Optical technology reports the position of the tip of the tool in every moment

Industry seeks a forceful response to the requirements of precision, increasingly larger, that the productive sector demand manufacturers of machine tool. The precision machines is conditional, in large part, by the measure of the position of the axes that produce the relative motion between workpiece and tool. This article describes a system of high-accuracy 3D position.

The traditional systems of measurement (encoders or rules) have inherent limitations because the point of capture of the position is far from the tip of the tool. The measure is undermined by the lack of perpendicular axes, due to acting efforts deformations and thermal deformations. Neither rules nor encoders can detect errors in positioning in perpendicular directions to own axes (lack of righteousness of address errors) when measured along the axis, or errors angular (roll, yaw, pitch) in each of them. The problem is aggravated in the case of parallel kinematic machines, in which there is no Cartesian axes.

Fatronik proposes a solution to this problem, through the development of a system of 3D position of precision for a new type of machine tool control is based on direct measurement of the position of the tip of the tool through the use of optical technology.

This situation has developed a measurement system using optical technology informs us of the position of the tip of the tool in every moment. It has also developed a new control system, in which the feedback loop is done with the signals obtained from the optical system. Once integrated the system into a prototype, will seek the integration of the system in industrial production machines, type machining or milling Centre.

The follower subsystem is based on laser interferometry, consists of an emitting laser stabilized, located in the solidarity-based platform to the machine, in which the beam is directed to a Prism retroreflector, located on the head of the machine.

There is a set of optical elements that divided and lead the beam laser to the different components of the Interferometer, optimizing the power of the signal. The system has incorporated two mirrors deflectors, which routed the beam laser from the platform towards the retroreflector mounted in the head and vice versa.

A PDS (Position Sensitive Detector) of two dimensions is used to detect deviations from the beam laser on the trajectory theoretical and to reorient it towards the retroreflector.

This system has been integrated into a three-axis milling machine, there have been changes and mechanical adaptations needed to accommodate the measurement system and driving beam laser between the head of the machine and the Locator System. It's a gantry type milling machine, with a platform on which is situated the system locator, and from which the beam of measure can have impact on the entire route of the head. In the design the interference in the transmission of the beam laser, thanks to the incorporation of a telescopic tube with flexible ends have been removed.

With a view to the integration of the measuring system has been necessary to make changes in the Cabinet of the milling machine, to accommodate and feed in the same various subsystems.

All this leads to a solution in real time, through the generation, from the system locator, the quadratic TTL signals, which are introduced directly to the control, replacing the current catchment systems signals.

The connection control allows to replenish the loop to regulate and correct the position of the head, the objective is that it not deviates from the default working path and thus make a more precise movements.

Fatronik has led this project that had been done with the collaboration of two partners, AIDO (technological Institute of optics), and the IAI (Industrial Automation Institute). It's a multidisciplinary project that has required unite capabilities in the field of optics, automation and control and mechanics and electronics of the machines.

The remove intrinsic errors of traditional systems of measurement, is a great improvement in the machining centers of high speed with the addition of this new system of measurement. Obtaining technical objectives of the project will lead to produce more precise machines which in turn will be used to manufacture better products.