CN117428568A - Numerical control machining cutting chatter suppression control method and system - Google Patents
Numerical control machining cutting chatter suppression control method and system Download PDFInfo
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- 238000005520 cutting process Methods 0.000 title claims abstract description 162
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Classifications
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- 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
- B23Q15/00—Automatic control or regulation of feed movement, cutting velocity or position of tool or work
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- 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
- B23Q11/00—Accessories fitted to machine tools for keeping tools or parts of the machine in good working condition or for cooling work; Safety devices specially combined with or arranged in, or specially adapted for use in connection with, machine tools
- B23Q11/0032—Arrangements for preventing or isolating vibrations in parts of the machine
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- 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
- B23Q17/12—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring vibration
Abstract
The application discloses a control method and a control system for suppressing cutting chatter of numerical control machining, which belong to the technical field of numerical control machining, and the method comprises the steps of collecting vibration state information of pre-machined parts with different rigidities and shapes in the cutting machining process; associating corresponding workpiece marks with the prefabricated workpieces with different rigidities and shapes; determining a spindle rotating speed interval of the same-rigidity pre-processed workpiece in stable processing and deep cutting based on different spindle rotating speeds and frequency combination states; determining optimal normalized variable spindle machining parameters in a cutting depth range; cutting by adopting optimal normalized variable spindle machining parameters, and performing variable spindle rotating speed machining cutting flutter inhibition; calculating a flutter difference value between the obtained flutter index quantity and a stability threshold value; when the flutter difference value is larger than the stable threshold value, calculating a feedback adjustment parameter corresponding to the rotating speed of the variable spindle through the flutter inhibitor, and carrying out feedback adjustment on the processing parameter of the variable spindle. The method has the effect of improving the chatter vibration inhibiting effect in the cutting machining process.
Description
Technical Field
The application relates to the technical field of numerical control machining, in particular to a method and a system for suppressing and controlling cutting chatter in numerical control machining.
Background
When a numerical control machine tool is used for carrying out numerical control cutting processing on a product, cutting chatter is easy to cause due to the reasons of complex appearance of a workpiece, improper cutting amount, improper machine tool rotating speed selection and the like; the cutting chatter can influence the normal motion track of a machine tool cutter so as to reduce the quality and the cutting size precision of the surface of a processed workpiece; excessive noise, cutter damage and the like can be caused, and the damage to cutters and machine tool equipment is large.
Therefore, the suppression control method capable of improving the suppression effect of chatter vibration in the cutting process has practical application value.
Disclosure of Invention
In order to improve the chatter suppression effect in the cutting machining process, the application provides a numerical control machining cutting chatter suppression control method and system.
The first technical scheme adopted by the invention of the application is as follows:
the control method for suppressing the cutting chatter of the numerical control machining comprises the following steps:
collecting vibration state information of the pre-processed parts with different rigidities and shapes in the cutting process; associating corresponding workpiece marks with the prefabricated workpieces with different rigidities and shapes;
determining a spindle rotating speed interval of the same-rigidity pre-processed workpiece in stable processing and deep cutting based on different spindle rotating speeds and frequency combination states; determining an optimal normalized variable spindle machining parameter within a set cutting depth range based on the workpiece identification;
cutting machining is carried out by adopting optimal normalized variable spindle machining parameters based on the workpiece mark, and machining cutting chatter suppression at variable spindle rotating speed is carried out;
calculating a chatter difference value between the obtained chatter index quantity and a set stability threshold value in the cutting process; and when the flutter difference value is larger than the stability threshold value, calculating a feedback adjustment parameter corresponding to the rotating speed of the variable spindle through a preset flutter suppressor, and carrying out feedback adjustment on the processing parameter of the variable spindle based on the feedback adjustment parameter.
By adopting the technical scheme, the workpiece mark comprises rigidity data, shape data, thickness data and the like of the workpiece; based on the vibration states of the preformed pieces with different rigidities and different shapes, measuring the stable cutting depth state of the preformed pieces with the same rigidity and the same shape under the conditions of different spindle speeds and frequencies, thereby testing the spindle speed interval of the cutting tool under the processing condition of stable cutting depth; before cutting processing is performed next time, cutting processing is performed by adopting optimal normalized variable spindle processing parameters (including spindle rotating speed amplitude and frequency) based on a workpiece mark, so that variable spindle rotating speed processing cutting chatter suppression operation is effectively performed; further, by comparing the set chatter index amount with the chatter difference value between the stability threshold values; when the chatter difference is larger than the stability threshold (the chatter characteristic phenomenon starts to appear but the chatter amplitude is smaller at the moment), the machining parameters of the variable spindle rotating speed are fed back and adjusted in time in the machining process of the numerical control machine tool so as to more accurately inhibit machining cutting chatter, and the cutting machining chatter inhibition effect is further improved.
In a preferred example, the present application: the method specifically comprises the steps of calculating the obtained flutter difference value between the flutter index quantity and a set stability threshold value in the cutting process:
acquiring vibration monitoring signals in the cutting process based on the information acquisition instruction, and confirming corresponding chatter index quantity according to the vibration monitoring signals; generating a record list based on the workpiece identification corresponding to the cut pre-machined workpiece;
calculating a minimum feedback adjustment parameter required by the flutter index quantity to reach the stability threshold value by combining the record list; comparing the minimum feedback adjustment parameter with a critical difference value and a limit difference value respectively according to a judgment rule;
when the minimum feedback adjustment parameter is greater than or equal to the critical difference value and smaller than the limit difference value, an automatic feedback adjustment instruction is sent to a driving terminal of the variable spindle;
and when the minimum feedback adjustment parameter is greater than or equal to the limit difference value, sending a processing stopping prompt message to a preset numerical control terminal.
By adopting the technical scheme, whether the chatter index quantity with the chatter characteristic index is provided is confirmed by collecting the vibration monitoring signal in the cutting process, and a record list is generated based on the collecting action and the corresponding collecting result (chatter index quantity), so that the frequency of occurrence of chatter of the machine tool, the time continuously in a stable state and the like are known by collecting the monitoring result; the method is more beneficial to monitoring the cutting chatter state of the machine tool.
The minimum feedback adjustment parameters are a minimum rotation speed amplitude difference value and a minimum frequency difference value when the rotation speed of the current variable spindle is adjusted to a stable state in a flutter state; when the minimum feedback adjustment parameter is smaller than the critical difference value, the numerical control machine tool is in a cutting depth stable state when cutting machining is performed; when the minimum feedback adjustment parameter is greater than or equal to the critical difference value and less than the limit difference value, the numerical control machine is positioned at the flutter inoculation section, and signals with flutter characteristics begin to appear; or the numerical control machine tool is in a very slight flutter state at the moment, the machining can be continued through timely feedback adjustment, and the flutter characteristics are slowed down and adjusted to a stable state; when the minimum feedback adjustment parameter is larger than or equal to the limit difference value, the flutter state of the numerical control machine tool is obvious, excessive noise, cutter damage and the like can be caused, and the machining needs to be stopped; the cutting adjustment is timely carried out by sending out a message for stopping the machining, so that the cutting adjustment is convenient to timely follow the cutting progress.
In a preferred example, the present application: based on the information acquisition instruction, vibration monitoring signals are acquired in the cutting process, corresponding vibration index quantity is confirmed according to the vibration monitoring signals, and the method specifically comprises the following steps:
collecting vibration monitoring signals in the machining and cutting process of a variable spindle, and extracting flutter characteristic indexes of the vibration monitoring signals to confirm corresponding flutter index quantities;
calculating the real-time weighted wavelet packet entropy of the vibration monitoring signal;
and calculating the weighted wavelet packet entropy of the vibration monitoring signal in a set time interval, comparing the weighted wavelet packet entropy with a weighted threshold of a preset vibration inoculation stage, and recording the weighted wavelet packet entropy into the record list.
By adopting the technical scheme, the vibration monitoring signals in the cutting process are acquired at the appointed time point based on the information acquisition instruction, the vibration monitoring signals comprise sound signals, acceleration signals, current signals and the like in the processing process, and the vibration monitoring signals are subjected to vibration feature recognition based on the set sampling frequency so as to cut vibration features; the difference value of the weighted wavelet packet entropy of the vibration monitoring signal and the weighted threshold value of the vibration inoculation stage is compared, so that the difference value is conveniently input into a vibration suppressor to perform feedback adjustment of vibration suppression again, and the vibration suppression precision is improved; and the weighted wavelet packet entropy of the vibration monitoring signal is compared with the weighted threshold value of the vibration inoculation stage and recorded in a record list, so that a tester can conveniently perform multiple test experiment adjustment when monitoring feedback adjustment inhibition parameters, and the vibration inhibition results of adjustment feedback with different rigidities and different shapes are identified and compared, so that the feedback adjustment efficiency of vibration inhibition is further improved.
In a preferred example, the present application: the calculation method of the weighted wavelet packet entropy comprises the following steps:
determining the number of wavelet packet decomposition layers L, wherein the wavelet packet coefficients of the J-th band of the L-th layer are defined as
Determining a weighted frequency band;
and respectively calculating the entropy values of the weighted wavelet packet in the steady state and the flutter state.
By adopting the technical scheme, in order to detect the chatter in the inoculation stage of the chatter in the numerical control machining process, the chatter detection method based on the weighted wavelet packet entropy is provided: in particular, due to the complexity and randomness of the cutting process, the energy ratio of each frequency band will be 2 in a steady state L And the fluctuation of the energy distribution mainly comes from the measurement errors caused by the cuttings and forced vibration, and the number of layers is decomposed based on wavelet packets to improve the frequency resolution.
In a preferred example, the present application: the method for calculating the entropy values of the weighted wavelet packet in the steady state and the flutter state respectively specifically comprises the following steps:
respectively establishing models of the energy distribution of the vibration monitoring signal in a frequency domain under a stable state and a flutter state;
in steady state, the ratio of the total energy occupied by each band is the same: e (E) L,j ＝2 -L ,J＝1,2,…,2 L The method comprises the steps of carrying out a first treatment on the surface of the Setting the main frequency of the vibration to be positioned in a p-th frequency band, and weighting the p-th frequency band to obtain a weighted wavelet packet entropy value in a stable state:
in the flutter state, the increased energy ratio of the p-th frequency band is increased to E L,p ＝2 -L +d,d>0；
The entropy reduction of the weighted wavelet packet caused by the vibration is p ′ ,p ′ Is a function of k, L, d, k, L, d respectively representing weights, wavelet decomposition levels, normalized energy increase, for each group L, d, p ′ There is an optimal weight.
By adopting the technical scheme, the weighted wavelet packet entropy value in the steady state and the flutter state is obtained; extracting flutter characteristic indexes in a computer to obtain flutter characteristic quantities; the method is convenient for identifying the vibration inoculation stage of the cutting vibration.
In a preferred example, the present application: the flutter suppressor comprises a PID controller or a fuzzy controller; comprising the following steps: taking the difference value of the weighted wavelet packet entropy of the vibration monitoring signal and the weighted threshold value of the preset flutter inoculation stage as the input of the PID controller or the fuzzy controller, wherein the output of the PID controller or the fuzzy controller is a feedback adjustment parameter, and the feedback adjustment parameter is the normalized amplitude and frequency of the rotating speed of the variable spindle.
By adopting the technical scheme, according to the output of the chatter controller, the numerical control program of the numerical control processing machine tool changes the normalized amplitude and the normalized evaluation rate of the variable spindle on line in the processing process, and cutting chatter inhibition is carried out by proper control parameters, so that the output (controlled quantity) of the control system of the numerical control program can be fed back and returned to the output of the chatter inhibitor, a closed-loop control system is formed, and the cutting quality of products is improved.
The second object of the present application is achieved by the following technical scheme:
a numerical control machining cutting chatter suppression control system comprising: for executing the numerical control machining cutting chatter suppression control method as described above,
the processing information acquisition module is used for acquiring vibration state information of the pre-processed parts with different rigidities and shapes in the cutting processing process; associating corresponding workpiece marks with the prefabricated workpieces with different rigidities and shapes;
the optimal parameter confirming module is used for determining a spindle rotating speed interval of the same-rigidity preformed piece during stable machining and deep cutting based on different spindle rotating speeds and frequency combination states; determining an optimal normalized variable spindle machining parameter within a set cutting depth range based on the workpiece identification;
the flutter suppression execution module is used for carrying out cutting machining by adopting optimal normalized variable spindle machining parameters based on the workpiece identification and executing variable spindle rotating speed machining cutting flutter suppression;
the feedback adjustment suppression module is used for calculating the obtained flutter difference value between the flutter index quantity and the set stability threshold value in the cutting process; and when the flutter difference value is larger than the stability threshold value, calculating a feedback adjustment parameter corresponding to the rotating speed of the variable spindle through a preset flutter suppressor, and carrying out feedback adjustment on the processing parameter of the variable spindle based on the feedback adjustment parameter.
By adopting the technical scheme, the workpiece mark comprises rigidity data, shape data, thickness data and the like of the workpiece; based on the vibration states of the preformed pieces with different rigidities and different shapes, measuring the stable cutting depth states of the preformed pieces with the same rigidity and the same shape under the conditions of different spindle speeds and frequencies, thereby testing the spindle speed interval of the cutting tool during stable cutting under the processing condition of stable cutting depth; before cutting processing is performed next time, cutting processing is performed by adopting optimal normalized variable spindle processing parameters (including spindle rotating speed amplitude and frequency) based on a workpiece mark, so that variable spindle rotating speed processing cutting chatter suppression operation is effectively performed; further, by comparing the set chatter index amount with the chatter difference value between the stability threshold values; when the chatter difference is larger than the stability threshold (the chatter characteristic phenomenon starts to appear but the chatter amplitude is smaller at the moment), the machining parameters of the variable spindle rotating speed are fed back and adjusted in time in the machining process of the numerical control machine tool so as to more accurately inhibit machining cutting chatter, and the cutting machining chatter inhibition effect is further improved.
In a preferred example, the present application: the feedback adjustment suppression module includes:
the cutting state monitoring submodule is used for acquiring vibration monitoring signals in the cutting machining process based on the information acquisition instruction and confirming corresponding chatter index quantity according to the vibration monitoring signals; generating a record list based on the workpiece identification corresponding to the cut pre-machined workpiece; the adjustment parameter comparison sub-module is used for calculating the minimum feedback adjustment parameter required by the flutter index quantity reaching the stability threshold value by combining the record list; comparing the minimum feedback adjustment parameter with a critical difference value and a limit difference value respectively according to a judgment rule; automatically adjusting the sub-module; when the minimum feedback adjustment parameter is greater than or equal to the critical difference value and smaller than the limit difference value, an automatic feedback adjustment instruction is sent to the driving terminal of the variable spindle;
and the processing stopping prompting sub-module is used for sending a processing stopping prompting message to a preset numerical control terminal when the minimum feedback adjustment parameter is greater than or equal to the limit difference value.
By adopting the technical scheme, whether the chatter index quantity with the chatter characteristic index is provided is confirmed by collecting the vibration monitoring signal in the cutting process, and a record list is generated based on the collecting action and the corresponding collecting result (chatter index quantity), so that the frequency of occurrence of chatter of the machine tool, the time continuously in a stable state and the like are known by collecting the monitoring result; the method is more beneficial to monitoring the cutting chatter state of the machine tool.
In summary, the present application includes at least one of the following beneficial technical effects:
1. the workpiece mark comprises rigidity data, shape data, thickness data and the like of the workpiece; based on the vibration states of the preformed pieces with different rigidities and different shapes, measuring the stable cutting depth state of the preformed pieces with the same rigidity and the same shape under the conditions of different spindle speeds and frequencies, thereby testing the spindle speed interval of the cutting tool during stable cutting under the processing condition of stable cutting depth; before cutting processing is performed next time, cutting processing is performed by adopting optimal normalized variable spindle processing parameters (including spindle rotating speed amplitude and frequency) based on a workpiece mark, so that variable spindle rotating speed processing cutting chatter suppression operation is effectively performed; further, by comparing the set chatter index amount with the chatter difference value between the stability threshold values; when the chatter difference is larger than the stability threshold (the chatter characteristic phenomenon starts to appear but the chatter amplitude is smaller at the moment), the machining parameters of the variable spindle rotating speed are fed back and adjusted in time in the machining process of the numerical control machine tool so as to more accurately inhibit machining cutting chatter, and the cutting machining chatter inhibition effect is further improved;
2. generating a record list based on the acquisition action and a corresponding acquisition result (flutter index quantity) so as to know the frequency of occurrence of flutter of the machine tool, the duration in a stable state and the like through acquisition monitoring results; the cutting chatter state of the machine tool is more convenient to monitor;
the minimum feedback adjustment parameters are a minimum rotation speed difference value and a minimum frequency difference value when the rotation speed of the current variable spindle is adjusted to a stable state in a flutter state; when the minimum feedback adjustment parameter is smaller than the critical difference value, the numerical control machine tool is in a cutting depth stable state when cutting machining is performed; when the minimum feedback adjustment parameter is greater than or equal to the critical difference value and smaller than the limit difference value, the numerical control machine is positioned at the flutter inoculation section, and signals with flutter characteristics begin to appear; or the numerical control machine tool is in a very slight flutter state at the moment, the machining can be performed in time through timely feedback adjustment, and the flutter characteristics are slowed down and adjusted to a stable state; when the minimum feedback adjustment parameter is larger than or equal to the limit difference value, the flutter state of the numerical control machine tool is obvious, excessive noise, cutter damage and the like can be influenced, and the machining needs to be stopped; the cutting adjustment is timely carried out by sending out a message for stopping the machining, so that the cutting adjustment is convenient to timely follow the cutting progress;
3. in order to detect the chatter in the inoculation stage of the chatter in the numerical control machining process, a chatter detection method based on weighted wavelet packet entropy is provided; in particular, due to the complexity and randomness of the cutting process, the energy ratio of each frequency band will be 2 in a steady state L And the fluctuation of the energy distribution is mainly sourced from measuring errors caused by cuttings and forced vibration, and the number of layers is decomposed based on wavelet packets to improve the frequency resolution.
Drawings
FIG. 1 is a flow chart of a method of digital machining cutting chatter suppression control in an embodiment of the present application;
FIG. 2 is a flowchart of step S4 in a numerical machining cutting chatter suppression control method according to an embodiment of the present application;
fig. 3 is a flowchart of step S41 in the method for controlling suppression of cutting chatter in digital machining according to an embodiment of the present application.
Detailed Description
The present application is described in further detail below with reference to the accompanying drawings.
In one embodiment, as shown in fig. 1, the application discloses a method for controlling the suppression of cutting chatter in numerical control machining, which specifically includes the following steps:
s1: collecting vibration state information of the pre-processed parts with different rigidities and shapes in the cutting process; the prefabricated parts with different rigidities and shapes are associated with corresponding part identifiers.
In the present embodiment, the vibration state information includes a steady state, a steady deep cutting state in the steady state, a chatter inoculation state, and a chatter state; the workpiece identification includes stiffness data, shape data, thickness data, etc. of the workpiece.
Specifically, vibration state information in the actual cutting process is collected so as to record whether cutting chatter can occur on the pre-processed parts with different rigidities at the same feeding speed, so that chatter influence factor analysis is conveniently carried out.
S2: determining a spindle rotating speed interval of the same-rigidity pre-processed workpiece in stable processing and deep cutting based on different spindle rotating speeds and frequency combination states; and determining the optimal normalized variable spindle processing parameters in the set cutting depth range based on the workpiece identification.
In this embodiment, the maximum stable machining depths corresponding to different normalized variable spindle rotation speed amplitude and frequency combinations at a certain spindle rotation speed are calculated by a semi-discrete method.
Specifically, before calculating the maximum stable machining cutting depth corresponding to different normalized variable spindle rotation speed amplitude and frequency combinations at a certain spindle rotation speed by using the semi-discrete method, model parameters such as modal quality, damping coefficient, natural frequency, cutting force coefficient and the like of the system can be measured.
Further, the optimal normalized variable spindle speed and frequency combination at a certain stable machining depth of cut under a certain spindle speed are determined and used as normalized variable spindle machining parameters, and the normalized variable spindle speed and frequency combination are stored in a database of a numerical control machining system.
S3: and carrying out cutting machining by adopting optimal normalized variable spindle machining parameters based on the workpiece identification, and executing variable spindle rotating speed machining cutting chatter inhibition.
Specifically, the numerical control machining system automatically selects normalized variable spindle machining parameters of a database in the numerical control machining system to perform deep cutting machining, and the variable spindle rotating speed flutter suppression operation is effectively performed.
The mode of changing the spindle rotation speed is a sinusoidal mode, namely the spindle rotation speed in a control program is taken as an average value, the actual spindle rotation speed is periodically changed in a sinusoidal mode, and the initial phase is arbitrary; and R parameters are used as transmission channels of numerical control NC data and PLC data to realize real-time writing of the spindle speed and the change frequency.
S4: calculating a chatter difference value between the obtained chatter index quantity and a set stability threshold value in the cutting process; when the flutter difference value is larger than the stable threshold value, calculating a feedback adjustment parameter corresponding to the rotating speed of the variable spindle through a preset flutter suppressor, and carrying out feedback adjustment on the processing parameter of the variable spindle based on the feedback adjustment parameter.
In this embodiment, the chatter index amount is an average value obtained by processing a signal having a chatter feature value based on a processing process and on-line in real time, and within a certain period of time; the collected signals can be one or more of sound signals, acceleration signals, current signals and the like; the flutter suppressor includes a PID controller and a fuzzy controller.
Specifically, when the chatter difference is greater than a stable threshold, cutting chatter is in an inoculation stage, and the rotating speed parameter of the variable spindle is subjected to feedback adjustment within the machine tool capacity range so as to improve the accuracy of chatter inhibition.
In one embodiment, as shown in fig. 2, in step S4, a chatter difference between the obtained chatter index amount and a set stability threshold is calculated during the cutting process; the method specifically comprises the following steps:
s41: acquiring vibration monitoring signals in the cutting process based on the information acquisition instruction, and confirming corresponding chatter index quantity according to the vibration monitoring signals; and generating a record list based on the workpiece identification corresponding to the cut pre-machined workpiece.
In the present embodiment, the vibration monitor signal is one or a combination of several of an acoustic signal, a cutting force signal, an acceleration signal, a spindle motor current, and a feed motor current. Performing flutter feature extraction processing on the vibration monitoring signal through a flutter detection algorithm at each very short time interval (the time interval is 10-100 ms) to confirm a real-time flutter index quantity; the record list is used for recording the mark of the preformed workpiece, the time of sending the information acquisition instruction, the vibration monitoring signal and whether the current machine tool is in a flutter state.
S42: calculating the minimum feedback adjustment parameter required by the flutter index quantity to reach the stable threshold value by combining the record list; and comparing the minimum feedback adjustment parameter with the critical difference value and the limit difference value respectively according to the judgment rule.
In this embodiment, the minimum feedback adjustment parameter is a minimum rotation speed difference value and a minimum frequency difference value when the rotation speed of the current variable spindle is adjusted to a steady state from the rotation speed of the current variable spindle in the chatter state.
Specifically, the minimum feedback adjustment parameters are respectively subjected to data comparison according to the judgment rule so as to facilitate the follow-up judgment of whether the technical control machine tool is in a stable stage, a flutter stage or a flutter inoculation stage.
S43: and when the minimum feedback adjustment parameter is greater than or equal to the critical difference value and less than the limit difference value, sending an automatic feedback adjustment instruction to the driving terminal of the variable spindle.
In this embodiment, when the minimum feedback adjustment parameter is smaller than the critical difference, it represents that the numerically controlled machine tool is in a steady state of cutting depth when performing cutting machining.
S44: and when the minimum feedback adjustment parameter is greater than or equal to the limit difference value, sending a processing stopping prompt message to a preset numerical control terminal.
In the embodiment, when the minimum feedback adjustment parameter is greater than or equal to the critical difference value and smaller than the limit difference value, the numerical control machine is positioned at the flutter inoculation section, and signals with flutter characteristics begin to appear; or the numerical control machine tool is in a very slight flutter state at the moment, the machining can be performed in time through timely feedback adjustment, and the flutter characteristics are slowed down and adjusted to a stable state; when the minimum feedback adjustment parameter is larger than or equal to the limit difference value, the flutter state of the numerical control machine tool is obvious, the transition noise, the cutter damage and the like can be influenced, and the machining needs to be stopped; the cutting adjustment is timely carried out by sending out a message for stopping the machining, so that the cutting adjustment is convenient to timely follow the cutting progress.
In one embodiment, as shown in fig. 3, in step S41, vibration monitoring signals are collected during cutting processing based on information acquisition instructions, and corresponding chatter index amounts are confirmed according to the vibration monitoring signals, specifically including:
s411: and collecting vibration monitoring signals in the machining and cutting process of the variable spindle, and extracting flutter characteristic indexes of the vibration monitoring signals to confirm corresponding flutter index quantities.
Specifically, the vibration monitoring signal is subjected to a chatter feature extraction process by a chatter detection algorithm every very short time interval (e.g., the time interval is set to 10-100 ms) to confirm a real-time chatter index amount.
S412: and calculating the weighted wavelet packet entropy of the real-time vibration monitoring signal.
Specifically, the extraction of the flutter characteristic index of the vibration monitoring signal is realized in a computer by calculating the entropy of the weighted wavelet packet.
S413: and calculating the weighted wavelet packet entropy of the vibration monitoring signal in a set time interval, comparing the weighted wavelet packet entropy with a weighted threshold value of a preset vibration inoculation stage, and recording a record list.
In this embodiment, the weighted wavelet packet entropy of the vibration monitoring signal is compared with the weighted threshold value of the vibration inoculation stage, the difference value between the weighted wavelet packet entropy and the weighted threshold value is calculated, the difference value is used as the input of the vibration controller, and the output of the vibration suppressor is used as the normalized amplitude and frequency of the variable spindle rotation speed.
Specifically, the recording list is used for recording the identification of the pre-processed workpiece, the sending time of the information acquisition instruction, corresponding vibration monitoring signals, corresponding vibration index amounts and the like; the stable and flutter state in the numerical control machining cutting process is convenient to record.
In one embodiment, the method for calculating the entropy of the weighted wavelet packet includes:
s10: determining the number of wavelet packet decomposition layers L, wherein the wavelet packet coefficients of the J-th band of the L-th layer are defined as
S20: a weighted frequency band is determined.
Specifically, the natural frequency of the machine tool system may be obtained by a modal experiment, and then the weighted frequency band is determined by the natural frequency.
S30: and respectively calculating the entropy values of the weighted wavelet packet in the steady state and the flutter state.
Specifically, the weighted wavelet packet entropy value is calculated to determine a chatter occurrence threshold and chatter judgment so as to select proper cutting parameters based on the chatter occurrence threshold for stable cutting.
In one embodiment, in step S30, the weighted wavelet packet entropy values in the steady state and in the flutter state are calculated, which specifically includes:
s301: and respectively establishing models of energy distribution of the vibration monitoring signal in a frequency domain in a stable state and in a flutter state.
S302: in steady state, the ratio of the total energy occupied by each band is the same: e (E) L,j ＝2 -L ,J＝1,2,…,2 L The method comprises the steps of carrying out a first treatment on the surface of the Setting the main frequency of the vibration to be positioned in a p-th frequency band, and weighting the p-th frequency band to obtain a weighted wavelet packet entropy value in a stable state:
s303: in the flutter state, the increased energy ratio of the p-th frequency band is increased to E L,p ＝2 -L +d,d>0；
S304: the entropy reduction of the weighted wavelet packet caused by the vibration is p ′ ,p ′ Is a function of k, L, d, k, L, d respectively representing weights, wavelet decomposition levels, normalized energy increase, for each group L, d, p ′ There is an optimal weight.
Specifically, obtaining weighted wavelet packet entropy values in a stable state and a flutter state; extracting flutter characteristic indexes in a computer to obtain flutter characteristic quantities; the method is convenient for identifying the vibration inoculation stage of the cutting vibration, and in the cutting vibration stage, the rotating speed parameter of the variable spindle is subjected to feedback adjustment within the machine tool capacity range so as to improve the accuracy of vibration suppression.
In an embodiment, the method for controlling the suppression of the cutting chatter vibration of the numerical control machining further includes:
taking the difference value of the weighted wavelet packet entropy of the vibration monitoring signal and the weighted threshold value of the preset flutter inoculation stage as the input of a PID controller or a fuzzy controller, wherein the output of the PID controller or the fuzzy controller is a feedback adjustment parameter, and the feedback adjustment parameter is the normalized amplitude and frequency of the rotating speed of the variable spindle.
Specifically, according to the output of the chatter controller, the numerical control program of the numerical control machine tool changes the normalized amplitude and the normalized evaluation rate of the variable spindle on line in the machining process, and cutting chatter suppression is performed by using proper control parameters, so that the output (controlled quantity) of the control system of the numerical control program is fed back and returned to the output of the chatter suppressor, and a closed-loop control system is formed, which is beneficial to improving the cutting quality of products.
It should be understood that the sequence number of each step in the foregoing embodiment does not mean that the execution sequence of each process should be determined by the function and the internal logic of each process, and should not limit the implementation process of the embodiment of the present application in any way.
In one embodiment, a numerical control machining cutting chatter suppression control system is provided, which corresponds to the numerical control machining cutting chatter suppression control method of the above embodiment.
The numerical control machining cutting chatter suppression control system comprises a machining information acquisition module, an optimal parameter confirmation module, a chatter suppression execution module and a feedback adjustment suppression module. The detailed description of each functional module is as follows:
the processing information acquisition module is used for acquiring vibration state information of the pre-processed parts with different rigidities and shapes in the cutting processing process; associating corresponding workpiece marks with the prefabricated workpieces with different rigidities and shapes;
the optimal parameter confirming module is used for determining a spindle rotating speed interval of the same-rigidity preformed piece during stable machining and deep cutting based on different spindle rotating speeds and frequency combination states; determining an optimal normalized variable spindle machining parameter within a set cutting depth range based on the workpiece identification;
the flutter suppression execution module is used for carrying out cutting machining by adopting optimal normalized variable spindle machining parameters based on the workpiece identification and executing variable spindle rotating speed machining cutting flutter suppression;
the feedback adjustment suppression module is used for calculating the obtained flutter difference value between the flutter index quantity and the set stability threshold value in the cutting process; when the flutter difference value is larger than the stable threshold value, calculating a feedback adjustment parameter corresponding to the rotating speed of the variable spindle through a preset flutter suppressor, and carrying out feedback adjustment on the processing parameter of the variable spindle based on the feedback adjustment parameter.
Optionally, the feedback adjustment suppression module includes:
the cutting state monitoring submodule is used for acquiring vibration monitoring signals in the cutting machining process based on the information acquisition instruction and confirming corresponding chatter index quantity according to the vibration monitoring signals; generating a record list based on the workpiece identification corresponding to the cut pre-machined workpiece; the adjustment parameter comparison sub-module is used for calculating the minimum feedback adjustment parameter required by the flutter index quantity to reach the stability threshold value by combining the record list; comparing the minimum feedback adjustment parameter with the critical difference value and the limit difference value respectively according to the judgment rule;
automatically adjusting the sub-module; when the minimum feedback adjustment parameter is larger than or equal to the critical difference value and smaller than the limit difference value, an automatic feedback adjustment instruction is sent to a driving terminal of the variable spindle;
and the processing stopping prompt sub-module is used for sending a processing stopping prompt message to a preset numerical control terminal when the minimum feedback adjustment parameter is greater than or equal to the limit difference value.
For specific limitations on the numerical control machining cutting chatter suppression control system, reference may be made to the above limitations on the numerical control machining cutting chatter suppression control method, and no further description is given here; all or part of each module in the numerical control machining cutting chatter suppression control system can be realized by software, hardware and a combination thereof; the above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules.
It will be apparent to those skilled in the art that, for convenience and brevity of description, only the above-described division of the functional units and modules is illustrated, and in practical application, the above-described functional distribution may be performed by different functional units and modules according to needs, i.e. the internal structure of the apparatus is divided into different functional units or modules to perform all or part of the above-described functions.
The above embodiments are only for illustrating the technical solution of the present application, and are not limiting; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art will understand; the technical scheme described in the foregoing embodiments can be modified or some of the features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application, and are intended to be included in the scope of the present application.
Claims (8)
1. The numerical control machining cutting chatter suppression control method is characterized by comprising the following steps:
collecting vibration state information of the pre-processed parts with different rigidities and shapes in the cutting process; associating corresponding workpiece marks with the prefabricated workpieces with different rigidities and shapes;
determining a spindle rotating speed interval of the same-rigidity pre-processed workpiece in stable processing and deep cutting based on different spindle rotating speeds and frequency combination states; determining an optimal normalized variable spindle machining parameter within a set cutting depth range based on the workpiece identification;
cutting machining is carried out by adopting optimal normalized variable spindle machining parameters based on the workpiece mark, and machining cutting chatter suppression at variable spindle rotating speed is carried out;
calculating a chatter difference value between the obtained chatter index quantity and a set stability threshold value in the cutting process; and when the flutter difference value is larger than the stability threshold value, calculating a feedback adjustment parameter corresponding to the rotating speed of the variable spindle through a preset flutter suppressor, and carrying out feedback adjustment on the processing parameter of the variable spindle based on the feedback adjustment parameter.
2. The numerical control machining cutting chatter suppression control method according to claim 1, wherein the calculating the chatter difference between the obtained chatter index amount and the set stability threshold value during the machining process specifically includes:
acquiring vibration monitoring signals in the cutting process based on the information acquisition instruction, and confirming corresponding chatter index quantity according to the vibration monitoring signals; generating a record list based on the workpiece identification corresponding to the cut pre-machined workpiece;
calculating a minimum feedback adjustment parameter required by the flutter index quantity to reach the stability threshold value by combining the record list; comparing the minimum feedback adjustment parameter with a critical difference value and a limit difference value respectively according to a judgment rule;
when the minimum feedback adjustment parameter is greater than or equal to the critical difference value and smaller than the limit difference value, an automatic feedback adjustment instruction is sent to a driving terminal of the variable spindle;
and when the minimum feedback adjustment parameter is greater than or equal to the limit difference value, sending a processing stopping prompt message to a preset numerical control terminal.
3. The numerical control machining cutting chatter suppression control method according to claim 2, wherein the vibration monitor signal is collected during the machining process based on the information acquisition instruction, and the corresponding chatter index amount is confirmed from the vibration monitor signal, specifically comprising: collecting vibration monitoring signals in the machining and cutting process of a variable spindle, and extracting flutter characteristic indexes of the vibration monitoring signals to confirm corresponding flutter index quantities;
calculating the real-time weighted wavelet packet entropy of the vibration monitoring signal;
and calculating the weighted wavelet packet entropy of the vibration monitoring signal in a set time interval, comparing the weighted wavelet packet entropy with a weighted threshold of a preset vibration inoculation stage, and recording the weighted wavelet packet entropy into the record list.
4. The method for suppressing and controlling the cutting chatter of the numerical control machine according to claim 3, wherein the method for calculating the entropy of the weighted wavelet packet comprises:
determining the number of wavelet packet decomposition layers L, wherein the wavelet packet coefficients of the J-th band of the L-th layer are defined as
Determining a weighted frequency band;
and respectively calculating the entropy values of the weighted wavelet packet in the steady state and the flutter state.
5. The method for suppressing and controlling the cutting chatter of the numerical control machining according to claim 4, wherein the calculating the weighted wavelet packet entropy values in the steady state and the chatter state respectively comprises:
respectively establishing models of the energy distribution of the vibration monitoring signal in a frequency domain under a stable state and a flutter state;
in steady state, the ratio of the total energy occupied by each band is the same: e (E) L,j ＝2 -L ,J＝1,2,…,2 L The method comprises the steps of carrying out a first treatment on the surface of the Setting the main frequency of the vibration to be positioned in a p-th frequency band, and weighting the p-th frequency band to obtain a weighted wavelet packet entropy value in a stable state:
in the flutter state, the increased energy ratio of the p-th frequency band is increased to E L,p ＝2 -L +d,d>0；
The entropy reduction of the weighted wavelet packet caused by the vibration is p ′ ,p ′ Is a function of k, L, d, k, L, d respectively representing weights, wavelet decomposition levels, normalized energy increase, for each group L, d, p ′ There is an optimal weight.
6. The numerical control machining cutting chatter suppression control method of claim 4, wherein said chatter suppressor comprises a PID controller or a fuzzy controller; comprising the following steps:
taking the difference value of the weighted wavelet packet entropy of the vibration monitoring signal and the weighted threshold value of the preset flutter inoculation stage as the input of the PID controller or the fuzzy controller, wherein the output of the PID controller or the fuzzy controller is a feedback adjustment parameter, and the feedback adjustment parameter is the normalized amplitude and frequency of the rotating speed of the variable spindle.
7. A numerical control machining cutting chatter suppression control system for executing the numerical control machining cutting chatter suppression control method according to any one of claims 1 to 6, comprising:
the processing information acquisition module is used for acquiring vibration state information of the pre-processed parts with different rigidities and shapes in the cutting processing process; associating corresponding workpiece marks with the prefabricated workpieces with different rigidities and shapes;
the optimal parameter confirming module is used for determining a spindle rotating speed interval of the same-rigidity preformed piece during stable machining and deep cutting based on different spindle rotating speeds and frequency combination states; determining an optimal normalized variable spindle machining parameter within a set cutting depth range based on the workpiece identification;
the flutter suppression execution module is used for carrying out cutting machining by adopting optimal normalized variable spindle machining parameters based on the workpiece identification and executing variable spindle rotating speed machining cutting flutter suppression;
the feedback adjustment suppression module is used for calculating the obtained flutter difference value between the flutter index quantity and the set stability threshold value in the cutting process; and when the flutter difference value is larger than the stability threshold value, calculating a feedback adjustment parameter corresponding to the rotating speed of the variable spindle through a preset flutter suppressor, and carrying out feedback adjustment on the processing parameter of the variable spindle based on the feedback adjustment parameter.
8. The digitally controlled machining cutting chatter suppression control system of claim 6, wherein said feedback adjustment suppression module comprises:
the cutting state monitoring submodule is used for acquiring vibration monitoring signals in the cutting machining process based on the information acquisition instruction and confirming corresponding chatter index quantity according to the vibration monitoring signals; generating a record list based on the workpiece identification corresponding to the cut pre-machined workpiece; the adjustment parameter comparison sub-module is used for calculating the minimum feedback adjustment parameter required by the flutter index quantity reaching the stability threshold value by combining the record list; comparing the minimum feedback adjustment parameter with a critical difference value and a limit difference value respectively according to a judgment rule; automatically adjusting the sub-module; when the minimum feedback adjustment parameter is greater than or equal to the critical difference value and smaller than the limit difference value, an automatic feedback adjustment instruction is sent to the driving terminal of the variable spindle;
and the processing stopping prompting sub-module is used for sending a processing stopping prompting message to a preset numerical control terminal when the minimum feedback adjustment parameter is greater than or equal to the limit difference value.
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