Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B5/00—Measuring arrangements characterised by the use of mechanical techniques
  • G01B5/28—Measuring arrangements characterised by the use of mechanical techniques for measuring roughness or irregularity of surfaces
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces

Definitions

• the invention relates to a method for swirl measurement on workpiece surfaces having surface structures, in particular machining tracks with a twist with respect to an axis. Furthermore, the invention relates to a device for carrying out this method.
• Workpiece surfaces in particular rotationally symmetrical workpiece surfaces, such as cylindrical, conical or otherwise shaped bore walls, cylindrical, conical or other outer peripheral surfaces of shafts, cones or similar workpieces or parts of workpieces, often have surface structures that are to the rotational or symmetry axis of the relevant Werk Swissoberflä- with a slope.
• Such surface structures can be used, for example, in the grinding of a corresponding arise the workpiece surface.
• the surface structure consists for example of a superposition of straight periodic twist grooves and short stochastically placed grinding marks.
• the periodic swirl grooves can lead to undesirable effects if the relevant
• Area e.g. should serve as a shaft sealing surface.
• a relative rotation between a sealing ring and the relevant workpiece surface may result in an oil feed effect in one or the other axial direction, which leads either to undesired oil losses or to dry running of the sealing ring. Both are undesirable.
• Even with plain bearings can occur by a surface structure containing a twist undesirable axial ⁇ late bine that may be undesirable. Methods have therefore been developed to measure the helix angle, which is usually in the range of a few minutes.
• DE 101 50 383 A1 discloses an image-optical measuring method in which a cylinder outer surface, which forms the workpiece surface to be examined, is projected in sections under a grazing light with a camera. The recorded image is subjected to comb filtering. The surface stripe structure is determined from the image data sets of many images taken in succession and the twist direction or the twist angles are determined therefrom.
• the method requires the evaluation of several hundred image data records, which leads to considerable amounts of data. Furthermore, depth information is missing in the recorded camera image, so that ultimately information about the depth of the twist structure is missing. This can be particularly troublesome if an occurring oil-conveying effect is to be assessed qualitatively or if the surface structure has intersecting swirling effects. structures, ie both twist with positive as well as negative sense, eg with different depth contains.
• the invention seeks to remedy this.
• the measurement effort to be driven should remain as manageable as possible in order to be able to carry out the measurement in a short time of at most a few minutes.
• the inventive method is based on the scanning of the workpiece surface for obtaining measured values along a line, which has both an axial component parallel to the axis of the workpiece surface and a peripheral component in the circumferential direction to the axis of the workpiece surface.
• the axial component and the circumferential component may be formed by separate contiguous or non-contiguous line sections extending in the axial direction and in the circumferential direction, respectively.
• the axial and circumferential components may also be contained in a single or multiple helical lines, in adjacent circular lines or other line shapes. If circular lines are used for scanning, the axial spacing of the circular lines is preferably so small that each shaft of the twist structure is cut in the axial direction by at least two circular lines.
• the pitch is so small that each shaft of the swirl structure is cut in the axial direction of at least two circular lines. This satisfies the sampling theorem. In the case of very steep swirls, it is therefore possible for at least a few circular lines (eg three or four) or a few turns for scanning to be sufficient in compliance with the sampling theorem (at least two samples per wave).
• At least one variable characterizing the twist is determined from the measured values. This characteristic variable may be, for example, the helix angle ⁇ , which corresponds to the pitch of the twist structure, ie the individual grooves or ribs, and is generally in the range of a few angular minutes.
• the mobility z can be determined, which can be regarded as the number of threads determined by the twist.
• a variable characterizing the twist can be the local, the average, the minimum or the maximum height of the twist structure, which is to be measured, for example, between the wave valley and the wave peak of the twist structure. The method according to the invention thus provides reliable and reliable measured values.
• the method according to the invention is based on the scanning of the workpiece surface along at least one line which has both an axial component and a peripheral component. If, for example, the line contains a circle as a section and if it detects the entire circumference of the workpiece surface as a full circle, the number of wave troughs and wave peaks to be measured on this line section determines the mobility.
• the perimeter component is supplied by the circle in this example. Vaults appear as the maximum of the measured radius r, whereas troughs appear as the minimum of the measured radius r.
• the mobility z can be determined, for example, on the basis of the number of wave crests or, alternatively, on the basis of the number of wave troughs.
• the scanning of the workpiece surface in the axial direction ie along the axial direction in an axial section of the line provided for scanning, can be used, for example, to determine the twist angle ⁇ .
• the axially oriented portion of the line forms or provides the axial component in this embodiment.
• the twist angle ⁇ can be calculated, for example, as the arc tangent of the ratio of the product of the mobility z and the wavelength ⁇ y measured in the axial direction to the circumference of the workpiece surface. This calculation gives the amount of twist angle, but not its sign.
• the linear scanning of the workpiece surface for example along a circular line and along a surface line, then suffices for determining important parameters characterizing the swirl.
• the workpiece surface can be scanned on a spiral. In the case of a cylindrical workpiece surface, this spiral is a helix. In the case of a conical workpiece surface, this spiral is a conical helix. In the case of a flat workpiece surface, the spiral is a spiral in the actual mathematical sense.
• the measured values along the line are recorded as measuring points in such a close sequence that the sampling theorem is satisfied, ie each wave is scanned at least twice, preferably several times.
• each wave is scanned at least twice, preferably several times.
• the usually encountered relatively small helix angle of a few minutes can in spiral scanning (with cylindrical workpiece surface Scanning along a helical line) at high speeds.
• workpieces with a diameter of a few tens of millimeters can be scanned at a speed of several hundred to several thousand revolutions per minute, with several thousand revolutions, such as five thousand revolutions, being made to provide a complete set of data.
• the pitch of the line on which the scan is performed may be relatively small, the lateral spacing of two windings of this line may be greater than the transverse to the swirl structure to be measured wavelength thereof.
• the measuring points distributed over the workpiece surface form a point cloud, from which both the axial component and the radial component of a hypothetical (synthetic) scan can be calculated out. From the point cloud those points can be selected that lie on an imaginary circular line. These points form the perimeter component. Accordingly, those points which lie on an imaginary axial line can be selected out of the point cloud. These points form the axial component.
• the advantage of this method is that both the workpiece and the measuring head, e.g. in the form of a stylus tip or an optical probe, are moved evenly. Measurement errors that could be generated by acceleration or deceleration of components of the measuring circuit are avoided.
• Circular line along a surface line possible to perform a scan on at least one circular line and / or generating line, which are closely adjacent to the first circular line or surface line. With spiral scanning this is unnecessary because of the close proximity of adjacent corridors of the spiral line.
• the pitch direction ie the sign, of the helix angle can be determined. It is also possible to carry out the scanning on two line sections which cut each other several or more times, for example because they have opposite slopes.
• the measurement can be carried out while the workpiece is rotating by moving the sensing device back and forth in the axial direction.
• the obtained point cloud again contains the axial component and the peripheral component.
• the method also makes it possible to obtain statements in the presence of competing swirl structures, e.g. with positive and negative slope, win.
• FIG. 1 shows a section of a workpiece surface with a twist structure and a line serving as a measuring path
• FIG. 1 with different lines serving as a measuring path
• 7 shows a measuring device for determining the twist structure of a workpiece surface in a schematic illustration
• Figure 9 is designed as a confocal microscope optical probe
• FIG. 10 shows a diagrammatic illustration of measured values obtained on a circular line for
• Figure 11 is a schematic representation of a strategy for the automatic adaptive determination of a
• FIG. 12 shows a flow chart of a combination strategy for the automatic adaptive definition of a scan line.
• FIG. 1 illustrates a cylindrical section of a workpiece surface 1, which in principle may be the outer surface of, for example, a pin or the inner surface of a bore.
• Section 1 of the workpiece surface is rotationally symmetrical about an axis 2 and in the example has a constant mean radius r.
• the radius r can also change along the axis 2 - the measuring method described below is not limited to cylindrical surfaces but can also be applied to other rotationally symmetric surfaces or even surfaces or in individual cases on surfaces in which the radius r as a function of the existing in cylindrical coordinates circumferential coordinate ⁇ varies.
• cylinder coordinates are assumed whose axial coordinate y is determined by the direction of the axis 2.
• the section 1 of the workpiece surface has a swirl structure 3, which is illustrated schematically in FIG. 1, and which may be made of a number of threads that wind around the axis 2 in the manner of a thread.
• the swirl structure 3 can be, for example, the result of an abrasive machining of claim 1 of the workpiece surface and consist of individual grooves or scoring sections which have a pitch angle with respect to the axis 2. This pitch angle is called the helix angle ⁇ .
• Figure 2 in which the twist angle ß is entered. It shows the inclination of a shaping element which determines the twist structure 3, for example a groove or a projection, with respect to a circular line.
• the twist structure 3 is illustrated as a development into the plane of the drawing.
• the swirl structure 3 is then scanned along a line 4 by means of a pushbutton, in which case measured values are taken in close succession along the line 4 or points are recorded.
• Each point has the coordinates r, y, ⁇ in accordance with the cylindrical coordinate system according to FIG. 1.
• each radius pair y, ⁇ given by the line 4 is assigned the radius r detected by the probe.
• the line 4 has a peripheral component 5 and an axial component 6.
• the line 4 has a section in the form of a circular line, which forms exclusively a peripheral component and has no component in the axial direction. All measured values on the section forming the circumferential component 5 have the same Y-coordinate.
• the axial component 6 is formed by a branch of the line 4, which extends parallel to the axis 2. All points on the corresponding branch of line 4 have the same circumferential coordinate ⁇ .
• one or more values characterizing the swirl can be determined from the measured values recorded along the circumferential component 5 of the line 4 and the measured values taken along the axial component 6.
• FIG. This illustrates the measured values recorded along the peripheral component 5 of the line 4 whose radius r is minimal when the valley of a groove is encountered during the measurement along the peripheral component 5 and whose radius r is maximum when a material region lying between two grooves 7, 8 9 is encountered.
• the point sequence is preferably substantially denser, so that the measured values along the circumferential component 5 are shown as a solid wavy line.
• the wavelength ⁇ y of the twist structure 3 in the Y direction that is to say the axial component 6 of the measurement carried out on the line 4, is determined. determined in the direction of the axial component 6.
• the wavelength ⁇ y is found as a distance between measured maxima or minima of the radius r. If the wavelength ⁇ y is reasonably constant, the local measured value can be taken. Otherwise, it is possible to average over several measured values.
• Wavelength .DELTA.y and frequency z are related to the circumference of section 1 of the workpiece surface.
• the arc tangent of this ratio is the desired helix angle ⁇ . This is thus determined in amount. After carrying out this simple measurement, it is thus possible to decide whether a workpiece surface has a structure with impermissible swirl or not.
• FIG. 3 shows, to divide the measuring line 4 into a plurality of lines 4a, 4b, each having a plurality of branches 16a, 17a, 18a or 16b, 17b, 18b.
• the branches 16a, 16b, 18a, 18b form the peripheral component of, for example, non-contiguous measuring line 4, while the branches 17a, 17b form the axial form component.
• the measurement is carried out as explained in connection with FIGS. 2 and 10.
• the waveforms taken along the branches 16a, 16b show a phase shift with respect to the angular coordinate ⁇ to each other.
• the waveforms taken along the branches 17a, 17b show a phase offset with respect to the Y coordinate. From the direction of the phase offset can be on the sign of the helix angle ß, ie positive or negative slope, closed.
• the line 4 may also be divided into other branches 16a, 16b, 16c, 16d and 17a, 17b, 17c, 17d, which may also intersect.
• the individual branches 16a to 17d of the line 4 can thus cover a large part of the workpiece surface.
• the method can be carried out repeatedly at several points of the workpiece surface, whereby the obtained twist angle ⁇ can be averaged. In addition, the method can be extended to lines 4 with locally non-constant slope.
• the twist structure 3 can be scan by means of a helical line 4, the helix, as illustrated in FIG. 6, again having a peripheral component 5 and an axial component 6. From the phase offset of the ripples of the individual turns 22, 23, the sign of the twist angle ⁇ can be determined. Thus, it is first determined whether the line 4 and the twist structure 3 are arranged the same or in opposite directions. Furthermore, it can be assumed that the number of wave crests and troughs on one turn, for example winding 22, is equal to the sum of the wave crests and wave troughs that would appear on the perimeter component 5 and on the axial component 6 when measured would. With the aid of the previously determined phase offset between the ripples of adjacent turns 22, 23, the twist angle ⁇ can also be determined. The determination of the
• Phase offset is particularly simple if the distance between the windings 22, 23, unlike in FIG. 6, is so small that the sampling theorem is satisfied, ie the phase offset between adjacent turns is less than a wavelength measured along the line 4 cut twist structure 3 is.
• the phase offset may possibly be determined by a correlation analysis of the course of the Measured values between adjacent windings 22, 23 are determined.
• FIG. 7 illustrates a simple device 24 for carrying out the above-described measurement.
• the device 24 has, for example, a device for rotating the workpiece in the form of a turntable 25 and a positioning device 26, with which a pushbutton 27 is rotatable at least in the direction of the rotation axis predetermined by the turntable 25, which coincides with the axis 2.
• the button 27 may for example be a mechanical button, as it is known as roughness button.
• the probe 27 is, for example, a mechanical probe with a diamond needle, the tip of which has a radius of curvature which is smaller than the width of the grooves to be scanned.
• optical buttons 27 are used, as schematically illustrated in FIG. 8 or FIG.
• the probe 27 according to FIG. 8 is designed as a white light interferometer. It has a light source 28 with a short coherence length, which illuminates the workpiece surface 33 via an optical path, for example consisting of optical fibers 29, 30, 31, and an objective 32. Fiber couplers 34, 35 provided in the light path connect a reference light path 36 and an interferometer 37. In the interferometer measuring light beam and reference light beam are superimposed and projected for example via a cylindrical lens 38 to a linear sensor 39. An evaluation device 40 evaluates the resulting interference pattern. Its position is a measure of the distance of the objective 32 from the respectively probed point of the workpiece surface 33.
• FIG. 9 illustrates the probe 27 in its embodiment, for example as a confocal microscope. In the illustrated advantageous embodiment, it operates with increased depth of field by utilizing multi-color light and a lens 42 with high chromatic aberration. On the optical axis 42 there is a focal line with a sequence of colored foci.
• An evaluation device with a color analyzer is connected to the light path via the phaser coupler 34. This can, as schematically illustrated, for example, consist of a prism 43 and a connected line sensor 44, which is connected to the evaluation device 40.
• the light of the color whose focal point lies on the workpiece surface 33 is reflected back into the probe 27 and deflected by the prism 43 in accordance with the light color.
• the line sensor 44 for example a line camera, thus receives light only on one or more pixels, the center of the illuminated spot being a measure of the distance between the workpiece surface 33 and the objective 41.
• buttons 27 of Figure 8 and 9 work quickly, so that the workpiece along the line 4 can be scanned at high speed. It can be measured in a short measuring time of a few seconds to minutes large parts of the workpiece surface. The measurement provides not only the helix angle ⁇ and possibly the number of gears z but also, if necessary, the depth of the swirl structure 3, measured in the direction of the R coordinate.
• FIG. 11 illustrates an adaptive strategy for defining a line 4 for scanning the workpiece and optionally for swirl detection.
• the strategy in the simplest case, assumes that there is a line 4 that is best suited for the complete scan of the spin. This line can be, for example, a helical line whose inclination can be set adaptively.
• the variation can be done by the pitch angle is increased, for example, gradually.
• the measurement can then be continued and completed at the pitch angle at which the sought twist parameters can best be calculated.
• Fig. 11 illustrates an adaptive strategy for defining a line 4.
• Stage 1 consists of two generatrices (vertical in the upper left partial image) and two circular lines (horizontal in the upper left partial image).
• the measuring program determined in a second stage (top center) from these measurements, the dominant ripples. If these are the same, the three parameters can be calculated. If not, a refinement measurement is performed in a third step (top right). In this case, at least one preferably two further generatrices are measured between the two already measured generatrices. In addition, a further preferably approximately centrally located between the two circular lines line can be measured. In a fourth step (bottom right) it is checked whether the determined dominant ripples are the same. If yes, the spin parameters are calculated.
• step 5 a further refinement measurement is carried out in step 5 by carrying out measurements on further generatrices and circular lines. Again, the dominant ripples on all lines (circles and generatrices) are determined and, if they are equal, the swirl parameters are calculated. If not, the program can abort and issue a corresponding error message.It is also possible to carry out a further refinement according to the above scheme until finally a valid measurement is reached.
• the measurements carried out in the different stages 1, 3 and 5 and optionally further refined measuring stages can be carried out with a constant uniform measuring point distance. It is also possible to reduce the measuring point distances from stage to stage in order to increase the probability of obtaining a valid, precise measurement with as few scanning lines as possible.
• Another adaptive measurement strategy is illustrated in FIG. It is a combined helix measurement with adaptive strategy.
• the axis of a reference cylinder is calculated. Then, in the step “Computational centering of the ith circle on the cylinder axis”, the measured circles are then centered on the cylinder axis by calculation, then in the step “Computational unwinding of the ith circle in the first surface line” the measured circles and Generating generatrices in a plane, as shown for example in Figure 11 in step 1, 3 or 5. Then a dominant waviness is determined in the step “Extract WD 1 -PrOfH from the i-th generatrix.” In the step “wavelength WDSm 1 associated wavenumber f ⁇ ", the associated wavelength is determined for each circular line i and each associated generatrix ,
• the axis of the reference cylinder is recalculated (optional) and each surface line is aligned accordingly in the step "Computational alignment of the i-th generatrix parallel to the cylinder axis" between the surface line and the cylinder axis with slightly conical workpieces that could otherwise lead to measurement errors or overflows in corresponding measuring devices or calculation programs.
• the step “Extract WD 1 -PrOfU from i-th line” from each generating line the WD Profile extracted. From this, the wavelength is determined for each jacket length in the step "wavelength WDSm 1 ".
• the most frequently occurring wavelengths are now determined from the wavelengths determined on the circular lines and on the surface lines.
• the method is self-adaptive because it automatically determines the wavelength based on the circular scan line and the cladding scan line. Whether the wavelength is determined on the basis of the circle lines or on the basis of the measured value group originating from the generatrix lines or on the basis of both groups of measured values results automatically.
• the Am- plitude and the phase of the wavelength WDSm, the twist depth, the workpiece diameter, the workpiece circumference, etc. are calculated.
• the measuring method according to FIG. 12 described so far can be integrated into the adaptive strategy according to FIG. 11 as a measuring method. It is also not limited to the measurement on circular lines and surface lines. Rather, it can also be performed on line sections that have different pitch angles.
• the evaluation can be carried out not only for the existing ripple of first dominance but also for the possibly present ripple of second dominance, with which the spin parameters can be determined not only for the first dominance but also for the second dominance. If, however, the dominant wavelength WDSm of the individual generatrices is not the same, no twist can be detected.
• the workpiece surface is preferably moved along a helical line of small pitch by coordinated measuring movement with a rotating component (peripheral component) and a linear component (axial component).
• a rotating component peripheral component
• a linear component axial component
• measuring points on the workpiece surface are detected in three dimensions.
• the probing of the workpiece surface can be done mechanically or without contact. The measurement allows in a simple, robust and safe way the determination of the swirl characterizing quantities including also the depth of the swirl structure 3 to be measured.

Landscapes

• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)
• Length Measuring Devices By Optical Means (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=37898513

Family Applications (1)

Country Status (2)

Cited By (1)

Families Citing this family (1)

Family Cites Families (4)

• 2006
  • 2006-01-12 DE DE200610001799 patent/DE102006001799B4/de not_active Expired - Fee Related
• 2007
  • 2007-01-11 WO PCT/EP2007/000201 patent/WO2007082669A2/fr not_active Ceased

Also Published As

Similar Documents

Legal Events