# Resolved Motion Rate Control, Rotational Part

I'm controlling 6 DOF robot arm based on image processing. Robot arm will grab the object. Below what my system looks

I can control the translational part of robot very well. But i cant control the rotational part. I mean i want the gripper facing down and rotate according angle of the object. Using jacobian equation $$\begin{bmatrix} dq1 \\ ... \\ dq6 \end{bmatrix}$$= J(q)^{-1}$$\begin{bmatrix} dx\\ dy\\ dz\\ drx\\ dry\\ drz \end{bmatrix}$$

I try using rotational equation from this paper but still no luck, what should i do for rotational part

Note : To generate the jacobian, im using SerialLink.jacob0 from Matlab Robotic Toolbox by Peter Corke

• Welcome to Robotics Albert H M, but I'm afraid that it is not clear what you are asking. We prefer practical, answerable questions based on actual problems that you face, so it's a good idea to include details of what you want to achieve, what you tried, what you saw & what you expected to see. Please take a look at How to Ask & tour for more information on how stack exchange works and work through the Robotics question checklist to edit your question to make it clearer. Jun 11 '19 at 18:25
• You said "I try using rotational equation from this paper but still no luck" - what does that mean? What inputs have you given it, what outputs did you get, and what were you expecting? You said you're using a Jacobian, but I don't really see Jacobians mentioned anywhere in the paper you linked. The paper has numbered equations - which rotational equation are you using? Why did you choose that equation? What is the overall behavior you're seeing? (Failure to converge, oscillations, something else, etc.) Jun 11 '19 at 18:29
• Is this a planar or 3D problem? Jun 11 '19 at 21:16
• @PeterCorke 3D problem, 6 DOF Robot Arm sir.. Jun 12 '19 at 3:20
• @Chuck, the problem i face right know actually how to get the orientation of end effector(for inv j input)I know how to get translational position from homogeneous transformation matrix (the last column). Then i try to find the orientation of end effector, i read several equation from JJ Craig, Introduction to robotic, and other several paper, but then i realize it used DH Parameter, meanwhile i use Modified DH parameter which use less variable. U know the input for inverse jacobian in RMRC is delta of position and orientation. Delta for orientation is something that i dont know till this day. Jun 12 '19 at 3:26

After a long-long research, i finally able to control the rotational part.

First of all, if you wanna control the orientation part you need to determine what kind of representation of orientation you wanna use. Available options :

1. Two Vector Representation
2. RPY Angle
3. Euler Angle
4. Unit Quarternion

If you use no 1, you only need geometrical jacobian (the original jacobian). I used the euler angle because 6 DOF robot has wrist joint (recommendation from several website). If using RPY and Euler as orientation, we need analytical jacobian. You can find how to calculate orientation error and analytical jacobian from this book

1. Corke, Peter P. (2017). Robotics, Vision and Control. Springer.
2. Siciliano, B. (2009). Robotic Modelling, Planning and Contol. Springer.

Hope this help anyone in future. Feel free to discuss and correct me