Target positioning systems and methods

A system for continuously calibrating a rotatable shaft so that the shaft is at a desired rotational orientation, the system comprising:

• a rotatable shaft having a lower end configured to support a target and an upper end operatively coupled to a powered drive unit configured to rotate the shaft among a plurality of rotational positions around an axis;
• a rotation disengagement mechanism operatively coupling the shaft to the powered drive unit;
• a position indicator associated with the rotatable shaft for detecting a rotational orientation of the rotatable shaft;
• and
• a control unit including a processor for executing code to direct the operation of the powered drive unit;
• wherein the system is configured to
• rotate the powered drive unit by an amount sufficient to rotate the rotation disengagement mechanism in a first direction by an amount greater than 360° to ensure the rotatable shaft is engaged with the powered drive unit;
• rotate the shaft in a second direction opposite the first direction;
• detect a rotational orientation of the rotatable shaft;
• and
• halt rotation of the shaft in the second direction when the detected rotational orientation of the shaft corresponds to the desired rotational orientation.

A method of positioning a rotatable shaft at a desired rotational orientation, the method comprising:

• rotating a powered drive unit operatively coupled to the rotatable shaft by an amount sufficient to rotate a rotation disengagement mechanism associated with the shaft in a first direction by an amount greater than 360′;
• while rotating the rotation disengagement mechanism, engaging the rotatable shaft with the powered drive unit so that the rotatable shaft rotates under the influence of the powered drive unit;
• rotating the shaft in a second direction opposite the first direction;
• detecting a rotational orientation of the rotatable shaft;
• and
• halting rotation of the shaft in the second direction when the detected rotational orientation of the shaft corresponds to the desired rotational orientation.

A method of correcting a rotational position of a rotatable shaft, the method comprising:

• rotating the shaft from a first rotational position to a second rotational position;
• detecting a first rotational orientation of the rotatable shaft at the second position;
• determining whether the rotational orientation of the rotatable shaft at the second position falls within a predetermined angular distance of a desired rotational position of the rotatable shaft;
• and
• if it is determined that the rotational orientation of the rotatable shaft at the second position does not fall within the predetermined angular distance, executing a corrective action, comprising:
• rotating a powered drive unit operatively coupled to the rotatable shaft by an amount sufficient to rotate a rotation disengagement mechanism associated with the shaft in a first direction by an amount greater than 360°:
• while rotating the rotation disengagement mechanism, engaging the rotatable shaft with the powered drive unit so that the rotatable shaft rotates under the influence of the powered drive unit;
• rotating the shaft in a second direction opposite the first direction;
• detecting a second rotational orientation of the rotatable shaft;
• and
• halting rotation of the shaft in the second direction when the detected second rotational orientation of the shaft corresponds to the desired rotational orientation.

A method of correcting a rotational position of a rotatable shaft, the method comprising:

• rotating the shaft from a first rotational position to a second rotational position;
• measuring an actual elapsed time tA during rotation of the shaft;
• comparing tA to an expected quantity of time necessary to rotate the shaft from the first rotational position to the second rotational position, tE;
• and
• if tA≠tE, determining that the rotatable shaft is not at a desired rotational position and executing a corrective action comprising:
• rotating a powered drive unit operatively coupled to the rotatable shaft by an amount sufficient to rotate a rotation disengagement mechanism associated with the shaft in a first direction by an amount greater than 360°;
• while rotating the rotation disengagement mechanism, engaging the rotatable shaft with the powered drive unit so that the rotatable shaft rotates under the influence of the powered drive unit;
• rotating the shaft in a second direction opposite the first direction;
• detecting a rotational orientation of the rotatable shaft;
• and
• halting rotation of the shaft in the second direction when the detected rotational orientation of the shaft corresponds to the desired rotational orientation.