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# Curve by equation (again)

## Curve by equation (again)

(OP)
Refering to back to a previous thread regarding creating a curve by equation.  After sorting out my problems with basic mathmatics I eventually got something similiar to what I was after, however I am a bit confused as to how pro is treating the values in the equations.

If I use microsoft excel to plot the curve according to a set of parameters I get one result, then i use pro with exactly the same equation and parameters I get a differnt result.  It is as if the units are different.

Can any body shine any light on this matter

kind regards

Dav

### RE: Curve by equation (again)

Dave,

If you could give us a little more background on how you have this setup thus far in Pro/e.  I would assume you are using a graph and trajpar to help with the curve?

Best Regards,

Heckler
Sr. Mechanical Engineer
SW2005 SP 2.0 & Pro/E 2001
Dell Precision 370
P4 3.6 GHz, 1GB RAM
XP Pro SP2.0
o
_`\(,_
(_)/ (_)

Do you trust your intuition or go with the flow?

### RE: Curve by equation (again)

(OP)
I am using a curve by equation method, using cartesian type coords system.  The equation for the curve is as follows: The curve is called a trochoid see http://mathworld.wolfram.com/Trochoid.html
for an explanation of the shape

/* ENTER TOOL STEP OVER
SO = 0.5
/* EMPIRICAL VALUE TO CORRECT SHAPE ERROR
SF = 0.0175
/* ENTER PROFILE ALLOWANCE
PA = 0.1
/* ENTER TOOL CUTTER DIAMETER
CD = 10
/* ENTER SLOT WIDTH
SW = 12.7
/* ENTER NUMBER OF REVOLUTIONS
N = 100

A = ( ( SO * SF ) / 3.141592654 ) / 2
B = ( ( SW - ( 2 * PA ) ) - CD ) / 2

x = ( A * ( t * N * 360 )) - ( B * sin ( t * N * 360 ) )
y = ( B * cos ( t * N * 360 ))
z = 0

The curve is going to act as tool path for milling cutter to follow.  If you use the same equations in Excel but remove the 'SF' term, you get what I think is the correct result, however when enter it in pro you get the wrong result.  This is why I have added the 'SF' term in the equation for 'A'

Cheers

Dav

### RE: Curve by equation (again)

I don't know if this will help (or if it's even correct).

/* (b > a) PROLATE CYCLOID
/* (b = a) CYCLOID
/* (b < a) CURTATE CYCLOID
/*
/* Curve originates on csys.
/* Extends +x (mainly for Prolate), +y.
/*
/* --------------------------------------------------------------------

ra = 4 /* radial segment a.
rb = 4 /* radial segment b.

/* Describe the reference circle center total translation; e.g. circumference.
c_ref = 2 * PI * ra

/* Describe the position of ref circle center as a function of t.
x_ref = t * c_ref

/* Describe reference circle, radial vector rotation at that (t) point.
ref_angle = 360 * (x_ref / c_ref)

/* Describe the angle with respect to csys.
/* (Initial vector direction is 6 o'clock ref csys.)
angle_wrt_csys = 270 - ref_angle

/* Define point rb x,y with respect to ref circle center (at t).
rbx_ref = rb * cos(angle_wrt_csys)
rby_ref = rb * sin(angle_wrt_csys)

/* Describe point with respect to csys.
rbx = x_ref + rbx_ref
rby = rb + rby_ref /* reference circle origin is x = 0, y = rb.

/* Assign the values.
x = rbx
y = rby
z = 0

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