Optics System

Fig 1. CAD Design of Optics System

Laser

Functional Requirements:

1. The laser must illuminate a ring at least 1mm thick inside the bore

2. Powered by a 5V power source

3. Operate in temperatures up to about 50°C

Table 1. Laser Details

Laser Circuit

All of the ROBO MAT components required a voltage of approximately 5V except the DC motors. However, the voltage output from the battery was 7.4V (up to 8.4V when fully charged), therefore, in order to be able to power the components, a circuit was built to regulate battery voltage (Figure 2). The voltage regulator circuit consisted of a LM7805 regulator, which regulated battery voltage to 5 consistent volt. Also a 0.47 Micro Farad capacitor was to assure stable output voltage at all time. The voltage regulator circuit also powered the Raspberry Pi and laser since they were both powered on 5V. In order to be able to control the laser (switching on and off) a power MOSFET (BS170) was used. The gate of the MOSFET was connected to an I/O pin of the Raspberry Pi. This pin was setup as an output, where 3.3V was sent to MOSFET to open the gate and let current pass from drain to source. This allowed the ground of the laser to connect to ground of the battery to turn on the laser.

Fig 3. Circuit Diagram for Laser Control

Fig 2. Circuit Schematic for Laser Control and Voltage Regulation

Conical Mirror

The conical mirror is from Edmund Optics. This mirror was used as part of the ring beam device to project the laser ring in the bore. The laser was shot at the mirror which then reflects the beam 360 degrees in a plane perpendicular to the length of the bore.

Camera

Function Requirements:

1. Greater than 0.05mm/pixel resolution in vertical direction (1060 pixels)

2. Controllable by microcontroller

3. Store images to microcontroller SD card

4. Take pictures every 1mm or record continuous video

5. Meet size constraint of 40mm x 40mm: determined from chassis design

6. Low power consumption (approx. < 200 mA)

Fig 4. 5MP Raspberry Pi Camera Board

The camera selected was the 5MP Raspberry Pi Camera Board (Fig 4). The camera captured the cross sectional laser image created from the laser hitting the conical mirror. This camera met the resolution requirements with 1800 pixel count in the vertical direction for video and 1944 pixel count in the vertical direction for pictures. Furthermore, the camera was specifically designed to be operated by the Raspberry Pi. Thus, the microcontroller and the camera functioned together with simplicity. The camera met the design constraints with a size of 25 mm x 20 mm. The frequency of image capture is an important element for the camera. The camera could record video at 30 FPS, more than fast enough to capture data of the entire bore. Finally, the power consumption of the camera did not exceed desired values. The camera required 100mAh to power it, a value which fell far below the maximum amperage available.

Despite these finding the distance between the camera and the mirror was chosen to be approximately 4 in. Bearing in mind that the 2.06 in is a minimum value, the goal of the ROBO MAT was to have an adjustable optics system. Since the distance between the conical mirror and the camera can easily be decreased the distance of 2.06 in can still be achieved it is desired. However, the adjustability will allow GA to be able to alter the optics system as they see necessary.

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