Force control of robot finger by pneumatic servo system and its application to apple selection handling

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To develop robot fingers for selection and handling of ripe and sweet apples, the grasp characteristics of human, manufacturing the finger controlled by pneumatics servo system, and nodestructive discriminating method of ripe and sweet apples are investigated. The results obtained are as follows :1. The human varies a grasp force to compensate for the inertial force of the object, and uses his slip sense to generate a grasping force just greater than the minimum required for grasping the object. Therefore we must realize the ability of fingers which can easily change a grasp force corresponding with the acceleration change.2. By using recently developed pneumatic servo valve, we made pneumatically controlled fingers to grasp some easily bruised material like an apple. From the experiments, for the position control of cylinder, PD control law is used and good results is obtained. In the case of grasp control, PD position control plus integral force control which compensate the error between the reference force and real grasp force gives a good results. It is also found that active force control method which considers the friction force as a disturbance is useful to cancel its effects and then it makes possible to handle apples without bruise.3. The precision of analysis by near infrared ray spectroscopy method for discriminating ripe and sweet apples is improved by using fixed type grating, and it has a good correlation with that by sugar content refractometer, and then it is concluded that near infrared ray spectroscopy method is practical apple selection.