The implementation of simultaneous trilateration to measure dynamic three-dimensional contours using the laser ball bar

Computer numerically-controlled (CNC) multi-axis machine tools are an integral part of modern manufacturing. These machines operate in an overall open-loop mode (i.e., although the positions of the individual axes are servo-controlled, the actual spatial coordinates of the tool or end-effector are unknown). Since the machining process is open loop, the ability to monitor the cutting tool/workpiece positional relationship and predict the final part dimensions is limited.; At this time there are no pre-process measurements which can be performed to accurately predict the final dimensions of a machined part. This produces a fundamental gap in the ability to model the machining process. Although static measurements may be performed on a given machine tool to characterize its (static positioning) accuracy, the final part dimensions are a function of the machine tool's dynamic spatial positioning accuracy. A tool which could dynamically measure the tool position along three-dimensional contours to micrometer accuracy would close this gap and permit rapid verification of CNC part programs.; This research describes the design and construction of a sensor, the simultaneous trilateration laser ball bar system (STLBB system), which has the capability of measuring these 3-D contours to micrometer-level accuracy. The data obtained from these 3-D measurements is useful for the evaluation of the controller performance during contouring and the measurement of the relative contributions of both quasi-static (geometric) positioning errors and controller errors to the part dimensional errors. The ability to verify the CNC part program without machining a series of test parts is another benefit of this sensor. This reduces scrap and increases the manufacturing process efficiency, especially in situations where machining time is high and material is expensive (e.g., the aerospace industry).; In order to completely close the open loop machining process, the effects of forced vibrations caused by the steady-state cutting forces on the final workpiece dimensions are also investigated. A simulation is included which computes the surface location errors introduced during the cutting process. These errors may then be applied as a type of post-processing filter to the STLBB dynamic path measurements to accurately predict the final machined part dimensions.