HK1185392B - Electromechanical actuator apparatus and method for down-hole tools - Google Patents

Description

Electromechanical actuator apparatus and method for downhole tools

Priority claims/related applications

U.S. provisional patent application serial No. 61/327585, filed on 23/4/2010 and entitled "electromechanical actuator apparatus and method for downhole tools," claims benefit under 35 USCs 119(e) and 120, which is incorporated herein by reference in its entirety.

Technical Field

The present apparatus is directed generally to electromechanical actuators and, in particular, to electromechanical actuators primarily for tools used in the gas and/or oil industry for production or production sites for wellbore drilling, workover, and/or drilling.

Background

Electromechanical actuator systems are generally well known and have existed for many years. In the downhole industry (oil, gas, mining, water, exploration, construction, etc.), electromechanical actuators may be used as part of a tool or system including, but not limited to, a reamer, an adjustable gauge (gauge) stabilizer, a vertically steerable tool, a rotary steerable tool, a bypass valve, a packer, a downhole valve, a whipstock, a locking or release mechanism, an anchoring mechanism, or a Measurement While Drilling (MWD) pulse generator. For example, in an MWD pulser, the actuator may be used to drive a pilot/servo valve mechanism that operates a larger mud hydraulically driven valve. Such valves may be part of a system for transmitting data from the bottom of a borehole (commonly referred to as downhole) near the drill bit back to the surface. The downhole portion of these communication systems is commonly referred to as a downhole mud pulser because the system generates programmable pressure pulses in a mud or fluid column that can be used to transmit digital data from downhole to the surface. Mud pulsers are generally well known and there are many different embodiments of mud pulsers and mechanisms that can be used to generate mud pulses.

Disclosure of Invention

Existing systems have one or more of the following problems/limitations that it is desirable to overcome:

larger, longer, heavier devices with a large number of components that make maintenance difficult and require more power than necessary.

Have a large number of parts and parts that are not easily accessible, thus complicating maintenance and reducing reliability.

Compensation of the elastic membrane with a resulting reduced durability, in particular in an environment that deteriorates the elastic membrane.

No damping, self-aligning system or controlled load rate feedback mechanism.

It is not firmly attached with a structural connection of "T-slot configuration" to simplify its mounting and dismounting.

One or more "debris traps" that do not separate the screen housing from the oil compensation, sealing portion and reduce the chance of downhole valve plugging in the screen housing.

No supplementary motor control for improving the reliability of the motor.

Accordingly, it is desirable and an object of the present disclosure to have an electromechanical actuator system that overcomes the limitations of the exemplary systems described above.

Drawings

FIG. 1 is a diagrammatic view of a preferred embodiment of an electromechanical actuator;

FIG. 2 illustrates an embodiment of the electromechanical actuator of FIG. 1;

FIG. 3 is a cross-sectional assembly view of an embodiment of the electromechanical actuator of FIG. 2;

FIG. 4 shows a block diagram of an embodiment of an electronic circuit set of the actuator;

FIG. 5 illustrates an embodiment of a circuit to convert a back electromotive force (EMF) signal into a Hall signal equivalent; and

fig. 6 illustrates an embodiment of MOSFET (metal oxide semiconductor field effect transistor) drive circuitry for an actuator.

Detailed Description

Detailed description of one or more embodiments

The apparatus and methods are particularly applicable to driving downhole tools, such as in wellbore drilling, workover, and production, and the apparatus and methods are described in this regard. Downhole tools that may be utilized, actuated and controlled with the apparatus and methods include, but are not limited to, reamers, adjustable gauge stabilizers, vertical steerable tools, rotary steerable tools, by-pass valves, packers, control valves, locking or release mechanisms, and/or anchoring mechanisms. For example, in one application, an actuator may be used to drive a pilot/servo valve mechanism for operating a larger mud hydraulically driven valve, such as in an MWD (logging while drilling) pulser. An example of an electromechanical actuator is now described in more detail below.

FIG. 1 is an illustration of an electromechanical actuator 20 that may be used, for example, in a downhole MWD pulser tool. The actuator may include first and second housings 22 housing a number of components of the actuator₁、22₂And is connected to the housing 22₁Upper valve bonnet 22₃And having no provision for oil-fillingOuter casing 22₁A replaceable screen 23 of the inner actuator member. Those parts of the actuator not within the oil filled housing can thus be more easily accessed by removing the replaceable filter screen, so that those parts are exposed for easier assembly and disassembly, and they can be more conveniently serviced. The actuators may also include a rotary actuator 25, a lead or ball screw 26 and one or more reciprocators 27 that drive a servo shaft of the downhole tool. The actuator may also have a damping and self-aligning member 27 that dampens vibrations from the actuator and compensates for misalignment between the components. In one embodiment (for a particular load set and temperature requirement), the one or more shock absorbing members 27 (as shown in FIG. 2) may be machined coil springs made of metal integral with the coupling between the reciprocating nut of the ball screw 26 and the shaft 28. However, the one or more shock absorbing members may take other forms and may also be made of different materials, as selected by those skilled in the art and according to the load and temperature requirements for a particular application. The actuator may also have a shaft 28, which shaft 28 is connected to the downhole tool via a compensating piston 29 and sometimes a buffer disc 32, the function of which is explained in more detail below. The damping disk 32 (see also fig. 2) may be made of a high temperature thermoplastic, but may be made of other materials depending on the load and temperature requirements for a particular application.

The actuator 20 may also have a fluid mortar removal and pressure compensation system 29 that balances the pressure within the actuator with the wellbore pressure. The actuator may also have a pressure-sealed power feed 30 that electrically connects the actuator to the electronic control element but isolates the electronic control element from fluid and pressure. In particular, when downhole, the pressure within the oil-filled pressure compensation system is substantially equal to the pressure in the wellbore, and this pressure is primarily a result of the column of fluid in the wellbore. The details of fluid mortar removal and pressure compensation system 29 are described in more detail below. The pressure-sealed power feed line 30 may have a metal body with sealing properties, metal conductors for the power feed line, and an electrical insulation and pressure-sealing member (typically glass or ceramic) between the metal body and each of the metal conductors. Alternatively, the pressure-sealed power feeding line 30 may be a plastic body having sealing properties and a metal conductor for the power feeding line.

The actuator may also have a set of electronic control elements 31 that control the overall operation of the actuator, as described in more detail below. The set of electronic control elements 31 is powered by an energy source (not shown) which may be, for example, one or more batteries or another source of electrical power. Further details of embodiments of the electromechanical actuator will now be described in more detail with reference to fig. 2.

Figure 2 shows an illustration of an embodiment of the electromechanical actuator of figure 1. A typical actuator system may utilize an elastic bellows/diaphragm system for pressure compensation, while as shown in fig. 2, the subject actuator may also include a piston 29 that is part of a fluid mortar removal and pressure compensation system 29. The piston compensation system is a dielectric fluid-filled chamber having properties for isolating worn, conductive, corrosive mud slurry used in drilling and well construction from the narrow clearance and/or non-corrosion resistant components of the actuator assembly 20, and/or electrical/electronic components while balancing the pressure differential from the wellbore fluid to the tool interface seal to minimize actuator load requirements and thus power requirements. In one embodiment, the actuator has a compact configuration (both in reciprocating and rotary) with the piston on the shaft 28. The piston is located in a position within the assembly to minimize the overall length of the system, improve access to seals and internal mechanisms, reduce part count, and enable pressure transmission.

The actuator configuration reduces costs by reducing the number of components and materials required for manufacture, simplifying machining, reducing weight and therefore logistics, and simplifying maintenance by providing improved access to components that often require replacement. The arrangement of the piston also eliminates a second set of fluid plenums 999 or ports in the housing as would be required in the case of a typical compensation system. The piston layout thus reduces shell OD (outer diameter) wear due to fluid mortar erosion by making the outer shell diameter more uniform by eliminating the air gallery, since the corrosive wear is usually concentrated directly downstream of the surface discontinuity.

The actuator embodiment shown in fig. 2 may have grease packing (pack) 41 on the ends to buffer the compensating system seal against the corrosive fluid slurry effects on the OD (outer diameter) and ID (inner diameter) of the piston 29. The bumper disc 32 helps retain grease and exclude large debris, and also provides additional lateral support for the shaft 28 extending therethrough. In one embodiment, the buffer disc 32 is vented to enable pressure transfer between the volume of grease packing and the wellbore fluid. Additionally or alternatively, the housing adjacent the buffer disc may also be vented to allow such pressure transmission. In one embodiment, the damping disk 32 is clamped between two shells that are threaded together (as shown in FIG. 1), so no other method of fastening or centering is required. The damping disc 32 may also be split or slotted to allow assembly/disassembly if elements of larger diameter than the shaft are attached to the end of the shaft and/or in positions such that the damping disc cannot be insert mounted around and over the shaft. The damping disk 32 may be flexible in the axial direction and rigid in the lateral direction, which in one embodiment is accomplished by including a plurality of radial slits from the inner diameter to a distance less than the outer diameter. In the event that debris becomes trapped or wedged between the reciprocating shaft and the inner diameter of the buffer disk, the axial flexibility of the buffer disk 32 is a release mechanism and also a pressure relief mechanism in the event that the pressurized fluid plenum becomes plugged. In other embodiments, the damping disk 32 can be a flexible compliant member that does not require venting. For example, the damping disc 32 can be a rubber diaphragm that stretches with volume changes in the above-described case without significantly adding load to the actuator and also flexes when reciprocating or rotating if attached to a shaft. The damping disk 32 can also be a combination of rigid and elastic materials for lateral support and axial flexibility.

The shaft 28 extending from the oil filled section, through the compensating piston 29 ID seal, through the grease packing 41, the buffer disc 32 and into the wellbore fluid may be of uniform diameter to prevent interference from any reciprocating movement of elements or debris that may find their way to the area.

In an alternative embodiment, the piston compensation and rejection system can be easily converted to an elastomeric diaphragm compensation system by removing the piston 40 and installing the elastomeric diaphragm assembly in the same sealing area. This embodiment of the actuator may be used in systems where it is desirable to eliminate seal friction effects, as is required for pressure measurement, fine control, or lower force actuators.

In the actuator, a rotary actuator 24, such as a dc (direct current) motor, is mounted, for example, with a ball screw or lead screw 25, integral with or attached to an output shaft of the rotary actuator 24. The lead screw 25 is rotated, the nut 1000 is linearly moved, reciprocated, and then coupled to one or more driven/reciprocating members/elements 40, 50, 1001, 28. Alternatively, the motor shaft can be attached to a ball screw or screw nut that rotates, the screw moves in an axial direction, and the screw 25 is integral with and coupled to one or more driven/reciprocating members/elements 40, 50, 1001. In the embodiment shown in fig. 2, the nut and attached or integral reciprocating member reciprocate as the shaft-lead screw rotates, but rotation of the reciprocating, axially moving member or members is prevented by an anti-rotation feature or member 1001. . The feature may be, for example, a pin, key, screw head, ball, or an integrally machined feature that slides along an elongated stop or slot 1002 in the surrounding actuator guide or surrounding housing. Alternatively, the anti-rotation member can be attached to or integral with the guide/housing and prevent rotation of the reciprocating member by sliding along a slit/slot or elongated stopper in one or more reciprocating members. Alternatively, the anti-rotation member can be clamped within an elongated detent or slot in both the one or more reciprocating members and the fixed member. The guide and/or surrounding housing is vented to allow fluid to pass between different chambers of varying volume as the actuator reciprocates. In one embodiment as shown in fig. 1, the guide is attached to the rotary actuator housing.

In one embodiment, the thrust generated by loading the reciprocating member is counteracted by a member that is a combined thrust/radial bearing within the rotary actuator. The member, i.e., the bearing, accommodates axial and radial loads while minimizing the torque requirements of the rotary actuator. Bearings of this type are well known. However, typically and in existing downhole actuators, one or more thrust bearings are provided on the exterior of the rotary actuator, while the rotary actuator retains only radial support bearings. If the radial bearing and the thrust bearing are incorporated into the actuator, as in the above-described device, the number of components is reduced, the reliability is improved, and the assembly/disassembly is simplified. However, the thrust bearing can alternatively or additionally be attached to or integrated within the actuator shaft or ball screw/lead screw without reciprocating parts as is often done.

Typical downhole actuator systems require oversized lead or ball screws, thrust bearings, and reciprocating components in order to accommodate the greater loads that may be caused by impacts at the reciprocating member. This can be the case when, for example, a rigid valve is arranged. In the actuator shown in fig. 1 and 2, the system components are significantly smaller by the addition of one or more integral or attached dampers 27 in fig. 1 (and dampers 40 in fig. 2) such as mechanical springs. The shock absorbing member reduces peak impact loads and accommodates misalignment, thereby reducing the strength requirements of other actuator components. One or more shock absorbing members 27/40 may be placed in-line or within the rotary actuator shaft, reciprocating member, or between the nut and the base, or on one or more thrust bearings, or in the drive device (external to the actuator). In one embodiment, it is integral with a coupling attached to the reciprocating member of the ball or lead screw 26, as shown in FIG. 2. The overall reduction in the load of the damper enables a reduction in the strength requirements of the component, enables a reduction in the size of the components and therefore the mass of the entire component, which in turn enables a reduction in the size and power requirements of the system. This is important, for example, in battery operated systems such as downhole devices where actuators may be used. Smaller components also enable smaller diameter assemblies that are often required in drilling, for example, in assemblies used in systems requiring high fluid flow capability or smaller diameter assemblies to be used in drilling or servicing smaller wellbores. This is also important when installing the assembly in the wall of a casing or pipe, as it can be shaped for certain tools. The shock absorbing members 27 also provide compliance in the preferred embodiment to accommodate component misalignment which is important to reduce wear and fatigue of system components. This compliance may also reduce stress, which also enables component size reduction, thus providing the benefits described above.

For a reciprocating system, the axial compliance of one or more shock absorbing members 27/40 can also be adjusted to control the rate of load increase and decrease, which provides a control feedback mechanism for the electronic device. For example, if one or more mechanical springs, the spring rate can be increased, decreased, or stepped to change the detectable load rate. For a rotary system, one or more torsion spring rates can also be adjusted as needed to provide feedback/control.

The one or more shock absorbers 27/40 in another embodiment include one or more mechanical springs that compress or expand when loaded. This reduces or increases the size of the gap that functions as a fluid channel or port. As the passage closes or opens, changes in one or more of the hydraulic flow areas cause a change in the load that can be detected electronically for control purposes. The port can also be integrated with a non-damping part, wherein openings will be superimposed which will function as channels or ports for the fluid. The unrestricted fluid passage/opening flow area thus varies with the position of the reciprocating member. In addition, the change in the flow area here also changes the load that can be detected with the control electronics.

FIG. 3 is a cross-sectional assembly view of an embodiment of the electromechanical actuator of FIG. 2. The actuator may also have a shaft 28 that is easily replaceable. As shown in fig. 2 and 3, the actuator 20 may have a shaft coupling 50 with a T-slot, the coupling 50 being laterally movable for installation and removal of the shaft until a piston or other member is installed that prevents lateral travel. After the piston 29 is installed, the shaft is clamped and prevented from lateral movement by the piston. The shaft 28 is sized to minimize diameter and volume changes with reciprocation while maintaining load capacity. The shaft is also sized to allow the piston seal to slide over the end fitting without damaging the piston seal. The shaft is also sized to minimize the mass of the drive system and thus reduce the inertia of the drive system to reduce the power requirements of the motor. The shaft 28 may be attached to the coupling 50 in other ways. For example, the shaft can be integral with, threaded onto, or secured with a clamp or threaded fastener. In the embodiment shown in fig. 3, the coupling provides for easy removal and reinstallation, while providing a more secure attachment. Although threaded fasteners may loosen under high vibration conditions, the coupling 50 does not.

The screen assembly 23 may surround the entire OD of the housing. The cavity 1004 between the screen ID and the housing slot acts as a debris trap on the downhole side of the pilot valve hole. The housing may capture a buffer tray as described above. The screen may be slotted or perforated and untwisted for fluid passage. Screen assembly 23 provides a more uniform OD than previously used systems and designs replaceable screens for easy replacement in the event of component erosion. The screen assembly 23 also uses a minimum number of stops/screws to reduce the chance of losing one downhole.

The seal against the fluid of the compensating system is not integral with the screen housing as in other systems. This allows the screen housing to be cleaned or replaced without destroying the compensating system. This is important because the screen assembly is prone to erosion due to OD discontinuities, and because fluid flows through the assembly when used as a valve. This also allows for replacement of the screen assembly in the field. This may be important to achieve matching of filter screen type to LCM (long chain molecules) or fluid type. This also simplifies the manufacturing process in which the screen and screen housing or drill type adapter can be changed on a preassembled actuator.

In another embodiment, the actuator assembly can be easily configured as a rotary system by replacing the ball screw or lead screw with a gear box and a shaft sealed through the compensating piston. If the motor torque alone is sufficient, no gearbox is required. Other systems, in contrast, either do not compensate or include complex magnetic couplings. The subject actuator assemblies may use a piston or interchangeable diaphragm compensation system while minimizing the overall length of the system and maintaining the other features and benefits described above.

The actuator comprises an electronic control element group 31. Fig. 4 shows an embodiment of the electronic component assembly 31 of the actuator 20. The electronics may include a state machine implemented in a Field Programmable Gate Array (FPGA) 60 based micro-power flash (flash) that controls the motion of the actuator through position feedback generated by motion sensing devices or back emf. The electronics may also include a set of drive circuits 62 controlled by the state machine and generating drive signals (back EMF signals) that drive the actuators 24. Those drive signals are also input to a set of sensorless circuits 64 that feed control signals back to the state machine that can be used to control the actuators if one or more of the motion sensing devices fail as described below. The electronic components may also include one or more well known hall effect sensors/transducers 66, which hall effect sensors/transducers 66 measure the motion/action (predetermined movement) of the actuator and feed signals back to the FPGA 60 so that the FPGA can adjust the drive signals for the actuator as needed. In one embodiment, the hall effect sensor is housed within a purchased motor assembly. However, other sensors such as acoustic resolvers, optical encoders, magnet/reed switch combinations, magnet/induction coils, proximity sensors, capacitive sensors, accelerometers, tachometers, mechanical switches, potentiometers, rate gyros, and the like may also be used for the actuators.

The transducer feedback signal from sensor 66 provides optimal power efficiency during all mechanism loading conditions and therefore increases battery life and reduces operating costs due to battery changes. The hall effect transducer is then prone to malfunction due to abusive downhole environments. Hall effect transducers are currently considered to be the preferred motion control devices because they are relatively reliable in abusive environments compared to other sensors. Thus, in the control electronics, if any one or more of the hall motion control devices (e.g., hall sensor a, hall sensor B, and hall sensor C) cannot return a diagnostic count, the firmware mechanism is to switch to the lower power efficiency back emf position feedback with the sensorless circuitry 64 at the applicable position. For example, the method may operate as follows: if Hall sensor B is unable to generate a diagnostic count, Hall sensor A will be utilized, back EMF signal B will be utilized, and Hall sensor C will be utilized. In which case power efficiency is not lost and reliability is maintained. If more than one Hall effect transducer fails, the firmware will rely entirely on back EMF position feedback (back EMF signal A, back EMF signal B and back EMF signal C) and now have a slight decrease in power efficiency, but still maintain proper operation.

Figure 5 illustrates an embodiment of a circuit to convert a back EMF signal into a hall signal equivalent. In the illustrated embodiment, the back EMF signals (phase a, phase B, and phase C) are switched with resistors, capacitors, and operational amplifiers (comparators), as shown, to generate hall signal a, hall signal B, and hall signal C if this is a three-phase system, as shown.

The electronic control component 31 can also provide diagnostic/logging data operations that can be used to omit critical tactical records. A typical method of storing non-volatile data is to write the data to fast memory, usually with large quantized paper segments, so that if a power anomaly or erasure occurs during the writing of a page, a large amount of data can be easily lost. A typical 1 kilobyte page may store the time of the diagnostic or run log data. To prevent such loss of data, in addition to flash memory, a new type of non-volatile memory can be utilized for fast single-byte writes instead of the large number of 1 kilobyte page writes that are sensitive to flash memory. In one embodiment, the non-volatile memory may be a ferroelectric random access memory (F-RAM), which is a non-volatile memory having a ferroelectric layer in place of typical dielectric layers found in other non-volatile memories. The ferroelectric layer enables the F-RAM to consume less power, operate continuously for 100 trillion write cycles, operate at 500 times the conventional flash memory write speed, and operate continuously in a cluttered downhole environment. Data loss is minimized by using the novel non-volatile memory by single byte transfer instead of 1 kilobyte data transfer.

The group of electronic control elements 31 may also have dedicated MOSFET (metal oxide semiconductor field effect transistor) gate driver circuitry 70 (see fig. 6 showing an embodiment of the MOSFET driver 70), which driver circuitry 70 is utilized to regulate the gate drive voltage applied to one or more MOSFETs 72 when the input voltage is varied, where the input voltage is typically supplied by a battery. MOSFETs are the preferred switches; however, any other switch can be used. In the circuitry, each MOSFET has a gate drive circuit 74 that generates a gate voltage for each MOSFET and a low voltage detection circuit and gate regulator 76 that controls the gate drive circuit 74, wherein it can provide a shutdown signal when the voltage is too low. Adjusting the gate voltage to the optimum voltage allows the MOSFET to consume minimal power over large input voltage variations, thus minimizing MOSFET temperature rise and increasing reliability. The electronic control element group 31 may also have a circuit 76 which disables the use of the MOSFETs if the input voltage falls to a level where the optimum gate voltage cannot be maintained, thus eliminating overheating and automatic destruction of the MOSFETs.

The downhole actuator described above also provides a simple method for filling oil into the actuator which facilitates ease of maintenance. In prior systems, some of which were compensated for with a diaphragm that collapsed under vacuum (when oil was removed) creating air pockets and possibly damaging the diaphragm. Also, removing excess oil from existing diaphragm compensation systems is more complicated because it is more difficult to access the diaphragm to remove oil from the diaphragm without a retainer that applies pressure to the diaphragm. The structure and openings required to integrate the diaphragm compensation system also add fluid volume to the system that must be compensated. In contrast, the downhole actuators described above allow the system to be vacuum-filled prior to installation of the compensating piston or diaphragm. Thus, the compensator (piston or diaphragm) can be removed prior to the vacuum-fill process and installed after the vacuum-fill is complete. In addition, excess oil is removed from the system by simply opening the ports and installing the compensating piston in the desired position.

The above-described actuator has all the following features which overcome the limitations of a typical system:

reduced number of parts to achieve the same function in a more efficient manner

Simplified cost, maintenance, and improved reliability by reducing part count and shaping parts for simplified access

Improved durability in use in environments where the elastic diaphragm is deteriorated compared to elastic diaphragm compensation with piston compensation

Increased damping, self-alignment, enabling the system to achieve smaller load bearing and reciprocating parts

Reduced cost, power requirements and size with a smaller number of parts

-adding one or more shock absorbing members and a hydraulic restriction scheme to provide a control feedback mechanism

Securely attaching the shaft with a T-slot configuration simplifying its installation and removal

Adding discs providing lateral support of the shaft without disturbing the reciprocating motion or pressure balancing

-separating the screen from the oil compensating seal portion

Adding debris traps to the screen housing reduces the chance of plugging downhole valves

Adding electronic device features to the drive circuitry for improved reliability

Increasing recorded diagnostic data critical to the performance of the actuator to aid fault analysis and other diagnostics

-adding circuitry to greatly improve MOSFET reliability over all input voltages and abusive environmental conditions

Adding redundancy to the motion control means operating and controlling the actuators to improve reliability over other typical systems.

Although the foregoing has been described with reference to particular embodiments of the present disclosure, it will be appreciated by those skilled in the art that changes in this embodiment may be made without departing from the principles and spirit of the disclosure, the scope of which is defined in the appended claims.

Claims (24)

1. A downhole tool actuator, comprising:

an oil-filled housing;

an actuator housed in the oil filled housing, the actuator generating a force applied to a downhole tool connectable to the actuator;

a damper member housed in the oil-filled housing and adjacent to the actuator, the damper member absorbing an impact from the actuator;

a compensation mechanism housed in the oil filled housing, the compensation mechanism balancing pressure within the actuator with wellbore pressure;

a shaft housed in the oil filled housing, the shaft transmitting the force of the actuator to a downhole tool connectable to the actuator; and

an electronic control system in a housing separate from the oil-filled housing, the electronic control system in electrical communication with the actuator for providing power and control signals to the actuator.

2. The downhole tool actuator of claim 1, wherein the actuator further comprises one of a rotary actuator and a shuttle.

3. The downhole tool actuator of claim 2, wherein the actuator further comprises a lead/ball screw coupled to the actuator and to the shaft, the lead/ball screw ensuring proper movement of the shaft based on the actuator movement.

4. The downhole tool actuator of claim 3, wherein the actuator further comprises a T-slot coupling connecting the shaft to the actuator.

5. The downhole tool actuator of claim 2, wherein the actuator further comprises an anti-rotation feature that prevents rotation of the shuttle.

6. The downhole tool actuator of claim 5, wherein the anti-rotation feature is one of a pin, a key, a screw head, a ball, and an integrally machined feature that slides along a slot in the oil filled housing.

7. The downhole tool actuator of claim 5, wherein the shock absorbing member is aligned with the shaft.

8. The downhole tool actuator of claim 7, wherein the shock absorbing member is a machined coil spring.

9. The downhole tool actuator of claim 1, wherein the shaft has a uniform diameter.

10. The downhole tool actuator of claim 1, wherein the compensating mechanism is a piston.

11. The downhole tool actuator of claim 10, wherein the piston surrounds the shaft so as to reduce the overall length of the actuator.

12. The downhole tool actuator of claim 1, wherein the compensating mechanism is an elastic diaphragm.

13. The downhole tool actuator of claim 1, further comprising a buffer disc adjacent the compensating mechanism that excludes debris and supports the shaft.

14. The downhole tool actuator of claim 13, wherein the buffer disc is a high temperature thermoplastic.

15. The downhole tool actuator of claim 13, wherein the buffer disc is perforated.

16. The downhole tool actuator of claim 13, wherein the oil filled housing further comprises a first housing and a second housing, and wherein the buffer disc is retained between the first and second housings.

17. The downhole tool actuator of claim 1, further comprising a pressure-sealed electrical feed line that insulates the electronic control system from pressure and fluid in the oil filled housing.

18. The downhole tool actuator of claim 1, wherein the electronic control system further comprises a set of sensors to generate a set of signals to measure the motion of the shaft, a state machine to generate a signal based on the set of sensor signals, and a set of drive circuits to generate a control signal for the actuator based on the state machine signal.

19. The downhole tool actuator of claim 18, wherein the state machine is a field programmable gate array.

20. The downhole tool actuator of claim 18, wherein each sensor is one of a hall effect sensor, a synchroresolver, an optical encoder, a magnet/reed switch combination, a magnet/coil induction sensor, a proximity sensor, a capacitive sensor, an accelerometer, a tachometer, a mechanical switch, a potentiometer, and a rate gyro.

21. The downhole tool actuator of claim 1, further comprising a valve housing having a replaceable screen to allow access to components not within the oil filled housing.

22. The downhole tool actuator of claim 1, further comprising a screen assembly attached to the debris-trapping housing.

23. A method for maintaining the downhole tool actuator of any one of claims 1-22, comprising:

assembling a downhole tool actuator having a housing, an actuator in the housing that generates a force that is applied to a downhole tool connectable to the actuator, a shock absorbing member adjacent the actuator that absorbs a shock from the actuator, a shaft in the housing that transmits the force of the actuator to the downhole tool connectable to the actuator, and an electronic control system in electrical communication with the actuator for providing power and control signals to the actuator;

filling oil into the housing; and

the compensating mechanism is installed in a housing that equalizes pressure within the actuator with the wellbore pressure.

24. The method of claim 23, further comprising removing excess oil from the housing by opening a port in the housing.