Patent Number: 
Section: claims

1. An articulated arm ( 11 ) to be put through an opening ( 4 ) of a slab ( 5 ) acting as cover for a tank ( 2 ), comprising an upper section ( 12 ) and a lower section ( 13 ) linked together by an articulation ( 14 ), a bearing placed around the opening and comprising a fixed ring ( 19 ), integral with the slab, and a turning ring ( 21 ), integral with the upper section ( 12 ), means ( 26 ,  27 ,  28 ) of control of the rotation of the turning ring, a tool ( 1 ) suspended from the lower section by a cable ( 6 ) of variable length, which extends above the slab and the arm and over a suspension pulley ( 15 ) to a free end of the lower section ( 13 ), a return pulley ( 16 ) set at the articulation of the sections, the cable passes under the return pulley ( 16 ) wherein the lower section is formed of two articulated parts ( 41 ,  42 ) and there are means of control ( 29  to  32 ) of an angle formed by the sections, the lower section is pivotable in vertical planes either in a back direction, or in a front direction in which the suspension pulley intercepts and catches the cable, and the lower section comprising girders ( 17 ) leaving a cross-section for passage of the tool when the lower section is pivoted in the back direction. 2. An articulated arm according to  claim 1 , characterized in that the parts of the lower section are articulated by an axle ( 43 ) situated on the front edges ( 44 ) in a pivoting direction of the lower section ( 13 ) relative to the upper section, and the parts of the lower section comprise locking means on their rear edges. claim 1 3. An articulated arm according to  claim 1 , characterized in that the means of control for rotating the turning ring comprise a gear with drive pinion ( 26 ) and toothed crown ( 28 ), the pinion and the crown being integral with one, respectively, of the rings. claim 1 4. An articulated arm according to  claim 1 , characterized in that the upper section ( 12 ) comprises a support structure ( 22 ) which can be screwed to the turning ring. claim 1 5. An articulated arm according to  claim 1 , characterized in that it comprises a plug ( 33 ), mounted on the turning ring and closing the opening, provided with a detachable part ( 34 ) for passage of the upper section. claim 1 6. An articulated arm according to  claim 1 , characterized in that it comprises a sealing joint composed of a continuous skirt ( 35 ) under the fixed ring ( 19 ) with its lower edge dipping into liquid filling a groove ( 36 ) surrounding the opening. claim 1 7. An articulated arm ( 11 ) to be put through an opening ( 4 ) of a slab ( 5 ) acting as cover for a tank ( 2 ), comprising an upper section ( 12 ) and a lower section ( 13 ) linked together by an articulation ( 14 ), a bearing placed around the opening and comprising a fixed ring ( 19 ), integral with the slab, and a turning ring ( 21 ), integral with the upper section ( 12 ), means ( 26 ,  27 ,  28 ) of control of the rotation of the turning ring, a tool ( 1 ) suspended from the lower section by a cable ( 6 ) of variable length, which extends above the slab and the arm and over a suspension pulley ( 15 ) to a free end of the lower section ( 13 ), a return pulley ( 16 ) set at the articulation of the sections, the cable passes under the return pulley ( 16 ) wherein there are means of control ( 29  to  32 ) of an angle formed by the sections, the lower section is pivotable in vertical planes either in a back direction, either in a front direction in which the suspension pulley intercepts and catches the cable, and the lower section comprising girders ( 17 ) leaving a cross-section for passage of the tool when the lower section is pivoted in the back direction. 8. An articulated arm according to  claim 7 , characterized in that the means of control for rotating the turning ring comprise a gear with drive pinion ( 26 ) and toothed crown ( 28 ), the pinion and the crown being integral with one, respectively, of the rings. claim 7 9. An articulated arm according to  claim 7 , characterized in that the upper section ( 12 ) comprises a support structure ( 22 ) which can be screwed to the turning ring. claim 7 10. An articulated arm according to  claim 7 , characterized in that it comprises a plug ( 33 ), mounted on the turning ring and closing the opening, provided with a detachable part ( 34 ) for passage of the upper section. claim 7 11. An articulated arm according to  claim 7 , characterized in that it comprises a sealing joint composed of a continuous skirt ( 35 ) under the fixed ring ( 19 ) with its lower edge dipping into liquid filling a groove ( 36 ) surrounding the opening. claim 7