CN104647132B  A kind of milling parameter Active Control Method based on magnetic suspension bearing electric chief axis  Google Patents
A kind of milling parameter Active Control Method based on magnetic suspension bearing electric chief axis Download PDFInfo
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 CN104647132B CN104647132B CN201410805910.7A CN201410805910A CN104647132B CN 104647132 B CN104647132 B CN 104647132B CN 201410805910 A CN201410805910 A CN 201410805910A CN 104647132 B CN104647132 B CN 104647132B
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 B—PERFORMING OPERATIONS; TRANSPORTING
 B23—MACHINE TOOLS; METALWORKING 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 METALWORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
 B23Q15/00—Automatic control or regulation of feed movement, cutting velocity or position of tool or work
 B23Q15/007—Automatic control or regulation of feed movement, cutting velocity or position of tool or work while the tool acts upon the workpiece
 B23Q15/12—Adaptive control, i.e. adjusting itself to have a performance which is optimum according to a preassigned criterion
Abstract
Description
Technical field
The invention belongs to Computerized Numerical Control processing technology field, more specifically, relate to a kind of milling parameter Active Control Method based on magnetic suspension bearing electric chief axis.
Background technology
In complexcurved class part fiveshaft numerical control processing Flutter Suppression, conventional method is based on Passive Control, these class methods are by regulating the technological parameters such as the speed of mainshaft, tool feeding cycle, maximum cuttingin, cutter length, angle between teeth, make system works in the below of salient angle effect point, thus obtain higher rotating speed and cuttingin under the prerequisite ensureing milling stability.Although passive control methods design and installation is simple, the stable region that it can adjust is very little, limited to the improvement of closed loop power.Therefore the control device changing the intrinsic dynamic characteristic of main axle unit must be adopted to suppress flutter, and this control device is namely based on the active control technology of magnetic suspension bearing electric chief axis.
The thought of magnetic suspension bearing electric chief axis active control technology is by configuring magnetic suspension bearing brake and sensor in spindle motor unit proper site, utilize the effect of FEEDBACK CONTROL, the overall dynamics performance of closedloop system is changed, thus the closedloop stabilization region of effective extension system, therefrom find the point that performance is more excellent, improve maximum metal milling rate.Active control technology has the ability of radical change system dynamics behavior, and therefore it suppresses the ability of flutter to be better than Passive Control technology far away.
Through the retrieval to existing document, find that there is following prior art: application number is 201310475810.8, publication No. is CN103769945A, name is called " vibration suppressing method and lathe ", this technology is by changing the speed of mainshaft to reach the effect suppressing flutter, belong to Passive Control, also limited for the ability improving working (machining) efficiency.
Summary of the invention
For the defect of prior art, the object of the present invention is to provide a kind of milling parameter Active Control Method based on magnetic suspension bearing electric chief axis, be intended to solve the workpiece surface quality caused because of selfexcitation chatter phenomenon in existing Digit Control Machine Tool Milling Process decline, the problem that milling efficiency is low.
The invention provides a kind of milling parameter Active Control Method based on magnetic suspension bearing electric chief axis, comprise the steps:
(1) when electro spindle generation milling parameter, the current displacement signal of electro spindle is gathered;
(2), after filter and amplification and differential process being carried out to described current displacement signal, the state vector Q (t) be made up of electro spindle displacement and speed is obtained; Described state vector Q (t) is the column vector of 4 dimensions;
(3) electro spindle displacement [F is obtained according to described state vector Q (t) _{x}f _{y}] ^{t}=C _{q}[Q (tT/N)Q (t)];
Wherein
(4) Fourier transformation is carried out to each element in cutting force dynamic matrix K (t), obtain cutting force harmonic wave dynamic matrix K _{α}(t), and according to cutting force harmonic wave dynamic matrix K _{α}t () obtains harmonic wave
Wherein cutting force harmonic wave dynamic matrix K _{α}(t) for each element in cutting force dynamic matrix K (t) carry out Fourier expansion front 2 α+1 item parts and, ω=2 π N/T is harmonic frequency, and α is the suitable positive integer chosen;
(5) according to described electro spindle displacement [F _{x}f _{y}] ^{t}with described trigonometric function column vector obtain harmonic displacement wherein harmonic displacement h (t) is 4 α+2 dimensional vectors;
(6) according to state displacement term coefficient matrix A and Lyapunov Equation Χ A+A ^{t}Χ=I obtains symmetric positive definite matrix Χ, obtains state weight coefficient [Λ according to symmetric positive definite matrix Χ _{1}Λ _{2}]=XB, according to state weight coefficient [Λ _{1}Λ _{2}] and described state vector Q (t) obtain the first self adaptation weight coefficient with the second self adaptation weight coefficient
Wherein, I is the unit matrix that 4 row 4 arrange, Λ _{i}four dimensional vectors, λ _{i}the vector of one dimension, i=1,2;
(7) according to described harmonic displacement h (t), described first self adaptation weight coefficient λ _{1}with described second self adaptation weight coefficient λ _{2}obtain the first adaptive rate with the second adaptive rate
Wherein, the first adaptive change rate second adaptive change rate Φ _{1}and Φ _{2}be respectively the symmetric positive definite matrix on two 4 α+2 rank of getting arbitrarily, the first adaptive rate with the second adaptive rate be 4 α+2 dimensional vectors;
(8) according to described first adaptive rate described second adaptive rate and described harmonic displacement h (t) obtains Self Adaptive Control electric current wherein Q _{c}t () is 2 dimensional vectors;
(9) by described Self Adaptive Control electric current Q _{c}t () acts on radial magnetic bearing, and produce corresponding magnetic field force, thus realizes suppressing the flutter of main shaft.
Further, described state displacement term coefficient matrix A is:
Further, described Cutting Force Coefficient matrix B is:
Further, described cutting force dynamic matrix is:
Further, described cutting force dynamic matrix K (t) take T/N as the periodic function matrix in cycle, i.e. K (t+T/N)=K (t), and then Fourier transformation can be carried out to each element in cutting force dynamic matrix K (t).
Further, it is larger that described positive integer α chooses, and approximate is more accurate, but computation complexity is larger.
Further, described 4 α+2 rank symmetric positive definite matrix Φ
_{1}and Φ
_{2}, can be taken as when α=1:
By the above technical scheme that the present invention conceives, compared with prior art, this technical scheme utilizes this feature of cutting force dynamic matrix cyclicallyvarying, employing Fourier space is similar to, design the selfadjusting Self Adaptive Control electric current along with main shaft change in displacement, and then suppress flutter by the intrinsic dynamic characteristic of magnetic suspension bearing change main axle unit, the beneficial effect carrying out Milling Process when axial cuttingin is larger and whole milling process still can be kept stable can be obtained, thus while ensure that workpiece surface quality, also improve milling efficiency.
Accompanying drawing explanation
Fig. 1 is milling Stability diagram, and transverse axis represents rotating speed size, and unit is rev/min; The longitudinal axis represents axial cuttingin size, and unit is millimeter;
Fig. 2 is closed loop control framework schematic diagram;
Fig. 3 is the agent structure schematic diagram of Milling Process Active Flutter Suppression System;
In figure, the implication of each label is as follows: 1 is milling cutter; 2 is handle of a knife; 3 is magnetic suspension bearing rotor displacement Autonomous test parts; 4 is radial magnetic bearing; 5 is magnetic suspension bearing rotor displacement Autonomous test parts; 6 is radial magnetic bearing; 7 is power amplifier; 8 is power amplifier; 9 is magnetically suspended bearing; 10 is PC; 11 is wave filter; 12 is workbench; 13 is workpiece.
Detailed description of the invention
In order to make object of the present invention, technical scheme and advantage clearly understand, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.
Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described further.It should be noted that at this, the explanation for these embodiments understands the present invention for helping, but does not form limitation of the invention.In addition, if below in described each embodiment of the present invention involved technical characteristic do not form conflict each other and just can mutually combine.
In actual Milling Process, to the speed of mainshaft Ω specified arbitrarily, when axial cuttingin b is very little, dynamic cutting force F _{t}t () is very little on the impact of whole milling process, namely whole milling process is all stable, but now milling efficiency is very low, does not meet our requirement; So wish that larger axial cuttingin is to obtain higher milling efficiency, but along with the increase of axial cuttingin b, whole system can be subject to dynamic cutting force F _{t}the impact of (t), the instability therefore become, produces chatter phenomenon, have impact on the crudy of workpiece; As shown in Figure 1, transverse axis represents the size of speed of mainshaft Ω, and the longitudinal axis represents the size of axial cuttingin b, with solidline curve in scheming for boundary, represent stability region (flutter not occurring) below curve, above curve, represent unstable region (generation flutter).
The present invention, in order to improve milling efficiency and ensure workpiece processing quality, the basis of Dynamic Model of Milling Process proposes a kind of milling parameter Active Control Method based on magnetic suspension bearing electric chief axis; Specifically comprise the following steps:
(1) set up milling dynamics equation, milling dynamics equation arranged and carries out state space transformation, obtaining state space equation;
(2) according to the milling dynamics equation set up, design Self Adaptive Control electric current Q _{c}(t).
More specifically, in step (), when main shaft is static, obtain the modal mass m of milling cutter system architecture, the dampingratioζ of milling cutter system architecture and the intrinsic pi ω of milling cutter system architecture by identification _{n}, the milling cutter system architecture modal parameter obtained when recycling main shaft is static replaces modal parameter during main shaft rotation milling, and then set up corresponding 2DOF system model to describe the vibration of main shaft, the spindle vibration model of acquisition is:
Wherein q _{1}(t) and q _{2}t () is the displacement in main shaft two frees degree.
Further, go out Cutting Force Coefficient by milling Experimental Identification, carry out dynamic cutting force F
_{t}(t) modeling; In conjunction with the cutting force COEFFICIENT K that identification obtains
_{t}with normal direction Cutting Force Coefficient K
_{r}, the dynamic cutting force model of foundation is
Wherein φ _{s}and φ _{e}represent the incision of cutter tooth opposite piece respectively and cut out angle.
And then can described in establishment step () milling dynamics equation be:
And state space equation is as follows described in step ():
Order,
Then abovementioned formula state space equation becomes:
Wherein, represent state velocity, A represents state displacement term coefficient matrix, and B represents Cutting Force Coefficient matrix, C _{q}represent hangover state displacement term coefficient matrix.
In step (two), Self Adaptive Control electric current Q _{c}t the design process of () is as follows:
(1) Fourier transformation is carried out to each element in cutting force dynamic matrix K (t), obtain cutting force harmonic wave dynamic matrix K _{α}(t), and according to cutting force harmonic wave dynamic matrix K _{α}t () obtains harmonic wave
Wherein cutting force harmonic wave dynamic matrix K _{α}(t) for each element in cutting force dynamic matrix K (t) carry out Fourier expansion front 2 α+1 item parts and, expression formula is: the constant vector that 2 unknown α+1 tie up can be set to; ω=2 π N/T is harmonic frequency, and α is the suitable positive integer chosen, and α is larger, and approximate is more accurate, but computation complexity is larger.At this, we choose α=2, can set further harmonic displacement as wherein electro spindle displacement [F _{x}f _{y}] ^{t}=C _{q}[Q (tT/N)Q (t)], the electro spindle displacement F in x direction _{x}with the electro spindle displacement F in y direction _{y}are all vectors of 1 dimension, x direction and y direction are perpendicular in the plane of main shaft, and x direction is mutually vertical with y direction, and h (t) is 4 α+2 dimensional vectors.
(2) according to state displacement term coefficient matrix A and Lyapunov Equation Χ A+A ^{t}Χ=I obtains symmetric positive definite matrix Χ, obtains state weight coefficient [Λ according to symmetric positive definite matrix Χ _{1}Λ _{2}]=XB, according to state weight coefficient [Λ _{1}Λ _{2}] and described state vector Q (t) obtain the first self adaptation weight coefficient with the second self adaptation weight coefficient wherein I is the unit matrix that 4 row 4 arrange, Λ _{1}and Λ _{2}all four dimensional vectors, λ _{i}the vector of one dimension, i=1,2.
(3) the first adaptive rate is designed with the second adaptive rate get arbitrarily two 4 α+2 rank symmetric positive definite matrixs, use Φ respectively at this _{1}and Φ _{2}represent, then make the first adaptive change rate be second adaptive change rate is again by separating the adaptive change rate of differential equation form, the first adaptive rate can be obtained with the second adaptive rate wherein the first adaptive rate with the second adaptive rate be 4 α+2 dimensional vectors.
(4) according to the first adaptive rate second adaptive rate and harmonic displacement h (t) obtains Self Adaptive Control electric current Q _{c}(t), its expression formula is: wherein Q _{c}t () is 2 dimensional vectors.
Further, the Self Adaptive Control electric current Q will calculated
_{c}t () is multiplied by corresponding magnetic suspension bearing electric chief axis COEFFICIENT K
_{amb}, the size obtaining the power that magnetic suspension bearing produces is: F
_{a}(t)=K
_{amb}q
_{c}(t), thus the closedloop control system (as shown in Figure 2) that formation one is stable, namely
Secondly, the online ACTIVE CONTROL based on Milling Process active flutter surppression device is carried out according to the Self Adaptive Control electric current of design; As shown in Figure 3, the critical piece needed for online ACTIVE CONTROL is made up of magnetic suspension bearing milling electro spindle, magnetic suspension bearing rotor displacement Autonomous test parts, magnetically suspended bearing, signal APU four major part; Wherein, magnetic suspension bearing milling electro spindle comprises the spindle units such as two radial magnetic bearings 4 and 6, cutter 1, handle of a knife 2; Magnetic suspension bearing rotor displacement Autonomous test parts comprise bandpass circuit, onelevel amplifying circuit, differential detection circuit, demodulator circuit, lowpass filter circuit etc., mainly integrated in the drawings 3 and 5 in; Magnetically suspended bearing is an integrated manipulator 9 based on DSP; Signal APU comprises wave filter 11, power amplifier 7 and 8, A/D and D/A signaling conversion circuit.Abovementioned parts are adopted to realize the online active flutter surppression of Digit Control Machine Tool Milling Process, its process is: spindle motor carry its tools 1 rotates and carries out Milling Process to workpiece 13, in the process when axial cuttingin b is larger, very easily there is flutter, our chatter phenomenon by producing in magnetic suspension bearing rotor displacement Autonomous test parts 3 and 5 RealTime Monitoring process; When detecting that chatter phenomenon occurs, magnetic suspension bearing rotor displacement Autonomous test parts 3 and 5 amplify through power amplifier 8 after vibration signal being passed to wave filter 11, then magnetically suspended bearing 9 is passed to by A/D conversion, and in PC10, show this vibration signal, vibratory output size is brought into the Self Adaptive Control electric current Q of offline design above simultaneously _{c}t () calculates Self Adaptive Control electric current Q in PC10 _{c}the size of (t), the Self Adaptive Control electric current Q finally will calculated _{c}t output signal that () obtains after magnetically suspended bearing 9 processes is processed through power amplifier 7 after being changed by D/A, be converted into current signal, act on radial magnetic bearing 4 and 6, produce the flutter of corresponding magnetic field force to main shaft to suppress, ensure that the stability of Milling Process accordingly.Point curve wherein in the visible Fig. 1 of closedloop control simulated effect, the stability region that the stability region that this closed loop point curve is formed is formed much larger than open loop solidline curve, namely when axial cuttingin is larger, closedloop system is also stable, and then improves working (machining) efficiency.
Those skilled in the art will readily understand; the foregoing is only preferred embodiment of the present invention; not in order to limit the present invention, all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.
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CN105700476B (en) *  20160428  20180501  上海交通大学  A kind of flutter Active Control Method under modelfree parameter and driver saturation 
CN106392753B (en) *  20160511  20180626  西安交通大学  A kind of intelligence milling electro spindle active cuttingvibration suppression system and method online 
CN106363450B (en) *  20160907  20181009  北京理工大学  A kind of online suppressing method of milling parameter 
CN108490789A (en) *  20180508  20180904  西安交通大学  A kind of electro spindle milling parameter robust Active Control Method and its active control system 
CN109396948A (en) *  20181116  20190301  华中科技大学  A kind of Active Control Method and system improving fiveaxis milling system processing stability 
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