Patent Number: 046408118
Section: claims

1. A linear motion device comprising: (a) an axially movable vertical drive shaft provided with a plurality of circumferential grooves equally spaced in the vertical direction, said drive shaft being arranged for connection with a nuclear reactor control rod at the lower end thereof, and  (b) two gripping devices axially spaced relative to said drive shaft, each of said devices having:  (c) wherein each of said pawls comprises an upper tooth and a lower tooth separated by a vertical distance equal to the distance between two successive grooves of said drive shaft and wherein said lower axis is located at a vertical distance below the tip of said upper tooth which is between one sixth and one fourth of the vertical distance separating the tips of said upper tooth and said lower tooth on one of said pawls. 2. Linear motion device according to claim 1 wherein said lower axis of said pawl is centered at a location situated below said upper tooth at a vertical distance of about 1/5 of the vertical distance separating the two tips of said engaging teeth on said pawl.