I have a robotic arm consist of three joints (servomotor for each joint), as shown in the figure below:
Each servomotor rotates around 180 degrees.
The angles of the theta2 and theta3 represent 90 degrees in the figure above.
I found the forward kinematics by using the parameters of DH convention, as shown in the figure above.
The Final Transformation Matrix is:
The position of the robotic arm end-effector is correct for any angle of theta1, theta2, and theta3 between -90 and 90 degrees.
My problem is in the inverse kinematics of the robotic arm, where, the theta2 always affected by theta3 and thus the response of theta2 incorrect, while theta1 and theta3 are always correct. Please see the cases below that show this problem.