Two years ago, TeoSys Engineering LLC (www.teo-sys.com) and Photoscribe Technologies (www.photoscribetech.com) developed an Excimer laser-based diamond etching system. The deep UV, pulsed laser effectively delivers short bursts of energy, burning microscopic pits (1 to 2 microns deep) onto a gem's surface to form the markings. But its $300,000 price tag limited its use to major diamond labs.
Once the companies determined that a machine with a $100,000 price tag could open up a substantially larger market, particularly at shopping mall jewelry shops, the challenge was on for engineers: How to reduce the cost of the machine by two-thirds, while making it easy enough to use by people other than skilled technicians and without reducing its core capabilities. "This was an exciting opportunity for us. A lot of times engineers don't have the chance to make a system better," says Engineer Dana Church, co-founder of TeoSys. She has an MS in Computer Engineering from the National Technological University in Fort Collins, CO.
Church and Managing Partner Emre Teoman developed the LMS 5X0—a desktop-size machine they claim is the smallest Excimer laser micromachining system in the world—in just five months, an impressive time span given the engineering constraints. "It's relatively easy to build a machine of this type for sophisticated users, but it's much more difficult to make a machine that someone can learn to use in a few hours," says Teoman.
Leaving no stone unturned, literally, in their push to cut cost out of the design, the two engineers altered many facets, from switching to a less powerful laser to incorporating a low-cost illumination system and an air-filtering machine that can be bought in retail stores (see sidebar next page). While these design changes made a big dent in the overall budget (the laser by far is the biggest cost component), a redesign of the machine's motion system involved some of the most interesting engineering trade-offs.
The LMS-5X0 creates marks by moving the diamond in the X and Y axes while the laser, which remains fixed, is firing. Precise motion control is a necessity for etching lines less than 5 microns deep onto the gem's "girdle," a circle that surrounds the underside of the diamond. A goal of the etching process is to make marks that aren't discernable to the naked eye, so the lines are often faint. It's not unusual for gemologists to want them a bit darker, so the inscriber makes it possible to repeat the engraving process with such fine precision that the original lines are only made deeper, not wider. Coordinated motion is mandatory, particularly in the moves that involve circular interpolation and vector positioning.
The motion control system therefore had to deliver the required precision, but be cost effective enough to meet the pricing goals. Its predecessor, the LMS 2500, had a full servo control loop, using 2-mm, high-precision, ground ball screw stages driven by a brushless dc servo motor, encoder feedback, and control card capable of handling eight axes of motion. But the machine offered far more functionality than the low-cost 5X0 family needed. Not to mention a 4-inch travel distance.
Although the maximum speed of the servo motor used is 115 mm/sec, Church points out that the laser limits the frequency to 350 Hz, which translates to 350 microns per second. "Because our vectors are generally 50 microns or less, we usually do not even go that fast in our application. In fact, with acceleration and deceleration, we never even get to a speed of 200 microns per second."
A stepper motor (really a hybrid of a variable reluctance and a servo motor) looked like a winning alternative to the engineers. Given the extra poles, stepping motors can be used in simple open-loop control systems, yet achieve a level of accuracy and repeatability that is comparable to servo. In small frame sizes, stepper motors (including motor, cables, and drive) cost about one-half to one-third less than servos, says Rich Lenzing, a product manager for stepper motors at Danaher. "The real advantage is that engineers don't need to pay for a feedback device. Moreover, if you look at the servo motor applications that fail, it's typically because of the feedback. A stepper motor will have less than half the failure rate of a servo."
TeoSys engineers selected a 0.9° stepper motor (Oriental Motor) with a resolution of 800 steps/revolution for their low-cost design. An advantage of this motor type compared to the more common 1.8° stepper motor, says Nick Johantgen, engineering manager of stepper motors at Oriental, is the increased stiffness. "That means that it takes more force to twist the shaft from where it wants to be, which translates into greater positioning accuracy than a 1.8° stepper motor." He also notes that steppers are particularly appropriate for applications involving short moves. "Servos have all those gains and settling times, where as a stepping motor can move to the spot you want and position more quickly," he says.
Axes of Motion: In TeoSys' diamond marking machine, the laser remains stationary while the damond can be moved in three dimensions (rotational {theta}, X and Y). A 0.9 degree stepper motor with a resolution of 800 steps/revolution provides the necessary positioning accuracy and repeatability.
By combining the motor with a custom leadscrew and precision track roller guide block, Church says that engineers were able to achieve a resolution of 1.526 microns per step. Through experimentation, they determined that the repeatability is 1.5 to 2 microns over a travel distance of several millimeters.
Though this low-cost system does not have the repeatability of the higher-cost system, Church says that a tradeoff in speed allowed the system to achieve acceptable performance. "Because the marks we make are so small, we have to contend with rapid acceleration and deceleration. The faster we go, the more error we introduce, which we cannot compensate for without encoder feedback. But that's not a limiting factor, since we are laser-limited to 30 microns per second and the application involves very short vectors (< 25 microns). Our average character line width is 10 microns, so a 1.5 to 2 micron error when we remark a string of text is not significant."
Engineers do not expect that the fact the LMS 5X0 is slower than its predecessor will be a problem. "Most users don't want to do a diamond every 30 seconds, they're happy with 3-4 minutes. This is not like making doughnuts," Teoman says. He notes that slowing down the speed makes it possible to use less powerful lasers, which also help reduce expenses.
An economical motion controller (the DMC-1822 PCI controller by Galil) provides coordinated motion on two axes, though it can handle up to four axes. It provides both circular interpolation and vector positioning—crucial capabilities for etching precise circles, arcs, and other marks on the diamond. Configurable for either steppers or servos, the low-cost (approximately $895) PCI controller is based on a 32-bit Motorola 68331 processor. A key reason for picking the board is that it did not require servo loop control to provide the degree of repeatability that engineers were seeking.
"This PCI controller is one of our most popular control cards because of the acceptable trade-off in cost versus capabilities," says Lisa Wade, marketing vice president at Galil. "Even when a motion card is going into a million dollar machine, we're finding that design engineers are still sensitive to price. They don't want to have to pay for features and capabilities they don't need."
The motion controller works in conjunction with a proprietary board built around a PIC processor from Microchip Technology. Designed by Teosys engineers to work in a PC environment, the board controls laser triggering, user interface, motor drives, and mode select switch.
Programmability was a necessity, since identification marks are generally stored in a CAD format. These DXF vectors are then converted to the motion programming language recognized by the motion control card using a translator that Church wrote.
Though motion control was instrumental to achieving both accuracy and cost cutting, Church notes that the system uses the simplest type of motion control out there. "Keep it simple stupid was our theme during the design," she says. The only feedback comes from the video imaging system, which does the "very difficult" task of showing both visual and UV data merged. The merged images are displayed in real time so users can see the diamond on the screen while it's being marked. That's important to ensure correct etching on the diamond.
Repeatability is assured because software records the movement of the gem during inscription. Successive passes for enhancing the depth of the image are controlled by the software, so any deviation is minimal. The software is written in PICBasic, a subset of Basic designed for Microchip's embedded applications. One focus of the software development was figuring out a way to prevent users from making mistakes during the etching process. "We specifically designed the system so that it doesn't leave a lot under user control. The software has steps one through ten, and then you're done. It even prevents the operator from doing steps out of sequence," says Church.
All-in-one-design: The LMS 5X0 diamond marking system is comprised of a laser, optics, visualization system, part holding jig, and computer.
Another plus: Like the original, the new machine uses a patented, intra-cavity variable aperture, giving operators greater beam control over a large focal depth. This builds a degree of "forgiveness" into the system to compensate for less-than-perfect focusing, while achieving the goal of perfect etch marks on the diamond.
Contributing writer Terry Costlow can be reached attcostlow@core.com.
One of the most time-consuming aspects of the redesign of the diamond etching machine was finding less-expensive alternatives. The laser in the new design, for example, is less powerful and slower. Engineers also reduced the UV optical path, as well as the number of UV optics.
They also searched for low-cost devices they could customize. Perhaps the most unlikely adaptation was employing a small flashlight as a lighting source.
"I modified a $10 Maglite, adding a special bulb, hooking it to our power supply and adding a spherical lens and a series of optics and turned it into a dark field illuminator," says co-inventor Emre Teoman, who holds an MS in mechanical engineering from the University of Michigan.
While he won't say exactly how much cost that trimmed from the overall design, Teoman notes that the more costly predecessor uses four fiber lights, splitting two of them to provide illumination from six different directions.
Another dramatic change was the adoption of an inexpensive microscope. The original etching system uses a proprietary design that was too expensive for the lower-cost model. Teoman eyed the huge number of inexpensive security cameras on the market, eventually picking a compact model that cost in the vicinity of $100. With some adjustments and the addition of lenses, it becomes a microscope that allows operators to see the tiny markings on the diamond.
While much of the design process focused on scaling down or eliminating some functions, there was one area that required adding functionality. The Excimer lasers will sometimes emit a bit of gas, and when the gas is refilled the noxious odor lingers.
The Excimer laser uses a fluorine gas that "smells bad, like rotten eggs," Teoman says. That's not a big deal in labs that have powerful venting. But jewelry customers aren't likely to be as accepting of that odor as lab technicians who know the laser is part of their job.
Filtering the air and removing odors from the gas became another facet of the new design. As with the flashlight, the designers headed to the mall for a solution. Scouring the compact air filtering systems in many shops, they "took a standard charcoal filter and modified it, putting it on top of the system to remove fluorine if there's a leak," Teoman says.
Now that the LSM 5X0 is in use, co-developers TeoSys and PhotoScribe are focusing on planning and technical support. Teoman notes that diamond marking systems might be one of the rare pieces of capital equipment that appreciates. Despite their value, gemstones sometimes resemble socks in the laundry. "Diamonds bounce like magic super balls, they have a mind of their own. People lose them inside equipment, so over time, that equipment may be worth more when it's old than when it's new," Teoman says.
One rock solid aspect of the new diamond etching machine is the laser technology. In fact, developer TeoSys Engineering LLC, an integrated laser system designer, manufacturer, and contract services provider, specializes in the micromachining of difficult materials like plastics and diamond, with feature sizes as small as one micron. TeoSys offers three major systems (one infrared, two ultraviolet), based on patented PhotoScribe technologies, at prices starting at $40K.
The laser's wavelength is a key to one of the big selling points for the PhotoScribe systems. "We guarantee in writing that we will not harm or crack the diamond," says Dana Church, principal systems and software engineer at TeoSys Engineering. During the design of the initial product, the LMS 2500, engineers picked a gas laser with a wavelength of 193 nanometers. That's also what's used in the new 5X0.
Lasers with higher wavelengths will work when everything is set correctly, so they are appropriate for systems operated by experienced technicians. But many potential users of the less expensive 5X0 lack technical skills, so the chance for errors is far greater.
That's where the type of the laser and its wavelength become important. Lasers at wave-lengths above 217 nm can crack the diamond if they are not focused precisely on the diamond's face. "If you focus beneath the surface of the diamond, you can create fissures, it's almost like blasting with dynamite that's put inside a rock wall," Church says.
The lower-wavelength UV Excimer laser only works at the surface of the diamond. That's because at that wavelength, the diamond is basically opaque to the laser, so it can't penetrate the surface of the stone. In contrast, diamonds are effectively transparent to lasers in the IR range or other high wavelengths, so improper focusing can cause problems.
Another factor is that the Excimer laser is what they sometimes call a cool laser. "IR is a thermal process that melts the diamond to make a mark," says Church. The heat can cause fractures or otherwise harm the gem, she says. The TeoSys laser is pulsed 30 times per second to blast a pit that's 1 to 2 microns deep.
Another key factor was to make sure that even though the laser is powerful enough to harm human eyes, the system still retained the Class 1 rating. It cannot be activated until all steps are completed to prevent laser radiation from escaping and possibly harming an operator. That was especially important given the commercial market for the 5X0.
David Benderly credits science and engineering for bringing the PhotoScribe/TeoSys diamond etching system to market. But without trying to sound like an Academy Award recipient, he also credits his family.
"The diamond industry is a very closed, conservative community, so it's very helpful that I'm a third-generation diamond person," says the president and CEO of Photoscribe Technologies Inc.
The diamond business is "all about trust," since it's a very high-risk market where people want to know who they're dealing with, he explains. Huge deals often end with just hand-shakes and financial details scribbled on scraps of paper. Technology hasn't made big inroads in what's often described as an "old world" field.
Diamond micromachining began more than two decades ago, but was mainly used only in the brand-conscious Japanese market until a few years ago. But branding has become a major megatrend in recent years. "A stone engraved by Tiffany's has credibility," Benderly says.
Another factor is that stolen gems are increasingly used to fund terrorism and other criminal activities. The diamond industry wanted to police itself, and inscription was one technique for tracking diamonds. Still another trend is that diamond vendors are also concerned about improvements in man-made diamonds, such as processes for turning inexpensive brown diamonds into gem-quality stones.
Even though his family name got him in the door, conservative diamond buyers who were worried about putting marks on stones wouldn't try the technology. Before a trade show, Benderly had an idea that helped illustrate the small size of the lines. He emblazoned the word "PhotoScribe" on a human hair, adding a human factor that stayed in people's memories, helping open up the market.
"Now we've got diamond inscription systems in diamond centers around the world," he says.
But the first product's $300,000 price tag limited it to the 10 major diamond labs and their satellites. After taking "hundreds of phone calls," Benderly and his associates determined that $100,000 was the price point that would open up a new market for diamond inscription machines. That became the target for the LMS 5X0.
Clippard Instrument Laboratory |
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