MACHINE-TOOL UNIT HAVING A TOOL SENSOR FOR SENSING A CUTTING-EDGE LOAD ON A TOOL

Abstract

A method for sensing a cutting-edge load in a motor-driven machine-tool unit having a stator unit and a rotor unit that is rotatable at least about an axis of rotation. The rotor unit includes a tool receiving unit that is adjustable along the axis of rotation and to which a clamping force can be applied, for fixing and clamping a releasably fixable tool shank of a tool. A tool head of the tool includes at least one individual cutting edge. A tool sensor is provided for sensing the load on the tool, the tool sensor being realized as an individual-cutting-edge sensor for sensing a cutting-edge load on the individual cutting edge.

Claims

1. A motor-driven machine-tool unit, having a stator unit and a rotor unit that is rotatable at least about an axis of rotation, the rotor unit comprising at least one tool receiving unit for receiving a tool, the tool receiving unit comprising a tool clamping device, which is adjustable in the longitudinal direction of the axis of rotation and to which a clamping force can be applied, for fixing and clamping a releasably fixable tool shank of the tool, a tool head of the tool comprising at least one individual cutting edge, there being at least one tool sensor provided for sensing the load on the tool, wherein the tool sensor is an individual-cutting-edge sensor for sensing a cutting-edge load on the individual cutting edge, and wherein the stator unit comprises at least the individual-cutting-edge sensor.

2. The machine-tool unit according to claim 1, wherein the individual-cutting edge sensor is an individual-cutting-edge force sensor for sensing an application of force to the individual cutting edge.

3. The machine-tool unit according to claim 1, wherein the individual-cutting-edge sensor, as viewed in the axial direction, is arranged at least partially at the level of the tool clamping device and/or of the tool receiving unit.

4. The machine-tool unit according to claim 1, wherein the individual-cutting-edge sensor is a contactlessly operating sensor for contactless sensing of the cutting-edge load on the individual cutting edge.

5. The machine-tool unit according to claim 1, wherein the individual-cutting-edge sensor is a proximity sensor for sensing a distance between the stator unit and/or the proximity sensor and at least a part of the rotor unit and/or of the tool receiving unit, this distance being such that it can be altered by the cutting-edge load on the individual cutting edge.

6. The machine-tool unit according to claim 1, wherein the individual-cutting-edge sensor is an axial sensor having at least one sensing region aligned in the longitudinal direction of the axis of rotation.

7. The machine-tool unit according to claim 1, wherein the rotor unit and/or the tool receiving unit comprise/comprises at least one marking.

8. A machine tool, comprising a tool and a machine-tool unit according to claim 1.

9. A method for sensing a cutting-edge load on a single cutting edge of a tool, there being used a tool head of the tool that has at least one individual cutting edge, the tool and/or a tool holder for holding the tool detachably fixed to a tool clamping device of a tool receiving unit of a rotor unit, being received by a motor-driven machine-tool unit, wherein in the clamping of the tool, the tool clamping device is adjusted in the longitudinal direction of the axis of rotation and/or arranged in a spindle head and/or the tool receiving unit of the rotor unit, the machine-tool unit having a stator unit relative to which the rotor unit is mounted so as to be rotatable about an axis of rotation, at least one tool sensor is used to sense the load on the tool, the tool sensor being an individual-cutting-edge sensor for sensing a cutting-edge load of the individual cutting edge, wherein the method comprises the following steps: arranging the individual-cutting-edge sensor on the stator unit, providing at least one sensor head of the individual-cutting-edge sensor for the purpose of determining a distance between the stator unit and/or the sensor head and at least a part of the rotor unit and/or of the tool receiving unit /spindle head, this distance being altered by the cutting-edge load on the individual cutting edge, measuring the distance from a part of the rotor unit and/or of the tool receiving unit /spindle head, recording at least one time-related and/or position-related sequence of the distance values measured by means of the individual-cutting-edge sensor and/or sensor head, and determining an axial runout and/or a radial runout and/or an angular change and/or a torsional moment exclusively taking into account the time-related and/or position-related sequence of the measured distance values to the part of the rotor unit /tool receiving unit /spindle head rotating relative to the individual-cutting-edge sensor and/or sensor head.

10. The method for sensing the cutting-edge load according to claim 9, wherein a marking is provided on the rotor unit and/or tool receiving unit/spindle head, the individual-cutting-edge sensor and/or sensor head senses the marking on the rotor unit during measurement, the current rotational speed/velocity of the rotor unit is sensed on the basis of the sensing of the marking by the individual-cutting-edge sensor and/or sensor head.

11. The method for sensing the cutting-edge load according to claim 10, wherein the current rotational speed/velocity of the rotor unit is determined on the basis of the marking in that: there is provided as a marking one such that marks a specific angular segment of the rotor unit during rotation, and the time required by the sensor head for the marking, in the case of a known angular segment, to pass the individual-cutting-edge sensor and/or sensor head is determined, and/or the time between two successive detections of the marking by the individual-cutting-edge sensor and/or sensor head is measured.

12. The method for sensing the cutting-edge load according to claim 9, wherein a groove is used as a marking, such that the region outside the groove and inside the groove have different distance values.

13. The method for sensing the cutting-edge load according to claim 9, wherein a time-related and/or position-related sequence of distance values, which is used as a reference measurement, is recorded before a first machining operation by the machine-tool unit and/or after a cleaning operation, collectively or individually for each tool used.

14. The method for sensing the cutting-edge load according to claim 9, wherein the marking is used as the initial point, and the initial point for the evaluation is assigned to the sequences of distance values in order to enable the distance values of different sequences to be assigned to one another.

15. The method for sensing the cutting-edge load according to claim 9, wherein an evaluation sequence of values is determined by means of at least one of the following calculations: a difference formation between two of the time-related sequences, and subsequently a Fourier transformation of the previously formed difference of the first and second time-related and/or positional sequence and/or a Fourier transformation of the sequences in each case, and subsequently a difference formation between the respectively Fourier-transformed time-related sequences and/or formation of the mean value of the time-related and/or position-related sequences with subsequent formation of the difference between the mean values.

16. The method for sensing the cutting-edge load according to claim 9, wherein the evaluation sequence is searched for a deviation or at least two deviations that exceed a predefined threshold value and, in the event of the threshold value being exceeded, a change in wear of a cutting edge and/or a breakage of a cutting edge and/or jamming of a cutting edge/clamping is assumed.

17. The method for sensing the cutting-edge load according to claim 15, wherein in the Fourier transform in the case of a frequency value corresponding to the number of revolutions per unit of time of the rotor unit, the difference value of the distances is compared with a threshold value and, in the event of the threshold value being exceeded, a change in wear of a cutting edge and/or a breakage of a cutting edge breakage and/or jamming of a cutting edge/clamping is assumed.

18. The method for sensing the cutting-edge load according to claim 17, wherein the determination of whether a change in wear of a cutting-edge and/or a breakage of a cutting-edge and/or jamming of a cutting-edge/clamping is/are present is performed by applying artificial intelligence.

19. The machine tool unit according to claim 1, wherein the machine tool unit is a multi-axis rotary head or a motor spindle.

20. The machine tool unit according to claim 1, wherein the tool comprises two, three or four cutting edges.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0096] An exemplary embodiment of the present invention is represented in the drawing, and explained in greater detail in the following on the basis of the figures.

[0097] FIG. 1 a schematic representation of a first machine-tool unit according to the present invention;

[0098] FIG. 2 a schematic representation of a part of the checking method according to the present invention for checking the clamping state;

[0099] FIG. 3 a diagram of the relationship between rotational speed and time, to illustrate the start-up of the rotor unit;

[0100] FIG. 4 a radially arranged groove applied to the measuring ring;

[0101] FIG. 5 a distance-time diagram in the detection of a groove;

[0102] FIG. 6 an illustration of an error estimation on the basis of the distance-time diagram;

[0103] FIG. 7 a schematic sectional detail of a motor spindle according to the present invention, with a radial sensor;

[0104] FIG. 8 a schematic sectional detail of a further motor spindle according to the present invention, with an axial sensor;

[0105] FIG. 9 a schematic cross-section, in the direction of the axis of rotation of the motor spindle according to FIG. 8, with two axial sensors according to the present invention;

[0106] FIGS. 10A and 10B show a milling tool to be monitored, having four cutting edges, schematically in a top view and a perspective view;

[0107] FIG. 11 a machining process of a groove, in schematic form, in which jamming of the chips has been caused by excessive feed motion; and

[0108] FIG. 12 a schematic axial deflection of a tool having four cutting edges, during one revolution of a drilling process.

DETAILED DESCRIPTION OF THE INVENTION

[0109] FIG. 1 shows a schematic representation of a machine-tool unit 1 that has a stator unit 2 and a rotor unit 3, it being the case in FIG. 1, in particular, that a spindle head is to be regarded as part of the rotor unit 3. The stator unit 2 has a ring 4 to which a sensor head, in the form of an axial sensor 5, is attached. The rotor unit 3 comprises a measuring ring 6 made of a metal, which here is advantageously made of a paramagnetic material. The axial sensor 5 is arranged so as to measure a distance to an end-face surface of the rotor unit 3. However, a lateral measurement, radial to the axis of rotation, is also conceivable. This surface to which the distance is determined is located on the measuring ring 6. The axial sensor 5 is realized as an eddy-current sensor in order that the most accurate measurements possible can be obtained despite any fouling.

[0110] The sensor head/axial sensor 5 is connected to an electronics unit 7; both together form a checking device 8, which in turn is connected to a machine control system 9 such that, if necessary, intervention in the control system can be effected in the event of excessive axial runout errors.

[0111] In the case of a particularly preferred further development, only one sensor head 5 is provided. It is conceivable to additionally use a trigger sensor, e.g. for recognizing an optical reference marking on the measuring ring 6, in which case such a trigger sensor may also be attached, for example, to the sensor ring 4. The marking may also be realized as a groove or the like. With such a trigger sensor, only the initial point for the measurements is triggered, so that, in the evaluation, the phase relationships of the measurement values to each other can be more easily defined. A trigger sensor is not absolutely necessary, and is also not represented further in FIG. 1.

[0112] The stator unit 2 comprises an enclosure 10 for the sensor ring 4, and also a bearing cover 11. There is a tool clamping device 12 attached to the rotor unit 3 (FIG. 1 shows the taper ring).

[0113] A sequence 20 of reference measurement values is first acquired in each case with the new machine-tool unit 1, using the available tools 50 (cf., for example, FIGS. 10A and 10B), which are clamped into a tool holder. This may be done in the factory or at the customer's site. A reference measurement can also be effected with a tool 50 or tool holders; however, this is not necessary as a matter of course, but in certain circumstances it increases the precision of the measurement and may possibly facilitate the detection of even small changes to/with a cutting edge 53 of the tool 50, especially if, for example, individual tools 50 or tool holders are to be used. During operation, a new sequence 21 of distance values is then subsequently determined for the same tool 50, or tool holder.

[0114] For example, the following procedure may be used to detect cutting-edge changes or loads:

[0115] 1. start-up of the spindle to nominal rotational speed,

[0116] 1.a. use of a general reference as described above, and/or from/by means of an electronic/electrical memory, and/or

[0117] 1.b. recording of a reference, in the time domain, that is only temporarily stored for as long as the machining process is running, and then comparison of this process/operation against this reference, and/or

[0118] 1.c (only) a reference FFT (see below) is formed, which in some cases is sufficient to identify changes in the spectrum, e.g. chatter,

[0119] 2.a. evaluation is then effected on individual revolutions in order to recognize cutting-edge changes with greater precision, and/or to realize a visualization, or display, and/or

[0120] 2.b. recording is effected at fixed intervals, i.e. evaluation (always) over a fixed interval, e.g. every 10 ms, and/or

[0121] 2.c the evaluation is realized by means of AI.

[0122] 3.a the result is visualized, and/or

[0123] 3.b operation is modified, such as modifying/adjusting the feed rate, and/or

[0124] 3.c control of the operation, or process.

[0125] A set of reference measurements may thus be performed for different tools 50 or tool holders; this operation increases the recognition accuracy. Since the sequences 20, 21 are preferably already recorded upon the start-up of the machine unit 1, and thus during an acceleration of the rotor unit 3, the position data of the respective distance values must be scaled to enable them to be compared with each other. In FIG. 2, the values are accordingly already scaled for the sequences 20, 21. In FIG. 2, the difference 22 is formed. Subsequently, a frequency analysis 23 of the signal is effected, in the form of a Fourier transformation. It is checked (method step 24) whether there is a deviation at a certain frequency, e.g. at the rotation frequency of the rotor unit 3, or at which frequencies such changes occur. If these exceed a critical and/or predefined/stored threshold value K (cf., for example, FIG. 11), there is a disturbance variable, or disturbance, present, e.g. a critical wear of a cutting edge 53, a breakage of a cutting edge 53 or a deformation due to a wedged chip in the region of a cutting edge 53 (amplitude evaluation: method step 25).

[0126] In series operation, the reference measurement may be performed at very short time intervals, in particular, after a tool change, possibly once during the first start-up phase, and the individual-cutting-edge check according to the present invention may preferably be performed during each/the entire machining phase. In FIG. 3, as an example, the rotor unit 3 is accelerated in the first 300 ms, during which a measurement value is already being taken. The rotational speed of the rotor unit 3 is represented as a function of the time progression t. The S-curve S shows a curve that is curved slightly to the left, i.e. a slow start-up in order to avoid jerky movements of the rotor unit. Linearization is not useful in this range because the acceleration is not constant and an approximation by disregarding the acceleration component is generally too inaccurate. Substantially, however, there is otherwise a constant acceleration, i.e. a linear dependence of the speed on the time t. If no axial runout can be detected here, machining can be performed, i.e. a tool 50 and tool holder are correctly clamped/fitted. Otherwise, braking may be necessary for safety reasons. From approximately 300 ms onwards, a constant speed of approximately 4000 revolutions per minute is attained for the machining example.

[0127] FIG. 4 shoes a section through a rotor unit 3 comprising a measuring ring 6 that has a groove N in the side region. The enlarged representation shows the edge regions F1, F2, which may be realized as flanks and which can be sensed at a correspondingly high sampling rate. Thus, for example, a current rotational speed/velocity can also be determined by when the sensor head senses the corresponding flanks at the beginning and end of the groove N. Since the angular range over which the groove N extends is known, the angular distance between these two flanks is also known, such that only the time interval between the occurrence of the flanks has to be determined.

[0128] FIG. 5 shows two illustrations showing the profile of the measured distance u between the sensor head 5 and the rotor unit 3 when the groove N passes the sensor head 5 at different speeds in each case, here once at 10 times the rotational speed/velocity. In the region of the flanks F1, F2, the dependence of the distance u on time is ramp-shaped, since the groove N also shows a ramp-shaped progression in the region of F1, F2. The profile is therefore compressed in time at a higher rotational speed/speed 10 v.sub.0.

[0129] FIG. 6, in turn, shows how an error in the linearization (disregarding the acceleration term) can be estimated in the case of short time intervals.

[0130] The same groove N is measured in direct time succession with respect to its distance u. Since there is uniform acceleration, the later measurement of the groove N, which is effected, for instance, at the rotational speed/velocity v1, is compressed compared to the previous one, i.e. v1>v0. There is one revolution between the two measurement events. In the linearization, it is assumed that the same rotational speed/velocity is present between both measurement events. The time interval between the two measurement events is the time between two points of the same flank F1 (or F2 respectively) at which the distance is the same. The maximum error can thus be estimated:

Δv/Δt=(v.sub.1−v.sub.0)/Δt.

[0131] FIGS. 7 and 8 show two further advantageous variants of the present invention, in which a motor spindle 3 of a machine tool is represented in section. As is usual in machine tool construction, one side of a collet chuck 1 having a plurality of clamping segments 2 is represented in the unclamped state (part almost not represented) and in the clamped state of the motor spindle 3, or collet chuck 1.

[0132] In the represented, clamped part of the motor spindle 3 of FIGS. 7 and 8, an individual-cutting-edge sensor 4 according to the present invention can be seen. In FIG. 7 this sensor 4 has a radially aligned effective range, and in FIG. 8 it has an effective range aligned in the axis of rotation D. Accordingly, a radial sensor 4 in the sense of the present invention is represented in FIG. 7, and an axial sensor 4 in the sense of the invention is represented in FIG. 8. Not visible in FIGS. 7 and 8, however, is an optionally usable second sensor 4 according to the present invention, since this, if used, would be/is arranged offset in the circumferential direction, in particular, by 90° or 180°, etc., and is thus not visible in the sectional representations. The arrangement with two sensors 4 according to the present invention is/would be visible in cross-section, e.g. in FIG. 9.

[0133] Changes in the cutting edges 53 of the tool 50, which is not represented in greater detail here in FIGS. 7 and 8, or resulting from a load, or application of force, to the tool 50, or to the cutting edges 53, that is directed axially and/or radially in relation to the axis of rotation D, a region X of a spindle shaft 5, or of a counter-holder 6, or stop/ring element 6, of the motor spindle 3, which is represented schematically in FIG. 7, becomes deformed, or widened, in the radial direction R. In this case an element 7 of the spindle shaft 5 transmits a clamping force F, or displacement and/or deformation, i.e. alteration, to the element 6. As a result, a distance 9, or air gap 9, between the rotor unit, or spindle shaft 5, and a stator unit 10 comprising the radial sensor 4 is altered, or reduced.

[0134] The state according to the above-mentioned reference measurement in the region X is the specified state within the meaning of the present invention, and an alteration, caused by force/changes in the cutting edges 53, of the sensed actual displacement and/or deformation, or the actual state, is accordingly used in an advantageous manner for monitoring/controlling the motor spindle 3, i.e. preferably for monitoring, or checking, of individual cutting edges.

[0135] In FIG. 8, an axially aligned deformation of a measuring arm 11 comprising the axial sensor 4, or an axial change A in the distance 9, can be sensed and processed further. This axial change A is in turn by a force/change F on the cutting edges 53, or axial and/or radial deformation/alteration on the cutting edges 53 of the tool 50, which is transmitted to the tool receiving unit 8 and to the element 6.

[0136] Represented in highly schematic form in FIG. 9 is a cross-section through the variant according to FIG. 8, illustrating the optional arrangement of two sensors 4. These two sensors 4, as well as two radially oriented sensors 4 according to FIG. 7, which are not represented in greater detail, are preferably arranged offset by 90° or 180° in the circumferential direction. Symmetrical or asymmetrical displacements and/or deformations/alterations of the counter-holder 6, or stop/ring element 6, of the motor spindle 3 and/or of the tool receiving unit 8, caused by the load on the individual cutting edges, can be sensed by the two sensors 4 and analyzed/evaluated in an advantageous manner.

[0137] Represented schematically in FIGS. 10A and 10B is a commercially available tool 50, or milling cutter 50. It has a tool head 51 that in this case, as an example, has four individual cutting edges 53, and a tool shank 52. The tool shank 52 is usually held in a tool holder, which is not represented in greater detail, and inserted into the tool receiver.

[0138] FIG. 12 shows an example of an axial deflection of a tool 50 having four cutting edges 53, such as the milling cutter 50 shown in FIGS. 10A and 10B, during one revolution of a drilling process. Shown clearly here are four peaks of the deflection caused by the four cutting edges 53. One peak in this case is slightly flattened, which indicates a somewhat impaired cutting edge 53, or a certain amount of wear.

[0139] Shown as an example for illustrative purposes in FIG. 11 is a process of machining a groove, in which a jamming of the chips has been caused by excessive feed motion. This can be seen in the middle region, at the two very high peaks. As an example, in FIG. 11 a predefined/critical threshold value K is drawn in the diagram, which has been exceeded by the second, particularly high peak. This is to illustrate that, for example, a stored threshold value K may be predefined as a specified-state/value and which, when exceeded as represented by an example in FIG. 11, can result in a machine reaction and/or in advantageous signaling, or output of a display/alarm. In this way, for example, a disadvantageous jamming of possibly excessively large chips at the machining point, or at one of the cutting edges 53, may result in an immediate stop and/or alarm, such that a breakage of the tool 50 or one of the cutting edges 53, or an inaccurate machining of the workpiece, can be prevented in an effective manner.

LIST OF REFERENCES

[0140] 1 machine-tool unit [0141] 2 stator unit [0142] 3 rotor unit [0143] 4 sensor ring [0144] 5 axial sensor [0145] 6 measuring ring [0146] 7 electronics unit [0147] 8 checking device [0148] 9 machine control system [0149] 10 enclosure [0150] 11 bearing cover [0151] 12 taper ring/tool clamping device [0152] 20 reference signal [0153] 21 measuring signal [0154] 22 difference operator [0155] 23 frequency analysis [0156] 24 frequency search [0157] 25 amplitude evaluation [0158] 50 tool [0159] 51 tool head [0160] 52 tool shank [0161] 53 cutting edge [0162] 101 collet chuck [0163] 102 collet-chuck element [0164] 103 motor spindle [0165] 104 sensor [0166] 105 spindle shaft [0167] 106 stop [0168] 107 element [0169] 108 tool receiving unit [0170] 109 distance [0171] 110 stator unit [0172] 111 measuring arm [0173] A change [0174] a acceleration [0175] D axis of rotation [0176] F force [0177] F1, F2 flanks at groove edges [0178] K threshold value [0179] N groove [0180] R direction [0181] t time [0182] u distance [0183] v.sub.0 rotational speed/velocity [0184] X region [0185] Δφ phase difference