NURBS machines medium applied research in high speed

The course of linear interpolation knife that builds CAM through system of machine tool numerical control is in given tolerance inline processing becomes course of NURBS interpolation knife, namely so called " smooth interpolation " (be like) of system of GE Fanuc numerical control, have NURBS interpolation operation by numerical control system again finally (1) seeing a picture. Nevertheless, arrive from the linear knife course of CAM the changeover of the NURBS knife course of CNC can be finished by numerical control system, also can undertake by special postposition processing, in this process, increased additional error. But those who machine a spare parts is smooth degree got rising, call so " smooth interpolation " . Graph means of treatment of interpolation of the first kind of 1 NURBS pursues interpolation of the 2nd kind of 2 NURBS machines means 2.

Adopt CAM system the course of knife of NURBS of geometrical model translate into that will define by NURBS in CAD, numerical control system by 3 kinds of parameter in knife course (factor of reference point, authority and node vector) have NURBS interpolation operation (2) seeing a picture. Course of nonexistent will linear knife changes this kind of way into the method error of NURBS knife course, precision is taller, it is a kind of more effective method. Because in last few years ability development rises NURBS interpolation, still do not have unified standard format at present, manufacturer develops NURBS form by his means, the NURBS standard that manufacturer of manufacturer of CAD/CAM development business, machine tool, final user and CNC control system needs to unite, be benefited from which, uniform NURBS standard also is the mark with NURBS technology mature trend. The G code form of typical NURBS interpolation is as follows (like FANUC) : G06.

2P_K_X_Y_Z_R_F_K_X_Y_Z_R_ ... K_X_Y_Z_R_K_K_K_ among them, g06.

2 express NURBS interpolation; P represents NURBS time; K is node; X, y, z expresses the coordinate of reference point; R expresses authority factor; F states feed is led. The advantage of course of NURBS interpolation knife basically reflects in: In the high speed treatment of complex form spare parts, use straight line segment to approach spare parts appearance, the displacement that to assure to machine precision code of every paragraphs of NC defines is lesser, consequently NC code becomes very giant, the NC code of three-dimensional spare parts should compare NURBS knife course to grow 10 ～ commonly 100 times. Because the memory of numerical control system is finite, often ask to numerical control system inputs CNC Machining code group by group in machining a process. DNC is to pass serial communication to realize NC code to transmit, transmission speed is in commonly 110 ～ 38, between 400 baud rate, the most commonly used is 9, 600 baud are led. If press code of every paragraphs of NC average 20 character, DNC transmission speed is every second 960 character, criterion every second can transmit code of 48 paragraphs of NC only, transmit speed actually to be able to achieve the half left and right sides of theoretical value only, below this kind of circumstance, the displacement of Duan Dingyi of the code that be like NC is 0.

25mm, the treatment feed speed with can contented DNC is 360mm/min, cannot satisfy the requirement that high speed machines at all, affect treatment speed to make the function of the machine tool gets be developinged adequately hard thereby. The method that solves this one problem is to use NURBS knife track, 2 it is to use network of system of computerized numerical control (DCN) , 1 DCN transmission speed is DNC transmission speed, 000 times the left and right sides. Graph the change of 3 linear interpolation and speed of NURBS interpolation feed 2.

Linear interpolation adds man-hour to be the velocity shock that reduces linear end, of numerical control system wait for function of treatment contrail monitoring (namely " before make a present of " function) add decelerate ceaselessly in linear end, and course of NURBS interpolation knife is inside permission treatment direction span, need not add decelerate, rose to machine speed (3) seeing a picture. 3.

In the NC of the average CNC system when high speed is machined code piece handles ability to often do not follow the previous generation to pile up paragraph of high speed to machine speed; Or lowered treatment rate; Or sacrifices to maintain high speed precision (increase length of straight line segment to raise code to carry out time) then; And displacement of course of knife of interpolation of a paragraph of NURBS often includes 10 ～ the displacement of course of 100 paragraphs of linear knives, reduced the demand that to the NC of CNC code piece handles ability, often can satisfy the requirement that high speed machines consequently. Express the 1 comparison that is interpolation of NURBS of some spare parts and linear interpolation treatment, by the watch visible NURBS interpolation compares linear interpolation handling time to reduce 30% above. Interpolation of watch 1 NURBS is the same as what linear interpolation machines to compare pattern of interpolation means standard linear 141min 56s 124min 54s 157min 38s4 of NURBS 102min 5s 75min 37s 111min 4s of mode of fast mode finish machining.

NURBS interpolation avoided with straight acting music, raised workpiece to machine precision consequently, improved exterior quality. If be in,express 2 in, with commonly used 1ms servo periodic numerical control system is exemple, although feed speed is the high speed treatment of 30m/min, the displacement inside unit servo cycle is only 0.

5mm, be in NURBS interpolation that is to say with 0.

The linear displacement of 5mm will approach. The displacement increment that is like linear knife course is 0.

5mm, criterion its code file can become very big, have the treatment with sound economy hard almost. Express the relation servo cycle between 2 feed speed and displacement increment the displacement increment Mm 2 that different feed rate falls inside Ms servo cycle.

5 10 18.

8 30 20 0.

833 3 3.

333 3 6.

266 6 10.

000 0 10 0.

416 6 1.

666 7 3.

133 3 5.

000 0 3 0.

125 0 0.

500 0 0.

940 0 1.

501 5 1 0.

041 6 0.

166 7 0.

313 4 0.

500 0 0.

4 0.

016 7 0.

066 7 0.

125 4 0.

200 0 0.

1 0.

004 2 0.

016 7 0.

031 3 0.

Software of CAM of a few high end already supported 050 0 course of NURBS interpolation knife, if UG begins to introduce interpolation of 3 coordinate NURBS from V13, the commercial CAM software that V16 rolled out the first to support interpolation of 5 coordinate NURBS is wrapped. Milling of high speed of interpolation of 5 coordinate NURBS can realize the lens face treatment with extremely tall precision, represented henceforth the development direction of CNC Machining. The NURBS interpolation of system of 2 computerized numerical control by the graph 1, 2 visible, want to realize NURBS curve interpolation, system of machine tool numerical control must have the function that supports NURBS interpolation, the system of FANUC, SIEMENS, 3 water chestnut wait partial numerical control that supports NURBS interpolation at present, and the control system of great majority supports the interpolation such as linear, circular arc only. To linear interpolation, by code Duan Dingyi's displacement decides machine displacement, because cross small displacement to be able to make NC code file too long, the influence machines speed, DNC communication cannot satisfy the transmission requirement of code, accordingly code of every paragraphs of NC is less than 0.

The displacement of 25mm satisfies treatment requirement hard commonly. To NURBS interpolation, by basis of oneself of numerical control system interpolation leads computation and give birth to the interpolation method of course of knife of didymous NURBS curve. Alleged interpolation is led (or call interpolation time, servo is periodic) it is to show numerical control system is used at measuring the real position of workbench to erupt simultaneously to give drive reference axis the time that mobile and constant pulse counts is periodic, in this for a short while inside, numerical control system is linear drive. Interpolation ratio is shorter, interpolation dot is apart from smaller, the treatment precision of the spare parts is taller also. Watch 2 listed the relation between speed of interpolation rate, feed and displacement of the smallest treatment, by the watch 2 visible and commonly used 1ms interpolation lead OK and contented general requirement. Company of American Creative Technology is three-dimensional model the interpolation rate that treatment of face high speed uses numerical control system is only 0.

11ms, make extremely high accuracy treatment becomes a possibility. Interpolation leads parameter of a be numerical control system main technique. Oneself of numerical control system leads computation by its interpolation and give birth to the interpolation method of course of knife of didymous NURBS curve, its interpolation time (interpolation is led) shorter, interpolation dot is apart from smaller, the treatment precision of the spare parts is taller also. The concern between chord error Dd and interpolation rate T is as follows in type of T ² 8r 8r of · of Dd= L ² = V ² : R is curvature radius, v is feed speed, l is chord. This shows, rate of bring down interpolation will rise treatment precision with the relation of square, if be on appearance of curvature radius R=50mm, with 18.

The speed of 8m/min is machined, rate of interpolation of numerical control system is 1ms, criterion by the watch L=0 of length of 2 knowable interpolation, 313mm, chord error Dd=0.

245µm, accordingly even if high speed treatment, precision is controallable also inside 1µm. This shows, interpolation leads index of a be numerical control system main technique, low interpolation rate matchs again with NURBS interpolation it is the efficient way that raises treatment precision. The core that NURBS curve interpolation realizes on CNC is interpolation implement come true, and interpolation implement algorithmic key is interpolation speed. Wait for treatment contrail monitoring (namely " before make a present of " ) a crucial technology that is numerical control system, its job principle is the numerical control code that while the computer controls a system to be machined in control, scanning needs treatment, adjust dynamicly according to the change of feed direction feed speed, if feed direction change is acuteness, wait for orbit monitoring to be able to be planted with some beforehand means decelerate, because the machine tool is characteristic,avoid and had appeared to cut with remain, if feed direction is tall even, raise feed rate quickly rate of the biggest process designing, wait for orbit monitoring to be able to be in every second 2, 000 change feed rate for many times, in order to achieve part handling time the shortest change, this can satisfy the rapid change of this kind of speed with respect to machine tool of demand numerical control. Course of linear interpolation knife is through reading in pretreatment piece will handle, the change of speed comes true with displacement of NC code Duan Dingyi for the unit, NURBS knife course is OK the change that achieves rate in order to define the reference point of NURBS and interpolation rate for the unit, more careful to the adjustment of speed, because machine direction of course of appearance NURBS knife likewise,compare linear knife course at the same time the change is little, allow to realize cutting with higher rate consequently. Monitoring of the make a present of before wanting those who realize NURBS interpolation, besides to the machine tool outside adding decelerate to spend ability to raise taller requirement, the key is the intelligent NURBS interpolation that implementation is based on successive trends to control feed rate, control feed rate according to the directional change of NURBS knife course namely, this is the way that will study henceforth, this is explicit develop on the foundation of interpolation of 3 axes NURBS 4, interpolation of 5 axes NURBS also is the stress that will develop henceforth. NURBS interpolation can achieve very high exterior cutting rate, this means the talent of main shaft rotate speed with very high need to satisfy a requirement (provide the) when treatment in the penknife especially. The place on put together is narrated, system of system of high speed main shaft, fast feed system, high-powered CNC control is the requirement that high speed of implementation NURBS interpolation machines. Interpolation of curve of 3 conclusion NURBS can provide treatment of the high speed of flowing stability, high accuracy, it is a kind of new interpolation way, becoming NC to make technology of a of the technology sex that prop up. CAD/CAM, CNC and tool manufacturer need give full cooperation the crucial technology that solves NURBS interpolation, provide uniform NURBS interpolation standard for final user. CNC Milling