Patent GB-1199081-A (GB)
Title: Centrifuge Rotor Stabiliser
IPC: B04B9/12
Filed: 1968-05-10
Abstract: 1,199,081. Centrifugal separators. BECKMAN INSTRUMENTS Inc. 10 May, 1968 [8 June, 1967], No. 22312/68. Heading B2P. In a stabilizing device 20 for a centrifuge rotor 10, a stabilizing member 64 rotatably mounted in a movable bearing assembly 116, 124, 142 is moved, by means of an electromagnet 94, 82 acting on a movable magnetisable armature 104 connected to the bearing assembly, into a rotor-engaging position in response to rotation of the rotor below a predetermined speed at which wobbling of the rotor may occur so as to restrain the rotor to rotate about its true axis of rotation. The stabilizing device 20 comprises a support plate 28 of generally triangular shape, Fig. 1 (not shown), extending across a chamber 16 defined by a steel housing 18 and carrying fixed pins, such as 32, and a spring- biased pin 40 which are made to selectively engage recesses, such as 36, 44, in brackets, such as 24, 26, secured to the housing 18 so as to position the device 20 in the chamber 16 at a selected level depending on the height of the rotor 10. The chamber temperature may be controlled by evaporator cooling coils. A bracket 66 extending across an opening 60 in the plate 28 supports a stationary housing 70 within which is mounted a magnetisable circular plate 80 having a annular lip 82 constituting a pole piece of the electromagnet which includes a coil 94 connected by leads 96 to an electric circuit for energisation of the electromagnet. The stabilizing member 64 is carried by the inner race of a ball bearing 142 the outer race of which is carried by an interior housing 124 made of self-lubricating plastics material, e.g. an acetal resin, and capable of moving laterally within an exterior housing 116 in frictional engagement therewith. The housing 116 has an upright cylindrical portion 118 press-fitted in a tube 114. The latter is press-fitted in the armature 104 and is slidable in a sleeve 88 press-fitted in the pole piece 82. The armature 104 is under cut at 106, Fig. 3a, to define an annular portion 108 having a bevelled lower surface which defines an air gap with a correspondingly tapered surface on the pole piece 82 so that the crosssectional area defined by the lines of magnetic flux remains substantially constant throughout the entire range of the armature. Downward movement of the armature is limited by an annular flat surface at the lower edge of the armature contacting a stop formed by the upper edge of the sleeve 88. Alternatively, the pole piece, instead of the armature, may be undercut or, again, the tapered surfaces may slope outwardly instead of inwardly. The movable portion, i.e. 64, 142, 124, 116, 114, 104, of the stabilizing device is biased to the retracted or rotor-released position by a helical spring 152 compressed between the armature 104 and the pole piece 82. The armature is also made of self-lubricating plastics material and may have a tapered or rounded lower end to facilitate its engagement with a sleeve 14 on the rotor. The means serving to energise the electromagnet below a predetermined speed of the rotor comprise a transducer 160 which senses the rotor speed and feeds a signal to a speed control circuit 162 having an output coupled, via a connection 64 and contacts in the recesses 44 and on the head 42 of the pin 40, to the leads 96. A diode 168 may be included in the circuit to rectify the current if the output from the circuit 162 is a.c. Reference has been directed by the Comptroller to Specification 1,055,768.