Neural Combinatorial Optimization on Heterogeneous Graphs:An Application to the Picker Routing Problem in Mixed-Shelves Warehouses

In recent years, machine learning (ML) models capable of solving combinatorial optimization (CO) problems have received a surge of attention. While early approaches failed to outperform traditional CO solvers, the gap between handcrafted and learned heuristics has been steadily closing. However, most work in this area has focused on simple CO problems to benchmark new models and algorithms, leaving a gap in the development of methods specifically designed to handle more involved problems. Therefore, this work considers the problem of picker routing in the context of mixed-shelves warehouses, which involves not only a heterogeneous graph representation, but also a combinatorial action space resulting from the integrated selection and routing decisions to be made. We propose both a novel encoder to effectively learn representations of the heterogeneous graph and a hierarchical decoding scheme that exploits the combinatorial structure of the action space. The efficacy of the developed methods is demonstrated through a comprehensive comparison with established architectures as well as exact and heuristic solvers

Ergonomic assessment of the posture of surgeons performing endoscopic transurethral resections in urology

<p>Abstract</p> <p>Background</p> <p>During transurethral endoscopic prostate and bladder operations the influence of an ergonomic redesign of the arrangement of the operation equipment - including the introduction of a video-assisted resection method ('monitor endoscopy') instead of directly viewing onto the operation area via the endoscope ('direct endoscopy') - was studied with respect to the postures of the surgeons.</p> <p>Methods</p> <p>Postures were analysed on the basis of video recordings of the surgeons performed in the operation theatre during live operations and subsequent visual posture estimation executed by an observer. In particular, head, trunk and arm positions were assigned to posture categories according to a newly developed posture classification schema. 10 urological operations with direct endoscopy and 9 with monitor endoscopy were included.</p> <p>Results</p> <p>Application of direct endoscopy coincides with distinct lateral and sagittal trunk and head inclinations, trunk torsion and strong forearm and upper arm elevations of the surgeons whereas operations with monitor endoscopy were performed with an almost upright head and trunk and hanging arms. The disadvantageous postures observed during direct endoscopy are mainly caused by the necessity to hold the endoscope continuously in close contact with the eye.</p> <p>Conclusion</p> <p>From an ergonomic point of view, application of the video-assisted resection method should be preferred in transurethral endoscopic operations in order to prevent awkward postures of the surgeons and to limit muscular strain and fatigue. Furthermore, the application of the monitor method enables the use of a chair equipped with back support and armrests and benefits the reduction of postural stress.</p