Date: Oct. 21, 1994

Project: DEIMOS

Author: Bill Shepard, Sr. Development Engineer

RE: Slit-Mask "Cutter"

RFO: Laser Based. Slit Mask Machining Tool

The intent of this document is to provide the information required by vendors to produce a quote for a Slit-Mask "Cutter", primarily with laser based technology in mind. The following major areas must be addressed:

1 Task Description

The Slit-Mask Cutter will be used to process Slit-Masks by making the following:

In other words, pre-processed slit-masks are brought to the slit-mask "cutter", set up and then the above user defined characteristics are added to produce the completed slit-masks. The machine must be able to produce 10 masks in one 8 hour shift.

The following are also required as defined in the sections below; --capability for electronics interfacing or slit-mask "handler interfacing" --throughput rate for the overall process including the production of several slit-masks and set up time for each mask in a production-like manner.

1.1 Slit Mask

A sample slit-mask is illustrated in the attached drawing, D1705.A.

a.The overall area that may require cutting or milling is 29" by 10" by 2" in the z-axis.
b.The mask itself consists of 4 pre-mounted sheets of 0.003" thick, #304 stainless steel.
c.The spherical surface (R= 83.6") of this "bumped" stainless steel will be within +/- 0.015" of a true sphere.
d.The masks are not re-usable; we will not cut the sheet metal, remove a sheet from a mask frame, and then attempt to re-install a pre-cut piece of sheet metal.

NOTE: We will consider alternative materials to the 0.003 thick stainless steel if the mechanical and optical properties (and cost) can be discussed and evaluated before hand.

1.2 Slitlets

a. A typical slitlet will be a 0.029" x 0.43" rectangular aperture. Another is 0.015" x 0.4".
b. The aperture tolerance is to be 1% on the width; +/- 0.00015"(7 um) worst case. Within +/-0.1% is a desired tolerance (not required).
c. Center to center spacing of the slitlets in the direction of the closer centers is to be +1-0.0005". More tolerance is allowed in the perpendicular axis (about 10 times).
d. The Cutter should be able to produce slitlets of arbitrary shapes; e.g. tilted slitlets, curved slitlets, and other shapes.
e. Absolute location repeatability (precision) along the 10" mask cutting/milling dimension is +/-0.0005". The 29" axis precision is 10 times this: +/-0.005".

1.3 Alignment

One or two small holes for alignment purposes may be required. These may be treated as additional slitlets on the mask with the capability to orient one slitlet perpendicular to the other. Alignment method for each mask must allow for the future plan to fully automate the process -- (via the handler interface).

1.4Mask Identification

a. The machine must be able to produce at least 10 unique identifying marks or patterns of holes that can readily be identified by the operator.
b. The mask identification must also be simply & cost effectively machine readable. One acceptable scheme is to use groups of up to four slits or holes to form a binary ID.

1.5 Handler Interface

The electronics controls needed to perform the following will be required:

a. start the cutting process,
b. select and/or load a program to process a different mask,
c. stop the cutting process,
d. shut off the beam for laser interlocking
e. whatever else required to fully automate the processing of 10 masks (in one shift)
f. the program input to the slit-mask cutter must accept HPGL &/or DXF formats.

By "handler interface", a set of electronic 110 signal lines are expected to be provided by the vendor. Opto-isolated inputs & outputs are preferred. Some beginning & end of shift operator tasks may be required even with the fully automated mode of operation. For example, this might include: check cooling water, turn on system power, turn on lamp power, start up some control program at the user interface of the mask-cutter.

The requirement of the fully automated running capability is to enable the basic system to complete a shift of 10 masks without any human intervention after some initial standard operating procedure and before some final operating procedures at the end of the shift. The handler interface to enable this mode is the vendor's responsibility and the actual mask handler with inputs for the interface is UCO/Lick Observatory's responsibility.

Documentation for all handler interfacing and instrumentation/controls electronics shall be included. The intent here is to enable design interfacing, troubleshooting, and maintenance planning as well as implementation. This should include:

a. schematics to the component level for all assemblies designed, fabricated, or otherwise assembled by the laser system vendor.
b. latter logic diagrams/schematics for any discrete relay logic controls - AC and/or DC.
c. latter logic diagrams/schematics or source code equivalents for Programmable Logic Controllers, or similar devices.
d. all available manuals and/or schematics from second source vendors
e. motor controller parameters, code, and/or schematics depending on whether hardware or software controls are used.

1.6 Throughput Rate

a. Ten masks must be completed within a single 8 hour shift (including set up, etc.)
b. Completing 10 masks within a 6 hour shift is desired.

2 Operator/Machine Environment

The typical operator will have no special training with the use of laser equipment. Many operators will be occasional users of the system. While some advanced programming interface capabilities are desired, a user friendly interfaceP'GUI" is also preferred.

2.1 Normal Operation

The system will be used on a daily bases to produce 10 masks at a time. The masks are for installation and loading into the telescope instrumentation immediately after completion on site. Operator required procedures such as wiping off debris or poking out any residual material by hand is highly undesirable and will probably lead to the selection of an alternative process.

2.2 Standard Maintenance

Since a single observing date is planned well in advance, the loss of a few hours of nighttime observing time is a major failure and the loss of a full day is catastrophic.

a. We want to know what Maintenance contracts are available.
b. We want to know what maintenance training is available to best equip local technicians to deal with scheduled and unscheduled maintenance.
c. We require a maintenance schedule covering a 1 year period.
d. We desire anticipated maintenance for 3 to 7 years after commission.

2.3 Laser Safety

a. A class I enclosure will be required. (delivery will be with this fully installed).
b. The enclosure must be removable to allow future plans to add on an automated mask handling device.
c. We must be equipped for class IV operation including goggles and other recommended equipment.
d. We want information on training for class W operation and maintenance.

2.4 Weather/Altitude Conditions

The machine will be operated and maintained in Mauna Kea, Hawaii at approximately 14,000 ft. above sea level - at the Keck Observatory. Where or if applicable, options such as high altitude brushes will be required (for dc motors with brushes). The weather is mostly consistent throughout the year, at about 0 Deg. Centigrade. However, we can readily provide water that is as warm as about 20 Deg. Centigrade, (if necessary).

2.5 Reliability/Down Time

a. Reliability is very critical. We require Mean Time Between Failure data for standard maintenance items and any critical system components needed to keep the system on line.
b. Reliable early warning/notice system for scheduled and/or unscheduled maintenance is strongly desired wherever possible.
c. We require sample reliability data from customers with similar systems/applications. Quantitative data such as percentage of actual down time against planned usage is preferred.
d. References to customers with similar applications are also strongly desired.

NOTE: "Similar applications" here refers to the task of cutting 0.003" sheet metal &/or cutting optically critical apertures out of a large spherical surface, etc. (The customer need not be using the system for telescopes or observatory instrumentation.)

3 Facilties

Facilities requirements for our intended site are required to ensure that we can begin using the machine as soon as possible after it is installed.

3.1 Electrical

a. We need to know what line voltages are required and what currents or KVA rating is required by the system.
b. Special filtering and/or isolation requirements or recommendations are also required.

3.2 Cooling

Cooled water is readily available for system cooling. We will need to know the temperature, flow rate, and BTU/hr required.

4 Samples/Process Demonstration

We will provide a small sample of "bumped" stainless steel to test the process. The vendor will then produce a sample subset with about 18 slitlets and a record of timing data & machine parameters used to produce it. Any options/special equipment such as "auto focus" required to achieve the desired results should be used for the sample. If not this should be noted and explained.

Areas of particular concern are as follows:

a. potential impact of the variations from a true sphere (+/-.015") on the ability to cut.
b. reliability of achieving the throughput rate - this may depend on the process.
c. distortion of the surface as a result of the particular laser process.

The sample will be used to demonstrate that the proposed process can achieve the desired results as outlined here, regardless of these concerns.