Three-dimensional laser calibration replaces one-dimensional laser calibration
Dr. Wang Zhengping, President of American Light Motion Company
Optodyne, Inc.
Compton, California, USA
Global competition and quality standards require higher positioning accuracy, smaller tolerances and higher feed rates for machine tools. In order to meet these requirements and produce high-quality, high-precision parts, the three-dimensional volumetric positioning accuracy of the machine tool must be measured.
Twenty years ago, the maximum positioning error of the machine tool was the screw pitch error and the screw thermal expansion error. But now most of the above errors have been greatly reduced, and the main errors of the machine tools have turned into verticality errors and straightness errors. In order to achieve high positioning accuracy of the three-dimensional space of the machine tool, all three displacement errors, six straightness errors and three perpendicularity errors on the machine tool must be measured and compensated. Using traditional laser interferometers to measure straightness and perpendicularity errors is more difficult and time-consuming. Usually requires a few days of downtime and requires experienced experts to take measurements.
Optodyne, Inc. has developed a new and breakthrough laser vector measurement technology for the measurement of three-dimensional volumetric positioning errors of machine tools (US Patent 6,519,043, 2/11/2003) This measurement method can be completed in a few hours instead of a few days in a conventional laser interferometer. Therefore, three-dimensional volumetric positioning error measurement and compensation become practical, and can achieve higher accuracy and smaller tolerances.
An Italian company JOBS SPA has been manufacturing standard machine tools driven by three- and five-axis high-speed linear motors since the 1980s. Two years ago, JOBS replaced the traditional laser calibration equipment with a laser Doppler interferometer (LDDM) licensed by Koto. Combined with three-dimensional volumetric positioning error measurement technology, or combined with the step-by-step diagonal measurement technology invented by Koto, LDDM makes JOBS easy to accurately measure and can detect problems before a crisis occurs in production operations. If the parts are not qualified, it will directly affect the production of the assembly and electrical departments. If the parts can not meet the specified tolerances, it will take more time to assemble to ensure that the machine can achieve the technical specifications of processing accuracy.
Using the three-dimensional volume laser calibration equipment of the company, JOBS spent very little time and obtained more complete data in a few measurements. This allows JOBS to clearly understand the errors of the machine tool and calibrate these errors in a timely manner, thus delivering users with more competitive quality and price.
The step-by-step diagonal measurement method used 4 identical diagonal settings and collected 12 sets of data. Based on the measured data, all three displacement errors, six straightness errors and three perpendicularity errors can be determined. The measured positioning errors can be used to generate a three-dimensional volume compensation table, which can be uploaded to the Siemens 840D controller to calibrate any positioning errors, thereby improving positioning accuracy.
JOBS reported that using a photodynamic interferometer and a step-by-step diagonal measurement method requires only a few measurements to obtain enough data to clearly show the state of the machine. JOBS easily solves some common problems, such as assembly errors, errors caused by temperature changes, and structural problems, without increasing assembly time. The quality of products produced by JOBS is getting better and better. Moreover, the step-by-step diagonal measurement used for three-dimensional volume calibration requires a maximum of 7 measurements, from which the type and magnitude of most errors can be learned. JOBS has determined to use this method to replace traditional instruments on the assembly line as optical collimators, rulers and granite platforms.
The LDDM technology used by JOBS Company adopts single-beam MCV-500 and dual-beam MCV-2002 to reflect the modulated laser beam back from a movable target. The beam with position information is detected and After processing, it is used to generate a look-up table, so that the controller can compensate the error. Since the return beam does not have the offset requirements as traditional laser interferometers, the setup is very fast. Only two components need to be adjusted: a single-hole laser head that emits and receives a laser beam, and a flat mirror as a target.
JOBS reported that the single-beam MCV-500 uses step-by-step diagonal measurement to allow three-dimensional volumetric positioning errors to be obtained with little interruption of assembly time, thus greatly reducing costs.
The laser and plane mirror are placed on the main axis and the table, and move along the X axis, Y axis, and Z axis of each axis step by step alternately, so that the repetition continues to the diagonal diagonal. After each step of all three axes moves, the diagonal positioning error is collected. This technology collects three times the amount of data and allows measurement of the displacement error when each axis moves.
The trajectory of the target movement is not a straight line, the lateral movement is larger. The traditional interferometer does not allow such a large lateral movement, and no data can be detected. The LDDM laser interferometer uses a flat mirror as the target, and movement parallel to the mirror will not transfer the laser beam or change the distance from the light source. Therefore, the measurement is not affected.
There can be up to four working position temperature sensors connected to the automatic temperature compensation unit. Automatic temperature compensation also provides compensation for changes in environmental factors such as air temperature, atmospheric pressure, and machine tool temperature.
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