# Region-Based Approach for Machining Time Improvement in Robot Surface Finishing
## 4 Case Study
### Experimental Setup  
Our numerical experimental setup featured the Universal Robots UR5e collaborative robot, known for its adaptability and widespread use in industries requiring precision in low-volume/high-mix production settings. The UR5e has a reach radius of 850 mm and a payload capability of up to 5 kg. Mounted on the robot is an MHP tool with a length of 284.5 mm, used for simulating the robot hammer peening machining task. The full layout of our flexible workstation setup used in the experiments is shown in Figure 3.  
The proposed method will be tested on two specific workpieces in the Autodesk Fusion 360 CAM (v.2.0.19994) and RoboDK (v5.6.8) software to compare region-based versus single-direction machining strategies' machining times. The impact of varying stepover distances was also analyzed, offering insights that could benefit various machining operations. The main goal was to achieve complete machining of the workpiece in the shortest time possible without exceeding the robot's maximum joint velocities.  
The approach and retract speed parameters control the feed rate of the robotic tool during the initial approach to the surface before machining, and the retraction away from the surface after machining, respectively. The transition speed is the feed rate used when moving between different regions of the workpiece, typically occurring at a higher speed to reduce non-cutting time. The stepover speed refers to the rate at which the tool moves horizontally between adjacent passes (stepover), where the speed is usually lowered. For MHP, the recommended machining stepover distance typically ranges from 0.1 to 2 mm [46]. The detailed machining parameters are shown in Table 1.  
Within this setup, machining paths were generated for two distinct scenarios to evaluate the effectiveness of our subdivision region-based approach on two workpieces, i.e., Workpiece No. 1 (WP1) and Workpiece No. 2 (WP2). Figure 4 shows four different machining toolpaths:  
1. Arbitrary Single-Directional Machining  
Initially, machining paths were created to operate solely along the \(x\)- and \(y\)-axes, respectively, as seen in Figure 4a-d. This scenario represents a more traditional approach, where the MHP tool moves linearly across the workpiece surface without altering its machining direction based on the surface topology or the underlying robotic kinematics.
2. Machining with Optimized Directional Methods  
* Single optimal direction machining (Figure 4e,f): The machining direction was determined based on a calculated workpiece MTI, optimizing the toolpath for the most efficient single direction across the entire workpiece.
* Region-based optimal directional machining (Figure 4g,h): This approach involves creating distinct optimal machining toolpaths for different regions within the workpiece. Each region was machined according to a direction that maximized the region MTI of the corresponding segment of the workpiece and the overall workpiece MTI.  
\begin{table}
\begin{tabular}{c c} \hline Approach speed [mm/s] & 500 \\ \hline Retract speed [mm/s] & 500 \\ \hline Transition speed [mm/s] & 500 \\ \hline Stepover speed [mm/s] & 20 \\ \hline Stepover [mm] & 0.1–2 \\ \hline \end{tabular}
\end{table}
Table 1: Machining parameters.