For decades we were taught to believe that if you ever wanted to measure anything properly, you needed a CMM.  A couple of decades ago, portable arms were released and although they seemed novel,

nothing would compare to the rigidity and accuracy of three linear scales and drives.  We were resigned to the fact that any improvement in CMMs would be only incremental.  We lived this way for decades.  Recently, however, optical CMMs began developing and maturing, which could be enough of a paradigm shift to become the revolutionary change the metrology market is looking for.

About the Optical CMM technology

While the technology comes in different “flavors,” most optical CMMs work around a similar principal.  Nikon Metrology’s optical CMM (KCMM) begins with three linear CCD cameras.  When light from an active infrared LED is detected, the three cameras triangulate its position in space.

If the cameras pick up two LEDs, it can calculate distance between the two LEDs in three dimensions.  If three LEDs are attached to a rigid body, the system can calculate x-y-z-i-j-k positioning of that body.

To take that further, if we use nine LEDs mounted on a rigid carbon fiber probe with a styli, we can accurately track the position of that probe in a volume up to six meters away from the cameras.

What we have is a coordinate measuring machine that is not bound by the constraints of scales and encoders.  However at this point, this paradigm shift has only replicated what an arm or a CMM does.  This is where the optical CMM’s story begins.

If you continue to add LEDs to your work piece, you can track x-y-z-i-j-k movement of your part and compensate for it.  Simply put, if your work piece moves, the system doesn’t care.  The part and/or the camera can get bumped and the system will notice the movement real time and adjust.  Here is where the paradigm shift comes into play.  In a CMM (either traditional or arm), the measurements are in reference to a physical MCS.  In the optical CMM, the measurements are relative between clusters of LEDs and not necessarily tethered to a fixed location in space.  This concept of dynamic referencing is the cornerstone of usability that an optical CMM can bring to any shop.

You can take the dynamic referencing concept a bit further and move the camera or part on purpose.  Either can help for part reachability or can extend the measurement volume over the standard six meters (without leapfrogging).

Let’s take the concept of dynamic referencing to a new elegant level.  Nikon Metrology found an automotive application where wanted to measure the clearance of a car engine to a closed hood on a finished car.  We placed six LEDs on the car.  Three were placed on the hood and three on the frame while the hood was closed.  We then opened the hood and turned off the three on the hood (only using the three on the frame).  We then proceeded to measure the car engine.  Since dynamic references were engaged, the system didn’t care that the car was on tires and not stable.  Then we turned off the LEDs on frame and turned back on the LEDs on the hood.  Since we kept the hood open, the system saw a movement in the hood and compensated for it.  Simply put, the system software closed the hood even though it was still open.  We measured the inside of the hood and in the software, very easily measured all of the clearance distances we were looking for.

Adding a laser scanner to the system is as simple as surrounding a laser line scanner with 40 LEDs.  This allows for a light, ergonomic laser scanning solution of larger work pieces.

In addition to using the probes, we can use the LEDs themselves and track their positions at speeds up to 1000 hz.  We can mount the LEDs to a work piece and track movement real time.  This methodology has been successfully implemented in earthquake labs, boat towing tanks, and manufacturing test benches to name only a few.

Successes

Richard Childress Racing is using the Nikon Metrology’s optical CMM to measure chassis/suspension geometry for it’s race cars.

They experience a 40% higher inspection turnaround.

The Volkswagen Group has successfully deployed over 20 Nikon Metrology optical CMMs in place for various inspection tasks.

Gehl uses Nikon Metrology optical CMMs in three different facilities to inspect large production fixtures for prototype verification and incoming inspection.  Their chassis inspection time has been reduced by 50%.

Future

The optical CMM technology is not tethered to incremental growth.  It can grow to increase accuracy and volume by adding cameras in different configurations.  Further, with core lens/camera corporations like Nikon becoming active in the technology, development will continue at the rapid pace of business today.

In the end, will an optical CMM replace your bridge CMM?  Today, maybe it will only to fill a specific need.  But in the future, who knows?