Thanks John,

We had some hall sensors that were placed properly on the PCB but when we
imported the Pick and place files into solid edge to create a 3D model and
mechanical check the halls we not placed correctly.  It turns out that
because of the part rotation on the PCB, protels calculated generated mid
x,y was different than my ref x,y (which is the center of the part).


-----Original Message-----
From: John A. Ross [Design] [mailto:[EMAIL PROTECTED]
Sent: Monday, August 25, 2003 1:47 PM
To: Protel EDA Forum
Subject: Re: [PEDA] Geometric Center

> -----Original Message-----
> From: Tim Fifield [mailto:[EMAIL PROTECTED]
> Sent: Monday, August 25, 2003 4:28 PM
> To: Protel EDA Forum
> Subject: [PEDA] Geometric Center
> Does anybody know how Protel 99SE calculates the geometric
> center (Mid x,y) in the pick and place files?


As far as I am aware the midx, midy co-ordinates are a re-calculated
'center' based on a boundary box around the extremities of the
electrical primitives for that part.

Same way as the center is calculated within the lib editor when you ask
it to set the component origin at 'center'

You can see the difference in the placement files, as components with
the origin already set as center in the library will have matching
values in the fields midx,midy & refx,refy, but parts with the origin
set at say pin 1, will have offset values in these fields.

Hence the reason parts like D2PAK/TO252/263 parts usually need a
'tweaked' offset in the library so that you can use the refx,refy values
in preference to the midx,midy ones.

If you use library parts with correctly set origins (mostly center is
fine) then you may find that the refx,refy columns are better to use
than the midx,midy ones.

Also watch the rotation values as they can cause some issues with post
processors for placement machines with their use of 0/360 deg values
which on some machines I have seen resulting in unnecessary head
rotations causing quite a delay on some multi head placement machines.

The rotation info is also handled worse if the library part orientation
is not already matched up with the part rotation as it rests in the
feeder pocket.

Still never figured out why it was names pick & place output as the file
contains no pick relevant information at all...

Hope this helps in some way.

Best Regards

John A. Ross

RSD Communications ltd

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