ACTIVE CHORD MECHANISM for Robots – 21002
An active chord mechanism (ACM) is a robot gripper that conforms to the shapes of irregular objects. An ACM is built something like the human backbone. A typical ACM consists of numerous small, rigid structures connected by hinges, as shown in the illustration.
The precision with which an ACM can conform to an irregular object depends on the size and number of sections. The smaller the sections, the greater is the precision. An ACM exerts uniform pressure all along its length. This pressure can be increased or decreased, according to the required task. One application of ACMs is to position or arrange fragile objects without damaging them. Another application is the picking of fruits and vegetables.
(2004-) Active Cord Mechanism (ACM) can operate tasks which are difficult for other robots, making use of its characteristic long thin body. For instance, in a narrow environment such as inside of a pipe, or in a disordered environment such as a disaster site, ACM has possibility of operating search and inspection task. However, we have a lot of problems operating ACM in practical use. In practical use, robots have to resist water and dust, and cope with unstable footing. ACM-R4 (Fig. 1), practical 3-dimensional ACM, is designed to investigate the possibility of practical use of ACM. ACM-R4 is equipped with devices for practical use such as water-proof mechanism.
ACM-R4 consists of a series of joint units (Fig. 2). Each unit has 1 DoF of bending. The bending axis of adjacent joints are different at 90 degrees mutually. This structure have been also adopted in ACM-R3, the previous model of ACM-R4, and have merits as following;
(1)The design of a 3-dimensional ACM becomes relatively easy.
(2)Joints’ range of motion become relatively large.
(3)The robot can be equipped with large wheels at the same axis of joints.
ACM-R4 has following 3 characteristics:
ACM-R4 has motors to drive wheels. In general, snake-like robots can generate propulsive force by undulating their body and don’t need motors for wheels. However, this movement requires large number of joints. We adopt active wheels from the viewpoint of practical use of snake-like robots.
(2)Dust- and water-proofing
ACM-R4 adopts shell structure and is equipped with rubber seals at the joints and wheel shafts. Experiments confirm continuous 3-hours operation in muddy water (Fig. 3).
To protect robot from a shock and overload expected in practical use, over load protection is implemented. ACM-R4 has a simple clutch using O-ring. The friction force of O-ring transmits the torque from an internal gear to the joint (Fig. 4).
Table. 1 shows the specification of ACM-R4. Experiments confirmed the ability of right-angle turn in 240-mm wide passage (Fig. 5) and climbing of 400-mm height step (Fig. 6). This clarified the probability of practical snake-like robots which operate in narrow and stepped environments. However, the operation of ACM-R4 is difficult, especially in stepped environment. We will study on methods to make the operation easy, for example, automatic adaptation to environments, and remote control via sensor signals on the robot.