US Patent 10041305 Actively controlled self-adjusting bits and related systems and methods

An actively controlled self-adjusting earth-boring tool includes a body carrying cutting elements and an actuation device disposed at least partially within the body. The actuation device may include a first fluid chamber, a second fluid chamber, and a reciprocating member dividing the first fluid chamber from the second fluid chamber. A connection member may be attached to the reciprocating member and may have a drilling or bearing element connected thereto. A first fluid flow path may extend from the second fluid chamber to the first fluid chamber. A second fluid flow path may extend from the first fluid chamber to the second fluid chamber. A rate controller may control a flowrate of a hydraulic fluid through the first and second fluid flow paths. The rate controller may include an electromagnet, and the flowrates of the hydraulic fluid may be adjusted by adjusting fluid properties of the hydraulic fluid.