A patient mountable robot includes a four link mechanism, three actuators, and a first robot base. The mechanism includes four links that form a closed loop structure. The four links include a base link that includes a spherical joint. The mechanism provides two rotational degrees of freedom about the spherical joint for a needle that is configured to pass through the spherical joint. A first actuator is attached to the mechanism and moves the mechanism to provide the first of the two rotational degrees of freedom. A second actuator is attached to the mechanism and moves the mechanism to provide the second of the two rotational degrees of freedom. The base link of the mechanism passes through the first robot base. A third actuator is attached to the first robot base and linearly translates the base link so that a translational degree of freedom is provided for the needle.