Upper limb rehabilitation robots are mainly used as a physical therapy method to passively or actively train the affected side. However, they are rarely implemented in accordance with the occupational therapy theory, which is dedicated to improving the sensorimotor coordination of hemiplegic patients by considering both healthy and affected limbs. To realize the occupational therapy concept in robot-assisted upper limb rehabilitation, we propose a new human-robot collaboration framework for hemiplegic patients that integrates healthy/affected limbs and robot. The strategy aims at achieving patient-specific movement capabilities and improving the participation of the affected limb during rehabilitation. To accomplish this task, we have addressed two essential issues: accurate motion estimation of the healthy limb and the rehabilitation trajectory learning technique. The posture estimation is achieved by introducing the calibration model to reduce static and time dependent errors during the measurement. We also introduce a force term to the conventional imitation learning method to improve the adaptability in integrating the affected side in cooperation with the robot. Various experiments have been conducted to validate the feasibility and effectiveness of our proposed dual-arm collaboration strategy.

For the traditional three-axis configuration of additive manufacturing (AM) platform, it is imperative to construct adequate support structures prior to the fabrication of overhanging features on the part geometry. To completely eliminate the use of support by taking advantage of the newly emerged five-axis AM platform, a novel multidirectional process planning algorithm for 3 + 2-axis AM is proposed in this paper. The core of the strategy is to decompose the model into support-free parts directly pertaining to the cusp-height constraint, each with its own build direction. The nozzle will follow the staged sequence to fabricate each individual part along its build direction, as facilitated by the adjustable orientation of the nozzle head on a five-axis platform. For model decomposition, a recursive downward flooding expansion algorithm is introduced to identify a surface patch in accordance with the support-free criteria. After being stitched as a watertight geometry, the decomposed part together with the remaining part will be archived into a prescribed hierarchy based on which the build sequence is readily established. Preliminary testing results have verified the effectiveness of the algorithm to handle the geometries of different types. Note to Practitioners-This paper was motivated by the deficiencies encountered in traditional three-axis additive manufacturing (AM). In practice, most commercialized 3-D printers are of three-axis configuration, on which it is required to construct support structures for those overhanging features on the part geometry. These support structures not only cost extra time and materials but also leave noticeable artifacts on the part surface even after the clean-up process. As an ultimate solution to this issue, the newly emerged five-axis AM platform is able to physically eliminate the need for support by properly and continuously adjusting the build direction. This, however, demands a delicate algorithm for determining the changing build direction for an arbitrary part that is currently unavailable. To simplify this challenging task, we took advantage of the 3 + 2 motion capability of the five-axis AM platform to progressively plan the three-axis printing process for a given freeform model. The core idea of our solution is to decompose the model by a flooding-like algorithm into individual support-free parts, each of which is printable along a fixed build direction without any support. The nozzle will then follow a prescribed sequence to print each part one on the other. The proposed algorithm is purely geometric, without taking into account the material property and the mass distribution. Preliminary testing results show that our approach is feasible and robust when dealing with limited geometries that abide a tree-like structure and features a clear flat base. Besides these geometric limitations, our current preliminary scheme for collision avoidance may become invalid upon an arbitrary complex geometry. We will further extend this method to cater to more sophisticated and general geometries.

In this paper, a boundary-conformed tool path generation method for either compound or trimmed surfaces are proposed, based on two powerful reparametrization schemes -- the discretized harmonic mapping and the convex combination mapping. By globally mapping a 3D surface onto a 2D unit square and then planning an iso-parametric curve in the 2D domain, the corresponding Cutter Contact (CC) curve on the original 3D surface is easily generated which conforms with the boundary of the surface. Based on this CC curve generation strategy, a CC curve expansion algorithm for covering the entire surface is designed which takes into account the machining accuracy requirement, i.e., The specified maximum cusp height. Tool paths generated in this way for compound or trimmed surfaces are boundary-conformed, smooth, and guarantee the required machining accuracy.