Patent Publication Number: US-9412507-B2

Title: Positioning system for an electromechanical actuator

Description:
BACKGROUND 
     Actuators are used in various mechanical devices to control the features and moving parts of these devices. Specifically, an actuator is a motor that is used to control a system, mechanism, device, structure, or the like. Actuators can be powered by various energy sources and can convert a chosen energy source into motion. 
     For instance, actuators are used in computer disk drives to control the location of the read/write head by which data is stored on and read from the disk. In addition, actuators are used in robots, i.e., in automated factories to assemble products. Actuators also operate brakes on vehicles, open and close doors, raise and lower railroad gates, and perform numerous other tasks of everyday life. Accordingly, actuators have wide ranging uses. 
     In the field of aeronautics, actuators are used to control a myriad of control surfaces that allow aircraft to fly. For instance, each of the flaps, spoilers, and ailerons located in each wing, require an actuator. In addition, actuators in the tail control the rudder and elevators of an aircraft. Furthermore, actuators in the fuselage open and close the doors that cover the landing gear bays. Actuators are also used to raise and lower the landing gear of an aircraft. Moreover, actuators on each engine control thrust reversers by which a plane is decelerated. 
     Commonly used actuators fall into two general categories: hydraulic and electric, with the difference between the two categories being the motive force by which movement or control is accomplished. Hydraulic actuators require a pressurized, incompressible working fluid, usually oil. Electric actuators use an electric motor, the shaft rotation of which is used to generate a linear displacement using some sort of transmission. 
     Although hydraulic actuators have been widely used in airplanes, a problem with hydraulic actuators is the plumbing required to distribute and control the pressurized working fluid. In an airplane, a pump that generates high-pressure working fluid and the plumbing required to route the working fluid add weight and increase design complexity because the hydraulic lines must be carefully routed. In addition, possible failure modes in hydraulic systems include pressure failures, leaks, and electrical failures to servo valves that are used to position control surfaces. However, one inherent feature of hydraulic systems is that hydraulic flight control systems can use damping forces to maintain stability after a failure has been detected. 
     Electric actuators overcome many of the disadvantages of hydraulic systems. In particular, electric actuators, which are powered and controlled by electric energy, require only wires to operate and control. However, electric actuators can also fail during airplane operation. For instance, windings of electrical motors are susceptible to damage from heat and water. In addition, bearings on motor shafts wear out. The transmission between the motor and the load, which is inherently more complex than the piston and cylinder used in a hydraulic actuator, is also susceptible to failure. In both electrical and hydraulic systems a mechanical failure of an actuator, e.g. gear or bearing failure, etc., can result in a loss of mechanical function of the actuator. In addition, electrical systems can fail. One type of electrical failure occurs when there is a failure of the command loop that sends communications to an actuator. Another type of electrical failure occurs when a power loop within the actuator fails, such as a high power loop to a motor. 
     As electronic actuator systems are increasingly used in aircraft designs, new approaches are needed to address possible failure modes of these systems. Fault-tolerance, i.e., the ability to sustain one or more component failures or faults yet keep working, is needed in these systems. Because electric flight control systems do not have hydraulic fluid available for damping, there is a need for alternative fail safe systems that can be used in the event of a failure. 
     SUMMARY 
     Provided are various examples of a shaft positioning system that can be used as a secondary fail-safe system for an electromechanical actuator when a primary system fails. According to various examples, the positioning system includes a shaft coupled to an electromechanical actuator. The shaft moves along a linear axis and the electromechanical actuator is free to translate during normal operation. An electromagnetic coil is positioned around at least a portion of the shaft. The electromagnetic coil produces a magnetic field when electrical current is applied. A metal housing surrounds at least a portion of the electromagnetic coil. The shaft is placed in a predetermined position when the metal housing is in contact with a first magnet and translational motion of the electromechanical actuator is restricted when the shaft is placed in the predetermined position. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the shaft positioning system also includes a spring coupled to the shaft. The spring holds the shaft in a retracted position when the electrical current is applied to the electromagnetic coil. The electromagnetic coil repels the first magnet when the electrical current is applied. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the metal housing attracts to the first magnet when no electrical current is applied to the electromagnetic coil. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the shaft positioning system also includes a second magnet. The second magnet has a weaker magnetic field than the first magnet. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the metal housing contacts the second magnet when the electrical current is applied to the electromagnetic coil. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the metal housing contacts the first magnet when no electrical current is applied to the electromagnetic coil. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the electromechanical actuator is a linear actuator. The shaft engages with a flange of the linear actuator when the shaft is moved into the predetermined position. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the shaft is part of a rotary actuator. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the shaft positioning system also includes a centering cam and a locking cam. The centering cam and locking cam engage when the shaft is in the predetermined position. The centering cam and locking cam are disengaged when the shaft is in a retracted position. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the shaft moves to the predetermined position during a power failure. 
     According to various examples, a mechanism includes a flight control computer system, a translating shaft having an axis, an electromechanical actuator that moves the translating shaft along the axis, and a shaft positioning system. The electromechanical actuator is communicatively coupled to the flight control computer. The shaft positioning system includes a shaft coupled to the electromechanical actuator. The shaft moves along a linear axis and the electromechanical actuator is free to translate during normal operation. The shaft positioning system also includes an electromagnetic coil positioned around at least a portion of the shaft. The electromagnetic coil produces a magnetic field when electrical current is applied. A metal housing surrounds the electromagnetic coil. In addition, the shaft positioning system includes a first magnet. The shaft is placed in a predetermined position when the metal housing is in contact with the first magnet and translational motion of the translating shaft and the electromechanical actuator is restricted when the shaft is placed in the predetermined position. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the mechanism also includes a spring coupled to the shaft. The spring holds the shaft in a retracted position when the electrical current is applied to the electromagnetic coil. The electromagnetic coil repels the first magnet when the electrical current is applied. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the metal housing attracts to the first magnet when no electrical current is applied to the electromagnetic coil. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the apparatus also includes a second magnet. The second magnet has a weaker magnetic field than the first magnet. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the metal housing contacts the second magnet when the electrical current is applied to the electromagnetic coil. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the metal housing contacts the first magnet when no electrical current is applied to the electromagnetic coil. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the electromechanical actuator is a linear actuator. The shaft engages with a flange of the linear actuator when the shaft is moved into the predetermined position. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the shaft is part of a rotary actuator. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the apparatus includes a centering cam and a locking cam. The centering cam and locking cam engage when the shaft is in the predetermined position. The centering cam and locking cam are disengaged when the shaft is in a retracted position. 
     In one aspect, which may include at least a portion of the subject matter of any of the preceding and/or following examples and aspects, the shaft moves to the predetermined position during a power failure. 
     These and other embodiments are described further below with reference to the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1B  are diagrammatic representations of a positioning system using electromagnetic and spring forces for an electromechanical linear actuator, in accordance with some embodiments. 
         FIGS. 2A-2B  are diagrammatic representations of an alternative positioning system using electromagnetic and spring forces for an electromechanical linear actuator, in accordance with some embodiments. 
         FIGS. 3A-3B  are diagrammatic representations of a positioning system using electromagnetic and magnetic forces for an electromechanical linear actuator, in accordance with some embodiments. 
         FIGS. 4A-4B  are diagrammatic representations of a positioning system used with an electromechanical linear actuator, in accordance with some embodiments. 
         FIGS. 5A-5B  are diagrammatic representations of a positioning system using electromagnetic and spring forces for an electromechanical rotary actuator, in accordance with some embodiments. 
         FIGS. 6A-6B  are diagrammatic representations of a positioning system using electromagnetic and magnetic forces for an electromechanical rotary actuator, in accordance with some embodiments. 
         FIGS. 7A-7B  are diagrammatic representations of a positioning system used with an electromechanical rotary actuator, in accordance with some embodiments. 
         FIG. 8  is a diagrammatic representation of an aircraft flight control system, in accordance with some embodiments. 
         FIG. 9A  is a process flowchart reflecting key operations in the life cycle of an aircraft from early stages of manufacturing to entering service, in accordance with some embodiments. 
         FIG. 9B  is a block diagram illustrating various key components of an aircraft, in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the presented concepts. The presented concepts may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail so as to not unnecessarily obscure the described concepts. While some concepts will be described in conjunction with the specific embodiments, it will be understood that these embodiments are not intended to be limiting. 
     INTRODUCTION 
     As electromechanical actuator systems are increasingly used in aircraft designs, new approaches are needed to address possible failure modes of these systems. Fault-tolerance, i.e., the ability to sustain one or more component failures or faults yet keep working, is needed in these systems. Because electric flight control systems do not have hydraulic fluid available for damping, there is a need for alternative fail safe systems that can be used in the event of a failure. 
     A primary flight control system requires the control surfaces to be stable even after failures occur in the actuation systems. In the case of a primary flight control system failure, the control surface must continue to be stable by either maintaining sufficient damping or locking in place. If the control surface is not damped or locked, the surface can become unstable, resulting in failure of the wing to function appropriately. 
     Various mechanisms are presented that are designed to stabilize primary flight control surfaces in the event of a failure to the primary flight control actuation system. In particular, various examples provide a secondary fail-safe system that positions and holds the flight control surface should the primary drive system fail, thereby providing stability of the flight control surface. Specifically, the positioning system includes an electromagnetic coil used to position and secure an electromechanical actuator, according to various examples. In case of a power failure, the shutdown of electric power, or a mechanical failure, the positioning system returns the electromechanical actuator to a predetermined position, such as a known or neutral position. In addition, according to various embodiments, the positioning system can automatically reset itself into an operating position after being placed into a predetermined position. 
     Although various examples described relate to the use of a positioning system for electromechanical actuators with aircraft designs, the positioning system can be used with various mechanical devices and vehicles. For instance, the positioning system can be used in commercial airplanes, military airplanes, rotorcraft, launch vehicles, spacecraft/satellites, and the like. Furthermore, the positioning system can be used in vehicle guidance control systems. In addition, the positioning system can be used in various devices such as, but not limited to, robots, land vehicles, rail vehicles, gates, doors, and the like. 
     System Examples 
     Various mechanisms are presented that provide an electromechanical shaft positioning system that can be used as a secondary fail-safe system when a primary system fails. With reference to  FIGS. 1A-1B , shown are diagrammatic representations of a shaft positioning system for an electromechanical linear actuator, in accordance with some embodiments. In particular, the positioning system in  FIG. 1A  is shown in a refracted position and the positioning system in  FIG. 1B  is shown in a protracted position. The shaft positioning system  100  combines the use of electromagnetic and mechanical spring forces to operate a shaft  103  that can be used to move an electromechanical actuator (not shown) to a predetermined position, such as a neutral or centered position. Application of the shaft positioning system is described in more detail with regard to  FIGS. 4A-4B and 8 . 
     In the example shown in  FIG. 1A , positioning system  100  includes a housing  101 , shaft  103 , spring  105 , magnet  107 , metal housing  109 , and electromagnetic coil  111 . Spring  105  can be any type of mechanical spring, such as a set of Belleville washers, bellows springs, etc. When an electrical current is supplied to electromagnetic coil  111 , the electromagnetic field produced causes the electromagnetic coil  111  to repel magnet  107 . As electromagnetic coil  111  repels magnet  107 , shaft  103  retracts and compresses mechanical spring  105 . In this configuration, spring  105  is counterbalanced by the operation of electromagnetic coil  111 . As shown, the shaft remains in a retracted position as long as an electrical current is supplied to electromagnetic coil  111 . 
     Upon a normal power shutdown, power failure, or mechanical failure, the spring  105  expands and pushes the shaft  103  towards magnet  107 , as shown in  FIG. 1B . The metal housing  109  is attracted to magnet  107  and attaches to magnet  107 , thereby moving and stabilizing shaft  103  into a predetermined position. 
     In the present embodiment, positioning system  100  combines the use of electromagnetic and mechanical spring forces to operate shaft  103  to adjust an electromechanical actuator to a predetermined position. For instance, shaft  103  can be used in case of a power failure to return the electromechanical actuator of a control surface or rotor blade to a safe position, or to return a control surface or rotor blade to a known position with accuracy during flight. In addition, positioning system  100  can drive an electromechanical actuator to a predetermined position and magnetically lock the electromechanical actuator and shaft  103  into a particular position. As described in more detail with regard to  FIGS. 4A-4B , the electromechanical actuator is stabilized when moved and locked into the predetermined position, such that movement of the electromechanical actuator is reduced and resisted. 
     In the present embodiment, positioning system  100  can be reset to a retracted position once a protracted position is no longer needed. In particular, an electrical current can be provided to electromagnetic coil  111  such that it repels magnet  107 . Attraction between metal housing  109  can be broken and the electromagnetic coil  111  can again repel magnet  107 , such as to cause shaft  103  to compress spring  105 . In this manner, the position of shaft  103  can be controlled and reset automatically depending on the amount and direction of the electrical current supplied to the electromagnetic coil  111 . 
     With reference to  FIGS. 2A-2B , shown is an alternate embodiment of a positioning system for an electromechanical linear actuator. In particular,  FIG. 2A  depicts the positioning system in a refracted position and  FIG. 2B  depicts the positioning system in a protracted position. The shaft positioning system  200  combines the use of electromagnetic and mechanical spring forces to operate a shaft  203  that can be used to move an electromechanical actuator (not shown) to a predetermined position, such as a neutral or centered position. Application of the shaft positioning system is described in more detail with regard to  FIGS. 4A-4B and 8 . 
     In the present embodiment, positioning system  200  includes a housing  201 , shaft  203 , spring  205 , magnet  207 , metal housing  209 , electromagnetic coil  211 , and spring housing  213 . Spring  205  can be any type of mechanical spring, such as a set of Belleville washers, bellows springs, etc. As shown in  FIG. 2A , spring  205  keeps shaft  203  in a retracted position. Specifically, the spring is allowed to fully extend and keep spring housing  213  away from magnet  207 . When an electrical current is applied to electromagnetic coil  211  in one direction, spring housing  213  is attracted to magnet  207  due to the magnetic forces induced by the current. 
     As shown in  FIG. 2B , spring housing  213  then attaches itself to magnet  207 , and shaft  203  is pushed into a protracted position and held in place by the attractive force between spring housing  213  and magnet  207 . Once spring housing  213  is attached to magnet  207 , the electrical current can be turned off. Shaft  203  then remains in this protracted position due to the attractive force between the magnet and the spring housing without any electrical current applied. 
     According to various embodiments, positioning system  200  can be reset to a retracted position once a protracted position is no longer needed. Specifically, to return the shaft to a retracted position, an electrical current can be pulsed through the electromagnetic coil  211  in the opposite direction from when the electrical current was applied to attract magnet  207  to spring housing  213 . By pulsing the electrical current through electromagnetic coil  211  in this manner, spring housing  213  can detach from magnet  207  and begin to repel magnet  207 . Once spring  205  is allowed to expand, thereby keeping spring housing  213  away from magnet  207 , no more electrical current needs to be applied to the electromagnetic coil  211 . In the present embodiment, if a power failure, normal power shutdown, or mechanical failure occurs, a secondary power source would be needed to return shaft  203  to a protracted position. 
     With reference to  FIGS. 3A-3B , shown is another embodiment of a positioning system for an electromechanical linear actuator. In particular,  FIG. 3A  depicts the positioning system in a retracted position and  FIG. 3B  depicts the positioning system in a protracted position. The shaft positioning system  300  combines the use of electromagnetic and magnetic forces to operate a shaft  303  that can be used to move an electromechanical actuator (not shown) to a predetermined position, such as a neutral or centered position. Application of the shaft positioning system is described in more detail with regard to  FIGS. 4A-4B and 8 . 
     In the present embodiment, positioning system  300  includes a housing  301 , shaft  303 , weak magnet  305 , strong magnet  307 , metal housing  309 , and electromagnetic coil  311 . As shown in  FIGS. 3A-3B , positioning system  300  uses two sets of magnets to move shaft  303  between a retracted and a protracted position. In order to keep shaft  303  in the retracted position depicted in  FIG. 3A , electrical current must continuously flow through electromagnetic coil  311  to attract it to weak magnet  305  and repel it from strong magnet  307 . Although electrical current must be continuously applied to electromagnetic coil  311  to keep shaft  303  in this position, metal housing  309  attaches to weak magnet  305  such that the shaft  303  is stabilized in this position and is limited to little or negligible movement. 
     In order to move shaft  303  to the protracted position, the electrical current must be reversed momentarily through electromagnetic coil  311  so that metal housing  309  will disconnect from weak magnet  305 . Once the metal housing  309  is disconnected from weak magnet  305 , it will attract to strong magnet  307  because strong magnet  307  will have a stronger magnetic pull on metal housing  309 . Once metal housing  309  has attached to strong magnet  307 , the electrical current can then be turned off because strong magnet  307  will keep shaft  303  in place. 
     In the event of a power failure, mechanical failure, or normal shut down, electromagnetic coil  311  will no longer be magnetized and the metal housing  309  will be attracted to the stronger of the weak magnet  305  and strong magnet  307  automatically. Once the metal housing  309  attaches to strong magnet  307 , shaft  303  is secured in a protracted position. This protracted position can be used to position and secure an electromechanical actuator in some examples. Application of the shaft positioning system is described in more detail with regard to  FIGS. 4A-4B and 8 . 
     In the present embodiment, positioning system  300  can be reset to a retracted position once a protracted position is no longer needed. In particular, electrical current can be provided to electromagnetic coil  111  such that it repels strong magnet  307 . Attraction between metal housing  309  and strong magnet  307  can be broken and electromagnetic coil  311  can again repel strong magnet  307 , such as to cause shaft  303  to move towards weak magnet  305 . Once metal housing  309  reaches weak magnet  305 , it attaches to weak magnet  305  and stays in place while the electrical current is applied. In this manner, the position of shaft  303  can be controlled and reset automatically depending on the amount and direction of electrical current supplied to the electromagnetic coil  311 . 
     With reference to  FIGS. 4A-4B , shown are diagrammatic representations of positioning systems used with an electromechanical linear actuator, in accordance with some embodiments. As shown, four positioning systems  401  are located within housing  400 . Translating shaft  403  passes through housing  400  and includes flange  405 . Flange  405  can project out from two sides of translating shaft  403  in some examples as shown, and can form a ring or other shape around translating shaft in other examples. Translating shaft  403  can reciprocate or translate  407  in the direction of its longitudinal axis between the retracted shafts of the positioning systems  401 . This translating shaft  403  can be a part of another mechanical system or actuator that provides control of translation  407  during normal operation. Depending on the application, translation can be in the range of about ½ inch in some examples, in the range of 5 to 10 inches in other examples, or any other distance depending on how the translating shaft  403  is used within a mechanical device or actuator. 
     In the present embodiment, positioning systems  401  serve as a secondary fail-safe system when a primary system fails. In particular, motion of translating shaft  403  can be controlled by an actuator (not shown) that is part of the primary system. During normal actuator operation, the positioning system shafts are held in a retract position, as shown. Examples of positioning systems that can be held in retracted and protracted positions are described above with regard to  FIGS. 1A-1B, 2A-2B, and 3A-3B . In the present embodiment, positioning systems like the ones described in conjunction with  FIGS. 3A-3B  are shown. However, any of the positioning systems previously described can be used to secure translating shaft  403  in a similar manner. 
     With the shafts of positioning systems  401  retracted, the translating shaft  403  is free to move through a normal stroke without interference from the positioning system shafts. However, during a power failure, mechanical failure, or normal shutdown, the positioning system shafts move into a protracted position and push up against the translating shaft flange  405 . In some examples, the positioning system shafts drive the translating shaft  403  to a predetermined position, such as a center or neutral position, and hold this position, as shown in  FIG. 4B . 
     Once the system has completed its task of stabilizing translating shaft  403 , and this configuration is no longer needed, the positioning systems  401  can be returned to a refracted position, as described in more detail above with regard to  FIGS. 1A-1B, 2A-2B , and  3 A- 3 B. The positioning system shafts can be restored to their original positions, and positioning systems  401  can be used again alongside the primary actuator as a fail-safe system during future operations. As described above, the positioning systems  401  can be activated during a failure of a primary actuator or system. However, in some examples, the positioning systems can be used at other times, such as during flight, to secure an actuator shaft in a predetermined position. As explained above, the positioning systems  401  can be moved between retracted and protracted positions automatically by providing electrical current to the systems. 
     In the example shown in  FIG. 4B , translating shaft is  403  held in a center position as its predetermined position. The positioning system shafts restrict the movement of the actuator and returns translating shaft  403  to a predetermined position. In some embodiments, the positioning system shafts can be positioned beforehand to control where the translating shaft  403  will end up when the positioning system shafts are in protracted positions. In other examples, the lengths of the positioning system shafts can be adjusted to accommodate a particular predetermined position. In some examples, the predetermined position can be a neutral position that achieves the optimal aerodynamic system, such as to reduce drag forces, etc. In other examples, a different predetermined location may be desirable. In some examples, the number of positioning system shafts may vary as appropriate to position the translating shaft  403 , e.g. one, two, three, four or more positioning system shafts on each side of the translating shaft  403 , or an unequal number of positioning system shafts on each side of translating shaft  403 . 
     With reference to  FIGS. 5A-5B , shown are diagrammatic representations of a shaft positioning system for an electromechanical rotary actuator, in accordance with some embodiments. In particular, the positioning system in  FIG. 5A  is shown in a refracted, unlocked position and the positioning system in  FIG. 5B  is shown in a protracted, locked position. The shaft positioning system  500  combines the use of electromagnetic and mechanical spring forces to operate a shaft  503 , locking cam  513 , and drive cam  515  with respect to each other such as to move an electromechanical actuator (not shown) to a predetermined position, such as a neutral or centered position. For instance, shaft  503  may be part of an actuator or can be an extension of an actuator. In addition, shaft  503  can be threaded in various examples, and can include roller screw or ball screw movement in some examples. 
     In the present embodiment, positioning system  500  integrates the electrical and mechanical functions of a spring applied electric clutch and brake to generate rotational motion that will allow an electromechanical actuator to be commanded or mechanically or electrically driven to a locked predetermined position in the event of a power shutdown, mechanical failure, or system fault. In one example, the positioning system can be used in an aircraft such that once the system mechanically locks so as to resist actuator movement of an item such as a rotor blade, the aircraft can continue the flight with all flight control authority, while active control of blade twist is not available in this locked position. 
     In the example shown in  FIG. 5A , positioning system  500  includes housing  501 , shaft  503 , spring  505 , magnet  507 , metal housing  509 , electromagnetic coil  511 , locking cam  513 , and driving cam  515 . Spring  505  can be any type of mechanical spring, such as a set of Belleville washers, bellows springs, etc. When an electrical current is supplied to electromagnetic coil  511 , the electromagnetic field produced causes the electromagnetic coil  511  to repel magnet  507 . As electromagnetic coil  511  repels magnet  507 , shaft  503  retracts and compresses mechanical spring  505 . In this configuration, spring  505  is counterbalanced by the operation of electromagnetic coil  511 . As shown, the shaft remains in a retracted position as long as an electrical current is supplied to electromagnetic coil  511 . 
     Upon a normal power shutdown, power failure, or mechanical failure, the spring  505  expands and pushes the shaft  503  (which can move via threads, roller screw, ball screw, etc.) and drive cam  515  into a protracted position until metal housing  509  attaches to magnet  507 , as shown in  FIG. 5B . When the metal housing  509  attaches to magnet  507 , driving cam  515  engages with locking cam  513  and shaft  513  is then stabilized into a predetermined position by the locking mechanism and the attachment of the metal housing  509  to magnet  507 . 
     In the present embodiment, positioning system  500  combines the use of electromagnetic and mechanical spring forces to operate shaft  503  and driving cam  515  to drive a rotary electromechanical actuator to a predetermined position. For instance, positioning system  500  can be used in case of a power failure to return the rotary electromechanical actuator of a control surface or rotor blade to a safe position, or to return a control surface or rotor blade to a known position with accuracy during flight. In addition, positioning system  500  integrates the functions of electromagnets and mechanical springs to drive an electromechanical actuator to a predetermined position and mechanically and magnetically lock shaft  503  into a particular position. When locked, shaft  503  resists movement of the rotary electromechanical actuator once it is placed into the predetermined position. Once the positioning system  500  is in the locked position, electrical power can be removed from the system. 
     According to various embodiments, positioning system  500  provides an ability to selectively lock and unlock movement of the shaft  503 , and consequently an attached actuator, with drive cam  515 . In particular, positioning system  500  can be reset to an unlocked/retracted position once a locked/protracted position is no longer needed. In particular, an electrical current can be provided to electromagnetic coil  511  such that it repels magnet  507 . Attraction between metal housing  509  can be broken and the electromagnetic coil  511  can again repel magnet  507 , such as to cause drive cam  515  to move away from locking cam  513  and to cause shaft  503  to compress spring  505 . In this unlocked position, shaft  503  can freely rotate. In this manner, movement, positioning, and locking of shaft  503  can be controlled and reset automatically depending on the amount and direction of the electrical current supplied to the electromagnetic coil  511 . 
     With reference to  FIGS. 6A-6B , shown are diagrammatic representations of a shaft positioning system for an electromechanical rotary actuator, in accordance with some embodiments. In particular, the positioning system in  FIG. 6A  is shown in a refracted, unlocked position and the positioning system in  FIG. 6B  is shown in a protracted, locked position. The shaft positioning system  600  combines the use of electromagnetic and magnetic forces to operate a shaft  603 , locking cam  613 , and drive cam  615  with respect to each other such as to move an electromechanical actuator (not shown) to a predetermined position, such as a neutral or centered position. For instance, shaft  603  may be part of an actuator or can be an extension of an actuator. In addition, shaft  603  can be threaded in various examples, and can include roller screw or ball screw movement in some examples. 
     In the present embodiment, positioning system  600  integrates the electrical and mechanical functions of a spring applied electric clutch and brake to generate rotational motion that will allow an electromechanical actuator to be commanded or mechanically or electrically driven to a locked predetermined position in the event of a power shutdown, mechanical failure, or system fault. In one example, the positioning system can be used in an aircraft such that once the system mechanically locks so as to resist actuator movement of an item such as a rotor blade, the aircraft can continue the flight with all flight control authority, while active control of blade twist is not available in this locked position. 
     In the example shown in  FIG. 6A , positioning system  600  includes a housing  601 , shaft  603 , weak magnet  605 , strong magnet  607 , metal housing  609 , electromagnetic coil  611 , locking cam  613 , and driving cam  615 . As shown in  FIGS. 6A-6B , positioning system  600  uses two sets of magnets to move shaft  603  between an unlocked/retracted and a locked/protracted position. In order to keep shaft  603  in the retracted position depicted in  FIG. 6A , electrical current must continuously flow through electromagnetic coil  611  to attract it to weak magnet  605  and repel it from strong magnet  607 . Although electrical current must be continuously applied to electromagnetic coil  611  to keep shaft  603  in this position, metal housing  609  attaches to weak magnet  605  such that the shaft  603  and driving cam  615  are stabilized in this position. In some embodiments, when the shaft  603  is in this position, the actuator attached to the positioning system  600  has free rotation and can move without interference from the positioning system  600 . 
     In order to move shaft  603  and drive cam  515  to a protracted position, the electrical current must be reversed momentarily through electromagnetic coil  611  so that metal housing  609  will disconnect from weak magnet  605 . Once the metal housing  609  is disconnected from weak magnet  605 , it will attract to strong magnet  607  because strong magnet  607  will have a stronger magnetic pull on metal housing  609 . Once metal housing  609  has attached to strong magnet  607 , the electrical current can then be turned off because strong magnet  607  will keep shaft  603  in place. 
     In the event of a power failure, mechanical failure, or normal shut down, electromagnetic coil  611  will no longer be magnetized and the metal housing  609  will be attracted to the stronger of the weak magnet  605  and strong magnet  607  automatically. Once the metal housing  609  attaches to strong magnet  607 , shaft  603  is secured in a protracted position with metal housing  609  attached to magnet  607 , as shown in  FIG. 6B . When the metal housing attaches to magnet  607 , driving cam  615  engages with locking cam  613  and shaft  603  is then stabilized into a predetermined position by the locking mechanism and the attachment of the metal housing  609  to magnet  607 . 
     In the present embodiment, positioning system  600  combines the use of electromagnetic and magnetic forces to operate shaft  603  and driving cam  615  to drive a rotary electromechanical actuator to a predetermined position. For instance, positioning system  600  can be used in case of a power failure to return a rotary electromechanical actuator of a control surface or rotor blade to a safe position, or to return a control surface or rotor blade to a known position with accuracy during flight. In addition, positioning system  600  integrates the functions of electromagnets and magnets to drive an electromechanical actuator to a predetermined position and mechanically and magnetically lock shaft  603  into a particular position. When locked, shaft  603  resists movement of the rotary electromechanical actuator once it is placed into the predetermined position. Once the positioning system  600  is in the locked position, electrical power can be removed from the system. 
     According to various embodiments, positioning system  600  provides an ability to selectively lock and unlock movement of the shaft  603 , and consequently an attached actuator, with drive cam  615 . In particular, positioning system  600  can be reset to an unlocked/retracted position once a locked/protracted position is no longer needed. In particular, electrical current can be provided to electromagnetic coil  611  such that it repels strong magnet  607 . Attraction between metal housing  609  and strong magnet  607  can be broken and electromagnetic coil  611  can again repel strong magnet  607 , such as to cause shaft  603  to move towards weak magnet  605 . Once metal housing  609  reaches weak magnet  605 , it attaches to weak magnet  605  and stays in place while the electrical current is applied. In this manner, the position of shaft  603  and drive cam  615  can be controlled and reset automatically depending on the amount and direction of electrical current supplied to the electromagnetic coil  611 . 
     With reference to  FIGS. 7A-7B , shown is one example of a positioning system used with an electromechanical rotary actuator. In the present embodiment, electromechanical rotary actuator  700  is shown with a positioning system installed. The positioning system includes shaft  703 , electromagnetic coil  711 , locking cam  713 , and drive cam  715 . Translating shaft  703  can translate freely along its longitudinal axis during normal operation. Depending on the application, translation can be in the range of about ½ inch in some examples, in the range of 5 to 10 inches in other examples, or any other distance depending on how the translating shaft  703  is used. 
     In the present embodiment, the positioning system serves as a secondary fail-safe system when a primary system fails. In particular, motion of translating shaft  703  can be controlled by the actuator, which is part of the primary system. During normal actuator operation, the positioning system shafts are held in an unlocked, retract position, as shown. Examples of positioning systems that can be held in unlocked/retracted and locked/protracted positions are described above with regard to  FIGS. 5A-5B and 6A-6B . As shown, locking cam  713  and drive cam  715  are not engaged during the unlocked/retracted position. However, during a power failure, mechanical failure, or normal shutdown, the positioning system moves into a protracted position and locking cam  713  and drive cam  715  engage to lock rotational and axial movement of shaft  703 . In some examples, the positioning system drives the translating shaft  703  to a predetermined position, such as a center or neutral position. 
     Once the system has completed its task of stabilizing translating shaft  703 , and this configuration is no longer needed, the positioning system can be returned to an unlocked/retracted position, as described in more detail above with regard to  FIGS. 5A-5B and 6A-6B . The positioning system shaft can be restored to its original position, and the primary actuator can resume free movement. As described above, the positioning system can be activated during a failure of a primary actuator or system. However, in some examples, the positioning system can be used at other times, such as during flight, to secure an actuator shaft in a predetermined position. In some examples, the predetermined position can be a neutral position that achieves the optimal aerodynamic system, such as to reduce drag forces, etc. In other examples, a different predetermined location may be desirable. As explained above, the positioning system can be moved between unlocked/retracted and locked/protracted positions automatically by providing electrical current to the systems. 
     Operating Examples 
     According to various embodiments, a positioning system (examples of which are described more fully above) can be used as a secondary fail-safe system when a primary system fails. In particular, such a positioning system can be used to address the challenge of returning electromechanical actuators to a known or neutral position in the event of a power failure, the shutdown of electric power, or a mechanical failure. With reference to  FIG. 8 , shown is a diagrammatic representation of an aircraft flight control system, in accordance with some embodiments. In particular embodiments, a positioning system can be used in aircraft control systems. Specifically, a positioning system can be used as a secondary fail-safe system when a primary actuator fails. 
     Aircraft (not shown for clarity, but well known in the art) are well-known to have wings that are attached to a fuselage. Control surfaces in the wings control the rate of climb and descent, among other things. The tail section attached to the rear of the fuselage provides steering and maneuverability. An engine provides thrust and can be attached to the plane at the wings, in the tail, or to the fuselage. Inasmuch as aircraft structures are well-known, their illustration is omitted here for simplicity. Various actuators control the movement of flight control surfaces in the wings, tail, landing gear, landing gear bay doors, engine thrust reversers, and the like. 
     In the present embodiment, one example of a control surface  815  is shown. In this example, translating shaft  809  is coupled to a pivot point  813  of a control surface  815  of an aircraft. Movement of the translating shaft  809  in the direction indicated by the arrows  811  is but one way that primary actuator  803  can cause a control surface, e.g., spoilers, flaps, elevators, rudder or ailerons, to move and thereby control the aircraft. Similar translation can control other flight control surfaces, fuselage doors, landing gear, thrust reverses, and the like. 
     According to the present embodiment, a flight control computer system  801  is electrically coupled to primary actuator  803  and positioning system  805 , both of which are located in housing  807 . In some examples, primary actuator  803  can be an electrically powered linear actuator. In other examples, primary actuator  803  can be an electromechanical rotary actuator. During normal operations, primary actuator  803  controls the movements of translating shaft  809 . Positioning system  805  is typically activated during a failure of primary actuator  803 . Accordingly, positioning system  805  does not interfere with primary actuator  803  or the movement of translating shaft  809  during normal operations. In addition, primary actuator  803  may operate for many repeated uses without positioning system  805  being triggered or activated. In addition, using a positioning system to control electromechanical actuators during such events as a power failure, mechanical failure, or normal shutdown, allows flight control computer  801  to know the position of the electromechanical actuator at all times, such that the flight performance of an aircraft can be predicted, in various examples. 
     Examples of Aircraft 
     An aircraft manufacturing and service method  900  shown in  FIG. 9A  and an aircraft  930  shown in  FIG. 9B  will now be described to better illustrate various features of processes and systems presented herein. During pre-production, aircraft manufacturing and service method  900  may include specification and design  902  of aircraft  930  and material procurement  904 . The production phase involves component and subassembly manufacturing  906  and system integration  908  of aircraft  930 . Thereafter, aircraft  930  may go through certification and delivery  910  in order to be placed in service  912 . While in service by a customer, aircraft  930  is scheduled for routine maintenance and service  914  (which may also include modification, reconfiguration, refurbishment, and so on). Although the embodiments described herein can be implemented during the production phase of commercial aircraft, they may be practiced at other stages of the aircraft manufacturing and service method  900 . 
     Each of the processes of aircraft manufacturing and service method  900  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include, without limitation, any number of aircraft manufacturers and major-system subcontractors; a third party may include, for example, without limitation, any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 9B , aircraft  930  produced by aircraft manufacturing and service method  900  may include airframe  932 , interior  936 , and multiple systems  934 . Examples of systems  934  include one or more of propulsion system  938 , electrical system  940 , hydraulic system  942 , and environmental system  944 . Any number of other systems may be included in this example. Although an aircraft example is shown, the principles of the disclosure may be applied to other industries, such as the automotive industry. 
     Apparatus and methods embodied herein may be employed during any one or more of the stages of aircraft manufacturing and service method  900 . For example, without limitation, components or subassemblies corresponding to component and subassembly manufacturing  906  may be fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft  930  is in service. 
     Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during component and subassembly manufacturing  906  and system integration  908 , for example, without limitation, by substantially expediting assembly of or reducing the cost of aircraft  930 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while aircraft  930  is in service, for example, without limitation, maintenance and service  914  may be used during system integration  908  to determine whether parts may be connected and/or mated to each other. 
     CONCLUSION 
     Although the foregoing concepts have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatuses. Accordingly, the present embodiments are to be considered as illustrative and not restrictive.