Automatic Generation of Five-Axis Continuous Inspection Paths for Free-Form Surfaces
IEEE Transactions on Automation Science and Engineering, 2017, 14(1): 83-97.
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 point-by-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 five-axis 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, we will try to relax this requirement and further increase the inspection efficiency.
Continuous inspection path; five-axis inspection; inspection efficiency; sampling accuracy