Control of high accuracy position is the crucial technology that develops machine tool of high accuracy numerical control. In recent years, we are aimed at the demand that expands machine tool of numerical control of homebred high accuracy, position of high accuracy of complete to digitlization closed circuit controlled a technology to undertake study, for the foundation with this development goes position of new-style digitlization complete closed circuit to control a system, undertook applied on machine tools of a variety of homebred numerical control, in complex nicety the spare parts machined a respect to obtain favorable result. Circumstance of design of the basic composition that leaves new-style to this kind system, dynamic structure, controller, application make farther introduction. One, the problem that system of control of position of groovy number type exists is current, digital type communicates servo to receiving wider and wider application in numerical control machine tool. The basic composition that controls a system by the place that its make is shown 1 times like the graph. In the graph, the collective composition such as module of drive of digital type servo and servo electric machinery closed circuit of angle of one high accuracy is followed use a system, its input the instruction pulse that gives out for numerical control system, output is electric machinery corner. In pile up dish of closed-loop control that waits to come true for feedback link place to fall with light, the corner of electric machinery axis will follow strictly the instruction is worth change. Pass gear deputy with deputy drive of guide screw nut, the workbench that the angular displacement of electric machinery is needed for place by changeover is linear displacement. See by the graph, although be the digital type of output with corner,servo itself is system of one closed circuit, but look from the angle that is final controlled variable with displacement of machine tool workbench, the positional control system that makes by its is system of one open loop however (or call system of half closed circuit) . Accordingly, its position controls precision not only concern with the function that controls a system, and still depend on greatly the rigid structure of the machine tool. Such, the error that the information in the system delivers link, error of mechanical transmission link and all sorts of nonlinear the influence of the element, can make instruction of workbench displacement deviate is worth, and open loop system cannot undertake to its again effective and corrective, make consequently machine of groovy numerical control, although the bed used high-powered digital formula servo also achieves tall treatment precision hard. 2, the composition of system of control of position of digital type complete closed circuit is solve afore-mentioned problems, the article puts forward position of complete closed circuit of a kind of digitlization to control a method, its are basic the thought is; On the base that has digital type drive to component of machine tool motion, introduce detect directly the digital type of final displacement measures athletic part link, with be gotten adequately and using systematic information, to the machine tool from feedback pilot angle the motion of each coordinate undertakes digitlizing controlling, form from this contain all sorts of errors source and nonlinear the system of digitlization complete closed circuit of link. Such, this system not only can make move the fixed position precision of the component by detect the measurement of link precision decision, and can mix to all sorts of interference nonlinear the effect that the element produces to athletic component displacement undertakes significant trends corrective, the actual displacement that makes allow when to carve athletic part always follows strictly the instruction is worth change, make sure the motion of each coordinate has the machine tool thereby very tall move, stable state precision. If the digitlizes position of complete closed circuit to control a system basic composition that forms according to afore-mentioned train of thought pursues 2 are shown. This system uses grating to detect as displacement of the lines the displacement information that device gets machine tool workbench directly, phasic difference gets after the buy before this information is passed is handled signal of 90 degrees two displacement pulse, its frequency and workbench displacement speed become direct ratio, its amount is workbench actual displacement quantity is divided with pulse equivalent. Displacement pulse is sent reversible tally to have count, the computation in this tally is worth the current and real position that represented workbench namely. The action of controller of the position in the system is, what be worth according to positional set-point and positional feedback is poor, control what the rule controls whole system to move by the digitlization that designs beforehand, with making sure workbench displacement follows strictly the instruction is worth change. 3, the dynamic structure of 2 systems is like dynamic structure of the system and controller blueprint the graph is shown 3 times, include object of controller of figure shift buy, broad sense and feedback channel 3 parts. Broad sense object by 0 rank maintain implement, the composition such as component of servo of communication of type of pulse generator, number, mechanical movement. Among them, 0 rank maintain implement having connection disperse link (digital controller) the bridge style with continuous segment. The task of pulse generator is the instruction pulse that the control signal that gives out according to positional controller produces control communication servo to move, accordingly this link is one scale link. Nextpage communication servo is the digital type in the system actuating device, from macroscopical on look, the corner of servo electric machinery becomes integral concern between θ and F of instruction pulse frequency, but from microcosmic on should consider the inertial character between θ and F further. The action of mechanical movement component is electric machinery corner changeover is workbench linear displacement, if mix transmission error nonlinear the influence of the element disturbs as the trends to the system will handle, also can regard this link for one scale link. Such, through proper processing, can express the transfer function of broad sense object to although include to detect,be feedback passageway device, before buy processing, information is delivered, a lot of link such as reversible computation, involve more complex information processing process. But from with workbench real position is an input, positional feedback is worth (the computation value in reversible tally is multiplied with pulse equivalent) the angle that is output looks, can regard feedback passageway for one scale link, can make through proper design L of ＝ of Gf(s) of its transfer function. It is considering broad sense object include one integral segment 3 rank system, to make the closed circuit system that makes by its has faster dynamic property. And dog brae input does not have stable state error, use PID adjuster to regard the position as controller, show algorithm to be actually: The Uk in type -- the output Ek of controller of cycle of K sampling -- between output of system of cycle of K sampling and input follow error Kp -- Ti of coefficient of proportionality -- Td of integral time constant -- the system after differential time constant uses PID control turns into, when be being debugged actually, discover, of systematic trends process exceed tone often very big, cannot work normally even sometimes. To solve this problem, right (the integral action in 2) type undertakes departing controlling. Had been in when the system namely cross a process, when tracking error is bigger, abolish integral control, make the system is I system, in order to assure steady work. Enter stable state to dog when the system when the process, join integral control to make the system turns into K system, the stable state error that with assuring to dog brae inputs is 0. The in controlling algorithm to be type Δ that gets from this -- stable state dogs interval controls function for further improvement, can use the computer to realize the flexibility of digital algorithm, in (undertake parameter is controlled changing on 3) type foundation, the different level that runs according to the system namely, to algorithm medium parameter KP, Ki, Kd takes different cost respectively, in order to obtain more the control effect of actor. 4, after experiment and applied system prototype are finished, athletic test had on a SK8140CNC Milling. Workbench of X of this machine tool, Y, Z all communicates servo drive by digital type, it is of resolution 0.
The grating feet of 005mm detects as displacement device. Span is with 50mm when the experiment go up to check a place a certain quantity ofly certainly endlong in each workbench journey, let workbench control next is in on these dots to have fixed position in the drive of this system next, locate at each o'clock 6 times, every fixed position undertakes metrical. Test eventuate: All measured value that go up at every o'clock and the difference that the instruction is worth all do not exceed 0.
01mm. This shows position of digitlization complete closed circuit controls a system to have good place to control precision. So far, system of develops control of position of digitlization complete closed circuit already was in tens of stages undertook applied on machine tool of homebred numerical control. The treatment precision of the machine tool of numerical control of new-style complete closed circuit that makes from this rises apparently, and precision maintains a gender very good, in mixed pattern spare parts and narrow opening department the spare parts machined a respect to all obtain favorable result. 5, conclusion is aimed at the demand that expands machine tool of numerical control of homebred high accuracy, position of complete to new-style digitlization closed circuit controlled a system to undertake study, main result is as follows: (1) undertakes digitlizing drive to component of machine tool motion, can eliminate Wen Piao effectively not only, 0 bleach the influence that wait, and can make object be accusinged has idealer dynamic structure, make function had the digitlizes system of complete closed circuit trends that forms from this to assure basically. (2) undertakes digitlizing detecting to the final displacement of athletic component, can get athletic part in real time exact position information, to control machine effectively through full closed-loop control transmission error is mixed nonlinear the influence of the precision that the element moves to machine tool coordinate laid a foundation. (3) benefit makes controller of figure shift buy with the computer, usable software implements the complex control law that takes logistic switch, make control system has position of complete closed circuit to be moved admirably, stable state function, the outline that raised numerical control machine tool effectively thereby machines precision. (4) applies a proof actually, by digitlization position of complete closed circuit controls machine tool of systematic pilot numerical control to machine a respect to have favorable effect in complex and nice spare parts. CNC Milling
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