Downhole instrument with angular rate sensor
A downhole instrument includes an instrument housing, a sensor yoke rotatably mounted within the instrument housing, and an angular rate sensor carried by the sensor yoke. A first rotational stop is mounted to the instrument housing that defines a first rotational position of the sensor yoke. A second rotational stop mounted to the instrument housing defines a second rotational position of the sensor yoke that is rotationally spaced from the first rotational position. A differential screw may be connected to the second rotational stop that is adapted to adjust a position of the second rotational position. A torsion coupling may be coupled between the rotational driver and the sensor yoke, where the torsion coupling is energized by the motor that rotates the sensor yoke with a returning force that resists movement of the sensor yoke away from the first rotational stop.
1 . A downhole instrument, comprising:
an instrument housing;
an angular rate sensor carried by a sensor yoke, the sensor yoke being rotatably mounted to the instrument housing such that the sensor yoke rotates about a pivot axis that is perpendicular to the longitudinal axis;
a first rotational stop mounted to the instrument housing, the first rotational stop defining a first rotational position of the sensor yoke;
a second rotational stop mounted to the instrument housing, the second rotational stop defining a second rotational position of the sensor yoke;
a rotational driver that is connected to rotate the sensor yoke; and
a torsion coupling coupled between the rotational driver and the sensor yoke;
wherein:
the rotational driver is configured to rotate the sensor yoke to the first rotational position and energize the torsion coupling with a returning force that resists movement of the sensor yoke away from the first rotational stop.
2 . The downhole instrument of claim 1 , wherein the rotational driver is further configured to rotate the sensor yoke to the second rotational position and energize the torsion coupling with a returning force that resists movement of the sensor yoke away from the second rotational stop.
3 . The downhole instrument of claim 1 , wherein the rotational driver comprises an electric motor, the electric motor having a powered state and an unpowered state, wherein the electric motor is configured to rotate the sensor and energize the torsion coupling in the powered state, and switch to the unpowered state after the torsion coupling is energized.
4 . The downhole instrument of claim 1 , wherein the rotational driver is a motor that is coupled to the torsion coupling by a gear reducer, the motor and the gear reducer having sufficient friction and inertia to resist the returning force of the torsion coupling.
5 . The downhole instrument of claim 1 , wherein the angular rate sensor comprises a sensitive axis, and wherein the sensitive axis is reversed in the first rotational position relative to the second rotational position.
6 . The downhole instrument of claim 1 , wherein the sensor yoke comprises a stop block that engages the first rotational stop in the first rotational position and the second rotational stop in the second rotational position.
7 . The downhole instrument of claim 1 , wherein the instrument housing has a longitudinal axis, and the pivot axis is perpendicular to the longitudinal axis.
8 . A method of operating a downhole instrument, the downhole instrument comprising an instrument housing, a sensor a sensor yoke rotatably mounted within the instrument housing about a pivot axis, and an angular rate sensor carried by the sensor yoke, the method comprising the steps of:
switching a rotational driver from an unpowered state to a powered state to cause the sensor yoke to rotate to a first rotational position in which the sensor yoke engages a first rotational stop that is fixed relative to the instrument housing, and to energize a torsion coupling that is coupled between the rotational driver and the sensor yoke;
after energizing the torsion coupling, switching the rotational driver to the unpowered state, wherein, with the rotational driver in the unpowered state, a returning force of the torsion coupling resists movement of the sensor yoke away from the first rotational position.
9 . The method of claim 8 , further comprising the steps of switching the rotational driver from the unpowered state to the powered state to rotate the sensor yoke to the second rotational position in which the sensor yoke engages a second torsion coupling, and to energize the torsion coupling, and switching the rotational driver to the unpowered state thereafter.
10 . The method of claim 9 , wherein the sensor yoke comprises a stop block that engages the first rotational stop in the first rotational position and the second rotational stop in the second rotational position.
11 . The method of claim 8 , wherein the rotational driver comprises an electric motor, wherein, in the powered state, an electrical current is applied to the electric motor, and in the unpowered state, an electrical current is not applied to the electric motor.
12 . The method of claim 8 , wherein the rotational driver is a motor that is coupled to the torsion coupling by a gear reducer, the motor and the gear reducer having sufficient friction and inertia to resist the returning force of the torsion coupling.
13 . The method of claim 8 , wherein the angular rate sensor comprises a sensitive axis, and wherein the sensitive axis is reversed in the first rotational position relative to the second rotational position.
14 . A downhole instrument, comprising:
an instrument housing;
a sensor yoke rotatably mounted within the instrument housing, the sensor yoke having a pivot axis;
an angular rate sensor carried by the sensor yoke;
a first rotational stop mounted to the instrument housing, the first rotational stop defining a first rotational position of the sensor yoke;
a second rotational stop mounted to the instrument housing, the second rotational stop defining a second rotational position of the sensor yoke that is rotationally spaced from the first rotational position; and
a differential screw connected to the second rotational stop and adapted to adjust a position of the second rotational position, the differential screw having a first pitch and a second pitch, wherein a differential between the first pitch and the second pitch define an effective pitch that is less than the first pitch and the second pitch.
15 . The downhole instrument of claim 14 , wherein the differential screw adjusts a position of the second rotational stop relative to the instrument housing.
16 . The downhole instrument of claim 14 , further comprising a locking screw that selectively locks the second rotational stop in a desired second rotational position.
17 . The downhole instrument of claim 14 , wherein the angular rate sensor comprises a sensitive axis that is reversed in the second rotational position relative to the first rotational position.
18 . The downhole instrument of claim 17 , wherein the differential screw is adapted to adjust the position of the second rotational position such that the second rotational position is 180 degrees separated from the first rotational position.
19 . The downhole instrument of claim 14 , wherein the sensor yoke carries a stop block that engages the first rotational stop in the first rotational position and the second rotational stop in the second rotational position.
20 . The downhole instrument of claim 14 , wherein the instrument housing has a longitudinal axis, and the pivot axis is perpendicular to the longitudinal axis.