Abstract:
Methods and apparatus are provided for determining torque in an environmentally isolated system. A drive system is coupled to the environmentally isolated system via a non-contact, magnetic coupling that has a known angular stiffness and at least two coupling sections. A relative deflection of each coupling section is optically measured, and the torque is determined based on the relative deflection and the known angular stiffness.

Description:
TECHNICAL FIELD 
       [0001]    The present invention generally relates to torque determination, and more particularly relates to a system and method of determining torque in a non-mechanically coupled rotating system. 
       BACKGROUND 
       [0002]    Numerous and varied methods have been derived for determining the torque on a rotating system. Some examples of known methods include the use of magnetic brakes, strain gage transducers, and system drive motor current. To implement the first method, a magnetic brake with a known magnetic field based on a current and associated reaction torque is coupled to a rotary portion of the system. During operation, the current supplied to generate the magnetic field is used to determine the applied torque. To implement the second method, a strain gage transducer is coupled to the rotating portion of the system and signals and power transferred across slip rings. Torque is derived based on the torsional stress in the shaft to which the gage is coupled. To implement the third method, a drive motor with a known torque constant is coupled to and drives the rotating portion of the system. The torque is then determined using the known torque constant and the current supplied to the system. 
         [0003]    Each of the above methods has its advantages. However, because each relies on a component being mechanically coupled, in one fashion or another, to the rotating system, these methods are unsuitable for determining the torque in an environmentally isolated rotating system with sufficient accuracy. 
         [0004]    Hence, there is a need for a system and method for determining torque in an environmentally isolated rotating system that does not rely on mechanical coupling to, or contact with, the rotating system. The present invention addresses at least this need. 
       BRIEF SUMMARY 
       [0005]    In one exemplary embodiment, a system for determining torque includes an outer rotor, an inner rotor, a first optical transceiver, a second optical transceiver, and a processor. The outer rotor includes an inner volume, and is responsive to a drive torque to rotate. The inner rotor is rotationally mounted, and is disposed at least partially within the inner volume of the outer rotor. The inner rotor is spaced apart from, and magnetically coupled to, the outer rotor to rotate therewith. The first optical transceiver is disposed adjacent the outer rotor. The first optical transceiver is configured to selectively transmit first incident light toward, and receive reflected first incident light from, the magnetic outer rotor. The first optical transceiver is further configured to generate a first signal in response to received reflected first incident light. The second optical transceiver is disposed adjacent the inner rotor. The second optical transceiver is configured to selectively transmit second incident light toward, and receive reflected second incident light from, the inner rotor. The second optical transceiver is further configured to generate a second signal in response to received reflected second incident light. The processor is coupled to receive the first signal and the second signal and is configured, upon receipt thereof, to determine torque on the magnetically permeable rotor. 
         [0006]    In another exemplary embodiment, a system for determining torque includes a magnetic coupling, a first optical transceiver, a second optical transceiver, and a processor. The magnetic coupling has a known angular stiffness, is adapted to receive an input torque and supply a drive torque to a load, and includes an outer rotor that is magnetically coupled to and an inner rotor. The first optical transceiver is disposed adjacent the outer rotor. The first optical transceiver is configured to selectively transmit first incident light toward, and receive reflected first incident light from, the outer rotor. The first optical transceiver is further configured to generate a first signal in response to received reflected first incident light. The second optical transceiver is disposed adjacent the inner rotor. The second optical transceiver is configured to selectively transmit second incident light toward, and receive reflected second incident light from, the inner rotor. The second optical transceiver is further configured to generate a second signal in response to received reflected second incident light. The processor is coupled to receive the first signal and the second signal and is configured to determine torque on the magnetically permeable rotor based on the known angular stiffness and the first and second signals. 
         [0007]    In still another exemplary embodiment, a method of determining torque in an environmentally isolated system includes coupling a drive system to the environmentally isolated system via a non-contact, magnetic coupling that has a known angular stiffness and at least two coupling sections. A relative deflection of each coupling section is optically measured, and the torque is determined based on the relative deflection and the known angular stiffness. 
         [0008]    Furthermore, other desirable features and characteristics of the torque determination system and method will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the preceding background. 
     
    
     
       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 wherein: 
           [0010]      FIG. 1  depicts a functional block diagram of a non-contact system for determining torque; 
           [0011]      FIG. 2  depicts the angular stiffness of an exemplary magnetic coupling in the form of a graph of torque versus slip; 
           [0012]      FIGS. 3 and 4  depict perspective and end views, respectively, of a test fixture with which the non-contact of  FIG. 1  may be used; and 
           [0013]      FIG. 5  depicts a cross section view of the exemplary test fixture depicted in  FIGS. 3 and 4 , taken along line  5 - 5  in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The following detailed description 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 or the following detailed description. In this regard, although a particular preferred embodiment is described as being implemented with a test fixture that is used to test bearing assemblies and to measure the drag torque of bearing assemblies, the system and method may be used with and in various other systems, components, devices, and environments. 
         [0015]    Referring first to  FIG. 1 , a functional block diagram of an exemplary non-contact torque determination system  100  is depicted, and includes a magnetic coupling  102 , a first optical transceiver  104 , a second optical transceiver  106 , and a processor  108 . The magnetic coupling  102  includes an outer rotor  112  and an inner rotor  114 . The outer rotor  112  is responsive to a drive torque to rotate, and includes a hub  116  and, in the depicted embodiment, one or more magnets  118 . The outer rotor  112  is thus referred to throughout the remainder of this document as the magnetic rotor. It will be appreciated that the hub  116  and magnets  118  could be integrally formed or separately formed and coupled to together. Moreover, although the drive torque may be supplied to the magnetic rotor  112  from any one of numerous sources, in a particular embodiment, which will be described in more detail further below, the source is a motor. 
         [0016]    The magnetic rotor  112  additionally includes an inner surface  122  that defines an inner volume  124 , and an outer surface  126 . In the depicted embodiment, the one or more magnets  118  are depicted as being disposed on or near the inner surface  122 . It will nonetheless be appreciated that the one or more magnets could be disposed on or near the outer surface  126 . A first reflective feature  117  is disposed on the outer surface  126 . The first reflective feature  117  provides a contrast surface reflection, the purpose of which is described further below. The first reflective feature  117  may be variously implemented. Some non-limiting examples include a surface feature that is formed in the outer surface  126  or a reflective strip that is disposed on the outer surface  126 . 
         [0017]    The inner rotor  114  is preferably formed, at least partially, of any one of numerous magnetically permeable materials. As such, it is referred to throughout the remainder of this document as the magnetically permeable rotor. The magnetically permeable rotor  114  is rotationally mounted, and is disposed, at least partially, within the inner volume  124  of the magnetic rotor  112 . The portion of the magnetically permeable rotor  114  that is within the inner volume  124  is spaced apart from, but is magnetically coupled to, the magnetic rotor  112 . Though not depicted, the magnetically permeable rotor  114  is preferably configured with one or more lobes, with the number of lobes preferably matching the number of magnets  118 . Thus, when the magnetic rotor  112  rotates, the magnetically permeable rotor  114  rotates synchronously therewith. The magnetically permeable rotor  114  may be rotationally mounted via various means and methods. In the depicted embodiment, however, it is rotationally mounted via one or more bearing assemblies  128  (only one depicted in  FIG. 1 ) and is coupled to a load. In a particular preferred embodiment, which is described in more detail further below, the load is a test shaft, which is rotationally mounted via the one or more bearing assemblies  128 . 
         [0018]    The magnetically permeable rotor  114  includes an outer surface  115 , which has a second reflective feature  127  disposed thereon. Similar to the first reflective feature  117 , the second reflective feature  127  provides a contrast surface reflection. The second reflective feature  127  may be variously implemented. Some non-limiting examples include a surface feature that is formed in the outer surface  115  of the magnetically permeable rotor  114  or a reflective strip that is disposed on the outer surface  115  of the magnetically permeable rotor  114 . 
         [0019]    As  FIG. 1  further depicts, the magnetically permeable rotor  114  is preferably disposed within a housing  125 . This housing  125  is preferably formed of a non-magnetically permeable material. As such, the magnetic rotor  112  and the magnetically permeable rotor  114  are both physically isolated and thermally isolated from each other. 
         [0020]    Before proceeding further it is noted that although the outer rotor  112  and inner rotor  114  are configured as (and referred to herein as) the magnetic rotor and the magnetically permeable rotor, respectively, this is merely exemplary of one particular embodiment. In other embodiments, the outer rotor  112  could be formed, at least partially, of any one of numerous magnetically permeable materials and concomitant lobes, and the inner rotor  114  could include the one or more magnets  118 . In such embodiments the outer rotor  112  may referred to as the magnetically permeable rotor, and the inner rotor  114  may be referred to as the magnetic rotor. In either of the embodiments, the outer rotor  112  and inner rotor  114  are magnetically, and non-mechanically, coupled together. 
         [0021]    Returning once again to the description, the first optical transceiver  104  is disposed adjacent the magnetic rotor  112  and is configured to selectively transmit incident light toward the magnetic rotor  112 . The first optical transceiver  104  is additionally configured to receive incident light that is reflected from the magnetic rotor  112 , and generate a first signal each time it receives reflected incident light from the magnetic rotor  112 . The second optical transceiver  106  is disposed adjacent the magnetically permeable rotor  114  and is configured to selectively transmit incident light toward the magnetically permeable rotor  114 . The second optical transceiver  106  is additionally configured to receive incident light that is reflected from the magnetically permeable rotor  114 , and generate a second signal each time it receives reflected incident light from the magnetically permeable rotor  114 . 
         [0022]    It is noted that, at least in a particular preferred embodiment, the first and second optical transceivers  104  and  106 , the magnetic rotor  112 , the magnetically permeable rotor  114 , and the first and second reflective features  117  and  127 , are implemented such that a characteristic of the first and second signals is varied each time the first and second reflective features  117  and  127 , respectively, rotate past the first and second optical transceivers  104  and  106 , respectively. The specific characteristic that is varied may be any one of numerous electrical characteristics. But in the depicted embodiment the amplitudes are varied. As such, the first and second signals are preferably manifested as pulse wave signals, such as, for example, the equal amplitude square wave pulse signals depicted in  FIG. 1 . 
         [0023]    It will be appreciated that the first and second optical transceivers  104  and  106  may be variously configured and implemented. In the depicted embodiment, the first and second optical transceivers  104  and  106  include substantially identical transceiver probes  132  that are in operable communication with substantially identical light source/sensor circuitry devices  134  via substantially identical fiber optic cables  136 . This is merely one example of an optical transceiver configuration and implementation. In other embodiments the first and second optical transceivers  104  and  106  may implemented such that the probes  132  light source/sensor circuitry devices  134  are integrally formed, thereby eliminating the need for the fiber optic cables. 
         [0024]    In the depicted embodiment, each transceiver probe  132  is coupled to receive, via its associated fiber optic cable  136 , incident light that is supplied from its associated light source/sensor circuitry device  134 . Each transceiver probe transmits the incident light toward, and receives incident light that is reflected from, the magnetic rotor  112  or the magnetically permeable rotor  114 , as the case may be. The reflected light that is received is supplied, via the appropriately associated fiber optic cable  136 , to the appropriately associated light source/sensor circuitry device  134 . 
         [0025]    The light source/sensor circuitry devices  134  each include one or more non-illustrated light sources, such as laser light sources or LEDs, to name just two, and further include suitable non-illustrated control and sensor circuitry. The control and sensor circuitries control the light sources, and implement suitable optical-to-electrical signal conversion of the reflected light. The control and sensor circuitries are additionally configured to implement suitable signal conditioning including, for example, analog-to-digital conversion, filtering, amplification, etc., as needed or desired. Although the light source/sensor circuitry devices  134  are depicted as two physically separate devices, both could be implemented in the same integrated circuit package. 
         [0026]    No matter the specific configuration and implementation of the first and second optical transceivers  104  and  106 , the first and second signals that the transceivers respectively supply are received by the processor  108 . The processor  108  is configured, upon receipt of the first and second signals, to determine the torque on the magnetically permeable rotor  114 , which in the depicted embodiment corresponds to the drag torque of the one or more bearing assemblies  128 . To do so, the processor  108  determines the phase difference between the first and second signals and, together with the angular stiffness of the magnetic coupling  102 , calculates the torque. 
         [0027]    The angular stiffness of the magnetic coupling  102  is predetermined, and may be graphically represented in the form of magnetic coupling torque (τ) versus slip (θ). An exemplary graph of magnetic coupling torque versus slip for one particular magnetic coupling  102  embodiment is depicted in  FIG. 2 . The depicted curve  202  has a least squares best-fit characteristic equation of: 
         [0000]      τ=0.0056θ 2 +0.1691θ−0.0014.
 
         [0000]    It will be appreciated that the depicted curve  202  and concomitant best-fit characteristic equation is merely exemplary of one particular magnetic coupling  102  embodiment, and that other curves and equations may apply for other magnetic coupling embodiments  102 . 
         [0028]    The angular stiffness of the magnetic coupling  102  is preferably stored in a non-illustrated memory. The memory may be on-board the processor  108  or be implemented as an external memory device that is readable by the processor  108 . In either case, the processor  108 , as was noted above, determines the phase difference between the first and second signals. The phase difference, as depicted in  FIG. 1 , corresponds to the slip (θ) of the magnetic coupling  102 . The processor  108  may then determine the torque (τ) using the known angular stiffness. 
         [0029]    The non-contact torque determination system  100  may be used to determine torque in any one of numerous systems, components, devices, and environments. In one particular preferred embodiment, the system  100  is implemented with a test fixture that is used to test bearing assemblies and to determine the drag torque of bearing assemblies. One particular physical embodiment of such a test fixture is depicted in  FIGS. 3-5  and, for completeness, will now be described. In doing so it is noted that like reference numerals in FIGS.  1  and  3 - 5  refer to like parts. 
         [0030]    Referring simultaneously to  FIGS. 3-5 , the test fixture  300  includes a housing assembly  302 , a test shaft  304  ( FIG. 5 ), and a drive torque source  306 . The housing assembly  302  is mounted on a base  308  and includes, among other components, a cooling assembly  312 , a plurality of bearing supports  314 , a bearing cover  316 , and a rotor cover  318 . These components, when properly assembled together, define an inner volume  322  that is preferably evacuated and held at a vacuum pressure. Some of the depicted fittings  324  facilitate this evacuation. The remaining fittings  324  facilitate the flow of cooling into and through the cooling assembly  312 . 
         [0031]    The test shaft  304  is rotationally mounted and within the housing assembly inner volume  322  ( FIG. 5 ) via a plurality of bearing assemblies  128 . The bearing assemblies  128  are disposed within housing assembly inner volume  322  and are each mounted in the housing assembly  302 . The test shaft  306  is coupled to the magnetically permeable rotor  114 , which is also disposed within housing assembly inner volume  322 . In particular, it is seen that the rotor cover  318  surrounds the magnetically permeable rotor  114  and encloses the magnetically permeable rotor  114  within the housing assembly inner volume  322 . Though the test shaft  306  may be coupled to the magnetically permeable rotor  114  using any one of numerous techniques, in the depicted embodiment these components are coupled together via mating threads that are formed on each component. 
         [0032]    The drive torque source  306  is mounted within a support, and coupled to, and is configured to supply a drive torque to, the magnetic rotor  112 . As was alluded to above, the drive torque source  306  may be variously implemented. In the depicted embodiment, however, it is implemented using a drive motor. The drive motor  306 , as may be appreciated, may also be variously implemented. For example, it may be implemented using any one of numerous pneumatic, hydraulic, or electric motors. In a particular preferred embodiment, the drive motor  304  is an electric motor. 
         [0033]    The test fixture  300  is preferably used to determine the drag torque of the bearing assemblies  128 . To do so, the test system  100  described above is implemented as part of the test fixture  300 . Preferably, the first optical transceiver  104  (or associated probe  132 ) is mounted on a mounting bracket  311  (see  FIGS. 3 and 4 ) that is secured to the base  308 , and the second optical transceiver  106  (or associated probe  132 ) is sealingly disposed in and through an opening  313  (see  FIG. 5 ) in the rotor cover  318 . 
         [0034]    The system  100  described herein determines bearing drag torque with an accuracy of about 0.01 in-ounces. The test system  100  provides these accurate torque determinations without having to mechanically couple the system  100  to the rotating load, and while thermally isolating the torque drive source from the rotating load. 
         [0035]    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.