A method for controlling movement of a robotic arm of a medical robot system,comprising:receiving an input value expressed in a controller device coordinate systemfrom a controllerdevice representative of a desired motion of a tool associated with the armdetermining acalculated motion of the tool based on the input value, the calculated motionbeing expressed inan observer coordinate system comprising a first axis oriented in fixedrelation with a tool axisand a second axis oriented orthogonal to the first axis, its projection into aplane defined by X-andY-axes of an orthogonal coordinate system defined relative to the referencestructure parallelto and pointing in the same direction as the X-axis determining a commandedmotion of the armbased on calculated motion and position of the arm and outputting anactuation signal to movethe arm in accordance with the commanded motion.
