Pumping stage for turbomolecular pumps

Abstract: The present invention refers to a pumping stage for turbomolecular pumps comprising a rotor disk (3), integral with a rotating shaft (4) operated by a motor, and a stator disk (1), integral with the pump body (2), where the stator disk (1) is a disk whose surface is substantially smooth that can assume, during the emptying cycle, a bladed configuration, by lifting radial sections (5) of the disk surface itself. Lifting of radial sections (5) is performed by at least one actuator device (11) controlled, through an electronic control device (12), by a pressure sensor (13) of the gas present inside the pump body (2).

Description: The present invention deals with a rotor-stator stage for turbomolecular pumps of the type in which a series of pumping stages is housed inside a cylindrical body. The pumping stages for turbomolecular pumps are traditionally composed of couples of disks, one of which, the stator disk, is integral with the pump body, while the other one, the rotor disk, is integral with a shaft, that is centrally placed with respect to the pump body and the stator disk and rotated by a motor. Such disks are both commonly equipped with blades, whose number is usually included between 2⊘ and 6⊘, oriented with opposite leads with respect to the rotation plan, in order to perform pumping of gas molecules, with the rotor disk, and changing of speed distribution of gas molecules, with the stator disk. In particular, the number of disk blades, and consequently their pitch, generates the capability of compressing gases at a certain speed. Function of the stator disk is mainly that of changing the speed distribution for gas molecules after they have been pumped by the rotor disk, to be intercepted and pumped by the rotor disk in the following pumping stage. If the pumping stage lacked a stator disk, the gas molecules could not be pumped by the rotor disk in the following stage; in fact, they leave the rotor disk with a speed distribution whose maximum is next to the opening angle of the rotor that pumped them, and therefore only a negligible part of them could be intercepted by the following rotor disk. Since these pumping stages are configured to obtain a high vacuum degree, that is very low pressures, the rotor-stator stage efficiency is high only next to low pressures inside the body, that is in extreme rarefaction situations where friction between pumping stage disks and present gas is negligible, while efficiency remains low at the beginning of the emptying cycle, during which the pump works with viscous gases and the process is governed either by a pre-vacuum pump or by possible stages with adequate geometries, integral with the turbomolecular pump shaft. In the first operating stage of the pump, that is when gas pressures in the body are next to the atmospheric one (about 1⊘⊘⊘ mbar), the presence of a traditional bladed stator disk is therefore disadvantageous, since its deflection function is negligible, while power absorption by friction with present gas is very high. Experimetally, it has been verified that a turbomolecular pump, realized with its pumping stages without a stator disk, absorbs, in a rotation steady state, about 17 Watts at 9⊘ Hz and about 5⊘ Watts at 16⊘ Hz, while a pump equipped with stages with traditional bladed stator disks absorbs about 19⊘ Watts at 8⊘ Hz. JP-A 63 26619⊘ describes a turbo vacuum pump comprising a stator made of shape memory alloy which allows the angle of the blades to be changed during the working cycle according to the current supplied to heating means. Purpose of the present invention is providing a pumping stage for turbomolecular pumps configured in such a way as to save the absorbed power during the initial stage of the emptying cycle without losses in the emptying capacity of the pump itself. These and other purposes are reached by the pumping stage for turbomolecular pumps as defined in claim 1. Further properties and advantages of the invention will better appear from the following description with reference to the enclosed drawing tables in which: Fig. 1 is a global view of the rotor-stator stage housed into the cylindric body, where the stator disk is a smooth disk; Fig. 2 is a view of a plurality of rotor-stator stages housed into the cylindric body, where the stator disks are represented in their configuration with a bladed surface; Fig. 3 is a top view of a section of the stator disk in a bladed configuration; Fig. 4 is a top view of a section of the stator disk in a smooth configuration; Fig. 5 is a partial view of a rotor-stator stage and stator disk of the following stage with the lifting mechanism for radial sections; and Fig. 6 is a partial view of a stator disk with hinged blades according to a modified embodiment. With reference to the enclosed figures, a preferred, but not limiting, embodiment of the invention will now be described. The pumping stage for turbomolecular pumps is composed of a stator disk 1, housed inside a turbomolecular pump body 2 and integral with it, and of a rotor disk 3, integral with the central shaft 4 rotated by a motor (not shown). On the upper surface of the stator disk 1, some blades 5 are present and fixed, through hinges 6, to the part of the stator disk 1 that is integral with the pump body 2. These blades 5 are furthermore equipped with control tie rods 7, operated by a pantograph mechanism 8 that transforms the vertical movement of a rod 9 into an horizontal movement. A hole 1⊘, drilled into the area of the stator disk 1 integral with the turbomolecular pump body 2, enables rod 9 to pass through the plurality of pumping stages included in the turbomolecular pump body 2. The control tie rod 9 is instantaneously operated by an actuator device 11 controlled, through an electronic control device 12, by a pressure sensor 13 inside the turbomolecular pump body 2, for example when a 1 mbar pressure is reached. In a modified embodiment of the invention, blades 5' are rotatingly fixed through eyelets 6' to the internal edge of the stator disk 1' part that is housed inside the turbomolecular pump body. In the configuration according to the invention with smooth stator disk, the pump absorbs about 2⊘ Watts at 8⊘ Hz and about 154 Watts at 16⊘ Hz. Moreover, in this latter configuration, the effect of the smooth stator disk being present is relevant as regards molecule deflection, distributing their speed again, even when the disk is kept in this configuration during the whole emptying cycle.

Claims: Pumping stage for turbomolecular pumps comprising a rotor disk (3) and stator disk means (1) integral with the pump body (2) and centrally drilled, characterized in that the stator disk means (1) includes liftable radial sections (5) whose lifting is controlled by at least one operating mechanism (8), said lifting causing the substantially smooth surface of the stator disk means (1) to assume, during the emptying cycle, a bladed configuration. Pumping stage for turbomolecular pumps comprising a rotor disk (3) and a stator disk (1), characterized in that the stator disk (1) is a circular crown, whose surface is substantially smooth, integrally engaging the internal surface of the pump body (2). Pumping stage for turbomolecular pumps according to claim 1, characterized in that said liftable radial blades (5) are hinged in one edge of the stator disk means that is integrally engaged with the internal surface of the pump body (2). Pumping stage for turbomolecular pumps according to claim 1, characterized in that said liftable radial blades (5) are rotatingly pivoted in the internal edge of the stator disk means that is integrally engaged with the internal surface of the pump body (2). Pumping stage for turbomolecular pumps according to claim 3 or 4, characterized in that the radial blades (5) are joined by connection means (7) rotatingly pivoted on the blade (5) edge, said connection means (7) being suitable to keep the blades (5) in the same opening or closing position. Pumping stage for turbomolecular pumps according to claim 5, characterized in that the rotation of the radial blades (5) is performed through a device including at least one pantograph mechanism (8), operated by a rod (1⊘) vertically sliding with respect to the rotation plan of the rotor disk (3), controlled by an actuator device (11). Pumping stage for turbomolecular pumps according to claim 1 or 2, characterized in that the stator disk means (1) is shaped, in the initial configuration of the emptying cycle, as a plane disk. Pumping stage for turbomolecular pumps according to claim 1 or 2, characterized in that the stator disk means (1) is shaped, in the initial configuration of the emptying cycle, as a frustum of cone. Turbomolecular pump including a pumping stage according to claim 6, characterized in that it further comprises an electromechanical device (11), and a pressure sensor (13) inside the pump body for producing a signal which, meant by an electronic control device (12), activates said electromechanical device (11).

Inventors: LEVI GIAMPAOLO, LEVI, GIAMPAOLO
Applicants: VARIAN SPA, VARIAN S.P.A.
Application year: 1992
Main classification: F04D19
IPC codes: F04D19