Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/14—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object using acoustic emission techniques
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
  • B23Q17/00—Arrangements for observing, indicating or measuring on machine tools
  • B23Q17/09—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool
  • B23Q17/0952—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool during machining
  • B23Q17/0971—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool during machining by measuring mechanical vibrations of parts of the machine
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
  • B23Q17/00—Arrangements for observing, indicating or measuring on machine tools
  • B23Q17/09—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool
  • B23Q17/0952—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool during machining
  • B23Q17/098—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring cutting pressure or for determining cutting-tool condition, e.g. cutting ability, load on tool during machining by measuring noise
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
  • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
  • G01N29/449—Statistical methods not provided for in G01N29/4409, e.g. averaging, smoothing and interpolation

Definitions

• the invention relates to a method for monitoring the machining of a workpiece, in particular when turning, by analyzing the sound emission detectable on the tool, which is converted with the aid of an electroacoustic converter into an electrical sound emission signal, which is filtered and determined with respect to it over a predetermined period of time Amplitude is compared with a predetermined adaptable threshold.
• the invention also relates to a device for carrying out the method with an electroacoustic transducer which is arranged on the tool holder and converts the sound emission signal and which feeds an averager via a high-pass filter, an amplifier and a detector, the output signal of which feeds the first input of a comparator, the second input of which . can be loaded with a threshold voltage.
• Such a method and such a device are known from US Pat. No. 4,332,161 and allow an output signal to be generated at the output of a comparator if the tool wear has exceeded a predetermined extent. Since the sound emission signal contains pulse-like chip breaking signals, the frequency and amplitude of which are not directly related to tool wear and machining quality, the output voltage of the integrator used for averaging is subject to interference, which is why the output voltage of the integrator and therefore the switching of the comparator cannot be reliably assigned to a given tool wear. The pending at the output of the integrator Voltage changes depending on the chip breaking sequence and is therefore not a reliable measure of tool wear.
• the object of the invention is to create a method and a device which make it possible to reliably detect all forms of wear and to reliably evaluate the chip breaking behavior.
• an average noise value of the sound emission signal is continuously formed, but the values of the sound emission signal that occur during the time windows assigned to the chip break signals are not taken into account for the averaging.
• a device for carrying out the method is characterized in that the averaging device is assigned a switching device by means of which the supply of the averaging device with the sound emission signal can be interrupted during the pulse-like chip breaking signals.
• FIG. 1 is a block diagram of a sound emission analysis device according to the invention.
• FIG. 2 shows a block diagram of the isolating stage of the sound emission analysis device according to the invention.
• the overall sound emission analysis device shown in FIG. 1 in the block diagram for monitoring the chip behavior and tool wear during machining, in particular when turning, allows the machining quality and the quality of the turning process to be continuously evaluated by using several different physical processes during the machining process Rotating generated sound emission is detected and processed.
• the sound emission to be evaluated is recorded in broadband on the tool holder with an electroacoustic transducer 1 shown schematically in FIG. 1.
• the electroacoustic transducer 1 is broadband and consists, for example, of a piezoelectric probe.
• the bandwidth of the converter extends from 20 kHz to 2 MHz.
• the converter 1 converts the sound emission occurring during the turning process into an electrical signal, which reaches a bandpass filter 3 via a line 2.
• the electrical sound emission signal reaching the bandpass filter 3 contains signal components which, during the turning process, are caused by the material separation, by the plastic deformation in front of the cutting edge, by frictional processes between the workpiece and the tool, and by frictional processes between the chip produced and the Tool, by breaking the chips and by breaking processes on the tool (tool breakouts).
• the breaking of the chips produces pulse-like chip break signals, the amplitude peaks of which are greater than the level of a continuous basic noise signal which arises from a cutting noise and a friction noise due to the physical processes mentioned above.
• the bandpass filter 3 is used to attenuate the low-frequency signal components of the chip break signals to such an extent that there is no longer any overlap of the individual chip break signals, which are very broadband and whose low-frequency components run back and forth in the tool holder relatively weakly damped and therefore the signal duration of the Determine chip break signals.
• undesired overlaps of the individual pulses of the chip breaking signals could occur without using a filter, which hinders their evaluation.
• the bandpass filter 3 is preferably adjustable to a lower limit frequency between 20 and 500 kHz.
• the upper limit frequency of the bandpass filter 3 is approximately 2 MHz.
• the bandpass filter 3 also serves to dampen machine noises.
• the filtered sound emission signal which is composed of the continuous background noise signal and the pulse-like chip break signals, passes via an amplifier input line 4 to a broadband amplifier 5.
• the broadband amplifier 5 serves, on the one hand, to convert the sound emission signal to the voltage required for further processing - strengthen.
• the broadband amplifier 5 contains a detector or absolute value generator in the form of a two-way rectifier or a squaring circuit if the subsequent stages require analog input signals, or an analog-digital converter if the subsequent stages are implemented in digital technology.
• the output of the broadband amplifier 5 feeds the signal inputs of an isolating stage 6 and a chip break signal processor 7.
• the isolating stage 6 makes it possible to separate the pulse-like chip break signals contained in the sound emission signal from the continuous background noise signal. It takes advantage of the fact that the pulse-like chip breaking signals Have amplitude peaks that significantly exceed the basic noise signal.
• the isolating stage shown in FIG. 2 has a comparator 8 which compares the amplified sound emission signal with a threshold value signal. The threshold value signal is always above the level of the background noise signal, so that only the pulses of the pulse-like chip break signals switch the comparator output from the first state to a second state. It is thus possible to detect and separate or hide the individual pulses of the chip break signals.
• the threshold value signal fed to the comparator 8 of the isolating stage 6 automatically adapts to the respective signal conditions. For this purpose, it is provided to derive the threshold value signal from the sound emission signal by averaging, the Sc all emission signal values being disregarded during the occurrence of the pulse-like chip breaking signals. As a result, the threshold value signal adapts itself independently of the chip break signals to the level of the respective continuous background noise signal, because by hiding the pulses of the chip break signals it is achieved that changes in the pulse amplitudes or the frequency of the chip break signals have no influence on the threshold value signal.
• the threshold value signal fed to the comparator 8 of the isolating stage 6 is generated by averaging the sound emission signal in each case over a predetermined period of time, the impulses of the chip breaking signals being masked out, however, during the averaging. are not taken into account.
• Such a separation of the basic noise signal associated with the cutting and rubbing noises and the Chip breaking signals associated with the breaking of the chips are expedient because the two signal components can change independently of one another.
• the pulses of the chip breaking signals are hidden to form the threshold value signal, since taking them into account when averaging the sound emission signal over a predetermined period of time would result in a signal which is not very useful, because changes in the level of the basic noise signal and the pulse amplitudes of the chip breaking signals differ in strength and can even take place in different directions.
• the separation stage 6 contains a tactile integrator or averager that continuously measures the mean, e.g. the RMS value of the basic noise signal determined over a predetermined period of time by averaging the sound emission signal by hiding the time segments which are assigned to the pulses of the chip breaking signals. Further details of the function of the construction of the separation stage 6 are explained below with reference to FIG. 2.
• the isolating stage 6 feeds, via a first output and a basic noise signal line 9, a basic noise signal processor 10 with data which are independent of the chip breaking frequency and the pulse amplitudes of the chip breaking signals.
• the basic noise signal processor 10 carries out a statistical analysis of the averaged basic noise signal.
• the averaged background noise signal is first parameterized by determining the " mean signal level of the background noise signal and the frequency of the dominating spectral component in the background noise signal in predefinable time intervals. This allows the basic noise signal processor to determine the distribution function of the main spectral components of the basic noise, and the distribution function of the level of the basic noise signal averaged over predeterminable time intervals and the scattering widths derived therefrom.
• the distribution of the averaged basic noise level is determined, for example, over a period between 1 and 10 seconds.
• the width of the distribution function of the averaged background noise level is a measure of the open spaces and / or scour wear.
• the basic noise signal processor 10 not only determines the frequency distribution of the averaged basic noise level, but also allows it to be analyzed by determining the respective maximum, width, skewness, excess and other variables.
• the evaluation processor 11 monitors in particular whether the distribution of the averaged background noise signal level exceeds a predetermined width. If this is the case, a corresponding output signal for further processing or for canceling the machining of the workpiece due to excessive tool wear is emitted via a wear output line 12. Even if the mean signal level or the frequency of the dominant spectral component indicates wear of the tool, which is clamped in the tool holder provided with the transducer 1, a signal is output on the wear output line 12 by the evaluation processor 11. In order to improve the monitoring of tool wear and to make it particularly reliable, and to monitor the chip behavior, in addition to evaluating the separated and averaged basic noise signal, an analysis and evaluation of the chip breaking signals is provided.
• the chip break signal processor 7 is supplied with input signals on the one hand via the output of the broadband amplifier 5 and on the other hand via a measuring gate signal line 13.
• the measuring gate signal line 13 supplies release signals generated by the isolating stage 6, which each tell the chip break signal processor 7 when 5 pulses of the chip break signal are present at the output of the broadband amplifier.
• the chip break signal processor 7 therefore only processes the sections of the sound emission signal assigned to the chip break signals.
• the chip breaking signal processor 7 has an internal clock which in particular allows the arrival times and the signal durations of the chip breaking signals to be determined.
• the chip break signal processor 7 also determines the peak amplitudes of the pulse-like chip break signals.
• the burst signal parameters ascertained by the chip breaking signal processor 7 arrive via a processor output line 14 to a frequency processor 15, which allows a statistical analysis of the various signal parameters and in particular determines distribution functions of the various parameters mentioned. Since the chip break signal processor 7 determines the arrival times and signal durations of the chip break signal pulses, the frequency processor 15 allows a distribution function of the time intervals between the individual pulses of the chip break signals to be determined. The frequency distribution determined shows that the chip break signals each consist of a signal group with several individual pulses. A signal group is assigned to each chip break, the chip break sequence determining the distances between the signal groups.
• the frequency processor 15 defines a signal distance filter from the distribution function of the intervals of the pulses of the chip break signals. All individual pulses of the chip break signals, the time intervals of which after the subsequent individual pulse are shorter than a value determined from the signal distance distribution function, are combined with the aid of the frequency processor 15 to form signal groups.
• the time intervals of the individual signal groups are determined, for example the time interval between the last signal in each group from the last signal in the next group.
• the values of the time intervals of the signal groups, which correspond to the time intervals between the chip breaks, are fed to a chip break sequence processor 17 via a first output line 16 for statistical analysis.
• the frequency processor 15 supplies frequency distributions of the signal amplitudes in the form of a distribution function of the peak amplitudes of the individual pulses in the chip break signals.
• the distribution function of the peak amplitudes is evaluated in an amplitude processor 19 which, in accordance with a development of the method on which the sound emission analyzer shown in FIG. 1 is based, also processes a distribution function of the energies of the pulse-like chip break signals in addition to the distribution function of the amplitudes. For this purpose, not only the maximum amplitudes of the individual pulses or bursts but also their energies are determined in the chip breaking signal processor 7, which energies result from the time integral of the amplitude squares over the duration of an individual pulse.
• the amplitude processor 19 allows the amplitude distribution of the chip break signals fed to it to be evaluated in a special way. For a predeterminable amplitude interval, which extends from small amplitudes to an amplitude below the maximum occurring amplitude, a distribution function is determined by an approximation function (best fit process) without taking into account the amplitudes above. Based on this function, which is derived from a part of the actually occurring amplitude distribution, the number of signals that should occur above a limit value due to this distribution function is then calculated. However, the amplitude processor 19 also receives the information regarding the actual number of signals via the second output line 18. Signals with amplitudes above the mentioned limit.
• the two values are compared with one another, ie it is checked whether the number of signals with amplitudes above the limit value corresponds to the number that can be calculated from the amplitude distribution of the signals below the limit value. Is the actual number of signals with amplitudes above the limit much larger than it should be due to the distribution function in the lower amplitude range, this is an indication of tool breakouts in the cutting surface.
• the number of amplitudes which exceed the specified limit value mentioned is fed to the evaluation processor 11 via an amplitude line 20.
• the evaluation processor 11 thus not only monitors parameters of the basic noise signal in the manner described above, but also parameters derived from the chip break signals.
• the evaluation processor 11 has, in addition to the input line assigned to the background noise signal and the amplitude line 20, a third input line 21 which is connected to the output of the chip breaking sequence processor 17. In this way, the evaluation processor 11 receives not only the distribution function of the continuous background noise and the number of amplitudes which exceed a certain limit value, but also information relating to the chip break sequence frequency determined by the chip break sequence processor 17.
• the chip break sequence processor 17 determines the frequency distribution of the time intervals of the signal groups for predeterminable periods. In addition, the chip break sequence processor 17 serves to carry out an analysis of this distribution function, the maximum of the distribution function, its width, etc. being evaluated.
• the time intervals between the signal groups correspond to the time intervals between the Chip breaks.
• the frequency distribution or the distribution function of the spacings of the signal groups corresponds to the distribution function of the chip break sequence and is therefore a measure of the chip lengths in the case of known processing parameters. Since the tool wear (flank and scour wear) correlates with a change in the chip lengths, the tool wear can be determined and evaluated from the statistical parameters of the chip break spacing distribution function with the aid of the evaluation processor 11. For this purpose, the characteristic values of the distribution function of the chip breaking sequence (maximum, width, etc.) are passed on to the evaluation processor 11 via the third input line 21.
• sample distributions are stored for the various distribution functions of the various signal parameters, which are compared with the determined distribution functions. For this purpose, deviations in the statistical moments are determined. The results of the distribution functions and their deviations from pattern distributions form the basis for the evaluation of the cutting behavior and tool wear by the evaluation processor 11.
• the evaluation processor 11 has a fault output 22 for indicating a fault in the case of contradicting input variables of the evaluation processor 11, as is the case, for example, with a chip clipper if an increasing wear noise occurs despite a constant chip breaking sequence.
• the evaluation processor 11 also has a documentation output 23, through which the input variables of the evaluation processor 11 are documented and output as a document for the quality of the machining process.
• One of the functions carried out by the evaluation processor 11 consists in comparing the input variables with predetermined limit values (pattern distributions). In the event of deviations from the target / actual situation, a malfunction of the turning process or tool wear is indicated in the manner specified below.
• the background noise signal processor 10 supplies values that lie outside the specified limit values and the values at the input connected to the amplitude line 20 also lie outside the limit values, a tool change is necessary since wear marks are exceeded.
• this is through separate hard-wired Units or possible through separate programmable processors. It is also possible to combine several processors to form a programmable processor.
• the isolating stage 6, which generates a threshold voltage which adapts to the basic noise in order to separate the pulses of the chip break signals independently of their amplitude and frequency, is described below with reference to an exemplary embodiment for an analog solution shown in FIG. 2 described in more detail.
• the isolating stage 6 containing the comparator 8 and shown as a block diagram in FIG. 2 is connected via an input line 50 to the output of the broadband amplifier 5. On the basis of the output signals of the broadband amplifier 5 arriving via the input line 50, the isolating stage 6 generates an averaged background noise signal which is coupled out via the background noise signal line 9.
• the chip break signal processor 7 shown in FIG. 1 is connected on the one hand to the output of the broadband amplifier 5 and on the other hand via the measuring gate signal line 13 shown in FIGS. 1 and 2 to the isolating stage 6.
• the input line 50 connects the output of the broadband amplifier 5 on the one hand to the first input 51 of a multiplexer 52 and on the other hand to the signal input 53 of the comparator 8, the comparative input 54 of which is supplied with a threshold value signal, which results from the description below Way is generated.
• the output of the multiplexer 52 is connected to the input of an averager 55, which integrates or averages the signal fed in via the multiplexer 52, in particular the continuous background noise signal.
• the averaging takes place over a predetermined period of time.
• the signal can be averaged in such a way that an RMS value is formed.
• the mean value generator 55 can be implemented by an RC element, or in the case of a digital solution, instead of the analog solution shown in FIG. 2, a computer with an accumulator and a dividing element, by means of which the mean value of a predetermined number of sample values of the Input signal is determined.
• the averager 55 shown in FIG. 2 supplies an analog mean value signal via an output line 56, the size of which is determined by the amplitudes of a predetermined period of time. This time period is given, for example, by the size of the integration capacitor when implemented by an RC element.
• the output line 56 is connected to the input of an analog / digital converter 57, which converts the analog mean into a digital mean and passes it on to a register 58 for temporary storage.
• Register 58 forms a digital sample and hold circuit which, among other things, prevents the arrangement from vibrating.
• the output of the register 58 is connected to the basic noise signal line 9, via which the current mean value of the basic noise signal can be coupled out to the basic noise signal processor 10.
• the digitized and averaged background noise signal reaches a digital / analog converter 60 via a coupling line 59, the output of which is connected to the second input 61 of the multiplexer 52.
• the multiplexer 52 can be switched over via a control input 62, so that either the signal at the first input 51 or the signal at the second input 61 can be switched through to the averager 55.
• the arrangement of the isolating stage 6 is such that the first input 51 is always switched through when the continuous background noise signal is present alone, while the multiplexer 52 is switched over when the chip break signals occur, so that the average background noise signal occurs during the duration of the chip break signals remains constant and is fed back to the mean value generator and the chip break signals occurring during this time do not influence the mean value on the output line 56 and the background noise signal line 9.
• the basic noise signal processor connected downstream of the isolating stage 6 is temporarily deactivated.
• the multiplexer 52 and the basic noise signal processor 10 are switched over via a control line 63, which is connected to an output of a measuring gate 64, which likewise generates a control signal for the register 58 and is connected to the register 58 via a control line 65.
• a measuring gate 64 Each time the pulse-like chip break signals occur, the measuring gate 64 generates the assigned signals, the multiplexer 52 being switched to the second input 61 via the control line 63 and the chip break signal processor 7 being released via the measuring gate signal line 13.
• the analog threshold voltage supplied to the comparison input 54 of the comparator 8 is generated with the aid of a threshold value generator 66 which is connected to the comparator 8 via a threshold value line 67.
• the threshold value generator 66 is connected on the input side via the output line 56 of the mean value channers 55 with the averaged background noise signal.
• this signal is processed in a multiplication circuit and a subsequent addition circuit.
• the averaged background noise signal is multiplied by an experimentally determined crest factor, which is between 1.4 and 8, for example.
• a constant offset voltage is then added in order to generate the threshold voltage for the comparator 8.
• the threshold generator 66 has an offset line 74 for the input of a constant offset and a crest factor line 75 for the input of an experimentally determined crest factor.
• the measuring gate 64 for switching the multiplexer 52 and releasing the chip break signal processor 7 is not controlled directly via the output line 68 of the comparator 8. Rather, the output line 68 is connected to a monostable multivibrator 69 that can be started repeatedly and a monostable multivibrator 70 that cannot be started repeatedly.
• the monostable multivibrator 69 serves as a delay circuit, the dead time of which can be set via a dead time line 70 and between 10 ⁇ sec and 1 msec. lies.
• the monostable multivibrator 69 is started.
• the measuring gate 64 is opened via the switching line 71, so that a The multiplexer 52 is switched to the second input 61 and the chip break signal processor 7 is released.
• the measuring gate 64 is closed again via the switching line 71, so that the multiplexer 52 is switched to the first input 51 and the background noise processor 10 is released. This is the case at the end of each pulse-like chip break signal.
• the monostable multivibrator 52 prevents the isolating stage 6 from blocking, since the multiplexer 52 is switched over to the first input 51 via the measuring gate 64 whenever there is a switchover to the second input 61 has elapsed a time that is longer than the longest expected time for a pulse-like chip breaking signal.
• This timeout is in the order of 10 to 100 msec and is communicated to the monostable multivibrator 72 via a timeout line 73.
• the comparator 8 thus switches on both monostable multivibrators 69 and 72 each time a pulse of the chip break signal occurs, and in the normal case, as can be seen from the above explanations, only the monostable multivibrator 69 effects the switching process of the multiplexer 52.

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• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
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• 1988
  • 1988-09-02 DE DE3829825A patent/DE3829825A1/de active Granted
• 1989
  • 1989-09-02 JP JP1509090A patent/JPH04500481A/ja active Pending
  • 1989-09-02 DE DE89909707T patent/DE58907252D1/de not_active Expired - Lifetime
  • 1989-09-02 WO PCT/DE1989/000572 patent/WO1990002944A1/de active IP Right Grant
  • 1989-09-02 EP EP89909707A patent/EP0433316B1/de not_active Expired - Lifetime
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