Apparatus and method for actuating arms

An apparatus for actuating arms comprising:

• a mandrel;
• at least one arm carried by the mandrel, the at least one arm being mounted to the mandrel to move between an expanded position, in which a part of the arm projects from the mandrel, and a retracted position;
• resilient biassing means associated with the at least one arm for biassing the arm towards its expanded position with a resilient biassing force;
• a holder associated with the at least one arm for restraining the arm against movement towards its expanded position, the holder being independent of the mandrel;
• and
• a driver acting upon the resilient biassing means for adjusting the resilient biassing force acting upon each arm, the driver being separate from the holder.

A method of actuating the arms of a data logging tool, wherein the data logging tool includes:

• a mandrel;
• at least one arm carried by the mandrel, and mounted to the mandrel to move between an expanded position, in which a part of the arm projects from the mandrel, and a retracted position;
• resilient biassing means associated with the at least one arm for biassing the arm towards its expanded position;
• restraining means associated with the at least one arm for restraining the arm against movement towards its expanded position;
• and
• drive means acting upon the resilient biassing means for adjusting a resilient biassing force acting upon the at least one arm;
• the method comprising the steps of:
• restraining the at least one arm in retracted positions;
• locating the tool within a borehole having a borehole wall;
• loading the previously unloaded resilient biassing means whilst the arms are restrained;
• positioning the tool in a desired position within the borehole;
• and
• releasing the retraining means to allow the resilient biassing means to urge the arms against the borehole wall.