[Physics] strapdown integration

integrationkinematicsterminology

I was reading this article where at a certain point the authors say

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First, we consider hinge (or pin) joints. There are several ways to estimate the joint angle of a hinge joint from the measured accelerations and angular velocities. Many of them use strap-down integration and some coordinate transformation.

I'm not sure if this term is used widely, but since it's about integration and kinematics, I thought it would have been a good idea to ask it here.

What's exactly strap-down integration? How is it different from "normal" integration?

Note: the context may not help much if you don't know anything about kinematics and the study of human body analysis. Feel free to migrate this question to a more appropriate Stack Exchange's website, if you think this belongs to another website.

Best Answer

There are essentially two ways to mount accelerometers for the purpose of navigation:

  1. Stabilized platform: an intertially stabilized platform is mechanized using either passive mechanical elements or active controls using gyro feedback and mounted within the body of the vehicle. This maintains a local level reference frame and from this frame one can integrate the accelerometers with respect to the intertial frame.
  2. Strap down navigation: By this method the accelerometers are fastened rigidly to the body frame of the vehicle. By this method, the signals together with the gyro signals must be processed and rotated on a moment by moment basis to account for the attitude changes in the vehicle to obtain principle axis, intertial accelelerations, velocity and displacement. This requires 3 axis measurements and either Euler or quaternion transformation mathematics.