Safety features
To ensure the patients’ safety, the robot’s movements were restricted to the respective patient’s passive ROM. An additional safety feature was an automated stop in case the active sum force of all axes exceeded 30 Nm. Moreover, a safety stop button for the supervising therapist was implemented.To give feedback about compensatory movements of the trunk or shoulder girdle, an alert was implemented to notify both therapists and patients if the patient’s shoulder position (i.e., the acromion) left the anticipated position. In case this position deviated more than a predefined threshold from the initial shoulder position, a visual alert was displayed in the gaming environment. Initially, the threshold of this shoulder compensation alert was set to a range of 5 cm around the ideal shoulder position. However, the alert tended to be displayed too early and too frequent and thus interrupted the gaming experience. After increasing the threshold to 7.5 cm, the alert only appeared in cases where a relevant compensatory movement was visually evident for the supervising therapist. The patients reacted adequately by actively correcting the position of their shoulder.