This paper addresses the problem in detecting contact forces between link elements and an object for inner link based grasps by assuming that contact locations are not given a priori. This problem is separated into two steps, i.e., the contact point sensing and the contact force sensing. An active sensing scheme to detect all contact points simultaneously is presented. The advantages of the proposed scheme are explained in detail by comparison with conventional approaches. After the contact points are obtained the contact forces can then be evaluated by using the torque sensors mounted on the robot arm (or fingers). The concept of contact force observability is also discussed.>