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# Setting Restrictions on IK Joints

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Hello, I''ve build a simple CCD inverse kinematic system. For each joint, I calculate the axis of rotation and the angle and finally convert it to a quaternion. The IK system works fine. Now I want to set restrictions on the joints, especially I want to say that for example joint A can only rotate about the x and y axis and only from -45 to +45 degress. I tested converting the quaternion to euler angles, setting the restrictions and converting them back to quaternion, but this is not always true. So my question is, how can I set restrictions to quaternions, so that rotations are limited? karlkoch

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I guess it''s a tough topic. Converting to euler angles seems intuitive, but it comes with its own problems. Frankly, I don''t know myself, but I''d be very interested on reading a good answer.

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http://3d.recoil.org/EG98_Paper.pdf

an simple but interesting paper.

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That paper makes use of an algorithm based on calculation of the Jacobian which is a very common way of solving IK for any type of mechanism in 3D. Search for a paper "A solution algorithm to the inverse kinematic problem for redundant manipulators" by Lorenzo Sciavicco and Bruno Siciliano. It describes (among other things) a technique to take joint limitations into account. However it is also based on calculation of the Jacobian.
I have no experience with CCD algorithm and don''t know if joint limitations can easily be implemented.

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