This paper presents a novel rotational serial variable stiffness actuator (SVSA) based on an Archimedean spiral relocation mechanism (ASRM), which is applied to linearly change the position of the pivot point of a lever as well as obtain a large range of motion and adjustable stiffness. Consequently, the ASRM introduced in this work contributes to a compact structure of the mechanical design without sacrificing the continuity of adjustable stiffness. In terms of the variable stiffness mechanism, two linear springs are assembled antagonistically on a spring shaft and rotate simultaneously with the output link. To improve the spring force transmission efficiency, these displacements of the springs are set to be perpendicular to the output link. A large deflection angle can therefore be achieved to obtain high passive energy storage ability. Moreover, the SVSA is also modeled to investigate the theoretical capabilities of the output stiffness and passive energy capability. Further control experiments are performed to quantitatively evaluate the physical performance of the SVSA. Our results demonstrate that the SVSA with a proportional-derivative feedback plus feedforward controller exhibits a fast response and high accuracy for both position and stiffness regulation and tracking tasks. In addition, the real output torque measurement verifies the fidelity of the SVSA for torque generation.

Upper limb exoskeletons show promise for improving functionalities required for stroke patients. Despite recent progress, most of current upper limb rehabilitation devices are still bulky, heavy, and less compliant to be applied. This article presents a cable-driven compliant upper limb rehabilitation exoskeleton robot (CURER) with a lightweight frame and comfortable human–robot interaction. A modular series elastic actuator (SEA) was designed to provide controlled torque for each active robotic joint, and Bowden cables were applied to transfer controlled torque to distal joints. A six-bar double parallelogram mechanism was designed to implement 3 active degrees of freedom (DOFs) of a shoulder. An actuated elbow with 1 DOF and a wrist with a passive DOF were also developed for CURER. The anthropomorphic shoulder, elbow, and wrist joints can minimize misalignment between human upper limbs and the robot. The length of anthropomorphic arm was adjustable for a wide range of users. It can apply up to a 33 N·m torque in shoulder flexion/extension, abduction/adduction, intra/extra rotation, and elbow flexion/extension, with a range of 7.6–8.0 Hz position bandwidth in each actuation. CURER has a large range of motion and can provide accurate torque control for stroke patients’ requirements. Besides, a comprehensive rehabilitation strategy including robot-in-charge mode and human-in-charge mode was developed for different recovery stages. Experiments carried out on CURER actuation units demonstrated good position and impedance control performance. Finally, a virtual reality training system was developed to assist the subjects to accomplish upper limb rehabilitation efficiently.

This paper focuses on the design, modeling, and control of a novel remote actuation, including a compact rotary series elastic actuator (SEA) and Bowden cable. This kind of remote actuation is used for an upper limb rehabilitation robot (ULRR) with four powered degrees of freedom (DOFs). The SEA mainly consists of a DC motor with planetary gearheads, inner/outer sleeves, and eight linearly translational springs. The key innovations include (1) an encoder for direct spring displacement measurement, which can be used to calculate the output torque of SEA equivalently, (2) the embedded springs can absorb the negative impact of backlash on SEA control performance, (3) and the Bowden cable enables long-distance actuation and reduces the bulky structure on the robotic joint. In modeling of this actuation, the SEA's stiffness coefficient, the dynamics of the SEA, and the force transmission of the Bowden cable are considered for computing the inputs on each powered joint of the robot. Then, both torque and impedance controllers consisting of proportional-derivative (PD) feedback, disturbance observer (DOB), and feedforward compensation terms are developed. Simulation and experimental results verify the performance of these controllers. The preliminary results show that this new kind of actuation can not only implement stable and friendly actuation over a long distance but also be customized to meet the requirements of other robotic system design.

The usage of parallel elastic actuators (PEA) in legged robots could potentially enhance the joints and increase energy efficiency by providing extra torques. However, the current design that adopts tension springs or spiral springs usually requires additional working space for PEA add-ons and enlarges size and mass too much. Besides, they often tune the spring parameters especially the spring constant by hand, failing to achieve optimal performance when considering multiple objectives. To tackle these issues, this article designs a compact dual-slide PEA (DS-PEA) leg that adopts a compression spring structure. Through integrating with a dual-slide mechanism, the PEA elements are attached tightly to the transmission, resulting in a small-size and light-weighted design. Furthermore, we adopt a multiobjective optimization method, i.e., multi-Pareto fronts quantify, to automatically choose the proper spring constant. Simulation and hardware experiments demonstrate that peak torque, motor power, and cost of transport for motion tracking are all largely reduced, even when working at multiple trajectories. Extensive hopping experiments further validate the dynamic motion capability and the energy efficiency of the delicate design. The compact DS-PEA leg will be used in a quadruped robot shortly.

Patient transportation in hospitals faces many challenges, including the limited manpower, work-related injuries, low efficiency of current bed pushing methods. This paper presents a new motorized robotic bed mover with omni-directional mobility to address this problem. This device is composed of an omni-directional mobility unit; a force sensing based human-machine interface (HMI) and control hardware with batteries and electronics. The proposed bed mover can be attached to the bottom of a manual hospital stretcher, transforming it into a powered omni-directional bed (OmniBed) that can be used only by one person. The function of the OmniBed is compared with that of a conventional powered bed, which only provides forward assistance with a fifth powered wheel. We perform a pilot study with 14 subjects to evaluate the performance of this OmniBed and benefits for hospital application. The experimental results show that the OmniBed can half the manpower while decreasing back muscle activities, revealing the potential health benefits for older staffs. The OmniBed also shows promising signs of high precision and handling in small spaces with its one-step "parallel-parking" ability. This device is more ergonomic, more effective and safer than the conventional powered bed.

Passive dynamic walking (PDW) has attracted much research attention due to its humanoid and energy efficient gaits. However, walking control of the passivity-based biped robot inspired by PDW still remains a challenge, for PDW is sensitive to disturbances. An walking controller is essential for practical passivity-based biped robots in real environments. This paper presents a deep reinforcement learning (DRL) controller based on deep Q network for planar passivity-based biped robot, to learn policies directly from inputs for bipedal walking task. First, the intelligent controller using deep Q network is trained, with PDW as reference trajectory. The learning experience from PDW could be helpful to implement a natural looking and energy-efficient gait. Then the trained deep Q network is utilized as the walking controller. Simulation results show that the DRL controller based on deep Q network makes the planar biped robot walk against original value disturbance, on different slope, level ground and varying slopes. The controller this paper presented could be used to improve the versatility of the passivity-based biped robot.