Manufacturing challenges with fabrication of large size mechanical harmonic drives

Mechanical harmonic transmissions are relatively new kind of drives having several unusual features. For example, they can provide reduction ratio up to 500:1 in one stage, have very small teeth module compared to conventional drives and very large number of teeth (up to 1000) on a flexible gear. If for conventional drives manufacturing methods are well-developed, fabrication of large size harmonic drives presents a challenge. For example, how to fabricate a thin shell of 1.7m in diameter and wall thickness of 30mm having high precision external teeth at one end and internal splines at the other end? It is so flexible that conventional fabrication methods become unsuitable. In this paper special fabrication methods are discussed that can be used for manufacturing of large size harmonic drive components. They include electro-slag welding and refining, the use of special expandable devices to locate and hold a flexible gear, welding peripheral parts of disks with wear resistant materials with subsequent machining and others. These fabrication methods proved to be effective and harmonic drives built with the use of these innovative technologies have been installed on heavy metallurgical equipment and successfully tested.

Challenging endoscopy reprocessing guidelines: a prospective study investigating the safe shelf life of flexible endoscopes in a tertiary gastroenterology unit.

Professional prac− tice guidelines for endoscope reprocessing re− commend reprocessing endoscopes between each case and proper storage following repro− cessing after the last case of the list. There is lim− ited empirical evidence to support the efficacy of endoscope reprocessing prior to use in the first case of the day; however, internationally, many guidelines continue to recommend this practice. The aim of this study is to estimate a safe shelf life for flexible endoscopes in a high−turnover gastroenterology unit. Materials and methods: In a prospective obser− vational study, all flexible endoscopes in active service during the 3−week study period were mi− crobiologically sampled prior to reprocessing be− fore the first case of the day (n = 200). The main outcome variables were culture status, organism cultured, and shelf life. Results: Among the total number of useable samples (n = 194), the overall contamination rate was 15.5 %, with a pathogenic contamination rate of 0.5 %. Mean time between last case one day and reprocessing before the first case on the next day (that is, shelf life) was 37.62 h (SD 36.47). Median shelf life was 18.8 h (range 5.27± 165.35 h). The most frequently identified organ− ism was coagulase−negative Staphylococcus, an environmental nonpathogenic organism. Conclusions: When processed according to es− tablished guidelines, flexible endoscopes remain free from pathogenic organisms between last case and next day first case use. Significant re− ductions in the expenditure of time and resources on reprocessing endoscopes have the potential to reduce the restraints experienced by high−turnover endoscopy units and improve ser− vice delivery.