MEASUREMENT OF CHARACTERISTIC VARIABLES OF A PRECISION MACHINING TOOL

Abstract

The invention relates to a machine for the precision machining of toothed workpieces, which machine comprises a tool spindle (30) for mounting a precision machining tool (31). The tool spindle can be driven to rotate about a tool spindle axis (B) by means of a tool spindle drive (32). A control device (70) takes at least one measurement of the distance from the precision machining tool (31) by means of a distance sensor (60) and, on the basis of said measurement(s), determines at least one characteristic variable of the precision machining tool, in particular the outer diameter thereof. The distance sensor can operate optically in particular.

Claims

1. A machine for finishing toothed workpieces, comprising: a tool carrier; a tool spindle for chucking a finishing tool, the tool spindle being attached to the tool carrier; a tool spindle drive for driving the tool spindle so as to rotate about a tool spindle axis; at least one distance sensor; and a control device configured to carry out, by means of the distance sensor, at least one distance measurement from a finishing tool chucked on the tool spindle and to determine, from the distance measurement, a characteristic parameter of the finishing tool.

2. (canceled)

3. The machine as claimed in claim 1, wherein the distance sensor is a distance sensor that operates in an optical manner and which is configured for generating a measuring light beam.

4. (canceled)

5. (canceled)

6. The machine as claimed in claim 1, wherein the distance sensor is a sensor that operates in a contacting manner, the distance sensor being spring-biased.

7. The machine as claimed in claim 1, wherein the control device is configured to determine a measure for the external diameter of the finishing tool from the at least one distance measurement.

8. The machine as claimed in claim 7, wherein the control device is configured to actuate the tool spindle drive in such a manner that the tool spindle rotates at a rotating speed that is variable as a function of the determined external diameter.

9. The machine as claimed in claim 7, wherein the control device is configured to actuate the tool spindle drive in such a manner that the tool spindle maintains a maximum permissible rotating speed that is variable as a function of the determined external diameter.

10. (canceled)

11. The machine as claimed in claim 1, wherein the control device is configured to carry out, by means of the distance sensor, distance measurements for a multiplicity of positions along the tool spindle axis and for a multiplicity of rotation angles of the finishing tool so as to obtain an image of a surface region of the finishing tool, and wherein the control device is configured to identify deviations of the obtained image of the surface region from an anticipated appearance of the surface region.

12. (canceled)

13. (canceled)

14. The machine as claimed in claim 1, wherein the distance sensor comprises a line laser which defines a beam plane.

15. The machine as claimed in claim 14, wherein the tool spindle and the distance sensor are arranged to be capable of being mutually aligned in such a manner that the beam plane contains the tool spindle axis so as to carry out simultaneous distance measurements for a multiplicity of positions along the tool spindle axis.

16. The machine as claimed in claim 1, wherein the control device is configured to compare at least one determined characteristic parameter with one or a plurality of comparative characteristic parameters and to identify inconsistencies.

17. (canceled)

18. (canceled)

19. The machine as claimed in claim 1, wherein the tool carrier is movable, in particular pivotable, about an axis so as to align the tool spindle in relation to the distance sensor.

20. The machine as claimed in claim 1, wherein the machine comprises a housing in which the distance sensor is received, wherein the housing has a window opening for the distance sensor, and wherein, for protecting the distance sensor against environmental influences, the window opening is closable by a closing device, and/or the interior of the housing is configured to be supplied with sealing air.

21. A method for measuring a finishing tool which is chucked on a tool spindle of a finishing machine such that the finishing tool can rotate about a tool spindle axis, the method comprising: carrying out at least one distance measurement from the finishing tool using a distance sensor; and determining at least one characteristic parameter of the finishing tool from the at least one distance measurement.

22. The method as claimed in claim 21, wherein the distance sensor is a distance sensor that operates in an optical manner and generates a measuring light beam, and wherein the method comprises aligning the measuring light beam to the finishing tool.

23. (canceled)

24. The method as claimed in claim 21, wherein a measure for the external diameter of the finishing tool is determined as the characteristic parameter.

25. The method as claimed in claim 24, further comprising: driving the tool spindle at a rotating speed that varies as a function of the determined external diameter.

26. The method as claimed in claim 24, further comprising: monitoring whether the tool spindle is driven at a rotating speed that is lower than a maximum permissible rotating speed, the maximum permissible rotating speed being variable as a function of the determined external diameter.

27. (canceled)

28. The method as claimed in claim 21, wherein a distance measurement is carried out for a multiplicity of positions along the tool spindle axis and for a multiplicity of rotation angles of the finishing tool so as to obtain an image of at least one region of the surface of the finishing tool, and wherein deviations between the obtained image of the surface region and an anticipated appearance of the surface region are determined.

29. (canceled)

30. (canceled)

31. The method as claimed in claim 21, wherein the distance sensor comprises a line laser which defines a beam plane, and wherein the method comprises: mutually aligning the tool spindle and the distance sensor in such a manner that the beam plane contains the tool spindle axis, and carrying out distance measurements for a multiplicity of positions along the tool spindle axis.

32. The method as claimed in claim 21, wherein the method comprises: comparing at least one determined characteristic parameter with one or a plurality of comparative characteristic parameters so as to identify inconsistencies.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Preferred embodiments of the invention will be described hereunder by means of the drawings which serve only for explanatory purposes and are not to be interpreted as limiting. In the drawings:

[0045] FIG. 1 shows a schematic view of a finishing machine according to a first embodiment;

[0046] FIG. 2 shows an enlarged detailed view of the machine of FIG. 1, wherein the rotary turret has been pivoted by 90 in relation to FIG. 1;

[0047] FIG. 3 shows the detailed view of FIG. 2 in a partially sectional manner;

[0048] FIG. 4 shows a schematic diagram for highlighting the interaction between the distance sensor and the CNC controller;

[0049] FIG. 5 shows a schematic diagram for highlighting the beam direction of the distance sensor relative to the workpiece spindle axis;

[0050] FIG. 6 shows a schematic diagram for highlighting the measurement of a grinding worm by way of a single distance sensor;

[0051] FIG. 7 shows a schematic diagram for highlighting the measurement of a grinding worm by way of two distance sensors mutually disposed at an angle;

[0052] FIG. 8 shows a schematic view of a finishing machine according to a second embodiment;

[0053] FIG. 9 shows an enlarged fragment from FIG. 8;

[0054] FIG. 10 shows a schematic view of a finishing machine according to a third embodiment; and

[0055] FIG. 11 shows the finishing machine of FIG. 10 in a position in which the tool carrier has been pivoted to a measuring position.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0056] A finishing machine for the hard finishing of gear wheels by generating grinding is illustrated in FIG. 1. The machine comprises a machine bed 10 on which a tool carrier 20 is disposed so as to be displaceable along a horizontal actuating direction X. A Z slide 21 is disposed on the tool carrier 20 so as to be displaceable along a vertical direction Z. A Y slide 22 is disposed on the Z slide 21, said Y slide 22 in relation to the Z slide 21 being pivotable about a pivot axis A parallel to the X axis, on the one hand, and displaceable along a shifting direction Y, on the other hand. The Y slide 22 carries a tool spindle 30 on which a finishing tool in the form of a grinding worm 31 is chucked. The tool spindle 30 comprises a tool spindle drive 32 so as to drive the grinding worm 31 for rotation about a tool spindle axis B.

[0057] A pivotable carrier in the form of a rotary turret 40 is disposed on the machine bed 10. The rotary turret 40 is pivotable about a vertical axis C3 between a plurality of rotary positions. Said rotary turret 40 carries two workpiece spindles 50 on which one workpiece 51 can in each case be chucked. Each of the workpiece spindles 50 can be driven for rotation about a workpiece spindle axis. The two workpiece spindles on the rotary turret are situated in diametrically opposite positions (that is to say so as to be offset by 180 in terms of the pivot axis of the rotary turret). In this way, one of the two workpiece spindles can be loaded and unloaded while a workpiece is being machined by the grinding worm 31 on the other workpiece spindle. Undesirable downtimes are largely avoided on account thereof. A machine concept of this type is known, for example, from WO 00/035621 A1.

[0058] A dressing device 80 which in FIG. 1 is situated on the rear side of the rotary turret 40 and therefore cannot be seen in the illustration of FIG. 1 is disposed on the rotary turret so as to be offset by, for example, 90 in relation to the workpiece spindles.

[0059] A distance sensor 60 is disposed on the rotary tower 40 so as to be diametrically opposite the dressing device and thus likewise offset by, for example, 90 in relation to the workpiece spindles. Said distance sensor 60 in the present example is an optical distance sensor. Said distance sensor 60 is protected against contaminations by a casing 41. In order to enable measurements using the distance sensor 60, the casing 41 has a window opening 42 which can optionally be closable by a slide or a flap. In order for the distance sensor 60 to be protected against contaminations, it is advantageous for the interior of the casing 41 to be supplied with sealing air (that is to say with air at some positive pressure in relation to the ambient pressure) such that an airflow is created through the window opening 42. The airflow sweeps across the distance sensor 60 and prevents contamination such as, for example, oil droplets accumulating on the distance sensor 60.

[0060] The machine comprises a CNC controller 70 which comprises a plurality of control modules 71 as well as an operator panel 72. Each of the control modules 71 actuates one machine axis and/or receives signals from relevant sensors. In the present example, one of the control modules 71 is provided for interacting with the distance sensor 60. Said module communicates with the internal controller of the distance sensor 60 and processes the measuring results of the distance sensor 60. The internal controller of the distance sensor 60 and the control module 71 interacting therewith conjointly form a control device in the context of this document.

[0061] An enlarged portion of the machine of FIG. 1 is illustrated in FIG. 2. FIG. 3 shows the same portion in a partially sectional manner, in which part of the casing 41 has been cut away so as to allow the view onto the distance sensor 60 in the interior of the casing 41. The rotary turret in this illustration, in relation to the orientation of FIG. 1, is pivoted about, for example, 90 about the vertical pivot axis C3 of said rotary turret, such that the distance sensor 60 is now situated opposite the grinding worm 31. The distance sensor 60 herein is aligned such that the beam direction of the measuring light beam emitted by said distance sensor 60 intersects the tool spindle axis B in a perpendicular manner.

[0062] FIG. 4 once again highlights the interaction of the distance sensor 60 and the corresponding control module 71.

[0063] The disposal of the distance sensor 60 relative to the grinding worm 31 is illustrated in FIGS. 5 and 6. It can be seen that the measuring light beam 61 runs horizontally and is aligned so as to be perpendicular to the rotation axis of the grinding worm, that is to say to the tool spindle axis B. However, the following alternative arrangements of the distance sensor are also conceivable: [0064] The measuring light beam 61 does not need to be aligned horizontally to the axis B. [0065] The measuring light beam 61 does not need to be aligned directly to the axis B. [0066] The measuring light beam 61 does not need to run so as to be perpendicular to the axis B. [0067] The measuring light beam 61 can in particular be aligned so as to be approximately parallel to the B axis and thus impact the tool laterally; the diameter of the tool in this instance can be determined in that it is established at which radial position of the distance sensor an abrupt distance variation is measured. [0068] The measuring light beam 61 can impact a reflector which is disposed behind the tool. [0069] The measurement can also be performed using two sensors which act as a transmitter and a receiver, respectively.

[0070] The measuring principle of the optical distance sensor is as follows. The measuring light beam 61 generated by the distance sensor 60 impacts the surface of the measured object (here the grinding worm 31) and from there is reflected in a diffused manner back to the distance sensor. The reflected beam is detected by the distance sensor 60, and the spacing between the distance sensor 60 and the surface of the measured object is calculated by the internal controller of the distance sensor 60 from the properties of the reflected beam.

[0071] Various operating modes for distance sensors of this type are known from the prior art.

[0072] According to a first known operating mode, a runtime measurement is performed. To this end, the excitation light of the measuring light beam is modulated by high-frequency, and the phase shift between the reflected light detected by the distance sensor and the excitation light is measured, said phase shift resulting from the runtime of the light. The runtime and therefrom the distance of the distance sensor from the measured object are derived from the phase shift.

[0073] According to a second known operating mode, the distance measurement is based on the triangulation method. In the case of this method, the measuring light beam is focused on the measured object, and the light spot created is observed by a camera that is disposed in the distance sensor so as to be laterally offset in relation to the light source (for example a camera having a line sensor). The angle at which the light spot is observed varies as a function of the distance of the measured object, and the position of the image of the light spot on the sensor of the camera varies correspondingly. The distance of the measured object from the distance sensor is calculated with the aid of trigonometric functions.

[0074] The same measuring principle can also be used for determining a distance profile along an axis on the surface of the measured object. The distance sensor in this instance is also referred to as a profile scanner. For measuring, a laser beam by way of a special optical system is widened so as to form a fan which generates a bright line on the measured object. The reflected light of this laser line is reproduced on a sensor matrix. For each point of the laser line on the image created on the sensor matrix, the distance is calculated, on the one hand, and the position along the laser line, on the other hand. A distance profile along the laser line is determined in this way.

[0075] Alternatively, the profile of the tool can also be determined using a spot laser and a relative movement of the tool in the axial direction in relation to the sensor.

[0076] Suitable distance sensors which operate according to one of the principles mentioned are commercially available. More detailed explanations pertaining to the distance sensors that can be used can therefore be dispensed with. Measuring accuracies in the range of 10 micrometers or better are achievable for the measured distances.

[0077] When a rotation of the tool about the tool spindle axis additionally takes place, an image of the entire tool surface can be obtained.

[0078] When the position of the distance sensor 60 relative to the tool spindle axis B is known and when the grinding worm rotates, the external diameter d of the grinding worm 31 can be determined from the measured minimal distance over a period of rotation. Moreover, further characteristic parameters such as, for example, the number of starts, the angular position, and the depth, of the grinding worm threads can be determined.

[0079] Said angular position can be utilized for correctly threading the dressing tool or a workpiece into the grinding worm threads.

[0080] A consistency test, or a coincidence test, can be carried out for the characteristic parameters determined. To this end, the characteristic parameters determined are compared with comparative characteristic parameters which have previously been stored in the CNC controller of the machine. Where deviations exist, the operator can be alerted thereto by way of suitable signals.

[0081] An image of the entire surface, or of a specific region of the surface, of the grinding worm 31 can be established when required with the aid of the distance sensor 60. To this end, a distance profile parallel to the tool spindle axis B can be established along the worm width b for a multiplicity of rotation angles of the grinding worm 31 about the tool spindle axis B, for example. In order for such a distance profile to be established, the distance sensor can be configured as a profile scanner as has been explained above, and/or the grinding worm 31 with the aid of the Y slide can be displaced relative to the distance sensor 60 along the tool spindle axis B.

[0082] Further characteristic parameters, for example characteristic parameters which describe the shape of the flanks of the grinding worm threads, can be determined from such an image of a surface region.

[0083] With the aid of an image of the surface, or of a surface region, of the grinding worm it can in particular also be checked whether the grinding worm is damaged, for example whether so-called grinding worm breakouts are present. In the case of a flawless grinding worm it is anticipated that the image of the surface region has very specific properties. It is thus anticipated, for example, that the external diameter of the grinding wheel does not abruptly vary along each grinding worm thread but represents a constant or an only gradually variable, consistent function of the rotation angle. However, in the case of a breakout on a worm wheel thread, an abrupt variation arises in the external diameter. A deviation of this type of the image of the surface region from an anticipated appearance can be readily identified in an automatic manner; corresponding algorithms for identifying patterns are known per se. Damage such as grinding wheel breakouts can be automatically identified in this way. In the case of the presence of such damage, the operator can be correspondingly warned, for example by the emission of an acoustic and/or visual alarm signal. Furthermore, the CNC controller 70 by means of special software can in a self-acting manner generate a start signal for automated procedures for damage limitation during grinding and dressing. For example, when only a small grinding wheel breakout has been identified in the peripheral region, the machining by grinding can potentially also be continued without compromising quality by renewed automatic dressing.

[0084] FIG. 7 illustrates that two or more distance sensors 60, 60 can also be used instead of a single distance sensor. In particular, the measuring light beams of said distance sensors can impact the finishing tool at a mutual angle, as is shown in FIG. 7. The measuring light beams 61, 61 of the two distance sensors 60, 60 in this figure are aligned to the tool spindle axis B but do not run so as to be perpendicular to the tool spindle axis, but at an angle of, for example, 1 to 20 in relation to the normal of the plane of said tool spindle axis. On account thereof, the flanks of the grinding worm threads can in particular be more precisely measured than when only a single measuring light beam which impacts the tool perpendicularly to the tool spindle axis is used.

[0085] A second embodiment of a finishing machine is illustrated in FIGS. 8 and 9. Said second embodiment comprises a contacting sensor 60. The sensor 60 in the present example measures the external diameter of a grinding worm 31. To this end, the sensor 60 defines a wide bearing surface which is wider than the distance of neighboring grinding worm threads. It is ensured on account thereof that the sensor 60 always bears on the external diameter of the grinding worm. The construction largely corresponds to the construction of the machine of FIG. 1. By contrast to the machine of FIG. 1, the distance sensor 60 however protrudes from the window opening 42 of the casing 41 so as to be able to be brought into contact with the surface of the finishing tool. The sensor in this embodiment can optionally be designed so as to be retractable and deployable in an automated manner such that said sensor when required can be deployed from the window opening 42. A closure for the window opening can also be provided here for the protection of the distance sensor, and/or it can be provided that the interior of the casing 41 is supplied with sealing air.

[0086] A third embodiment of a finishing tool is illustrated in FIGS. 10 and 11. Only a single workpiece spindle 50 which is disposed so as to be locationally fixed on the machine bed 10 is present in this embodiment. The entire tool carrier 20 is pivotable about a vertical axis (the so-called C1 axis) to various positions in relation to the machine bed 10, and as in the first embodiment is displaceable radially in relation to the workpiece spindle 50 along the so-called X axis. The tool spindle 30, as in the first embodiment, is displaceable in relation to the tool carrier 20 along a vertical Z axis and in the Y direction along the workpiece spindle axis, and pivotable about a horizontal axis (so-called A axis). The grinding worm in the machining position of FIG. 10 can be brought to engage with the workpiece. The tool carrier 20 in relation to this machining position can be pivoted about the C1 axis by, for example, 180. In this dressing position (not illustrated in the drawing) the grinding worm can be dressed by a dressing device 80. A machine having such a machine concept is known from DE 196 25 370 C1, and reference is made to said document for further details.

[0087] The distance sensor 60 in this embodiment is attached in a locationally fixed manner to the machine bed 10 with the aid of a holder 62. In the position of FIG. 11, the tool carrier 20 has been pivoted so far until the distance sensor 60 is opposite the grinding worm 31. The grinding worm 31 in this position can be measured by the distance sensor 60.

[0088] The invention is not limited to the above exemplary embodiments. Rather, it becomes obvious from the above description that a multiplicity of modifications are possible without departing from the scope of the invention. In particular, a profile grinding wheel, a combination of grinding worm and profile grinding wheel, or any other type of finishing tool can be used instead of a grinding worm in all embodiments. The distance sensor can also be disposed on a displaceable slide instead of a pivotable rotary turret, as is the case in the first and second embodiments, wherein said slide can carry one or two workpiece spindles. It is also conceivable that the workpiece carrier is not pivoted toward the distance sensor, as is the case in the third embodiment, but that the workpiece carrier is displaced toward the distance sensor.

TABLE-US-00001 LIST OF REFERENCE SIGNS 10 Machine bed 20 Tool carrier 21 Z slide 22 Y slide 30 Tool spindle 31 Grinding worm 32 Tool spindle drive 40 Rotary turret 41 Casing 42 Window opening 50 Workpiece spindle 51 Workpiece 60 Distance sensor 61 Measuring light beam 62 Sensor holder 70 CNC controller 71 Control module 72 Operator panel 80 Truing apparatus X, Y, Z Machine axes A Pivot axis of tool B Tool spindle axis C1 Pivot axis of tool carrier C3 Pivot axis of rotary turret b Worm width d External diameter