Improvements to Robotic Off-Line Programming Principal investigators:- Prof. Graham Parker and Gary Bonser

It is widely accepted that the Off-Line Programming (OLP) of robot workcells offers a number of manufacturing benefits. New programs can be developed using a computer simulations of the workcell away from the factory floor and when complete can be downloaded to the real workcell and the new task can be performed. A screenshot from an MSRR used simulation package, IGRIP by Deneb, is shown above. OLP results in minimal downtime enabling very small batch sizes to become economic thus increasing production flexibility.

The major limitation to the widespread use of OLP is the problem of checking that the dimensions of the real and model workcells match up to within a fraction of a millimetre - this is the process of workcell parameter calibration. The parameters to be calibrated can be grouped into a number of areas: (1) Robot Arm Signature Parameters: the lengths and orientations of the arm links; (2) Tool Offset: the distance from the tool attachment point at the end of the arm to the tip of the tool the robot is carrying; (3) Workpiece Localisation: checking the position of the parts that the robot is to process.

Research within the MSRR Group has been directed at all three OLP problem areas outlined above. In the first instance, a laser based, non-contact, 3D motion tracking instrument - Optotrac. This can be used to measure the position of a robot as it moves throughout its work space at velocities of up to 5m/s and with an accuracy of better than 0.5mm. This is the ideal tool for performing the arm signature calibration. Results to date for a typical robot show that before calibration off-line generated programs gave real workcell accuracies of worse than 10mm; after calibration accuracy is better than 1mm. Optotrac can also be used to investigate dynamic effects. For instance, it has been used to analyse the velocity profiles and cornering accuracy of robots performing spraying applications. This leads to better programming for more even material deposition.

For tool offset calibration a non-contact optical sensor is currently being developed. Tests to date show a reduction in the time to calibrate a robot tool from tens of minutes to tens of seconds. Designed originally for arc welding gun measurement, this can not only be used to measure the offset but also to monitor the condition of the tool and might be applied to the inspection of a wide range of other automatic devices such as cutting tools on NC machines.

Once the arm signature and tool offset have been accurately calibrated the robot can be used as a measuring device to perform part localisation. Other sensors are also being developed within the MSRR group to aid this task.

This work was most recently funded by the EPSRC (grant no: GR/H88206, "General calibration strategies for off-line programming of robotic arc welding workcells").

Further information :-

Graham Parker
Mechatronic Systems and Robotics Research Group,
School of Mechanical and Materials Engineering,
University of Surrey,
Guildford, Surrey, GU2 5XH,
United Kingdom.
tel : (01483) 879283
fax: (01483) 306039
email: g.parker@surrey.ac.uk

Back to MSRR Homepage

These pages are administered by Maarten Michielen (m.michielen@surrey.ac.uk)
All legal boffs please read this copyright and disclaimer notice.
Last change: April 2000