# Human-Robot Cooperative Control Based on Virtual Fixture in Robot-Assisted Endoscopic Sinus Surgery
###### Abstract  
In endoscopic sinus surgery, the robot assists the surgeon in holding the endoscope and acts as the surgeon's third hand, which helps to reduce the surgeon's operating burden and improve the quality of the operation. This paper proposes a human-robot cooperative control method based on virtual fixture to realize accurate and safe human-robot interaction in endoscopic sinus surgery. Firstly, through endoscopic trajectory analysis, the endoscopic motion constraint requirements of different surgical stages are obtained, and three typical virtual fixtures suitable for endoscopic sinus surgery are designed and implemented. Based on the typical virtual fixtures, a composite virtual fixture is constructed, and then the overall robot motion constraint model is obtained. Secondly, based on the obtained robot motion constraint model, a human-robot cooperative control method based on virtual fixture is proposed. The method adopts admittance control to realize efficient human-robot interaction between the surgeon and robot during the surgery; the virtual fixture is used to restrain and guide the motion of the robot, thereby ensuring motion safety of the robot. Finally, the proposed method is evaluated through a robot-assisted nasal endoscopy experiment, and the result shows that the proposed method can improve the accuracy and safety of operation during endoscopic sinus surgery. e 2019 9 1 2019  
multi-arm surgical robots, and single-port type surgical robots. From the perspective of control, there are mainly three control modes. The first mode is the passive control mode, in which the surgeon locks or loosens the robot joints by operating buttons, pedals, etc., and constantly drags and adjusts the posture of the robot. This passive control mode is simple and reliable, and can meet the requirements of minimally invasive surgery to a certain extent, for example, the surgical robot Tiska [1] developed by [PERSON], the Point Setter and UniARM [2,3] developed by Mitaka, and the EndoArm [4, 5, 6] developed by Olympus. Although the above passive control mode can basically realize the function of assisting surgeon in holding the endoscope in surgery, the robot still needs the surgeon to manually operate the button, pedal, etc. to loosen or lock all the joints, and the control has low efficiency and low intelligence. The second mode is the active control mode, in which the surgeon's head movement and voice are used to control the motion of the robot. For example, the active surgical robot, Aesop [7, 8, 9, 10], can use the voice control mode to drive the endoscope at the end of the robot to the desired spatial pose; the surgical robot, Endo Assist [11, 12], can control the motion of the endoscope at the end of the robot with the movement of the surgeon's head. The third mode is the master-slave control mode, which is often used in multi-arm surgical robot systems, such as Laportek [13, 14], Zeus [15, 16, 17], Da Vinci [18, 19], Miro Surge [20, 21, 22, 23], and Raven [24, 25]. The surgeon controls the slave robot arms at the main console, and switches the control of each slave arm by pedals. The ratio of the surgeon's input motion to the output motion of the robot can be adjusted in the master-slave control mode, achieving finer operation than the human hand. At the same time, the signal-filtering algorithm can eliminate the influence of the surgeon's hand tremor, improving the quality of surgery. According to the above analysis, the passive control mode is simple and reliable, but the surgeon needs to manually adjust the posture of the nasal endoscope during the operation; the adjustment is awkward and has a low level of automation. The master-slave control mode is generally applicable on active surgical robots in the form of a multiple-arm, such as the Da Vinci robot.