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RayCAD
Integration of optical and mechanical design
based on
AutoCAD |
General Concepts of RayCAD for AutoCAD
RayCAD
optical design software integrated with AutoCAD provides optical designers with the power and tools mechanical designers
have enjoyed for some time. Spreadsheet entry is replaced by simple CAD
commands such as Move, Rotate, Point and Drag. Packaging is enhanced
when optical components and actual ray traces are present in the
mechanical design. Implementing optical components as single surface
objects enables the creation of uncommon multi-surface components and
waveguides. A rendering feature converts surfaces and ray traces to
objects ready to be rendered providing a photorealistic presentation.
The
operation of RayCAD for AutoCAD is consistent with the way systems are drawn
and designed in AutoCAD. All of the familiar
commands like Move, Rotate, Stretch and many others are used to point
and drag surfaces and input rays into the configuration. For example, to
move an array of input rays that represent a light source off the
central axis, use the Stretch command and drag the whole array of input
rays to a new location (this is opposed to going to a spread sheet and
keying in a new starting point and angular directions for each of the
rays).
Optical
components and ray tracing are all done in 3D space as shown below.
AutoCAD's viewing and view ports, along with Dview, Zoom and
Orbit, are used to evaluate the ray traces. After placement of two or
more surfaces and two or more input rays, RayCAD for AutoCAD can run a ray trace.
The
computational portion of the program is written in C++. The range of
values of critical internal calculation is 1.2e± 4952 with 19 digits
accuracy. The root finder keeps solving for a zero root until less than
0.1e-15 is achieved. This portion is used for such tasks as calculating
surface to ray intersections, surface interactions (reflection,
refraction and diffraction), aperture openings, indexes, random ray
generations, etc. The heart of the program is in the ray to surface
intersection and interaction routines. 3D vector math is used
throughout.
The
algorithm used for ray to surface intersection varies depending upon the
surface type. In the case of a ray intersection with a swept surface
such as an aspheric, there must be a point on the ray and a point on the
curve when swept around the surface axis which must coincide. From the
perspective of a point on the surface being swept, the approaching ray
appears as a hyperbola. The ray equation described as such and the
aspheric equation is solved to find a common point. At that point, a
normal to the surface is generated.
Then,
depending on the type of surface encountered (reflection, refraction or
diffraction), the appropriate optical formula is applied using necessary
information like wavelength, index, diffraction order. This produces a
new ray start point with a direction determined by the optical
properties and surface shape. This process is then repeated for each
surface and starts over for each input ray generated.
Surface creation
A surface
is made, and edited, using a dialog box allowing a preview of the
curvature and also ensures that parameters are valid. For example,
generating a spherical surface using a one inch diameter and a radius
less than .5 will produce an error and the user is prompted with
suggestions to correct the problem.
Within
the dialog box, select curvature, diameter, holes, size, shape, provide
the radius and, in the case of an aspheric, eight coefficients.
Surfaces
can also be imported from a catalog of lenses (including aspherics) to
use as they are or those surfaces can be edited to suit. AutoCAD's Copy,
Mirror and Array commands can be used to multiply surfaces.
There are
three means of providing glass material. A catalog of glass material is
available using refractive index formulas to compute the index for a
particular wavelength. A second method is to supply a file containing
several wavelengths with associated indexes and a curve fit is performed
over a narrow range containing the desired wavelength. The third method
is a single wavelength and single index can be supplied "on the fly."
The
medium default is the index of air but can be modified if components are
operating in a different environment.
There is
also the ACAD Optical Object Modeling feature. 3D Objects, 3D
Faces, Edge, 3D Mesh, Revolved, Tabulated, Ruled and Edge Surfaces can
be grouped and assigned optical properties such as Glass Material,
Reflectivity or Opaque. These objects become optical components and are
intersected and ray traced like regular RayCAD for AutoCAD Surfaces
The
combination of RayCAD for AutoCAD's optical surfaces and the ability to change
mechanical objects drawn in AutoCAD into part of the optical design is
very powerful. Being able to turn covers, brackets, mounts, shafts,
bearings, etc. into reflectors or blockers is useful in analyzing for
stray light. Using these objects also means you can design optical
components with any shape and size required. They can be made out of
optical glass and will refract being wavelength specific like regular
optical components.
Source modeling
A source
is modeled using lines as vectors to provide a starting point and a
direction. Any number of lines can be gathered and serve as input rays.
Two input rays are sufficient for a ray trace and are also sufficient to
produce a random distributed generation of input rays and a grid trace
dividing the first surface into rows and columns.
Performing the ray trace as a grid is very useful since rays are
produced in an orderly row and column fashion and can clearly illustrate
aberrations and other distortions.
Operation
Ray
tracing can be either sequential or non-sequential. The ray tracing
command begins a search of the data base for blocks of surfaces and
looks up X Y Z location, rotation and twist. It will also read the
attributes for index data. After doing the calculations it returns X Y Z
coordinates representing ray to surface intersections. If a ray
intersects a surface, the point of intersection and the surface normal
at that point are calculated, and a new direction for the ray is
computed using appropriate refraction, diffraction or reflection.
Optimizing can fine tune the position and curvature of a surface or a
group of surfaces. Curvature optimizing will automatically adjust
curvature variables (i.e., radius, conic and aspheric constants) in an
attempt to bring two rays to a point. Positioning optimization will
automatically move a group of surfaces using a lead surface for its
direction in an attempt to bring two rays to a point or a parallel.
A command
titled Adjust provides a means of studying ray intersections. A
cross-sectional slice of rays can be viewed (preferably many rays) and
moved up and down along the normal of a selected surface clearly showing
the distribution of rays at that point. These cross-sections can also be
placed in separate views and each view is automatically updated when a
ray trace is performed.
Right:
Four views show slices of cross-sections of ray bundles taken from
Positions 1-4 as indicated
Also, a spot diagram can be projected onto any surface. Spot diagrams
help visualize the image quality. A large number of rays are traced in
either a random or grid formation to form spots on a selected surface.
There are
several ways to identify obstructed rays - by changing the color of rays
in question, by eliminating rays not in question, or by simply pointing
to rays and a grip mark identifies each intersection point. Since rays
are polylines, the polyedit command is also useful in allowing a
crosshair to be stepped through each intersection point.
It
takes very little effort to experiment. Each component is composed of
separate surfaces. You can combine several shapes, even surface types,
into one component. For example, a pentagon prism with some side
reflected, a beamsplitter in the middle, and a refractive grating on
another can be constructed. Caution is given - some creations may not be
able to be manufactured. Non-sequential ray trace is illustrated in the
image below which shows a ball and a hollow cone where rays are making
multiple bounces inside the ball and the close up of the cone
illustrates multiple bounces in the cone wall.
Each ray
keeps track of the medium it's in. If there is a near zero contact point
between two glass surfaces, the applied index will be the ratio of the
two glasses indexes, otherwise the ratio of the medium and the glass
index is used. The ratio order depends upon ray entering or exiting the
glass. The medium can be defined to be other than air.
All
optical surfaces and ray traces are created directly in AutoCAD,
therefore all familiar commands like Move, Rotate, Stretch,
Copy, Array and many others can be used to add and position surfaces
into the configuration the design requires. A ray trace can be performed
at any time.
Communication between
RayCAD for AutoCAD
and other optical software
The ZEMAX
Interface feature allows import and export of .ZMX optical data files
and glass index data.
RayCAD's
users who also use ZEMAX Optical Design Software or are working with
designers who work with ZEMAX had requested this interface. Using RayCAD
for AutoCAD for initial layout and idea generation, ZEMAX for critical optimization
and again RayCAD for final opto/mechanical packaging is a powerful
combination. It's ideal for the opto/mechanical designer who may
encounter existing ZEMAX designs or is interfacing with a ZEMAX user.
Client Communication
Pictorial
rendering is a powerful way of selling ideas through the development
cycle and a great way to view and approve a product long before
completion. The Render-Ready feature allows optical surfaces and ray
traces to be rendered for a picture perfect presentation. It's used with
a rendering package to simulate transparency, diffusion, reflection and
refraction of surface properties and to define shadows. The design is
rendered, complete with rays traced, to create a photorealistic picture.
Right: Pictures show optical and mechanical layouts modeled in
AutoCAD with RayCAD, then rendered.
Summary
The
concept of software add-ons is not new. Every package operating under
Windows is an add-on to Windows. It doesn't make any sense to design
Windows over and over again, and it doesn't make sense for an optical
design package to recreate a CAD environment.
There are
tremendous benefits from integrating optics and mechanics. Communication
between optical and mechanical designers, creativity enhancement,
increase in the number of people now having the ability to implement
optics in their design, and improvement in package design due to
integration are to cite just a few.
Being
able to create opto/mechanical designs in the AutoCAD environment is unique. The open architecture of AutoCAD allows a
designer the freedom to model just about anything and it's a tool that
allows the imagination to run free.
© 2015 RayCAD. All rights reserved.
AutoCAD is a registered
trademarks of Autodesk, Inc.
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