Abstract: A mechanical arm linkage for use in wellbore measuring instruments provides a linear correcting linkage assembly for pivotally connecting a sensor in linear sliding relationship to a non-linearly articulated moving arm member.

Abstract: A wellbore logging instrument is disclosed of the type having a density pad maintained in close proximity to the tool body, and a decentralizing arm pivotally mounted on the body and arranged to swing outward against the borehole to move the tool body and density pad against the opposite borehole wall. The apparatus includes a linkage assembly to provide a slight extension of the density pad at any selected time in the borehole.

Abstract: A borehole instrument having four arm pad members utilizes four independent bow springs, each of the bow springs being anchored to the instrument at one of their ends and being individually slidably mounted at their other ends to the instrument. A push-pull rod activated by a solenoid within the instrument causes each of the slidable collars connected to the bow springs, respectively, to move down and thus close the instrument for easy passage through the borehole when not logging. When the push-pull rod is pulled up, each of the bow springs acts independently to cause the individual pads to make contact with the borehole wall. In an alternative embodiment, spring-driven pad linkage assemblies are likewise closed by pushing on the push-pull rod and are allowed to open and move out against the borehole wall when the rod is pulled up by action of the solenoid.

Abstract: An earth borehole instrument has a plurality of wear link members adapted to engage the borehole walls which are pivotally attached through articulated mechanical arms both to a fixed collar and to a spring-loaded slidable collar on the instrument. The articulated arms for each wear link member consist of a pair of power arms which are each pivoted at a center point on the wear link adapted to engage the borehole wall and a pair of sensing arms which are pivotally connected, respectively, to the ends of the wear link. In an alternative embodiment, a bow spring is mounted on the underside of the power arms for maintaining the wear link flat against the borehole wall.