In Partial Fulfillment of the Requirements for the Degree of Master of Science

Pradheebaa Srinivas

will defend her thesis

Gray Scale Encoder - Design, Calibration and Statistical Analysis

Abstract

An encoder is an electro-mechanical device that helps to measure mechanical motion by generating digital signals that can be decoded into position data. The most common types of encoders involve an encoder strip/scale sliding in between a source and sensor circuit. An optical encoder is a widely used encoder which uses a light source at one side and an electric photodiode at the other side. A thin linear encoder strip slides smoothly in between them. The photodiode senses the light passing through the gaps between the lines and converts these signals into digital signals which can then be interpreted using a microcontroller. In Medical Robotics lab at University of Houston, optical linear and optical rotary encoders are used as position sensors for various applications. This research presents an idea of using an alternative form of encoder. This device uses a thin strip of gray scale instead of a standard linear encoder strip sliding between a white light LED source and a mini photocell that picks up the light intensity of the emerging signal. The type of gray scale and the number of shades of gray in a gray scale strip is determined by the number of bits in the pixel value of the gray scale. This research makes use of four different types of grayscales – 2 bit, 4 bit, 8 bit and 16 bit grayscales. The gray scale encoder circuit is mounted on to a linear stage actuator that is powered by a stepper motor. The linear stage is fitted with the linear encoder strip and the gray scale encoder strip and the rotary encoder is attached to the stepper motor. The study involves design and calibration of a gray scale encoder unit using different experimental set up. The gray scale encoder is first calibrated by analyzing the theoretical and experimental data. The theoretical data are obtained by using the known standard formula and the experimental data are obtained by sliding the gray scale smoothly in between the source – sensor circuit. The second step of calibration involves using the rotary encoder in the stepper motor as the known variable, the linear encoder is calibrated. The experiment is repeated in order to understand how accurate the linear encoder is with respect to the rotary encoder. Then, again using the rotary encoder as a reference, both the gray scale encoder and the linear encoder are calibrated. All the experimental data are converted to linear functions using MATLAB. The study involved a detailed statistical analysis of the calibration data in all the three calibration experiments and the results were discussed.

Date: Wednesday,November 30,2016
Time: 2:30 PM
Place: PGH 550
Advisor: Dr. Nikolaos V Tsekos, Dr. Weidong Shi

Faculty, students, and the general public are invited.