Abstract:
Apparatus, systems, and methods are provided for temperature compensating a torque sensor. One apparatus includes a shaft temperature detector and a temperature compensation circuit configured to alter tensile and compression voltages representative of tensile and compression stresss, respectively, due to a torque being applied to the shaft based on shaft temperature. A system includes a sensor configured to generate tensile and compression voltages representative of tensile and compression stresss, respectively, due to a torque being applied to a shaft, a shaft temperature detector, and a junction box. The junction box is configured to alter the tensile and compression voltages based on shaft temperature. One method includes receiving tensile and compression voltages representative of tensile and compression stresss, respectively, due to torque being applied to a shaft, altering the tensile and compression voltages based on shaft temperature, and determining the amount of torque based on the altered tensile and compression voltages.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention generally relates to sensors, and more particularly relates to systems and methods for temperature compensating a torque sensor. 
       BACKGROUND OF THE INVENTION 
       [0002]    The amount of weight a helicopter is capable of carrying is dependent on the amount torque the helicopter engine (or engines) is able to apply to the rotor shaft. The amount of torque a helicopter engine is able to apply to the rotor shaft at any particular time is known to change based on factors such as, for example, weather (e.g., temperature, wind, atmospheric pressure, humidity, precipitation, etc.), location, altitude, and/or other similar environmental conditions. As such, helicopters often include a torque sensor for detecting the amount of torque the engine(s) is/are presently are applying to the rotor shaft so that the amount of weight the helicopter is capable of carrying may be properly determined. 
         [0003]    One type of torque sensor (e.g., a magnetostrictive torque sensor) generates a tensile voltage (V t ) and a compression voltage (V c ). The tensile voltage V t  represents stress in the tensile direction due to the torsional strain on the rotor shaft, and the compression voltage V c  represents stress in the compression direction due to the torsional strain on the rotor shaft. The amount of torque applied to the rotor shaft may then be inferred from these voltages in accordance with the following conditioning equation: (V t −V c )/(V t +V c ). 
         [0004]    In some helicopters, torque sensors may be located on or near the helicopter engine. As such, the accuracy of the torque sensor may be adversely affected by the amount of heat the engine generates. This is because, at least in part, some torque sensors, such as magnetostrictive torque sensors, are constructed with magnetically permeable material. As is known, the magnetic permeability of some materials is temperature dependant and so, therefore, may be the sum V t +V c . Specifically, as the permeability of the sensor material increases with temperature, V t  and V c  may also increase. An increase in both V t  and V c  increases the magnitude of the denominator in the conditioning equation (rather than remaining constant), which results in a decrease in the amount of indicated torque as temperature rises. Since the variations in torque sensor temperature from engine to engine are not controlled, variations in indicated torque may result. 
         [0005]    Accordingly, it may be desirable to provide systems and methods for compensating a torque sensor based on the temperature of the rotor shaft. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    Various exemplary embodiments provide an apparatus for temperature compensating a torque sensor configured to output a tensile voltage and a compression voltage representative of a tensile stress and a compression stress, respectively, due to a torque applied to a shaft. One apparatus comprises a temperature detector in thermal communication with the shaft and a temperature compensation circuit coupled to the temperature detector and configured to be coupled to the sensor. The temperature compensation circuit also configured to receive a signal from the temperature detector representing a shaft temperature and to alter the tensile voltage and the compression voltage based on the shaft temperature. 
         [0007]    Systems for measuring an amount of torque being applied to a shaft are also provided. One system comprises a torque sensor coupled to the shaft and a temperature detector in thermal communication with the shaft. The sensor is configured to generate a tensile voltage and a compression voltage representative of a tensile stress and a compression stress, respectively, due to a torque applied to the shaft, and the temperature detector is configured to detect the shaft temperature. The system also comprises a junction box coupled to the sensor and the temperature detector, wherein the junction box is configured to alter the tensile and compression voltages based on the shaft temperature. 
         [0008]    Methods are also provided for temperature compensating a sensor configured to output a tensile voltage and a compression voltage representative of a tensile stress and a compression stress, respectively, due to a torque being applied to a shaft. One method comprises the steps of receiving the tensile and compression voltages and altering the tensile and compression voltages based on the temperature of the shaft. The method also comprises the step of determining the amount of torque being applied to the shaft based on the altered tensile and compression voltages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
           [0010]      FIG. 1  is a block diagram of one exemplary embodiment of a system for determining the amount of torque is being applied to a shaft by an engine; 
           [0011]      FIG. 2  is a schematic of an exemplary embodiment of a junction box for temperature compensating a torque sensor included in the system of  FIG. 1 ; and 
           [0012]      FIG. 3  is a flow diagram of one exemplary embodiment of a method for temperature compensating a torque sensor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. 
         [0014]      FIG. 1  is a block diagram of a system  100  for measuring an amount of torque being applied to a shaft  105  by an engine (not shown). In one embodiment, shaft  105  is coupled to a helicopter engine, and torque applied to shaft  105  is utilized to generate lift by rotating the rotors of the helicopter. Other embodiments of system  100  contemplate that shaft  105  may be utilized in other engine-driven applications (e.g., electric motors, motor vehicle engines, etc.) where it may be desirable to know the amount of torque an engine is applying to a shaft. 
         [0015]    As illustrated in  FIG. 1 , system  100  includes a torque sensor  110  and a temperature detector  115  in thermal communication with shaft  105 . System  100  also includes a junction box  120  coupled to torque sensor  110  and temperature detector  115 , a ratiometric detector/power supply (RDPS)  125  coupled to junction box  120 , and a display  130  coupled to RDPS  125 . 
         [0016]    Torque sensor  110  may be any hardware, circuitry, and/or device capable of determining the amount of torque an engine is applying to shaft  105 . In one embodiment, torque sensor  110  is configured to generate an AC tensile voltage (V t ) representative of the amount of torsional strain in shaft  105  in the tensile direction and to generate an AC compression voltage (V c ) representative of the amount of torsional strain in shaft  105  in the compression direction. 
         [0017]    Temperature detector  115  may be any hardware, circuitry, and/or device capable of resistively determining the temperature of shaft  105 . In one embodiment, temperature detector  115  comprises a resistive temperature detector or RTD formed of, for example, platinum, nickel, or other similar material capable of determining the temperature of shaft  105 . In another embodiment, temperature detector  115  comprises a thermistor. 
         [0018]    Junction box  120  comprises a calibration circuit  1210 , an isolation circuit  1220 , and a temperature compensation circuit  1230 . Calibration circuit  1210  may be any hardware, circuitry, and/or device capable of converting AC voltage to DC voltage and adjusting the DC voltage so that system  100  produces a calibrated torque output. With reference now to  FIG. 2 , calibration circuit  1210  is coupled to and is configured to receive AC tensile voltage V t  and AC compression voltage V c  from torque sensor  110 . Calibration circuit  1210  is also configured to convert AC tensile voltage V t  and AC compression voltage V c  to DC tensile voltage (V t ′) and DC compression voltage (V c ′), respectively, as is known in the art. Furthermore, calibration circuit  1210  is coupled to and configured to provide DC tensile voltage V t ′ and DC compression voltage V c ′ to isolation circuit  1220 . 
         [0019]    Isolation circuit  1220  is configured to isolate calibration circuit  1210  from temperature compensation circuit  1230 . That is, isolation circuit  1220  is configured to create high input impedance and low output impedance between calibration circuit  1210  and temperature compensation circuit  1230 . In one embodiment, isolation circuit  1220  comprises a non-inverted unity gain circuit  1222  configured to receive DC tensile voltage V t ′ and a non-inverted unity gain circuit  1224  configured to receive DC compression voltage V c ′ from calibration circuit  1210 . Isolation circuit  1220  may also include one or more diodes  1226  to protect unity gain circuit  1222  and/or  1224 , and a resistor  1228  coupled to the output of unity gain circuit  1222  and/or  1224 . 
         [0020]    Temperature compensation circuit  1230  may be any hardware, circuitry, and/or device configured to increase and/or decrease the magnitude of DC tensile voltage V t ′ and/or the magnitude of DC compression voltage V c ′ to generate a temperature compensated tensile voltage (V t ″) and/or a temperature compensated compression voltage (V c ″). Furthermore, temperature compensation circuit is coupled to temperature detector  115  and configured to receive a signal from temperature detector  115  representing the temperature of shaft  105 . During operation, the magnitude of DC tensile voltage V t ′ and/or the magnitude of DC compression voltage V c ′ is increased/decreased based on the sensed temperature of shaft  105  received from temperature detector  115  (discussed below). In one embodiment, in response to an increase in shaft temperature, temperature compensation circuit  1230  is configured to increase the magnitude of DC tensile voltage V t ′ when generating temperature compensated tensile voltage V t ″ and to decrease the magnitude of DC compression voltage V c ′ when generating temperature compensated compression voltage V c ″. Specifically, the DC tensile voltage V t ′ is increased by substantially the same magnitude or amount as the DC compression voltage V c ′ is decreased when generating the temperature compensated tensile voltage V t ″ and the temperature compensated compression voltage V c ″, respectively. 
         [0021]    The effect of temperature on the magnetic permeability of the material used to construct torque sensor  110  determines the amount the DC tensile voltage V t ′ is increased and the amount the DC compression voltage V c ′ is decreased. Accordingly, torque sensor  110  may require different amounts of compensation based on the material used to construct torque sensor  110 . Furthermore, some materials used to construct torque sensor  110  may not require temperature compensation at all or may require temperature compensation to occur only when shaft  105  temperature exceeds a threshold temperature. 
         [0022]    In one embodiment, and with continued reference to  FIG. 2 , temperature compensation circuit  1230  comprises a fully differential amplifier  1232  coupled to unity gain circuits  1222  and  1224 . Specifically, fully differential amplifier  1232  comprises a non-inverted operational amplifier (OP AMP)  1234  having a non-inverted input coupled to the output of unity gain circuit  1224  and a non-inverted OP AMP  1236  having a non-inverted input coupled to the output of unity gain circuit  1222 . The output of OP AMP  1234  is coupled to its own inverted input and to the non-inverted and inverted inputs of OP AMP  1236 . The output OP AMP  1236  is coupled to the non-inverted and inverted inputs of OP AMP  1234  and to a switch  1243  via a node  1285 . Switch  1243  is configured to switch between a resistor  1250  (which is coupled to a node  1280 ) when system  100  is operating in a “normal” or uncompensated mode (discussed below) and temperature detector  115  (which is also coupled to node  1280 ) when system  100  is operating in a “temperature compensation” mode (also discussed below). 
         [0023]    Fully differential amplifier  1232  also comprises a plurality of resistors  1261 - 1268 . Specifically, resistor  1261  is coupled to the output of OP AMP  1234  and to a node  1270  coupled to the inverted input of OP AMP  1234 , resistor  1262  is coupled to the output of OP AMP  1234  and to a node  1275  coupled to the inverted input of OP AMP  1236 , resistor  1263  is coupled to the output of OP AMP  1234  and to the non-inverted input of OP AMP  1236 , resistor  1264  is coupled to the output of OP AMP  1236  and to node  1270 , resistor  1265  is coupled to the non-inverted input of OP AMP  1234 , resistor  1266  is coupled between the output of OP AMP  1236  and RDPS  125 , resistor  1267  is coupled between the output of OP AMP  1234  and RDPS  125 , and resistor  1268  is coupled to node  1275  and node  1280 . 
         [0024]    As discussed above, temperature compensation circuit  1230  is configured to operate in a normal mode or a temperature compensation mode. In one embodiment, if the temperature of shaft  105  is below a threshold temperature (which varies with the material used to construct torque sensor  110 ), switch  1243  is configured to couple resistor  1250  to temperature compensation circuit  1230 . As a result, the DC tensile voltage V t ′ and/or the DC compression voltage V c ′ are not altered. If the temperature of shaft  105  is greater than the threshold temperature, switch  1243  is configured to couple temperature detector  115  to temperature compensation circuit  1230 . As a result, the DC tensile voltage V t ′ and/or the DC compression voltage V c ′ may be compensated. In an alternate embodiment, switch  1243  may be manually switched between the normal mode and the temperature compensation mode. In yet another embodiment, switch  1243  and resistor  1250  are both omitted and temperature detector  115  is coupled to node  1285  so that temperature compensation substantially always occurs. 
         [0025]    With reference again to  FIG. 1 , junction box  120  is coupled to RDPS  125 . In one embodiment, RDPS  125  is a digital processor configured to receive compensated tensile voltage V t ″ and compensated compression voltage V c ″ and calculate the amount of torque being applied to shaft  105  based on compensated tensile voltage V t ″ and compensated compression voltage V c ″. In one embodiment, RDPS  125  is configured to divide the difference of the compensated tensile voltage V t ″ and the compensated compression voltage V c ″ by the sum of the compensated tensile voltage V t ″ and the compensated compression voltage V t ″. This calculation can be represented by the following equation: (V t ″−V c ″)/(V t ″+V c ″). Accordingly, since in various embodiments the DC tensile voltage V t ′ is increased by substantially the same magnitude or amount as the DC compression voltage V c ′ when generating the compensated tensile voltage V t ″ and the compensated compression voltage V c ″, respectively, the denominator (V t ″+V c ″) remains substantially constant. 
         [0026]    System  100  also includes a display  130  coupled to RDPS  125 . Display  130  is configured to receive a signal from RDPS  125  indicating the amount of torque being applied to shaft  105  and display the amount of torque being applied to shaft  105  to, for example, a user. 
         [0027]      FIG. 3  is a flow diagram of one exemplary embodiment of a method  300  for temperature compensating a torque sensor (e.g., torque sensor  110 ) in communication with a shaft (e.g., shaft  105 ) coupled to an engine. Method  300  begins by receiving a tensile voltage (V t ) and a compression voltage (V c ) from torque sensor  110  (step  310 ). Method  300  also includes receiving the temperature of shaft  105  from a temperature detector (e.g., temperature detector  115 ) (step  320 ). 
         [0028]    The temperature of shaft  105  is compared to a threshold temperature to determine whether the shaft temperature is greater than the threshold temperature (step  330 ). If the shaft temperature is greater than the threshold temperature, method  300  proceeds to step  350 . On the other hand, if the shaft temperature is greater than the threshold temperature, the tensile voltage V t  and/or the compression voltage V c  are altered (step  340 ). 
         [0029]    In one embodiment, altering comprises increasing the tensile voltage V t , whereas in another embodiment, altering comprises decreasing the compression voltage V c . In another embodiment, altering comprises increasing the tensile voltage V t  and decreasing the compression voltage V c , wherein the tensile voltage V t  is increased by substantially the same amount as the compression voltage V c  is decreased. In each of the various embodiments, the tensile voltage V t  is increased and/or the compression voltage V c  is decreased as the shaft temperature increases. 
         [0030]    Method  300  also comprises determining the amount of torque being applied to the shaft based on the tensile voltage V t  and the compression voltage V c  (step  350 ). In one embodiment, determining the amount of torque comprises dividing a difference of the tensile voltage V t  and the compression voltage V c  by a sum of the tensile voltage and the compression voltage, as represented by the equation: (V t −V c )/(V t +V c ). In this equation, V t  and/or V c  may have been altered in step  340 , or both remain unaltered via step  330 . 
         [0031]    The amount of torque may then be displayed on a display (e.g., display  130 ) (step  360 ). The amount of torque may then be used to determine, for example, how much weight an aircraft (e.g., a helicopter) is capable of lifting at that particular moment (step  370 ). 
         [0032]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.