(1990-) The manipulator that has many joints is called multi-joint manipulator, which is wide-studied as can do various jobs. But the problem of weight increase arises in practical designing. The necessary output torque at a base link increases by the increase of link numbers, which causes an actuator enlargement, and consequently a weight-increase. In order to overcome this vicious circle, many mechanisms have been proposed which sometimes consist of: a concentration of actuators at the base, a Light-Weight Design. However, these solutions could not acquire enough effects.

So we have developed multi-joint manipulator with spring weight compensation mechanism called Float Arm III and IV (Fig.1). This mechanism consists of springs and parallelogram linkage mechanism. The reason having parallelogram linkage mechanism is the weight compensation force is invariable to the posture of the manipulator (Fig.2). However, the weight also increases with the number of joint since springs are needed more and more for the moment compensation.

To overcome this problem, we developed the multi-joint manipulator with wire-driven weight compensation mechanism called Float Arm V (Fig.3). There are the following three features in this mechanism: 1. Wire-Driven weight compensation (Fig.3 (a)), 2: The tension amplification by using the double pulley (Fig.3 (b)), 3: The wire arrangement nearby the yaw rotational axis (Fig.3 (c)).

The wire is stretched from link to link so there needs the wire tension amplification at every joint. In order to it, the “Double Pulley” is employed. The difference between the two diameters can generate optimal wire tension amplification for all joints. And the wire always moves according to arm movement since it is arranged arm to arm. The wide length between the wire and the yaw rotational axis changes the tension. The effect of this proposed compensation mechanism is almost constant wire twisting by setting wire nearby the yaw axis even if the arm moves. This mechanism will be utilized to a mobile robot-loaded patrol type surveillance camera that can work in factory, plant and nuclear reactors.

Fig.1 Float Arm III, IV

Fig.2 Parallel and Serial Link Mechanism

Fig.3 The Basic Concepts of the Float Arm V With Wire-Driven Weight Compensation Mechanism