Hyungwon Shim

A new concept and technologies of multi-legged underwater robot for high tidal current environment

In this paper, we present a new concept of multi-legged seabed robot for high tidal current environment. The robot moves on seabed by walking with 4 or 6 legs which is different moving mechanism from the existing underwater thrust system such as screw or Caterpillar. The main concept to endure the high current is utilization of hydrodynamic forces acting on the body and legs. The advantage of this concept is that the robot is able to have high stability in positioning as well as that the robot is less disturbs the seabed environment than other thrust system. In order to optimize the configuration of the leg with respect to tidal current, an optimization problem is formulated. And a simplified model of hydrostatic and hydrodynamic forces acting on the legs is presented. Presented model can be used for optimization of body and leg configurations, and for drag-optimal path planning of legs. Because the shape of leg is a main factor to the hydro dynamic forces, a design of slender leg is also presented in this paper.

Approximated Generalized Torques by the Hydrodynamic Forces Acting on Legs of an Underwater Walking Robot

In this paper, we present the concept and main mission of the Crabster, an underwater walking robot. The main focus is on the modeling of drag and lift forces on the legs of the robot, which comprise the main difference in dynamic characteristics between on-land and underwater robots. Drag and lift forces acting on the underwater link are described as a function of the relative velocity of the link with respect to the fluid using the strip theory. Using the translational velocity of the link as the rotational velocity of the joint, we describe the drag force as a function of joint variables. Generalized drag torque is successfully derived from the drag force as a function of generalized variables and its first derivative, even though the arm has a roll joint and twist angles between the joints. To verify the proposed model, we conducted drag torque simulations using a simple Selective Compliant Articulated Robot Arm.

A development of a transformable caterpillar equipped mobile robot

This study develops a transformable caterpillar equipped mobile robot(CALEB-2) and a set of strategy for overcoming obstacles. The developed mobile robot CALEB-2 is equipped with 6 driving motor units for traversing uneven terrain with redundant maneuverability. Two of them are driving motor units which generate caterpillar driving force and the rest four driving motor units are for the arm rotation control. The left and right caterpillars are supported by two arms respectively, and all the four arms can rotate around there rotation axes, in consequence by the rotating arms the shapes of each caterpillars can be changed separately. To keep the tension of 2 driving caterpillars optimally, we develop a sliding arm mechanism(caterpillar tension regulator). Also, the CALEB-2 is equipped with 4 PSD distance sensors and 2 tilt sensors for its maneuvering purpose. Moreover all of the 6 driving motor units of CALEB-2 can be operated independently. With the equipped sensors and the redundant maneuverability this study develops an ascending and a descending procedure to/from an obstacle. And this study shows the effectiveness of the developed transformable caterpillar mechanism by the ascending and the descending operation.

An In-situ Correction Method of Position Error for an Autonomous Underwater Vehicle Surveying the Sea Floor †

Abstract This paper presents an in-situ correction method to compensate for the position error of an autonomous under-water vehicle (AUV) near the sea floor. AUVs generally have an inertial navigation system assisted with auxiliary navigational sensors. Since the inertial navigation system shows drift in position without the bottom reflection of a Doppler velocity log, external acoustic positioning systems, such as an ultra short baseline (USBL), are needed to set the position without surfacing the AUV. The main concept of the correction method is as follows: when the AUV arrives near the sea floor, the vehicle moves around horizontally in a circular mode, while the USBL tran-sceiver installed on a surface vessel measures the AUVs position. After acquiring one data set, a least-square curve fitting method is adopted to find the center of the AUVs circular motion, which is transferred to the AUV via an acoustic telemetry modem (ATM). The proposed method is robust for the outlier of USBL, and it is inde-pendent of the time delay for the data transfer of the USBL position with the ATM. The proposed method also reduces the intrinsic position error of the USBL, and is applicable to the in-situ calibration as well as the initializa-tion of the AUVs’ position. Monte Carlo simulation was conducted to verify the effectiveness of the method.

A model estimation and multi-variable control of an unmanned surface vehicle with two fixed thrusters

This paper presents a dynamic model estimation using system identification (SI) technique and a multivariable controller design for an unmanned surface vehicle (USV) with two fixed thrusters. The catamaran shaped USV has been developed for marine research and surveying exploration in costal area. To validate the automatic control performance of USV, which is designed by classical PID controller, we carried out experiments to keep the USVs position at a fixed point and to track predefined positions. As a result, we have found that it needs time-consuming efforts to tuning the weight between heading and speed controller since the yawing and surge motions are tightly coupled to the two thrusters. In order to solve the problem, it is necessary to introduce the multivariable controller design method. And a numerical dynamic model is required for the model based design. This paper addresses the estimation of a dynamic model of the USV based on the experimental results and the design of Linear-Quadratic (LQ) controller based on a multivariable control method. To verify the efficiency of the designed controller using the estimated dynamic model, numerical simulations were carried out.

Finite Element Analysis of CFRP Frame under Launch and Recovery Conditions for Subsea Walking Robot, Crabster

This study applied finite element analysis (FEA) to the body frame of the 200-meter class multi-legged subsea walking robot known as Crabster (CR200). The body frame of the CR200 is modeled after the ribcage of a human so that it can disperse applied external loads. It is made of carbon-fiber-reinforced plastic (CFRP). Therefore, the frame is lighter and stronger than it would be if it were made of other conventional materials. In order to perform FEA for the CFRP body frame, we applied the material properties of the CFRP as obtained from a specimen test to an FE model of CFRP frame. Finally, we performed FEA with respect to the load conditions encountered when the robot is launched into and recovered from the sea. Also, we performed FEA for the frame, assuming that it was fabricated using a conventional material, in order to compare its characteristics with CFRP.

Finite Element Analysis of Carbon Fiber Reinforced Plastic Frame for Multi-legged Subsea Robot

This paper describes a finite element analysis (FEA) of the body frame of a subsea robot, Crabster200 (CR200). CR200 has six legs for mobility instead of screw type propellers, which distinguishes it from previous underwater robots such as remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs). Another distinguishing characteristic is the body frame, which is made of carbon fiber reinforced plastic (CFRP). This body frame is designed as a rib cage structure in order to disperse the applied external loads and reduce the weight. The frame should be strong enough to support many devices for exploration and operation underwater. For a reasonable FEA, we carried out specimen tests. Using the obtained material properties, we performed a modal analysis and FEA for CR200 with a ready posture. Finally, this paper presents the FEA results for the CFRP body frame and the compares the characteristics of CFRP with conventional material, aluminum.

Development of a Specialized Underwater Leg Convertible to a Manipulator for the Seabed Walking Robot CR200

This paper presents the development of a specialized underwater leg with a manipulator function(convertible-to-arm leg) for the seabed walking robot named CRABSTER200(CR200). The objective functions of the convertible-to-arm leg are to walk on the seabed and to work in underwater for precise seabed exploration and underwater tasks under coastal area with strong tidal current. In order to develop the leg, important design elements including the degree of freedom, dimensions, mass, motion range, joint structure/torque/angular-speed, pressure-resistance, watertight capability and cable protection are considered. The key elements of the convertible-to-arm leg are realized through concept/specific/mechanical design and implementation process with a suitable joint actuator/gear/controller selection procedure. In order to verify the performance of the manufactured convertible-to-arm leg, a 25bar pressure-resistant and watertight test using a high-pressure chamber and a joints operating test with posture control of the CR200 are performed. This paper describes the whole design, realization and verification process for implementation of the underwater convertible-to-arm leg.

Development of leg with arm for the multi-legged seabed robot “CR200”

This paper presents the development of leg with arm for the CR200 as multi-legged seabed robot as design points, fabrication factors and experiments. The design points of leg with arm were presented and also the manufactured leg with arm was showed. In order to verify the design factors, the experiment of joint driving, pressure-resistant and watertight with 25bar were performed.

Mobility and agility analysis of walking robot

This paper presents a mathematical framework for mobility and agility analysis of multi-legged walking robots. The method is acceleration analysis in consideration of the frictional ground contact. This method is based on both unified dynamic equation for finding the acceleration of a robotpsilas body and constraint equation for satisfying no-slip condition. After the dynamic equation representing relationship between actuator torques and body acceleration, is derived from the force and acceleration relationship between foot and bodypsilas gravity center, the constraint equation if formulated to reconfigure the maximum torque boundaries satisfying non-slip condition from given original actuator torque boundaries. From application of the reconfigured torques to the dynamic equation, interested acceleration boundaries are obtained. The approach based on above tow equations, is adapted to the changes of degree-of-freedoms of legs as well as friction of ground. And, the method provides the maximum translational and rotational acceleration boundaries of bodypsilas center that ar achievable in every direction without ocurring slipping at the contact points or saturating all actuators. Given the torque limits in infinite norm-sense, the resultant accelerations are derived as a polytope. From the propose method, we obtained achievable acceleration boundaries of 4-legged and 6-legged walking robot system successfully.