Apparatus with linear movement

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:
• (i) a set of identical pawls each pivotally connected to a first support for pivotal movement about an upper horizontal axis into and out of engagement with said grooves,
• (ii) an actuation member axially movable between a first position and a second position with respect to said support, and
• (iii) link means pivotally connected to said pawls about a lower horizontal axis located at a level lower than said upper axis and pivotally connected to said actuation member, said link means being located and dimensioned for causing pivotal movement of said pawls into engagement with said grooves responsive to movement of said actuation member into its first position and out of engagement with said grooves upon movement of said actuation member into said second position.
• (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.