The copy of machine tool of fictitious axis numerical control method of 3 axle control

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  • source:WILDA CNC Machining
Of machine tool of numerical control of 1 introductive and fictitious axis appear to be considered as this century to provide revolutionary machine tool to design a breakthrough most. If fill the dominant position that cent develops this kind of new-style machine tool to go up in the structure, it is the function open up that raises a machine tool substantially likely a new approach. Through analysing discovery: To be based on the fictitious axis machine tool of Stewart platform principle directly commonly, its rotate the reasonable exercise limits of coordinate compares convention machine tool of 5 coordinate numerical control wants small much (have 20 ~ only normally 30 degrees, and 5 coordinate machine tool can achieve) of 90 degrees of above, and the adds a general to reduce a machine tool substantially effective work space as corner coming back. Although complex structure can enlarge corner limits, but the structure is complex, make sure Gao Gang is spent hard, accordingly, machine tool of common and fictitious axis suits to machine the spare parts that big range, much coordinate moves not quite. But look from another angle, the complex part that needs much coordinate treatment in actual production is minority after all, and the treatment of the common still and groovy part that takes dominant place. Accordingly, how does research use the structural characteristic of fictitious axis machine tool, its advantage is produced on the high speed of groovy spare parts, efficient treatment, will have real sense more. Copy of fictitious axis machine tool the basic idea of method of 3 axle control is, imitate the control method of machine tool of existing 3 coordinate numerical control, spend motion to undertake controlling to the 6 freedom of fictitious axis machine tool, look from external characteristic, make fictitious axis machine tool and convention machine tool of 3 coordinate numerical control is equivalent. Such, system of automatic process designing can use the 3 coordinate that have all sorts of maturity not only at the fictitious axis machine tool that 6 freedom spend directly, and through copy 3 axle control can make main shaft unit undertakes translation moves only, enlarged the working space of fictitious axis machine tool substantially, make its produce bigger effect. In addition, pass copy 3 axle control, still can reduce the complexity that controls a system effectively, reduce the cost of the machine tool significantly thereby, be helpful for this kind of new-style machine tool popularizing application inside bigger range. The advantage that machine tool of 2 fictitious axes has convention is machined pursues a kind of 1 typical structure that is fictitious axis machine tool, this structure but end is a kind so called " construction of 6 lever platform " . Its are specific the meaning is, grow 6 degree of drive lever changeably (abbreviation drive lever) one aspect of the matter secures Yu Jingping stage (like foundation or machine tool frame) on, the other one aspect of the matter of drive lever and use platform connection, connect with main shaft unit namely receive. Such, adjust the length of 6 drive lever, the feed that can make main shaft and cutting tool photograph make a demand to workpiece moves. Undertake be controllinged accurately through controlling a system to move to feed, can process a work that accords with a requirement. Graph the basic structure of machine tool of 1 fictitious axis has the advantage with incomparable machine tool of groovy numerical control in view of fictitious axis machine tool, and these advantages realize high speed, high accuracy to machine place to need just about, because this regards the efficient treatment of groovy spare parts as equipment its, produce its advantage with utmost ground. 3 copy because the fundamental of 3 axle control is fictitious the slideway that nonexistent edge secures direction to direct in axial machine tool, the not true existence such as the X of rod of cutting tool movement that CNC Machining place needs, Y, Z, accordingly, although need to obtain three-dimensional cutting tool to move only (attitude is constant only positional change) , also need to moving platform to undertake 6 freedom spend control. Copy method of 3 axle control is the imitate convention that puts forward according to the structural characteristic of fictitious axis machine tool the method of a kind of control of machine tool of 3 coordinate numerical control. Its jumping-off place is: When machining groovy spare parts with fictitious axis machine tool, install the cutting tool in main shaft to need three-dimensional translation exercise only, its attitude is fixed cost. Such, although have 6 motion freedom with the main shaft unit that uses platform solid couplet,spend, but involve real time calculative to be 3 translation freedom to spend only. For this the article uses heart of cutting tool ball or end panel center fastens medium coordinate Xm, Ym, Zm to represent cutting tool position in machine tool coordinate, calculate in real time through algorithm of 3 coordinate interpolation its displacement quantity. In the meantime, building one origin to be located in the cutting tool coordinate of heart of cutting tool ball or end panel center is, its reference axis axis of the Xm that Xt, Yt, Zt fastens with machine tool coordinate respectively, Ym, Zm is parallel. The corner coming back that circles axis of Xm, Ym, Zm with frame of department of cutting tool coordinate expresses to change the attitude of platform, it is its setting calm value. Such, to moving platform edge Xm, Ym, Zm the motion of these 3 coordinate undertakes be calculated in real time and be controllinged in real time, the roll that circles axis of Xm, Ym, Zm to using platform undertakes real time is controlled deciding a value, can come true to spend control to moving the full free t of platform, realize the control of 3 coordinate linkage that moves to cutting tool then. Because law of this one party does not need to undertake to changing platform attitude real time is calculated, such, can reduce map of false or true and amount of linkage pilot computation effectively not only, the control of the fictitious axis machine tool that still can spend 6 freedom brings into convention S of 3 coordinate number accuses category of machine tool pilot, have the aid of controls a method to undertake to this kind of new-style machine tool linkage is controlled at mature 3 coordinate. By the structure of fictitious axis machine tool knowable, the length Li(i=1 of the 6 drive lever that is component of the main shaft that prop up as a result of the controlled variable that can accuse directly in this machine tool, 2, ... , 6) , namely the virtual campaign rod of this machine tool () of abbreviation solid axle, because this wants to undertake to using the campaign of platform full free t spends control, realize the accurate control of contrail of pair of cutting tool motion then, need to will move platform motion to dictate (empty axis dictates) in changing solid axle space, go carrying out, arrive through solid axle space of empty axis space go against map automatically to come true. Can make copy from this the implementation plan of method of 3 axle control, if pursue,2 are shown. Graph 2 copy block diagram of principle of method of 3 axle control the moving process of this system is: Above all, the input information that gives out according to program of spare parts numerical control generates contrail of cutting tool motion in real time, the hope exercise that tries coordinate of Xm of edge of the cutting tool in dividing space of axis giving theory, Ym, Zm namely is measured; Next, pass computation of map of false or true, the athletic statement that the hope of will fictitious axis carries momentum changeover is 6 drive lever is worth; Finally, have the follow-up control that solve Ou to the length of each drive lever, make time length and hope length actually consistent, adopt machine tool structure implicit solid reality arrives of empty go against map, the contrail of cutting tool motion that can get according with dictating asking, make sure cutting tool attitude is given constant value. The job that contrail of motion of cutting tool of space of 4 empty axis creates contrail of cutting tool motion is: The cutting tool method that gives out program of spare parts numerical control (the geometrical curve that has nothing to do with time and machine tool character in empty axis space) changeover is as characteristic as time and machine tool (if sum decelerate character,wait) the contrail of cutting tool motion that the disperse that contacts changes. Its beg solution process to be as follows: Of mathematical model build the precision that makes to assure orbit, in copy parameter is used to change direct interpolation algorithm in 3 axle control. Its should nod is: To be built to facilitate by interpolation curve calculative parameter turns mathematical model: The U in X=f1(u)y=f2(u)z=f3(u) (1) type -- ginseng is variable, u ∈ [0, 1] requirement makes function calculation is not involved when orbit is calculated in real time with its, need to be decreased through the frequency is added rarely only by can finish except operation. For example, to circular arc interpolation, type (the particular form of 1) is: (The M in 2) type -- invariable matrix, when interpolation the dot is located in when 4 quadrant of one ~ , its take a value to be respectively: R -- circular arc radius such, orbit computation is OK and absolutely means undertakes, namely the computation of coordinate of each contrail dot is with model coordinate origin fiducial undertake, can eliminate thereby accumulate an error, assure interpolation calculative speed and precision effectively. Add decelerate to control the contrail of cutting tool motion that generates to make to satisfy a machine tool to add decelerate character to ask, can wait for affirmatory first-rate to add decelerate curve according to the dynamic character of the machine tool, store its in control system. In systematic moving process, scan above all around a certain number of block, analyse the metabolic trend of feed speed, decide the feed speed F of the hope; Read the K of feed speed fold that takes operation face plate to go up next, undertake correction to F with its, get Fnew of target feed speed, fnew=K.

F; Farther, undertake Fnew and Fold of uptodate feed speed comparative, and the Fk(mm/min) of adds computation of decelerate character curve to give current sampling cycle instantaneous feed speed according to the machine tool. Speed and the geometry that because interpolation is calculated,the error is controlled is not a kind of static state are calculated, it must make the distance between current interpolation dot and dot of before one interpolation satisfies feed speed to reach impose the requirement such as decelerate, make sure the interpolation between this 2 o'clock is straight even at the same time line segment and be in by the error between interpolation curve given inside allow poor limits. For this, need to be control target with instantaneous feed speed, in order to allow an error to restrain a condition linear to interpolation end length spends Dtk to undertake controlling. Its method is as follows: Above all, press the Fk of instantaneous feed speed that adds decelerate computation to give out, with computation leaving type current sampling cycle hopes mediumly chord (without the interpolation when the tie linear end length spends) : (The Dt1 in 3) type -- hope chord, mm T -- sampling is periodic, ms next, according to the error of sampling interpolation relation computation restrains chord: (The E in 4) type -- the permission between interpolation contrail and hope contrail error R -- the curvature radius of contrail of hope of interpolation point point is final, decide according to the opposite size of Dt1, Dt2 the extraction of Dtk is worth. Namely, if hope chord Dt1 is less than tie chord Dt2, make current interpolation straight Dt1 of = of Dtk of line segment length, take Dtk=Dt2 otherwise. Task of calculative of contrail of interpolation of interpolation contrail computation is: In each sampling cycle, according to the interpolation that above gets linear end length spends Dtk, the coordinate that before interpolation contrail is duped, real time computation nods is worth. Its computation process is as follows: Above all, beg the Du that gives current interpolation cycle according to joining following concerns between variable increment Du and Dt: (The Du/ds in 5) type -- because interpolation frequency is taller,ginseng variable is led to the change of curvilinear arc length, the arc length in cycle of a sampling and chord are very adjacent, when be being calculated actually so, can make Du/ds ≈ Du/Dt. Take U one increment Du so, beg the Dt that gives correspondence, can get needs Du/ds. Although this expresses to be able to have little effect to feed speed approximately, but won't produce any effects to interpolation contrail precision. In sampling interpolation, orbit precision is main contradiction, the coordinate computation that interpolation nods must be aimed absolutely truly, and the accuracy of speed of motion of contrail of interpolation drop edge is in minor position, can be patient of is tiny error. The result that such getting assured orbit precision already, raised computational rate again. Next, calculate what current sampling cycle joins variable to take a cost: Uk=uk-1+Du (6) is final, uk era enters type (1) , the coordinate that before computation gives interpolation contrail to be duped, can nod is worth Xk, yk, zk. Till arrive at interpolation terminus,repeat above process ceaselessly, the interpolation contrail that can get whole disperse is changed. How does computation of map of 5 false or true move according to the three-dimensional cutting tool in empty axis space statement cost is right the length of lever of the 6 drive in solid axle space undertakes be controllinged accurately, it is to realize copy of fictitious axis machine tool the another crucial question of 3 axle control. To solve this problem, the empty axis motion that must produce interpolation dictates changeover is instruction of real axle control, its beg solution process to be as follows: Above all, according to copy 3 axes treatment needs to make axes of machine tool main shaft and workbench plane normal ask parallelly, affirmatory main shaft is initiative attitude At = 0, bt = 0. What decide platform Ct coordinate according to spare parts appearance and treatment requirement is optimal beforehand set buy Ct0. Next, before treatment begins in returning reference point to operate, will move platform to move At=0, bt = 0, ct=Ct0 condition, make cutting tool axes and working mesa perpendicular, at=0 of cutting tool attitude, bt=0. Right now, the structure according to using platform is attainable on its 6 strong point (of 6 drive lever move end points) the initiative position Pxi in department of cutting tool coordinate, Pyi, Pzi(i=1, 2, ... , 6) . Be like K hour, the cutting tool contrail that computation of 3 axes interpolation produces dictates the value is Xk, Yk, Zk, it is make sure cutting tool attitude is constant, should make the 6 coordinate costs in moving end points to be fastened in cutting tool coordinate fixed, the in moving end points to fasten in machine tool coordinate coordinate that can get 6 drive lever from this is worth: Xdi=Xk+PxiYdi=Yk+Pyi   (I=1, 2, ... , of the 6 drive lever that gets above 6)Zdi=Zk+Pzi (7) basis move the Jing Duan with end points coordinate and machine tool foregone structure to nod coordinate, press type can get K hour the hope value of length of each drive lever, namely with Xk, yk, the solid axle coordinate of Zk correspondence is worth: (The Xji in 8) type, Yji, Zji -- static end points of 6 drive lever fastens medium coordinate to be worth space of 6 solid axles in machine tool coordinate 6 axes linkage controls contrail of cutting tool of empty axis space to generate is a kind of thick interpolation, when feed when rate is higher, thick interpolation straight line segment will be longer. Accordingly, to assure the smooth stability of linkage of 6 drive lever, interpolation of following essence of life can undertake in solid axle space. Above all, through false or true space of axis of map general empty (three dimensional space) interpolation is linear paragraph commutation is solid axle space (6 dimension space) straight line segment, its length is: (The Li0 in type of 9)     -- thick interpolation is periodic in the begining solid axle coordinate is worth next, the shift of contrail of solid axle space in begging a cycle of each essence interpolation is apart from: The T1 in Dl=L/(T1/T2) (10) type, T2 -- the sampling of interpolation of thick, essence is periodic, ms then, begin N from this straight line segment the mobile quantity of each drive lever is periodic end of interpolation of essence of life: × of DLin=n × Dl (Li-Li0)/L     (I=1, 2, ... , 6) (11) is farther, can get N hour to take a cost actually each drive staff is longly by next type, namely solid axle motion dictates the value is: Lin=Li0+DLin   (I=1, 2, ... , 6) (12) is final, adopt system of the follow-up control that solve Ou [3] the actual length that assures drive staff and hope length are consistent, the solid axle linkage that can achieve contrail of contented cutting tool to ask is controlled. 7 systems implementation developed copy of fictitious axis machine tool according to the means that offers system of 3 axle control, if the graph is shown 3 times,its are comprised basically. This system is a foundation with system of personal computer of Pentium Ⅱ , in its the interface that development of outfit proper motion adds on patulous bus line gets stuck, in order to realize the information exchange between control system and drive system. Software of numerical control system by C language + mixture process designing of 32 assembly language comes true. Graph 3 control system comprises block diagram when this system works, operation personnel can pass the I/O equipment such as floppy disk driver to input treatment place to want information, can pass the senior editor function that the system provides, undertake modification to the information that already inputted. Of the machine tool move to operate face plate to undertake controlling through computer clavier and numerical control by operation personnel, the concerned message that the system runs is shown through form of form of chromatic CRT to in an attempt to and data come. The L6 of ~ of solid axle L1 to the machine tool uses this system servo of communication of type of high accuracy number undertakes drive is controlled, each axis all uses closed-loop control means. Detect device uses high accuracy grating, in order to assure the displacement precision of solid axle. The logistic order that the switch in the system measures control to be used at controlling a machine tool partly moves, if control cutting tool changes, tray exchange, main shaft is opened stop, cooling system, journey protects those who wait for link to move. Switch quantity controls partial general and servo control to close suitably, finish the control of process of machine tool job jointly. Fictitious axis machine tool has 8 verdict rigid structure simple, stiffness tall, benefit is machined at realizing high speed wait for an advantage, but also exist rotate coordinate is effective the work area when small, much coordinate machines corner is narrow wait for defect. Accordingly, answer to produce its advantage in the high speed of groovy spare parts, efficient treatment. Pass copy 3 axle control, decreased effectively to control systematic complexity, reduced the totle drilling cost of the machine tool significantly thereby, be helpful for fictitious axis machine tool popularizing application inside bigger range. CNC Milling CNC Machining