Handheld haptic devices often face challenges in delivering stiffness feedback with both high force output and good backdrivability, especially under practical constraints on power consumption, size, and weight. These difficulties stem from the inherent performance limitations of conventional actuation mechanisms. To address this issue, we propose a lightweight, low-power handheld device that provides wide-range stiffness feedback through a novel dual actuation design composed of two key components. A programmable spring (PS), implemented via an adjustable lever arm, enables tunable physical stiffness. Two electrostatic clutches (ECs) are integrated to compensate for the inherent limitations of PS-based interactions in stiffness display range, rendered object size, and free motion capability. The feedback force arises passively from the reaction of the PS and ECs to user input, effectively lowering both power consumption and actuator torque demands. A fully integrated prototype was developed, incorporating wireless communication, control, and power modules. The results of the evaluation experiments and user studies demonstrate that the device effectively renders stiffness across the full range, from free motion to full rigidity, and delivers more realistic elastic feedback compared to conventional electric motor-based systems.

With the development of virtual reality, the practical requirements of the wearable haptic interface have been greatly emphasized. While passive haptic devices are commonly used in virtual reality, they lack generality and are difficult to precisely generate continuous force feedback to users. In this work, we present SmartSpring, a new solution for passive haptics, which is inexpensive, lightweight and capable of providing controllable force feedback in virtual reality. We propose a hybrid spring-linkage structure as the proxy and flexibly control the mechanism for adjustable system stiffness. By analyzing the structure and force model, we enable a smart transform of the structure for producing continuous force signals. We quantitatively examine the real-world performance of SmartSpring to verify our model. By asymmetrically moving or actively pressing the end-effector, we show that our design can further support rendering torque and stiffness. Finally, we demonstrate the SmartSpring in a series of scenarios with user studies and a just noticeable difference analysis. Experimental results show the potential of the developed haptic display in virtual reality.

This paper developed a 4-degree-of-freedom cable-driven upper limb rehabilitation robot and proposed a control algorithm of the passive training for this robot. Comparing with the conventional cable-driven rehabilitation robot, the workspace of this robot is increased by optimizing the distribution of the cable attachment points and by improving the mechanical design. The rotation structure of the upper arm module can change the distribution of the attachment points as needed, by which the cable tension planner can be satisfied in almost all cases. At the meantime, the internal/external rotation of shoulder joint can be achieved without the change of the cables configuration, which is also important for increasing the workspace and comfortability of utilization. The activities of daily living (ADLs) training can be achieved well without any manual adjustment. The related controller for passive training is designed, which includes a higher controller for trajectory tracking and a lower controller for keeping cable tension as the output of the tension planner in real-time. The passive training experiments are conducted on five healthy subjects of different body size. The results demonstrated that the passive training can be achieved well on different subjects and the cable tension controller is also working effectively.