Off-Line Programming Specification For Superior Accuracy

The following is an excerpt from PSA's specification document regarding Robot Off-Line Programming. It is intended for PSA's integrators.

General Guidelines for all applications

Off-Line Programming

In order to minimize robot launch time and improve the quality of robot paths, off-line programming is required as a standard for all applications. The robot paths for all different parts need to be generated through CAD simulation. The corresponding physical parts will no longer be provided. Robot programming on the floor needs to occur through downloading of these simulated robot paths into the robot controller.

The robot paths need to be generated in the car coordinate frame, i.e. the coordinates of the points need to be expressed in the car frame. In case of spot welding the programmed points need to have the same coordinates as in the CAD model.

Calibration of the robot-cell

In order to compensate for the errors coming from the actual robot and part fixture location, calibration of the robot-cell allows determining the relation between the car frame and the robot frame. This calibration is required for the robot programs downloaded from simulation.

For this operation, we require the use of the DynaCal system from Dynalog because of its accuracy, its speed, and its adaptability in spot-weld installations. The measurement basis of this system, which comes under the form of a small unit, is a precision cable connected to a high- resolution optical encoder. In the case of a standard spot-weld application, the calibration procedure consists of consecutively locating the unit to a minimum of 3 locating pins on the fixture and of connecting the other side of the cable through an adaptor to the spot-weld gun’s TCP. For each locating pin, several robot positions are generated, and the corresponding cable measurements are used by a PC-based software to calculate both the fixture frame and the TCP frame. We invite those integrators or their subcontractors who do not own or know this system yet to contact Dynalog in order to learn more about this calibration procedure.

The classical method of using the robot to teach some points on the fixture to define the alignment is no longer accepted.

Absolute Accuracy Robot Calibration

A robot is generally capable of repeating the same move towards a specific point in space, over and over, within a high level of tolerance (referred to as 'unidirectional Repeatability'), generally well below 0.1mm.

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DynaCal Robot Calibration System

The DynaCal system delivers the highest possibly Absolute Accuracy for your complete robot-cell. The system comes with its own proprietary measurement hardware, but is also compatible with laser trackers, camera-based systems, etc.

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Offline Programming with No Touchup

Robots have historically been taught manually, i.e. using the robot's 'teach pendant' to manually drive the robot's TCP to the desired point along the part to be operated on, while visually verifying – as much as feasible ...

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