| Abstract | Inertial Measurement Units (IMUs) are used to obtain data about an object’s motion. They contain three orthogonal accelerometers and three rate gyroscopes to measure linear accelerations and angular velocities. By integrating these data, the position and orientation of a object can be measured at all times. These IMUs are used extensively at the Institute for Ocean Technology (IOT), and consequently there are a number of devices available on the premises. Selecting an IMU for a certain application is challenging, so to ease the process, a simultaneous and direct performance comparison of eight of the available units at IOT was proposed. As there was no available apparatus for completing these comparison tests, a suitable apparatus had to be designed and fabricated. The concept selected for the test apparatus was a pendulum capable of swinging in two axis by means of a two degree-of-freedom universal joint. The pendulum arm itself was four meters in length such that the natural frequency of the apparatus was 0.25 Hz. The pendulum arm assembly was supported by a four-legged frame, similar in design to a tripod, with the universal joint joining the top of the frame to the top of the arm. Two angle encoders coupled to the universal joint measured the angle of the arm, and a platform that contained all of the IMUs was fastened to the bottom of the arm. Having all of the IMUs fastened to one platform ensured that the devices were experiencing the same motion, therefore a direct comparison of each unit’s performance was valid. The apparatus was fabricated in IOT’s machine shop and assembled on the premises. Although a number of calibrations have to be performed on the apparatus before reliable results can be produced, preliminary tests were conducted as a “proof of concept”. Preliminary testing was successful, therefore a thorough assessment of the performance of each IMU will be performed using this apparatus in January 2011. |
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