Recently, the importance of mechanical transparency in human-assistive robots has grown. Traditionally, its primary goal was minimizing interaction forces during assistance. However, under this conventional definition, mechanical transparency was not considered when an interaction force was required during assistance. This research focuses on achieving mechanical transparency within the context of shoulder motion in upper extremity exoskeletons for rehabilitation. Our primary goal is maintaining interaction forces at target values, even with motion disturbances. To this end, we developed a shoulder actuation testbed for exoskeletons, incorporating a fusion hybrid linear actuator distinguished by high back-drivability, robust torque generation capability, and safety features. To attain mechanical transparency, we created a model for calculating the required joint torque, accounting for gravitational dynamics, and subsequently determined the necessary actuator output. The system characteristics were evaluated based on the joint torque generated by the actuator. The actuator utilized pneumatic pressure to generate force and compensated for kinetic friction using electromagnetic forces. The results showed that the compensation by the electromagnetic force reduced the root mean square error of the torque to less than 60% in relation to pneumatic pressure alone. This demonstrated the ability to generate consistent torque with high robustness to motion disturbances.

Various actuators have been developed to improve the performance of cooperative robots. Multi-degree-of-freedom (multi-DOF) electromagnetic actuators can rotate multi-DOF by a direct drive and can contribute to system miniaturization and higher precision. However, the biggest challenge is to increase the output because the torque cannot be amplified using a reduction gear. To solve this problem, this paper focuses on a hybrid actuation with a pneumatic actuator, which has a large output density. In this study, we propose a two-DOF pneumatic-electromagnetic hybrid actuator that integrates a bellows pneumatic actuator and a two-DOF electromagnetic actuator. First, the concept, design, and operating principle are presented. Next, the torque control method, dynamic model, and attitude control system are shown. In the torque analysis, the maximum torque of the proposed actuator is four times larger compared with a conventional two-DOF electromagnetic actuator of the same size. The dynamic simulation results show that attitude control is possible with hybrid actuation. Based on the results, a hybrid multi-DOF actuator using multiple drive sources is proposed for the first time.

Magnetic lead screw (MLS) is a feed screw that allows non-contact power transmission. The MLSs have some advantages such as reduction of particle emission and improving positioning accuracy. However, conventional MLSs need a supporting mechanism using linear guides or slide bearings. They deteriorate the advantages of MLSs because of friction. In order to solve this problem, we propose a magnetically levitated lead screw (MLLS) for complete non-contact transmission. The proposed magnetic structure and operating principle are verified through a three-dimensional finite element method. The suspension force, thrust, and torque characteristics are investigated, and the effectiveness of the MLLS are clarified.

Locomotion on the rough and variable ground surfaces is crucial for robots to complete various tasks. Recent advancement in numerical computation allow such locomotive robots to manipulate in real environments using a model-based control framework. This approach is successful if the precise model it is obtained. However, it is not always feasible to use the precise model because there are various factors related to both the robot and its surroundings. In this paper, we report the locomotion experiments with 2 types of legged robot that can change its behavior by switching connection patterns among hydraulic cylinders mounted on the robot's legs. An actuator network system (ANS) is used to switch mutual interconnection of cylinders. The switching connection allows the robots to realize not only adaptive locomotion to the environment but also operation of the traveling direction.

Conventional hybrid actuators can achieve a better force/torque bandwidth than a single principle actuator without losing back-drivability. However, hybrid actuators occupy space at least equal to the sum of the volumes of two or more actuators and multiple transmissions consisting of timing belts, gears, links, tendons, or Bowden-cables. Designs in which space and structural elements of a hybrid actuator are integrated have not been sufficiently studied. This paper presents an original development work on the design of an integrated pneumatic-electromagnetic hybrid linear actuator (iPEHLA). In the integrated design, hybrid components of an air cylinder and a linear motor were arranged around a single shaft, and the pneumatic and electromagnetic actuators shared the same moving parts (i.e., piston and moving part) and internal cylindrical spaces (i.e., cylinder and stator). Consequently, space required was less than the sum of the volumes of the two actuators. To verify the feasibility of this novel integrated design, the iPEHLA was designed and prototyped by modifying parts of a commercially available pneumatic cylinder integrated with electromagnetic components. The performances of the iPEHLA under pneumatic actuation and hybrid actuation were compared with respect to a feedforward friction compensation. The experimental results demonstrated that the novel design maintained its hybrid properties.

To achieve a realistic task by a recent complicated robot, a practical motion planning method is important. Especially in this decade, sampling-based motion planning methods have become popular thanks to recent high performance computers. In sampling-based motion planning, a graph that covers the state space is constructed based on reachability between node pairs, and the motion is planned using the graph. However, it requires an explicit model of a controlled target. In this research, we propose a motion planning method in which a system model is estimated by using Gaussian process regression. We apply our method to the control of an actual robot. Experimental results show that the control of the robot can be achieved by the proposed motion planning method.

We have been studying small sized direct-drive electromagnetic linear actuators and their control method. These actuators were able to emulate the viscoelastic characteristics of the human muscle by PD position control to respond to external forces flexibly. However, their thrust force was not enough in order to apply to legs and shoulders of robots. In this paper, we present a novel small cylindrical linear vernier motor for artificial muscle of humanoid robots. First, the structure and operating principle of the proposed linear vernier motor are described. Then, the thrust and detent force of the motor are shown by 2D finite element analysis and measurement on a prototype. As the result, the validity of the simulation is discussed. Finally, the effect of the position controller with the disturbance observer on reduction of detent force and deviation between target and actual mover position is clarified.

The compliance of muscles with external forces and the structural stability given by biarticular muscles are important features of animals to realize dynamic whole body motions such as running and hopping in various environments. For this reason, we have been studying an electromagnetic linear actuator. This actuator can emulate the behavior of a human muscle such as the spring-damper characteristics by quick control of the output force (i.e. impedance control) and it is expected to be used as an artificial muscle. In this paper, we develop a monopedal robot possessing bi- and mono-articular muscles implemented by linear actuators. Thanks to the biarticular muscle, the bouncing direction of the robot can be controlled by changing the stiffness ellipse at the endpoint (i.e. foot) of the robot. We confirm that the bouncing direction of the robot can be controlled and hopping can be achieved by changing the stiffness ellipse.