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RISS 인기검색어
- 검색키워드
- 주제어 : Hand tendon forces (검색결과 2 건)
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Optimum design of handle shape through biomechanical modeling of hand tendon forces
공용구 Pennsylvania State University, Graduate School col 2001 해외박사
A biomechanical hand model was developed to estimate tendon forces of the main flexor muscles, flexor digitorum profundus and flexor digitorum superficialis, in each finger and to suggest optimal handle designs based on the user's hand and finger sizes. Experimental force data were collected from force sensitive resistors (FSR) which were placed on the palmar surface of the fingers. These data were then applied to the hand model in order to predict the tendon forces and also used to compare the magnitudes and distributions of the finger and phalange forces in maximum gripping and pulling tasks. Two handle shapes (double frustum and oval), two hook positions (center and off-center) with small or medium and large sizes, resulted in a total of ten different handles which were evaluated. Force data and Borg's subjective ratings of perceived exertion (RPE) were recorded for each condition. In the maximum gripping task, the finger force distributions showed that the middle finger exerted significantly more force and the little finger exerted notably less force than did the other fingers. There was no significant difference between the index and ring fingers. The results of the pulling task were different from patterns found with the maximum gripping task. The index and middle fingers contributed an average of 55.2% of total pulling force and the contribution of the ring finger was smaller, followed by the little finger with the smallest contribution. The contributions of the index and middle fingers were not significantly different. Phalange force distributions for the gripping and pulling tasks also indicated significant differences from each other. The force imposed by the distal phalange was significantly higher than that imposed by the middle and the proximal phalanges in the gripping task, while the force exerted by the proximal phalange was always higher than those exerted by the others in the pulling task. Results of the finger tendon force showed that the average tendon forces of the small-double frustum handles were significantly lower than those of the other handles in both tasks. Large-double frustum handles always showed the largest finger tendon forces. Lower tendon forces were also demonstrated for the off-center hook handles rather than the center hook handles. These results were also supported by significantly lower subjective ratings. All subjects generally preferred the small and medium-double frustum handles and medium-oval handles over the large handles. Subjects also reported higher preference for the off-center hook handles for the gripping task. All subjects were categorized based on the 'Normalized Handle Size (NHS)' for the each handle type. Results of the correlation between subjective ratings and NHS showed the lowest tendon force ranges of NHS were approximately at 45∼75% and 50∼65% for double frustum and oval handles, respectively. Normalized tendon forces calculated from the biomechanical hand model were lower at 45∼65% and 55∼75% for double frustum and oval handles, respectively. Finally, the potential optimal finger handle sizes, which have the less finger tendon forces, were recommended based on the 'Normalized Finger Size (NFS)' ranges. The lowest tendon force ranges of NFS were 80∼110%, 80∼110% and 90∼120% in the gripping task and 90∼120%, 80∼110% and 90∼120% in the pulling task for index, middle and ring fingers, respectively. The results of this study indicate that the biomechanical hand model is valid technique for predicting the finger tendon forces and evaluating hand tool designs and that are double frustum handle with an off-center hook is preference for pulling tasks such as meat handling.
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Development of robotic hand with passive variable transmission
This paper presents a way to improve performance of a tendon driven robotic hand using Passive Variable Transmission. The concept of research was inspired by the human pulley mechanism which changes the moment arm of tendon by pulleys, which makes it possible for a human hand to rapidly and powerfully grasp an object. To mimic the pulley mechanism of the human hand, Passive Variable Transmission is applied, which changes the path of the tendon wire passively as the human hand pulleys do. This PVT Mechanism is a transmission for a tendon driven mechanism, which varies a moment arm of a tendon wire by changing the lengths of compliant material when the tension of the tendon wire is changing. If the tension of the tendon wire is small, the moment arm remains short. As the tension gets bigger, the moment arm increases. Thus, when the joint rotates without load, the moment arm is short and the joint rotates rapidly. On the other hand, if the joint is blocked by an obstacle, the tension increases, which increases the moment arm, and the joint generates a bigger moment. The goal of this research was to develop a suitable PVT design for a small finger structure. After trying a number of concept designs, the spring type PVT was chosen. This spring type PVT has been tested to certificate that this PVT can change the tendon wire moment arm passively. Before fabricating the robotic hand, the parametric study was conducted. Based on the results of the parametric study, parameters of the spring type PVT was decided, and a robotic hand was fabricated. By comparing with an existing tendon driven robotic hand, H2 hand from Meka, it was confirmed that the fabricated robotic hand used 20% rated output and showed 40% grasping performance. There has been a structural limitation on robotic hands in mimicking the grasping performance of human hands. This paper will show prospective view of using the Passive Variable Transmission Mechanism to improve the grasping performance of robotic hands.
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