Numerically controlled position using trilateral coordinates

Abstract

Cartesian coordinates are generally used in mechanical engineering and for accurate position location the guideways must ee extremely straight and slide skew must be carefully controlled. Accurate tools and inspection machines are consequently expensive. Research into tensioned wire measuring systems has shown that lengths to several hundred feet can be rapidly measured with accuracies of better than 10 ppm of measured length. These transducers, not needing guideways, can be used to realize trilateration coordinate measurement. The use of trilateration is described in a number of applications. The first group consists of applications where a manipulating system already exists, for example, retro fit of digital-readout to machines such as a boring mill, a radial drill and a flame-cutting gantry. The second group includes cases where the component itself is used to support the transducers and a small machine tool placed at the machining area. This technique eliminates the need for a cartesian framework, facilitates in situ machining with low capital cost plant and enables more than one simultaneous operation on the same component. A description is given of an experimental two-axis system (range of controlled measurement, 10 × 20 m and resolution, 20 μm) controlling the position of a high performing cartesian manipulator (range 0·5 m × 0·5 m).