## 5 Experiment and Analysis
In the electrical industry, drilling on circuit boards is a common procedure, and manual drilling is labor-intensive and heavy for a human. The drilling procedure is accomplished by automatic mechanisms usually, thus, SDA5F performed the drilling procedure on the circuit board during the experiment. Figure 4: The error between the nominal pose and the actual pose of R1. The unit of position error in (**a**) is mm. The unit of orientation error in (**b**) is rad. Figure 6 shows the experimental setup. Two six-axis force sensors were mounted on the flanges of R1 and R2, respectively. The circuit board was fixed by the fastening tool, which was mounted on the force sensor 1. The drilling EE was mounted on one side of the force sensor 2. The weights of the drilling EE, fastening tool, and force sensors were measured before their installation. From Equation (44), the deformation can be calculated and compensated to the pose control of the robot. Ten poses were measured with and without the compensation first, and the results were used to calculate the deformation as shown in Figures 7 and 8. The error of position and orientation of both arms are calculated by Equations (49) and (50). Figure 7a illustrates the position error of R1. The accuracy of the position has improved and the maximum position value is less than 1.81 mm. Figure 7b illustrates the orientation error of R1, and the maximum orientation value is less than 0.0019 rad. Figure 8a illustrates the position error of R2. The accuracy of the position has improved and the maximum position value is less than 1.72 mm. Figure 8b illustrates the orientation errors of R2, and the maximum orientation value is less than 0.0037 rad. Figure 9 shows the drops in the position error and orientation error of the EE. Figure 9a shows that the position error is better than the before, as expected after the calibration. Figure 9b shows that the orientation error is better than the before, as expected after the calibration as well. The identification results show that the joint stiffness of the SDA5F robot was not very small, thus there were slight drops in the errors. Furthermore, the residual errors were caused mainly by the geometrical kinematic errors of the robot that were beyond the aspect of this paper. Nevertheless, Figure 9 depicts the improvement of the accuracies of the EEs. Figure 5: The error between the nominal pose and the actual pose of R2. The unit of position error in (**a**) is mm. The unit of orientation error in (**b**) is rad. Figure 8: The pose deviation of R2. (**a**) With the compensation; (**b**) Without the compensation. Figure 6: The drilling operation. EE: end-effector. Figure 7: The pose deviation of R1. (**a**) With the compensation; (**b**) Without the compensation. During the experiment, a carbide drill was used for the procedure, and the drill diameter was 0.5 mm. The circuit board was mounted on the supporting side, which was R1, and the six-axis force sensor 1 measured the supporting forces and torques. The circuit board was 200 mm \(\times\) 150 mm \(\times\) 2 mm in size. The target location of the drilling operation was chosen on the circuit board, and the feed rate was set manually. The location was important for the drilling operation, and the pose of the drilling EE was calculated based on the forward kinematic equation mentioned above. In addition, the pose error of the EE and the drill axis direction were important for the performance of the drilling operation, and the deformation compensation was added to the control loop of the robot controller. After the compensation, the location can be chosen precisely. The drill axis direction was perpendicular to the plane of the circuit board. During the drilling operation, the velocity of the drill was set to about 0.001 mm/r manually in order to be a constant element, and the measurement can be concise during the drilling operation as the force sensors have high accuracy.