# Lessons Learned from Investigating Robotics-Based, Human-like Testing of an Upper-Body Exoskeleton
## 3 Methods and Results
### Approach B: Direct Attachment
#### 3.2.3 Results  
With the help of the learned DMPs, we executed the same lift and lowering motion ten times, respectively, with the support of the exoskeleton and without the exoskeleton attached to the robot. Figure 7 shows the recorded joint torque profiles for the first five joints in the upper plots, and the last plot shows the z-position of the end effector. Since the attachment is made after joint 5, the remaining joints are not influenced by the support of the exoskeleton and are not considered here. All the torque signals are filtered using a moving average with a window size of 30, equivalent to a 30 ms time window. The graphs in blue represent the mean joint torques without the support and the black ones with the support of the exoskeleton.  
In the lifting and lowering motion, joints 2 and 4 contribute significantly (refer to the robot configuration in Figure 6). The impact of exoskeleton support is evident in their respective torque profiles. Joint 2 exhibits consistently lower torque throughout the execution, while joint 4 initially shows higher absolute torque but decreases below the unsupported torque signal as the motion progresses. The sign of the torque difference depends on the direction of \"positive\" rotation, and notably, joint 4 flips the sign indicating the controller working against the support. Additionally, other joints exhibit changes in torque profiles. Particularly, joints 1 and 5 show increased torque with the exoskeleton attached, contrasting with the near-zero torque without it. This might be attributed to the  
Figure 6: The experiment setup for the direct attachment approach is depicted in the left figure, illustrating the attachment of the robot to the exoskeleton. The right figures display the setup without the attachment of the robot to the exoskeleton, serving as reference measurements.  
constraint forces and disturbances induced by the attachment, potentially explaining the higher starting torque at joint 4.  
While these measurements provide support for the concept of testing exoskeletons with robots, their interpretation in the context of a systematic testing approach is limited. The recorded measurements are specific to a particular sequence of robot configurations. Changing the robot's configuration, especially when testing different exoskeletons, may alter the robot joint trajectories. Consequently, comparing torque profiles alone would lack meaning, as torques would be recorded at different robot configurations.  
To address this, a criterion independent of the robot's configuration and joint trajectory is required. One approach could involve evaluating the contact wrench at the attachment point as a metric for the interaction force, thereby generating an assistive profile. However, careful consideration is needed to exclude constraint forces resulting from non-constraint-consistent motion. Regarding the interaction with the environment, potential interaction will be limited due to the coupling with the exoskeleton. However, by creating a specialized environment, it should be possible to study the effects of contact wrenches exerted by the robot end effector. Nevertheless, a lot of simplifications regarding the interface, interaction, and motion have been introduced, making it challenging to justify this approach for a systematic testing framework.