A handheld robot, comprising: a main body, having an inner space; a grip connected to the main body; a kinematic mechanism, having six degrees of freedom and disposed inside the inner space of the main body, the kinematic mechanism 2. comprising a stationary plate, a mobile plate, a plurality of actuating units and a plurality of connecting rods, the actuating units being mounted on the stationary plate and connected with the mobile plate via the connecting rods, the stationary plate being connected to the main body; a tool connector connected to the mobile plate; a tool connected to the tool connector and having a distal threaded segment and a proximal non-threaded segment connected with the threaded segment along an axial direction, wherein a diameter difference exists between an outer diameter of the threaded segment and an outer diameter of the non-threaded segment; and wherein the outer diameter of the threaded segment is smaller than the outer diameter of the non-threaded segment; a positioning unit, disposed on the mobile plate for tracking the position and orientation of the tool; a positioning system, for tracking the positioning unit; and a force sensor disposed between the tool connector and the mobile plate along the axial direction of the tool, the force sensor being for measuring a deviation force that deviates the tool from a predetermined path, wherein the deviation force is generated between the tool and an object in coordination with the diameter difference existing between the threaded segment and the non-threaded segment, and wherein the handheld robot combines the position and orientation information of the tool acquired by the positioning unit and the positioning system with the deviation force information measured by the force sensor, and utilizes the combined information to adjust the position of the tool so as to keep the tool within the predetermined path. a main body, having an inner space; a grip connected to the main body; a kinematic mechanism, having six degrees of freedom and disposed inside the inner space of the main body, the kinematic mechanism 2. comprising a stationary plate, a mobile plate, a plurality of actuating units and a plurality of connecting rods, the actuating units being mounted on the stationary plate and connected with the mobile plate via the connecting rods, the stationary plate being connected to the main body; a tool connector connected to the mobile plate; a tool connected to the tool connector and having a distal threaded segment and a proximal non-threaded segment connected with the threaded segment along an axial direction, wherein a diameter difference exists between an outer diameter of the threaded segment and an outer diameter of the non-threaded segment; and wherein the outer diameter of the threaded segment is smaller than the outer diameter of the non-threaded segment; a positioning unit, disposed on the mobile plate for tracking the position and orientation of the tool; a positioning system, for tracking the positioning unit; and a force sensor disposed between the tool connector and the mobile plate along the axial direction of the tool, the force sensor being for measuring a deviation force that deviates the tool from a predetermined path, wherein the deviation force is generated between the tool and an object in coordination with the diameter difference existing between the threaded segment and the non-threaded segment, and wherein the handheld robot combines the position and orientation information of the tool acquired by the positioning unit and the positioning system with the deviation force information measured by the force sensor, and utilizes the combined information to adjust the position of the tool so as to keep the tool within the predetermined path.