Geometrical instruments – Straight-line light ray type – Alignment device
Reexamination Certificate
2000-09-11
2002-10-22
Fulton, Christopher W. (Department: 2859)
Geometrical instruments
Straight-line light ray type
Alignment device
C033S644000, C356S621000, C356S400000
Reexamination Certificate
active
06467178
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to tool center point calibration systems. More particularly, the invention relates to a method and system for automatically determining a tool center point for a beam tool.
BACKGROUND ART
In the automotive industry, a common activity is the removal of material from various internal and external parts to create various holes and shapes. Conventional approaches to this activity have involved casting sections of the part, punching the unwanted material out of the sections, and subsequently welding the sections together. This approach, however, has its drawbacks. For example, the additional welding step can be quite expensive and time consuming. Furthermore, the casting of sections as opposed to complete parts, increases overall manufacturing costs.
In response to the above and other difficulties associated with the “punch and weld” approach, laser cutting has rapidly evolved. The result is that now complete parts can be fabricated and then the unwanted material can be removed with a laser cutting tool. While this approach has resulted in significant cost savings and benefits, there is still room for improvement. For example, the typical laser cutting tool has a tool center point (TCP) that is typically defined by the laser manufacturer. The TCP is generally measured from the robot's tool mounting plate and will often have an accuracy on the order of tens of millimeters. In order for laser cutting to serve as a legitimate alternative to the punch and weld approach, the robot handling the laser head must be able to position the TCP at very precise locations. Thus, the robot controller must know exactly where the TCP is at all times.
Typical approaches to determining the TCP for conventional tools involve a well known process of repeatedly moving the TCP to a fixed point with various tool orientations and taking orientation readings. From these readings, the robot controller can determine the TCP. The difficulty with this approach, however, is that a significant amount of time and effort is required to manually jog the TCP to the fixed point in order to take the coordinate readings. In fact, it is extremely difficult to get the required accuracy when performing this type of calibration.
Furthermore, the “manual jog” approach is best suited for tools with a physical TCP (i.e. “touching” tools). In other words, beam cutting tools have a TCP that is located somewhere in the center of it's beam, and is therefore not visible in the physical TCP sense. Thus, the calibration technician cannot precisely know when the TCP has reached the fixed point during the calibration procedure. Another difficulty is that the nozzle of the laser head can be of many different designs, making it difficult to use any type of “beam breaking” device (as in the conventional bull's-eye) to determine the TCP. It is therefore desirable to provide a method and system for determining a TCP for a laser cutting tool that does not fall subject to the aforementioned difficulties. It is also desirable to provide a solution that is cost efficient, automatic, and self-adjusting.
SUMMARY OF THE INVENTION
In a first aspect of the invention, a method for determining a tool center point (TCP) for a beam cutting tool is provided. The method includes the step of oscillating the tool across an aperture assembly such that light from the tool periodically passes through the aperture assembly. Center point coordinate information is then determined based on passage of the light through the aperture assembly. The method further provides for calculating the TCP based on the center point coordinate information. Preferably, these steps are repeated for a plurality of tool orientations. Passing the light through the aperture assembly in a controlled fashion enables the TCP to be determined without skilled labor, manual processes, or significant expense.
In a second aspect of the invention, a TCP calibration system is provided. The calibration system includes an aperture assembly having an aperture for allowing light from a beam cutting tool to create an image inside the aperture assembly. The calibration system further includes a light sensing device for capturing an image created on the aperture assembly. The light sensing device generates a signal corresponding to the light intensity emitted from the aperture assembly.
REFERENCES:
patent: 5251156 (1993-10-01), Heier et al.
patent: 5457367 (1995-10-01), Torne
patent: 5675229 (1997-10-01), Thorne
patent: 5718054 (1998-02-01), Kitajima
patent: 5813128 (1998-09-01), Bailey
patent: 5910719 (1999-06-01), Thorne
patent: 6175413 (2001-01-01), Lucas
Poljén Christian
Svensson Tommy
ABB Automation Inc.
Fulton Christopher W.
Harness & Dickey & Pierce P.L.C.
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