FB: re: cam testing setup..
Looks nice, but without knowing exactly how it works, and being unable to grasp it and get a feel of its rigidity, the skinny prong that serves as a rest stop for the (I assume) angular encoder looks kind of flexible. Is it stiff enough to accurately resolve the angular positions? What sort of angular resolution is obtained? Does the “encoder” also drive rotation of the cam or is it rotated manually?
On the other end, how about a little description of the cam “follower” assembly, below the LVDT? Looks like some sort of physical contacter. Is it “sharp” or radiused, and will it give a true profile if radiused? Can lobe phase angles also be determined by moving it to another cam?
Just curious.
IO,
Over the last 25 years or so, I've used several "cam checker" set-ups. They have varied from the original low priced, entry level "Cam Doctor" (~ $4K and needed a desktop), up to and including an Andrews Products fully automated EZCAM M52 (?) (I don't know the cost on this, but it was at a professional level race team) which is/was "state of the art". It also required a dedicated desktop. I've posted the photos of my current Performance Trends "Cam Analyzer" (~ $4K, but can be attached to a laptop.) I've also spent a lot of time accumulating and processing data by hand. My thoughts follow.
Some facts I know about encoder resolution:My original Cam Doctor: Linear resolution: +/- .00025" Rotary resolution: +/- .1 degree Fixture: Anodised aluminum plate, reasonably stable.
Andrews EZCAM: " unknown " unknown BUT, both were very good and state of the art. Cam mfg quality.
Fixture: Granite base and tool steel, very stable.
My current Cam Analyst: " +/- .000030" " +/- .01 degree Fixture: Anodised aluminum extrusions, reasonably stable.
http://www.andrewsproducts.com/camshaft-inspection/ezcam-details-softwareAnswers to your questions: (Sorry for the cut and paste, but I'm still a slow and crappy typist . . . . .)Looks nice, but without knowing exactly how it works, and being unable to grasp it and get a feel of its rigidity, the skinny prong that serves as a rest stop for the (I assume) angular encoder looks kind of flexible. Is it stiff enough to accurately resolve the angular positions?
Yes, but you definitely need to pay attention to this on this fixture.What sort of angular resolution is obtained? Does the “encoder” also drive rotation of the cam or is it rotated manually?
The angular resolution is very high. Manual cam rotation drives the encoder, but there is a motorized option to turn the cam for an additional $1800.On the other end, how about a little description of the cam “follower” assembly, below the LVDT? Looks like some sort of physical contacter. Is it “sharp” or radiused, and will it give a true profile if radiused?
There are several follower "options" from Perf Trends and you have the ability to produce a follower precisely to mimic the ones used in the application. The one in the photos is a PT item with a .75" diameter ball to mimic a .75" roller wheel. I also have PT's "virtual" flat follower. I'm planning to machine some application specific followers for certain engines I work with. The follower must match what is used in the application to produce an accurate profile of cam/valve motion in use. This accuracy may not be necessary when just "comparing" cam lobes, but this is a judgment call that cam mfg's hate.Can lobe phase angles also be determined by moving it to another cam?
Lobe phasing can be accurately determined on ONE cam where the rotary encoder is not moved. When comparing from cam to cam, the rotary indexing is re-initialized, typically referencing the centerline of the #1 intake lobe. Phasing comparisons are then accurate from cam to cam.
My overall thoughts:A/ If I was manufacturing cams, I would want the highest resolution and stability possible. As in "rock solid". This is the route mfg's take, as well they should.
2/ Erratic rotary motion can affect measurement quality, especially the derivatives. Ie, velocity, acceleration and jerk. USUALLY, the software has some setting for filtering erratic motion, but this defeats accuracy. The trick is to have even rotary motion, (however it is achieved) and linear sampling at high rotary rates of data accumulation, say, 100 samples per degree. Since all the software "smoothes" the data, more data points is better than less.
d/ Since what I'm doing is checking/identifying what a cam is, the most important aspect to me, and perhaps others in this situation, is repeatability. Currently, I can remove and reset and re-test a cam and get results within .0005" for lift and .1 degree for duration. I find this acceptable for my purposes. In communications with cam mfg's I know and use, the data I generate matches the data they generate within the specs I listed on the same sample cam.
z/ Any of these fixtures produces data far more easily and far more accurately than trying to accumulate this type of data by hand. As discussed way back in this thread, even large diameter degree wheels and high resolution dial indicators leave something to be desired. Since I pulled the trigger on this fixture, I've had the opportunity to re-measure some of the cams I had "profiled" by hand. Understandably, the results from the fixture are far more accurate than the "by hand" data, especially for the derivatives. Since this is important to some of the analysis I'm doing, this dictates which direction I need to take. Others may choose differently, depending on their needs.
Yes, I think $4K systems are inferior to $25K systems, but as long as the fixture is not "flimsy", I expect "usable" results can be generated, depending on the operator. ALL these setups use commercially available rotary and linear encoders and the ones used by PT are similar to the ones used by Comp Cams and Andrews Products. The talent of the operator, the quality of the encoders, and the software manipulation of the data are the key issues.
So you pay your money and take your choice . . . . . . . .
Fordboy
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