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- Equation driven curve - unit error

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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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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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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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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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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:

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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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:

Glenn

Autodesk T-Splines Component Development

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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?

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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 work, the length>50. It also fails if the height is =1.0mm

Kirk

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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

Autodesk T-Splines Component Development

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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:

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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