Patent Publication Number: US-2022220841-A1

Title: Survey instrument

Description:
REFERENCES TO RELATED APPLICATIONS 
     This application claims priority of U.S. provisional application Ser. No. 62/841,214 filed on Apr. 30, 2019, having a common assignee with the present application, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     Field 
     This invention relates generally to the field of borehole surveying instruments and more particularly to an attitude survey instrument with a rotating sensor gimbal. 
     Description of the Related Art 
     In the field of borehole surveying, the measurement of azimuth while in the borehole at all a nominal borehole azimuth and dip angles is highly desirable. One key technical requirement to achieve measurement in all attitudes is to remove systematic bias from all sensor measurements. One method of doing this is by rotating the sensors in multiple rotational positions to make the systematic bias observable and therefore measurable. Historically and for practical mechanical reasons, sensor rotation in a small diameter borehole is easily done for sensors that have their sensitive axis cross wise to the borehole and very difficult for sensors that nominally have sensitive measurements along the borehole. 
     It is therefore desirable to provide a means for rotating a sensor and measuring systematic bias of the sensor ultimately providing a bias corrected measurement along the borehole axis. 
     SUMMARY 
     In one aspect the present invention may be said to comprise a sensor gimbal system comprising: a sensor gimbal with a sensor PCB and a sensor, said sensor gimbal configurable to rotationally orient a sensitive axis of the sensor with respect to the sensor gimbal system; a sensor motor to rotate the sensor gimbal between a first orientation and a second orientation; and a flex circuit between the sensor PCB and an electronic circuit board, wherein the flex circuit is routed to reduce signal distortion and/or kinking during rotation. 
     Optionally the flex circuit is routed on a curved path. 
     Optionally the sensor gimbal system further comprises a curved path frame to route the flex circuit. 
     Optionally the sensor gimbal system according further comprises shielding on one or both sides of the flex circuit. 
     Optionally the sensor is mounted using epoxy or a silicon adhesive (such as silicon epoxy to isolate vibrations and stresses from rotation of the sensor gimbal. 
     Optionally the flex circuit, curved path routing, shielding and/or silicon adhesive reduce bias. 
     Optionally the sensor gimbal system is mounted on an IMU gimbal, tool chassis of a survey instrument, or an outer rotating assembly. 
     Optionally the sensor comprises a MEMs gyro. 
     Optionally the sensor gimbal system further comprises a sub-chassis on which the sensor is mounted with an epoxy, or a silicon adhesive (such as silicon epoxy), the sub-chassis attached to a gimbal frame of the sensor gimbal. 
     Optionally the flex circuit incorporates a substantially 360° encirclement of the sensor and sensor PCB in the unrotated position, the flex circuit received in a track in a sub-chassis engaging the sensor PCB to a sensor gimbal frame. 
     Optionally a companion track is present in the sensor gimbal frame for alignment of the flex circuit. 
     In another aspect the present invention may be said to comprise a method for manufacture of a rotating gimbal assembly according to any one of the statements above, the method comprising: soldering the MEMs gyro sensor to the sensor PCB; epoxying or silicon adhering (e.g. using such as silicon epoxy) the soldered sensor PCB to the sub-chassis; attaching the sub-chassis to the gimbal frame; and, attaching the rotating gimbal frame to the tool housing and calibrating the rotating gimbal. 
     In another aspect the present invention may be said to comprise a survey instrument comprising a sensor gimbal system according to any statement above. 
     Optionally the survey instrument further comprises an IMU gimbal, wherein the sensor gimbal system is mounted on the IMU gimbal. 
     Optionally the IMU gimbal is rotatable about a longitudinal axis of the survey instrument. 
     Optionally the survey instrument has a tool chassis, and the sensor gimbal system is mounted on the tool chassis. 
     The embodiments disclosed herein provide a sensor gimbal system employing one sensor gimbal on which a sensor is mounted. The sensor gimbal is configured to orient a sensitive axis of the sensor along either an Y axis or a Z axis of an IMU gimbal or to rotate the sensitive axis of the sensor  180 ° for positive and negative alignment with the Z axis of a survey tool. A sensor motor assembly is configured to rotate the sensor gimbal between a first hard stops and a second hard stop. In a first implementation, when rotated against the first hard stop the sensor sensitive axis is coincident with the Y axis of the IMU gimbal and when rotated against the second stop the sensitive axis of the sensor is coincident with the IMU Z axis. In a second implementation when rotated against the first hard stop the sensor sensitive axis is aligned with the +Z axis and when rotated against the second hard stop the sensor sensitive axis is aligned with the −Z axis of the survey instrument. A dowel pin extends from the sensor gimbal to engage the hard stops. A flex circuit has a flex cable from a sensor PCB, on which the sensor is mounted, to an electronic circuit board. 
     Also described herein is a sensor gimbal system comprising: one sensor gimbal on which a sensor is mounted, said sensor gimbal configured to rotationally orient a sensitive axis of the sensor with respect to a survey instrument; a sensor motor assembly configured to rotate the sensor gimbal between a first hard stop and a second hard stop; a dowel pin extending from the mating bevel gear configured to engage the hard stops; and a flex circuit having a flex cable from a sensor PCB to an electronic circuit board. 
     Optionally the flexible length of the flex circuit is predetermined with a curved path frame ensuring that the flex circuit cable does not kink. 
     Optionally the sensor gimbal system further comprises a sub-chassis on which the sensor is mounted with an epoxy, the sub-chassis attached to a gimbal frame of the sensor gimbal. 
     Optionally the sensor comprises a MEMs gyro. 
     Optionally the IMU gimbal is rotatable about a longitudinal axis of the survey instrument in which the IMU gimbal is mounted and the sensor gimbal is mounted to the IMU gimbal. 
     Optionally the sensor motor rotates a bevel drive gear that engages a mating bevel gear to rotate the sensor gimbal, wherein when rotated against the first hard stop the sensor sensitive axis is coincident with a first axis of the IMU gimbal and when rotated against the second stop the sensitive axis of the sensor  24  is coincident with a second axis of the IMU gimbal. 
     Optionally the sensor motor rotates a toothed drive belt engaging a mating toothed gear to rotate the sensor gimbal between the first and second hard stops. 
     Optionally the sensor gimbal is mounted to a frame of the survey instrument. 
     Optionally the sensitive axis of the sensor is aligned with a Z axis of the survey instrument with the gimbal rotated to the first hard stop and rotated 180° with the gimbal rotated to the second hard stop. 
     Optionally the hard stops are adjustable. 
     Optionally the flex cable includes a layer of high magnetic permeability material on at least a portion of one side of the flex cable. 
     Optionally the flex cable includes a layer of high magnetic permeability material both sides of the flex cable. 
     Optionally the flex cable is routed along at least one curved path frame. 
     Optionally the flex cable incorporates a substantially 360° encirclement of the sensor and sensor PCB in the unrotated position, the flex cable received in a track in the sub-chassis engaging the sensor PCB to the sensor gimbal frame. 
     Optionally a companion track is present in the sensor gimbal frame for alignment of the flex cable. 
     Optionally the flex cable is adhesively engaged in the companion track. 
     Also described herein is a method for manufacture of a rotating gimbal assembly as described above, the method comprising: soldering the MEMs gyro sensor to the sensor PCB; epoxying the soldered sensor PCB to the sub-chassis; attaching the sub-chassis to the gimbal frame; and, attaching the rotating gimbal frame to the tool housing and calibrating the rotating gimbal. 
     Optionally the step of epoxying the sensor PCB to the sub-chassis employs a silicon epoxy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will be better understood by reference to the following detailed description of exemplary embodiments when considered in connection with the accompanying drawings wherein: 
         FIG. 1A  is a side view depiction of an exemplary implementation the sensor gimbal in the attitude survey instrument; 
         FIG. 1B  is an expanded view of a partial profile of the implementation of  FIG. 1A ; 
         FIG. 2A  is a top view depiction of the implementation of  FIG. 1A  with a partial case removal over the sensor section for clarity; 
         FIG. 2B  is an expanded view of the partial case removal of the implementation of  FIG. 2A ; 
         FIG. 3A  is a sectioned depiction of the example implementation along lines III of  FIG. 2B  with the sensor gimbal in the unrotated position; 
         FIG. 3B  is the sectioned depiction of the example implementation along lines III of  FIG. 2B  with the sensor gimbal in the rotated position; 
         FIG. 4  is a sectioned depiction of the sensor gimbal along lines IV of  FIG. 1B ; 
         FIG. 5  is a sectioned depiction of the sensor gimbal along lines V of  FIG. 2B ; 
         FIG. 6A  is a pictorial representation of a second implementation of the sensor gimbal system in the attitude survey instrument; 
         FIG. 6B  is a pictorial representation of the sensor gimbal system; 
         FIG. 7A  is a sectioned depiction of the second implementation of the sensor gimbal with the gimbal in an unrotated position; 
         FIG. 7B  is a sectioned depiction of the second implementation of the sensor gimbal with the gimbal in a 180° rotated position; 
         FIG. 8A  is a detailed pictorial view of the sensor gimbal; 
         FIG. 8B  is a section pictorial view of the sensor gimbal; 
         FIG. 8C  is a detailed pictorial view of the sensor flex cable PCB mounted in a gyro plate for engagement in the sensor gimbal; 
         FIG. 9  is a detailed pictorial view of the motor assembly and rotational drive elements; and, 
         FIG. 10  is a flow chart of a manufacturing method for the implementations described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Implementations shown in the drawings and described herein provide a downhole survey instrument having a combination of a sensor gimbal and an IMU gimbal to collect a series of measurements adapting the sensor gimbal configuration based on the sensor measurements taken in the sequence. The concept can be extended to include all the sensors in the IMU but the most practical and simplest configuration to implement is displayed in the drawings. A first example implementation is shown in  FIGS. 1A and 2A , a survey instrument  10  includes an IMU gimbal unit  12 , which may be implemented as disclosed in U.S. Pat. No. 9,714,548 issued Jul. 25, 2017 entitled Apparatus for Single Degree of Freedom Inertial Measurement Unit Platform Rate Isolation. The IMU gimbal  12  houses an accelerometer package  14 , an X axis gyro  16  and a Y axis gyro  18 . A sensor gimbal system  20  employing the exemplary implementation is also mounted in in the survey tool  10  on the IMU gimbal unit  12 . Details of the sensor gimbal system  20  are shown in  FIGS. 3A, 3B, 4 and 5 . 
     In the exemplary implementation, the sensor gimbal system  20  employs one sensor gimbal  22  on which a sensor  24  (that comprises a Z gyro in the example) is mounted. The sensor gimbal can orient the sensitive axis of the sensor  24  along either a first axis (the Y axis in the example implementation) or a second axis (the Z axis in the example implementation) of the IMU gimbal unit  12  as will be described in greater detail subsequently. A sensor motor assembly  26  rotates a bevel drive gear  28  that engages a mating bevel gear  30  on the sensor gimbal  22  to rotate the sensor gimbal between two hard stops providing a first position and a second position. When rotated against a first hard stop  32  (seen in  FIG. 5 ) as shown in  FIG. 3B , the sensor  24  sensitive axis  34  is coincident with the Y axis of the IMU designated IMU Mode  1 . When rotated against a second stop  36  (seen in  FIG. 5 ) the sensitive axis  34 ′ of the sensor  24  is coincident with the IMU gimbal Z axis designated IMU Mode  2 . A dowel pin  38  (seen in  FIG. 5 ) extending from the mating bevel gear  30  engages the hard stops  32 ,  36 . In the implementation shown, the hard stops  32 ,  36  are threaded screws allowing adjustment of the stop positions. 
     A flex circuit  39  provides the ability to move an analog signal from the sensor  24  through a flex cable  40  from a sensor PCB  41  to an electronic circuit board  42  without distorting the analog signal. The analog signal can distort due parasitic coupling to the gimbal chassis as well as other circuitry near the flex cable  40 . For this reason, the flex cable is routed and managed during rotation and where possible to maintain a large and consistent clearances to minimize the magnitude of parasitic coupling and therefore analogue signal distortion. The flex cable  40  is managed to route along a curved path frame  44  ensuring that the flex cable  40  does not kink preventing mechanical and electrical failure of the conductors. 
     For the exemplary implementation, bevel drive gear  28  and mating bevel gear  30  are machined with only the needed teeth for the rotating movement of 90 degrees. As seen in  FIG. 5 , the hard stops  32 ,  36  employ adjustment screws mounted in the gimbal system case  45  or case cover to calibrate the rotating gimbal to achieve desired performance. Preloaded angular contact ball bearings  46  are employed to support the sensor gimbal  22 . The purpose of the bearings is to ensure low friction transfer to the rotating platform and high precision of rotation. 
     The sensor  24  has a nominal sensitive axis along the borehole. The implementation described herein provides the sensor gimbal  22  and the motor assembly  26 , bevel drive gear  28  and mating bevel gear  30  to rotate sensitive axis  34  of the sensor  24  into directions both along the borehole as well as crosswise to the borehole. A sub-chassis  48  on which the sensor  24  is mounted on the sensor gimbal  22 , the support structure for rotation including the bearings  46 , the motor assembly  26 , bevel drive gear  28  and mating bevel gear  30  to drive the gimbal, precision hard stops  32 ,  36  to define the rotational positions, and the flex cable  40  used to connect the electrical signals from the sensor  24  to the larger instrument assembly provide the rotating sensor gimbal system  20  for bias elimination. 
     The sensor gimbal system  20  is mounted on board the IMU gimbal unit  12 , which is capable of a 360° rotation about a longitudinal axis of the survey instrument  10 . An initial 90° rotation of the sensor gimbal  22  brings the sensor  24  orthogonal to the rotation of the IMU gimbal unit  12 . The IMU gimbal unit  12  may then be rotated by 180° for bias calculation. 
     The sensor  24  used can be a gyroscope, an accelerometer, a magnetometer or a combination of more than one of these types of sensors. The preferred embodiment uses a MEMS gyroscope, and\or a MEMS accelerometer mounted on the sensor gimbal  22 . But the implementation is not limited to these devices. A silicon adhesive is used to attach the sensor  24  to the sub-chassis  48  to ensure vibration and stresses from rotation of the sensor gimbal  22  is isolated from the MEMs gyro. Additionally, the sensor is mounted to the flex circuit with the flex circuit attached to the sub-chassis with silicon adhesive. 
     In alternative implementations, the sensor gimbal can be mounted off the IMU gimbal unit  12  on the tool chassis of the survey instrument  10  or on an outer rotating assembly. A second example implementation is seen in  FIGS. 6A and 6B  wherein a sensor gimbal system  21  is engaged in the survey instrument  10  separate from the IMU gimbal  12 . As seen in detail in  FIGS. 7A, 7B and 8A-8C , as in the prior implementation, the sensor gimbal system  21  includes one sensor gimbal  23  on which a sensor  24  (that again comprises a Z gyro in the example) is mounted. The sensor gimbal  23  is configured to orient the sensitive axis  34  of the sensor  24  in a first orientation +Z (as seen in  FIG. 7A ) or, after full rotation, a second orientation −Z (as seen in  FIG. 7B ) for a first position and second position. A sensor motor assembly  27 , best seen in  FIG. 9 , rotates a toothed drive belt  29  that engages a mating toothed gear  31  to rotate the sensor gimbal  23  between two adjustable hard stops  33 ,  37 . Idler pulleys  50  maintain tension in the drive belt  29 . As in the prior implementation a dowel pin  38  integral with the sensor gimbal frame  43  is employed to engage the hard stops  33 ,  37  and, as in the initial implementation, the hard stops are threaded screws in the gimbal system case  45  or a case cover allowing adjustment of the stop positions. 
     In alternative implementations, a rotation sensor may be employed to sense position of the sensor gimbal  23  and control sensor motor assembly  27  for rotation of the gimbal to the desired positions. 
     As in the initial implementation, flex circuit  39  connects the sensor  24  through a flex cable  40  from sensor PCB  41  to electronic circuit board  42 . In the example implementation, the flex cable  40  is shielded on both sides by a layer of high magnetic permeability material that prevents the signals from being corrupted from the change in position from one position to another. In the example implementation the high magnetic permeable material is a foil tape such as Mu-ferro foil &amp; tape 3208 series produced by Holland Shielding Systems BV, Jacobus Lipsweg 124, 3316BP Dordrecht, the Netherlands. In alternative implementations, the flex cable may have a full shield on all sides, full shield on one side or partial shielding in specific locations to avoid signal corruption. The flex cable is also routed and managed during rotation and where possible to maintain a large and consistent clearances to minimize the magnitude of parasitic coupling and therefore analogue signal distortion. 
     As in the initial implementation, the flex cable  40  is managed to route along a curved path frame  44  during rotation (as seen in  FIGS. 7A and 7B ) ensuring that the flex cable  40  does not kink preventing mechanical and electrical failure of the conductors. A supplemental path ramp  49  is employed for positioning of the flex cable  40  in the unrotated position as seen in  FIG. 7A . To accommodate the rotation of the sensor gimbal  23  through 180° the flex cable  40  incorporates a substantially 360° encirclement of the sensor  24  and sensor PCB  41  in the unrotated position, being received in a track  49   a  in a sub-chassis  48  engaging the sensor PCB  41  (seen in detail in  FIG. 9C ) to the sensor gimbal frame  43 . In the example implementation a companion track  48 B is present in the sensor gimbal frame  43  for alignment of the flex cable  40 . The flex cable  40  may be adhesively engaged in the companion track  48 B to maintain appropriate tension for shaping of the flex cable in the rotated position of the gimbal as seen in  FIG. 7B . 
     As in the prior implementation, angular contact ball bearings  46  or similar bearings provide rotational support for the sensor gimbal  23 . As seen in  FIGS. 8A and 8B , bearings  46  are supported in the gimbal frame  43   
     The sensor  24  used can be a gyroscope, an accelerometer, a magnetometer or a combination of more than one of these types of sensors. The preferred embodiment, as in the initial implementation, uses a MEMS gyroscope, and\or a MEMS accelerometer mounted on the sensor gimbal  22 . But the implementation are not limited to these devices. In addition, packaging of the digital and analog electronics for the sensor may be selectively distributed between the sensor PCB  41  and the electronic circuit board  42 . In certain implementations the digital and analog electronics as well as the sensor are engaged on the sensor PCB  41  to rotate with the sensor gimbal  22  thereby further reducing potential signal corruption in the flex cable which then only transmits final digital sensor data to data acquisition components on the electronic circuit board  42  for uphole transmission. For sizing considerations in the rotating element, analog circuitry may be consolidated on the sensor PCB  41  with digital components remaining on the electronic circuit board  42  and the flex cable  40  connecting analog to digital signals. To provide the smallest rotating element only the sensor  24  is mounted on the sensor PCB  41  for attachment to the gimbal frame  43 . 
     A method for manufacture  1100  of the rotating sensor gimbal system  20  is accomplished as shown in  FIG. 10  for a MEMs gyro as the sensor  24 . The flex circuit design has two circuit boards (PCBs) on either side of the flex cable  40 , namely the MEMs sensor PCB  41  and the electronics circuit board  42 . The MEMs gyro sensor  24  is soldered to MEMs sensor PCB  41 , step  1002 . 
     The sensor  24 , soldered to the MEMS flex PCB in step  1102 , is attached to the sub-chassis  48  using a silicon adhesive, step  1104 . The silicon adhesive is to isolate the MEMs gyro from vibration and stresses caused by the rotating gimbal. These vibrations and stresses can produce unwanted bias shift during gimbal rotation. 
     The sub-chassis  48  is attached to the gimbal frame  43  (seen in  FIG. 4  for the first implementation and  FIG. 9C  for the second implementation) of the rotating sensor gimbal  22 ,  23 , step  1106 . Including a sub-chassis allows for ease of manufacture. The MEMs gyro is soldered to the MEMs flex PCB first (Step  1002 ) and then glued to the sub-chassis (step  1004 ). By taking care during this process, the MEMs is isolated from unnecessary vibrations and stresses. 
     The rotating gimbal frame is attached in a housing of the survey instrument, step  1008 , and calibration of the rotating gimbal is performed. 
     Having now described various embodiments of the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.