Design And Implementation Of Accurately Measuring System On Joint Angles

Rang of motion (ROM) is a common inspection item of clinical rehabilitation medicine and disability identification. In rehabilitation medicine, the doctor regards ROM as an important indicator which is used to assess the level of recovery of patients’joint after operation. In the field of disability identification, the staff determines the degree of the limb disability through measuring ROM of the injured. If we can not accurately identify the level of disability, it will cause a lot of judicial disputes. Therefore, to improve the measurement accuracy of ROM is a very urgent clinical need.At present, the universal protractor is a widely used tool in clinic. This method is simple, but the precision is usually very low to estimated to 5°. Later, it was proposed to calculate ROM with using X-ray and photography. When we use X-ray, the accuracy of measuring ROM has improved, but X-ray itself is harmful to human body, so it is not suitable to be used frequently. The photographic method has strict requirements on the shooting angle so that its repeatability is quite low. In view of this situation, this paper proposes to resolve ROM through using Euler angle. Firstly, we should fix three passive balls on every body membrane and then bind the body membrane at each end of the joint to maintain relatively static relationship between passive balls and the limb. After that, we can establish an appropriate joint coordinate system according to the spatial relationship between these passive balls and then map the motion of the joint as the rotation of the joint coordinate system around the axis. Then through the Polaris Vicra we can obtain the coordinates of the passive balls in the device coordinate system and translate them into the coordinates of joint coordinate system. Finally, according to the coordinates of the three balls in the joint coordinate system, we will calculate the rotation matrix of the joint coordinate system and then resolve the Euler angle with the matrix. This design also increased the registration method to eliminate the error caused by the chain reaction of the motion of the joint so it will greatly improve the intelligent level of the algorithm and the accuracy of measurement results.After the clinical practice, it proves that the measurement accuracy of the system designed in this paper can reach 0.2° and it can also display the result on time. So it could sufficiently meet the needs of practical applications.