Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C29/00—Component parts, details or accessories of pumps or pumping installations, not provided for in groups F04C18/00 - F04C28/00
  • F04C29/0021—Systems for the equilibration of forces acting on the pump
  • F04C29/0035—Equalization of pressure pulses
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C18/00—Rotary-piston pumps specially adapted for elastic fluids
  • F04C18/08—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
  • F04C18/12—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type
  • F04C18/123—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type with radially or approximately radially from the rotor body extending tooth-like elements, co-operating with recesses in the other rotor, e.g. one tooth
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C23/00—Combinations of two or more pumps, each being of rotary-piston or oscillating-piston type, specially adapted for elastic fluids; Pumping installations specially adapted for elastic fluids; Multi-stage pumps specially adapted for elastic fluids
  • F04C23/001—Combinations of two or more pumps, each being of rotary-piston or oscillating-piston type, specially adapted for elastic fluids; Pumping installations specially adapted for elastic fluids; Multi-stage pumps specially adapted for elastic fluids of similar working principle

Definitions

• the present invention relates to vacuum pumps, in particular to dry pumps and to the design for the final stage of a multi-stage dry pump.
• Dry pumps are widely used in, for example, the semiconductor manufacturing industry to provide clean, low pressure (often vacuum) environments in a process chamber in which wafers can be manufactured.
• the pump mechanisms of dry pumps come in a variety of forms, one of which generally comprises one or more rotors housed by a stator.
• the rotors are suitably shaped so as to draw gas from the process chamber into the pump inlet, and exhaust the pumped gas from the pump outlet.
• the rotor may comprise a number of rotor elements arranged in series along the axis of rotation of a common rotary shaft.
• each Roots rotor element has two or more substantially similarly shaped and sized lobes, each lobe extending radially from the axis of rotation of the rotary shaft.
• the lobes are arranged in rotational symmetry about the rotational axis of the shaft.
• early stages of the pump i.e. those nearer the pump inlet
• Pairs of rotors may be arranged in close contact with each other but not touching.
• Each rotor element is arranged at an angle to the opposing rotor element to form a stage such that, when the two rotary shafts rotate, the lobes from one rotor element pass through the spaces between the lobes of the other.
• the Northey, or "claw” mechanism Another mechanism is known as the Northey, or "claw" mechanism.
• the lobes described for the Roots stage above are replaced by sickle or claw shapes arranged rotationally symmetrically about the rotational axis of the rotary shaft.
• a third mechanism operating on similar principles to the Roots and claw mechanism is sometimes referred to as a ball and socket arrangement.
• the rotors are aligned in pairs in parallel.
• the first rotor comprises one or more rotor elements, each having a cross section which is generally circular but has a number of sockets cut into the circumference of the circle and equally spaced radially about the rotational axis of the shaft.
• the second rotor comprises one or more corresponding rotor elements each of a generally circular cross section and having protrusions extending from their circumference, these protrusions being shaped and located so as to intermesh with the sockets of the immediately adjacent rotor element on the first rotor.
• Each pair of cooperating rotor elements is called a stage.
• Such pulsation can cause various problems, for example, it can be very distracting to persons working in the environment to have to hear such a regular pulse for prolonged periods. There is also a danger that, should the pulses reach the harmonic frequency of components in the containment vessels, these components may be excited and vibrate vigorously, which may result in excessive noise.
• silencers or mufflers it is known to use silencers or mufflers to reduce the noise occurring at the exhaust of a pump. In certain circumstances, the use of silencers is not desirable. Some semiconductor manufacturing processes create dusty or condensable materials which can be hazardous if they collect in significant quantities and are exposed to air (for example during service or maintenance of the pump). If used in such environments, silencers and mufflers can result in an accumulation of such hazardous end products making the servicing or maintenance issues more difficult.
• the present invention seeks to provide a vacuum pump which alleviates some of the previously described problems associated with pulsation at the pump exhaust.
• a vacuum pump comprising a chamber housing first and second intermeshing rotor elements located on respective shafts and adapted for counter-rotation within the chamber, at least one of the rotor elements comprising a plurality of protrusions extending from a centre of rotation, the protrusions being rotationally asymmetrically arranged around the centre of rotation of the rotor element.
• the protrusions may, for example, take the form of lobes of a Roots rotor element, claws of a claw rotor element or the protrusions (or spaces between sockets) of a ball and socket arrangement.
• each protrusion has an apex radially spaced from the centre of rotation.
• the sector angle between each pair of apices as subtended at the centre of rotation is different to the equivalent angle between the adjacent pair of apices.
• the sector angles between the apices may be randomly selected. Desirably each of the sector angles is different to all others, though this is not essential.
• the plurality of protrusions is desirably three or more, more preferably between 3 and 9.
• the plurality may comprise 4, 5, 6 or 7 protrusions.
• the protrusions may be formed integrally with the rotor element or, alternatively, the protruding components may be formed separately and assembled to subsequently form the rotor element.
• the rotationally asymmetrical rotor element is desirably positioned as the last rotor element of the pump, in use, adjacent to the exhaust (or outlet) of a pump.
• the pump may also comprise intermeshing, rotationally symmetrical rotor elements.
• the invention provides a vacuum, or dry, pump including a rotor comprising at least one rotationally asymmetrical Roots rotor element including a plurality of protrusions rotationally asymmetrically arranged around the centre of rotation of the rotor element.
• the present invention also provides a vacuum pump comprising a pump inlet for receiving fluid to be pumped, a pump outlet for exhausting pumped fluid, and a stator housing first and second shafts adapted for counter-rotation within the stator and each having located thereon a plurality of rotor elements such that the rotor elements on the first shaft intermesh with the rotor elements on the second shaft, wherein each of the intermeshing rotor elements proximate the outlet comprises a plurality of protrusions extending from a centre of rotation, the protrusions being rotationally asymmetrically arranged around the centre of rotation of the rotor element.
• Figure 1 shows one embodiment of a multi-stage pump
• Figure 2 shows a cross section of Figure 1 taken along line XX;
• Figure 3 shows a configuration of a single stage of the pump of Figure 1 ;
• Figure 4 shows an alternative embodiment of a single stage of the pump of Figure 1.
• FIG. 1 shows schematically an embodiment of a multi-stage vacuum pump.
• the pump comprises two parallel aligned rotary shafts 2a, 2b each carrying a rotor assembly 1 a, 1 b in the form of a series of rotor elements.
• the shafts 2a, 2b are mounted in bearings 3a, 3b, 3c, 3d.
• the shaft 2b is driven by a drive mechanism 3, a timing gear arrangement (not shown) connecting the two shafts 2a, 2b to ensure that the two shafts counter-rotate in synchronisation.
• the rotor elements 1a, 1 b are located within a housing unit 4, which defines a stator element comprising a series of chambers each housing a respective pair of rotor elements 1a, 1 b.
• each of the rotor elements 1a, 1 b has a Roots-type profile.
• the shafts 2a, 2b are separated by a distance which is less than twice the maximum radius of a rotor so that, as shaft 2b rotates, the rotors intermesh such that the lobes of the rotor elements 1 b pass through the spaces between the lobes of the rotor elements 1a.
• FIG 2 shows the axial gas flow path through the pump illustrated in Figure 1.
• a pump inlet 7 provided in the housing 4 communicates directly with the first stage of the pump, that is, with the chamber housing the pair of intermeshing rotor elements 1a, 1 b located closest to the inlet 4, to convey gas received from, for example, a process chamber to the first stage of the pump.
• Channels 6 are provided between adjacent stages to direct the pumped gas from the outlet of one stage to the inlet of the next.
• a pump outlet 5 is provided in communication with the exhaust stage, that is, with the pair of intermeshing elements located closest to the outlet 5, to allow the pumped gas to be exhausted from the pump.
• FIG 3 illustrates Roots rotor elements for forming the exhaust stage of the pump in Figure 1.
• Each element has a centre of rotation R from which radially extends five lobes.
• Each lobe has an apex A1 , A2, A3, A4, A5 the radii of which are oriented around the centre of rotation of the rotor element.
• the sector angle i.e. the internal angle between the radii of adjacent apices
• the ball and socket stage comprises a first, "ball” rotor element generally designated 21 and a second, “socket” rotor element generally designated 22.
• the ball rotor element comprises a central piece 23 of substantially circular cross section and five protrusions 24a, 24b, 24c, 24d, 24e that are spaced radially at unequal angular separations about the centre of rotation R of the central piece 23.
• protrusions may be manufactured separately and then joined to the central piece during subsequent assembly of the rotor. Alternatively they may be formed as an integral part of the central piece.
• the socket rotor element comprises a single piece 25 which comprises a piece of substantially circular cross section having cut therefrom five sockets 26a, 26b, 26c, 26d, 26e to leave five protrusion 27a, 27b, 27c, 27d, 27e spaced radially at unequal angular separations about the centre of rotation R of the piece 25, so that, during use, the protrusions 24a, 24b, 24c, 24d, 24e intermesh with the sockets 26a, 26b, 26c, 26d, 26e to draw the pumped gas through the pump.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Applications Or Details Of Rotary Compressors (AREA)
• Non-Positive Displacement Air Blowers (AREA)
• Rotary Pumps (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=28052677

Family Applications (1)

Country Status (5)

Cited By (4)

Families Citing this family (2)

Citations (5)

• 2003
  • 2003-08-18 GB GB0319344A patent/GB0319344D0/en not_active Ceased
• 2004
  • 2004-08-02 JP JP2006523664A patent/JP2007502932A/ja not_active Ceased
  • 2004-08-02 EP EP04767951A patent/EP1656504A1/en not_active Withdrawn
  • 2004-08-02 WO PCT/GB2004/003316 patent/WO2005019652A1/en active Application Filing
  • 2004-08-16 TW TW093124573A patent/TW200513594A/zh unknown

Patent Citations (5)

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