Image Number 5 for United States Patent #6896306.
Actuator mechanism for a two-bucket grab device and having two grab arms arranged to move as pincers with respect to one another, has two hydraulic pivot motors with journals of the respective pivot shafts projecting from the motor housing and supporting the grab arms. Each of the pivot motors has a cylindrical tubular piece provided with an internal thread designed to engage an external thread on the respective pivot shaft. The tubular piece is a ring piston axially-displaceably, but non-rotatably held in a cylinder space formed in one of the respective bucket housings. Pitch of the threads is sufficiently large for the ring piston to transmit required torque to the respective pivot shaft by axial displacement of the ring piston. The displacement path of the ring piston between two annular cylinder chambers corresponding to high and low pressure chambers which can be loaded with hydraulic oil, corresponds to the desired pivot angle of the two arms of the grab bucket.