Strain your brain. How do you calculate acceleration?

[jstolaruk]

O/T CMMs

CMM's are typically maintained in controlled environments, temp. and humidity. Smaller units are attached to granite bases that have a very low temperature coefficient and high themal enertia. CMMs should be calibrated at least once a year and their "maps" of actual position in all axises are updated using laser inteferometers or similar instruments to achieve the desired volumetric accuracy. Most are servo controlled with linear scale feedbacks.

Mfgs are Browne & Sharpe, Zeiss, Mitutoyo, etc.. Renishaw is the most popular touch probe brand.

 

[Terry Woods]

This is for the "kids"... so I'll let it go.

Good to hear someone mentioned the Jerk issue.

"da/dt" can be a son of... some guy from... Oregon, Illinois, Iowa, or maybe Wisconsin, or some such.

So... what do you call... "dj/dt"?

It must have something to do with how quickly a radically changing factor can change more radically yet again.

 

[PhilipW]

Peter,

Is there some angle here...if you have both a position and aceleration sensors, that the resolution of the position sensor could be considerably relaxed. The dollars not spent on a super high resolution position sensor might go someway towards paying for the acelerometer?

 

[CroCop]

This is for the "kids"... so I'll let it go.

Good to hear someone mentioned the Jerk issue.

"da/dt" can be a son of... some guy from... Oregon, Illinois, Iowa, or maybe Wisconsin, or some such.

So... what do you call... "dj/dt"?

It must have something to do with how quickly a radically changing factor can change more radically yet again.

There is no universally accepted name for the fourth derivative, i.e. the rate of change of jerk, The term jounce has been used but it has the drawback of using the same initial letter as jerk so it is not clear which symbol to use. Another less serious suggestion is snap (symbol s), crackle (symbol c) and pop (symbol p) for the 4th, 5th and 6th derivatives respectively. Higher derivatives do not yet have names because they do not come up very often.

http://math.ucr.edu/home/baez/physics/General/jerk.html

 

[Peter Nachtwey]

Oddly enough

Is there some angle here...if you have both a position and aceleration sensors, that the resolution of the position sensor could be considerably relaxed. The dollars not spent on a super high resolution position sensor might go someway towards paying for the acelerometer?

You are right about not needing the super high resolution feedback unless it is needed for final static position control when an accelerometer is available. However, in many cases the higher resolution doesn't cost that much more if any more. I see the main issue is that a simple PID can't be used.

One should expect to pay more for the feedback devices for high performance systems where calculating the acceleration and jerk are necessary.

Snap, crackle and pop. Sounds ok but the s in snap would be confused with the s in laplace transforms.

 

[Rick Densing]

No one seems to care so I will end this here.

Peter,
Your window for answering was from 12:16am till 1pm CST on a Sunday.

I was actually thinking about your question as I lay in bed last night. Don't give up so soon.

 

[Rick Densing]

jstolaruk, that is some machine if it can measure accurately. I wonder how they compensate for the thermal expansion and all the slop in the joints?

To expand, some CMM's measure to the millionths of an inch. We sometimes have to hold tolerances in the ten-thounsandths of an inch, so at min they need to be an order of magnitude better.

The probe that actually touches the part us usually an industrial gem or other stable crystal.