This manuscript describes a robot fish, the surface of which is composed of a flexible thin plastic film. Its internal mechanism, including an actuator (e.g. a servomotor), is encapsulated in the plastic film by a vacuum packaging machine. This plastic film has electromagnetic wave-transmitting properties, allowing sensors, wireless charging modules, and communication devices to be arranged within the device. To simplify the waterproofing and pressure resistance properties of the robot, the inner portion of the robot fish is filled with insulating fluid, such as industrial oil. The transmission performances of these devices, which utilize electromagnetic waves, may worsen due to the tendency of water or insulating fluids to attenuate the electromagnetic waves. This study therefore experimentally investigated the transmission performance of these devices, while taking into account the effects of water or insulating fluid. These devices were subsequently applied to our fish robot; enabling us to verify its performance by using infrared sensors to assess its autonomous locomotion.

In this paper, we describe the rolling of a tensegrity robot driven by a set of pneumatic soft actuators. Tensegrity is a mechanical structure consisting of a set of rigid elements connected by elastic tensional elements. Introducing tensegrity structures, we are able to build soft robots with larger size. Firstly, we show the prototype of a six-strut tensegrity robot, which is driven by twenty-four pneumatic McKibben actuators. Second, we formulate the geometry of the tensegrity robot. We categorize contact states between a six-strut tensegrity robot and a flat ground into two; axial symmetric contact and planar symmetric contact. Finally, we experimentally examine if rolling can be performed over a flat ground for individual sets of the actuators and discuss the strategy of rolling.

In this paper, we propose a pitch and roll control system based on a float-shift mechanism for small underwater robots. The proposed system presented here takes advantage of the restoring moment generated by the gravity force and the buoyancy force. The proposed system can maintain the attitude of a robot in its desired orientation. In previous works, we developed a prototype system that only controls the pitch angle of a robot. This paper extends the control system to provide roll and pitch control. In this paper, we explain the static model of the proposed system and how to control the pitch and roll angles of an underwater robot. Next, we conduct numerical analysis in order to investigate the performance of the proposed system. Lastly, we show that the proposed system is able to change the pitch and roll angles of an underwater robot though several experiments in a test tank.

In this paper, we present the design and development of an attitude control system for a human-sized ROV (Remotely Operated Vehicle) with a dual-manipulator system. The main operations of the ROV are sampling operations for biological researches, geological researches and archaeological explorations in Lake Biwa, the biggest lake in Japan. In order to achieve these operations, we propose an attitude control system and explain the availability of the proposed system in this paper. For the design of the attitude control system, simulation analysis was conducted. Based on the analysis, a pitch angle control system was designed and developed as the prototype of the attitude control system. An experiment was conducted in a test tank to demonstrate the effectiveness of the proposed system. The result shows that the developed system is useful for pitch angle control of the ROV.

As described in this paper, we propose an attitude control system for underwater vehicle/manipulator systems (UVMSs) based on control of the position of the center of buoyancy with respect to the center of gravity. Control of the center of buoyancy is accomplished using movable float blocks. The attitude control system is useful to control the pitch angle of UVMSs to enhance their performance and to improve their efficiency of underwater operations. A UVMS that has two 5-degree-of-freedom (DOF) manipulators was developed to verify the effectiveness of the proposed attitude control system. This paper presents a numerical study and some experimental results obtained using the UVMS with the attitude control system. We experimentally confirmed that the proposed system can change the pitch angle of the vehicle between -120 and +105 deg. In another experiment, attitude-maintenance control was conducted. Results show that the proposed system can maintain the vehicle's horizontal attitude during motion of the manipulators.

We describe here the development a joint mechanism for underwater robotic manipulators. Arms of underwater robots require small-scale bodies and high waterproofing properties. In most of underwater robots, electric motors are used as actuators to drive the robotic arm/arms, but using electric motors for underwater manipulators may be problematic due to the size/weight of the robotic arm and need to waterproof the electric motors. We develop a joint mechanism composed of combinations of rigid and flexible members, which can be deformed by a prismatic actuator fixed onto two rigid parts. We utilize a leaf spring as the flexible joint and a McKibben actuator driven by water hydraulic pressure as the prismatic actuator. The number of members in this mechanism is smaller than that of a mechanism composed of a combination of one pulley and one coil spring. One advantage of this mechanism is the avoidance of gears, thus eliminating sliding parts from the joint.

This paper presents wiping motion as a task during which the movement and deformation of a deformable object occur simultaneously. During the wiping motion of a deformable object, there is contact, but no relative movement, between the manipulator and the object, while there is both contact and relative movement between the object and the floor during the displacement of the object. We first describe wiping motion and distinguish wiping slide from wiping deformation by displacement of the internal points of an object. In addition, we show that a wiping motion is an extended system of pushing and sliding of rigid objects. As an example of wiping motion, we utilize grasping of a fabric, and we demonstrate the grasping motion of a fabric using a single-armed gripper.

In this paper, we describe the design of a deformable robot with a tensegrity structure that can crawl and we show the results of experiments showing the ability of these robots to crawl. We first describe a tensegrity structure, composed of struts and cables, and its characteristics. We next explain the principle of crawling by robot body deformation, followed by a classification of the methods by which a body can be deformed and the contact conditions of the robot through the cable-graph of the tensegrity structure. We also describe topological transition graphs that can visualize crawling from each initial contact condition. We then discuss the characteristics of the proposed robot in terms of design freedom. Finally, we show experimentally that the prototype of a tensegrity robot can crawl.

This paper describes a stochastic static analysis of link angle driven by actuator bundles. We first demonstrate a movement of a link driven by actuator bundles in terms of high driving force. The variation of actuator parameters influences the movement of this mechanism. We confirm the link may shift and twist because of the variation of actuator parameters. We then introduce stochastic analysis to investigate the link angle considering the variation of actuator parameters. In the result, the variation of the link angle converges to zero when the number of actuator is large enough. In addition, we reinforce the result through dynamic simulation considering the variation of the parameters of actuators.

We introduce a robotic prototype of an arm with a loosely coupled joint, modeled on the human joint. A viscoelastic object functions as cartilage and soft actuators as muscles. First, we show that although viscoelastic object affords smooth movement owing to shift in the center of rotation, the repeat accuracy of the joint is poor under open-loop control. The repeat accuracy was much improved by visual feedback. Under P control, the prototype was shown to be highly robust against mechanical disturbance owing to its good mechanical compliance.

We describe here a mechanism for controlling angles of a human-like joint using length sensors in threedimensional (3D) space. This joint mechanism, which is called a loosely coupled mechanism, includes a viscoelastic object and soft actuators in place of the cartilage and muscles of a human arm. To confirm motion of the link using one length sensor, we constructed a prototype of the mechanism in two-dimensional (2D) space. Based on this prototype, we constructed a 3D loosely coupled mechanism with length sensors, and we were able to control two projecting angles of the 3D prototype. In addition, we propose an appropriate method of measurement to reduce errors in measurement due to the length sensors. Using this method, we found that, for each projecting plane, the errors were less than 1.0 deg in our 3D prototype.

One of features of soft object manipulation is motion during deformation of the soft body. We analyze the stability of soft object manipulation by simultaneous control of motion and deformation. We model and formulate manipulation by simultaneous control of the motion and deformation of soft object. We then use the symmetric linear mass-damper-spring model for a simple analysis of its dynamical behavior. Second, we analyze the stability of the system. Thus, we show that an adequate feedback gain stabilized the system in PID control. This adequate feedback gain ranges between two positive values. The object cannot be stably controlled at too high a gain; neither can, it be regulated at too low a gain since the object is movable. Furthermore, we unravel the features of soft object manipulation by simultaneous control of motion and deformation

We analyze the stability of dynamic control on contact with a soft interface, the viscoelastic material between a manipulating finger and manipulated object. First, we model a dynamic control system on contact with a soft interface. The system is described in continuous-discrete time. Second, we formulate the dynamics using the modified z-transform in the continuous-discrete time system for feedback and feedforward control. Thus, we show that the stability of the system depends on viscoelasticity of the soft interface for feedback control. In particular, we point out that, in critical stability, the relationship between material viscosity and sampling time is not monotonous. Next, we analyze this phenomenon by the root locus method. Finally, we compare the stability analysis by the modified z-transform, simulations based on the Runge-Kutta method, and a regular z-transform. Thus, we demonstrate that the relationship is specific to the continuous-discrete time system.

This paper describes a stability and graspability analysis in grasping task, taking fingertip dynamics into consideration. First, a soft-fingered grasping task is modeled and formulated. A stability analysis is presented using formulated equations. We also show that grasping force converges to a constant value that is independent of fingertip dynamics. Using a soft-fingered hand mechanism that we built, we confirm that grasping force can easily be regulated by controlling saturated P. Second, through simulation, we verify the effect of fingertip dynamics on sampling time. We investigate the dependency of fingertip dynamics and sampling time on graspability. In addition, we build a variable dynamics fingertip (VDF) to confirm the simulation results.

We will develop a manipulator system that can handle randomly located, moving parts. Vision algorithm to detect the planar motion of a part is implemented on an FPGA-based realtime vision system. Trajectory of a manipulator is replanned in realtime according to the detected location of a part. We will present the control architecture and will show experimental results,.