The focal position in Laser Cutting detects methodological research

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Treatment of foreword Laser Cutting has cut precision speed of tall, cut fast, fuel factor low, free from contamination, wait for an advantage without noise, received wide application in car, shipping, aerospace and electronic industry. And the relative position between quality of Laser Cutting treatment and laser focus and workpiece is having close relationship, assuring the reasonable relative position between laser focus and cut object is one of keys that make sure Laser Cutting machines quality. The focal position of laser focusing cannot be measured directly, but can detect through indirect method. Process a system to a Laser Cutting, its focus position is decided by the optical focus of focusing lens, it is changeless that in focusing lens so particular case leaves its position (the fuel factor that takes no account of focusing lens) , because this is OK,through detecting focusing lens is mixed will be detect secondhand by the relative position between treatment object focus and be concerned by the position between treatment object. Laser focus and the position that be opposite by the photograph between treatment object can pass inductance displacement sensor and capacitance sensor to detect, in use has actor drawback each. The response of inductance sensor frequency is inferior, not quite apply to high speed is machined and resemble! Dimension treatment needs to be not the circumstance that the contact detects so; Capacitance sensor, have answer speed fast, detect precision is advanced advantage, but the existence in using a process is nonlinear the influence of the interference of the plasma cloud with the generation in sufferring Laser Cutting easily to machine a process and gush broken bits. The generation way of position error of focus of the laser in treatment of discussion Laser Cutting of article general system controls systematic composition with what eliminate an error automatically. Discussed composition of testing system of two kinds of sensor and the inadequacy that in be being used actually, exist and overcome method respectively on this foundation. The generation of position error of the focus in process of 1 Laser Cutting is in Laser Cutting process, generation focus and be machined the element that changes relative to positional happening between object surface is very much, by treatment workpiece surface the geometrical error of means of clip of outfit of scraggly, workpiece, machine tool and machine tool are in what laden force falls to be out of shape, workpiece is machining the heat in the process to be out of shape etc metropolis cause laser focus position and ideal to give the seat (process designing position) produce deviation. Some errors (the geometrical error that is like a machine tool) have regularity, can undertake compensating through mensurable compensation method, but some errors are random error, can pass only online detect and control will eliminate, these errors are: 1.

The object of Laser Cutting of error of 1 workpiece geometry is plank or enclothe model spare parts, as a result of all sorts of? Because of influence, treatment object surface is had rise and fall rough, and the appearance that also can produce laminose part in the influence of the fuel factor in cut process is out of shape, to 1 dimension laser beam machining, enclothe shape in suppress what the appearance also can produce in the process is rough, all these, focus of metropolis generation laser and be happened to change randomly by the position of treatment object surface and good place. 1.

The work that the error Laser Cutting that unit of clip of 2 workpiece outfit emerges processes is to be put in acicular on workbench, as a result of machining error, long with workpiece between wear away and the burn of laser, needle bed can appear scraggly, this kind rough the random error that also can produce the position between thin stencil steel and laser focus. 1.

The error that 3 process designing produce is in process of treatment of 1 dimension Laser Cutting, the treatment contrail on complex curved surface is to pass linear, circular arc to wait for those who plan to close, these drafting that add up to curve and real curve to be put in certain error, these errors make actual focus and the relative position that machine object surface and position of ideal process designing produce certain error. And system of some teach programming also can introduce a few deviation. Position of the focus in 2Laser Cutting process is online detect if the graph is shown 1 times,comprise with what control a system, position of Laser Cutting focus is online detect comprise by the part such as controller, testing system, executive device with control system. Detect according to focal position the concern that controls system and system, focal position detects control system cent is independent type and compositive type two kinds. Position of independent style focus detects the compensation control that uses alone reference axis to undertake focal position error with control system, rigid structure is complex, cost is higher, but can cooperate to use with all sorts of numerical control systems and Laser Cutting machine tool. And the rod of a feed that compositive type uses itself of Laser Cutting machine tool (machine to plane) or the synthesis of many feed axis (machine to 1 dimension cut) the compensation that campaign will come undertake focal position error. This kind of means has a structure simple, cost is low, adjust easily wait for an advantage, but requirement and numerical control system unite a design, taller to the open sex requirement of numerical control system. 2.

1 capacitance sensor detects circuit is shown 2 times like the graph, capacitance sensor detects the pulse signal that circuit processes circuit to wait to turn capacitance signal into corresponding frequency by oscillator of firm frequency of amplifier of harmonious oscillator, signal, crystal, synchronous circuit, mixing circuit, signal, $ ? (Through undertaking frequency sampling and processing to pulse signal, get corresponding capacitance. The capacitance here is the capacitance that two plate form between cut nozzle and cut object. Apparent its capacitance has outside Shanghaiguan besides the area with two plate, still concern with the distance between the medium between plate, plate. And this distance is concerned with the distance between laser focusing lens and workpiece, concern with the distance between laser focus and workpiece namely, so capacitance is mixed approximately the distance between focal position and cut object is concerned. This is capacitance sensor detects the principle of focal position. Can see from inside the graph, the relation between frequency and focal position error is nonlinear relation, must undertake through the computer linearization is handled. In the meantime, because capacitance still is concerned with the medium between plate, detect so the plasma cloud that gets the generation in machining a process easily as a result and influence of gush broken bits, must try to overcome. 2.

2 inductance sensor detects circuit is shown 1 times like the graph, because used circuit of newest large scale integration, of inductance sensor detect circuit is simpler, and integrated circuit used new modulation demodulation method and algorithm, decreased previously detect graph frequency modulation of type of heterodyne of " of graph of block diagram of system of control of 1 focus position detects circuit method because the photo corner of the incentive signal of sensor, frequency and amplitude drift are right detect the influence of the result, rose to detect greatly precision and stability. Sensor signal measures head displacement to become the voltage signal of direct ratio with sensor through getting after processing, become corresponding frequency signal through alternating circuit is changed, through the computer processing got position error signal of the focus. As a result of the inherent character of inductance sensor, to be being measured the frequency of signal has certain restriction (hundreds of) , not quite apply to high speed to machine a circumstance, in the meantime, detect for contact as a result of its means, can use at plane to machine a circumstance only. The cloud effect to focal place testing system is in the plasma in 3 cut process the instant that workpiece had be notted cut to wear, laser and metallic interaction, record of cloud and mist produces between nozzle and treatment object plasma, change the medium between capacitance plate, generate interference to capacitance sensor thereby. In regular cut process, auxiliary gas plasma from cut in seaming, blow medicinal powder, lesser to influence of capacitance sensor generation. But when if machine speed to be mixed too quickly,just beginning cut, because workpiece was not cut completely to wear, laser can produce plasma cloud near illuminate dot, generate interference to capacitance sensor, serious when make sensor cannot work normally even, serious effect machines quality. Graph (disturb sketch map for plasma. By electromagnetism principle knowable, the capacitance between two plate of photograph adjacent is the ε in type of C= ε S/h---Between plate dielectric constant) it is commonly (1) S---Plate is relatively effective area H---If the distance between two plate does not have the interference of plasma, so, according to type (the capacitance that 1) place measures is mixed plate (nozzle and treatment object) between the distance becomes inverse ratio, can go to the lavatory by capacitance seek a space between two plate, beg then a focus and by the relative position between treatment object. But, mix when nozzle be machined when plasma or gush broken bits existing between the object, the dielectric between capacitance plate is not air, its dielectric constant produces change. By capacitance? Manage formula, right now the capacitance between two plate is: ε of C= ε S1 /[(h-h1)+h1 / the ε in S2/h (2) type of ε of ε 1]+ 1---The dielectric constant H1 of plasma---The ply S1 + S2 =S of plasma cloud is the area that has plasma cloud or gush broken bits and the area that do not have the area of plasma cloud or gush broken bits respectively. If plasma cloud distributings to be mixed at nozzle equably,be machined in the certain height limits between the object, be apart from between the two plate that capacitance sensor measures for: H=(h-h1)+ H1 ε / the error theory that ε 1 (3) detects is worth: ε of Δ H = H-h = H1 (/ ε 1 -1) (4) from type (4) is knowable, the size of the error is decided by the dielectric constant of the ply of cloud of the plasma between plate and plasma. And plasma dielectric constant has very great value, can reach the quantitative level of 105. So by type (4) can see plasma cloud or gush broken bits to detecting the influence of the result is very big, document [2 ~ 4] reachs, if the ply of plasma cloud is 1 ~ 2mm, the academic error that is apart from between the two plate that detect by capacitance sensor also achieves 1 ~ 2mm, the precision index that position of focus of laser of apparent short of detects (for ± 0.

2mm) . 4 sensor optimize design technology to reduce plasma cloud because plasma changed capacitance,to detecting the influence plasma of the result is to the interference of capacitance sensor the medium between two plate. Accordingly, to remove the plasma interference to capacitance sensor, be about to make the medium between two plate does not get electric capacity the influence of plasma, the central alveolus that can increase cirque form plate and move capacitance sensor to plasma two kinds of methods come true beyond the cloud. (1) should remove the plasma effect to capacitance, be about besides the plate sensor of plasma park electric capacity. Consider what distributing all round the dot to plasma cloud is edge cut, because this can be like a graph,5 show: The central alveolus diameter of will round annular plate expands to 2 ~ 3mm of built-in insulation high temperature resistant material of pottery and porcelain, because capacitance sensor plate is hollow, below the circumstance that takes no account of edge effect, the plasma cloud near illuminate dot is mixed to sensor capacitance detect the value does not produce an effect, use this kind of method to reduce the disturbing influence of plasma cloud effectively so. (2) is machined to planar Laser Cutting, still can undertake indirect measurement through mechanical drive method. Follow to be moved by treatment object through one machine namely, machine go up to carry and detect sensor forms plate, through detecting the distance between sensor and this machine detects secondhand laser focus and by the position between treatment object. This kind of method is OK utmost avoided ionic cloud and gush broken bits to be opposite detect the influence of precision, also developed capacitance sensor to answer swift advantage. Position of focus of 5 conclusion laser detects with one of crucial technologies that controlling is Laser Cutting treatment, to fast cut treatment, focal position detects the control precision that precision and fast sex will affect focal position directly and treatment quality, capacitance sensor is had detect sensitivity is tall, answer swift advantage, can overcome its through the linearization of all of computer science department nonlinear; The plasma cloud of the generation in eliminate treatment process through special sensor structure and gush broken bits are right detect the influence of the result, raise its to machine the use effect in the system in Laser Cutting. CNC Milling