Inventor General Discussion

Inventor General Discussion

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*Expert Elite*
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Registered: ‎04-27-2005
Post 11 of 24

Re: Equation driven curve - unit error

11-27-2013 07:55 PM in reply to: 19112033

Max,

After I looked at what Glen worked out, it appears that a portion of your formula is outside the range of -1 to +1,

 

In the (1-2*x/50) portion.... if x>0, then this would be greater than 1 and can't be evaluated.

 

Kirk

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Registered: ‎11-23-2013
Post 12 of 24

Re: Equation driven curve - unit error

11-28-2013 05:36 AM in reply to: karthur1

Thank you all for your replies. This is a really professional forum with great members.

 


karthur1 wrote:

Max,

After I looked at what Glen worked out, it appears that a portion of your formula is outside the range of -1 to +1,

 

In the (1-2*x/50) portion.... if x>0, then this would be greater than 1 and can't be evaluated.

 

Kirk


Well, if I insert 1 for x in this portion, the result is 0.96. If I insert 50, the result is 0.6. So all this should be in the possible range of -1 to +1. 

And you can calculate the arccos of 0.96 without problems, it's around 16.3. 

 

Could you explain to me how you came to the conclusion, that if you insert a value for x>0, you will get a result greater than 1?

 

Thanking you for your help,

Max

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Post 13 of 24

Re: Equation driven curve - unit error

11-28-2013 07:29 AM in reply to: 19112033

Max,

I made an error... if x<0 then the formula is greater than +1, which is outside the range of ACOS.

 

Kirk

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Registered: ‎11-23-2013
Post 14 of 24

Re: Equation driven curve - unit error

11-28-2013 11:41 AM in reply to: karthur1

No problem, nobody's perfect.

 

I've set the boundaries from xmin=0 to xmax=50, so there should be no negative value for x. So this part of the equation should not cause the error present in inventor. But what does? I can easily plot the function outside of autodesk, so the equation itself shouldn't be the problem. Even when I'm including dimensions, I get an error concerning the computation of the arcsine, complaining that something is out of the boundary range... But I can't find evidence for that.

 

I'm still unsure weather it is a problem with autodesk or with my equation.

 

Maybe I should note, that I can use this equation in other CAD programs, but can't get it to work with Inventor.

 

Looking forward to an answer,

Max

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Post 15 of 24

Re: Equation driven curve - unit error

11-28-2013 11:59 AM in reply to: 19112033

See the last message on the end of the first page ...  GlennChun wrote:

 


 

Once the tmin and tmax are changed to -1 and 1, respectively, Inventor shows an error message:

 

acos_bug.png

 

I'm logging a defect against the above issue in ACOS and ASIN.  Defect number is 1510653.

 


 

So it seems that it is a problem with Inventor and not necessarily with your equation.

 

HTH

 

 

 

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Post 16 of 24

Re: Equation driven curve - unit error

11-28-2013 01:21 PM in reply to: 19112033

Hi Max,

 

The Equation Curve command in Inventor does not take -1 or 1 as an input for the acos or asin function.  I logged a defect (1510653) yesterday against this issue.  The valid input values should be in the range of [-1, 1], but the Equation Curve command currently takes (-1, 1).

 

Since you set xmin to 0 and xmax to 50, the input for your acos, 1-2*x/50, ranges from 1 to -1, which are perfectly valid.  However, an error occurred in Inventor due to the defect in the Equation Curve command.  A workaround is that you set xmin to 0.000001 and xmax to 49.999999 so that the input for your acos can range from 0.999... to -0.999...  I recommend to define a user parameter for the tolerance in the Parameters dialog:

 

workaround_for_acos_asin_boundaries.png

 

Glenn

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Post 17 of 24

Re: Equation driven curve - unit error

11-28-2013 05:59 PM in reply to: GlennChun

Glen,

I was looking at this equation again. In the equation that the OP gave, he used a "length" variable in teh ACOS(x) function.  I noticed that you went ahead and substituted a hard number there (50mm). I was trying to work this out using the "length" variable and could not get it to work.  I noticed that when the length variable is <10, the function fails.  If I put 9.9mm in the denominator, I get this error.  Can you explain why?

 

2013-11-28_1945.png

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Post 18 of 24

Re: Equation driven curve - unit error

11-28-2013 07:27 PM in reply to: 19112033

Max,

Here is a part that has your equation in it.  How does this compare to the results you were getting in the other grapher? 

 

No guarantee that this is 100% correct, but it does plot.

 

The length and width are user parameters that you can change.  In order for this to workthe length>50.  It also fails if the height is =1.0mm

 

Kirk

 

2013-11-28_2113.png

 

 

 

 

Employee
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Post 19 of 24

Re: Equation driven curve - unit error

11-28-2013 09:11 PM in reply to: karthur1

Hi Kirk,

 

In each of the attached parts, I added a variable 'length' in the Parameters and initially set it to 50.  The equation curve is correctly plotted when I changed the length to any positive number, such as 100, 10, 9.9, 5, and 1.

 

Explicit

 

length in mm

tol: 0.000001 mm

 

y(x):  acos(1 ul - 2 ul * x / length) / 1 rad

 

xmin:  tol

xmax: length - tol

 

Parametric

 

length in ul

tol: 0.000001 ul

 

x(t):  t

y(t):  acos(1 ul - 2 ul * t / length) / 1 rad

 

tmin:  tol

tmax:  length - tol

 

 

The length of the curve in Y direction is always 1.  The length of the curve in X direction is the value of the variable 'length' (more precisely, 'length' - 2 * tol).

 

Glenn

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Post 20 of 24

Re: Equation driven curve - unit error

11-29-2013 06:35 AM in reply to: karthur1

Hi Glenn,

I used length, defined in Inventor as 50mm, as a placeholder for the value 50. Since I didn't want to mess around with the units, I repalced it with a hard value.

 

So, when I plot the function in a normal plotter, I get this result, which is as it should be:

plot.PNG

 

So I don't understand how you get these crazy shaped curves in the posts above.

 

Thank you for your help so far,

Max

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