A Two Degrees-of-Freedom Floor-Based Robot for Transfer and Rehabilitation Applications

TL;DR

This work introduces a mobile floor-based two-DOF STS robot capable of switching between force-controlled rehabilitation modes and a speed-controlled transfer mode. By configuring a two-DOF planar arm on a lightweight base, the system applies independent vertical and forward forces, enabling Follow Me, Weight Unloading, CoM Balance, and Transfer profiles with adjustable $F_z$ and $K_y$. Experimental validation with healthy adults demonstrates near-natural STS kinematics under Follow Me, precise vertical unloading, and the ability to reproduce fixed-transfer trajectories while revealing practical limitations in actuation and framing. The device offers a versatile platform for integrating transfer and rehabilitation in clinical settings, with potential to tailor training to individual mobility levels and reduce the need for separate equipment or room allocations.

Abstract

The ability to accomplish a sit-to-stand (STS) motion is key to increase functional mobility and reduce rehospitalization risks. While raising aid (transfer) devices and partial bodyweight support (rehabilitation) devices exist, both are unable to adjust the STS training to different mobility levels. Therefore, We have developed an STS training device that allows various configurations of impedance and vertical/forward forces to adapt to many training needs while maintaining commercial raising aid transfer capabilities. Experiments with healthy adults (both men and women) of various heights and weights show that the device 1) has a low impact on the natural STS kinematics, 2) can provide precise weight unloading at the patient's center of mass and 3) can add a forward virtual spring to assist the transfer of the bodyweight to the feet for seat-off, at the start of the STS motion.

Figures (16)

• Figure 1: 2-DOF Sit-to-stand assistance robot
• Figure 2: Workspace effector force field for control modes. For modes A to C, the black arrows represent the orientation and magnitude of the assistance force from the force controller deployed to the patient's CoM according to its position. For C mode, the red vertical axis represents the anchor point for the virtual spring $K_{y}$. For D mode, the dashed line represents the fixed trajectory from the speed controller.
• Figure 3: Model of the joints, linkages and actuators of the robot's arm. The structure is divided into two main segments, the horizontal linkage (linkage CDE) in blue and the vertical linkage (linkage AC) in red. Angles $q_{A}$ and $q_{C}$
• Figure 4: Configurations for force-controlled and speed-controlled of the device. For force control, both DOFs are free and both actuators can apply forces on the structure. For speed control, the device is restricted to one DOF around joint C, and only actuator 2 can apply forces on the structure.
• Figure 5: Overall design of actuator 1 with listed components