The most common tungsten cable configurations in surgical robots include 8×19, 7×37, and 19×19 configurations. Mechanical cable with tungsten wire 8×19 includes 201 tungsten wires, 7×37 includes 259 wires, and finally 19×19 includes 361 helical stranded wires. Although stainless steel is used in a variety of applications, including numerous medical and surgical devices, there is no substitute for tungsten cables in surgical robotics.
But why is stainless steel, a well-known material for mechanical cables, less and less popular in surgical robot drives? After all, stainless steel cables, especially micro-diameter cables, are ubiquitous in military, aerospace, and most importantly, countless other surgical applications.
Well, the reason why tungsten cables are replacing stainless steel in surgical robot motion control isn’t really as mysterious as one might think: it has to do with durability. But since the strength of this mechanical cable is not only measured by its linear tensile strength, we need to test strength as a measure of performance by collecting data from many scenarios suitable for field conditions.
Let’s take the 8×19 structure as an example. As one of the most commonly used mechanical cable designs to achieve pitch and yaw in surgical robots, the 8×19 greatly outperforms the stainless steel counterpart as the load increases.
Note that the cycle time and tensile strength of the tungsten cable increased with increasing load, while the strength of the alternative stainless steel cable decreased dramatically compared to the strength of tungsten at the same load.
A stainless steel cable with a load of 10 pounds and a diameter of approximately 0.018 inches provides only 45.73% of the cycles achieved by tungsten with the same 8×19 design and wire diameter.
In fact, this particular study immediately showed that even at 10 pounds (44.5 N), the tungsten cable worked more than twice as often as the stainless steel cable. Given that, like all components, micromechanical cables inside a surgical robot must meet or exceed stringent regulatory requirements, the cable should be able to withstand anything thrown at it, right? Thus, the analysis shows that using the same diameter 8×19 tungsten cable compared to stainless steel cable has both an inherent strength advantage and ensures that the robot is powered by the stronger and more durable cable material of the two options.
In addition, in the case of the 8×19 design, the number of cycles of a tungsten wire rope is at least 1.94 times that of a stainless steel wire rope of the same diameter and load. Moreover, studies have shown that stainless steel cables cannot match the elasticity of tungsten, even if the applied load is gradually increased from 10 to 30 pounds. In fact, the gap between the two cable materials is increasing. With the same load of 30 pounds, the number of cycles increases to 3.13 times. The more important finding was that margins never decreased (to 30 points) throughout the study. Tungsten has always had a higher number of cycles, averaging 39.54%.
Although this study examined wires of specific diameters and cable designs in a highly controlled environment, it demonstrated that tungsten is stronger and provides more cycles with precise stresses, tensile loads, and pulley configurations.
Working with a tungsten mechanical engineer to achieve the number of cycles required for your surgical robotic application is critical.
Whether stainless steel, tungsten or any other mechanical cable material, no two cable assemblies serve the same primary winding. For example, usually microcables do not require the strands themselves, nor the near-impossible tight tolerances of the fittings applied to the cable.
In many cases, there is some flexibility in choosing the length and size of the cable itself, as well as the location and size of accessories. These dimensions constitute the tolerance of the cable assembly. If your mechanical cable manufacturer can implement cable assemblies that meet the application’s tolerances, these assemblies can only be used in their actual environment.
In the case of surgical robots, where lives are at stake, achieving design tolerances is the only acceptable outcome. So it’s fair to say that ultra-thin mechanical cables that mimic the surgeon’s every move make these cables some of the most sophisticated on the planet.
The mechanical cable assemblies that go inside these surgical robots also take up small, cramped and cramped spaces. It’s actually amazing that these tungsten cable assemblies fit seamlessly into the narrowest of channels, on pulleys no larger than the tip of a child’s pencil, and do both tasks while maintaining motion at a predictable number of cycles.
It’s also important to note that your cable engineer can advise cable materials ahead of time, potentially saving time, resources, and even costs, which are key variables when planning a sound go-to-market strategy for your robot.
With the rapidly growing surgical robotics market, simply providing mechanical cables to aid movement is no longer acceptable. The speed and position with which surgical robot makers bring their marvels to market will certainly depend on how easily the products are ready for mass consumption. That’s why it’s important to note that your mechanical engineers research, improve and create these cable assemblies every day.
For example, it often turns out that surgical robotics projects may start with the strength, ductility, and cycle counting ability of stainless steel, but still use tungsten at a later stage in the development of robotics.
Surgical robot manufacturers typically used stainless steel early in robot design, but later chose tungsten due to its superior performance. While this may seem like a sudden change in approach to motion control, it’s just masquerading as one. The material change is the result of a mandatory collaboration between the robot manufacturer and the mechanical engineers hired to manufacture the cables.
Stainless steel cables continue to establish themselves as a staple in the surgical instrument market, especially in the field of endoscopic equipment. However, while stainless steel is capable of supporting movement during endoscopic/laparoscopic procedures, it does not have the same tensile strength as its more brittle but denser and therefore stronger counterpart (called tungsten). resulting tensile strength.
While tungsten is ideally suited to replace stainless steel as the cable material of choice for surgical robots, it is impossible to appreciate the importance of good collaboration between cable manufacturers. Working with an experienced ultra-thin cable mechanical engineer not only ensures that your cables are produced by world-class consultants and manufacturers. Choosing the right cable manufacturer is also a surefire way to make sure you prioritize the science and pace of build plan improvement, which will help you achieve your motion control goals faster than competitors trying to achieve the same.
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