Classifications

• • 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
  • F16C29/00—Bearings for parts moving only linearly
  • F16C29/02—Sliding-contact bearings
  • F16C29/025—Hydrostatic or aerostatic
• • 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
  • F16C32/00—Bearings not otherwise provided for
  • F16C32/06—Bearings not otherwise provided for with moving member supported by a fluid cushion formed, at least to a large extent, otherwise than by movement of the shaft, e.g. hydrostatic air-cushion bearings
  • F16C32/0662—Details of hydrostatic bearings independent of fluid supply or direction of load
  • F16C32/067—Details of hydrostatic bearings independent of fluid supply or direction of load of bearings adjustable for aligning, positioning, wear or play
  • F16C32/0674—Details of hydrostatic bearings independent of fluid supply or direction of load of bearings adjustable for aligning, positioning, wear or play by means of pre-load on the fluid bearings
• • 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
  • F16C39/00—Relieving load on bearings
  • F16C39/06—Relieving load on bearings using magnetic means

Definitions

• the present invention relates to a static bearing conveying apparatus having magnetically preloading and motional error correcting functions. More particularly, the present invention relates to a static bearing conveying apparatus, which comprises a table and a guide having simple construction, and which is adapted to generate preload using magnetic force and to adjust a floating gap through variation in magnetic force applied to generate the preload, thereby providing magnetically preloading and motional error correcting functions.
• Preload for static bearings is generated by magnetic force of a permanent magnet, and the magnetic force is varied to maintain a floating gap of the static bearings by use of an electromagnetic coil. This construction is based on the fact that the rigidity of the static bearings based on the preload is inversely proportional to the floating gap.
• the floating gap required for the static bearings can be adjusted by changing the intensity of magnetic force through change of electric current applied to the electromagnetic coil, and errors in angular motion and in linear motion horizontal to a conveying direction of a conveying system can be corrected according to structure of a correcting unit.
• a conventional conveying system employing static bearings is shown.
• a double-sided pad type conveying apparatus comprises a guide 20 located below a table 10 to maintain sufficient rigidity of the static bearings and having guide surfaces 21 and 22 formed on opposite sides thereof to guide the static bearings, and a pair of bearing pads 30 fixed in parallel to each other on the table 10 while facing the guide surfaces 21 and 22.
• the present invention has been made in view of the above problems, and it is an object of the present invention to provide a static bearing conveying apparatus, which can be simplified in structure by applying a magnetic preloading device to a conveying system employing static bearings, while correcting motional error via active control of magnetic force.
• a static bearing conveying apparatus employing static bearings and having magnetic preloading and motional error correcting functions, the apparatus comprising: a guide having a guide surface formed on one side facing a table; magnetic preload units provided between the guide and the table to generate preload; and a motional error correcting control unit comprising a controller to control the magnetic preload units, and a power amplifier to apply electric current according to a control signal from the controller.
• Each of the magnetic preload units may comprise a permanent magnet, a core collinear with magnetic fluxes from the permanent magnet, and an electromagnetic coil wound around the core, and located between static bearing pads and the guide to generate the preload, so that a floating gap for the static bearings can be corrected by changing magnetic force generating the preload, and errors in angular motion and linear motion in a direction horizontal to a conveying direction of a conveying system can be corrected according to structure of a correcting apparatus.
• the static bearing conveying apparatus is a one-sided pad type apparatus which has a guide surface formed only on one side of a guide, and a pad fixed to a table to face the guide surface, thereby simplifying the structure of the table and the overall guide while reducing the volumes of the table and the overall guide.
• the guide surface requiring precise machining is formed only on one side of the guide, thereby facilitating guide surface machining as well as reducing the machining costs thereof.
• the magnetic preload units in the apparatus apply magnetic force to the static bearings to generate preload on the static bearings through permanent magnets, and adjust a floating gap of the static bearings by adjusting the magnetic force using an electromagnetic coil, thereby reducing motional errors occurring upon conveyance on the table and remarkably enhancing precision of a conveying system.
• FIG. 1 is a cross-sectional view illustrating the construction of a conventional double-sided pad type static bearing conveying apparatus
• FIG. 2 is a cross-sectional view illustrating a single-sided pad type static bearing conveying apparatus having preloading and motional error correcting functions according to the present invention
• FIG. 3 is an exemplary view illustrating a single-axis guide which can be corrected in motional error by the single side pad type static bearing conveying apparatus according to the present invention
• Fig. 4 is a graph depicting relationship between a floating gap of static bearings and a gap between a core and a guide of the static bearing conveying apparatus having the preloading and motional error correcting functions according to the present invention.
• Fig. 5 is a graph depicting relationship between variation in a floating position of the static bearings and electric current of an electromagnetic coil.
• Fig. 2 is a cross-sectional view illustrating a single-sided pad type static bearing conveying apparatus having preloading and motional error correcting functions according to the present invention.
• the static bearing apparatus comprises a guide 20 having a guide surface 21 formed on one side of the guide 20 which guides a table 10, a plurality of static bearing pads 30 fixed to the table 10 so as to face the guide face 21, and magnetic preload units 40 equipped to the table 10 to generate preload by virtue of magnetic force and to control a floating gap of the static bearings by changing the magnetic force serving to generate the preload.
• the magnetic preload units 40 are equipped to both sides of the table 10 to generate the preload, which can act as attracting force between the table 10 and the guide 20 to equilibrate the floating gap required for the static bearings with floating force of the static bearings.
• Each of the magnetic preload units 40 comprises a permanent magnet 41 to generate magnetic preload, a core 43 having the permanent magnet 41 fixed thereto and collinear with magnetic fluxes from the permanent magnet 41, and an electromagnetic coil 42 wound around the core 43.
• the permanent magnet 41 is supported by a fixing bracket 45 supported on the table 10.
• each of the magnetic preload units 40 is adapted to control the intensity of magnetic force according to magnetic fluxes generated from the permanent magnet 41 and to a direction of electric current applied to the electromagnetic coil 42, i.e. to control a gap G between the static bearing pads 30 and the guide 20 via variation in intensity of electric current of the electromagnetic coil 42.
• the magnetic preload unit 40 is preferably designed using variables including a material and a size of the permanent magnet 41, a cross-sectional area of the core 43, and a gap between the core 43 and the guide surface 21 so as to match a required preloading force.
• the gap G between the static bearing pads 30 equipped to the table 10 and the guide 20 must be maintained at a distance of 10 ⁇ m, and the gap between the core 43 of the magnetic preload unit 40 and the guide 20 must be maintained at a distance of about 500 ⁇ 2,000 ⁇ m.
• the static bearing conveying apparatus of the present invention is adapted to be linearly moved by an actuator which comprises a discrete linear motor 50, a ball-screw or a voice electromagnetic coil to cause linear motion of an object, and comprises a conveying unit, which includes a conveying actuator and a feedback sensor or includes a linear scale and a laser feedback device to control a conveying location.
• an actuator which comprises a discrete linear motor 50, a ball-screw or a voice electromagnetic coil to cause linear motion of an object
• a conveying unit which includes a conveying actuator and a feedback sensor or includes a linear scale and a laser feedback device to control a conveying location.
• the magnetic preload units 40 are connected to a motional error correcting control unit 60 which comprises a controller to control the magnetic preload unit 40, and a power amplifier to apply electric current to the magnetic preload unit 40.
• the controller comprises a digital controller (DSP board or PC), and calculates the motional error of the conveying system based on information about locations and errors of the conveying system.
• An additional correction signal for compensating the motional error is converted into an associated electric current, which is applied to the electromagnetic coil of the magnetic preload unit 40.
• the magnetic preload units 40 can arbitrarily correct the floating gap G ( ⁇ m) of the static bearings between the static bearing pads 30 and the guide 20, and the gap gm (mm) between the magnetic preload unit 40 and the guide 20 by changing magnetic force of the permanent magnet 41 applied to generate preload through change of electric current applied to the electromagnetic coil 42.
• Correction and control of the floating gap G by virtue of the magnetic preload can be used as a means for correcting errors in linear motion which is horizontal to the conveying direction, and is caused by a machining error on the guide surface 21 upon linear motion of the table 10 in the conveying direction.
• the guide surface 21 for guiding the static bearing pad 30 is formed only on one side of the guide 20, only one-side precise machining is required for forming the guide surface in comparison to the conventional apparatus requiring two-side precise machining, thereby lowering the machining costs as well as simplifying the structure of the table and allowing easy manufacturing of the apparatus.
• FIG. 3 is an exemplary view illustrating the overall construction of a single-axis guide using the static bearing conveying apparatus having the magnetically preloading and motional error correcting functions according to the present invention, in which two magnetic preload units 40 are equipped to both sides of the guide 20, thereby enabling correction of errors in perpendicularly linear motion, in pitch motion and in rolling motion upon conveyance of the table.
• Fig. 4 is a graph depicting relationship between the floating gap G ( ⁇ m) of the static bearings and the gap gm (mm) of the magnetic preload unit for the guide in the static bearing conveying apparatus having the preloading and motional error correcting functions according to the present invention.
• Fig. 5 is a graph depicting relationship between variation in the floating gap G ( ⁇ m) of the static bearings and electric current A of the electromagnetic coil.
• the floating gap G ( ⁇ m) of the static bearings is 10 ⁇ m
• the standard electric current A of the electromagnetic coil is set to 0 A.
• the floating gap of the static bearings is changed according to the electric current of the electromagnetic coil, and it can be appreciated from Fig. 5 that when the electric current of the electromagnetic coil has a positive value (+), the floating gap of the static bearings is decreased, and on the contrary, when the electric current of the electromagnetic coil has a negative value (-), the floating gap of the static bearings is increased.
• the floating gap G of the static bearings can be adjusted by changing the magnetic force generating the preload through control of the electric current applied to the electromagnetic coil, which enables the guide surface to be used to correct the motional error caused by a geometrical error on the guide surface upon conveyance on the table.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Magnetic Bearings And Hydrostatic Bearings (AREA)
• Support Of The Bearing (AREA)
• Control Of Position Or Direction (AREA)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (1)

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Cited By (2)

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Citations (6)

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• 2005
  • 2005-08-23 WO PCT/KR2005/002775 patent/WO2007024031A1/en not_active Ceased
  • 2005-08-23 US US11/993,469 patent/US7942099B2/en active Active
  • 2005-08-23 JP JP2008518008A patent/JP2008546965A/ja active Pending
  • 2005-08-23 EP EP05781086.3A patent/EP1917447B1/en not_active Expired - Lifetime

Patent Citations (6)

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