Precision in a Micron Realm
The precision of a system of measurement laser defines by a part by his repetibilidad, and on the other hand by the absolute accuracy of the measurement. For the user, this last is the most important since it defines the degree of precision of the measurements realizar when they measure pieces of work with characteristics very diverse. The reason of this roots in the principle of operation of the system. In few words, a system of measurement laser uses a barrier of light that works like a simple switch. When a tool of rotation breaks the do, generates a signal of jump and transmits to the control to register positions of the axles of the machine. The standard software integrated in the control of the machine compares a value of reference calibrated with regard to the values measured of the tool and afterwards extrapolates the length and radio of the tool, entering these values of automatic form in the table of tools.
For his manufacturing, a staggered profile short along the axis X. The difference of height by each step is of 1 µm.
Independently of the manufacturer of the laser, a signal of jump only generates when a true percentage of the do of light has been shaded. For this reason, when they realizar measurements of tools of characteristics very different (for example, diameter, form, irradiate of cut, etc) the do shades of different forms and can give place to imprecisions, especially in systems laser with a simpler optics. When measuring tools smaller, is especially the geometry of the edge the one who exerts a greater influence on the result of the measurement. The different geometries of the tools of cut, shade the do of different forms which does that they reach different depths for each tool cunado the laser sends the signal of jump to the control CNC. For this reason, what minor was the diameter of the do, lower will be the error of measurement created by the different geometries of tool, as a smaller diameter of the do reduce to the minimum the error of shaded for each type of tool. What this means regarding the process of mechanised is that, when they use different tools, create dimensional deviations in the piece of work. The systems with diameters of do bigger measure small tools as if they were longer of what are, because the tool has to to go in very deep in the do to arrive to the percentage of necessary shadow to command the signal of jump to control.
Do of the laser focused
To counter this,
The piece of work is ranurada from And+ to And- by the staggered profile with the end to check the precision of positioning of the machine. In the machines of high range, the tool does the first contact with the surface of piece exactly in the place specified by the user.
Processes of Reliable Production
Really, what explains in a process of mechanised is the precision obtained in the final piece, which sees influenciada by a big number of factors, each one of which plays his paper. The fluctuations of temperature of the machine and of the surroundings of the same, the wear of the tool and the changes in the length of the husillo of the machine to different speeds, all they have a direct impact in the result of the mechanised in a rank of hundredth of millimetre. With the systems of measurement laser, as LaserControl NT of Blum-Novotest, can check with precision the influence of each one of these factors. In any case, if it schemes it in if it does not have a precision of suitable positioning, even a system of measurement laser more precise has his limits. That is the reason by which Blum offers methods and solutions especially developed. This allows us test the precision of the current machine in a piece and corroborate the level of precision obtained in the measurements by means of laser Blum.
Checking the precision of positioning of the machine
To test the precision of positioning of the machine has employed a staggered profile with ladders of 1 micra and has mechanised the parallel piece to the axis X, as it shows in the Figure 1. The difference of height of a step to another (in the axis Z) is of 1 micra. The precision of positioning checks milling slots to different heights distributed along the axis And. This does several times, adjusting every time the depth of cut in 1 micra. It employs a microscope to identify the exact step where realizar the cut. As it shows in the Figure 2, in an excellent machine, produces a uniform cut and of constant profile perpendicular to the steering of cutting. This gives him to the user information on the quality of the precision of positioning of the machine.
The absolute precision is the crucial characteristic for the user. In tools with similar characteristics, the Blum LaserControl Nano NT reaches a precision of ± 0,5 micras.
Determining the absolute precision
Exists the possibility to realizar another type of essay to show the precision of a system of measurement by laser. The necessary requirement for this type of proof is to have testado previously the precision of the machine. In this proof, several pieces of work of characteristics very different (for example diameter, form of the tool) are measured without contact by means of system of laser immediately before the process of cutting. Once realizar the measurement, mechanises in the centre of the staggered structure to a diemsion Z clear-cut. (Of And + to And-). Finally, by means of a microscope check the depths micrométricas where the first cutting of each tool was realizar. The position of the first cutting gives us the precision micrométrica like answer to the question of how of precise has been my measurement. If it appreciates a positive variation, the value obtained in the measurement is greater to the length of tool and vice versa. The tool SF6 sample the confirmation that the line zero of the short tool the staggered structure.
Absolute precision to ± 0,5 µm
In the essay, have measured 4 cylindrical milling cutters (SF) and four milling cutters of ball (KF) with a diameter of 0,1 / 0,3 / 1 and 6 mm. As it appreciates in the Figure 3, when it uses a system of standard measurement by means of laser 'LaserControl Nano NT', the distortion of the values measured (Figure 4) is of so only ± 1 µm. However, if it already is known before selecting the system laser that in the machine go to employ only tools with similar characteristics (for example, diameter of the tool) (see also the Figure 4: Tools SF1; SF0.1; SF0.3; KF1; KF0. 3; KF0.1), can increase the absolute precision until a rank of ± 0,5 micras.
The proofs realizar in a centre of mechanised of high range under conditions of mechanised controlled.
Possibility to measure tools of until 5 µm of diameter
The diameter of the minimum tool that can measure , essentially depends on the conditions in which it uses the team. The systems of measurement Blum are designed in such a way that they guarantee a reliable and precise measurement, even in conditions of mechanised desfavorables, and for a wide variety of types of machine. In the micro-mechanised, there is different conditions that can observe apart from the seen previously. For this reason, Blum has available devices especially adapted for different types of tasks and surroundings of measurement. If it needs measure tools extremely small for special applications, Blum pre-configures the systems laser before being delivered with the purpose to satisfy to the maximum the needs of the customer.
En última instancia, the level of precision obtenible always reduces to an interaction between the centre of mechanised and the system of measurement. If they go to manufacture pieces of maximum precision, on the one hand needs of an excellent machine and on the other hand, that the system of measurement this positioned and tieed up so that it contribute a maximum precision, this yes, keeping the speed of twist of royal cutting of the cabezal. If it requires precision in a rank micrométrico, a system of measurement laser of Blum is the only solution.
