Automatic Generation of Five-Axis Continuous Inspection Paths for Free-Form Surfaces

Abstract

Continuous five-axis sweep scanning is an emerging technology for free-form surface inspection, which, unlike the traditional three-axis inspection that works in a pointby-point manner, keeps the stylus tip in constant contact with the surface during the scanning, and thus could tremendously improve the inspection efficiency. However, at present, it mostly depends on humans to plan a five-axis inspection path, which severely affects the potential use of this new technology. In this paper, we report a practical algorithm, which is able to automatically generate a five-axis inspection path for an arbitrary free-form surface. The crux of this algorithm is that the unique kinematic characteristics of the five-axis inspection machine are fully considered and utilized when a path is planned. As a direct result of this consideration and utilization, the inspection efficiency is tremendously increased, often 20-30 times better than an inspection path obtained by any traditional path planning algorithm that disregards the inspection machine itself. The experiments performed by us have fully validated this point.Note to Practitioners-This paper was motivated by the current deficiency in the automatic generation of five-axis continuous inspection paths for free-form surfaces. Existing automatic inspection path planning algorithms are mainly designed for the traditional three-axis and three + two-axis point-by-point inspection process, which is time-consuming and unable to be utilized for the much more efficient five-axis continuous inspection because of the drastically different working patterns between them. We present a novel five-axis inspection path generation algorithm that strives to take full advantages of the unique characteristics and the working capacities of the fiveaxis inspection machine, where an inspection path is defined by a trajectory curve of the probe head and the corresponding sweep curve of the stylus tip. Starting with a near-optimum partitioning of the surface, we carefully design oscillating patterns for the sweep curve, while at the same time, try to shorten and smooth the trajectory curve as much as possible, with the given inspection sample accuracy always upheld. A five-axis inspection path thus generated will, in general, match the kinematical loads on the stylus and the probe head with their respective kinematic capacities (i.e., the limit on the speed and the acceleration of an axis). As a direct result of this design, the five-axis inspection machine is able to work under the maximum or near-maximum working capacity of every axis, thus tremendously shortening the total inspection time, often 20-30 times as compared with a path generated by a traditional method, such as the isoplanar method. Our algorithm is particularly suitable for the five-axis continuous inspection of large free-form parts, such as those in automobile and aerospace industry. Currently, our method is a suboptimal solution, since the surface partitioning is required to start from the boundary of the surface. In the future, ...

Surface form inspection with contact coordinate measurement: a review

“…In the field of surface partitioning, various kinds of methods have been proposed, i.e. geometric partitioning methods [109,110], harmonic mapping [111,112], and geodesic skeleton [56,113]. The geometric partitioning methods partition the surface according to its geometric shape.…”

“…The path planning on elementary shapes is relatively simple. Hu et al [110] partitioned the surface into several stripe-like regions. The geometric partitioning methods would segment the surface into many small patches, which results in frequent air-moves between different patches.…”

Adaptive sampling strategy of five-axis inspection for free-form surface reconstruction

“…The existing sampling strategies for five-axis inspection can be mainly divided into three categories: uniform sampling [17], adaptive sampling [18,19] and regional planning sampling [20]. Shen et al [17] adopted a simple and fast algorithm to assign sampling paths over the to-be-inspected surface by dividing the parameter intervals equally.…”

“…Shen et al [17] adopted a simple and fast algorithm to assign sampling paths over the to-be-inspected surface by dividing the parameter intervals equally. Hu et al [18] proposed the concept of nominal sweeping curves, which are generated according to the estimated chord error between two points. Although nominal sweeping curves ensure that the chord error is less than a user-defined threshold, they are not the final sampling paths.…”

“…CH To verify the effectiveness of the proposed algorithm, another two five-axis scanning sampling algorithms, i.e. uniform parametric sampling (UPS) algorithm [18] and nominal curve sampling (NCS) algorithm [19], are used to conduct the same inspection task. Besides, a very dense ( 2.5mm row spacing) Zigzag path is used to measure the surface and its inspection results served as a benchmark.…”