| 摘要 |
A compound linkage arm assembly for providing a substantial force to initially extend an arm assembly from a sonde without increasing the driving force in the opening mechanism. A linear drive mechanism initially acts upon a linkage within an arm assembly of the tool. The links unseat and force the arm away from the tool without much force from the drive mechanism. Once the arm is moved away from the tool by the full extension of the links, push rods act directly upon the arm to contact the bore hole wall. The advantage of this arrangement is that the linear drive mechanism is not required to exert a great amount of lateral force upon the arm to obtain the initial extension. The links acting between the arm and the sonde body provide the lateral force necessary to extend the arm. Once the links have been fully extended, the linear drive mechanism is able to act directly upon the arm the remainder of the distance since sufficient later forces are generated by the geometry between the drive, the push rod and the arm pivot points.
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