Patent Number: 
Section: claims

1. Method for determining friction forces occurring on a moving object in a guide, using a speed sensor, comprising the following steps of a calculation process: V 1 =f 1 ( t ),  V 2 =f 2 ( t );  V 4 =g 4 ( d );  V 5 =V 4 xe2x88x92V 3 =g 5 ( d );  F additional =M (xcex35xe2x88x92xcex34)= f ( d ), wherein  1) measuring and recording changes in the velocity V 1  of the object initially before the occurrence of friction:  xe2x80x83wherein f 1  is a function of time (t);  2) calculating distance of travel d 1  with integrated change in velocity of the object before the onset of friction, to obtain the change in velocity, V 1 =g 1 (d) in relation to distance of travel:  xe2x80x83wheein g 1  is a second function of distance (d), and (u) is a time value;  3) measuring and recording the change in velocity V 2  of the object after the onset of friction:  4) calculating distance of travel d 2  with integrated change in velocity of the object, after onset of friction, to obtain the change in velocity V 2 =g 2 (d) relation to distance of travel;  5) calculating the difference of velocity V 3  between the two velocities V 1  and V 2  in relation to travel before and after onset of additional friction, F additional ;  6) calculating the change in velocity V 4  of the object in relation to distance of travel, before the onset of friction, using a predetermined calculation program, wherein  7) subtracting the difference of velocity V 3  from this change in velocity V 4 , the difference V 3  in measured velocity changes:  xe2x80x83to obtain the difference of velocity V 5 ; and  8) deducing, by differentiation between V 4  and V 5  and multiplication by the weight M, the additional friction forces acting on the movement of the object;  xe2x80x83and wherein xcex3 is the acceleration of the object, and subscripts 4, 5 represent successive values in the said calculation process. 2. Method according to  claim 1 , applied to a pressurized water nuclear reactor, the moving object being a mobile assembly formed of a control rod and control cluster, the guide being the lowering channel, the speed sensor being a rod position indicator (RPI) used to measure velocity. claim 1