Device and method for checking bores in or edges on an object of measurement

A method for checking bores in or edges on an object of measurement, and in particular for recognizing burrs. A prepared object of reference is scanned with a distance sensor in correlation with scanning the prepared object of reference with another distance sensor. The measurement signals of the two distance sensors are then compared.

The present disclosure relates to the subject matter disclosed in German patent application No. 102 32 131.0 of Jul. 11, 2002, which is incorporated herein by reference in its entirety and for all purposes.

BACKGROUND OF THE INVENTION

The invention relates to a device and a method for checking bores or edges and, in particular, for recognizing burrs in or on an object of measurement.

Burrs can occur where workpieces are machined and chips are thereby removed from the material of the workpieces. For example, burrs can occur on bores or edges. Burrs can cause a disturbance for a number of reasons. There should, for example, be no burrs at interfaces which are to be sealed as this would influence the sealing effect. It may be desirable for there to be no projection of material on workpieces. The presence of burrs which drop off during component assembly can be a nuisance. If they fall off during operation of a unit, this can destroy it. Burrs at the edges of the material of a workpiece to be coated can result in irregular paint densities. Sharp-edged burrs on outer workpiece surfaces can cause injury due to cuts.

It is, therefore, often necessary to make a check for burrs after the machining of the workpiece, and this may involve two aspects, namely a qualitative burr check as to whether burrs are present and a quantitative check as to whether, for example, a certain tolerance for the height of a burr is exceeded.

A sensor device for checking burrs, which is universally employable in a simple way, is described in German patent application No. 101 03 177.7, which corresponds to the U.S. patent application Ser. No. 047,447 on Jan. 14, 2002 and belongs to the applicant of the present application. These patent applications are not previously published.

SUMMARY OF THE INVENTION

In accordance with the present invention, a device for checking bores in or edges on an object of measurement, in particular, for recognizing burrs, which can be used in a simple way, is provided.

This is accomplished in accordance with the invention by a first distance sensor with a detector head being provided, the detector head being positionable at a distance from the object of measurement and detector head and object of measurement being movable relative to one another, the detector head coupling electromagnetically with the object of measurement or the object of measurement being able to be acted upon with an electromagnetic signal by the detector head, and the coupling with the object of measurement or an electromagnetic reaction signal of the object of measurement to the signal acting upon it being a function of a distance between detector head and object of measurement so that this distance is determinable in a contact-free manner, and a surface of the object of measurement being scannable by the detector head in a contact-free manner, a second distance sensor with a detector head also being provided, by means of which an object of reference is scannable in correlation with the first distance sensor, and a comparator being provided for comparing the measurement signals of the first distance sensor and the second distance sensor so that the object of measurement is characterizable in relation to the object of reference.

Owing to the inventive use of a distance sensor as a separate component, with this distance sensor interacting with the workpiece and the interaction depending on the distance between distance sensor and workpiece, a surface examination of a bore or edge, in particular, as burr check, can be carried out in a simple way. The distance sensor forms a sensor field which couples locally with the workpiece. As a result, inner workpiece surfaces (i.e., also bore surfaces) can also be checked when the distance sensor is inserted accordingly into the workpiece. The checking is carried out without any contact being made and so simple and, in particular, also mechanical use is enabled.

Owing to the object of measurement and an object of reference being scanned in a correlated manner, a deviation between object of measurement and object of reference can be deduced in a simple way, for example, from a difference between measurement signals of the two distance sensors. If the object of reference is ideally prepared, a difference then means that the object of measurement contains a flaw. It can then be determined from the height of the differential signal, for example, whether the object of measurement is still usable or has to be eliminated from the production process, i.e., lies beyond a tolerance range.

With the inventive device, a quick and simple examination of objects of measurement can be carried out, for example, in series production, and automation of this examination with respect to the evaluation is also possible.

Aside from burrs, other deviations in relation to the prepared bores in the object of reference are also recognizable, for example, deviations in shape or deviations in dimension.

In particular, provision is made for the first distance sensor and the second distance sensor to be of essentially the same design so as to enable a simple comparison to be made between object of measurement and object of reference.

Further provision is made for first distance sensor and second distance sensor to be coupled to one another in a fixed distance relationship and/or angular relationship during a checking procedure. For example, for linear displacement of the second distance sensor with respect to the object of reference there should be a rigid coupling with the first distance sensor. A correlated or synchronized movement of the two distance sensors is thereby automatically ensured. If a rotational movement of the second distance sensor relative to the object of reference is carried out, then a rotational movement of the first distance sensor relative to the object of measurement should also be correlated with the first aforementioned rotational movement.

A guide device is advantageously provided for guidance of the second distance sensor relative to the object of reference in a defined manner, and, in particular, for linearly displaced guidance thereof relative to the object of reference and/or for rotation relative thereto. Depending on the use, the guide device may be designed such that a linear displacement is permitted only in one direction, only in one plane or in all three spatial directions.

In particular, the first distance sensor then follows the guidance of the second distance sensor so that the object of measurement is scannable in a guided manner.

It is particularly advantageous for the object of reference to be prepared so that it represents the ideal case, and any deviation from the object of reference constitutes the detection result.

In particular, the comparator forms a differential signal for the measurement signals of the first distance sensor and the second distance sensor. A direct comparison can thus be made in a simple way so as to be able to characterize the measurement result on the object of measurement relative to the object of reference. If the differential signal has an immeasurably small value this means that there are no differences between object of measurement and object of reference in the measured range. If the differential signal has a finite value, then corresponding differences were detected. Conclusions can then also be drawn about the origin of this difference from the absolute value of the differential signal, for example, whether it is a burr and what type of burr it is.

In particular, provision is then made for the comparator to comprise a threshold value switch for inhibiting noise signals and the like with respect to formation of the difference or for rejecting signals below a tolerance threshold as insignificant.

It is particularly expedient for the first distance sensor and the second distance sensor or a first distance sensor combination and a second distance sensor combination, which comprise the first distance sensor and the second distance sensor, respectively, and at least one further distance sensor, and with which the object of measurement and the object of reference, respectively, is scannable, to comprise a plurality of areas of sight. Via this plurality of areas of sight, an alignment and, in particular, a coaxial alignment of a distance sensor or a distance sensor combination in a bore can, for example, be checked, and, where necessary, readjusted. Moreover, such a plurality of areas of sight is suitable for enabling exact characterization, in particular, with respect to absolute evaluation. Furthermore, a larger surface area can be simultaneously scanned, with the result that a checking procedure can be carried out faster.

It is advantageous for an area of sight, in particular, of the first distance sensor or the first distance sensor combination to be arranged so as to point in a direction in which the distance sensor or distance sensor combination is displaceable towards the object of measurement. As a result, a warning signal can be generated if there is a danger of collision with the object of measurement, and this can be thereby avoided. Such dangers of collision exist, for example, if a bore is not drilled to a sufficient depth.

Furthermore, it is expedient for areas of sight to be arranged such that the same surface area of the object of measurement and the object of reference is scannable upon linear movement of the first distance sensor and the second distance sensor, respectively, or of the first distance sensor combination and the second distance sensor combination, respectively. If the areas of sight are of different configuration, for example, with respect to the electromagnetic coupling to the corresponding object, an absolute statement can then also be made regarding the distance from the object of measurement and the object of reference, respectively, by way of the respective area of sight and the measurement signals associated therewith, and, in particular, when a difference is formed.

Provision may also be made for areas of sight to be arranged such that an identical surface area of the object of measurement and the object of reference, respectively, is scannable upon rotational movement of the first and the second distance sensor, respectively, or the first and the second distance sensor combination, respectively. This covers the special case where areas of sight face opposite surfaces of a bore. With corresponding measurement signals associated with the areas of sight, an alignment of a distance sensor or a distance sensor combination within a bore can then be carried out so as to achieve, for example, an ideal coaxial guidance with a high degree of precision.

Provision may be made for one or several areas of sight to be externally or internally selectable for optimum adaptation of the measurement to a use.

It is particularly advantageous for a distance sensor or a combination of several distance sensors to be designed as a probe which is insertable into a bore. Such a bore can thereby be scanned so to able to check the bore, in particular, for burrs.

In practice, it is of importance for object of measurement and object of reference to be made of a metallic material. Engine blocks, for example, which have a large number of bores, are a typical example of use.

It is advantageous for the first and the second distance sensor to be an inductive sensor which couples inductively with the object of measurement and the object of reference, respectively. Such an inductive sensor couples electromagnetically with a metallic material. This enables advantageous measurement of distances from a workpiece, and a measurement is insensitive to contaminations such as oil, as the inductive coupling remains substantially uninfluenced thereby insofar as the contamination is non-metallic.

To provide a plurality of areas of sight on a sensor, an inductive sensor advantageously comprises a plurality of coils. A coil then supplies a corresponding measurement signal, and quantitative statements regarding distances can then be determined with a high degree of accuracy, for example, from the difference between such measurement signals of various coils. This difference evaluation can be carried out internally in the inductive sensor.

A further object underlying the invention is to provide a method for checking bores in or edges on an object of measurement, and, in particular, for recognizing burrs, which enables bores to be checked in a simple and accurate way.

This object is accomplished in accordance with the invention by a prepared object of reference being scanned by a distance sensor and by the object of measurement then being scanned in correlation therewith by a further distance sensor and by a comparison being made of the measurement signals of the two distance sensors.

The inventive method has the advantages set forth hereinabove in conjunction with the inventive device.

Further advantageous embodiments have also been explained hereinabove in conjunction with the inventive device.

The following description of preferred embodiments serves to explain the invention in greater detail in conjunction with the drawings.

DETAILED DESCRIPTION OF THE INVENTION

When a workpiece and, in particular, a metallic workpiece is machined with a chip-removing tool, in particular, a metal-cutting tool, burrs can form on outer and inner surfaces, such as bore intersections, or at edges of the workpiece. This is shown schematically inFIGS. 1atocfor bores.

One differentiates between various types of burr: The so-called burr of burr type1, generally designated10inFIG. 1a, is formed as a simple burr in the shape of a circumferential edge elevation, with the height of the burr exceeding 0.15 mm. A burr of burr type2is also a simple burr with a burr height of approximately 1.1 mm.

A burr of burr type3, generally designated12inFIG. 1b, is also referred to as a crown burr because a circumferential edge14of this burr is of jagged configuration. The height of the burr of burr type3is approximately 0.65 times the diameter of the bore16in the workpiece18, on which the burr is formed.

A burr of burr type4is a simple burr having a bore cap suspended from the workpiece (not shown in the drawings). In a burr of burr type5, generally designated20inFIG. 1c, the circumferential edge22is very irregular in its height and protuberances24are formed, but—in contrast to the burr of burr type3—these are not distributed around the entire edge22of the burr20.

In accordance with the invention, a device for checking bores and workpieces, in particular, their edges, is provided (FIG.5), with which it is possible to detect whether a burr is actually formed on a surface of an object of measurement. In particular, quantitative statements regarding a burr are also obtainable with the inventive device, for example, what dimensions it has or what type of burr it is. By corresponding measurement of the object of measurement various important items of information are then obtainable for the further processing of the object, such as, for example, whether subsequent machining is required for removal of a burr or reduction of the size of a burr. With a series of workpieces, examination of a tool may also be carried out by the change in the burr within the series of workpieces being monitored over time: For example, the blunting of a drilling tool may be determined from the type of burr formation on bore edges.

Furthermore, bores can be checked with respect to their dimensions or edges with respect to their accuracy.

FIG. 2shows schematically an embodiment of a first distance sensor, generally designated26therein, comprising a detector head30. The detector head30has an active surface32, via which it can electromagnetically couple with a workpiece34as object of measurement. The coupling is determined by a distance36between the active surface32of the detector head30and the workpiece34.

In the embodiment shown inFIG. 2, the distance sensor26is an inductive proximity sensor which inductively couples via the generation of eddy currents with the workpiece34, which, to this end, must be made of a metallic material. For this purpose, the detector head30of the distance sensor26has a coil38facing the active surface32as inductive element, with which the metallic workpiece34inductively couples.

In the embodiment shown, the coil38is provided with a pot core40. A base area of the pot core40essentially defines the active surface32. The area of a pot core cap41corresponds approximately to the active surface32. A sensing area42of the distance sensor26lies in front of the active surface32.

The distance sensor26also comprises, for example, an oscillator44, a demodulator46and an output driver50. An analog output signal is made available at an output52of the distance sensor26, for example, a voltage signal which is a function of the distance between the active surface32of the detector head30and the workpiece34.

Alternatively, provision may be made for a coil38of the distance sensor26to be without a core. For example, a metallic workpiece34influences the amplitude of the oscillating oscillator44by inductive coupling, and the amplitude and/or frequency and/or phase of the oscillator44is a measure of the distance36.

The interaction of the distance sensor26occurs only via the active surface32which in its configuration and positioning relative to the workpiece defines the sensing area42. The distance sensor26with its detector head30can be positioned locally on the workpiece34and interaction then occurs locally between the detector head30and the workpiece34owing to a local sensor field. If there is a burr in the sensor field42, the electromagnetic (inductive) coupling between the active surface32and the workpiece34is thereby influenced, and the output signal52changes accordingly. Local information about the workpiece is thereby obtained, namely whether a burr is present, if the signal changes accordingly, and quantitative information about the burr is, in turn, obtainable from the change in the signal itself.

The distance sensor26inFIG. 2has been described by way of example as an inductive distance sensor which couples inductively with the workpiece. Provision may, however, also be made for the distance sensor to be a capacitive distance sensor which couples capacitively with the workpiece34. Here, too, the coupling is an electromagnetic coupling, and again this electrostatic coupling is influenced by the distance36. In this case, as well, a burr check may be carried out on the workpiece34from an output signal of a corresponding capacitive distance sensor.

In the embodiment shown inFIG. 2, the active surface32is formed symmetrically around a longitudinal axis54of the distance sensor26. The sensor field42is then also formed symmetrically around this longitudinal axis54insofar as no coupled workpiece34is present, and when a workpiece34is coupled, this is also symmetrical in relation to the longitudinal axis54of a distance sensor26positioned at a distance, at least in the area of the effective sensing area42.

An effective sensing area of the distance sensor26(the sensor field42) therefore has an area of sight with a direction of sight which is essentially parallel to the longitudinal direction54of the distance sensor26.

Provision may also be made, as shown schematically inFIG. 3, with a distance sensor56with a longitudinal direction58, for an active surface60to be oriented transversely to this longitudinal direction58such that a corresponding area of sight defined by a sensor field62has a direction of sight64which is oriented essentially transversely and, in particular, at right angles to the longitudinal direction58of the distance sensor56.

The area of sight of a distance sensor may be adjusted in a defined manner, and, in particular, restricted by screening elements in order, for example, to thereby achieve a high local resolution. Screening elements arranged accordingly influence the formation of the sensor field between the distance sensor and the workpiece. In the case of an inductive distance sensor, these may, in particular, be screening elements which influence the induction of eddy currents in the metallic workpiece34or, in the case of a capacitive distance sensor, these may be screening elements which influence the formation of the electric field between an active surface and the workpiece.

At the output52there is an analog output signal containing the distance information for the distance between detector head30and workpiece34. Preferably, a separate evaluation unit to which this signal of a measuring head is transmitted cordlessly or through a line (not shown in the drawings) is also provided. The evaluation unit then determines from the burr information indirectly contained in the signal, by means of an evaluation algorithm, direct information about the burr formation, namely, in particular, about location and extent. For example, a comparison with a reference signal, corresponding to the burr-free workpiece at the same sensor position, is made for this purpose.

A distance sensor may also be an optical distance sensor, such as, for example, a light scanner. Such an optical distance sensor is described in German patent application No. 101 03 177.7, filed on Jan. 22, 2001, which corresponds to the U.S. patent application Ser. No. 047,447 on Jan. 14, 2002 and belongs to the applicant of the present application. Reference is hereby made explicitly to the content of these patent applications, which are not previously published.

An embodiment of an inventive device for checking bores66of an object of measurement68(FIG.4), which, in particular, is metallic, comprises a first distance sensor70, as described, for example, hereinabove with reference toFIG. 2, and designated26therein. This first distance sensor70is, for example, probe-shaped so that it can be inserted into a bore66.

An object of reference72prepared so as to correspond to an ideal workpiece is provided for checking such a bore66. Accordingly, if the object of reference72and the object of measurement68exhibit no deviations in their characteristics, the object of measurement68with its bores66then fulfills all the requirements to be met by it.

The object of reference72has identically arranged bores74corresponding to bores66, but these are prepared so as to be ideal and, in particular, free from burrs.

The inventive device for checking the bores66of the object of measurement68then comprises (at least) one second distance sensor76which is of the same design as the first distance sensor70. This second distance sensor76can be inserted into the bores74of the object of reference72in order to measure the corresponding surfaces of the object of reference72.

The two distance sensors70and76are coupled to one another in such a way that when the bore74is scanned by the second distance sensor76, the bore66of the object of measurement68is correspondingly scanned.

If, for example, the second distance sensor76is displaced linearly in the bore74, the first distance sensor70is then rigidly coupled to the second distance sensor76in such a way as to be guided in the bore66of the object of measurement68associated with it in correlation or synchronization with the guidance of the second distance sensor76relative to the bore74of the object of reference72. The guidance is carried out by a guide device in the direction of the X- and/or Y- and/or Z-axes (the guide device is not shown in the drawings).

Provision may also be made, when the second distance sensor76is turned in the bore74, for the first distance sensor70to also be turned with angular synchronization in the bore66of the object of measurement68, so that, in principle, it is always the same relative surface area that is scanned by the two distance sensors70and76, with the second distance sensor76scanning the object of reference72and the first distance sensor70scanning the object of measurement68.

A measurement signal of the second distance sensor76is transmitted through a line78or cordlessly to a comparator80. The measurement signal of the first distance sensor70is transmitted to this comparator80through a line82or cordlessly. The comparator80can then compare the incoming measurement signals of the two distance sensors70and76with one another, and, in particular, generate a differential signal and, where required, a summation signal. One can then read off from the differential signal whether there is a difference between the object of measurement68and the object of reference72. As the object of reference72is usually prepared so as to be ideal, this difference then originates from deviations of the object of measurement68from the ideal case. These deviations are due, in particular, to burrs in the bores66. Differences in the dimensions of the bores66or unmade transverse bores and the like may also be the cause.

The comparator80comprises, for example, a threshold value switch for eliminating noise signals in connection with the difference measurement or for excluding differential signals below a tolerance threshold, so that when the threshold value in the differential signal is exceeded, it can be assumed that there is a significant difference between object of measurement68and object of reference72, i.e., there is a significant difference between bores74and66.

Moreover, the type of deviation can then be concluded from the signal shape of, for example, the differential signal or a summation signal. For example, the presence of a burr can be concluded and the type of burr recognized, or a deviation in the dimensions can be concluded.

The two distance sensors70and76are guided in a correlated and, in particular, synchronized manner with respect to their respective workpieces by the guide device not shown in the drawings. Where workpieces are produced in series, only one object of reference72need be provided for checking a multiplicity of objects of measurement68.

In principle, the guide device is designed such that insertion into corresponding bores of the object of measurement and the object of reference is possible in all spatial directions. As described hereinabove, provision is preferably also made for rotation of the second distance sensor76relative to the bore74and of the first distance sensor70relative to the bore76to be possible with angular correlation.

In particular, the inventive device may also comprise further distance sensors of substantially the same design so as to be able to simultaneously examine a plurality of bores66in the object of measurement68, in particular, when these are arranged in parallel.

Provision may also be made, as shown schematically inFIG. 5, for several distance sensors84,86to be combined into a distance sensor combination88which is inserted into a bore66and74, respectively. A first distance sensor combination is then provided for measuring the object of reference72, and a second distance sensor combination is provided for measuring the object of measurement68.

At least two distance sensors84,86having different areas of sight90,92are provided in such a distance sensor combination88. In particular, these areas of sight90,92do not overlap, and, for example, face opposite surfaces areas94,96of a bore. When such a distance sensor combination88is rotated in the bore, in a certain rotational position the area of sight90then scans a surface area which has previously been scanned by the area of sight92.

The alignment of the distance sensor combination88within a bore98can be optimized by the provision of at least two areas of sight90,92. In particular, the distance sensor combination88can then be aligned coaxially with an axis of symmetry100of a cylindrical bore98. In turn, the accuracy with which the distance sensor combination88is guided in the bore98is thereby improved.

In particular, a control circuit relating to the object of reference72can thus be formed to ensure that the second distance sensor combination88for scanning the bore74of the object of reference72is guided exactly coaxially with the corresponding axis100of this bore74. For example, a differential signal is formed from the signals associated with the two areas of sight, and a finite value is then indicative of a deviation from the coaxial guidance. If the first distance sensor combination for scanning the bore66of the object of measurement68is guided in synchronization with the second distance sensor combination and, in particular, is rigidly guided relative thereto, the presence of, in particular, burrs can then be concluded from differences between the areas of sight90and92, insofar as no such differences with respect to the second distance sensor combination in the bore74of the object of reference72exist.

Alternatively or additionally, provision may be made for a distance sensor26itself to have a plurality of areas of sight, for example, for the distance sensor84shown inFIG. 5to have the area of sight90and an area of sight104offset in the longitudinal direction102, with, for example, a smaller distance of a detector head106from the longitudinal direction102than a detector head108providing the area of sight90.

In the embodiment shown, the distance sensor84, if it is an inductive sensor, then comprises a first coil108for creating the area of sight90and a second coil110for creating the area of sight104.

The distance from the bore surface94can then be determined from different measurement signals relating to the two areas of sight90and104, which are detected within the sensor84, by a differential signal being formed accordingly. A highly precise guidance of a single distance sensor84or a distance sensor combination88within a bore98is also achievable in this way.

The distance sensor86may also comprise a further area of sight112.

When the distance sensor84is moved linearly in the direction100within the bore98, the area of sight104then scans a surface area of the bore which had previously been scanned by the area of sight90or vice versa, depending on the direction of movement of the distance sensor84within the bore98.

Provision is preferably made for areas of sight, for example, areas of sight90,92,104,112to be able to be added on or omitted as required. This can be done externally through the operator or by an external evaluation device or internally by a corresponding sensor circuit. The inventive device can thereby be optimally adapted to a particular use by adjustment of the area of sight.

A further distance sensor112having an area of sight114on a detector head116pointing in the direction of a direction of movement of the combination88may also be provided. In particular, the first distance sensor or the first distance sensor combination is provided with such an area of sight114. Thus, if there is a danger of collision with the object of measurement68, a warning signal can be emitted (when the detector head116detects proximity to a wall), in order to discontinue further movement. A collision owing, for example, to insufficient depth of the bores on the object of measurement is thereby avoided.

In accordance with the invention, examination of a bore66in the object of measurement68(or an edge of the object of measurement68) and, in particular, a check for a burr, is carried out by the object of reference72being previously prepared and object of measurement68and object of reference72then being held at a fixed distance from one another. The second distance sensor is positioned at a distance from the object of reference72, and the first distance sensor70is thereby simultaneously positioned at a certain distance from the object of measurement68. A local sensor field forms between the second distance sensor76with its detector head30with an active surface and the object of reference72. The same applies accordingly to the first distance sensor70and the object of measurement68. The distance of the detector head of the second and first distance sensors76and70, respectively, from the object of reference72and the object of measurement68, respectively, can be detected via this sensor field. In accordance with the invention, however, there is no need for absolute determination of the distance as the differential signal between the first distance sensor70and the second distance sensor76is evaluated.

An equivalent surface area of a bore74and66, respectively, of the object of reference72and the object of measurement68, respectively, is scanned by the correlated movement of the detector heads of the two distance sensors76and70. A finite differential signal above a threshold indicates a difference, and as the object of reference72has been ideally prepared, this difference is due to deviations of the bore66in the object of measurement68from an ideal shape. These deviations can, in turn, be caused by, for example, burrs which have been correspondingly detected by the first distance sensor70.

The comparison of the measurement signals of the two distance sensors70and76can be converted by the inventive device into a relative measurement without absolute measurement signals having to be evaluated in detail. (If, however, in addition to recognition of a burr or recognition of a deviation, quantitative statements regarding the origin of the deviation are to be made, then such a quantitative evaluation of the differential signal is required.)

The second distance sensor76scans the object of reference72locally, and the first distance sensor70scans the object of measurement68locally.

Further details are given in German patent application No. 101 03 177.7, filed on Jan. 22, 2001, which corresponds to the U.S. patent application Ser. No. 047,447 on Jan. 14, 2002 and belongs to the applicant of the present application. Reference is hereby made explicitly to the content of these patent applications, which are not previously published.