A Separable Digital Protractor Based on IMU for Angle Measurement

To achieve a digital access to measurement of relative attitude between two separate objects, a separable digital protractor based on IMU is designed. The protractor consists of a pair of arms, with an IMU and a Bluetooth applied on each of them. Data of the two IMUs are transmitted to a processor on one arm and are used for IMU pose estimation. Since the IMU is rigidly tied to the arm, each estimated IMU pose is just that of the attached arm. By comparing the poses of the arms, we can achieve measurement of their relative attitude. Quaternion and Kalman Filter are used for pose representation and estimation respectively. Experiments are conducted on the accuracy and feasibility. Results show the angle measurement error is less than 2o, which is within the tolerance of most applications. With the help of wireless technology, the proposed protractor can bring lots of convenience in angle measurement for separate objects.