Market conditions fluctuate abruptly in today’s competitive environment and leads to imprecise demand information. In particular, market demand data for freshly launched products is highly uncertain. Further, most of the products are generally manufactured through complex multi-stage production systems that may produce defective items once they enter the out-of-control state. Production management of a multi-stage production system in these circumstances requires robust production model to reduce system costs. In this context, this paper introduces an imperfect multi-stage production model with the consideration of defective proportion in the production process and uncertain product demand. Fuzzy theory is applied to handle the uncertainty in demand information and the center of gravity approach is utilized to defuzzify the objective function. This defuzzified cost objective is solved through the analytical optimization technique and closed form solution of optimal lot size and minimum cost function are obtained. Model analysis verifies that it has successfully achieved global optimal results. Numerical experiment comprising of three examples is conducted and optimal results are analyzed through sensitivity analysis. Results demonstrate that larger lot sizes are profitable as the system moves towards a higher number of stages. Sensitivity analysis indicates that the processing cost is the most influencing factor on the system cost function.

Industries need a mechanism to monitor the workers’ safety and to prevent Work-related Musculoskeletal Disorders (WMSDs). The development of ergonomics assessment tools helps the industry evaluate workplace design and worker posture. Many studies proposed the automated ergonomics assessment method to replace the manual; however, it only focused on calculating body angle and assessing the wrist section manually. This study aims to (a) propose a wrist kinematics measurement based on unobtrusive sensors, (b) detect potential WMSDs related to wrist posture, and (c) compare the wrist posture of subjects while performing assembly tasks to achieve a comprehensive and personalized ergonomic assessment. The wrist posture measurement is combined with the body posture measurement to provide a comprehensive ergonomics assessment based on RULA. Data were collected from subjects who performed the assembly process to evaluate our method. We compared the risk score assessed by the ergonomist and the risk score generated by our method. All body segments achieved more than an 80% similarity score, enhancing the scores for wrist position and wrist twist by 6.8% and 0.3%, respectively. A hypothesis analysis was conducted to evaluate the difference across the subjects. The results indicate that every subject performs tasks differently and has different potential risks regarding wrist posture.

Bike sharing systems (BSS) have been widely accepted as an urban transport scheme in many cities around the world. The concept is recently expanded and followed by many cities to offer citizen a “green” and flexible transportation scheme in urban areas. Many works focus on the issues of bike availability while the bike performance, i.e., life cycle issues and its sustainability, for better management has been abandoned. As a consequence, mismanagement of BSS would lead to cost inefficiency and, the worst case, end with operation termination. This study proposes a design science approach by developing an Overall Bike Effectiveness (OBE) framework. By incorporating the concept of overall equipment analysis (OEE), the proposed framework is used to measure the bike utilization. Accordingly, the OBE is extended into Theoretical OBE to measure the sustainability of the early-stage of BSS. The framework has been verified and evaluated using a real dataset of BSS. The proposed method provides valuable results for benchmarking, life cycle analysis, system expansion and strategy planning toward sustainability. The paper concludes with a discussion to show the impact of the proposed approach into the real practices of BSS including an outlook toward sustainability of BSS.