Many of us are familiar with stents – interventional cardiac devices used to prop (and keep) open blood vessels that had been blocked. Although stent manufacturing may appear to have stabilized a little over the past few years, a look backward (and forward a bit) shows that we’ve come a long way to arrive at what many might consider a “standard” processing system today.
A Long Time Ago, in a Galaxy Far, Far Away (well, umm… France)
Despite the feeling that stents have been around forever, treatment of vascular blockage using this type of device has only been widely accepted practice since around 1986. The first surgical deployment of a stent to treat cardiac restenosis was made in Toulouse, France. The device itself had all of the self-expanding characteristics we have come to know and love, but was made of woven surgical steel fibers, as opposed to the laser micro-machined devices ubiquitous today.
A Not-So Long Time Ago
So what about those little laser-machined tubes? Well, the first systems used to produce them were pretty primitive by today’s standards.
Pretty rough, huh? This type of system was standard fare in the late 80s leading into the 90s. Consider that even the dinosaur shown above was an “optimized” solution. The first stent cutting concept used a worm-and-wheel rotary stage that had its speed increased to a whopping 60 rpm for this application! Measured against our current expectations of micron-level feature sizes and parts being produced in tens of seconds or in a few minutes, can you imagine what kind of limited performance this beast could offer? Have no fear, though – the future was just around the corner…
A Little While Ago
Throughout the 90s, technology in stent production improved noticeably. The lasers became more reliable and the motion systems were assembled with optimization in mind. The overly large rotary stage was replaced with a lighter-weight alternative, and workpiece holders (e.g., chucks, collets) were optimized to reduce inertia and increase system dynamics.
Better mechanics, linear amplifiers, and a controller with dedicated laser processing features – now we’re talking! However, this was still a component-level solution, and not designed totally “from the ground up” for stent cutting.
Now look how far we have come.
That’s more like it! Fully optimized linear and rotary subsystem, designed from the start for cylindrical laser processing. Not only have the motion controller features grown exponentially over the past decade, but the overall mechanical solutions available today (and featured in the above image) are perfectly balanced in regards to driving through the center of mass, sensing position as close as possible to the laser work-point, and locating bearing support about the system’s center of stiffness. It doesn’t get any better than this! Or, does it?
Tomorrow (But Sooner Than You May Believe!)
Although some incremental improvements continue to be made to the servo stages used for this type of laser process, far, far greater dynamics are demanded. Non-metallic stent materials may not be able to be machined in one pass. So, if multiple processing passes are required, then the stages must go multiple times faster and still maintain the same error budget in order to keep cycle times from spiraling out of control.
But, what if we decided to move the tool instead of the part? In other words, why not think about using high speed (and highly accurate!) laser scanning galvanometers to rapidly dance the beam across the part instead of lugging heavy servo stage mechanics back-and-forth and round-and-round? Although some details still need to be sorted out – for instance, how to cut a continuous vector path without still being forced to rotate the part rapidly back and forth – the solutions are out there, and we will be seeing them in practice soon.
Then, imagine what the pictures above will look like in comparison!