WO1988004787A1 - Rotary device - Google Patents
Rotary device Download PDFInfo
- Publication number
- WO1988004787A1 WO1988004787A1 PCT/US1987/003216 US8703216W WO8804787A1 WO 1988004787 A1 WO1988004787 A1 WO 1988004787A1 US 8703216 W US8703216 W US 8703216W WO 8804787 A1 WO8804787 A1 WO 8804787A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- rotor
- rotary device
- fluid
- motor
- radially
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
- G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
- G02B26/10—Scanning systems
- G02B26/12—Scanning systems using multifaceted mirrors
- G02B26/121—Mechanical drive devices for polygonal mirrors
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C17/00—Sliding-contact bearings for exclusively rotary movement
- F16C17/04—Sliding-contact bearings for exclusively rotary movement for axial load only
- F16C17/045—Sliding-contact bearings for exclusively rotary movement for axial load only with grooves in the bearing surface to generate hydrodynamic pressure, e.g. spiral groove thrust bearings
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S310/00—Electrical generator or motor structure
- Y10S310/06—Printed-circuit motors and components
Abstract
A rotary device for use as a precision element such as an optical scanner. The device comprises a rotor (12; 62) which includes a driven element such as a polygon (14; 64) having a plurality of mirror surfaces thereon, means (18; 63) for supporting the rotor (12; 62) for rotational movement, and a drive motor for the rotor. The rotor supporting means (18; 63) includes a thrust bearing (44, 49, 42; 76, 78, 73). In order to provide a rotary device having a low profile and a minimum of parts, a planar motor (16, 30; 74, 68) is used as the drive motor, and the permanent magnet (16; 68) of the motor is incorporated in the rotor (12; 62). The thrust bearing (44, 49, 42; 76, 78, 73) includes means (42; 73) for directing an axial force against a radial surface (44; 76) of the rotor (12; 62) when the motor is actuated.
Description
ROTARY DEVICE The present invention relates to a rotary device, and more particularly, to such a device for supporting and driving a precision element such as an optical scanner.
Certain types of optical scanners include polygon mirrors which are operated at high speeds, for example, in excess of 10,000 rpm. When these scanners are used in applications such as laser printers, the speed of the polygon mirror must be controlled within very narrow limits, and the mirror must be supported for vibration—free movement. In order to provide stable, low—friction supports for the mirrors, various types of bearings have been used, including air bearings.
One example of a bearing arrangement for a mirror scanner is shown in U. S. Patent No. 4,512,626, to Kamiya et al. The Kamiya et al. patent discloses a polygon mirror fixed to a spindle which is rotatably supported in a scanner housing. The spindle is radially supported by two bearings of a dynamic pressure type, and is axially supported by a magnetic thrust bearing. A rotor magnet for the scanner drive motor is carried on the spindle. One of the main problems with the bearing and drive arrangement disclosed in the patent is that it makes the scanner too large and complex for many applications.
It is also known in the art to form herring- bone grooves in the spindle of an optical scanner to serve as an air bearing. However, this type of bearing requires a relatively long spindle which increases the height of the scanner and also introduces problems in maintaining the dynamic balance of the scanner.
It is an object of the present invention to overcome the problems in the prior art described above and to provide a rotary device having an improved support and drive means. In accordance with one aspect of the invention, there is provided a rotary device comprising a rotor which includes a first element of a motor, means for supporting the rotor for rotational movement, the supporting means including a second element of a motor, the device having a thrust bearing characterized in that the motor elements are elements of a planar motor, and the thrust bearing includes a first radially—extending surface on the rotor and a second radially extending surface on the supporting means.
In one embodiment of the present invention, the rotary device is in the form of an optical scanner-which-comprises—a *ρσrygxτriτavi-πg^ a* plurality of mirror surfaces. The polygon is supported on a rotor which is mounted for rotation on a spindle. The rotor is driven by a planar motor, and parts of the motor are incorporated in the rotor. The rotor is supported in an axial direction by an air bearing. The rotary device of the present invention has a low profile which makes it particularly suitable for certain applications, for example, for use as an optical scanner in laser printers. The reduction in the overall height of the device is accomplished through the use of a planar motor and the incorporation of an air thrust bearing which is operable on a radial surface of the rotor. As a result of this arrangement, the device is considerably simplified and is thus relatively inexpensive to manufacture. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:
Fig. 1 is an elevational view, with parts shown in section, of one embodiment of the present invention;
Fig. 2 is a sectional view, taken on line 2-2 of Fig. 1;
Fig. 3 is a top plan view of a second embodiment of the present invention; and
Fig. 4 is an elevational view, with parts shown in section, of the second embodiment of the present invention.
With reference to Fig. 1, there is shown an illustration of a rotary device of the present invention in the form of an optical scanner 10. Scanner 10 comprises a rotor 12 which includes a polygon 14 and a permanent magnet 16. Rotor 12 is supported for rotation on a spindle 18 which is mounted in a support plate 20 fixed to a housing 22 of the scanner 10. - *
Polygon 14 comprises a plurality of scanner surfaces in the form of mirror surfaces 15. When polygon 14 is rotated, an input light beam is directed to the mirror surfaces 15 through a window 17, and an output .light beam from surfaces 15 is scanned across a receiving medium (not shown). Scanner 10 could be used, for example, in a device such as a laser printer (not shown) to scan a modulated light beam across a photosensitive surface.
A generally planar coil.30 is mounted in a lower portion 32 of housing 22, and the coil 30 rests on a flux plate 34. When a current is supplied to coil 30, magnet 16 interacts with a rotary field produced by coil 30 to function as a motor to drive the polygon 14.
The motor formed by magnet 16, coil 30, and flux plate 34 can be of a planar type well known in the art. The motor can be a brushless D.C. motor in which Hall sensors (not shown) are used for
controlling the commutation of current. For such a motor, magnet 16 could be a multipolar permanent magnet, and coil 30 could be in the form of a coreless stator having a plurality of coil elements arranged on opposite sides of a dielectric sheet. Further, coil 30 could be formed by printed circuit techniques. One example of a motor of this type is shown in U.S. Patent No. 4,413,895, granted November 8, 1983. A ball bearing 40, mounted in housing 22, supports rotor 12 when the rotor is at rest. When the rotor 12 is being driven, an air thrust bearing provides axial support for the rotor 12 in a manner to be explained hereinafter. As shown in Fig. 2, grooves 42 are formed in a radially—extending thrust surface 44 of magnet 16, and the grooves 42 extend from the outer periphery of magnet 16 to a land 45 at the center portion of the magnet 16. Grooves 42 are - generally radially extending and are preferably spiral shaped. The grooves 42 enable the magnet 16 to function as one part of a thrust bearing for rotor 12. Coil 30, which has a radially—extending planar bearing surface 49 positioned opposite surface 44, functions as the other part of the thrust bearing. When a current is supplied to coil 30, rotation of magnet 16 causes movement of air between surface 44 and surface 49 in a direction transverse to the grooves 42. Since the resistance to air flow is less along the grooves 42 than it is across the grooves, flow is induced along the grooves 42.
Capillary blockage of the Induced flow causes the pressure in the air gap between surfaces 44 and 49 to rise above ambient pressure. The pressure gradient is in a direction normal to the direction of relative motion between surface 44 and surface 49. It Is the viscous pumping action of the bearing, formed by surfaces 44, 49, and grooves 42, that enables it to
support a dynamic load along the axis of rotation of rotor 12. The axial movement of rotor 12 due to the axial force of the air bearing is relatively small. It has been determined, for example, that maximum stability of the rotor 12 is achieved when, the axial, movement of rotor 12 is about 0.0004 inch. This axial movement of rotor 12 also determines the air gap between magnet 16 and coil 30, and a gap of 0.0004 inch is well within the limits necessary for optimum performance of the motor.
The design of grooves 42 can be either ■•in-pump," in which the flow of air is radially inward, or "out-pump" in which the flow is radially outward. The direction of air flow is determined by the direction of rotation of magnet 16 and by the orientation of the grooves 42, including the location of the grooves relative to the boundaries of the magnet 16. With the grooves 42 arranged as shown in Fig. 2 and with magnet 16 rotating in a counter- clockwise direction, the air flow will be radially inward, as indicated by arrows 51 in Fig. 1. When the air reaches spindle 18, it is exhausted through an annular space 50 which is shown relatively large for purposes of illustration, but is actually the normal clearance between spindle 18 and polygon 14. The air could also be exhausted through axially— extending grooves (not shown) on either spindle 18 or polygon 14. It is also contemplated that, to achieve radial stability under some operating conditions, herringbone grooves (not shown) could be formed on spindle 18. Although the present invention has been described herein as using air as the fluid which exerts an axial force on rotor 12, it will be apparent that other fluids, such as oil, could be used in practicing the invention.
With reference to Figs. 3 and 4, there is shown a second embodiment of the present invention. As shown in Fig. 4, a rotary device in the form of an optical scanner 60 comprises a rotor 62 which is movable on a spindle 63. Rotor 62 includes a polygon 64 which is supported on a sleeve 66. As polygon 64 is rotated, a light beam directed onto the polygon 64 through a window 67 will be scanned across a receiving medium (not shown). Carried on sleeve 66 are a permanent magnet 68 and flux plates 70 and 72. Magnet 68 is adapted to interact with a stationary coil 74 to drive rotor 62 in the manner described above for scanner 10. Sleeve 66 comprises a planar thrust surface 76 having radially—extending grooves 73 formed therein which function in the manner described previously for grooves 42. Air from grooves 73 is exhausted along an annular space 75 between spindle 63-and sleeve όδ.-.-When a current is supplied to coil 74 to drive rotor 62, air drawn in between surface 76 and a planar bearing surface 78 on a housing 80 serves to support rotor 62 in an axial direction. Although no means is shown for supporting rotor 62 at rest, it will understood that a roller bearing (not shown) similar to bearing 40 in scanner 10 could be incorporated in scanner 60. Further, other axial support means could be used, for example, a magnetic device adapted to exert an axial force on rotor 62 when rotor 62 is first moved from a rest position and when rotor the 62 is being returned to the rest position.
The invention has been described in detail with particular reference to certain embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. Thus, although the rotary device of the present invention has been described with reference to optical scanners which
utilize a polygon, it will be apparent that the invention can be used in a scanner (not shown) in which a hologon is the scanning element. The present invention could also be used in a rotary device (not shown) for supporting and driving an information—bearing element, for example, a device in which an optical disk is the driven element, or a device in which the driven element is a magnetic storage element such as a floppy disc.
Claims
1. A rotary device comprising a rotor (12;62) which includes a first element (16,30;68,74) of a motor, means (18;63) for supporting said rotor (12;62) for rotational movement, said supporting means (18;63) including a second element (16,30;68,74) of a motor, said device having a thrust bearing characterized in that said motor elements (16,30;68,74) are elements of a planar motor, and said thrust bearing includes a first radially—extending surface (44;76) on said rotor (12;62) and a second radially extending surface (49;78) on said supporting means (18;63).
2. A rotary device according to Claim 1, characterized in that means is included on one of said- radially—extending surfaces (44,49;76,78) for receiving a fluid upon rotation of said rotor (12;62) and for- controlling-said fluid.-such that the fluid * exerts an axial force on the rotor (12;62).
3. A rotary device according to Claim 2, characterized in that said first element is a magnet (16;68).
4. A rotary device according to Claim 2, characterized in that said second element is a motor coil, (30;74).
5. A rotary device according to Claim 2, characterized in that said means for receiving and controlling fluid comprises grooyes (42;73) formed in one of said radially extending surfaces (44;76).
6. A rotary device according to Claim 1, characterized in that said rotor includes a driven element (15;64) which is adapted to interact with an external device.
7. A rotary device according to Claim 6, wherein said driven element is a scanner element (15;64).
8. A rotary device comprising a rotor (12;62) having a surface (15;64) thereon for directing a light beam onto a receiving surface, means (18;63) for supporting said rotor (12;62) for rotational movement characterized in that said rotor (12;62) has a radially—extending thrust surface (44;76) thereon, said supporting means (18;63) has a radially—extending bearing surface (49;78) arranged opposite said thrust surface (44;76), and means (42;73) is provided on one of said radially—extending surfaces (44,49;76,78) for receiving a fluid upon rotation of said rotor (12;62) and for controlling said fluid such that the fluid exerts an axial force on the rotor (12;62).
9. A rotary device according to Claim 8, characterized in that said rotor (12) comprises a magnet (16), and said thrust surface (44) is located on said magnet (16).
10. A rotary device according Claim 8, characterized in that said rotor (62) comprises a sleeve (66) mounted on a spindle (63), and said thrust surface (76) is located on said sleeve (66).
11. A rotary device according to any one of Claims 8—10, characterized in that said means for receiving and controlling a fluid comprises spiral grooves (42;73) formed in said thrust surface (44,76), and said grooves (42;73) function as a viscous pump.
12. A rotary device according to Claim 9, characterized in that a motor coil (30;74) is located opposite said thrust surface (44; 76), said bearing surface (49;78) is on said coil (30;74), and said magnet (16;68) and said coil (30;74) are elements of a brushless D.C. motor which drives said rotor (12;62).
13. A rotary device according to Claim 8, characterized in that bearing means (40) is positioned to support said rotor (12) when said rotor (12;62) is at rest.
14. A rotary device according to Claim 13 characterized in that said rotor (12) is adapted to move away from said bearing means (40) when said rotor is driven.
15. A rotary device for use in scanning a light beam across a receiving medium, said device comprising a rotor (12,62) having a surface thereon for directing a light beam onto a receiving surface, means (18,63) for mounting said rotor (12,62) for rotation, and means (16,30;68,74) for driving said rotor (12,62) characterized in that said driving means comprises a planar motor having generally a planar first element (16;68) and a generally planar second element .(30^74), and one of said elements (16,30;68,74) is operatively connected to said rotor (12,62).
16. A rotary device according to claim 15, characterized in that said one element (16,30;68,74) comprises a radially—extending thrust surface (44;76), and said support means (18;63) comprises a radially—extending bearing surface (49;78) arranged opposite said thrust surface (44;76).
17. A rotary device according to Claim 16, characterized in that said thrus-t and bearing surfaces (44,49;76,78) comprise means (42;73) for receiving a fluid and for controlling the fluid such that said fluid exerts an axial force on said rotor (12;62).
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE8888900423T DE3778883D1 (en) | 1986-12-16 | 1987-12-07 | ROTATIONAL DEVICE. |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US94212086A | 1986-12-16 | 1986-12-16 | |
US942,120 | 1986-12-16 | ||
US123,836 | 1987-11-23 | ||
US07/123,836 US4958098A (en) | 1986-12-16 | 1987-11-23 | Rotary device |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1988004787A1 true WO1988004787A1 (en) | 1988-06-30 |
Family
ID=26821948
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1987/003216 WO1988004787A1 (en) | 1986-12-16 | 1987-12-07 | Rotary device |
Country Status (5)
Country | Link |
---|---|
US (1) | US4958098A (en) |
EP (1) | EP0293455B1 (en) |
JP (1) | JPH01501577A (en) |
CA (1) | CA1296208C (en) |
WO (1) | WO1988004787A1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0433483A1 (en) * | 1989-12-19 | 1991-06-26 | Ebara Corporation | A rotation device supporting a polygon mirror |
GB2266009B (en) * | 1992-04-08 | 1996-08-07 | Fluid Film Devices Limited | Improvements in or relating to electric motors |
US5565052A (en) * | 1992-03-05 | 1996-10-15 | Industrieanlagen-Betriebsgesellschaft Gmbh | Method for the production of a reflector |
Families Citing this family (16)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5325006A (en) * | 1990-04-27 | 1994-06-28 | Hitachi, Ltd. | Sealed magnetic fluid bearing for polygon mirror drive motor |
GB2246400B (en) * | 1990-07-28 | 1994-01-26 | Glacier Metal Co Ltd | Magnetic bearings |
GB2268984B (en) * | 1992-07-23 | 1996-04-03 | Glacier Metal Co Ltd | Magnetic bearing back-up |
KR960701560A (en) * | 1993-02-03 | 1996-02-24 | 프랑크 씨. 지뷰 | METHODS AND APPARATUS FOR IMAGE PROJECTION |
DE4433021C2 (en) * | 1994-09-16 | 1999-04-15 | Forschungszentrum Juelich Gmbh | Device for breaking flow vortices on a tangential and turbulent surface |
JPH09303383A (en) * | 1996-05-09 | 1997-11-25 | Konica Corp | Rotary device and light deflecting device |
US6169354B1 (en) * | 1996-05-24 | 2001-01-02 | Halo Data Devices, Inc. | Thin film electric motors |
JPH10184685A (en) * | 1996-12-25 | 1998-07-14 | Fuji Xerox Co Ltd | Magnetic bearing |
US6054786A (en) * | 1999-05-27 | 2000-04-25 | Halo Data Devices, Inc. | Method and system for providing a spherical bearing in a thin film reluctance motor |
US6204588B1 (en) | 1999-05-27 | 2001-03-20 | Halo Data Devices, Inc. | Rotor capable of being used as a recording media |
DE10332438A1 (en) * | 2003-07-16 | 2005-04-14 | Studiengesellschaft Kohle Mbh | Materials encapsulated in porous matrices for reversible hydrogen storage |
SG139520A1 (en) * | 2003-08-12 | 2008-02-29 | Sony Corp | Methods for producing hard disk drives of reduced size, hard disk drives produced by the method, and systems including the hard disks. |
DE10361229B4 (en) * | 2003-12-24 | 2012-01-26 | Minebea Co., Ltd. | Spindle motor with storage system |
DE102006037543B4 (en) * | 2006-08-10 | 2009-08-27 | Aerolas Gmbh, Aerostatische Lager- Lasertechnik | Device with a directly driven rotary body and aerostatic bearing |
TWI440424B (en) * | 2008-10-17 | 2014-06-01 | Sunonwealth Electr Mach Ind Co | Thin dissipating fan |
GB2519060B (en) * | 2013-08-08 | 2016-08-03 | Yasa Motors Ltd | Cooling of axial flux motors - centrifugal |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
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GB1524662A (en) * | 1977-03-24 | 1978-09-13 | Univ Southampton | Agnetic disc stores |
DE2903197A1 (en) * | 1978-01-27 | 1979-08-02 | Matsushita Electric Ind Co Ltd | ROTARY HEAD ARRANGEMENT FOR A MAGNETIC RECORDING AND PLAYBACK DEVICE |
US4413895A (en) * | 1982-03-22 | 1983-11-08 | Eastman Kodak Company | Electromagnetic actuator having a compliant armature |
EP0097852A2 (en) * | 1982-06-24 | 1984-01-11 | Kabushiki Kaisha Toshiba | Rotating mirror scanner |
EP0229911A1 (en) * | 1985-11-28 | 1987-07-29 | Ebara Corporation | Electrically powered apparatus |
Family Cites Families (10)
Publication number | Priority date | Publication date | Assignee | Title |
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NL134857C (en) * | 1969-02-24 | 1900-01-01 | ||
US3891282A (en) * | 1973-12-12 | 1975-06-24 | Litton Systems Inc | Lubricated assemblies |
CH611990A5 (en) * | 1977-01-17 | 1979-06-29 | Sulzer Ag | |
US4332428A (en) * | 1979-01-16 | 1982-06-01 | Matsushita Electric Industrial Co., Ltd. | Rotary mechanism with axial bearings |
DE2934085A1 (en) * | 1979-08-23 | 1981-03-26 | Papst Licensing Gmbh, 78549 Spaichingen | TACHOGENERATOR |
DE3303499A1 (en) * | 1982-02-05 | 1983-08-25 | Nippon Seiko K.K., Tokyo | DYNAMIC GAS STORAGE |
EP0121829B1 (en) * | 1983-03-30 | 1987-05-20 | Wyler AG Wasserwaagen und Messwerkzeuge | Bearing element for a gas bearing |
DE3526166C2 (en) * | 1984-07-23 | 1996-05-02 | Asahi Chemical Ind | Brushless electric motor and method of manufacturing a coil unit therefor |
US4726640A (en) * | 1985-09-24 | 1988-02-23 | Ricoh Company, Ltd. | Optical deflector with a pneumatic and a magnetic bearing |
JPH034220A (en) * | 1989-05-31 | 1991-01-10 | Konica Corp | Silver halide photographic sensitive material |
-
1987
- 1987-11-23 US US07/123,836 patent/US4958098A/en not_active Expired - Fee Related
- 1987-12-07 WO PCT/US1987/003216 patent/WO1988004787A1/en active IP Right Grant
- 1987-12-07 EP EP88900423A patent/EP0293455B1/en not_active Expired - Lifetime
- 1987-12-07 JP JP63500706A patent/JPH01501577A/en active Pending
- 1987-12-10 CA CA000553974A patent/CA1296208C/en not_active Expired - Fee Related
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1524662A (en) * | 1977-03-24 | 1978-09-13 | Univ Southampton | Agnetic disc stores |
DE2903197A1 (en) * | 1978-01-27 | 1979-08-02 | Matsushita Electric Ind Co Ltd | ROTARY HEAD ARRANGEMENT FOR A MAGNETIC RECORDING AND PLAYBACK DEVICE |
US4413895A (en) * | 1982-03-22 | 1983-11-08 | Eastman Kodak Company | Electromagnetic actuator having a compliant armature |
EP0097852A2 (en) * | 1982-06-24 | 1984-01-11 | Kabushiki Kaisha Toshiba | Rotating mirror scanner |
EP0229911A1 (en) * | 1985-11-28 | 1987-07-29 | Ebara Corporation | Electrically powered apparatus |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0433483A1 (en) * | 1989-12-19 | 1991-06-26 | Ebara Corporation | A rotation device supporting a polygon mirror |
US5565052A (en) * | 1992-03-05 | 1996-10-15 | Industrieanlagen-Betriebsgesellschaft Gmbh | Method for the production of a reflector |
GB2266009B (en) * | 1992-04-08 | 1996-08-07 | Fluid Film Devices Limited | Improvements in or relating to electric motors |
Also Published As
Publication number | Publication date |
---|---|
JPH01501577A (en) | 1989-06-01 |
US4958098A (en) | 1990-09-18 |
CA1296208C (en) | 1992-02-25 |
EP0293455A1 (en) | 1988-12-07 |
EP0293455B1 (en) | 1992-05-06 |
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