8.1 Description and Requirements
The purpose of the SlitMask Cutter machine is to process a set of SlitMasks within an 8 hour shift. A night's set may contain up to 16 masks (8 each side). By "processing", we mean the cutting of small slitlets into the mask material. The processed SlitMasks must also be ready for immediate installation and use in the instrument; if the operator must wipe the SlitMasks clean after they are processed, this would be unacceptable. This is because of our plan to fully automate the process.
As part of the process automation, each mask will be uniquely identified using a machine readable identification code that is impressed by the SlitMask Cutter during fabrication.
In order to achieve these tasks with the requirements we have, laser machining technology appears to provide the best solution. The particulars of the process may vary, depending on which vendor is selected to provide the machine.
The vendor will provide the basic SlitMask Cutter and then UCO/Lick Observatory Engineering will design and fabricate the SlitMask handling machinery to fully automate the process. We have begun to select the vendor for the SlitMask Cutter by generating a Request For Quote (RFQ), which has been sent out to three companies that manufacture this type of equipment (refer to Appendix E). More on this is discussed in 8.3, SlitMask Cutter Specifications.
The goal is to be able to load an entire set of up to 16 masks in an automatic mask handling machine that would then insert each mask into the cutter and remove it when completed. We envision that this device would be closely modeled on the SlitMask Cassette Holder/Loader used in the DEIMOS instrument. The device for the SlitMask Cutter is called the SlitMask Cutter/Loader.
Note: The latest revision of the RFQ sent to vendors (Appendix E) refers to 10 masks
instead of 16 (a recent update).
8.2 SlitMask Processing
In the laser equipment industry, there are a variety of laser machining tools that are
intended for the same task as needed for DEIMOS. We have chosen the mask material
such that less powerful lasers would be required to cut the slitlets. The following descriptions indicate appropriate options for our task requirements.
Laser Engraving Machines: These machines typically employ water cooled YAG,
CO2, or YLF lasers. The laser beam is used to vaporize or discolor small areas of material
surfaces, which produces a visible mark for identification or other purposes. These systems can be powerful enough to vaporize steel material to depths as great as 5 or 6 mils.
In CW mode lasers, a small beam is focused on the material with diameter anywhere from
3 to 6 mils and a shallow "beam waist" or "depth of focus" which varies a lot depending
on the type of engraving desired. This focused spot is then moved around on the material
surface at high speeds to engrave the desired pattern; moving mirrors are used to steer the
beam. In TEA mode lasers, a large beam passes through a mask with the desired pattern
which may have diameters as large as 3 inches, and the entire pattern is impressed on the
material at once.
Laser Cutting Machines: These machines typically employ water cooled YAG or CO2
lasers with much greater output power than those of the laser engraving machines. The
systems have pulsed mode lasers that rapidly dump the entire power of the laser cavity and
recharge for the next pulse. The beam is focused at or near the material with cutting diameters ranging from 5 to 20 mils, and a very long "beam waist" is typical. Either the
focused beam is moved mechanically with a 2 to 5 axis output mechanism, or the part is
moved instead.
Micromachining Tools: These machines are a hybrid of the engraving and cutting
machines. Typically, more delicate materials are cut with CW lasers, and focused spot
sizes from about 3 mils or 75 µ down to 30 µ with a very shallow beam waist. These systems may employ water cooled lasers or more stable, diode pumped lasers which are air
cooled.
The vendors have a variety of different machines using one or more of the laser types
described above. The use of one of the above laser machines and lasers such as a CO2
Cutting Machine, YAG engraving machine, or a YLF micromachining tool, determines
the particular laser process. The vendors will use their experience with some subset of
these systems to determine the best process that will achieve our goals, as outlined in the
RFQ (Appendix E).
"Pre-processed" masks are the mask frames with bumped sheets of 3 mil thick steel
attached to the SlitMask Frame (refer to Figure 5.1). We plan to use the SlitMask Cutter
to process these pre-processed masks. The following is performed when a SlitMask is
"processed":
As noted the basic machine as we receive it from the vendor will be a semi-automatic
system that requires operator intervention to set up for each prerocessed SlitMask, load
and start the desired programs, and then remove the processed SlitMask. All the requirements will be met with this semi-automatic system with the exception that the operator
must manually load and unload each SlitMask as it is processed. The SlitMask handling
machinery that we construct will automate an entire lot of SlitMasks and will be a robotic
device similar to the device planned for the instrument itself (refer to Section 5.5, Mask
Cassette Holder/Loader).
8.3 SlitMask Cutter Specifications
The specifications for the basic SlitMask Cutter are included with in the RFQ (Appendix E Request For Quote). This RFQ has been sent out to three vendors, one of which has
already provided a quote based on an early version of the requirements not very different
than the current version (see Section 8.10, Commercial Options and Prices).
As a reference for the material of this section, we note the various safety classifications of laser systems that currently exist. There are four general class categories:
Our intent is to provide a general description of each laser class; therefore, the actual
power and energy threshold values are not given here. It is important to note that these
classifications apply to both a laser and a laser system. As a result of this, it is possible to
have a class IV laser, for example, that is enclosed in a light-tight enclosure in such a way
as to make the entire laser system a class I system. When certain maintenance functions
are performed on such systems, it may be necessary to treat them as class IV systems.
One of the most significant updates in our new requirements is for a removable class I
laser enclosure to be provided by the vendor (see Section 8.9, Costs). Shortly after the
system is installed by the vendor, it will be operated by users who are not operating the
laser equipment on a frequent or regular basis and who mostly do not have prior experience or training to operate class IV laser systems. Therefore, this is an important requirement.
The requirements for the SlitMask Cutter/Loader will be very similar to those for the
SlitMask Cassette Holder/Loader in DEIMOS. The most significant differences are the
additional requirement of a class I laser enclosure around the mechanism and a less stringent requirement on the z-axis location accuracy.
To facilitate the required preventive maintenance and service of the SlitMask Laser
Cutter, training is a key point. Since there will be a long time between the initial installation of the basic system in Santa Cruz and the final installation of the complete system in
Hawaii, we plan to have training sessions in two phases. The first phase is for the development use and maintenance in Santa Cruz, and the second phase is for the final installation in Hawaii. The first phase of training will be presented by the laser vendor to the Lick
development staff in Santa Cruz. The second phase will be presented by the laser vendor
and the Lick development staff to the appropriate staff in Hawaii. This is one budget item
that may not have been considered until now. Once a vendor is selected, we can determine
more accurately what this cost is.
8.4 Software, Interfacing, Data Files
The software for the operation of the SlitMask machine will depend on the particular
vendor selected. IBM PC compatible based user software is typical. DOS, Windows, and/
or OS2 based applications may run the SlitMask machine, depending on the vendor.
A remote handler interfacing to the Lick SlitMask Handler is included in the RFQ, and
we will clarify this as quotes are generated. Adequate documentation of the electronic
hardware and software protocol for this interface is a critical factor. We plan to review
these items carefully and as early as possible to ensure that we can achieve our goal with
the SlitMask Cutter/Loader.
We are looking at HPGL and DXF data file formats with a strong preference toward
HPGL to input the slitlet information graphically. HPGL is included in the ART quote.
Additional laser parameters will be stored by the SlitMask machine and may also be
remotely loadable (this has to be looked into more).
8.5 Archiving Issues/SlitMask Identification
The task here is to identify which SlitMasks have actually been loaded into the cassette without relying on human/operator record keeping. Two possible approaches are
being looked into for this at this time. In either case, a machine readable code is placed on
the SlitMask in such a way that it can be read while in the instrument and in place.
Binary Coded Machine Reading: Approximately 65,000 unique SlitMasks can be
identified with 16 positions (bits) where beams from 16 small light sources are either
reflected off of an unused portion of the SlitMask back to a detector or the light doesn't
adequately reach the detectors. Either holes in the SlitMask or engraved parts of the Slit-Mask surface could stop the light from triggering the detectors. At 16 new masks a night,
it would take at least 10 years to run out of unique identification codes.
Another approach is to identify each mask among the 16 masks processed that night.
(This requires only 4 bits.) Then each map of slits that is used to produce a mask is also
identified -- this would be simply the HPGL or DXF file name that is sent to the Cutter.
The Cutter would then send the nightly mask number (1 through 16) back to the telescope
computer along with the file name of the map used to cut the mask. The telescope computer then has the identification of the masks, but only after the Cutter confirms that it was
properly processed.
It will also be possible to write labels on masks that can be read by humans. Moving
the laser quickly will discolor the material without writing through, and arbitrary messages can be written.
8.6 Fabrication/Materials
Thus far, the pre-processed mask material planned is 0.003" thick #304 stainless steel
and this is a critical factor in determining the laser process of the SlitMask Cutter. At this
point we are also allowing the vendor to propose alternative materials if this can improve
reliability, throughput, or cost. The material for the frame that holds these sheets of steel
is not critical to the laser processing, (assuming the size or weight does not dramatically
increase).
The process to shape the steel to an 83.6" radius curvature is where the sheets are
"bumped" into shape. The process to form the spherical shape is important since this currently determines the +/- 0.015" tolerance on the spherical surface. If a vendor can propose
an alternative material, it may become cost effective to preform the material to the desired
spherical shape.
The cutter itself will be completely manufactured by the vendor. Depending on the
final laser process, compressed air or nitrogen may be required as well.
8.7 Mask Equipment at Other Observatories
At this time the CFH Telescope in Hawaii has a laser based SlitMask cutter manufactured by FLOROD, one of the three vendors that we have selected to generate a quote.
This equipment is for flat SlitMasks whereas ours have spherical surfaces. Since the laser
machines use a focussed beam this is important, depending on the particular laser process.
After discussing this with ART, they have added an autofocus option to their quote to handle this. FLOROD is aware of this difference and they expressed no concern over it. This
is because they plan to pivot the output beam about an 83.6" radius, and they plan to use a
cutter machine which has a longer beam waist than the micromachining tool that ART is
proposing.
8.8 Test Plan
8.8.1 Initial Vendor Tests
Tests have actually started as of 10/3/94 at each of the three vendors selected to provide quotes. These are their independent trials of the various laser technologies available
to each vendor and experimentation with the programming parameters used to cut 0.003"
thick steel sheets. At this point the vendor may decide to try alternative materials if this is
needed to meet our requirements. From these tests the vendors determine the best type of
laser and process, given their resources and experience, to generate a quote to meet our
requirements.
8.8.2 Sample/Process Demonstration Test
This test is intended to demonstrate that the basic system the vendor intends to sell us
is capable of meeting our requirements. We will provide sample sheets of the steel
"bumped" to the correct radius (83.6") -- these will be one of the four separate sheets used
to form the pre-processed SlitMask. The vendor will then set up this piece and produce
the required mask. Any deviations from the process they actually intend to provide will
be noted, and test data will be sent to us for evaluation along with the processed samples.
From these processed samples, our measurements, vendor data, and the written quote, we
will select the vendor. We do not plan to commit funds to a vendor until these test results
and accompanying information are evaluated.
8.8.3 Vendor Site Acceptance Test
This test is intended to verify that the basic system is fully meeting all requirements
before shipping from the vendor. We do not plan to allow shipping to occur until all
requirements are meet at the vendor site without any deviations from the final process; that
is, the system will not be shipped with any temporary solutions/fixes.
8.8.4 Initial Site Installation Test
This test is intended to verify that the basic system is performing as required after
shipping and installation at the UCO/Lick shops; the same procedures as those used at the
vendor site will be followed. This will determine that we can provide the required facility
hook-up to the machine and test the facility specifications which the vendor is required to
provide (see attached RFQ).
8.8.5 Commissioned Site Installation Tests
These tests are intended to verify fully automated system operation before and after
shipping to Hawaii. These will be similar to the two tests for the basic system (before and
after shipping). From a known operational status (before shipping), this will test the
Weather/Altitude requirement to ensure the capability to operate this system on Mauna
Kea.
Note: At this time it has not been determined if we will install the system on the summit or at Headquarters. A review of the advantages for each of these alternatives has yet
to be completed.
All of these tests need to be incorporated into the contract with the vendor once the
vendor is selected and the details of their quote are known.
8.9 Costs
As mentioned in 8.1.3, SlitMask Cutter Specifications, a quote has already been
obtained based on an early version of the requirements sent to ART. This original figure is
$127,000 (plus tax). Updates to requirements may result in a noticeable increase in this
figure as yet to be determined. From discussions with ART, this increase is anticipated to
be in the 15% to 40% range.
Typically, the cost impact of adding a class I enclosure can vary depending on the particular enclosure. More important than the material costs are the vendor costs involved to
ensure that class I operation is achieved. Within the next two weeks we should receive
actual quotes on this. Given our need for remote training (in Hawaii) in addition to the
factory training, along with the other updates in the requirements, we should anticipate a
figure as high as $200,000.
By designing and fabricating the SlitMask Cutter/Loader system ourselves, we will
shift a great deal of the costs from an external purchase of materials to internal labor
(without a vendor markup). For this task, this should work in our favor since we have the
engineering skills to handle this and similar requirements will exist for the SlitMask Cassette Holder/Loader. In practice, we will be able to use the prototype of the SlitMask Cassette Holder/Loader (which we will need to build anyway) as the SlitMask Cutter/Loader.
8.10 Commercial Options and Prices
The laser systems industry in general is not a very large one. These are also expensive
high-technology machines that do not have a large commercial market base. A number of
these companies have also gone out of business as a result of stiff competition and high
costs involved in manufacturing and supporting these types of products. The end result is
that there are not very many commercial options to choose from, and we need to look at
the stability of the vendor as well.
The following three vendors, each with locations in California, have been selected to
generate quotes:
8.10.1 ART
ART is the first company that we contacted. They are a small company with less than
10 employees and 6 years of company experience with laser technology. They specialize
in very high precision positioning stages and micromachining applications. The types of
laser systems they provide include those based on diode pumped YAG lasers and higher
powered, Q-Switched CW YAGs. They have already provided a quote based on earlier
system requirements that have changed some and are preparing an updated quote now.
ART is a relatively new and small company in this business, which makes them a
higher risk where company stability is concerned. Their high precision and micromachining expertise is a benefit when considering the precision and accuracy of slitlet placement
and the smoothness of the slitlet edges we require. However, it is more difficult to reliably
achieve our throughput requirements with the process they have chosen; at present their
throughput estimates are close to our tolerance.
8.10.2 Lumonics
Lumonics is one of the largest companies in this industry, and they have two centralized locations in the US including one in California, which has been in the laser business
for over 20 years (they have about 600 employees). Different divisions of the company
specialize in applications, including industrial laser cutting, laser engraving, and scientific
lasers. Lumonics has 3 other world-wide locations, and they are a fully owned subsidiary
of Sumitomo (a huge Japanese corporation). The types of laser systems they provide
include those based on TEA lasers, Q-Switched CW YAGs, Pulsed YAGs, CO2 lasers, and
others. The RFQ has been received and they will begin preparing a quote on 10/31/94.
Lumonics is a relatively large and experienced company in this business which makes
them a low risk where company stability is concerned. They do not specialize in the high
precision stages as ART does, but they have a great deal of experience in the level of precision that we require. Depending on the particular process they choose, there may be
some risk where smoothness of the slitlet edges is concerned. Their broad range of applications experience is also a benefit.
8.10.3 FLOROD
FLOROD has about 45 employees. They have been in the laser business for 20 years,
and they have provided a system for a very similar application in Hawaii, e.g., the CFH
SlitMask. This application was for a flat SlitMask -- more details on this have yet to be
researched. They specialize in laser cutting, precision resistor trimming systems, and
other applications. The types of lasers they provide include Q-Switched CW YAGs,
Pulsed YAGs, CO2 lasers, and others. They have begun preparing a quote now.
FLOROD is an experienced company in this business, but they are not very large
which makes them a medium risk where company stability is concerned. They have some
micromachining expertise with precision cutting expertise which is a benefit. The range
of applications experience they have is good match for the requirements we have, so this
can also be viewed as a benefit.
8.11 Major Challenges
The challenges for the SlitMask Cutter include:
1) Potential impact of the variations from a true sphere (+/- .015") on the ability to cut
reliably: With systems like that quoted by ART, a very short depth of focus makes this a
potential concern. They feel they have resolved this with a standard autofocus feature and
are not concerned; however, we need to ensure that this works reliably.
2) Reliability of achieving the throughput rate - this may depend on the process: The
ART system has to make three passes to cut through our material. Because we are close to
our tolerance here, we need to ensure that degradation of system performance, or additional time between processing masks does not lead to unacceptable throughput.
3) Distortion of the surface as a result of the particular laser process: Some of the
other laser processes involve more powerful lasers (for better throughput) and this may
lead to a concern that the surface may become distorted due to the greater power. If this
becomes a concern, at worst we will have to stick with the laser process we currently have
been quoted.
4) Damage to expensive components: One other potential concern is that there are
some expensive components in these lasers. With inexperienced operators there is some
risk of costly damage due to operator error. This concern can be minimized by taking precautions and ensuring that proper trained operators are always present when the machine
is used.
A potential concern for the SlitMask Cutter/Loader is:
5) Reliability in positioning the masks over time: This is a complicated robotic system and many factors of the design have yet to be determined. While this type of system
has not been designed at Lick before, it has been provided by robotics companies in large
automated factory applications. It is also a simplified version of the SlitMask Cassette
Holder/Loader in the instrument. The most important simplifying difference is that the z-axis placement is not a concern for this machinery because the laser cutter must deal with
this axis itself.
Note: The two approaches we have seen to deal with the z-axis placement are an autofocusing option and a combination of a pivoting output device with a long output beam
waist. (Refer to section 8.2, SlitMask Processing and 8.7, Mask Equipment at Other
Observatories for more details.)
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