Remote Touchscreen-Controlled Defense Turret Senior Design Documentation Courtney Mann, Brad Clymer, Szu-yu Huang Group 11

6. Relevant Technologies

1. Rangefinders

In order to properly track the location of the target, it is essential for the control system to know not only the horizontal and vertical distance in a given frame but the depth as well, so that the angle at which to fire the gun can be correctly computed to reach the target of choice. Since the camera will supply only a two dimensional rendering of the target field, the system will need an additional component to fill in the missing depth information. A rangefinder is exactly suited to this purpose; the next question becomes which type of rangefinder will best match the specific requirements of the project. The appropriate solution must have a range at minimum equivalent to the gun, which was estimated to be approximately 30 meters. In addition, it must have relatively good accuracy, in order to effectively aim the gun. After a variety of different types of rangefinders were researched, the top selections were infrared rangefinders, ultrasonic rangefinders and a laser pointer in conjunction with an image sensor.

IR rangefinders use triangulation to calculate target distance, where a pulse of light is sent out and reflected off an object. The angle it returns is proportional to the distance, which can then be easily calculated. IR rangefinders offer fairly good immunity to interference from any ambient light, as well as indifference to target color, and their simplicity, low power requirements and small size make them popular in many robot designs. Their disadvantages lie in their small detection range and the thinness of the beam width, which means that if the object is not directly in front of the beam, it will not be detected. Another problem with this option is that due to the triangulation process, there also exists a minimum range, meaning there will be errors in detecting any objects that are closer than this.

Another alternative, the ultrasonic rangefinder, operates on the same basic principle as the IR rangefinder but with sound instead of light. The radar emits a mostly inaudible sound, and then waits for the return echo that bounces off the object. The time taken between transmission and reception can be used to calculate the distance of the object. This method is relatively inexpensive… Also, the echo can be distorted easily by factors such as angle of the object relative to the rangefinder and material properties, which could potentially give erroneous results.

A third option is to use a simple laser pointer, such as the kind used as a presentation tool, in combination with an image sensor. The laser is offset from the sensor a known distance, with their axes lined up parallel to each other, as illustrated in the figure below. The sensor uses an algorithm to detect the brightest pixels in the image, which is the point where the laser beam is reflecting off of an object. The object’s distance can then be computed by simple geometry, based on Equation 2 given below. Figure 5 depicts the setup of the sensor and the laser pointer. While the expense for this system exceeds the options mentioned previously, the range is also greater, which is a primary factor in the decision. The other main requirement, which was the attainment of a high level of accuracy, can be achieved with a high resolution image sensor, such as a 1024x1 image sensor from Panasonic.

2. System Processer Board

FPGA

Microcontrollers