By Scott Dailey and Connor Chiuchiolo
Surgical robotics is so explosive an area of minimally invasive surgery science that even ordinary people know it’s rapidly becoming a healthcare mainstay. As a matter of fact, people having no background in medicine whatsoever, nor the manufacturing expertise to produce these amazing machines, at some point, will undergo a surgical procedure with the help of a surgical robot. That surgical robotics is becoming normalized and is today a perfectly acceptable approach to performing ambulatory surgical procedures means the ushering in of promises like shorter hospital stays, fewer complications after the hospital, and best of all, a quicker restoration of quality of life.
And as instruments designed to perfectly simulate the surgeon’s limbs, the doctors themselves enjoy the benefits of less potential for fatigue during agility-summoning maneuvers over protracted periods of time. Add to that, the opportunity for a surgical robot to reach smaller, tighter spaces, within narrower cavities, and it’s understandable why there’s so much enthusiasm and optimism surrounding the deployment of surgical robots in health care networks around the world.
But for all these reasons, and many others, a surgical robot cannot fail in the field in any way big or small, under any circumstances, nor for any length of time.
Subsequently, makers of the tungsten miniature mechanical cables helping mimic the surgeon’s movements involves thousands of hours of collaboration with the surgical robotics makers ensuring such motion actuation achieves a critical factor of safety that far exceeds the requirements of the designed environment.
Tungsten Cable: Superior Strength, Ultrafine Footprint
If a surgical robot is using mechanical cable to achieve pitch and yaw in its end affecters, then that robot’s mechanical cables are constructed of either stainless steel or tungsten. Of the two cable materials, quite recently tungsten has become the clear favorite in the making of these cables. While stainless steel has enjoyed decades of a sterling reputation as the ideal cable material, along a myriad of sophisticated surgical instruments, tungsten’s malleability, combined with its superior load and cycle capacities, has made it the preferred mechanical cable material among surgical robot makers.
The diameters of the tungsten mechanical cables simulating a surgeon’s arms, hands and fingers varies from one application to another. But the cables inside these tight, small, crowded spaces are potentially as small as 0.016” Ø, or the very same thickness as four stacked sheets of garden-variety 8.5×11 office paper.
Even more astounding is the diameter of the monofilaments used to strand these complex tungsten (or stainless steel) mechanical cables. Carl Stahl Sava Industries has stranded tungsten cable, for instance, from wire as small as 0.0007″ Ø, which makes the monofilaments 70% the size of a single human hair (~0.001″ Ø).
Achieving the required factor of safety, while maintaining such a small form factor allows these tungsten mechanical cables to make their way over pulleys roughly the diameter of a through hole resistor.
The Repeatability of Extremely Tight Tolerances
The precision with which tungsten mechanical cable assemblies are executing the surgeon’s motions, requires that the fittings applied to the cables likewise meet a rigid factor of safety as well. After all, the surgical robot is performing minimally invasive surgery on a human being; so clearly the margin for error is zero.
Thus, even further contributing to the elegance of these fascinatingly small, yet Herculean cables, is the tolerances the cable’s fittings must achieve. Tolerance, loosely defined in cable manufacturing, is the disparity in size from the required measurement of a fitting. So, if a fitting applied to a tungsten mechanical cable assembly meant to be 0.200” ± 0.004” Ø, is actually .205” Ø, the fitting would be out of tolerance because it is not within the rigid surgical robotics application requirements. And even when the ideal tolerance for fittings being applied to tungsten mechanical cable is achieved at, for example, ±0.004″, it’s in the repeatability of the manufacturing operation that makes the production of these cable wonders such a rigorous, but satisfying, research and development endeavor.
Not only must these fittings be ± the thickness of a single sheet of the office paper at 0.004″, but fittings must achieve this tolerance over every last assembled part. Given how thin a sheet of paper is, accomplishing this manufacturing feat only once is impressive. But doing it over the course of an entire production run, and throughout the lifespan of a surgical robot’s commission? Well, it becomes rather plain to see what a manufacturing victory it is to reproduce these tolerances over millions of tungsten mechanical cable assemblies and possibly thousands of surgeries.
Punctuating the challenging proposition it is to produce tungsten cables for surgical robots, Sava’s Design Engineer, Connor Chiuchiolo said, “the mass production of surgical robotics cable assemblies is a labor of love. It’s an engineering tightrope achieving these tolerances. Yet, exploring the boundaries of what can be done in surgical science is its own reward.”
Tungsten Cable: THE R&D Process
Tungsten cable for surgical robotics places unique and complex research and development demands on the mechanical engineers tasked with producing them. But even once the cable assemblies have moved past the R&D process, which in surgical robotics can take years to complete, the work has only begun.
Beyond the multitude of operational and production validations needed to perfect the cable assemblies themselves, production, tool and die and other skilled operators must then mobilize to design, deploy and maintain a manufacturing environment that ensures the seamless and reliable development of thousands or even millions of parts – across decades sometimes. Even when the tungsten cable assembly prototypes are proving successful in lab testing, automations, as well as Kanban, 5S and cellular manufacturing strategies put in place the infrastructure necessary to mass produce cables and cable assemblies that assures that one piece to the next, they are indistinguishable from one another.
Sponsored content by Carl Stahl Sava Industries