Robotic Demining | Linear Encoders

Linear Encoders Positioning Device

The linear encoders

This is a picture of the inside of the box where the linear
encoders are kept. The reels hold the string and the wires run
from the encoders to the computer input to constantly feed
information.

Task Description:

Positioning is one of the most important functions of the demining robot. Previously it used dead reckoning, but dead reckoning does not provide the accuracy necessary to ensure complete coverage of an area, and it is very important to ensure this so that all mines are found.
One of the current solutions to this problem involves linear encoders. Two strings wrapped around reels inside the robot are attached to two poles at given locations. The encoders measure the changing lengths of the strings as the robot moves, and using simple trigonometry given the the lengths of the strings and the known, fixed distance between the two poles, the robot determines its location.

position diagram

The largest disadvantage of this system is the error involved in the encoders themselves. If covering large areas error is created because the string used does not wrap exactly the same each time it is reeled in and out. However this process can produce an accuracy of 1/8" in spaces up to 30' x 30', and can immediately correct for any dead reckoning error based on its coordinates. This has been tested over a variety of surfaces, including being taken outside and tested on grass. On top of that level of accuracy, the entire system can be implemented for less than $50, which is very inexpensive in comparison to other positioning methods such as GPS or DGPS.

Return to the Robotic Demining page

Positioning is one of the most important functions of the demining robot. Previously it used dead reckoning, but dead reckoning does not provide the accuracy necessary to ensure complete coverage of an area, and it is very important to ensure this so that all mines are found. One of the current solutions to this problem involves linear encoders. Two strings wrapped around reels inside the robot are attached to two poles at given locations. The encoders measure the changing lengths of the strings as the robot moves, and using simple trigonometry given the the lengths of the strings and the known, fixed distance between the two poles, the robot determines its location.

The largest disadvantage of this system is the error involved in the encoders themselves. If covering large areas error is created because the string used does not wrap exactly the same each time it is reeled in and out. However this process can produce an accuracy of 1/8" in spaces up to 30' x 30', and can immediately correct for any dead reckoning error based on its coordinates. This has been tested over a variety of surfaces, including being taken outside and tested on grass. On top of that level of accuracy, the entire system can be implemented for less than $50, which is very inexpensive in comparison to other positioning methods such as GPS or DGPS.