DE4134454A1 - Contactless process monitoring of machine tools, esp. with automatically interchangeable tools - clamping workpiece so that forces arising during processing and causing geometric changes of tensioned body are measured - Google Patents

Abstract

The method of contactless process monitoring of machine tools, esp. with automatically interchangeable tools, involves monitoring the forces (13) arising during processing of a workpiece as a measure of the process parameter or parameters being monitored. When a threshold is exceeded, a signal is generated. A body (7) is clamped under tension between adjacent parts or in a bore in the machine so that its geometric shape changes, caused by the workpiece processing and the tensioning forces, can be measured. USE/ADVANTAGE - For indexable insert. Eliminates force measurement errors and yields accurate measurements.

Description

The invention relates to a method for contactless pro time monitoring of machine tools with in particular automa table changeable tools, especially indexable inserts in machine tools in which by the at the factory Piece machining with the forces occurring as a measure for the process parameter (s) monitored and if exceeded a signal is emitted at a predetermined limit value.

The invention further relates to a device for performing of the method mentioned, in which in at least one cylinder a force measuring element is clamped in a force-locking manner is connected to an evaluation device.

In workpiece processing, such as forming or cutting, In particular the cutting, forces act between the tool and the workpiece, which are also on the tool Impact machine parts. These process forces enable re conclude whether the molding process in its entirety runs in the intended manner, in particular can if the process forces are monitored, an impending plant at an early stage broken tool or excessive tool wear registered will.

According to the state of the art, a variety of are used Sensors of various designs and functions. These Sensors record ver on the machines or machine parts different physical parameters, which after conversion into elec trical signals available to a computer for evaluation be put.  

For example, DE 38 08 572 C2 describes a device device for breakage and wear monitoring of exchangeable Tools, with the relative change of position in an induction measuring coil and / or a Hall probe induces a voltage where in the inhomogeneous magnetic field and / or the magnetic field change one on the tool carrier and / or the basic tool holder and / or the turret disk attached magnet is measured or the influence caused by a machine part nes is measured from the outside applied magnetic field. The be Magnetic sensors that strike are from the outside a machine part created at a distance. If there is foulness tongues of the machine part surface or too due to maschi vibrations and temperature effects other changes clearances between the surface of the machine part and the magnetic sensor, errors in measurement results can occur ten.

DE 34 07 620 C2 and EP 02 60 373 B1 describe measurement directions with electromechanical transducers described in used the bore of a machine part and ver can be stretched. With radial forces on the Sensor, namely a piezoelectric transducer, becomes one Generates voltage that can be used as a measurement signal. The piezo However, electrical converters have the following disadvantages. On the one hand the transducers have a low zero stability, so that it cannot be ruled out that a measured value during the measurement falsifying intrinsic drift of the piezo elements occurs. Farther affects the drift behavior of the piezoelectric elements due to temperature fluctuations at the installation site and can eli at most by complex compensation circuits be mined. Piezoelectric transducers react sensitively even when exposed to coolants and cutting agents, the only can be countered with a complex seal, which turns out to be complex and small due to the small size of the holes proves difficult. Because the signal behavior and the sensitive  difference of piezoelectric elements from part to part Lich, must with each change of a piezoelectric element A new zero point adjustment can also be carried out. A another disadvantage of piezoelectric sensors is the lack Stability of the measurement signals over a longer period. Therefor the primary causes are the signs of the Sen sensors and the resulting loss of adhesion between the sensors and those broken into the machine parts sensor bores. At best, this can counteract this be counteracted that the highest surface qualities in the Use sensors and the manufacture of the sensor mounting hole be det. However, there is not always a fine column at the installation site machine parts can be worked.

It is therefore an object of the present invention to begin with to further develop the named method and the device, that errors in the force measurement are largely excluded the, the method and the device easy to handle should be. In particular through simple construction and always reproducible measurement results should have a high reliability casualness and cost-effective handling for monitoring machine parts.

The task is described on the one hand by that in claim 1 bene procedure solved, the innovation of which is that between the neighboring parts or in a hole in the factory a machine so clamped under pretension is that its geometric shape change, which is due to the at a workpiece machining in addition to the preload forces occur, is measured.

The measuring principle according to the invention is based on the fundamental Consideration that a body clamped under pressure is a Shape changes experienced when tensile or compressive forces at the clamping location Act.  

The body preferably has at least one plate or a substantially flat or curved surface in the leader state whose geometric change is measured. These Geometric change can in particular come from a thickness change plate, a change in diameter or a change the curvature of the plate or surface.

Optical, optical, magnetic, capacitive or acoustic processes. Preferential however, non-contact measuring methods are used fen, for example the change of path of a piece of land the curved surface as an axial movement due to radial loading determine influence.

After further training, the body can enter a blind hole or groove of a machine part indirectly via a sleeve or be immediately clamped. The plate or essentially flat or curved surface of the body is available for measuring the Thickness or for axial distance measurement, d. H. for measurement in Direction of the longitudinal axis of the drill, an optical, capacitive or magnetically working sensor without contact. From level measurements by optical, capacitive or inductive means or the measurement of changes in distance are in principle be knows. To be emphasized here are inductive or eddy current measurement move using Hall sensors, Wiegand sensors, saturation core probes and distance sensors based on the eddy current principle. Furthermore, capacitive proximity sensors are in extreme Mi. niaturization available, which is suitable for the measuring process nen. Opto-electronic measuring methods using smaller ones LEDs and corresponding photo elements can be just if inexpensive to implement.

According to a further embodiment of the invention, the plate or the substantially flat or curved surface of the ge named body with slits or crevices that are  due to the forces that occur during workpiece machining push together and expand again when the load is released, so that a return from the degree of collapse and expansion drawn to the radial or tangential forces can be.

The surface or plate in question preferably has in the center point and / or an opening around it, from which the slots or gaps essentially radially outward extend outside.

According to a specific embodiment of the invention is the body ferromagnetic or permanent magnetic, the relative axial change in position of the curved surface due to radial or tangential force in an induction coil and / or Hall probe induces a voltage. By measuring the inhomo gene magnetic field and / or the magnetic field change, in particular even when one or more are used in the width changing gap or gaps in the plate or the flat or curved surface, a drift-free measurement can be carried out leads. For example, a frequency and amplitude-stable oscillator a solenoid with a change selstrom high frequency are fed. If the plate or the flat or curved surface as a conductive measurement object approaches the electromagnetic field of said coil, so eddy currents are induced in the coil, causing the excitation field are opposed. This will eventually become the Ampli tude on the sensor coil as a function of the distance to the measuring object project changed. The change in the Ma produced by the coil gnetfeldes and thus the desired change of the off output signal under load is due to that on the plate or the flat or curved surface of the existing gaps supports if these columns when the sensor is loaded Push together, but widen again when the load is released.  

According to an alternative procedure, the body is Illuminated transmitted light method, the transmitted light proportions are measured. Already when using one over the entire irradiated area translucent curved surface surfaces that act like a diverging lens change depending on Degree of curvature of the curved surfaces the transmitted light shares. Here too, the effect can still be selectively by light permeable gaps or slits while otherwise absorbent domed surface are reinforced if as a result of a Squeeze or stretch the gaps or slits or expand.

Alternatively, it is also possible to at least the body partially reflective and the axial movement of the Area by measuring the in given directions to measure the reflected light components. When using a curved surface, this then serves as a concave mirror with a corresponding reflection behavior. Here, too, the right reflective surface through cracks or slits be "interrupted", what with a contraction or exposing of the slits lead to different reflection behavior leads additionally to the changed direction of light scattering. in the For the purposes of the present invention, transmitted light and Combination reflection measurements of the type described above nated and carried out together in parallel.

According to a further embodiment of the invention, the plate or the curved or flat surface blackened or light have permeable halftone dots or lines, in particular a line grid, with about with CCD lines or so-called Field grid transmitted or reflected light components can be measured. When using halftone dots, lines or grids can, in principle, also apply to radiation Diffraction phenomena that occur are used as measured quantities the.  

Finally, it is also possible to stop the axial displacement to measure coherent curved surface areas interferometrically, especially the axial movement of the center of the surface when stretching or to observe compression of the curved surface.

The ge to carry out the measurement methods described above suitable device is described in claim 14. Here a force sensor is in at least one cylindrical bore ment clamped non-positively, with an evaluation device device is connected, the force measuring element having a body one lying substantially perpendicular to the longitudinal axis of the bore the plate or substantially flat or curved surface is whose diameter, thickness and / or curvature at radi aler and / or tangential force changes. The plate or area or a part of it lies with the evaluation device connected measuring element to determine the geome trical change of shape of the plate or surface without contact opposite. In particular, the measuring element is a distance sensor Measurement of axial movements due to radial or tangenti all forces on the circumference of the bore in a curved Surface occur.

As already explained above, the measuring element can be a kapa citation, inductive or optical sensor.

The individual further preferred device features are in claims 15 to 25, their advantages and radio way from the above explanations of the procedure results.

Embodiments of the invention are shown in the drawings posed. Show it

Fig. 1 is a schematic view of an inventive device SEN,

Fig. 2 tung a concrete embodiment of this Vorrich, clamped in a blind hole of a machine element,

Fig. 3a, 3b to 7a, 7b respectively, embodiments of the erfindungsge MAESSEN apparatus, clamped in a Sackboh tion, in each case in the unloaded and through which occur during machining forces loaded steady state.

As already mentioned at the beginning, devices according to the invention which are suitable for clamping in a blind bore of a machine part are known in principle from DE 34 07 620 C2 or EP 02 60 373 B1. These devices consist essentially of a pressure- or force-sensitive sensor element 1 , the conical or keilför expanded in an inner or guide sleeve 3 with a part formed at the front end. As can also be seen in detail from FIG. 2, the inner sleeve 3 is connected via an external thread with a preload nut 6 , which interacts with a substantially cylindrical outer sleeve 5 , in such a way that by rotating the inner sleeve 3 about its longitudinal axis relative to the outer sleeve 5 a prestress can be generated in the region of the conical part 2 of the inner sleeve 3 . According to FIG. 2, the front side of the preload nut is supported on a corresponding annular surface of the outer sleeve. In principle, the bias can also be generated by the fact that the outer sleeve itself has an internal thread that cooperates with a corresponding external thread of the inner sleeve. However, it is advisable to use a lock nut to determine the preload. If the inner sleeve is pulled axially into the outer sleeve, the effect on the lower end face of the inner sleeve is such that it is loaded in the radial direction. In the present case, the end face represents the body 7 serving as a mechanical transducer, the geometric change of which can be measured. This geometric change can be in the form of a change in thickness resulting from compression, a change in the radius of curvature or a change in the width of radially milled slots. Sensor 1 , which records this geometric change, is connected to an evaluation device (not shown ) via measuring lines 8, which are known in principle.

As can be seen in detail from FIG. 2, the device shown in FIG. 1 is inserted and clamped as a measuring probe in a blind bore 10 of a machine element or machine part. This hole is made on the machine element at a location in which significant partial forces in the form of material stresses can be measured with regard to the machining process. The mechanical transducer 7 is essentially circular and thus flat and has a central opening in the region of the center of the circle, from which radially extending slots 11 extend. The inner sleeve 3 is under prestress in the outer sleeve 5 and this clamped non-positively in the blind hole. The amount of preload is adjusted via the axial displacement of the inner sleeve 3 relative to the outer sleeve 5 , with slots 12 of the outer sleeve 5 making this expandable at its lower end when the cone is pulled further into the outer sleeve via the clamping nut.

The unloaded sensor 1 is shown in FIG. 3a, while FIG. 3b shows the loaded state when radial forces act on the outer sleeve 5 . While the slots 11 according to FIG. 3 have a distance that can be predetermined by the prestressing, the load with radial forces 13 leads to a narrowing of the slots 11 according to FIG. 3b. If an inductive sensor is used, the change in the slots 11 has an effect as a change in the magnetic field, which allows conclusions to be drawn about the extent of the force 13 .

The end face 7 shown in FIGS. 4a, b, on the other hand, is a closed, plate-shaped circular area which is essentially flat in the unloaded state ( FIG. 4a). As can be seen from FIG. 4b, however, the radial force 13 leads to a compression of the flat end face 7 , in which it bulges inwards or outwards ( FIG. 4b). The extent of the curvature or the change in the surface curvature is directly related to the magnitude of the radial forces that occur 13 . This curvature of the surface 7 is accompanied by an axial displacement of the surface parts, in particular the center of the surface, which can be detected inductively or optically by the sensor 1 . The Ra dial force measurement is thus attributed to a measurement of the axial change in position from the surface 7 relative to the sensor 1 .

An alternative measurement form is shown in FIGS . 5a and 5b. Here, the guide element 3 is also guided in a circular shape at the front end, ie in the form of a sleeve with a closed end face 7 . If radial forces 13 are now exerted on the inner sleeve 3 by means of the outer sleeve 5 , the associated compression of the body 7 leads to a change in the thickness and thus to a change in the damping behavior which can be measured by changing the magnetic permeability. The arrangement of FIGS. 5a and 5b only requires that the body 7 is sufficiently elastic, which can be realized, for example, that ferro- or permanent magnetic parts 14 are enclosed in an elastic plastic body 7 .

The structure corresponding in principle is shown in FIGS. 6a and 6b, but the sensor 1 works optically there and measures the different reflection behavior of the circular plate 7 in the unloaded and loaded state. By the action of the radial forces 13 , the end face 7 is compressed, which leads to a compression of the reflecting and / or absorbing Parti angle 14 in the otherwise translucent circular disc 7 . The changed reflection behavior is directly related to the magnitude of the radial forces 13 .

Fig. 7a and 7b also show an optical measuring method. The sensor 1 is equipped with at least one light-emitting diode 15 and one receiver diode 16 . The light rays 17 emitted by the diode 15 are partially reflected by the circular plate 7 as re reflected rays 18 to the receiver diode 16 , in part they also pass through the radial slots 11 . The transmitted light components strike a reflector 19 , which also reflects part of the transmitted light components back onto the receiver diode 16 . Now, as shown in Fig. 7b, the inner sleeve 3 strikes with radial forces 13 , the slots narrow so that the light emitted by the LED 15 is completely reflected by the plate 7 and measured by the receiver diode 16 who can. By increasing the radial forces 13 , the proportion of the light reflected at the circular plate 7 , which can be determined as a measure of the force 13 , inevitably increases. In principle, it is also possible to arrange the receiver diode 16 at the location of the reflector 19 and to measure only the light components let through by the columns 11 there .

Claims (25)

1. Method for contactless process monitoring of machine tools with in particular automatically exchangeable tools, in particular indexable inserts in machine tools, in which the forces occurring during the machining of the workpiece with the tool ( 13 ) as a measure of the process parameter or parameters to be monitored and monitored If a predetermined limit value is exceeded, a signal is emitted, characterized in that a body ( 7 ) is clamped between adjacent parts or in a bore of the machine tool under pretension in such a way that its geometrical shape change, which occurs as a result of the forces occurring during workpiece machining in addition to the pretension ( 13 ) occurs, is measured. 2. The method according to claim 1, characterized in that the body in the prestressed state has at least one plate ( 7 ) or a substantially flat or curved surface ( 7 ), the geometric change is measured. 3. The method according to any one of claims 1 or 2, characterized in that the change in thickness of the plate of the body pers ( 7 ) is measured. 4. The method according to any one of claims 1 to 3, characterized ge indicates that the geometric change by means of opti shear, magnetic, in particular eddy current magnetic, capacitive or acoustic measurement without contact is communicated. 5. The method according to any one of claims 1 to 4, characterized in that the body ( 7 ) in a blind bore ( 10 ) or groove of a machine part is clamped indirectly via a sleeve ( 5 ) or directly and that the plate ( 7 ) or the essentially flat or curved surface ( 7 ) of the body is an optical, capacitive or magnetically working sensor ( 1 ) without contact. 6. The method according to any one of claims 1 to 5, characterized in that the plate ( 7 ) or the substantially flat or curved surface ( 7 ) has slots ( 11 ) or columns, which result from the forces occurring during a workpiece machining device ( 13 ) push together, but expand again when the load is released and their pushing together and / or expanding is measured. 7. The method according to claim 6, characterized in that the plate ( 7 ) or the surface ( 7 ) has an opening arranged in the center or around this, from which the slots ( 11 ) or columns extend substantially radially outwards . 8. The method according to any one of claims 1 to 7, characterized in that the body ( 7 ) with the plate or the substantially flat or curved surface is ferromagne table or a permanent magnet and that their relative axial change in position due to radial or tangential force in an induction coil and / or Hall probe induces a voltage, the inhomogeneous magnetic field and / or the magnetic field change being measured. 9. The method according to any one of claims 1 to 8, characterized in that the body ( 7 ) with the plate or the substantially flat or curved surface is irradiated by the light process and the transmitted Lichtan parts are measured. 10. The method according to any one of claims 1 to 9, characterized in that the plate or the substantially flat or curved surface of the body ( 7 ) has at least partially reflective surface areas and the axial movement of the surface by measuring the reflected light components ( 18th ) is measured. 11. The method according to any one of claims 1 to 10, characterized in that the plate ( 7 ) or the substantially flat or curved surface ( 7 ) has blackened or translucent halftone dots ( 14 ) or lines. 12. The method according to claim 11, characterized in that the plate ( 7 ) or the substantially flat or ge curved surface ( 7 ) has a grating. 13. The method according to any one of claims 1 to 12, characterized in that the axial displacement of the plate ( 7 ) or the substantially flat or curved surface areas are measured interferometrically. 14. Device for performing the method according to one of claims 1 to 13, in which in at least one cylindri's hole ( 10 ) a force measuring element ( 5 , 3 , 7 , 1 ) is clamped non-positively, which is connected to an evaluation device, characterized in that the force measuring element ( 1 ) is a body ( 7 ) having a circular plate lying substantially perpendicular to the longitudinal axis of the bore or a substantially flat or curved circular surface, the diameter, thickness and / or curvature of which are radial and / or tangential force effect changes, and that the plate or the substantially flat or curved surface or part thereof is opposite a measuring element connected to the evaluation device for determining the geometric shape change without contact. 15. The apparatus according to claim 14, characterized in that the measuring element is a distance sensor ( 1 ) for measuring axial movements due to a surface curvature or a Meßele element for determining the plate thickness. 16. The apparatus according to claim 14 or 15, characterized in that the measuring element is a capacitive, inductive or optical sensor ( 1 ). 17. The device according to one of claims 14 to 16, characterized in that the plate ( 7 ) or in the wesentli Chen flat or curved surface ( 7 ) has slots ( 11 ) or columns, which occur as a result of the forces occurring in a workpiece machining Push ( 13 ) together, but widen again when the load is released. 18. The apparatus according to claim 17, characterized in that the plate ( 7 ) or surface ( 7 ) has an opening arranged in the center or around this, from which the slots ( 11 ) or columns extend substantially radially outwards. 19. Device according to one of claims 14 to 18, characterized in that the body ( 7 ) with the plate or the substantially flat or curved surface is ferromagnetic or permanent magnetic and the measuring element from a magnetic coil (induction coil) and / or a Hall - There is a probe through which the inhomogeneous magnetic field and / or the magnetic field changes can be measured. 20. Device according to one of claims 14 to 18, characterized in that a light source is provided on the plate ( 7 ) or the substantially flat or curved surface ( 7 ) and that the measuring element is an optoelectronic sensor ( 1 ) . 21. The apparatus according to claim 20, characterized in that the light source is a light emitting diode ( 15 ) and the Meßele element is a photo element ( 16 ), such as a photodiode or a photoresistor. 22. The apparatus according to claim 20 or 21, characterized in that the body ( 7 ) is at least partially transparent and the light source ( 15 ) and the opto-electronic sensor ( 1 ) on different sides of the plate or the substantially flat or curved surface are arranged in the bore of the machine part. 23. The apparatus of claim 20 or 21, characterized in that the light source ( 15 ) and the opto-electronic sensor ( 1 ) both on the same side of the plate ( 7 ) or the substantially flat or curved surface ( 7 ) are arranged in the bore of the machine part ( 9 ) and reflected light components ( 18 ) can be measured. 24. The device according to any one of claims 20 to 23, characterized in that the plate ( 7 ) or in the wesentli chen flat or curved surface ( 7 ) blackened or translucent screen dots ( 14 ) or lines, preferably in the form of a grating. 25. The device according to any one of claims 20 to 24, characterized is characterized by an interferometric measuring arrangement.