FR2546797A1 - METHOD AND DEVICE FOR MONITORING MACHINING CONDITIONS ON A MACHINE TOOL - Google Patents

Abstract

A.PROCEDE FOR MONITORING THE WORKING CONDITIONS ON A MACHINE-TOOL; B. CHARACTERIZED BY MEASURING PERIODICALLY THE ULTRASONIC EMISSION 1 OF THE MACHINING PROCESS AS WELL AS TWO CHARACTERISTICS OF THE MACHINING POWER 4, 7 AND WHEN EXCEEDING A SETPOINT AREA OF THE DISPERSION OF THE VALUES OF MEASURES, A SIGNAL IS DELIVERED AND STORED 14, 15, 16, THE SIMULTANEOUS APPEARANCE OF THESE SIGNALS FOR THE THREE PHYSICAL QUANTITIES 18 IS INTERPRETED AS A TOOL BREAKAGE 19 WHILE THE SIMULTANEOUS APPEARANCE OF TWO SIGNALS 23 IS INTERPRETED AS ONE ALARM SIGNAL FOR ANOMALIES IN THE PROCESS 25; C. THE INVENTION CONCERNS THE MONITORING OF AUTOMATIC MACHINE TOOLS.

Description

Method and device for monitoring conditions

machining on a machine tool ".

  The invention relates to a method and an arrangement

  to monitor machining conditions on a machine tool by continuously monitoring

  physical characteristics of the machining process, these large

  being exploited with regard to a state-of-the-art

  machining cessation highlighting tool breakage

or anomalies of the process.

  The machining by chip removal, automa-

  to a large extent, by machine tools

  program programs with automatic feeding of

  these projects, involves constant monitoring of the

  Machining process with regard to incidents and anomalies, as well as an automatic control of tool breaks From the detection of incidents and anomalies

  abnormalities in the machining process, it is possible to take

  to avoid them From the detection of a rup-

  tool, it is necessary to implement an interruption

  immediate machining to avoid damaging consequences.

  significant injuries occurring during tool breaks, such as

  the destruction of the surface of the workpiece and / or the destruction of machine parts In the case of machine tools operating automatically, it is possible, from the tool break signal, implement , in addition to the interruption of the machining, also a replacement 2.-

of the tool.

  In the case of machine tools which are used for the machining of different workpieces and for different machining operations, the monitoring shall as far as possible be independent of these conditions.

tions.

  By document DD-WP 105 739 it is known from

  from a sudden drop in the machining effort, or the increase of this effort beyond a normal value, the conclusion of a tool break. But this evolution of the effort of machining does not result in all cases,

  of a tool break The type and course of a rup-

  tool can vary so various that with this known device, on the one hand, all the tool failures occurring can not be detected and on the other hand,

  certain changes in machining causing an increase in

  the machining effort can be interpreted as

  wrong way like a tool break.

  In the case of another known device (DE-OS 22 51 333), measured values are formed from

  components of the machining effort, relative values

  of the effort of advancement in relation to the primary effort

  In this case, two comparative operations are performed to recognize the machining center and the return force relative to the main machining force.

  a tool break In the first comparison operation

  its, the actual value of a certain component of

  the machining effort is compared to an associated limit value

  In this second comparison operation, each of the relative values is compared to a predefined relative value. Thanks to this method, a large number of tool breaks can be recognized - but, however, the erroneous decisions are too frequent.

  to enable exploitation without the intervention of

  This is a result of the fact that, for example, because of sink holes, or in the case of turning and deviations from

  from the cylindrical form, different impulses

  rasites occur which are interpreted as

  tools which can lead to an unjustified interruption of the machining process or to

stopping the machine tool.

  Another way of proceeding in order to definitively distinguish a tool break from other influences

  disruptive is known from DE-OS 30 43 827.

  In this process, in addition to the comparisons

  previously known sound with the measured values of the components of the machining force, the average values of these measured values and other differential values

  are formed and, moreover, the evolution of the values

  as regards their evolution over time, is exploited and monitored. The erroneous decisions concerning

  a possible tool break can certainly, thus, reduce

  to a minimum, but for this purpose the expenditure on technical

  a high level of calculation, already high without this, is further increased to allow the formation of quotients and the operations of comparison of the components of the machining effort. The very extensive operations of treatment of the measured values to be carried out, increase in this case automatically the tendency to breakdowns, and the introduction of the evolution over time of the calculated quotients of the quantities of measures,

  to decide on a tool break, can

  to make a reaction too late as regards the

  machining interruption from the moment when a

tool break -

  All these known devices based on the measurement of the machining forces, require on the support of the tool or on the support of the workpiece, suitable detectors for the measurement of the forces As each detector element measuring a present effort 4.-

  its very function, an elastic deformation, these ele-

  Measuring instruments alter the rigidity of the machine tool

  in the transmission of forces between the tool and the part-

  lumber. Other known devices (DD-WP 146 501, DE-OS 2 125 426), which avoid, during the monitoring of machining processes, provisions that alter the rigidity of the machine tool, detect the anomalies of the process

  by measuring vibrations originating at the point of

  in the form of impact noise signals or ultrasonic signals By exploiting these signals, we can distinguish changes in the machining process according to different causes, such as, for example, defects in the homogeneity of the material, modifications of the shape of the chips, and also a tool wear But a

  exploitation of these measured values is not pos-

  sible with regard to a tool break, because too many

  different factors of influence give rise to the appearance

  vibrations, even in the case of a tool whose condition

is still irreproachable.

  The object of the invention is to provide a method and a

  positive to monitor the machining conditions, process

  and device by which a tool break is de-

  with a relatively low level of expenditure and

  you and can be distinguished from other anomalies of the process.

  The problem underlying the invention is to create a method for monitoring the machining conditions on a machine tool by permanently measuring several physical quantities characterizing the machining process, these quantities being exploited from the point of view of a state of the machining process indicating tool failure or process anomalies, in which, instead of the measurement of the forces affecting the rigidity of the machine, parameters determining the control of the process of the machine will be introduced machining, and which will indicate 5.-

  clearly and with certainty, without any additional combination

  by calculating the different parameters between them,

  process abnormalities as well as break-ups

  The problem underlying the invention also involves the creation of a device for implementing this method.

  This problem is solved according to the invention

  in that the ultrasonic emission of the machining process and two characteristic magnitudes of the machining power are measured as physical magnitudes, and the quantities thus measured are periodically called the measured values of each. physical quantities being exploited with regard to their deviation, from a predefined setpoint of their dispersion, so that when the dispersion of the measured values exceeds this setpoint, a signal is delivered and stored until at the next call, the simultaneous intervention of these signals for all three physical quantities being interpreted as a tool failure signal, while the simultaneous intervention of two signals over a period of time derived from time machining, being interpreted as a

  alarm signal for process abnormalities

  characteristics of the power of

  are the main driving power and the

  in advance To decide on the overtaking

  of the set range of the dispersion of the measured values

  are based on the dispersion of the ten

last measured values.

  The mechanism for implementing the procedure

  Discloses sensors for the ultrasonic emission of

  machining, for the main drive power and for the feed drive power.

  each sensor is arranged a door whose entry com

  mutation is connected to the output of a pulse generator.

  Pulsed signals control the doors 6.- after the others The door outputs are connected to an operating circuit which determines the deviation from a predefined dispersion and the extension of a range.

  setpoint of the dispersion, the output of this circuit of

  ploitation being respectively connected to an organ of

  memory associated with each of the value generators of

  The outputs of the three memory devices are connected

  corded via a combination device to the input of state of a signal memory indicating

  tool break, while the outputs of

  two memory devices are, via an associated combination device, connected to a door

  collector OR, the output of which is connected via

  of a timed device at the input of setting to the state of a memory of alarm signals indicating the anomalies

  of the process, and whose erase input is

  to be activated by the start of each new

cutting of the machining process.

  It is preferably intended as a temporary

  porisé, a monostable multivibrator.

  The process according to the invention is based on the following concepts: In monitoring systems, there is

  should be used as much as possible as criteria for

  monitoring, parameters of the machining process that are, to a large extent, independent of the various machining conditions, as well as the various influences of the materials

  and raw parts The exploitation of quantities

  turing the machining process, and their evolution over the duration of a few revolutions of the workpiece, to obtain a clear tool break signal, is too slow from the point of view of an immediate interruption of machining to pocket damaging consequences To be able, as far as possible, to take into account all the anomalies involved in the machining process, anomalies 7. caused by sinkholes, changes in chip shapes, chip jams, defects of

  forms and sides of the workpiece, and for

  see, on the other hand, eliminate parasitic signals, inter-

  accidentally coming only one time, of different parameters, as well as parasites intervening periodically (false-rounds), without having to follow the values of measurements intervening on several revolutions of the workpiece, the present method consists in apprehending cyclically of

  permanently by the measurement technique, three parameters

  the machining process is mutually complementary and reacts differently to process anomalies, and

  to deliver a tool break signal only when

  simultaneous viations for these three parameters, out of

  the set range of their dispersion.

  As research has shown, a rup-

  tool is always related to a sudden modification of the measured values. Moreover, it occurs

  also, due to process anomalies, changes in

  measurement values that can not be

  the changes caused by a break in

  til But these changes in values of measurements taking

  birth due to process anomalies, do not manifest themselves

  not the same for the three measurement parameters

  res It is furthermore added that the deviations of one of the three measurement signals are exploited as

  accidental quantities, and remain

  for triggering consequent provisions.

  During the simultaneous intervention of deviations of two

  their measured values, manifesting themselves over a predetermined period of time

  finished, it is delivered an alarm signal that allows

  closes to a process anomaly or to a regulation fault, which can for example be remedied by modifying cutting values The increase or the fall of the power parameters for a depth of cut 8.-

  continuously increasing or decreasing

  as, for example, when shooting a cone

  of a cylindrical blank, is distinguished from the anomalies of the process in that it is not the absolute magnitude of the parameter but its deviation from a pre-defined setpoint of dispersion which is exploited for this purpose, the dispersion is established for each of the quantities measured from several measured values, for example ten,

  * this dispersion being updated by each new variation

  their measurement added in addition to leaving the oldest of the ten measurement values aside Slow growth or fall of the absolute measured values while the predefined dispersion range is maintained, is not detected by the monitoring device -The knowledge

  absolute magnitudes of the parameters are therefore superfluous.

  Thanks to this mathematically statistical treatment of

  their measured, and thanks to the calculation of the dispersion, of

  very small fluctuations in the measured values are compensated

  sudden changes then causing a net

  increased dispersion Thanks to the choice of

  persion, as a control variable, the modifications

  sitive and negative values measured, are taken into

count the same way.

  Parameters corresponding to the ultrasonic emission, the main drive power and the drive power in advance, we can deduce the clear discrimination criteria between the anomalies of the process and a tool break While a modification

  sudden simultaneous measurement of the measured quantities of the three para-

  meters leads to the conclusion of a tool break, the modification

  simultaneous cation of two of the three parameters must be

  interpreted as a process anomaly.

  It thus appeared that

  a sudden change in the power of training

  ment and advance driving power-

9:

  and, as a result, a net overrun of

  a sign of the dispersion of these parameters, but that, on the other hand, the ultra-sonic emission reacted infrequently and thus did not exceed the set range of this dispersion. The simultaneous occurrence of exceeding the set span of the main drive power and the advance drive power, do not

  also not in this case, by an alarm signal

  because the time criterion is also necessary for the pre-

  presence of this condition, is not delivered because already the

  their following measurements, after passage of the location of the shrink, corrected the dispersion to be exploited When changes in the shape of the chips,

  Another anomaly in the process is the ultra-

  sonic exceeds the set range of this dispersion, but on the other hand, the main driving power and the feed-in power, do not show any

  exceeding their set point ranges.

  When jamming chips,

  of the set range appear as well

  in the ultrasound emission than in the power of training.

  in advance, such overruns triggering for example an alarm signal when, over the predefined period of time,

  no normalization of the state of the process takes place.

  But this state of the process is distinguished from a break in

  because in this case, there is no overshoot of the set range of the main drive power. In the case of periodic fluctuations in the measured values of the power, which are caused by the out-of-roundness of a draft film, the criterion

  ultrasonic emission brings only small changes

  fications that do not exceed the range of the dispersion and thus also stand out

net, of a tool break.

  10.- The process according to the invention can be completed, especially for various machining conditions,

  as they occur on machining contours,

  or machining cuts on different sections of

  diameters, with memorized setpoint values as-

  different values measured and which have been de-

  Experimentally and automatically finished by machining samples, that is to say that for different sets of programs of different machining contours on a part

  the set values of the three measured variables

  respectively associated with these programs, can be called. With the solution according to the invention,

  first of all, when operating a machine,

  China automatic tool without operator intervention,

  that, on the one hand, this machine tool or the work piece

  are not damaged due to an undetected tool break, and that, on the other hand, the machine tool is not stopped as soon as there is a fault in the process without

tool breakage.

  Other advantages of the method according to the invention reside in that the detection of the measured values does not interfere with the transmission of the forces of the machine tool and that also the work space

  of the machine tool is not limited. In addition, a

  simple measurement of the measured values is obtained from

  the main driving power or the power of

  In addition, it is not necessary to

  necessary to combine by calculation the measured values,

  the result of which is a reduced circuit expenditure.

  te, that the signal of a tool break is delivered without delay. The device for implementing the method is represented on a connection diagram of

principle.

11.-

  A sensor of measured values 1 for the emission

  ultrasound is connected to the output via

  In the same way, a measurement value sensor 4 for the main drive power is connected to a port 6 via a processing circuit. 5, and

  a sensor of measured values 7 for the power of

  advance feed is connected via a

  processing circuit 8 at a gate 9

  change of doors 3; 6; 9 are connected to the outputs

  effective, respectively time-shifted, of a cir-

  cooked distributor 10 which can be controlled by a transmitter

  pulser 11 The outputs of the gates 3; 6; 9 are connected via an analog converter /

  digital 12 to an operating circuit 13.

  At the exit of the operating circuit 13, are

  connected memory organs 14; 15; 16 associates

  corresponding to each sensor of measured values 1; 4; 7, the state-of-state inputs S of these members being connected to effective outputs respectively shifted in time from the divider circuit 10 and are capable of

  to be synchronously called by the respective entries

  switching valves 3; 6; 9 A memory of

  their set point 17 is connected upstream of the circuit of ex-

  13, this memory containing elements of

  associated settings for each of the measured value sensors.

  rees 1; 4; 7, the corresponding channel can be called

  from the outputs associated with it, of the

  The operating circuit 13 is also capable of being activated by a pulse transmitter 11

  through the splitter circuit 10

  memory organs 14; 15; 16 are connected as inputs to an AND gate 18, whose output is connected to the state input S of a memory 19

  characterizing the tool break The outputs of respecti-

  12.- Vement two memory organs 14; 15 or 14; 16 or 15; 16 are connected to an AND gate 20 or 21 or 22 respectively associated, whose outputs are

  connected to a common OR gate 23 whose exit is

  linked through a timed organ 24 to the

  setting of the S-state of an alarm memory 25

  alarm clock 25 is also connected by its entrance

  release for the support of the signal present in the

  setting of state S to pulse transmitter 11 by

  via a NOR gate 26 and by the distributed circuit

titeur 10.

  The operating mode of the device is as follows:

  The measured values of the ultra-

  sound, main drive power and feed drive power are detected in

  permanence by the measured value sensors corresponding to

  weights 1; 4; 7 and are applied through the processing circuits 2; 5; 8 associated with these sensors

  respectively at gates 3; 6; 9 Thanks to the issuer of

  pulses II and to the distribution circuit 10 connected to the following

  te, the doors 3; 6; 9 are switched successively in

  time, so that the measurement values are applied

  through the analogue converter /

  12, one after the other on the operating circuit

  13 This treatment consists of the calculation of the dispersion from ten values

* current measurements and in the comparison of this dis-

  Measured values with a set span of the predefined dispersion from the value memory

  17 correspondingly to the value of

  sure called for treatment with the door 3; 6; 9

  from the measured value sensors 1; 4; 7, the

  their associated setpoint in the value memory of con-

  sign 17, is also called by the impulse transmitter Il 13.-

  p 4 through the dispatcher circuit-10 The re-

  The result of this operation appears, either in the form of a "null" digital signal if the dispersion target range is not exceeded, or in the form of a digital "erase" signal with the range deposit

  the dispersion is exceeded, at the exit of the circuit of ex-

  ploitation 13 and therefore, the memory organs 14; 15; 16.

  Among these memory organs 14; 15; 16 the organ corresponds to

  is activated by the transmitter of impulse

  11 by means of the distribution circuit 10, so that the result present in the event of an "erase" signal, and therefore in the event of exceeding the set range of the dispersion, puts the memory element in the state , while in the event of a "null" signal, so in case of not exceeding the dispersion setpoint, it returns to the state

  memory organ The outputs of the media organs

  moire 14; 15; 16 are statically connected to the inputs of the AND gate 18 so that when exceedances of the dispersion setpoint exist for the three

  measured values the memory 19 is set to the state, that is,

  that is, a tool break signal is issued when

  that the set range of the disc is exceeded

  two of the three measured values, the temporal organ

  porise 24 is controlled via the AND gate

  corresponding 20 or 21 or 22, as well as by

  the door OR 23 In the case of the

  monostable multivibrator as a temporal organ.

  at 24, it is only when the input signal is present beyond the switchover time that the signal is applied

  at the state input S of the alarm memory 25.

  The taking into account of the state input S in the alarm memory 25, in order to obtain a clear separation of the activation signals from the processing of the measured values, takes place at different synchronization times. i.e. via the synchronization signal 14.-

  negative during the synchronization pause.

  tervalle, the memory organs 14; 15; 16 restored to the original state by the disappearance of the exceedances of the

  of the dispersion, bring back the multivibrator monosta-

  It is thus guaranteed that overruns of the set point range occurring for a short time do not lead to the issuance of an alarm signal and are not reported as anomalies of the process. when they have not varied over a minimum period of time The alarm memory 25, just like the memory 19, used to indicate a tool break, are returned to their starting position by erasing signals. external (L) after the suppression of the disturbances In the case of the alarm memory 25 this takes place with the start of each new section In the case of the memory

  19, the erasure is carried out after the replacement of the

He broke up.

: 15 -

Claims (2)

REVENDICATI ONS) A method for monitoring the machining conditions on a machine tool by continuously measuring a plurality of the physical quantities characterizing the machining process, these quantities being exploited from the point of view of a state of the machining process revealing tool failure or process abnormalities, characterized in that the ultrasonic emission (1) of the machining process and two characteristic magnitudes of the machining power are measured as physical quantities. stroke (4,7) and these measured values are referred to as -periodically (11, 10), the measured values of each of the physical variables being operated with respect to their deviation from a predefined target range of their dispersion, so that when exceeding this set point of the dispersion of the measurement values, a signal is delivered, which is stored (14, 15, 16) until the call imnmediately following the appearance simultaneous of these signals for the three physical variables (18) being interpreted as a tool break (19), while the simultaneous appearance of two signals (23), beyond a time period derived from the time of cut, is interpreted as an alarm signal for process anomalies (25).   2) The process according to claim 1, wherein   characterized in that the characteristic quantities of the   machining power are the main drive power   Cipal and drive power in advance.   Process according to any one of the   1 and 2, characterized in that in order to decide to exceed the set range of the dispersion of the measured values, the dispersion of the ten last measured values.   4) Arrangement for implementing the procedure   dice according to any one of claims 1 to 3,   in that measuring sensors are provided.   16. (1; 4; 7) for the ultrasonic emission of the machining process, for the main drive power and for the feed drive power, a gate (3;   6; 9) being arranged after each sensor of   their measured values (1; 4; 7), this door being connected by   its switching input at the output of a transmitter of im-   pulses (11) whose pulsed signals control the doors (3; 6; 9) one after the other, while the outputs   of these doors (3; 6; 9) are applied to a circuit of   detecting (13) determining the deviation from a predefined dispersion and exceeding a range of   of this dispersion, the output of this circuit of   ploitation being connected to a memory member (14;   ; 16) respectively associated with each of the speed sensors   their measured O 1; 4; 7), and the outputs of the three organs   memories (14; 15; 16) being connected via the   combination member (18) at the entry of   in the state (S) of a signal memory (19) indicating the rup-   tool, while the outputs of respectively two memory members (14; 15; 16) are connected by   through a combination organ which is   associated with an OR gate (23) whose output is connected via a timed organ (24) to the state-of-state input (S) of a signal memory. 5 (25) indicating the process abnormalities, and whose erase input (L) is likely to be activated with the start of each new cut of the machining process.   5. Device according to claim 4,   characterized in that it is intended as a timed organ (24) a monostable multivibrator.