Isamu Nishida

Estimation Method of Muscle Fatigue and Recovery Progress Using a Muscular Fatigue Model

This study investigated a mechanism of muscle fatigue and proposed a muscular fatigue model to evaluate muscle fatigue progress under several muscular force patterns. Previous studies have already proposed a muscular fatigue model. However, these previous studies discussed about the condition of the maximum voluntary contraction. The new point of this study is considering several muscular force patterns including muscle recovery progress. This study proposed the method to estimate the endurance time for keeping constant forces considering the physical characteristics. This study also proposed the method to estimate the iteration numbers for keeping constant forces with interval. To validate the effectiveness of the proposed method, experimental verifications were conducted. The experimental results had a good agreement with the evaluation of muscle fatigue progress using the proposed method. The results of this study will provide ergonomically safe and efficient working environments considering the physical properties of each worker.

Method of Movement Simulation in Lifting Operation Considering theRole of Antagonistic Muscles and Biarticular Muscle

The efficiency priority working environments without considering the physical property of workers make the workload of workers increased and make the efficiency of workers decreased unintentionally under an aging society with a declining birth-rate. Therefore, it is necessary for plant managers to design the safe and efficient working environment considering the physical characteristic. This study suggested the method to simulate various motion patterns in the lifting operation with the parameters obtained from the actual lifting operations. This study also evaluated the muscle force of each muscle during simulated motions using the musculo-skeletal model considering the role of antagonistic muscles and biarticular muscle. Therefore, this study evaluated the quality of various lifting operation patterns from the muscle force point of view. As a result, this study succeeded to simulate various motions considering the role of antagonistic muscles and biarticular muscle related to the physical characteristic. The results of this study will make it possible to allocate workers optimally and result in a productivity improvement of industry.

Process planning system of 5-axis machining center considering constraint condition

This study proposes the method of the process planning for 5-axis machine tools. In our previous study, the process planning, in which the Total Removal Volume is divided by the planes parallel with the XY, YZ or ZX plane to analyze machining sequence from top to bottom of the target product, is proposed. In this study, the process planning system in which the Total Removal Volume is divided by all planes (including slope planes) existing on the target product is proposed. Furthermore, the design constraint or the designers intention such as discontinuous through holes which have the same central axis is considered in this process planning. A case study was conducted and the result showed that the proposed method can design efficient multiple process plans for the machining operation. These multiple process plans or machining sequences allow users to select adaptively the suitable process plan or machining sequence based on the property of 5-axis machine tool to be used under the design constraint.

Muscle Force Prediction Method Considering the Role of Antagonistic Muscle

Conventional musculoskeletal model often uses the optimization method to estimate muscle forces. However, the optimization method unfortunately does not usually consider the role of antagonistic muscles, which act in opposite direction to the prime motion or for restriction of rotational joint motion. Therefore, this study proposes a new method to estimate muscle forces considering the role of the antagonistic muscle during 3-dimensional motion. In this model, it is assumed that the agonist muscle is connected to the antagonistic muscle by a coupled spring. Joint torque is defined as the summation of the torques derived from the agonist muscles and the torques derived from the antagonistic muscles. Each muscle force can be estimated to keep balance among the torques generated by the agonist muscles and the antagonistic muscles respectively. The experiments were conducted to validate the proposed method to estimate muscle forces. Surface electromyograms (sEMG) were measured to compare with the estimated muscle forces. The experimental results showed that the estimated muscle forces had a good agreement with the sEMG of muscles.

Simulation Method of Working Condition in Lifting Operation Considering the Role of Antagonistic Muscles and Biarticular Muscle

The efficiency priority working environments without considering the physical property of workers make the workload of workers increased and make the efficiency of workers decreased unintentionally. Therefore, it is necessary for plant managers to design the safe and efficient working environment considering the physical characteristic. The objective of this study is to propose the method to determine the optimal working condition considering the physical characteristic of each worker in the lifting operation. To this end, this study suggested the method to simulate working condition considering muscle forces during motion in the lifting operation, and evaluated the muscle force of each muscle during motion using the musculo-skeletal model considering the role of antagonistic muscles and biarticular muscle. Accordingly, the optimized workable weight for each worker was estimated. As a result, this study can be used to simulate the optimized working condition considering the physical characteristics including muscle forces. This study may help the plant manager to design the working condition and determine personnel distribution according to physical characteristic of worker.

Editor Note: Journal of Ergonomics

Journal of Ergonomics functions as a platform for the dissemination of latest research developments pertaining to multifarious key aspects of interaction of human beings and other components of a system. The journal specifically emphasizes the publication of manuscripts that correspond to the process of attaining and maintaining overall wellbeing in human beings. The current issue of the journal also published many such articles that function to contribute to the persisting levels of understanding of human behavior, human interactions, etiological and environmental factors involved in the manifestation of a disease.