Abstract:
A tri-modal—energy storage mode, fail-safe mode, and operating mode—fail-safe actuator with low overall power consumption and specifically low fail-safe power consumption due to energy storage pawling mechanisms. Stored energy is discharged at a controlled rate in fail-safe mode. The actuator&#39;s sequencing through its three modes is enabled by a dual-cam/clutch system which is powered separately from the operational (shaft control) system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority for all similar material that is part of the following Provisional Patent Applications: ROTARY ELECTRIC ACTUATOR WITH A MECHANICAL SPRING RETURN BACK-UP, Ser. No. 60/148,602, inventor Thomas Edward Coe, filed on Aug. 12, 1999; and IMPROVEMENTS TO ROTARY ELECTRIC ACTUATOR WITH A MECHANICAL SPRING RETURN BACK-UP, Ser. No. 60/213,035, inventor Thomas Edward Coe, filed on Jun. 21, 2000. 
    
    
     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&#39;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 valve actuators requires that the stored energy be maintained by a constant power supply, for example, U.S. Pat. No. 5,195,721. In this invention, a compression spring is used, versus a power spring, and the fail-safe spring is maintained in position by a solenoid, requiring around, but less than, 20 watts of power. 
     The patents noted herein provide information regarding the developments that have taken place in the field of fail-safe electric actuator technology. Clearly the instant invention provides many advantages over the prior art inventions noted above. Again it is noted that the invention, in comparison with prior art rotary fail-safe electric actuation, provides the following advantages: 
     higher torque/volume ratio; 
     improved simplicity of operation and maintenance 
     increased speed control; and 
     reduced power consumption to maintain fail-safe mode. 
     BRIEF SUMMARY OF THE INVENTION 
     An actuator that provides increased torque/volume ratio, improved simplicity of maintenance and repair, increased speed control, and reduced power consumption to maintain fail-safe mode is disclosed. To increase the torque/volume ratio during normal and fail-safe operations, a novel clutching mechanism that enables three separate actuator modes is disclosed. To reduce complexity in maintaining and repairing the actuator, a dual motor system and the use of power springs are disclosed. One of the motors is used for sequencing operations, and the other for controlling actuator output. And finally, to reduce power consumption for maintaining fail-safe mode, and for maintaining torque during fail-safe operation, a power spring system, pawling mechanisms, and supporting clutching system are disclosed whereby energy is stored in power springs, maintained through pawling and worm gear systems, and released during clutch-controlled failure mode operation. Energy is maintained in the power springs not by a constant energy source but by gear locking mechanisms, which allow rotation in only one direction. When in fail-safe mode, the positioning or main power spring is released at a controlled rate through the interaction of the clutching system and an escapement mechanism. 
     The basic function of the disclosed actuator is to direct energy flow through three separate modes of operation: energy storage mode, run mode, and fail-safe mode. During power-up, the smaller of the two motors delivers the required amount of energy to the smaller of the two power springs to achieve desired tension in the spring so that spring can be used to drive the cams which set the actuator&#39;s mode properly during fail-safe operation. This spring is later used during fail-safe operation and its stored energy is maintained through a worm gear locking mechanism. Also during power-up, the larger of the two motors delivers the required amount of energy to the larger of the two power springs, the main spring, the spring that drives the output during fail-safe operations. The stored energy in this spring is maintained through a specially-formed pawl which has a tooth positioned between gear teeth in one of the cam gears. Upon completion of energy storage, the actuator is placed into run mode. Once in run mode, the actuator is free to function normally. During a power or signal loss, the actuator is taken out of run mode and placed in fail-safe mode through the energy stored in the smaller of the two springs. This condition allows the main spring to discharge, driving the output to full clockwise or counterclockwise positioning. Each of these modes is discussed in the following paragraphs. 
     When power is supplied to the actuator, electronic circuitry determines the condition of the actuator. If the actuator is in low energy state, the secondary or sequencing motor drives the cam mechanism which sets the clutches properly, providing a path for energy to flow to the power springs. Energy storage continues until the tension required to rotate the main spring shaft overcomes a pre-load spring and trips a micro switch, cutting power to the motor. Energy storage is maintained as described above. 
     After the first micro switch has been tripped, the secondary or smaller motor continues to drive the cam mechanism in the same direction until the final position micro switch is tripped. The clutch mechanism is now providing a path for the larger motor to drive the output gear train of the actuator with the fail-safe springs fully wound and on stand-by. At this point, the actuator is operating normally. 
     During loss of signal or power interruption, the actuator circuitry applies reverse polarity across the solenoid, which causes the solenoid plunger to extend, with the aid of a small spring. The solenoid plunger/spring combination removes or disengages the worm from the worm wheel, which allows the smaller spring to discharge, thus forcing the cam/clutch mechanism to return to the initial low energy condition. In this position, after placing the motor gear train in a neutral position, a path is provided for the main power spring to discharge to the output of the actuator. As the spring is unwound, an escapement mechanism, which is located between the drive gear and the main spring, controls the rate of release of the energy. The escapement, a clockworks-type mechanism, rocks between the spring and drive gear, periodically engaging on its edge with the drive gear, which slows the rate of energy release from the main spring. The rate of release of the spring&#39;s energy is selectable based upon the desired reverse time of the actuator. 
     The dual-cam subsystem is comprised of two slotted cams, two interlocked cam gears, and two bearing cup assemblies, among other parts. The cams are hollow cylinders housing bearing cup assemblies and cam pin drivers which are attached each to the interlocking cam gears. Pins, one for each cam, which are elongated, solid, thin cylinders, are slidably inserted through cam slots, bearing cup assemblies, and cam pin drivers. The slots spiral partially up the circumference of the cams. Thus, the rotation of the interlocked cam gears causes the pins to move within the slots, among other things, and the position of the pins within the slots relative to each other indicates the actuator&#39;s mode. 
     Connected concentrically with the dual-cams are the dual-clutches comprised of clutch shafts, gears, pinions, and clutch bodies. Each clutch body is a disk which is slidably positioned on the clutch shaft between pinions and gears at each of the ends of the clutch shaft. Each pinion is also disk-shaped, and is fabricated with slots for accepting pins. On each face of each clutch body disk are positioned retractable is tapered pins which retract into the recesses in the clutch body upon pressure. Within the clutch body and adjacent to the base of each pin is a spring that lies between the two pins protruding from opposite sides of the clutch body disk. The pins are designed to retract only so far as the spring will allow, but far enough so that the pin will not inhibit the movement of the clutch body or pinion with respect to each other until the pin is anchored in a slot. During gear changes, the tapered pins become seated in the slots of either one of the slotted output pinions that surround the clutch assembly on the clutch assembly shaft. Because the output pinions are slotted, the tapered pins do not have to line up exactly before engaging. Also, the pins are tapered at such an angle as to reduce the force required to overcome the friction that occurs between the pins and the slots during gear changes. 
     Thus, the disclosed electric rotary actuator is comprised of novel components that accomplish fail-safe energy storage, controlled energy release during fail-safe operation, dual clutch and cam subsystems that provide for three separate modes of operation within a relatively small volume and with a relatively small power consumption. 
     It is therefore an object of the present invention to provide increased torque/volume ratio in both normal and fail-safe modes through a novel clutching mechanism, the use of power springs, and other novel design features. 
     Another object of the present invention is to provide an increase in reliability through reduction in complexity in operation and maintenance. Separation of functionality and control of various functions through dual motors provides decoupling of interactions and thus a reduction in the complexity of problem-solving and operational downtime. Unique design provides for some on-site maintenance, which also can reduce effective downtime. 
     A further object of the invention is to provide reduced power consumption required for maintaining fail-safe capability. Reduction in power consumption is accomplished through the improved way in which stored energy is maintained through pawl and worm gear mechanisms. 
     A further object of the invention is to provide increased speed control during positioning. This is accomplished through the novel escapement mechanism of the instant invention. 
     A yet still further object of the invention is to provide a design that can accommodate either DC or AC motors. 
     A yet still further object of the invention is to provide a design that can accommodate either a latching or non-latching solenoid. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     These and further objects of the present invention will become apparent to is those skilled in the art after a study of the present disclosure of the invention and with reference to the accompanying drawing which is a part hereof, wherein like numerals refer to like parts throughout, and in which: 
     FIG. 1 is a perspective drawing of the side view of the actuator showing many of its major components. 
     FIG. 2 is a perspective drawing of the actuator from the opposite side from FIG. 1 showing many of its major components. 
     FIG. 3 is a parts diagram of most of the major components of the rotary electric actuator and their positions in relation to each other. 
     FIGS. 4A and 4B are worm gear/cam spring coupling top views showing the cam spring in high energy mode (FIG. 4B) and low energy mode (FIG.  4 A). 
     FIGS. 5A and 5B are worm gear/cam spring coupling top angles perspective views showing the cam spring in high energy mode (FIG. 5B) and low energy mode (FIG.  5 A). 
     FIG. 6 is a perspective diagram of the internals of the actuator featuring the main spring pawling system in high energy mode (pawl engaged in toothed edge of upper clutch pin receiver plate). 
     FIG. 7 shows the geometry of the pawl of the preferred embodiment that accomplishes powerless energy storage in the main power spring. 
     FIG. 8 shows diagrammatic views of various parts of the controlled energy release subsystem including the preferred embodiment escapement. 
     FIG. 9 is side perspective view of the preferred embodiment escapement. 
     FIG. 10 illustrates a diagrammatic view of another escapement embodiment. 
     FIG. 11 is a perspective drawing from the same side view as FIG. 1 but having the bearing cup assembly exposed, i.e. having no right hand side cam gear nor cam. 
     FIGS. 12A,  12 B, and  12 C are diagrams of the configuration of clutch pin within the cam slot when the actuator is in its various modes, and perspective views of the side-by-side cams and the bearing cup assembly respectively. 
     FIG. 13 is a parts diagram for the bearing cup assembly of the cam/clutch system. 
     FIG. 14 is a detailed diagram for the clutch assembly including clutch pin geometry view. 
     FIG. 15 is a detailed diagram for the clutch assembly viewed from a different perspective from FIG.  14 . 
     FIG. 16 is a parts diagram for the clutch assembly. 
     FIGS. 17A and 17B are two views of the anti-backwinding pawl. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1,  2  and  3 , electric actuator  10 , which can be designed to deliver virtually any required torque, comprises energy storage, operational, and fail-safe subsystems which operate in conjunction to provide full clockwise or counterclockwise positioning of, for example, a damper or valve, through output shaft  11 . Actuator  10 , to accommodate the functionality embodied in the three possible subsystems, has at least tri-modal capability. This capability is provided by the dual clutch/cam mechanism depicted in FIGS. 11-16. Components of actuator  10  that provide energy storage mode are depicted in FIGS. 4-7 and those that depict fail-safe mode are depicted in FIGS. 8-10. 
     Referring now to FIGS. 11-16, tri-modal capability is accomplished by virtue of the fact that each of the dual clutches can be in one of two possible gears, thus indicating up to four possible modes: both up, both down, left up/right down, and right up/left down. “Up” and “down” indicate the position of clutch body  401  on clutch assembly shaft  402  at any given time. Pin  403  indicates modality as follows: referring to FIG. 12A, when pins  403  are positioned at 120° position  450  within circumferential cam slots  924 , actuator  10  is in run mode. When pins  403  are positioned at 65° position  452  within circumferential cam slots  924 , actuator  10  is in energy storage mode, and when pins  403  are positioned at 0° position  454  within circumferential cam slots  924 , actuator  10  is in fail-safe mode. 
     Other features of the novel cam/clutch configuration are as follows. Referring to FIGS. 14-16 clutch pins  405  are tapered and slots  409  are also tapered in the direction  408  of pinion output gears  323 . Each clutch body assembly comprises disc-shaped clutch body  401  having retractable tapered pins  405 , secured between an upper and a lower plates  410  by screws  303 . Pins  405  can be any size, but must be tapered at an angle of 3-7°, depending upon the surface finish. Also comprising each clutch body assembly are clutch pin receiver plates  434  floatably disposed along clutch assembly shaft  402 . Clutch body  401 , clutch assembly shaft  402 , and clutch rod  407  are recessed with roller recesses  420  large enough to accept pin  403  and rollers  406 . Clutch receiver plates  434  are recessed with slots  409  to accept clutch pins  405 , the seating of which clutch pins  405  subsequently engages gears. Thus, retractable clutch pins  405  can be properly seated in slots  409  more quickly than if clutch pins  405  were each required to mate with an analogous hole in receiver plate  434 . When clutch pins  405  are seated in slots  409 , they remain so seated until gear shifting occurs. However, because clutch pins  405  are not required to exactly match identically-sized holes in clutch pin receiver plate  434 , gear shifts can be accomplished much more quickly with slots  409 . Additionally, clutch pins  405  have at their bases spring recesses  413  which house clutch pin springs  412 . Thus, when clutch pins  405  are attempting to engage with slots  409 , but when they are flush with the non-slotted parts of clutch pin receiver plate  434 , clutch pins  405  retract to enable smoother and quicker gear transitions. Clutch body  401 , mounted upon clutch rod  407 , houses clutch pin springs  412  and, when they are retracted, clutch pins  405 . Sequencing of modes, powering the cam/clutch mechanism to switch from energy storage to run mode, is cam motor  107 . Cam bodies  921 , covered during operation by cam covers  112 , and bearing cup  503  are slotted with openings that must be large enough to house pins  403  and rollers  406 . In the preferred embodiments, cam body slot  924  extends over half of the circumference of cam body  921 . Pins  403  are narrow cylinders, in the preferred embodiment, and roller  406  are fabricated to be slidably disposed upon pins  403  enabling low-friction insertion of pins  403  into slots  924  and recess  504 . 
     Note that pressure from the device that actuator  10  is positioning could cause float of the cam/clutch mechanism while one clutch is in “up” position (during fail-safe or power storage mode). To prevent this unwanted movement, and referring now to FIGS. 1 and 17, anti-backwinding pawl  550  engages with one of a plurality of notches  551  in lower clutch pin receiver plate  436 . Head  553  of pawl  550  is fabricated symmetrically so that pawl  550  can be used for both lower clutch pin receiver plates  436  in right- or left-handed positions. Edges  554  are squared so that the downward movement of clutch body  401  releases pawl  550  so that receiver plate  436  can spin freely to accept clutch pins  405  and thus switch modes. 
     Referring now to FIGS. 4-7, power storage subsystem components are power spring  702 , cam spring  1702 , cam motor  107 , and motor  105 . Note that motors  105  and  107  can be any source of power, and springs  702  and  1702  can be any means for energy storage. In this mode, both cam spring shaft  102  and main spring shaft  101  wind their respective springs  1702  and  702 . Cam motor  107 , the operations sequencing motor, also winds cam spring  1702  during energy storage mode. Motor  105 , the operational motor, also winds main spring  702  during energy storage mode. When cam spring  1702  is completely wound, and referring now to FIGS. 4A,  4 B,  5 A, and  5 B, its high energy state is maintained by its physical position with respect to worm gear  650 . FIGS. 4B and 5B illustrates cam spring  1702  in high energy state, i.e. worm gear  650  is adjacent to cam spring  1702 , thus maintaining its wound condition. When main spring  702  is completely wound, motor  105  turns off, cam motor  107  again turns on, the cams move the clutches into run mode, i.e. the clutches are in the opposite up/down position from fail-over mode, and then motor  105  turns back on to begin operational positioning. Main spring  702  is completely wound when pre-load spring  150  reaches a certain tension that causes micro-switch  151  to be tripped. High energy state in main spring  702  is maintained as a result of the interlocking of pawl  2201  with the toothed edge  552  of clutch pin receiver plate  434  as in FIGS. 6 and 7. In the preferred embodiment, and referring now to FIG. 7, pawl  2201  is comma-shaped, comma nib  2203  having a flattened, but thick, edge which fits between the teeth of toothed edge  552  to prevent backwinding of the gear, and thus retains main spring  702 &#39;s stored energy until fail-safe operation. 
     Operational mode, the mode in which the actuator is running normally, begins when main spring  702  is completely wound and pawled. Cams  921  and clutches  401 , the mechanisms by which actuator  10  operates in one of its possible modes, are operationally interconnected through bearing cup assemblies  246 . Cam pin driver  902  is recessed  905  to accept the head of retaining screw  244 , thus allowing for a linear response in bearing cup assembly  246 . Operationally, dual cams are driven by cam motor  107  through gears  901  mounted on cam pin drivers  902  which rotate in directions opposite each other, thus providing a rotative response, or torque, in bearing cup assembly  246 . While rotating, cam pin drivers  902  drive pins  403  through rollers  406  which follow cam slots  924 . Bearing cup assemblies  246  are forced up or down by the cams. The force is supplied by thrust bearings  501 , which, in the preferred embodiment, are trapped between bearing retainer clips  502  and clutch actuators within bearing cup  503 . In the preferred embodiment, bearing retainer clip  502  is a non-joining circularly-shaped single-wire spring clip. Thrust bearings  501 , attached to clutch rods  407 , when moving in the −y direction apply a force on clutch rods  407 , or when moving in the +y direction, referring to FIG. 16, apply a force on retainer screws  244 , which in turn pull clutch rods  407 . Clutch rods  407  maintain the vertical (y-direction) position between the cams and clutch bodies  401  by means of the previously-described forces and by pins  403  and rollers  406  which fit into recesses  420  in clutch bodies  401 . 
     Referring to FIGS. 8,  9 , and  10 , during fail-safe mode, which usually involves some type of power interruption, the cam/clutch and pin/roller configurations reflect this mode as described above, and fail-safe subsystem components control actuation. Referring to FIGS. 4A and 5A, first, solenoid  704  triggers worm gear  650  out of its pawled, energy storage, condition. Cam spring  1702  is released, which signals to the cam/clutch mechanism to change gears, and thus enables the unwinding of main spring  702 . At this point, main spring  702  reverses the movement of shaft  11  at the rate that main spring  702  could unwind. Since it might not always be desirable or possible to release energy at that high a rate, in the preferred embodiment, and referring to FIGS. 1,  8 , and  9 , escapement  2301  can be used to adjust spring  702 &#39;s discharge rate. Alternately, escapement  252 , referring to FIG. 10, can be used for the same purpose. Escapement  2301  comprises a clockworks-type mechanism with a substantially triangularly-shaped cavitied  2321  plate that is notched  2303 . Adjacent to the cavitied plate is an indexing/positioning shaft  2313  having, upon its circumference, escapement nub  2311 . During normal operations, nub  2311  rests in notch  2303 , but during fail-safe mode, escapement  2301  rocks between main spring  702  and drive gear  2323 , which interlocks with cog wheel  2305  through gear  2307 . During fail-safe mode, main spring shaft  101 , underlain by plate  2401 , begins to unwind. In the process, escapement  2301  is nudged, which in turn nudges drive gear  2323 . The discharge rate of main spring  702  is controlled by the rate at which escapement  2301  rocks, which is controlled by flywheel  2309  underlain by and attached to control springs  1703 . Escapement  2301  must drag along flywheel  2309  and control springs  1703  as it rocks. Thus the size of these control devices determines the rate at which energy is discharged. 
     Another escapement geometry comprises ramp gear  250  which is attached to spring shaft  101 . Ramp gear  250  is a large-toothed disk falbricated to engage and temporarily interlock with escapement  252  through escapement  252 &#39;s rocking motion. Escapement  252  is fabricated with two teeth, one near each end in the preferred embodiment, for interlocking with escapement  252  which is designed to operate in conjunction with ramp gear  250  and with gear  254  which is engaged at outer edge  260  of escapement  252 . As main spring shaft  101  unwinds, escapement  252  teeth become alternately engaged at one end of escapement  252 , disengaged completely, and then engaged at the other end of escapement  252  with ramp gear  250 . During this cycle, gear  254  alternately engages and disengages with escapement edge  260 , providing resistive inertia that slows the rotative speed of the escapement. As spring  702  unwinds, spring gear  13 , which interlocks with drive gear  2323 , moves shaft  11  at the desired energy discharge rate. 
     It should be understood that the invention is not limited to simply actuator applications, but the same system, apparatus or device may be used for any type of clutched, fail-safe, spring-driven application. The uses expressly noted and suggested inferentially and otherwise, and the various methods of use and many of the invention&#39;s attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement of the parts thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the forms hereinbefore described being merely preferred or exemplary embodiments thereof.