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The quantitative evaluation of product usability is important for product design. Most products, e.g. digital cameras, remote controls, and cellphones, have holding and operation parts where the hands are placed. The pinching effort which is the feeling when an user picks up and controls a product is important for product usability. Demands for product design that considers the pinching effort have increased. However, quantitative evaluation of sensibility is difficult. A questionnaire survey using a semantic differential method is commonly used for the subjective evaluation of the usability. In recent years, quantitative evaluation methods have been proposed based on physical data that are measurable by sensors. Radhakrishnan & Nagaravindra (1993) analyzed the force distribution during grasping a tube. Kong& Freivalds (2003) measured the maximum pulling force, the surface EMG (electromyogram), and the contact force, when pulling seven different meat hooks. They also developed a biomechanical hand model to estimate the tendon force. These research methods addressed the quantitative evaluation of a power grasp using the whole hand (palm and fingers). On the other hand, some research methods in biomechanics have proposed an accurate musculoskeletal model of the human hand and fingers; An et al. (1979) established a three-dimensional normative hand model based on X-ray image analysis. Brook et al. (1995) introduced a dynamic index finger model using a set of moment arm coefficients and elongation equations. Sueda et al. (2008) developed a method for generating motions of tendons and muscles for hand animation. Holzbaur et al. (2005) developed a biomechanical model of the upper extremity, Flanagan et al. (2006) discussed control strategies of the human fingertips, Valero-Cuevas (2005) proposed a detailed model of the human finger, including neuro-musculo-skeletal interactions. Also, in robotics, there have been a lot of research methods related to skin and muscle modeling. For example, Nakamura et al. (2005) proposed a computation method of somatosensory information from motion-capture data. Tada & Pai (2008) developed a simple finger shell model that is efficient to quickly simulate the finger surface deformation. However, these research methods were not applied to the quantitative evaluation of product usability. A goal of this research is to design an evaluation system of product usability using a simulation in conjunction with multiple sensors, such as contact sensors, pressure sensors, and force sensors. Fig. 1 shows the concept of the evaluation system, which is designed to correlate the obtained sensor data with the human sensory information. Ikeda et al. (2008) has 7

Pinching Effort Evaluation Based on Tendon Force Estimation