# Usability Test for an Over-Ground Walking Assistance Robotic Device Based on the Mecanum Wheel
## 4 Discussion  
Andago, one of the most widely used over-ground walking-assistance robots in clinical settings, supports natural weight shifting during walking through dynamic body weight support and offers a safe environment for practicing a wide range of real-life walking scenarios, such as turning, stopping, and obstacle avoidance [11]. In addition, its frame is smaller than that of standard door frames, allowing for better spatial accessibility, and users can walk with greater naturalness owing to hands-free operations [20]. These mechanical advantages contribute to improved gait ability in patients with stroke [21] and a reduced fear of falling in older adults [22]. Accordingly, this study conducted a usability evaluation (satisfaction survey and in-depth interview) to compare the newly developed OWAR-MW with the commercial COWAR system (Andago), focusing on three categories: safety, operability and functionality, and convenience, as perceived by physical therapists and patients with stroke. The satisfaction survey indicated that the OWAR-MW showed a tendency towards lower average satisfaction scores than COWAR in all three categories among all participants. In particular, the average scores in the safety category were significantly lower for OWAR-MW than for COWAR for physical therapists (4.02 vs. 3.37, \(-\)0.65, 16.21%) and patients with stroke (4.90 vs. 4.04, \(-\)0.87, 17.80%). As Andago has undergone structural optimization through commercialization and has demonstrated clinical and mechanical safety in previous studies, users are likely to feel more confident when using it [4; 12; 20]. In contrast, the OWAR-MW appeared to induce a sense of insecurity due to incomplete structural features (absence of handles) and technical immaturity (delays in motion tracking and control). Unlike Andago, OWAR-MW does not have handles and requires users to rely solely on the harnesses for support, which may cause feelings of instability. To ensure smooth \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Categories** & **Physical Therapists (n = 9)** & **Stroke (n = 9)** \\ \hline Safety & -The drive unit poses a potential risk of foot entrapment during ambulation. & -The absence of handles induces a sense of instability during walking-The actuator exhibits delayed responsiveness in tracking user movement. \\ \hline Operability and Functionality & -A latency exists between user motion detection and actuator tracking. & -Motion detection sensitivity is low, yielding delays during directional changes and stopping; The device operation is not intuitive and requires improvement. \\ \hline Convenience & -The harness application procedure is complex and lacks ease of use. & -The harness is uncomfortable, particularly due to the thigh straps, which interfere with natural movement. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Main findings of in-depth interviews (n = 18). and stable mobility in various terrains, walking-assistive robots require advanced control algorithms that precisely detect and respond to user movements [23]. However, in the OWAR-MW, delays and low precision between the sensor system and the actuator resulted in discrepancies between the user-intended direction and the robot's movement during straight walking, turning, and in-place rotation. These structural (e.g., handle addition) and technical (e.g., improved sensor-based control algorithms) factors that negatively affect the perceived safety should be prioritized in further developments for commercialization. In terms of operability and functionality and convenience, patients with stroke rated the OWAR-MW significantly lower than the COWAR (operability and functionality: 4.83 vs. 4.33, \(-\)0.49, 10.20%; convenience: 4.87 vs. 4.49, \(-\)0.38, 7.82%). In contrast, physical therapists did not show substantial differences in satisfaction with these categories, suggesting that the OWAR-MW falls short of the clinical expectations of end-users with mobility impairments in terms of ease of operation and functional completeness.