TECHNICAL FIELD 0001 The present invention concerns a rotor of the type intended to be driven in rotation about a central axis of rotation and wherein a number n of seats for receiving a product to be centrifuged are provided, the seats being arranged eccentrically relative to the axis of rotation.

BACKGROUND OF THE INVENTION 0002 The invention applies, for example, to the centrifuging of biological products. 0003 For the centrifuging of such products, rotors of frustoconical shape are generally used in which the seats have been provided in the form of recesses. These seats are elongate in shape and, for each rotor, are regularly distributed about its axis of rotation. The seats are intended to receive, for example, tubes containing the products to be centrifuged and closed by means of stoppers. 0004 A centrifuge using such a rotor generally comprises a trough, equipped with cooling means and in which the rotor is mounted on a rotational drive head. 0005 In ultra-centrifuges, that is to say, centrifuges driving the rotors at speeds of the order of 20,000 r.p.m., the occurrence of excessive noise nuisance such as whistling has been observed. 0006 It is an aim of the invention to solve this problem by limiting the excessive noise nuisance caused by the driving in rotation of rotors of the aforesaid type.

SUMMARY OF THE INVENTION 0007 To this end, the subject of the invention is a rotor of the aforesaid type, wherein the geometric image of at least a first seat, through a geometric rotation about the axis of rotation in a first direction of rotation and an angle of 360/n, is different from a second seat which directly follows the first seat in the first direction of rotation. 0008 According to particular embodiments, the rotor may comprise one or more of the following characteristics, taken singly or in all the combinations technically possible: 0009 the seats are invariant through a geometric rotation about the axis of rotation and an angle strictly greater than 360/n, 0010 n is an even number greater than or equal to 4 and the seats are symmetrical in pairs relative to the axis of rotation, 0011 the seats are of a substantially analogous shape, elongate in a respective longitudinal direction and the second seat is substantially the image, through a geometric transformation, of the geometric image of the first seat, 0012 the geometric transformation comprises a geometric rotation by a non-zero angle in a plane orthogonal to the axis of rotation, 0013 the geometric transformation comprises a geometric rotation by a non-zero angle in a plane containing the axis of rotation and the longitudinal direction of the geometric image of the first seat, 0014 the geometric transformation comprises a geometric translation by a non-zero distance in a plane orthogonal to the axis of rotation, 0015 the geometric transformation comprises a geometric translation by a non-zero distance in a plane containing the axis of rotation and the longitudinal direction of the geometric image of the first seat. 0016 A further subject of the invention is a centrifuge comprising a trough, a rotor intended to be disposed in the trough, and means for driving the rotor in rotation, characterised in that the rotor is a rotor as defined above.

BRIEF DESCRIPTION OF DRAWING 0017 The invention will be more clearly understood on reading the following description, provided solely by way of example and with reference to the appended drawings, in which: 0018 FIG. 1 is a diagrammatic side view of a centrifuge according to the invention, 0019 FIG. 2 is a diagrammatic view from above of the rotor of FIG. 1, 0020 FIGS. 3 and 4 are views analogous to FIG. 2, respectively illustrating a second and a third embodiment of the rotor, 0021 FIG. 5 is a diagrammatic enlarged sectional view of the rotor of FIG. 4, along the broken line V-V, 0022 FIG. 6 is a view analogous to FIG. 5, illustrating a fourth embodiment of the rotor, 0023 FIG. 7 is a view analogous to FIG. 2, illustrating a fifth embodiment of the rotor, and 0024 FIG. 8 is a view analogous to FIG. 5, illustrating a sixth embodiment of the rotor.

DESCRIPTION OF PREFERRED EMBODIMENT 0025 FIGS. 1 and 2 illustrate diagrammatically a centrifuge 1 which comprises a trough 2, a rotor 3 disposed in the trough 2, and means 4 for driving the rotor 3 in rotation about a substantially vertical axis of rotation A. 0026 In a conventional manner, the trough 2 comprises a movable access door 6 and means for cooling its internal atmosphere, which cooling means are not shown in the drawings. 0027 The rotor 3 is a rotor of generally frustoconical shape with a central axis A. It is equipped with a removable closure lid 7. The lid 7 has not been shown in FIG. 2. 0028 The rotor 3 is for example made from metal and four seats, arranged eccentrically relative to the axis A, are provided therein, that is to say, a first pair of seats 81 and 82 and a second pair of seats 101 and 102. It will be noted that the seats 101 and 102 are not shown in FIG. 1. 0029 The seats 81 and 82 of the first pair are symmetrical to each other relative to the axis A. The seats 101 and 102 of the second pair are symmetrical to each other relative to the axis A. 0030 The seats 81, 82, 101 and 102 are of an analogous shape, elongate in a respective longitudinal direction D. 0031 As can be seen in FIG. 1 for the seats 81 and 82, each direction D is inclined relative to the axis of rotation A and intersects it at a geometric point located above the rotor 3 and its lid 7. 0032 The seats 81, 82, 101, and 102 open into the upper surface 12 of the rotor to make it possible, when the lid 7 is withdrawn, to introduce into the seats recipients containing the product(s) to be centrifuged, for example tubes closed by means of stoppers. 0033 In FIG. 1, the distance separating the seats 81, 82, 101 and 102 from the outer lateral surface 14 of the rotor 3 has been exaggerated to facilitate illustration. 0034 As can be seen in FIG. 2, the distribution of the seats 81, 82, 101 and 102 about the axis of rotation A is irregular. 0035 If such distribution were regular, the rotor 3 would be invariant through a geometric rotation of axis A and angle equal to 90 (/2 rad). Thus, the geometric image I (double-dash/dotted line) of the seat 81 through such a rotation in a first direction S1 would coincide with the seat 101, which seat directly follows the seat 81 in that direction S1. 0036 In the rotor of FIGS. 1 and 2, the seat 101 does not coincide with this image I but, in a view from above, is offset angularly from the image I by a non-zero angle centred on the axis A and negative with respect to the direction S1. 0037 In other words, the seat 101 is the image, through a geometric rotation of axis A and angle , of the image I. 0038 Thus, the longitudinal directions D of the seats 101 and of the image I form, in a view from above, an angle centred on the axis A and negative when considering the direction S1. 0039 The angle is, for example, 420 and may more generally be between 2 and 10. 0040 It will be noted that in FIG. 2, the amplitude of the angle has been exaggerated in order to facilitate illustration. 0041 Similarly, the seat 102 is offset angularly, in a view from above, from the image, not shown, of the seat 82 through the aforesaid rotation. 0042 Thus, the seats 81, 82, 101 and 102 are invariant through a geometric rotation of axis A and angle equal to 180 ( rad) but not through a rotation of axis A and angle equal to 90 ( rad) as in the state of the art. 0043 It was found, when driving the rotor 3 in rotation at relatively high speeds, typically above 10,000 r.p.m., that the excessive noise nuisances such as whistling are severely reduced, or even eliminated. 0044 It is considered at present that the reason for this reduction or elimination of excessive noise nuisance may be as follows. When the rotor 3 is driven in rotation, the areas Z (FIG. 1) of the outer lateral surface 14 of the rotor 3 which are located radially opposite the seats 81, 82, 101 and 102 deform, under the action of centrifugal force, radially outwards more severely than the areas of the outer lateral surface 14 that are located between the seats. The reliefs thus created on the surface 14 are, like the seats 81, 82, 101 and 102, invariant through a geometric rotation of axis A and angle equal to 180 ( rad), and not through a geometric rotation of axis A and angle equal to 90 as in the state of the art. Thus, the frequencies and the intensities of the acoustic waves produced during the driving in rotation of the rotor are modified and the excessive noise nuisances are reduced, or even eliminated. 0045 Moreover, the imbalances caused by the irregularity of arrangement of the seats are relatively small and acceptable owing to the fact that a is relatively small. 0046 According to a variant of the embodiment of FIGS. 1 and 2, the angle may be positive with respect to the direction S1. 0047 More generally, other arrangements of the seats 81, 82, 101 and 102 may be envisaged. 0048 Thus, in the embodiment of FIG. 3, the seat 101, in a view from above, is laterally translated, relative to the image I of the seat 81, in the opposite direction from the direction S1, by a non-zero distance d. Thus the longitudinal directions D of the seat 101 and of the image I of the seat 81are substantially parallel and spaced laterally from one another. 0049 The distance d is for example 2 mm and may more generally be between 1 and 5 mm. 0050 It will be noted that in FIG. 3 the distance d has been exaggerated. 0051 Since this distance is relatively short, the difference between the centrifuging forces to which the products received in the seats 81, 82, 101 and 102 will be subjected will remain sufficiently small and acceptable for the homogeneity of the centrifuging treatment. Similarly, the imbalances caused by the irregularity of arrangement remain acceptable. 0052 According to a variant not shown, the seat 101, in a view from above, may be offset laterally from the image I of the seat 81in the direction S1. 0053 More generally, the seat 101, in a view from above, may be the issue of a geometric translation of the image I, the direction of this translation being not necessarily orthogonal to the direction D of the image I. 0054 Still more generally, the seat 101, may be deduced from the image I of the seat 8through a geometric transformation in a radial plane containing the axis of rotation A and the longitudinal direction D of the image I. 0055 Thus, FIGS. 4 and 5 illustrate a third embodiment wherein the longitudinal direction D of the seat 101 is offset angularly by a non-zero angle relative to the longitudinal direction D of the image I in the aforesaid plane P (FIG. 4). The plane P also contains the direction D of the seat 101 and corresponds to the right-hand half-plane of FIG. 5. Thus, the seat 101 is the image, through a geometric rotation of angle in the plane P, of the image I. 0056 It will be noted that the angle may be positive or negative. The angle has for example a value of 4 and may more generally be between 2 and 10. 0057 FIG. 6 illustrates another embodiment wherein the seat 101 is obtained from the image I through geometric translation by a substantially constant non-zero distance in the radial plane P. Thus the directions D of the seat 101 and of the image I are substantially parallel and spaced from one another. The aforesaid translation may be such that the seat 101 is closer to or further from the outer lateral surface 14 than the image I. 0058 It will be noted that in FIGS. 5 and 6 the angle and the distance have been exaggerated. 0059 It will also be noted that the angle or the distance are small enough on the one hand for the homogeneity of the centrifuging treatment undergone by products received in the seats 81, 82, 101 and 102 to be satisfactory and on the other hand for the imbalances to be reduced. 0060 More generally, the above principles may be applied to rotors comprising any number of seats. 0061 They may also be combined with one another for the same seat. 0062 Thus, FIG. 7 illustrates yet another embodiment wherein the seat 101 is the image, through a geometric transformation, of the image I, the geometric transformation comprising a geometric rotation and a geometric translation in the plane of FIG. 7 which is orthogonal to the axis of rotation A. 0063 More precisely, the rotation is a rotation of axis A and angle . 0064 The translation is a translation in the plane of FIG. 7 by a non-zero distance d in a direction which is not orthogonal to the direction D of the image I. 0065 The combination of a rotation and a translation within the geometric transformation allows the seat 101 to remain close enough to the image I to limit the differences between the centrifuging force undergone by a product contained in the seat 101 and the centrifuging force of a product received in the seat 81. 0066 Thus, the homogeneity of the centrifuging treatment undergone by products received in the seats 81, 82, 101 and 102 is increased. Moreover, this combination makes it possible to reduce the imbalances and also the difference in appearance between a rotor incorporating the principles of the invention and a conventional rotor. 0067 Similarly, FIG. 8 illustrates another embodiment wherein the seat 101 is obtained from the image I by a geometric transformation comprising a geometric rotation and a geometric translation in the radial plane P which comprises the axis of rotation A and the longitudinal direction D of the image I. 0068 More precisely, the rotation is a rotation of non-zero angle and the translation is a translation by a non-zero distance in a direction orthogonal to the axis of rotation A. 0069 Here again, the combination of a translation and a rotation makes it possible to increase the homogeneity of the centrifuging treatment undergone by products received in the seats 81, 82, 101 and 102, to limit the imbalances and to reduce the aesthetic problems. 0070 More generally, the geometric transformation between the image I and the seat 101 may comprise a translation and/or a rotation in a plane orthogonal to the axis of rotation A, and a translation and/or a rotation in a radial plane containing the axis A. 0071 Generally, also, the translations and rotations described previously may be applied, for example each separately to a respective pair of seats when the number of seats is even and strictly greater than 4. 0072 Preferably, the seats are symmetrical in pairs relative to the axis A. Thus, when the rotor 3 is equipped with an even number n of seats, the rotor 3 will be invariant through a geometric rotation of axis A and angle 180, thereby making it possible to limit the imbalances. More generally, an invariance through a geometric rotation of axis A and angle strictly greater than 360/n will make it possible to limit the imbalances. 0073 In order to avoid the occurrence of excessive noise nuisance, there will still be at least a first seat, the geometric image of which, through a geometric rotation about the axis of rotation A and an angle 360 /n in one direction of rotation, is different from a second seat of the rotor, the second seat directly following the first seat in the selected direction of rotation.