# Lessons Learned from Investigating Robotics-Based, Human-like Testing of an Upper-Body Exoskeleton
## 3 Methods and Results
### Approach C: Specialized Human Arm Dummy
#### 3.3.3 Results  
The trained DMPs were employed to execute ten sequences of hand-guided lifting and lowering motions, both with the support of the exoskeleton and without the exoskeleton attached to the arm dummy. Throughout the arm lift motion, the robot maintains a similar configuration, avoiding a null-space self-motion of the elbow. Figure 10 displays the recorded mean joint torque profiles, with the support of the exoskeleton represented in black and without support in blue. All torque signals are filtered with a moving average of window size 50, equaling a 50 ms time window.  
Figure 9: Setup for a human arm dummy in starting position of the arm-raising motion. The dummy rests in the arm shell and is fixed to the exoskeleton via the standard device closure.  
The robot's configuration at the start of each motion is depicted in Figure 9. Observing this configuration reveals that joints 2, 4, and 6 directly contribute to an upward motion of the robot end effector. Therefore, evaluating the torque profiles of these three joints is of particular interest. The sign of the difference between the curves (comparing joints 2 and 4) depends on the direction of \"positive\" rotation. For all three joints of interest, it is evident that the absolute torque required to lift the arm is reduced. Without the exoskeleton, joint 2 is needed to lift the arm upwards. With the support, however, the required torque is temporarily completely alleviated. There is even a torque in the opposite direction applied between the 9-13 s mark, indicating that the robot needs to compensate for the exoskeleton's support to remain at the desired configuration.  
Joints 1, 3, and 5 demonstrate the need for a different torque profile to follow the desired trajectory. While a relatively constant torque is applied without the exoskeleton, the interaction force creates torsion that needs compensation, particularly around the base (joint 1) and before the elbow (joint 3). Steps in the joint torque diagrams in Figure 10 are noticeable around the 16-20 s interval, potentially originating from the exoskeleton's pneumatic actuator releasing air abruptly during the downward motion of the arm.  
This approach offers a more realistic interface with the human arm model compared to the previous approaches discussed above. However, it still has shortcomings related to softness, potential interaction with the environment, and achieving truly human-like  
Figure 10: Joint torques of ten executions of hand-guided motions with support of the exoskeleton (black) without (blue). The last plot shows the z-position of the end effector, which indicates the raising until 12.5 subsequent lowering.  
motion. While challenges associated with softness and human-like motion might be solvable with further research, the interaction with the environment may always be limited by the human arm dummy.  
The recorded joint profiles support the idea of robotic-based testing for exoskeletons. However, torque profiles alone are not suitable as evaluation metrics due to their configuration-dependent nature. Therefore, more sophisticated metrics are needed, such as the interaction pressure measured by a pressure pad between the exoskeleton interface and the human arm dummy. Additionally, it might be possible to leverage the realistic dimensions of the human arm model to calculate interaction torques in the shoulder of the human arm dummy and generate an assistive shoulder torque profile. This requires an accurate model of the human arm and realistic human motion generation, considering that the shoulder frame moves within the execution. By addressing this challenge, a reasonable, transferable metric could be developed to evaluate different exoskeletons.