Parametric path modeling for an optical automatic seam tracker and real time robotic control system

A method of operating a robot system including:

• a robot controller operating with a taught path;
• a control processor for iteratively controlling an effector end with an error representing control signal in relation to a recovered path derived by the control processor from said robot controller;
• a seam sensor vision having a look-ahead optical sensor for deriving successive 2-D light stripe images representing discrete successive transversed views of the seam as sensed at successive locations upon the seam a predetermined distance ahead of the effector end;
• an image processor for treating each of said strip images in real time to derive in relation to each image a first signal representative of the coordinates for the respective sensed locations;
• and
• a control processor responsive to a second signal indicative of the present effector end position and to said first signal for generating said control signal as an indication of an error between present effector end position and corresponding sensed location;
• with the following steps being performed by said control processor;
• storing and classifying said first signal coordinates for sensed locations obtained ahead of the effector end as a function of the elapsed distance since a first location sensed at the start of the seam sensing process;
• said first signal coordinates following each other in the succession of sensed locations to form a discrete series of signals of different magnitudes;
• grouping such discrete signals according to a common algebraic characteristic typical of a particular seam model;
• storing such seam model grouped discrete signals as a function of the successively encountered sensed locations;
• said control processor performing the following additional steps:
• calculating and storing iteratively in response to said control signal and to said second signal the elapsed distance of the effector end since a start position thereof;
• deriving iteratively with said second signal for a present effector end position and with said control signal for a present positioning operation of the effector end successive positions representing the taught path as recovered therefrom;
• extrapolating by a predetermined amount from past positions on said recovered taught path to an anticipated position thereon;
• extrapolating by said predetermined amount from past elapsed distances to an anticipated elapsed distances for said effector end;
• determining with corresponding seam model grouped discrete signals in relation to said anticipated elapsed distance the coordinates of the corresponding sensed locations and deriving said first signal accordingly;
• and
• controlling by feedforward the robot controller in response to the control signal derived from said first and second signals.

A robotic control system including:

• a robot controller operative to position an effector end in relation to a seam;
• an image processor operative with an optical seam tracker and a look-ahead sensor mounted on said effector end a distance ahead therefrom to provide successive sensed locations on the seam;
• and
• a control processor responsive to an instantaneous present position of the effector end and operative upon said robot processor for control of the effector end toward an anticipated position by feedforward in relation to a corresponding seam location derived from said image processor;
• the image processor providing an indication of the successive sensed locations on the seam counted at respective elapsed distances from a starting point on the seam;
• an indication of the successive effector end positions being derived from the robot processor and received by the control processor and counted at respective elapsed distances from said starting point;
• wherein said corresponding seam location is ascertained by the control processor in relation to successive sensed locations derived from the image processor and to an elapsed distance corresponding to said anticipated position;
• wherein the robot has a taught path and the control processor derives from the robot processor a recovered taught path, an extrapolated elapsed distance being ascertained on said recovered taught path by the control processor matching said anticipated position, and wherein the corresponding seam location is derived from said sensed locations as a function of said extrapolated elapsed distance;
• said sensed locations being stored and grouped within the control processor in a function generator so as to form as a discrete function of elapsed distances a seam model;
• said extrapolated elapsed distance being applied by the control processor to said functions generated as a variable representative signal so as to derive a signal representative of said corresponding location.

A method of combining the operations of a seam sensor with the operations of a robotic system controlling an effector end in relation to the seam comprising the following steps:

• sensing successive discrete locations on the seam ahead of the effector end while concurrently storing data representing seam coordinates at each of said seam locations as a function of the elapsed distances from the first of such seam locations;
• modeling the stored data to generate a model representing the coordinates of said seam locations as a function of the elapsed distance;
• deriving from the robotic system a representation of the effector end coordinates for successive discrete locations thereof;
• calculating iteratively from said derived effector end coordinates an indication of the elapsed distance for each of the successive effector end locations and from the first of such effector end locations;
• extrapolating from a present and a last effector end location an anticipated effector end location at an elapsed distance therefrom;
• deriving from the stored data in said model the coordinates of the effector end at said anticipated effector end elapsed distance;
• and
• controlling the robotic system in relation to said derived effector end coordinates.