# A Telepresence System for Therapist-in-the-Loop Training for Elbow Joint Rehabilitation
## 5 Conclusions  
The inconvenience of visiting a rehabilitation centre is expected to create an increasing demand for home-based rehabilitation. These demands could be met by an effective tele-rehabilitation system that exploits up-to-date internet technology, although robotic therapy on its own is not sufficient compared to manual therapy [2]. In this paper, a new robotic rehabilitation training platform that is motivated by the requirement of adjusting the training strategy and intensity in a patient-specific manner is proposed. A visually-shared model was designed whereby the motion of the therapist and patient are measured and mapped to the corresponding object's motion. The force generated by the therapist can be transferred to the patient for delivering training, while real-time force feedback can be provided to the therapist to know the amount of force being applied to patients in real time. Both assistive therapy in the early stages and resistive therapy in the later stages of stroke can be performed because the exoskeleton was designed with a SEA principle by which the passive character of the actuator's non-backdrivability can be improved. Moreover, patient safety is a key factor for the system design. In our proposed system, both the hardware of the exoskeleton device [24] and the real-time monitor on  
Figure 12: Position of the orange and purple objects in the visual model.  
Figure 13: Exerted assistive and resistive force by the therapist by means of the exoskeleton.  
the therapist side can guarantee patient safety. Unlike other tele-rehabilitation systems, the real-time monitor not only includes monitoring with a screen but also involves the haptic feelings, which is directly fed back to the therapist through the haptic device. Economical and practical points were also considered during the initial exoskeleton device design [24]. The weight of the exoskeleton device is only 1.3 kg and easy to wear by the caregivers or patients themselves.  
The patient and slave sides that are distributed at both ends of the platform were represented by a 2-port network model for keeping the transparency. Although the therapist-in-the-loop training was not performed in a real network environment, we evaluated the patient-exoskeleton and therapist-haptic interaction for the high transparency requirement that real-time feedback can be provided so that the therapist knows the force being applied on the patient's forearm, and the force transmission is bidirectional. The therapist-in-the-loop training system suggests that the therapist could adjust the training strategy and intensity as needed. Our future work will focus on a user-study with a larger group and then on patient-based clinical experiments with the proposed platform via real telepresence environments. In addition, the delay-related instability problem will be studied, especially for the condition that the system is operated under network-transmission delay.  
Conceptualization, S.Z., Q.F.; methodology, S.Z.; formal analysis, S.Z.; writing--original draft preparation, S.Z., Q.F.; funding acquisition, S.Z., Q.F. and Y.F.; writing--review and editing, S.Z., Y.F., and S.G. This work was supported in part by the National Natural Science Foundation of China (Grant No. 61703124), the Self-Planned Task of State Key Laboratory of Robotics and System (HIT) (SKLRS201714A), Innovative Research Groups of the National Natural Science Foundation of China (51521003) and Innovative Cooperation Project of Tianjin Scientific and Technological Support (18 PTZWHz20090). The authors declare no conflict of interest.