-safe actuator that employs a spring which is wound to store energy during operation of the electric drive motor, and an electric clutch operable to disengage the drive motor from the actuator output shaft in response to loss of power from the electrical supply whereby the spring drives the valve in the opposite direction. This device depends on an electric clutch means for switching to power-fail mode. U.S. Pat. No. 5,915,668 discloses a valve actuating apparatus including an actuator having a spring connected to the valve control arm or the clutch assembly for normally biasing the clutch assembly to a first position along the guide member such that the valve control arm is in the closed position. Upon interruption of power, the spring forces the engagement member of the clutch assembly out of engagement with the detent in the guide member and the spring forces the clutch assembly to slide back along the guide member to the first position and rotates the valve control arm to the closed position. In this case, the power-fail spring is forcing the clutch assembly, not the valve control shaft.
U.S. Pat. No. 4,595,081 discloses an electric motor that rotates a valve shaft one direction and a spring which is wound during driving of the shaft by the motor. The motor drives the output shaft and winds the return spring by way of a speed-reducing, torque amplifying gear train. To enable the use of a lighter return spring and the use of a gear train effecting greater torque amplification from the motor to the output shaft, intermediate gears in the drive train apply winding torque to the return spring differentially of the drive torque applied to the output shaft. This device requires intermediate gears and the time differential to switch between the gears. U.S. Pat. No. 5,662,542 discloses an actuating drive with a spring return feature including an electric drive, a reduction gearing having a return spring tensionable by the actuating movement and serving for the spring return movement, a clutch between the electric drive and the reduction gearing and a centrifugal brake device actuated during the spring return movement.
Devices that could effect fail-safe actuation without a spring rely on bias force and clutch mechanisms. For example, U.S. Pat. No. 5,988,319 discloses an apparatus for effecting actuation of a device having a home position and a set position. The apparatus returns the device to the home position upon loss of power to the apparatus. In this invention, a bias member having a cocking mechanism and a release mechanism is disclosed as the preferred embodiment. The bias member provides a bias force to a bias shaft when the cocking mechanism is cocked and the release mechanism is released; the release mechanism is released when power is lost to the actuator. U.S. Pat. No. 4,533,114 discloses an actuator for a rotary valve including a fail-safe mechanism for automatically opening or closing the valve upon the occurrence of a predetermined condition, and for allowing manual operation of the valve. A biased clutch activates the fail-safe mechanism and also couples a worm-gear drive for effecting the manual operation of the valve.
Of foremost concern in actuator design is reducing the physical size of an actuator while maintaining or increasing its torque output. This can be accomplished by novel design and engineering of the component parts of the actuator. One critical component of the electric actuator is the clutching-declutching mechanism, the size and efficiency of which is crucial to actuator torque/volume output. Current technology for clutching mechanisms comprises intermediate gears to effectuate continuous operation between gear changes. U.S. Pat. No. 5,490,433 discloses a transmission subunit with an intermediate shaft having continuous gears of progressive pitch diameters (ramp gears) interposed between pairs of conventional gears. The geometry of the continuous gears permits input gears, output gears, and/or idler gears to freely and independently slide longitudinally the length of the intermediate shaft without disengaging. Helical or spur cut gears can be used throughout. During shifting, an idler quickly passes from a conventional gear to an intermediate, continuous gear where it changes speed ratio progressively until the new ratio is achieved. At this point the idler quickly moves on to the next conventional gear to complete the shift cycle. An automatic locking mechanism assures precise, fixed alignment. This invention requires the presence of ramp gears to implement shift continuity, a requirement that adds volume and reduces torque output because of idle time during gear changes. In addition, torque output is further reduced by clutch pin friction and pin alignment delay.
Reliability in electric actuators has to do with downtime due to failure which is, in part, determined by the actuator's ease of maintainability. Easy to maintain actuators reduce net downtime and thus increase reliability. Reducing actuator complexity is one way to reduce downtime. Highly complex actuators interweave sequencing and operational activities and drive them with the same motor. With these types of devices, isolating a failure, either while testing the device or during operations, can be difficult due to the complex operational sequences required to accomplish actuation. In addition, maintaining such a device can be more complex. Dividing functionality to simplify individual sequences is one way to reduce complexity. The current technology usually comprises one motor that drives both the sequencing of operations in the actuator as well as the output of the actuator. For example, U.S. Pat. No. 5,195,721 discloses a fail safe valve actuator that is powered by an electric motor. A valve stem with a helical groove is moved in one direction by a ball nut rotated by the electric motor to move a valve member to its operating position. The valve member is held in operating position by a solenoid. When power fails, a spring moves the valve stem in the other direction to move the valve member to its fail safe position. In this device, a centrifugal brake is required to limit torque to protect the electric motor from the high torque created when the valve stem abruptly stops moving when the valve member reaches its operating position and when the power fails and the valve stem is moved rapidly to its fail safe position by the spring. Also, energy to power the fail-safe mode is usually stored during normal operation and released upon detection of the condition. The current technology in most fail-safe mechanisms for electric
Davis & Bujold P.L.L.C.
Herrmann Allan D.
Valvcon Corporation
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