Ratajczak, Adam, and Mariusz Janiak. “Motion Planning of the Underactuated Manipulators With Friction in Constrained State Space”. Journal of Automation, Mobile Robotics and Intelligent Systems, vol. 5, no. 3, Jan. 2013, pp. 33-40, https://www.jamris.org/index.php/JAMRIS/article/view/172.