AbstractThe spatial cable-driven parallel robots (CDPRs) with low DOF (degree-of-freedom; n < 6) are like the physiological structure of bone and muscles, which are suitable for designing humanoid joints. Therefore, the type synthesis of the CDPR is of great interest for the design of new humanoid wrist joints. In this paper, we present a type synthesis of the coupled-input CDPRs to design a 3DOF wrist. Coupled input means that one actuator controls more than one cable. First, the Yamanouchi symbols of the coupled-input CDPRs are listed using the permutation group. In addition, two winding methods for the cable and the actuator are defined in the coupled-input CDPRs. Finally, a topology configuration of the coupled-input CDPR suitable for the 3DOF wrist model is determined based on a comparative analysis of the workspaces of a class of coupled-input CDPRs. It is shown that type synthesis of the coupled-input CDPRs is an effective way to innovate low DOF CDPRs.

AbstractA compliant constant-force mechanism (CCFM) is a specific type of compliant mechanism that serves as a passive force regulation device. When subjected to a load, it undergoes deformation, resulting in an almost consistent output force regardless of changes in input displacement. Traditional methods used to design CCFMs typically rely on either stiffness combination or parametric optimization based on existing design configurations. To enable the direct synthesis of CCFMs according to desired boundary conditions, this study proposes a systematic topology optimization method. This method includes a new morphology-based scheme designed to ensure the connectivity of the topological results, thereby achieving this objective. Using this approach, a CCFM suitable for end effector applications is designed and manufactured through 3D printing. Four of these CCFMs are then utilized to create an innovative compliant constant-force end effector for robotic operations on uneven surfaces. The experimental results demonstrate that the presented design achieves output force modulation through elastic deformation, eliminating the need for additional sensors and controllers to regulate the output force. The presented design can be mounted on a robotic arm to provide overload protection and maintain a consistent force output during operation when encountering irregular and uneven surfaces.

AbstractCollisions at high-speed can severely damage robots with non-backdrivable drivetrains. Adding an overload clutch in series can improve the robot’s collision tolerance without compromising its high dynamic performance. This paper aims at determining the speed above which overload clutches are required in a two-link manipulator arm. Furthermore, the optimal clutch topology as function of the impact velocity is investigated. Third, it is evaluated if adding clutches can lower the impact force on the arm. Finally, the maximum speed is identified below which impact-aware robot control is possible. The latter requires that none of the clutches decouple during an intentional collision with the environment. These answers are obtained through collision simulations and experiments with a custom build two-link arm. It was found that adding a clutch reduces the torque experienced by the drivetrain by an order of magnitude and below the limit momentary peak torque of the strain wave gears that are used. Adding a clutch to the elbow joint of the two-link arm was effective in protecting the shoulder as well if the impact occurred at the tool center point. With respect to a rigid elbow joint, the clutched elbow joint reduced the collision force at the tool by only 8%. To demonstrate that the arm is impact-aware, a box of 8 kg is approached, impacted, and pushed at 1 m/s without decoupling a clutch, nor damaging the robot’s hardware.

AbstractThe fish-like propulsion robot is becoming a profound intelligent equipment due to its excellent swimming ability and good environmental adaptability. In this paper, we propose the oscillating fin based on the fish swimming mechanism, which is compounded with the locomotion modes of sway and yaw. The kinematic and dynamic models are established to study the locomotion mechanism of the oscillating fin. The hydrodynamic performance of underwater locomotion is investigated to analyze the velocity, the propulsive force, the pressure, the propulsive efficiency, and the vortices property. Finally, the experimental measurements of the robot with oscillating fin propulsion are carried out to analyze the underwater propulsion of the oscillating fin and the unsteady fluid flow with Strouhal number. The results illustrate that the propulsive force is fluctuating, and the velocity is increasing to the maximum value. The underwater propulsion velocity could reach 1.2 m/s in a period of 0.4 s. Besides, the high- and low-pressure regions change alternatively, and the fin deforming process illustrates the vortices property and the locomotion mechanism analyses. The propulsive efficiency of the oscillating fin with compound waves is increased by 11% compared with that of the one without deformation. The experiments of the robot prototype verify the numerical simulation, and the propulsive velocity with a period of 0.4 s is two times larger than that of a period of 0.8 s. The Strouhal number of each motion mode is obtained through theoretical and experimental analyses.

AbstractFor a single degree-of-freedom spatial mechanism, a reference frame attached to any of its links produces a continuous motion of this frame. Given the progression of this frame from the start through the end of the mechanism’s motion, this paper seeks to identify specific points relative to this moving reference frame. The points of interest are those that can be coupled with a second point determined in the fixed frame to act as the end joint locations for a spherical–prismatic–spherical (SPS) driving chain. If the selection of the point pair is made such that the change in distance between them as the mechanism moves is strictly monotonic, then the SPS chain they define is potentially capable of driving the mechanism over the desired range of motion. This motion is referred to as locally P-drivable because a global solution is not ensured by the process proposed herein. This synthesis process can avoid singularities encountered by actuating the mechanism at one of its original joints. The proposed approach enables the dimensional synthesis of a single degree-of-freedom mechanism to focus on creating circuit-defect-free solutions without concern for potential singular positions. The actuating chain can then be determined as a separate step in the synthesis process. This paper also considers motions that are not P-drivable and the specialization to planar systems with the synthesis of a P-drivable revolute–prismatic–revolute (RPR) chain.