This paper presents the development and evaluation of Ringbot, a novel leg-wheel transformer robot incorporating a monocycle mechanism with legs. Ringbot aims to provide versatile mobility by replacing the driver and driving components of a conventional monocycle vehicle with legs mounted on compact driving modules inside the wheel. The paper covers the hardware and software implementation of a prototype robot. The Ringbot prototype features a wheel and two driving modules located inside, each equipped with a 3-DoF leg for balancing, steering, and legged motions to assist monocycle driving. The driving control is achieved through decoupled speed controller and steering controller. In addition, active-legged motions are implemented and managed through a finite-state machine. The controllers for wheeled driving and legged motions were tested in a simulation environment, as well as on the hardware prototype, to verify the concept of a monocycle with legs and evaluate the prototype's capabilities.

Although many soft robotic skins have been introduced, their use has been hindered due to practical limitations such as difficulties in manufacturing, poor accessibility, and cost inefficiency. To solve this, we present a low-cost, easy-to-build soft robotic skin utilizing air-pressure sensors and 3D-printed pads. In our approach, we utilized digital fabrication and ROS to facilitate the creation and use of the robotic skin. The skin pad was fabricated by printing thermoplastic urethane (TPU) and post-processed with an organic solvent to secure air-tightness. Each pad consists of a TPU shell and infill, so the internal air pressure changes in response to tactile stimuli such as force and vibration. The internal pressure is measured and processed by a microcontroller and transmitted to the PC via a serial bus. We conducted experiments to investigate the characteristics of the skin pads, and the results showed that the developed robotic skins are capable of perceiving interaction force and dynamic stimuli. Finally, we developed the dedicated soft robotic skins for our custom robot designed in-house, and demonstrated safe and intuitive physical human-robot interaction.

In this paper, we present an add-on system that enhances the capabilities of a quadrupedal robot. The addon system efficiently allows the integration of two 6-DOF manipulators with a quadruped as a single system. The design of the system is developed with modularity as an important principle, allowing for versatility and adaptability in various applications of mobile manipulation. With the modular design, the system can easily be used for mobile-manipulation tasks but also as a system for human entertainment. We show the modular and versatility of the system through applications in a home setting and various entertainment settings. The proposed system leads to an enhanced level of human-robot interaction with more engaging and interactive experiences.

This paper describes the development of a 1-DOF kinesthetic force display device in the form of an arm training simulator that replicates the haptic feeling of lead-pipe rigidity in the elbow joint. Patients with lead-pipe rigidity have uniformly elevated muscle tone throughout the range of motion, which is an important clinical sign for diagnosing Parkinson’s disease during a neurological examination. The simulator could provide training opportunities for healthcare trainees to learn and practice the assessment technique for lead-pipe rigidity. The simulator was driven by a series elastic actuator in order to have more accurate joint torque control in a safe and cost-effective manner for rendering abnormal muscle resistance. A mathematical model of lead-pipe rigidity based on hyperbolic tangent was proposed to recreate the elevated muscle resistance at different Unified Parkinson’s Disease Rating Scale (UPDRS) 0-3. Performance of the simulator was evaluated through benchtop tests and rigidity simulation tests. Preliminary results suggested the simulator had good torque control accuracy (an average RMSE < 0.27 Nm) and good fidelity in mimicking clinically-measured lead-pipe rigidity at UPDRS 0-3.

In this paper, we present the second version of a reconfigurable modular legged robot, Snapbot V2. The mechanical design of Snapbot V2 is enhanced for better dynamic performance and robust connection with modular legs. A motion generator for locomotion is developed to achieve various locomotion skills in one to six-leg configurations. The locomotion is tested on a multi-body dynamic simulation model and implemented on a physical robot as well. A visual detection is implemented with a camera module to recognize the robot's configuration. By detecting the particular color of the parts at the leg module, the robot can recognize the number and location of the connected legs. Based on the recognized configuration, Snapbot V2 selects the proper locomotion style automatically.

This paper presents a 6 DOF leg mechanism for a humanoid robot. The proposed Hybrid Leg is designed to combine serial and parallel mechanisms and consists of a pair of twin 3 DOF serial chains in parallel. A 5-bar-linkage mechanism is implemented to the serial mechanism to generate 2 DOF motion regarding hip and knee pitch rotation. The hardware prototype is designed by matching the kinematic specification of a commercial robot's leg to compare the proposed mechanism with a conventional serial leg. We derive the analytical expressions of its forward and inverse kinematics. End-effector workspaces are shown with plots and inverse dynamics analysis of Hybrid Leg and serial leg with a given walking gait trajectory is presented. Hardware experiment is conducted with a prototype to verify the simulated workspace and trajectory tracking performance.

In this paper, we present the design and performance evaluation of a bipedal robot that utilizes the Hybrid Leg mechanism. It is a leg mechanism that achieves 6 DOF with a combined structure of serial and parallel mechanism. It is designed to have a light structural inertia and large workspace for agile bipedal locomotion. A new version of Hybrid Leg is fabricated with carbon fiber tubes and bearings to improve its structural rigidity and accuracy while supporting its weight. A pair of Hybrid Legs is assembled together for bipedal locomotion. In the assembly, we adopt a pelvis structure with an yaw angle offset to enlarge the feet workspace, inspired by the toe-out angle of the human feet. The workspace and range of velocity are presented in simulation and verified with hardware experiments. We also demonstrate a simple forward walking motion with the developed robot.