Automatic Sweep Scan Path Planning for Five-Axis Free-Form Surface Inspection Based on Hybrid Swept Area Potential Field

Abstract

Sweep scan is an emerging five-axis inspection technology of retrieving geometric data from free-form surfaces. Compared with the traditional surface inspection by coordinate measuring machine (CMM) that works in a point-by-point manner, sweep scan is able to make the stylus tip continuously sweep at high speed on the surface to inspect, whilst acquiring the 3-D point data accurately and efficiently. However, at present, for an arbitrary free-form surface, it still heavily depends on humans to manually generate a suitable sweep scan path. This paper presents a practical sweep scan path planning method, which can automatically generate an efficient sweep scan path for an arbitrary free-form surface. The resultant sweep scan path is able to cater to the shape of the surface to inspect and the unique kinematic characteristics of the typical five-axis inspection machine, so as to achieve a tremendous increase in inspection efficiency. The experiments performed by us show that when compared with some existing automatic sweep scan path generation algorithms such as the simple zigzag method, the proposed method is able to reduce the total inspection time by as much as seven times. Note to Practitioners —This paper is motivated by the lack of effective automatic sweep scan path planning methods for arbitrary free-form surfaces. Although there is a rich body of five-axis CMM path planning methods for inspection of free-form surfaces, they are mainly designed for the traditional inspection mode, i.e., the point-by-point measurement. Compared with the traditional discrete way of CMM inspection, sweep scan has a quite different inspection mode, which tremendously boosts the inspection efficiency by maintaining the constant contact between the stylus and the surface to inspect. The traditional five-axis inspection path planning methods are no longer applicable to sweep scan. Up to date, only a very handful few of automatic sweep scan path planning methods are reported and they seem to be very difficult to implement and no optimality of inspection efficiency is discussed. We present a practical algorithm for automatic generation of sweep scan paths for inspection of an arbitrary free-form surface. The algorithm is novel in that, by considering both the surface shape and the unique kinematic characteristics of a typical five-axis inspection machine, it tries to globally minimize the total inspection time. In our experiments, the sweep scan paths, generated by the proposed method, are found to outperform that of some traditional simple sweep scan path generation methods such as the zigzag method by a large margin in terms of total inspection time (while the data acquisition accuracy is maintained at the same level). The method is particularly suitable for those industrial parts that are large but relatively smooth, such as windmill blades and automobile panels.