**3.1 Mechanism**

100 The Future of Humanoid Robots – Research and Applications

It is shown that the basic performance of the developed robot hand. The movable range of joints is as shown in Table 1. 0 [deg.] is extended position and the flexion direction is the

Thumb (deg.) Others (deg.) IP Joint 0 -110 DIP Joint 0 - 95 MP Joint 0 -110 PIP Joint 0 - 95 CM1 Joint 0 -110 MP1 Joint 0 -110 CM2 Joint 0 -110 MP2 Joint 0 -110

The step responses of every finger are shown in Fig. 5. From this figure, DIP & PIP operates slower than the other joints. As the PIP joint is operated with the DIP joint, the load of DIP & PIP is about twice larger than the other joints' one. Thus, DIP & PIP operates with about half the angular velocity. Therefore this Universal Robot Hand II has enough response velocity

Typically, the robot finger is classified into a hard finger and an elastic finger. In the hard finger, the rotation of the actuator responds plainly to the angle of the joint. In the elastic finger, the fingertip can be moved with elastic members depending on the external force. However, a human finger acts as both a hard finger and an elastic finger depending on a situation. Thus, Torque Limiter Mechanism is fitted into the joint of this Universal Robot Hand II. With this mechanism, driving mechanism in joints is started to skid from setup skidding torque. By implementation with this mechanism, the driving mechanism can be

protected against overload, and the robot hand may grasp objects flexibly.

plus direction. This movable range of robot hand is similar or over the human's one.

**2.2 Basic performance** 

Table 1. Movable range of each joint

Fig. 5. Result of step response experiments

**2.3 Superior function** 

for our future study.

Torque Limiter Mechanism is constructed by a fixed plate, a rotating plate and rollers held between these plates as shown in Fig. 6. These rollers are tilted on an angle of degrees. The skidding torque *T* is expressed in (1).

$$T = \mu r P \sin \alpha \tag{1}$$

where, is the coefficient of the friction between rollers, plates. *r* is the radius of rollers, and *P* is the pressure by the adjustment nut. Every 20 joints of this robot hand have this mechanism as shown in Fig. 7.

Fig. 6. Inner structure of finger joint with torque limiter mechanism

Fig. 7. Cross-section view and side view of torque limiter mechanism

Development of Multi-Fingered Universal Robot Hand withTorque Limiter Mechanism 103

commonly-used robot hand has engaged DIP and PIP joints in imitation of human joints. On the other hand, in case of grasping a thin object with human fingers, these fingertips are collimated, and increases area of contact between these finger pads. Thus, developed robot hand operates skidding mechanism in the DIP joint. Robot fingertips are collimated, and increases area of contact in Fig. 10 (b). Herewith, developed robot hand doesn't pinch a thin

In this experiment, the protection of drive train is verified. The outline of this experiment is shown in Fig. 11. The DIP and the MP2 are fixed with a bump against the mechanical stopper. The PIP is flexed at a tilt, 45 [deg.], and the skidding mechanism is tried and enabled to operate with tuning the adjustment nut. The adjustment nut of MP1 is clenched up to the disabled angle. Drive the MP1 and contact hardly the fingertip to a rigid object. Keep sliding the PIP to a bump against the stopper of the PIP joint and fastening the fingertip on the object for a few seconds. Extend the MP1 to a bump against stopper of the MP1 joint. Values of the fingertip force and the encoder (MP1) are measured during this

object with a point contact but with plane contact.

Fig. 10. Clip operation with thin object

**4.1 Alleviation of impact force 4.1.1 Experimental setup** 

Fig. 11. Impact force experiment

**4. Experiments** 

experiment.

Fig. 8. Angle of adjustment nut vs skidding torque

Fig. 8 shows the relation between the clenched angle of an adjustment nut and the skidding torque. From Fig. 8, the skidding torque is adjustable from maximum to minimum of motor torque. In other word, this finger is able to be adjusted as a hard finger or a passive finger.
