The remote center of motion (RCM) is an essential issue during minimal invasive surgery where the surgeon manipulates a medical instrument inside the human body. It is important to ensure that the tool should not apply forces on the incision wall in order to prevent patient harm. The paper shows a geometric method for computing the intended robot velocity vector for respecting the RCM constraints. In addition, the proposed solution deals with the latter constraints as the highest task priority. A second task function is added, which is projected in the null space on the first task, to follow a 3D path inside the cavity. As result, this method helps the surgeon to execute more sophisticated motion within the patient body with high accuracy; since the results shows standard deviation around 0.004mm and 0.089mm of RCM task error and positioning task error, respectively.