Centralizing devices for use in bore-holes

An assembly of a centralizing device and a sensor or other operational tool, the device being for use down-well in maintaining the sensor or other operational tool in a location accurately centralized on the axis of the bore hole irrespective of the angular orientation of the device and tool at any given location, said device comprising

• an elongate body member having a longitudinal axis, which axis is, in use, maintained coincident with the longitudinal axis of the bore hole, the elongate body member having a plurality of spaced slots distributed around its circumferential surface, each said slot extending parallel to said longitudinal axis,
• a corresponding plurality of two-armed assemblies spaced around the longitudinal axis of the elongate body member, each arm of each assembly being pivotally connected at a radially outer location at end portions of the arms, and capable of being accommodated substantially wholly within the envelope defined by the elongate body member when the arms are in a retracted configuration,
• radially outer pivots providing the pivotal connection at the radially outer end portions of the respective said arms,
• two slide blocks each having external cross-sections within the confines of the outer cross section of the elongate body member, each slide block defining a plurality of recesses corresponding to the number of two-armed assemblies, each said recess receiving an inner end portion of a said arm,
• each said slide block serving as an abutment for the resilient means at one end portion thereof, and having
• conformation means at the other end portion thereof, and each inner end portion of each arm of each said two-armed linkage having
• conformation means co-operating with corresponding said conformation means of the slide block
• the action of the resilient means on the hollow slide blocks being such that the conformation means of the slide blocks and of the arms causes the arms to pivot outwardly, the force acting on the arms being substantially constant irrespective of the angular orientation by virtue of the co-operating conformation means of the slide blocks and of the arms.

An assembly comprising two centralizing devices for use down-hole in defining an axial alignment within the borehole, each said centralizing device comprising,

• an elongate body member having a longitudinal axis and having a plurality of spaced slots distributed around its circumferential surface, each said slot extending parallel to said longitudinal axis,
• a corresponding plurality of two-armed assemblies spaced around the longitudinal axis of the elongate body member, each arm of each assembly being pivotally connected at a radially outer location at end portions of the arms, and capable of being accommodated substantially wholly within the envelope defined by the elongate body member when the arms are in a retracted configuration,
• radially outer pivots providing the pivotal connection at the radially outer end portions of the respective said arms,
• two slide blocks each having external cross-sections within the confines of the outer cross section of the elongate body member, each slide block defining a plurality of recesses corresponding to the number of two-armed assemblies, each said recess receiving an inner end portion of a said arm,
• means retaining the respective inner end portions of the arms in a respective one of the slide blocks,
• anti-friction members, each mounted at a said radially outer pivot of the two-armed assemblies and intended for contacting engagement with the surrounding structure of the bore hole,
• means at at least one end of the elongate body member for connecting it to the other said centralizing device, and
• resilient means acting on at least one of said slide blocks to bias the two-armed assemblies outwardly from the body member so that the anti-friction members are always, in use, in contact with the surrounding structure of the bore-hole,
• the devices together defining an axial alignment between them.