Calibration method for tool center point of a robot manipulator

A calibration method for a tool center point (TCP) of a robot manipulator, the robot manipulator comprising a drive mechanism, a controller for controlling the drive mechanism, a tool assembled to a distal end of the drive mechanism and having a tool center point (TCP), and a sensor positioned on a distal end of the tool;

• the robot manipulator has a basic tool coordinate system having three axes, the calibration method comprising the following steps:
• providing an assistant indicating tool cooperating with the robot manipulator, the assistant indicating tool comprising a planar top surface and an inclined surface defining an included angle a relative to the horizontal plane;
• driving the tool to move to face the inclined surface, sensing a distance H1 between the position of TCP and the inclined surface;
• defining a preset position P0 of the TCP and establishing a preset coordinate system TG based on the preset position P0 comprising three coordinate axes WG-axis, VG-axis and UG-axis, the VG-axis projecting to the inclined surface at a same height;
• driving the tool to rotate relative to UG-axis of the preset coordinate system TG by substantially 180 degrees, resulting in the actual TCP of the tool moving to a position P2;
• the sensor sensing a distance H2 between the position P2 and the inclined surface, establishing the relationship:
• Δw=|H1-H2|*tan(90°-α)/2, thus obtaining the value of the Δw;
• updating the position parameters of the preset TCP by adding the value of the deviation Δw, and then establishing a new preset coordinate system based on the updated preset TCP comprising three coordinate axes WG'-axis, VG'-axis and UG'-axis, the VG'-axis projecting to the inclined surface at a same height;
• driving the tool to rotate relative to UG'-axis of the preset coordinate system at substantially 90 degrees, resulting in the actual TCP of the tool moving to a position P3;
• the sensor sensing a distance H3 between the position P3 and the inclined surface, establishing the relationship:
• Δv=|H1-H3|*tan(90°-α), thus obtaining the value of the Δv;
• updating the position parameters of the preset TCP by adding the value of the deviation Δv, and then establishing a newly preset coordinate system based on the updated preset TCP, driving the tool to move over the planar top surface, and then the sensor sensing a distance H4 between the TCP and the planar top surface;
• driving the tool to rotate relative to an axis of the newly preset coordinate system parallel to the horizontal plane by substantially θ degrees, resulting in the actual TCP of the tool moving to a position P5;
• the sensor following the tool rotating θ degrees, and sensing a distance H5 between the position P5 and the horizontal surface;
• and then establishing the relationship Δu=(H4-H5*cosθ)/(1-cosθ), thus obtaining the value of the Δu;
• comparing the deviation ΔP(Δw, Δv, Δu), wherein ΔP is the deviation between the preset position P0 and the actual position of the TCP, with a maximum allowable deviation of the robot manipulator;
• wherein, if the deviation ΔP is less than or equal to the maximum allowable deviation of the TCP of the robot manipulator, the preset position P0 of the TCP is thereby considered as the actual position of the TCP and completing the coordinate correction work;
• if the deviation ΔP is greater than the maximum allowable deviation of the robot manipulator, then, updating the position parameters of the preset position of the TCP by adding a deviation Δu, and repeating the calibration method for the tool center point till the final deviation is less than or equal to the maximum allowable deviation of the robot manipulator.