**3.1 Experimental setup**

**Figure 26** displays the setup of the developed system for detecting 6DOF variations of the robotic arms end effector, which comprises the developed structured-light 3D scanner, a wafer handling robot, and a computer. The specifications of these three modules are listed in **Table 2**.

**Figure 26.** *Experimental setup.*


#### **Table 2.**

*System specifications.*

**Figure 27.**

*Schematic diagram of the 3D structured-light measurement probe.*

#### **3.2 Design of 3D structured-light measurement probe**

The 3D structured-light measurement probe, as shown in **Figure 27**, is designed according to the triangulation measuring principle. As can be seen, it comprises a structured-light projector and a camera, with the projector's optical axis and the camera's optical axis intersecting at a point and forming a triangular relationship with each other. Moreover, the greater the angle between the projector and the camera, the better the depth resolution is. Under a trade-off between the effect of light shielding and depth resolution, this system adopts an included angle of 30°. Moreover, to avoid blurring or poor contrast of the image taken by the sensor module, the measurement depth range is defined as the area where the contrast between the nearest focus surface and the farthest focus surface of the camera lens in the modulation transfer function (MTF) diagram, was maintained above 70%. As shown in **Figure 28**, the area is a trapezoid space, and the camera's field of view is gradually enlarged from the front to the back focal plane.

#### **Figure 28.**

*Schematic diagram of the structured-light probe measurement range.*

**Figure 29.** *Engineering drawing of the structured-light probe: (a) internal structure and (b) external view.*

**Figure 29** is the engineering drawing of the structured-light measurement probe designed by Autodesk Inventor. As shown in the actual image (**Figure 30**), the internal structure includes a DLP projection module, an image sensor, a perspective

**Figure 30.** *Actual internal image of the probe.*

#### **Figure 31.** *Actual appearance image of the probe.*

lens, Arduino Mega 2560, and a breadboard. Arduino Mega 2560 is to synchronize the trigger signal between the camera and the projector. The measurement probe's outer shell (**Figure 31**) is made of high-strength aluminum alloy to avoid deformation by external forces. The two side covers of the measurement probe are designed for heat dissipation so that the heat generated by the hardware device can be removed through the heat dissipation holes.
