The Xiris Blog

Using a Trigger Signal on a Weld Camera

Posted by Cameron Serles on Tuesday, March 15, 2016 @ 06:00 AM

 

   Traditionally, cameras that have been used to record images of various welding processes are implemented with a free running image trigger.  This means that images from the camera are acquired as fast as the camera can send them, and only when the camera can send them.  However, with a digital Weld camera, such as the Xiris XVC-1000, images can be acquired from the camera when given the signal to do so via the image trigger.  This creates an opportunity to tie the image acquisition to a specific event.  A typical example of such an event is during a laser weld cycle where the laser power may take several milliseconds to ramp up to full power or to form a keyhole and then, once at full power, may be pulsed to achieve a particular welding effect.

   In any of these situations, it can be interesting to acquire an image at a very specific point in time to see a specific feature.  This can be done very precisely with the XVC-1000 using an external trigger signal generated during a specific event, such as the point when laser power peaks during a cycle.  When combined with a programmable exposure time, images of very specific events, such as only during laser on during a pulsed laser application, can be acquired.

    In other types of welding, such as pulsed GTAW, a trigger could be sent at a particular point for each pulse, which when combined with a programmable delay and programmable exposure time, would allow image acquisition to take place at a very specific point in the weld cycle.  The benefit is the ability to view the weld pool consistently during a high or low point in the weld cycle and monitoring how it would grow or shrink over time.  Another benefit would be for wire fed welding, where the effect of the weld pulse on the wire position as it enters the weld pool could be monitored.

   In GMAW processes, the image trigger could be aligned with a specific voltage or current event during the wire contact/expulsion cycle.  By acquiring an image at exactly the same point in the weld power cycle, it is possible to study how droplet formation and transfer rates change over time.

   Lastly, for alternating polarity welding applications, an image trigger signal could have great value in assisting the operator in setting up the weld torch and determining the ideal weld parameters for each polarity by triggering only on that portion of cycle when the power conditions are met.

 An example of a free-running video versus a triggered video.  Note: the triggered image acquisition for this video was done at a slow rate, of about 2 Hz.

Conclusion

   The use of a trigger signal can greatly improve the quality of images of most welding processes when using a camera such as the Xiris XVC-1000.  By clamping the trigger to a specific power event, images can be acquired at a precise point in the weld cycle, allowing for better set up and diagnostics of the welding process.

For more information on how Xiris Weld Cameras can help monitor your weld processes, visit Xiris.com 

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Topics: quality control, weld camera, Laser welding, High Dynamic Range, productivity, Laser cutting

Using Area of Interest (AOI) to Achieve High Frame Rates with a Weld Camera

Posted by Cameron Serles on Tuesday, March 01, 2016 @ 06:00 AM

 

  All digital cameras, including the Xiris XVC-1000 Weld Camera, have a digital output signal that is limited by the speed at which data can stream out of the camera.  This limits the frame rate of the camera and is a function of the frame size of the camera.  For the XVC-1000, the camera can output 55 frames per second at full resolution of 1280 x 1024 pixels.  However, it is possible to create a faster frame rate by reducing the size of the image, or Area of Interest (AOI).  For example, if the height of the AOI is cut to half the full frame image size, then the frame rate can run twice as fast, e.g. approximately 110 frames per second, or if cut to a quarter its height, the frame rate will be over 200 frames per second.  If a very small window is made that could see a small weld process such as a laser spot and a thin weld, the frame rate could run up to 1000 frames per second.  This can be very useful in certain situations where features of very short duration need to be monitored.

   As an example, many industrial laser welding processes have their laser powered ON for very short durations, usually far less than 2 seconds.  This would require a higher speed imaging capability to see exactly what was happening on the weld.  As the Area of Interest in a laser process is a long thin rectangular area – typically the weld spot, the seam and a narrow weld pool, reducing the AOI can sometimes be done on a laser process to good effect.  The result is a high speed image capture that captures the detail of the laser spot and immediate area around it.

 Mar_2_-_Using_AOA_image.png

Using the AOI to create a Faster Image

 Summary

   A digital Weld Camera with Area of Interest capability can be used to image very small, narrow regions of interest at high speeds by reducing the Area of Interest of the camera.  As such, Weld Cameras can be used as a valuable tool for set up and alignment of high speed laser processes. 

For more information on how Xiris Weld Cameras can help monitor your weld processes, visit Xiris.com 

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Topics: quality control, weld camera, Laser welding, High Dynamic Range, productivity, Laser cutting, AOI

Imaging the Changing Intensity of the Laser Spot

Posted by Cameron Serles on Tuesday, February 16, 2016 @ 06:00 AM

 

  A major challenge that manufacturers face when integrating a weld camera to a laser weld process is the changing amount of reflected light that comes back to the camera.  Huge swings in brightness of reflected light can cause challenges when trying to produce a good image, requiring a high dynamic range camera with the ability to change quickly to rapid brightness variations. 

  To explain this phenomenon, it is useful to look at how the incident laser light hits the substrate during a welding or cutting process and how the reflected light bounces back to the camera.

Stage #1: Once the Laser is Powered ON

  When the laser is first powered on, the substrate is typically flat and perpendicular to the rays of incident light of the laser as the surface has not been melted by the laser radiation at this point.  As a result, a high amount of light from the laser gets reflected right back to the laser beam delivery optics and eventually to the camera, creating a momentary flash of intense brightness.  This bright reflection could saturate and even damage some cameras.

Feb_16_image_1.pngStage #1: Initial Incident Light Reflected

 

Stage #2: The Molten Layer Develops

  After a brief period, the laser starts to melt the surface of the substrate, creating a small concave molten layer.  The reflected light going back into the laser beam delivery system reduces as there is a bit of focusing of the reflected light rays.

 Feb_16_image_2.pngStage #2: Development of Molten Layer

 Stage #3: Vaporization and Cavity Formation

After a little more time, a deeper cavity is formed as the laser vaporizes some of the substrate material.  At this point, the laser light is bouncing around the cavity and even less light makes its way back to the camera.

 Feb_16_image_3.png

Stage #3: Vaporization and Formation of Cavity

 

Stage #4: Keyhole Formation in Substrate

The final stage is once a Keyhole is formed.  This is a deep, narrow cavity in which the metal is melted, some of it vaporized and then it flows around the cavity and solidifies.  At this point, the laser light hits the keyhole, bouncing all around the keyhole and most of it gets absorbed into the substrate, with only a little of the light making its way back to the laser beam optics and camera.

 Feb_16_image_4.png

Stage #4: Keyhole Formation

   The process of moving through the above four stages could take a few hundred milliseconds.  During this process, there is a huge variation of light that bounces back to the camera.  For example, the light bouncing back during the Keyhole Formation stage could be 10-15% of the light received during the initial irradiation of light right after the laser is powered on.  As a result, a weld camera that has been specifically designed for the huge range of light variation such as the Xiris XVC-1000 is necessary to properly image the laser welds through the start up of the laser beam.

Summary

  Cameras have been integrated into laser welding and cutting machines for some time as a valuable tool for set up and alignment of the laser head to the workpiece.  However, traditionally, once the laser power was turned on, the cameras were not able to see the laser light.  To do this, a high dynamic range weld camera such as the Xiris XVC-1000 is required to see the enormous range of light reflected back from the substrate and deal with the huge range of brightness of laser light reflected back to the camera.

For more information on how Xiris Weld Cameras can help monitor your weld processes, visit Xiris.com 

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Topics: quality control, weld camera, Laser welding, High Dynamic Range, productivity, Laser cutting

Blob Analysis Tool for Weld Monitoring

Posted by Cameron Serles on Tuesday, February 02, 2016 @ 06:00 AM

 

  Image Processing is slowly making its way into the welding world.  With the advent of high dynamic range weld cameras such as the Xiris XVC-1000, images of welding processes can be made with enormous ranges of brightness.  As a result, it is now possible to monitor and record good quality video of most welding processes using an HDR camera.  With good quality images of the weld pool, arc and seam, the next logical step is to incorporate image processing into the camera system to extract additional information to help operators better control the welding process.

  The BlobAnalyzer tool from Xiris is a powerful Blob Analysis tool that can measure a variety of properties of objects within a region of interest.  Data can be generated from the properties and then monitored or analyzed so that objects measured or sorted based on their shape parameters.  The net result is a new way for fabricators to enhance the monitoring and controlling their weld processes.


BlobAnalyzer.png

The Blob Analysis tool includes properties such as:

 Area                 Centroid           Perimeter         FormFactor        BoundingBox

 Orientation         Eccentricity      EulerNumber    Hole Count        TouchesBorder

 FeretDiameter    GrayMass        GrayMean        Compactness

Conclusion

  By incorporating image processing tools such as Blob Analysis into their weld camera systems, machine builders can measure features of their weld processes in a way that has never before been possible.  It is now possible to find features in an image, such as the weld arc, or seam, that could allow for further monitoring or analysis, or form the foundation for seam tracking or weld pool geometry analysis.

For more information on how Xiris Weld Cameras can help monitor your weld processes, visit Xiris.com 

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Topics: weld camera, Laser welding, High Dynamic Range, weld monitoring, Laser cutting

Off Axis Mounting of a Weld Camera onto Laser Processes

Posted by Cameron Serles on Tuesday, January 19, 2016 @ 02:04 PM

Off Axis Mounting of a Weld Camera onto Laser Processes

A High Dynamic Range Weld Camera can provide great benefit to a laser welding or cutting process by being able to see the melt pool and seam while the laser is on.  In this blog we explore an additional method of mounting cameras to the laser welding or cutting process – Off Axis mounting of the camera.

 Off Axis mounting of Weld Camera

Off Axis mounting of a weld camera is when the camera is mounted separately from the laser beam delivery head in such a way that it is aimed at the work surface where the laser makes contact.  It contains completely separate optics and lighting components with its own mounting mechanism.  Because of the flexibility of location, a camera that is mounted off-axis can be placed at any position around the laser head to get the best image.  These locations can be categorized as:

  1. Forward looking: to see the seam and work environment prior to the weld;
  2. Backward looking: to see the weld pool and weld bead after welding; or
  3. Sideways looking: to gain an overall perspective of the weld environment.

Co-axial_image_1.png

Off Axis Camera Mounting Relative to Laser Beam Delivery System

 In the above image, a simple laser beam delivery system is shown with a camera mounted obliquely to the laser beam optics.  This provides the ultimate in mounting flexibility to get the best possible image desired.  There are a number of advantages and disadvantages of this type of set up:

 Advantages:

  • More mounting options as to where and how to place the camera relative to the laser head, with various optical configurations and fields of view possible;
  • Extra lighting can be added to see additional background detail that is farther away from laser source and not illuminated by the laser itself.

 Disadvantages:

  • A separate, sometimes complex mounting system is required that needs to be mechanically coupled to the laser head so that both units travel in tandem without relative movement.
  • As most laser beam delivery systems are much larger than the beam spot, the camera has restricted access to be able to view the immediate area around laser spot, making obtaining a good image challenging in some situations.

  Summary

Weld Cameras can be integrated into laser welding and cutting machines using an Off Axis mounting technique.  Such a technique provides the ultimate in flexibility to acquire different types of images as required by the machine designer, yet not be constrained by the optics in the laser beam delivery system.

For more information on how Xiris Weld Cameras can help monitor your weld processes, visit Xiris.com 

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Topics: quality control, weld camera, Laser welding, High Dynamic Range, productivity, Laser cutting

Coaxial Mounting of a Weld Camera onto Laser Processes

Posted by Cameron Serles on Tuesday, January 05, 2016 @ 02:30 PM

Coaxial Mounting of a Weld Camera onto Laser Processes

A High Dynamic Range Weld Camera can provide great benefit to a laser welding or cutting process by allowing examination of the melt pool and seam while the laser is on.  In this blog we explore one method of mounting cameras to the laser welding or cutting process:  Coaxial or On-axis mounting of the camera.

In coaxial mounting, the camera is mounted parallel to, and pointing in the same direction, as the laser source.  The image delivery optics for the camera are combined with the laser beam delivery optics via a beam splitter so that the camera shares part of the final optical path through which the laser beam travels.

 A depiction of an On-axis camera mount configuration is presented below.  In this configuration, the camera has the straight through optics while the laser beam is coming in from the side via a beam splitter.

Camera_picture.png

On-axis camera mounted to laser beam delivery system

 There are both advantages and disadvantages to this type of camera set up on the laser process.

 Advantages:

  • Results in a small form factor package that can be tightly integrated into the laser optics head.
  • Operator is able to see the weld in real time because the actual laser optics are used.
  • Camera lighting can be tightly controlled inside the laser optics, minimizing external influences.
  • Operator is able to monitor the work environment pre-weld for alignment; in real time during welding for laser beam monitoring; and post weld to ensure the quality of the weld.

 Disadvantages:

  • Resulting image quality is dependent on the design of the optics contained in the image delivery system. In certain situations, an additional light may be required to illuminate the work piece in such a way as to make it visible through the image delivery optics (see drawing above).
  • There may be coatings or filters on some of the optical components in the laser beam delivery system that inhibit specific wavelengths of light from travelling up the image delivery optics. This may reduce the visibility of some of the darker background areas around the laser.
  • Reflections may appear in the image due to any misalignment in the image delivery system.
  • Because the camera’s optical path is the same as that followed by the laser beam delivery, there is a limited field of view which may not allow the camera to see all of the features of interest.

 Summary

Weld Cameras can be integrated into laser welding and cutting machines using a coaxial or on-axis approach where the camera uses the same optics as used by the laser.  Such an approach provides a physically compact solution but the visible field may be limited by the optics in the beam delivery system.

For more information on how Xiris Weld Cameras can help monitor your weld processes, visit Xiris.com 

Sign up to receive our Weld Video of the Month

Topics: weld camera, Laser welding, High Dynamic Range, productivity, Laser cutting

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