# Development and Assist-As-Needed Control of an End-Effector Upper Limb Rehabilitation Robot
## 5 Discussion and Conclusions  
In this paper, we have developed a new end-effector upper limb rehabilitation robot (EULRR) first, which can enable a patient's arm to carry out a spatial movement, and then have presented a controller to provide motion assistance for assist-as-needed training of the patients with upper limb motor dysfunction. The controller enables the patient's arm to have spatial freedom by constructing a virtual channel around the predetermined training trajectory. This controller would construct a normal force field around the virtual channel to provide assistance when moving out of the allowed virtual channel. Then, the controller is implemented based on the EULRR and validated through a preliminarily male subject experiment in different conditions. The results show that for the defined motion scenario, the subject has full freedom when moving along the predetermined trajectory within the virtual channel that is constructed by the controller and is assisted by the robot according to the controller when moving out of the virtual channel. Although the EULRR designed in this paper can carry out rehabilitation training on the spatial trajectory, the trajectory in the testing is limited on the horizontal plane in this paper in order to let the subject feel the trajectory in the Unity scene better. However, the controller proposed in this paper does not depend on the choice of training trajectory, and its performance will not be affected for any spatial trajectory.  
As a pilot study, the limitations are that only a healthy subject was recruited to do the experiment testing to validate the effectiveness of the proposed controller, and the simple testing Unity scene was used to provide visual guidance for the testing. In the next step, the controller is planned to be used in elderly volunteers and patients with upper limb motor dysfunction to help to increase the intensity of the rehabilitation therapy by assisting the arm movement and by provoking active participation. Besides, we will also develop the Unity game scene and redesign the handle further to collaborate with the proposed controller for the testing task in the close future.  
**Author Contributions**: In this work, [PERSON] conceived and designed the experiments; [PERSON] gave some constructive suggestions; [PERSON] performed the experiments; [PERSON] and [PERSON] analyzed the data; [PERSON] guided the writing of the article and made some modifications; [PERSON] wrote the paper. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research is supported by the National Natural Science Foundation of China (Grant No. 61973205) and the National Key Research and Development Program of China (Grant No. 2018 YFC2001601) and the Science and Technology Commission of Shanghai Municipality (Grant No.18511108302).  
**Acknowledgments:** The authors are grateful to the anonymous reviewers and the Editor for their valuable comments and suggestions on improving this paper.  
**Conflicts of Interest:** The authors declare no conflict of interest.