a measurement sensor according to the invention and such as illustrated in fig1 and 2 is formed of several components assembled together , that is : two metallic support plates 1 and 2 , made of steel or aluminium , placed facing each other , and measurement devices formed of six piezoelectric cylinders p1 to p6 placed between the two plates 1 and 2 . each plate 1 and 2 is for example of a circular shape and has two roughly planar main and opposite faces 1a , 1b for plate 1 and 2a , 2b for plate 2 . the two plates 1 and 2 are situated facing each other with their main faces 1a and 2a lying opposite one another and separated by a distance d . the six piezoelectric cylinders p1 to p6 are placed between the two faces 1a and 2a of the two plates 1 and 2 , and their axes are directed along six directions d1 to d6 to form a triaxial structure of ternary symmetry which is indeformable , for example . as can be seen from fig2 the six piezoelectric cylinders p1 to p6 are evenly spaced towards the periphery of the two plates 1 and 2 . with reference to fig3 a general principle has been shown in a perspective view enabling directions d1 to d6 of the axes of the six piezoelectric cylinders p1 to p6 to be defined . more precisely , the two parallel cutting planes pc1 and pc2 ( fig1 ) which pass respectively through the centres of the two end faces of the piezoelectric cylinders p1 to p6 have been considered . these centres a1 to a6 for cutting plane pc1 and b1 to b6 for cutting plane pc2 are respectively on two circles which do not necessarily have the same diametre , these two circles are represented by two ellipses e1 in plane x1 - o1 - y1 and e2 in plane x2 - o2 - y2 on the perspective in fig3 . in practical terms , the six points a1 to a6 are spaced around a circle along a ternary symmetry , that is three pairs of points a1 - a2 , a3 - a4 and a5 - a6 are defined spaced at 120 ° from one another . in a similar manner , the six points b1 to b6 are also spaced along a ternary symmetry , and the six directions d1 to d6 are respectively defined by the six pairs of points a1 - b1 to a6 - b6 . the choice of the position of points a1 to a6 and b1 to b6 is carried out according to the conditions of use of the sensor and is therefore not necessarily predetermined . the two end faces of each cylinder p1 to p6 respectively come into contact with the faces 1a and 2a of plates 1 and 2 . to be able to align the axes of these cylinders p1 to p6 along directions d1 to d6 , six suitable cavities c1 to c6 are arranged on each of faces 1a and 2a of plates 1 and 2 . considering , for example , piezoelectric cylinder p6 , cavity c6 of plate 1 in which one end of cylinder p6 is to engage has a planar surface s1 which is perpendicular to direction d6 along which cylinder p6 is to be aligned , and cavity c6 of plate 2 in which the other end of cylinder p6 is to engage has a planar bearing surface s2 which is also perpendicular to direction d6 along which cylinder p6 is to be aligned , these two surfaces s1 and s2 being parallel to one another . the cavities for the other cylinders p1 to p5 have the same characteristics . fastening means are provided to assemble the piezoelectric cylinders p1 to p6 to the two plates 1 and 2 . in practical terms , a fastening means is provided per cylinder , a means which is formed by a screw 10 which axially pierces the cylinder . to this end , the plate incorporates six passages 12 which are drilled between two main faces 1a and 1b of plate 1 along parallel axes to the six directions d1 to d6 . each passage 12 , on the main face 1a of the plate 1 , opens out at the surface s1 of an associated cavity and perpendicularly to surface s1 . in an analogous manner , plate 2 incorporates six passages 14 which are drilled between the two main faces 2a and 2b of plate 2 along axes which are parallel to directions d1 to d6 . each passage 14 , on the main face 2a of plate 2 , opens out at surface s2 of an associated cavity and perpendicularly to this surface s2 . on the main face 1b of plate 1 , a countersink 16 is for example machined around each passage 12 to be able to house the head 10a of a screw 10 , and passage 14 of plate 2 which is axially aligned with passage 14 is tapped to work positively in conjunction with the threaded part 10b of the screw 10 . an insulating washer 17 is advantageously brought around each end face of the piezoelectric cylinders p1 to p6 . the electrical outputs ( not shown ) of the sensor are located at the piezoelectric cylinders and are connected to processing circuits to carry out measurements of the strains received by each piezoelectric cylinder . the central part of each plate 1 and 2 can be drilled with a central clearance opening 18 . this opening 18 , machined by removing material , enables the sensor to be made lighter and can , for example , be used for the passage of cables . lastly , a cap can be put onto the sensor which nevertheless leaves the two outer end faces 1b and 2b of the two plates 1 and 2 free to enable them to be fastened between two mechanical parts . to make the sensor easier to assemble , notably the assembly of the piezoelectric cylinders p1 to p6 , the invention also proposes a manufacturing process which consists , from the basis of a cylindrical metal part 20 made of , for example steel or aluminium , in carrying out the operations described hereafter with reference to fig4 a - 4e . a first stage of the process , illustrated in fig4 a , consists in machining , on the outer wall of the cylindrical part 20 , six cavities c1 to c6 evenly spaced around the cylindrical part 20 , each cavity marking out two plane bearing surfaces s1 and s2 , parallel to each other and perpendicular to the direction along which a piezoelectric cylinder associated with each cavity is to be aligned . the distance separating the two surfaces s1 and s2 corresponds to the thickness of the piezoelectric cylinders which will be assembled afterwards . in a second stage illustrated in fig4 b , six passages are drilled in the cylindrical part 20 respectively associated with the six cavities c1 to c6 , each passage passing through the associated cavity and being drilled along an axis which is perpendicular to the two surfaces s1 and s2 of said cavity , such as to mark out the two axially aligned passages 12 and 14 illustrated in fig1 . thereafter , countersinks 16 are machined around the apertures of these passages 12 which open out to the outside of the cylindrical part 20 . in a third stage illustrated in fig4 c , additional machining is carried out , notably the drilling of the central opening 18 and the tapping of the passages 14 . in a fourth stage illustrated in fig4 d , the cylindrical part 20 is cut so as to obtain two plates 10 and 12 , the cutting plane being perpendicular to the axis of the cylindrical part 20 and passing through cavities c1 - c6 , each cavity thereby being sectioned into two parts . in a final stage illustrated in fig4 e , the piezoelectric cylinders p1 and p6 are assembled in cavities c1 to c6 and are fastened in place by means of screws 10 . according to one functioning mode of the above - described sensor , the load transmitted , for example , by plate 1 can be shown by a wrench t ( t ). this wrench notably creates tensile / compression stress on the piezoelectric cylinders p1 - p6 , and these stresses generate electrical charges which , after integration , become electrical voltages . if we represent by v ( t ) the vector formed by the six voltages from piezoelectric cylinders p1 - p6 , any wrench t generates , in the pass - band of the sensor , a linear response of the type : knowing v ( t ) which is the vector of the measurements supplied by the sensor , the wrench is calculated as follows : ## equ1 ## where m ! must be known by being calculated or identified . one way to know m ! is to proceed by an identification means on a test bench . in this technique , the sensor is subjected to a series of known wrenches t ( t ). the method of the generalised least error squares is applied to determine the matrix m !. as the number of tests can be very much above the order of the matrix being sought after , the pseudo - inverse method is used : the first three components of the wrench tx ( t ), ty ( t ), tz ( t ) are the three force components and mx ( t ), my ( t ) and mz ( t ) are the three moment components , given that the reference mark is the one in which the matrix m ! is expressed .