Abstract:
A method for determining a load on a driven component of a rotating or stationary electromechanical system includes locating a rotationally flexible shaft portion in operable communication with a driving component having a drive rotor rotable about an axis and the driven component. The shaft portion is operably connected thereto. Angular positions of the drive rotor and the driven component are determined. A magnitude of a load on the driven component is calculated based on a difference in angular position of the drive rotor and the driven component and a known torsional rigidity of the shaft portion.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein generally relates to electromechanical systems. More specifically, the subject disclosure relates to torque sensing in electromechanical systems. 
         [0002]    With recent advances in electric motor and electric motor drive technology, it has become advantageous to replace the traditional mechanical, pneumatic and hydraulic systems on vehicles such as aircraft, spacecraft, ships and land vehicles with electrically driven systems. Electrically driven systems offer the advantages of greater efficiency, reduced weight, higher reliability, reduced environmental and fire hazard from hydraulic fluid, reduced maintenance cost and smaller packaging. In load carrying applications such as electromechanical actuators, starter-generators, electrically driven pumps, rotational torque in excess of safe design margins, or overload torque, can occasionally be applied to the system. Safety during an overload condition is of the utmost importance. 
         [0003]    The need to sense the mechanical overload condition requires that the load be sensed and acted upon in an appropriate time frame to prevent mechanical or electrical damage to the system and the external surroundings. Typically, mechanical or electrical load/force sensors are used to protect drive systems. Adding sensors to an actuation system, however, reduces its reliability and increases the overall system complexity. Mechanical actuation systems require accurate mechanisms that allow relief of the mechanical loads that exceed a design threshold. Mechanical safety features such as shear shafts, brakes, slip clutches and load sensors have traditionally provided overload protection but have limitations. Similarly, hydraulic and pneumatic actuation systems typically utilize a spring loaded pressure relief valve that opens when the system pressure/system load exceeds the design threshold. The art would well receive an overload protection apparatus that provides accurate system protection without increasing complexity of the system or reducing the overall system reliability. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the invention, an electromechanical system includes a driving component having a drive rotor rotable about an axis and a driven component rotable about the axis. A rotationally flexible shaft portion is located in operable communication with the drive rotor and the driven component. The shaft portion is operably connected thereto such that rotation of the drive rotor about the axis drives rotation of the driven component about the axis. A difference in the amount of rotation of the drive rotor and the driven component is indicative of a load on the driven component. 
         [0005]    According to another aspect of the invention, a method for determining a load on a driven component of an electromechanical system includes locating a rotationally flexible shaft portion in operable communication with a driving component having a drive rotor rotable about an axis and the driven component. The shaft portion is operably connected thereto. Angular positions of the drive rotor and the driven component are determined. A magnitude of a load on the driven component is calculated based on a difference in angular position of the drive rotor and the driven component and a known torsional rigidity of the shaft portion. 
         [0006]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  is a schematic view of an embodiment of an electromechanical system; 
           [0009]      FIG. 2  is a cross sectional view of a portion of an embodiment of an electromechanical system; 
           [0010]      FIG. 3  is a schematic view of another embodiment of an electromechanical system; 
           [0011]      FIG. 4  is a cross-sectional view of a portion of an electromechanical system; and 
           [0012]      FIG. 5  is a schematic cross-sectional view illustrating torque applied to an embodiment of an electromechanical actuation system. 
       
    
    
       [0013]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Shown in  FIG. 1  is an electromechanical system including a first component, for example, a turbine engine  10 , and a second component, for example, a starter motor  12  for the turbine engine  10 . In some embodiments, the starter motor  12  is an electrical motor. The starter motor  12  includes a starter rotor  14  which is connected to a turbine rotor  16  via a turbine shaft  18  extending between the starter rotor  14  and the turbine rotor  16 . The turbine shaft  18  includes a rotationally flexible shaft portion  20  located between the starter rotor  14  and the turbine rotor  16 . 
         [0015]    The angular positions of both the turbine rotor  16  and the starter rotor  14  are known at any given time. To obtain the rotational position data, in some embodiments each of the starter motor  12  and the turbine engine  10  include at least one rotor position sensor  22  which is capable of detecting the angular position of the starter rotor  14  and the turbine rotor  16 , respectively. In some embodiments, the starter motor  12  is a switched-reluctance (SR) motor, a brushless DC motor, inductance motor, or other motor which includes an existing rotor position sensor  22  used for commutation of the starter rotor  14 . In some embodiments, other types of motors may be utilized, and a position sensor  22  such as, for example, a resolver, secured to a turbine shaft  18  to determine angular position of one or more of the starter rotor  14  or the turbine rotor  16 . In other embodiments, a position of one of starter rotor  14  may be determined without the use of a rotor position sensor  22 . In these embodiments, angular position of the starter rotor  14  is determined mathematically via an algorithm which utilizes a known profile of, for example, voltage distribution and/or current, as the starter rotor  14  rotates about an axis  26  of the starter motor  12 . Because the voltage profile of the starter motor  12  is known as a function of angular position of the starter rotor  14 , the angular position of the starter rotor  14  can then be determined by measuring the voltage and/or current at a desired point and comparing the measured values to the known profile. 
         [0016]    The rotationally flexible shaft portion  20  is located along the turbine shaft  18  between the starter rotor  14  and the turbine rotor  16 , in some embodiments between two rotationally rigid portions of the turbine shaft  18 . As shown in  FIG. 2 , in some embodiments, the shaft portion  20  is a torsional spring  28  connected to the turbine shaft  18 . The torsional spring  28  has a known spring constant or amount of twist per unit of force applied to it. While a torsional spring  28  is shown in  FIG. 2  as the shaft portion  20 , it is to be appreciated that other configurations of shaft portions  20  with a known amount of rotational flex, or twist, per unit of applied force may be utilized. For example, the shaft portion  20  may be a solid shaft with a known amount of rotation flex per unit of applied force. 
         [0017]    Referring again to  FIG. 1 , knowing the angular position of both the starter rotor  14  and the turbine rotor  16  and the spring constant of the shaft portion  20  establishes a nominal relationship between rotation of the starter rotor  14  and the turbine rotor  16 , such that for any rotational position of the starter rotor  14 , a nominal position of the turbine rotor  16  can be understood. Such an arrangement can be useful in many situations. For example, knowing the position of the start rotor  14  and the turbine rotor  16  as well as the spring constant of the shaft portion  20 , a load of the turbine engine  10  can be determined. Further, the arrangement may be utilized for health monitoring of the turbine engine  10 . By sampling the starter rotor  14  position and the turbine rotor  16  position at the same time, a delta position can be calculated. Since there is a known spring constant between the starter rotor  14  and the turbine rotor  16 , then the torque load of the turbine engine  10  can be determined. If the torque load falls outside of the nominal for the given operating conditions (temperature, air density, etc.) then maintenance on the turbine engine  10  may be warranted. 
         [0018]    Shown in  FIG. 3  is another embodiment of an electromechanical system. In this embodiment, the first component is, for example, an electromechanical actuator  30 , which is in some embodiments linear or rotational, which is connected to a drive motor  32  and driven thereby. The drive motor  32  includes at least one rotor position sensor  22  which is capable of detecting an angular position of a drive motor rotor  34  of the drive motor  32 . 
         [0019]    The electromechanical system includes a brake mechanism  36  located at one end of a motor shaft  38 . As shown in  FIG. 4 , in some embodiments, the brake mechanism  36  includes a braking gear  40  affixed to the motor shaft  38  and a ratcheting pawl  42  attached to a ratcheting servo  44 . The braking gear  40  includes a plurality of braking gear teeth  46  into which the ratcheting pawl  42  is engageable to stop rotation of the motor shaft  38  at a desired point thereby stopping actuation of the electromechanical actuator  30 . While a ratcheting pawl and braking gear brake mechanism  36  is described herein, it is to be appreciated that embodiments including other types of braking mechanisms  36  are within the scope of the present disclosure. 
         [0020]    The motor shaft  38  includes a rotationally flexible shaft portion  20  located between drive motor  32  and the brake mechanism  36 . As above, in some embodiments, the shaft portion  20  is a torsional spring  28  connected to the motor shaft  38 . The torsional spring  28  has a known spring constant or amount of twist per unit of force applied to it. The torsional spring  28  has a keyway  48  which is receptive of a braking gear shaft  50 . While a torsional spring  28  is shown in  FIG. 4  as the shaft portion  20 , it is to be appreciated that other configurations of shaft portions  20  may be utilized. For example, the shaft portion  20  may be a solid shaft with a known amount of rotation flex per unit of applied force. 
         [0021]    During operation of the electromechanical system, the drive motor  32  drives the electromechanical actuator  30  to a desired position via rotation of the motor shaft  38 . The brake mechanism  36  is then engaged to stop rotation of the motor shaft  38 . Due to forces acting on the electromechanical actuator  30 , a torque may act on the motor shaft  38 . This torque is monitored via the drive motor  32  having the shaft portion  20 . Because of the presence of the shaft portion  20  having a known spring constant, torque applied to the motor shaft  38  while the brake mechanism  36  is engaged allows rotation of the drive motor rotor  34  and a non-flex portion  52  of the motor shaft  38 . This rotation is illustrated in  FIG. 5 , showing the relative positions of an unloaded rotor  14   a  and a rotor position of a loaded rotor  14   b . The movement of the rotor  14  is sensed by the position sensor  22 , or by the sensing algorithm. Knowing the amount of rotational movement and the spring constant of the shaft portion  20  allows for the applied torque to be calculated. In some embodiments, the applied torque may have predetermined limits for electromechanical system integrity or safety reasons. If the applied torque exceeds the predetermined limit, the braking mechanism  36  may be released allowing rotation of the motor shaft  38  which in turn results in activation of the electromechanical actuator  30  such that the torque on the motor shaft  38  is relieved. 
         [0022]    The electromechanical system having the shaft portion  20  and rotor position sensing either via a rotor position sensor  22  or other means, eliminates the need for a direct torque sensor in the electromechanical system  10 . 
         [0023]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.