Hiroya Yamada

Snake-like robots [Tutorial]

We have introduced the biomechanical research on snakes and developmental research on snake-like robots that we have been working on. We could not introduce everything we developed. There were also a smaller snake-like active endoscope; a large-sized snake-like inspection robot for nuclear reactor related facility, Koryu, 1 m in height, 3.5 m in length, and 350 kg in weight; and several other snake-like robots. Development of snake-like robots is still one of our latest research topics. We feel that the technical difficulties in putting snake-like robots into practice have almost been overcome by past research, so we believe that such practical use of snake-like robots can be realized soon.

Study on the 3D shape of active cord mechanism

Snake-like robots and hyper-redundant manipulators have been called active cord mechanism (ACM), and they have been one of fields of robotics. However, general study on the spatial shape of ACM has not been conducted enough so far. In this paper, we propose a effective method for analysis of the 3D shape of ideal continuous ACM models. In addition, we show some important characteristics of ACM using this method. The results help us understand the characteristics and possibility of ACM

A passive weight compensation mechanism with a non-circular pulley and a spring

We propose a new weight compensation mechanism with a non-circular pulley and a spring. We show the basic principle and numerical design method to derive the shape of the non-circular pulley. After demonstration of the weight compensation for an inverted/ordinary pendulum system, we extend the same mechanism to a parallel five-bar linkage system, analyzing the required torques using transposed Jacobian matrices. Finally, we develop a three degree of freedom manipulator with relatively small output actuators and verified that the weight compensation mechanism significantly contributes to decrease static torques to keep the same posture within manipulators work space.

Stabilization of the head of an undulating snake-like robot

In this paper, we discuss about stabilization of the head of a snake-like robot. In prior research snake-like robots usually shook the head during undulating motion. However, a snake-like robot is usually equipped with a camera on the head, so the swing of the head is problem. To solve this problem, we propose a control method to stabilize the head of an undulating snake-like robot. In the proposed method, the motion of the neck is controlled to cancel the undulation of the body in order to stabilize the head. In this study, first we derived the formulas for this method, and confirmed the effectiveness by simulation. Then we implemented that control on a real snake-like robot and showed the availability of the proposed method.

A snake-like robot for real-world inspection applications (the design and control of a practical active cord mechanism)

In order to inspect narrow and unstructured environments such as disaster sites, snake-like robots should have rugged construction, but at the same time be sufficiently sensitive to detect contact with their environments. In addition, control which allows the robot to adapt to its environment is also essential. Thus, we studied both design and control of snake-like robots for real-world inspection application, and through this developed our new prototype named ‘ACM-R4.1’. The ACM-R4.1 integrated a torque sensing function, a camera system, dust- and water-proofing, a mechanical torque limiter, and terrain adaptive control into its compact body. Particularly, the torque sensing system and the terrain adaptive control based on that allows us to operate the robot in challenging environment without observing the robot directly. We also showed the feasibility of our concept through the testing of the ACM-R4.1. In this paper, we describe the concept design of a snake-like robot for real-world inspection application and detailed design and experiments of the ACM-R4.1.

3 axial force sensor for a semi-autonomous snake robot

Now that mobile robots are getting tested more and more in challenging areas, difficulties in control, particularly when the robot cannot be seen, have appeared. In this research a mobile snake robot with actuated wheels is given the ability to sense its surroundings through its wheels by 3DOF force sensors, so that semi-autonomous control can be realized. This will simplify necessary operator commands and improve situation awareness through information feedback.

Snake-like active wheel robot ACM-R4.1 with joint torque sensor and limiter

In order to inspect inside narrow and unstructured environments, the snake-like robots should have ruggedness of the structure and at the same time function to detect the contact of the body to the environments. This paper proposes a snake-like active wheel robot named “ACM-R4.1” with torque sensor and torque limiter on each of the joints. Introduced torque sensor is composed of 2 thin ring plates holding steel balls in the oval cavities in between and a rubber ring producing compressing force of the thin ring plates in the narrow gap of a joint. Applied torque of the joint produces small sliding motion of the ball inside oval cavities and thus measurement of the small displacement of these plates enable to detect the applied torque. Overload-protection to the joint actuator is made by the sliding motion of the rubber which acts after the ball motion in the cavities and they hit the end of cavities. We made theoretical consideration of design of the torque sensor and did torque measurement experiments by using constructed snake-like active wheel robot ACM-R4.1. We also demonstrated the terrain adaptive motion of ACM-R4.1 by using the torque sensors.

Loop forming snake-like robot ACM-R7 and its Serpenoid Oval control

This paper discusses the design of a new snake-like robot without wheels, named ACM-R7. It has 18 DOFs, is 1.6m in length and weighs 11.7kg. It features a water-tight structure, a large motion range pitch joint of ±90 degree and a high output-power actuator arrangement, based on the coupled drive concept. Furthermore the control method “Loop Gait” is discussed. For this gait the ACM-R7 forms a loop shape and rolls like a wheel on the rim. We introduce the “Serpenoid Oval” for the loop shape. It s formed by a smooth sinusoidal angular motion of the joints. Moreover we consider the modification of the “Serpenoid Oval” for steering and obstacle avoidance. The performance is then verified by several motion experiments.

A Radial Crank-type continuously variable transmission driven by two ball screws

Power-to-weight ratio of actuators is extremely important for robots, particularly mobile robots. The combination of electric motor and speed reducer, which is the most common driving mechanism for robots, can utilize the motor in the area where its power output is high when the reduction ratio is appropriately designed relative to the load. However, in the case of applications in which the load significantly changes, the motor has to be operated in the area where its power output significantly drops. This problem has restricted the capability of mobile robots, especially biologically inspired robots. Therefore in this paper I focus on a continuously variable transmission (CVT). Crank-type CVTs, which have been used for robotic joints, have the major disadvantage of a limited range of motion due to the dead point of the crank. Thus, this paper proposes the Radial Crank-type CVT (RC-CVT), which overcomes this limit of range of motion by increasing the number of links driving the crank of the CVT. This RC-CVT holds promise as an efficient robotic joint as it can utilize ball screws. This paper shows the equations of kinematics and statics of the RC-CVT and also describes the design and test of the prototype. The application to a quadruped robot is also introduced.

Development of a coupled tendon-driven 3D multi-joint manipulator.

Very long-reach snake-like robotic arms in the range of 14 meters are expected to be used in decommissioning work inside nuclear reactor containers. We developed a tendon-driven system which has the advantage of placing electronic devices protected in the arms base part which stays out of the reactor container, and only few expensive highly radiation hardened sensors and tools are mounted in the arm tip. Generation of large joint torque is necessary to realize such a very long arm. We applied the concept of coupled tendon-driven mechanism formerly used to generate restricted two dimensional motions, and extended its concept by proposing a new joint arrangement which makes possible three dimensional motions in a large workspace. Mechanical design, compact storage method and derivation of the arm motion control are detailed. Moreover, we built a preliminary mechanical prototype called ”Mini 3D CT-Arm”, and the experimental results demonstrated the validity of the newly proposed concept.