In-process relative robot workcell calibration

In a robotic workcell having a robot, a sample workpiece, a calibration station and a tooling system, a method for off-line relative calibration comprising the steps of:

• determining the tool center point of the robot;
• creating a relative reference between the robot and the sample workpiece;
• making relative measurements of the sample workpiece to calculate calibration parameters;
• calculating a work-object coordinate compensation matrix;
• and
• calibrating the tooling system, wherein calibrating the tooling system comprises
• moving the robot to a first contact point between the robot and the tooling system;
• recording the force between the robot and tooling system;
• repeating the above procedure until only a substantially normal force is generated;
• transferring and calculating the residual error between the robot and the tooling system by converting force error components into position variation;
• and
• calculating the error-compensation matrix and adding into a tooling coordinate frame.

A method for calibration of a robotic workcell including a robot, a sample finished workpiece, a calibration station, and a tooling system, the method comprising:

• making reference measurements of the sample finished workpiece in the calibration station;
• making reference measurements of a raw unfinished workpiece in the calibration station;
• performing a comparison of the reference measurements of the sample finished with the reference measurements of the raw unfinished workpiece;
• and
• calculating a work-object error compensation matrix based upon the comparison.

A method for relative calibration of a robot work cell, the robot work cell comprising a robot, a sample workpiece, a tooling system, a force sensor and a calibration station including a displacement measurement sensor, the method comprising:

• tool calibration;
• workobject calibration comprising
• programming calibration paths on a surface of the sample workpiece to define calibration movements for the measurement of workobject surface positions relative to the displacement measurement sensor,
• defining a workobject geometry in a cartesian coordinate system with orthogonal x-, y-, and z-axes, in which the workobject can be translated dx, dy and dz and rotated dRx, dRy and dRz,
• obtaining the calibration paths from a reference position of the workpiece relative to a robot mounting plate and from closed two-dimensional cross sectional workpiece profiles in parallel xy-planes,
• calibrating dz by measuring a relative distance between the reference position of workpiece and the robot mounting plate,
• after running calibration paths, utilizing one dimensional displacement measurements from the calibration station to calculate relative errors dx, dy and dRz of an actual workpiece profile relative to a corresponding ideal workpiece profile,
• calculating errors in dRx and dRy based upon the distance between the workpiece profiles and at least two sets of dx, dy and dRz,
• calculating dx, dy,dz,dRx,dRy, dRz for the workobject,
• moving the robot to approach and touch the tool;
• performing tool calibration using a force sensor mounted on arms of the robot;
• and
• calculating a tool coordinate relative to the calibrated workobject.