# global equations slowing SW11 when used in constraint

Question asked by Philippe Vallee on Mar 1, 2012

Hi,

I draw lenses assembly (the lenses and their barrel) and I want my design to be as parametric as possible. In general, the lenses shape will slightly change over time until the design is frozen and sent to the machine shop. The barrel must follow the lens when they change. The way I do it is that I start with an empty assembly and build the lenses in context. Then I sketch the barrel around the lens.The way I dimension the barrels is such that if the lenses change slightly, the barrel will follow. But first I create a folder of equations, which should be called a folder of constant. Those constants define the lenses. For example, if I had two lens the equation folder of the assembly would look like :

"L1_R1" = 123.12

"L1_R2" =  345.89

"L1_DIA" = 120.00

"L1_TH" = 10.23

"L2_R1" = 100.11

"L2_R2" = 100.11

"L2_DIA" = 120.00

"L2_TH" = 14.00

"L1_L2" = 5

L1_R1 would define the radius of curvature of surface 1 of lens 1. L1_R2 would be the same but surface 2. L1_DIA would define the diameter of lens 1. Same thing for lens 2. L1_L2 would define the distance between lens 1 and lens 2.

Each lens is designed in context and is sketched using those "global equations". This works relatively well. But using global equation to constrain the lenses relatively to each other really slows things. My current design has 9 lenses. I'm at the point where all the lenses are designed and I want to build the barrel in context. But now drawing lines in context is painfully slow (I click and wait, then I can drag normally to draw a line, then I click to define the end of line and I wait again until I can drag again to another point.). To make things faster, I need to de-activate the equations relatively to the constraints ! Has anybody ever noticed that ?

Is using "many global constant equation" to drive a design something that make sense or should it be avoided ? Is there any other way ?