Frequently Asked Questions

Below are frequently asked questions about CAItech's technology.

1.   How do you convert the points to surfaces?
In our software we see a graphical image of the datacloud (see Figure 2, Data Cloud Example ). We can zoom, pan and rotate it like you would do with any 3D CAD model on your monitor.  During setup, the setup person clicks on a toolbox to get the type of primitive surface he wants, like plane, hole, cylinder, sphere, edge.  Then he clicks on the datapoints of that surface.  Our patented algorithms determine the boundary of that primitive and then convert it into a solid model file.  See Figure 3, Solid Model Surfaces Example .  We use the least squares fit method.  For example if it's a plane, we take those points that belong to that plane and fit them to a plane the best way possible.

2.   Do you use your own software or something like Geomagic?
Our software is very similar to Geomagic's except that we've concentrated on mechanical shapes rather than bio-shapes.  Like Geomagic, we convert dataclouds to solid model files used in CAD software. 

However, our software is part of the inspection machine itself, not third-party software that you buy separately.  As part of the machine, our software controls how the part is scanned rather than simply analyzing the data after the scan.  For example, we don't have to "raster scan" -- tediously moving the sensor back and forth over the entire part.  Instead we can scan just those regions where the important features are.  We can scan quickly over regions that don't require much data, but scan slowly over regions where many data points are needed to get accurate dimensons (see Model 600C - Operation ).  Our software is integrated into the machine to inspect parts as fast and accurately as necessary.

3.   Does your machine measure like a CMM?
A CAItech machine is more like an NC milling machine than a Coordinate Measuring Machine (CMM).  While confocal optics sensors are the most accurate available, they weigh two kilograms (4 pounds).  To quickly move a sensor that heavy requires more force than you usually find in CMM motion control.  And like a good NC machine tool, servo motors with position feedback from glass scales locate the sensor very accurately, typically to a few microns. 

In our low-end machines, (Model 50L or Model 50C ), we move the sensor beam rather than the sensor.  The sensor beam is positioned by mirrors and the heavy sensor is stationary.  For more accurate inspecting, the sensor must be kept within its focal range, called "range tracking".  Our high-end machines (Model 600C or Model 150C ) adjust the sensor's standoff to get the most precise datapoints.  We bring the sensor to the part instead of bringing the part to the sensor.

Our machines are not simply a CMM with an optical sensor replacing the touch probe.  Like an NC milling machine, they are robust machines that have been designed to quickly and accurately move a heavy load.

4.   How does surface finish affect accuracy?
All optical inspection machines capture light that reflects off the part. They measure the location of the part's surface by processing this reflected light by whatever sensor is used. The amount of light reflected back depends on the part's surface finish. There are four categories of surfaces that don't reflect light well: shiny (light reflects away like a mirror, little reflects back to the sensor), black (the surface absorbs light and little reflects back), transparent (the surface transmits the light rather than reflects it) and oblique (most of the light reflects away, little gets back to the sensor).

The more sensitive the sensor to reflected light, the more accurate it will locate a point on the part.  Our highest accuracy machines (Model 50C , Model 600C and Model 150C ) use a confocal optics sensor because it is accurate even when the reflected light is low.  It's 10 times better than our Model 50L that uses a laser triangulation sensor.  We can usually measure machined and black surfaces that are less than 45 degrees from perpendicular and get a point accuracy of +/- 10 microns.  If surfaces are too shiny or too black, our 4 and 5 axis machines can adjust to be more perpendicular to a surface, capturing more reflected light.  It takes longer, but we get better measurements.

5.   How do you measure dimensons from a datacloud?
We get dimensional accuracy by averaging points on each part surface used.  Our sensor typically gets a thousand points on each part surface, each point accurate to +/-10 microns.  Suppose those points are from a plane. We do a least squares fit of all thousand points to find that plane's 3D location.  As on a CMM, the more points that define that plane, the more accurate we know it's location.  With a thousand points on a plane, we can find the 3D location of the plane to a few microns.

Once you've located a second plane the same way, you can find the distance between them, a length dimension.  If you find the angle between them, that's an angular dimension.  If it's a hole and you least squares fit a cylinder to that hole, then you know the hole's diameter and its center location.  Finding the distance between that hole and a plane is a calculation using solid model geometry -- just like your 3D CAD software does.  And remember, the location of each solid model surface is ten times more accurate than any point in its datacloud.

Even if the sensor is accurate to +/- 10 microns, averaging a thousand points won't help unless you know very accurately where the sensor is and where it's pointing.  We use servo stages with glass scales that are accurate to a few microns.  Then we calibrate the machine -- much like a CMM is calibrated at the factory -- to be sure that every point in the inspection volume is accurate.  Not just repeatable, but accurate.

6.   Must the machine be in a temperature controlled room?
CAItech's patented software uses "3D fiducials" to compensate for changing shop temperature.  3D fiducials are portions of the part holding fixture that we can locate accurately in three dimensions.  We scan these fiducials when a part is first set up (see SETUP PHASE of Example ).   Since we get over a thousand points from each fiducial, we can locate the fixture with micron accuracy.

Later during an inspection, these fiducials are automatically rescanned.  We determine their new location and orientation in a few seconds before each new part inspection.  In software we adjust the fixture's new location and orientation to be the same as it was during setup.  Inspection datapoints then become relative to the fixture, not to the sensor (which has shifted its location due to temperature distortion).  It gives accurate compensation to changing shop temperatures.

7.   Can the machine inspect as well as a touch probe?
An optical sensor can't measure a cavity that's filled with oil and it can't measure transparent surfaces like a touch probe can.  On the other hand, it can measure fragile or deformable surfaces that a touch probe can't.  See Figure 5, Lead Coplanarity, Model 50C - Applications ).  And it can measure small fillets that would challenge touch probes.

A good rule of thumb is that an optical sensor can measure any surface that you can see with your eye.  Your eye works the same way as the sensor: light reflected from the part's surface determines its shape.  Even surfaces that are partly obstructed can be readily measured.  See Figure 3, Pin Bore Groove, Model 150C - Applications for an example of measuring a surface that can't be seen completely.

8.   Can it measure hole depth?
The confocal optics sensor of our newest inspection machines measure coaxially.  That means the measuring is done in the same direction as the sensing beam, not from an off-axis angle as in a triangulation sensor.  With a 5-axis motion system (Model 150C ), the sensing beam can be moved to look down into holes.  Hole depth can be measured accurately so long as the hole is no deeper than about 10-15 diameters.

9.   How many dimensions can you inspect?
Our patented software is not limited by the number of dimensions that can be inspected.  For first-article inspection, hundreds of dimensions on a part can be determined.  For more details see Figure 12 (INSPECTION PHASE, Example ).

However, most applications of our machines are for in-process inspection.  The emphasis is on quickly inspecting many parts rather than checking one part for many dimensions.  For example, a machinist may want to check a part after he removes it from an NC machine tool to be sure a few critical dimensions are still in tolerance.  He wants to detect errors such as a broken bit or a mis-fixtured part before more value is added to the part.