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An innovative patented technique of sliding bearing system in rotary cone bit which can realize the early warning of bearing failure so as to prevent the wear-induced cone loss is introduced in the paper. Specially designed based on mechanical principle of self-locking due to friction, a smart unit, set in the shaft of bearing, was invented to monitor radial wear and stop the running of bearing when the wear reaches the predetermined allowance. The unit is composed of a roller which is installed in a recess serving both as a monitor and a stimulator, and a curved wedge fixed in a wedge-shaped groove to lock up the bearing timely. In this paper, the basic operating mechanism of such a technique is stated;the analytical relationship between the critical wear of bearing and its structural parameter is set up;and the structural design criteria are analyzed and discussed.A series of tests were made to verify the mechanical features and the reliability of the new art,including the static simulated experiments and the rock drilling tests with roller cone bits. The effectiveness and reliability of the system are proved adequately by the trial results.