Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
  • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
  • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
  • G01D5/347—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells using displacement encoding scales
  • G01D5/34707—Scales; Discs, e.g. fixation, fabrication, compensation

Definitions

• the invention relates to a method for holding a scale on a carrier.
• a scale is to be attached to one of the machine parts, and a scanning unit is attached to the other of the mutually movable machine parts. In the position measurement, a measurement graduation of the scale is scanned by the scanning unit.
• a short, possibly limited to the contact surface force path can be achieved for example by wringing (atomic van der Waals forces).
• wringing atomic van der Waals forces
• scales of glass or glass ceramic are used with negligible expansion coefficient.
• These standards can be processed well, so that here the wringing of optically polished mating surfaces is customary, as described in DE 101 53 147 A1. Wringing is a very drift-stable attachment method for standards. In the case of an exposure, however, there is a risk that the scale will peel off or partially loosen. The outer edges of an impacted scale can therefore be unstable if alternating stresses occur at the edge (eg due to acceleration or temperature variations) and as a result these edge zones are repeatedly peeled off and blown up.
• the object of the invention is to provide a method by which a scale can be kept as drift-stable as possible but detachable on a support.
• Another object of the invention is to provide an arrangement with a carrier and with a detachable and yet stably fixed scale.
• Figure 1 shows a first embodiment of an arrangement with a carrier and a scale attached thereto in a side view
• Figure 2 shows the arrangement of Figure 1 in plan view
• Figure 3 shows a second embodiment of an arrangement with a carrier and a scale attached thereto in a side view
• Figure 4 shows a third embodiment of an arrangement with a carrier and a scale attached thereto in a side view
• Figure 5 shows a fourth embodiment of an arrangement with a carrier and a scale attached thereto in a side view
• FIG. 6 shows the arrangement according to FIG. 5 in plan view
• Figure 7 shows a fifth embodiment of a device with a fixed scale in a plan view
• FIG. 8 shows the arrangement according to FIG. 7 in cross section
• Figure 10 shows a seventh embodiment of an arrangement with a carrier and a scale attached thereto in a plan view
• Figure 11 shows an eighth embodiment of an arrangement with a carrier and a scale attached thereto in a side view; - A -
• Figure 12 shows a ninth embodiment of an arrangement with a carrier and a scale attached thereto in a side view
• Figure 13 shows a tenth embodiment of an arrangement with a carrier and a scale attached thereto in a side view
• Figure 14 shows an eleventh embodiment of an arrangement with a carrier and an attached thereto
• Figure 15 shows a twelfth embodiment of an arrangement with a carrier and a scale attached thereto in a plan view
• FIG. 16 shows the arrangement according to FIG. 15 in section
• Figure 17 shows a thirteenth embodiment of an arrangement with a carrier and a scale attached thereto in a side view
• Figure 18 is a fourteenth embodiment of a
• each of the bodies 1 and 2 to be clamped has in each case a live electrode 211, 212 as anode or cathode, against which a voltage U is applied, and thereby the two opposing electrodes 211 , 212 are charged opposite.
• the carrier 2 is in this case as a live electrode (electrically conductive material or semiconductor material) or with a live electrode (in particular coating with an electrically conductive material or semiconductor material) and the scale 1 having a measuring graduation 15 as counterelectrode (made of electrically conductive material or semiconductor material or Coating a non-conductive material scale with an electrically conductive material or semiconductor material).
• a dielectric 12, 22 is provided, in the illustrated example, a layer of dielectric 12 on the substrate 19 of the scale 1 and a layer of dielectric 22 on the support 2 is attached.
• the scale 1 and the carrier 2 are each provided with a power connection.
• the live electrodes which are connected to the voltage source are arranged together on one of the bodies to be connected and the electrode on the other body forms a kind of coupling electrode in which counter-charges form partially in the region opposite to the live electrodes.
• the carrier 2 or the scale 1 the two live, so contacted electrodes.
• the Bipolar clamping is preferable because the contacting effort can be limited to one component.
• the bipolar electrostatic clamping is therefore preferably used.
• both live electrode anode 211 and cathode 212 are provided together on the carrier 2 and the counter electrode is formed in each case in an electrically conductive body 11 of the scale 1 from.
• the bipolar electrostatic clamping is therefore realized and the live electrodes 21 1, 212 are arranged jointly on the carrier body 2. This arrangement facilitates the handling of the scale 1, since only the carrier body 2 must be provided with electrical contacts and leads.
• FIG. 1 shows the side view of the carrier 2 with the scale 1 held thereon by electrostatic clamping
• FIG. 2 shows the plan view.
• the scale 1 has a measuring graduation 15 in the form of an incremental measuring graduation 15 which is photoelectrically scanned for position measurement in the measuring direction X.
• the measuring graduation 15 may be a reflective amplitude grating or a phase grating, which serves in a known manner for highly accurate interferential position measurement.
• the scale 1 consists of a substrate 19 made of glass or glass ceramic, z. B. ZERODUR and has on its underside an electrode in the form of a conductive, thin metal layer 11, which is covered with a thin dielectric 12.
• the carrier 2 has on its upper side an electrode in the form of a thin metal layer 21 1, 212, which also has a thin Dielectric 22 is covered.
• the metal layer 211, 212 of the carrier 2 is structured in the form of two separate voltage-carrying electrodes 211 and 212, to which an electrical voltage U is applied by external contact points.
• the electrode 211 is designed as an anode and the electrode 212 as a cathode.
• Favorable dielectrics are Si 3 N 4 , Ta 2 O 5 , Y 2 O 3 , Al 2 O 3 or AlN. They have a high relative dielectric constant ⁇ R and a high dielectric strength.
• Typical layer thicknesses for the metal layers 11 and 211, 212 forming the electrodes are between 20 nm and 2 ⁇ m, those for the dielectric 12 and 22 between 50 nm and 400 ⁇ m.
• a material for the metal layers 11 and 21 1, 212 low-stress metals such as aluminum are advantageous.
• TCO transparent and electrically conductive layer
• the mutually contacting contact surfaces of scale 1 and carrier 2 are each formed by the dielectric 12 and 22. These contact surfaces are executed over a large area at least largely over the entire extent of the scale 1.
• the surfaces on which the scale 1 has contact with the carrier 2 can also be designed in an advantageous manner such that the entire facing surfaces of scale 1 and carrier 2 (mounting surfaces) do not touch each other.
• spaced elevations 23 are formed on the scale 1 and / or on the carrier 2, which form the contact surfaces. This has the advantage that when joining scale 1 and carrier 2, air can escape from the intermediate space through the channels 24 between the elevations 23 to the outside.
• the dielectric 22 of the carrier 2 is structured by elevations 23 and depressions 24 are formed in it alternately.
• the contact surface is thereby small compared to the mounting surface and distributed in many small individual surfaces over the mounting surface.
• the requirement for dust-free mounting surface decreases considerably.
• the structuring of the dielectric 22 can be achieved either by a partial reduction of the thickness or by a complete removal.
• the formation of elevations 23 and depressions 24 by structuring can take place in a manner not shown alternatively or additionally also on the scale 1, by alternatively or additionally structuring the dielectric 12 of the scale 1 accordingly.
• elevations 23, which form lying between the elevations 23 and outwardly leading channels 24 may also be provided by a structured metal layer 11 of the scale 1 and / or a metal layer 211, 212 of the carrier 2.
• a height profile is created and the dielectric 12, 22 applied flat, as shown in Figure 4 based on the metal layers 211, 212 of the carrier 2.
• the channels 24 are preferably open all the way to the outer surrounding area, so that a pressure equalization can take place and if necessary trapped air can escape.
• the elevations 23 are laid as contact surfaces in the region of the bessel points of an elongated scale 1.
• the electrodes 211, 212 are arranged symmetrically to the Bessel points and thus to the support surfaces, so that in the calculation of the support no resulting torque acts on the scale 1.
• the advantage of this embodiment is that the flatness of the support 2 has at most a negligible influence on the tension and flatness of the scale 1 and therefore does not have to be manufactured so precisely. In practice, one achieves extremely high accuracy of a position measuring device with such an arrangement of scale 1 and carrier 2.
• the support 2 consists of support elements 28 on a base body 26.
• the support elements 28 may be sprinkled on the base body 26, glued, clamped or screwed. Between the support elements 28 and the main body 26 and solid joints can be arranged, which on the one hand not transfer the Anschraub mechanism on the scale 1 and / or on the other hand allow a maximum force-free length extension of scale 1 relative to the base body 26.
• FIG. 7 shows a top view of a support element 25 with solid-body joints 29 arranged on both sides of the scale 1.
• the solid joints 29 are transverse to the measuring direction X extending material webs, which allow a direction of measurement X directed movement of the support element 25 relative to the screw A.
• the attachment point A is used for fixed fixing of the support element 25 on a base body 26 shown in Figures 5 and 6.
• Figure 8 shows a cross section of this arrangement.
• the attached to the support member 25 electrodes 211, 212 are connected to an electrical voltage U and cooperate with the scale 1 attached to the electrode 11.
• the dielectric 12 is provided in each case.
• FIG. 9 shows the electrostatic clamping of a flat two-dimensionally extended scale 1, as is customary, for example, in two-dimensionally measuring cross-grating measuring devices.
• three offset by 120 °, symmetrically arranged elevations 23 are provided.
• the radial distance from the center is chosen so that, in spite of gravity, the lowest possible angle of inclination or the greatest possible flatness is achieved.
• the electrodes 11 on the scale 1 should here remain essentially limited to the electrode surfaces 211, 212 of the carrier 2 and are advantageously designed bipolar.
• two independent pairs of electrodes 211, 212 and 213, 214 are provided, which are supplied by two independent voltage sources U1, U2. If one of the power supplies fails, the scale 1 still remains attached.
• Electrode structure 211, 212 and 213, 214 which is each assigned to a voltage source, should as far as possible be distributed over the mounting surface.
• the embodiment according to FIG. 11 largely corresponds to the embodiment according to FIG. 3, except that additional mechanical fastening elements 3 are provided which nonetheless securely hold the scale 1 in the event of a failure of the power supply U.
• the fasteners 3 fix the scale 1 advantageously at locations that are located away from a measurement pitch 15 for position measurement.
• the fastening elements 3 may be spring elements 3, which engage milled pockets in edge surfaces of the scale 1.
• the embodiment shown in FIG. 12 combines the type of fastening with the type of electrostatic clamping.
• the opposite outer surfaces of the dielectric 12 of the scale 1 and the dielectric 22 of the carrier 2 are sprinkled together. If the roughness of the dielectrics 12, 22 is not sufficiently small, they still need to be polished slightly after the layer deposition (sputtering, sputtering or plasma process PECVD). With this attachment, you do not need a redundant design of multiple pairs of electrodes, as always a sufficient contact pressure is present.
• the electrostatic clamping prevents the peeling of the impact, since the long-range electrostatic forces even in poor local contact conditions in which the short-range van der Waals forces are already very low or no longer exist, a sufficient Ensure contact pressure.
• the contact surfaces are interrupted, so that during assembly no air bubbles are trapped in the contact surfaces, or the remaining air remains in the contact surfaces can escape in a short time.
• the design of the electrostatic clamping corresponds to the embodiment of Figure 3.
• the dielectric 12, 22 of the preceding examples is realized by a thin foil 4, which is introduced between the scale 1 and the carrier 2.
• the scale 1 and the carrier 2 must be provided in this case only with a simple electrode layer 11, 211, 212, which can be done in a Bedampfungs Republic. The costs can be significantly reduced.
• film 4 plastic films e.g. Teflon in question, but also thin glass foils.
• the film thicknesses are advantageously in the range 20-400 microns. This type of fastening is particularly advantageous if scales 1 made of metal are used. They can be used without coating since they themselves form the electrode 11.
• an oil film 5 is introduced between the dielectric 12 of the scale 1 and the outer metal layer 211, 212 of the carrier 2. He remains limited due to its Kapilar tendency in the very thin gap area.
• This oil film 5 prevents, on the one hand, that small volumes of air are trapped between the scale 1 and the support 2, in which corona discharges can also occur at high field strength.
• the scale 1 can slide over the oil film 5 and thus retain its length. This type of mounting is particularly interesting when the support 2 has a high thermal expansion (such as aluminum) and scale 1 has a very small thermal expansion (such as Zerodur).
• FIGS. 15 and 16 an advantageous kinematic three-point mounting of a flat scale 1 (in particular a Cross grid plate) suspended from the carrier 2 is shown.
• FIG. 15 shows the plan view of the spatial arrangement of the electrodes 211, 212 on the carrier 2
• FIG. 16 shows a cross section in the region of two supporting points with the scale 1.
• the scale 1 again has the electrode 11 and the support 2 carries the live electrodes 211 and 212 arranged.
• the scale 1 is only on three spaced-apart arranged elevations 23 on the carrier 2.
• the elevations 23 are formed by punctiform regions of the dielectric 22 of the carrier 2.
• This deformation can be compensated by a corresponding contact pressure, which is generated by the electrostatic clamping and which corresponds and counteracts the gravity exactly, but which must be significantly lower than the contact pressure in the area of the contact surfaces.
• a corresponding contact pressure which is generated by the electrostatic clamping and which corresponds and counteracts the gravity exactly, but which must be significantly lower than the contact pressure in the area of the contact surfaces.
• electrodes 211, 212 of larger area are arranged outside the elevations 23 than in the remaining area.
• the goal is to achieve a high evenness and thus a high accuracy of scale 1.
• the lower contact pressure outside the elevations 23 and thus outside the contact surfaces can be achieved in a simple manner by a corresponding structuring with narrow but widely spaced electrode surfaces 211, 212. In the area of the contact points, however, the area occupation with electrodes 211, 212 must be high.
• the elevations 23 (contact surfaces) and the remaining mounting surfaces can each be occupied by two independent pairs of electrodes and supplied with separate voltage sources. By
• Electrode structures must have small lateral spacings between 1 .mu.m and 500 .mu.m in order to generate as inhomogeneous as possible an electric field.
• the substrate 19 of the scale 1 consists in this embodiment of a nearly insulating material, but having a certain proportion of mobile charges.
• Movable charges can be, for example, ions (eg Na +) or ionizable impurities which allow the charge to jump from impurity to impurity.
• Suitable materials include, for example, sodium-containing glass types and Zerodur.
• this effect of the slowly decaying holding force can also be used for all the embodiments explained above if dielectrics 12 or 22 or 4 are used which have movable charges. In most cases, the contact pressure is also significantly higher, since the distances between the opposite charges are lower (Johnson Rahbeck effect).
• the utilization of this effect is particularly advantageous for fixing the scale 1 for highly accurate photoelectric position measurement, since here scales 1 made of glass ceramic, in particular Zerodur be used.
• the scale 1 is coated on the underside with a planar electrode 11, for example a metal layer 11.
• the carrier 2 carries a pair of electrodes 211, 212, which is covered with a dielectric 22, and which is preferably made thicker to form elevations 23, which form the contact points. The region between the elevations 23 forms the channels 24.
• an electrically conductive layer for example a metal layer 6 is applied to the elevations 23 of the dielectric 22, which is in electrical contact with the electrode 11 of the scale 1.
• the dielectric 22 now has no direct contact with the opposite electrode 11 of the scale 1.
• the influence of the moving charges in the dielectric 22 is thereby significantly reduced.
• the contact pressure arises only in the areas outside the contact surfaces, ie outside of the elevations 23rd
• the layer structure of the scale 1 can be selected such that mechanical stresses caused in the layers are compensated.
• the layer material and the layer thicknesses are determined so that in these layers caused mechanical stresses compensate each other.
• the layers may have a fine structuring.
• the measuring graduation 15 of the scale 1 is an electrically conductive material on an electrically non-conductive substrate (glass or glass ceramic), then this measuring graduation 15 can simultaneously also form the electrode 1 1 of the scale 1.
• the measuring graduation 15 forming the electrode 11 can be arranged on the surface of the substrate 19 facing or facing away from the carrier 2 be arranged and consist of a continuous or non-continuous layer, in particular reflective layer.
• multi-dimensional position measurement scales 1 are increasingly used with a two-dimensional measurement graduation 15, in particular with an intersecting measurement graduation, also called a cross lattice. It is necessary to attach relatively large scale 1 (about 40 cm x 40 cm) on a surface of a support 2.
• the support 2 to which scale 1 is to be attached is made of glass-ceramic (e.g., ZERODUR) having a coefficient of expansion close to zero, the invention can be advantageously used.
• glass-ceramic e.g., ZERODUR
• Such a machine with a scale with a two-dimensional measuring graduation is explained in US 2004/0263846 A1, to which reference is made here.
• a plurality of scales 1 may be attached two-dimensionally next to one another like a mosaic on a machine surface 2 of, for example, 1 m ⁇ 2 m in order to cover the required measuring range of approximately 1 m ⁇ 2 m.
• the scales 1 with the particular photoelectrically scanned measuring graduation 15 in the required precision namely namely only in sizes of about 40cm x 40cm relatively uncomplicated in the required quality manufacturable.
• Each of these scales 1 with a two-dimensional measuring graduation 15, also called a cross grid can now according to the invention be attached to the machine part 2 as a carrier.
• the force path is extremely short and includes only the area between the metal layer 11 of the scale 1 and the metal layer 211, 212 of the carrier 2. He remains so on the volume of the dielectric 12, 22nd limited. The scale 1 and the carrier 2 thus remain almost completely stress-free. Residual stresses in the scale 1 arise in practice only if the contact surfaces are not flat. The specification of the flatness must be interpreted according to the requirements.
• the contact pressure is evenly distributed over the contact surfaces. Even if small dust particles are trapped between the contact surfaces, the contact pressure is hardly affected since the distance dependence drops only with 1 / d 2 . In contrast, the van der Waals forces of an impingement fall with 1 / d 6 and are limited only to atomic distances.
• the contact pressure of a Ansprengung is therefore very uneven and undefined in practice. If the contact pressure is distributed unevenly and the scale and the carrier expand differently thermally, there may be local shifts between scale and carrier, which can not be accepted in high-precision applications.
• the electrostatic connection is solvable, defective standards 1 can be replaced if required.
• the strength of the electrostatic connection with a suitable choice of the dielectric 12 and 22, its thickness and dielectric strength as well as the applied voltage U exceed that of an exposure.
• a temperature of the scale 2 can occur, which leads to measurement errors. In practice, this occurs, for example, at a scale 1 of Zerodur and a carrier 2 with high thermal expansion, such as aluminum.
• the contact pressure clamping force, holding force
• the time intervals between the momentary voltage shutdowns may be based on the typical time intervals for relevant temperature changes. The entire process can be easily controlled electronically without manual intervention.
• the surfaces on which the scale 1 has contact with the carrier 2 can be structured as desired and do not have to be identical to the entire facing area of the scale and the support (mounting surface), as is the case with wringing.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Transmission And Conversion Of Sensor Element Output (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

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• 2007
  • 2007-01-18 EP EP07702852.0A patent/EP2002216B1/de active Active
  • 2007-01-18 CN CNA2007800124892A patent/CN101416031A/zh active Pending
  • 2007-01-18 WO PCT/EP2007/000404 patent/WO2007112796A1/de not_active Ceased
  • 2007-01-18 JP JP2009501869A patent/JP4982554B2/ja active Active
  • 2007-03-08 US US11/715,637 patent/US7549234B2/en active Active

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