MBD Drives Endoscope Design

The ECHELON FLEX surgical stapler.

Endoscopic surgery is a delicate business. While all surgery requires a steady hand, endoscopic surgery requires doctors to probe into a patient’s body through a small incision, sometimes no longer than 5 mm. To work in such tight constraints, endoscopic surgeons manipulate sophisticated tools with grace and precision, and designing those instruments efficiently requires the same level of care.

Ethicon Endo-Surgery specializes in developing endoscopic tools. To build these complex machines, engineers at Ethicon have to overcome numerous product design challenges, including building sophisticated micromachines that are safe to use inside a human body. Take for example Ethicon’s ECHELON FLEX Stapler.

All endoscopic procedures begin with an incision and end with a closure. Along the way, sometimes it’s necessary for surgeons to make multiple internal incisions and closures. To do this, doctors need an endoscopic stapler capable of closing a wound. Since the 1970s, endoscopic surgeons have been using staplers that required a lot of force to operate, not something any patient or doctor wants to hear.

In 2011, Ethicon developed the first motor-driven endoscopic stapler, reducing the force required to close incisions while also increasing the precision of staple placement. But as time passed, it became obvious that embedded controllers could make their motor-powered stapler even better. Building integrated electronic systems into a tool, however, drives a whole new level of complexity. So, model-based design (MBD) became critical to this advancement in endoscopic instruments.

To begin their development process, Ethicon engineers were concerned that they had little experience developing embedded control (EC) systems that would be used to drive the actions of their stapler. In the past, the company had reached out to third-party developers to build their products’ EC infrastructure. But in the case of the ECHELON FLEX, Ethicon wanted a much quicker, integrated product development cycle. Sending a prototype back and forth between off-site systems engineers every time a design review was required was no longer good enough.

To change this dynamic, Ethicon turned to MathWorks' Simulink and their Simulink Design Optimization software. After building a plant model of the ECHELON motor and hooking it up to a processor, the company was able to simulate the mechanical properties such as torque, dynamic frictions, moment of inertia and other parameters that would affect the performance of their stapler.

Control system design for the ECHELON.

With an accurate plant model for their design engineers to leverage, Ethicon started developing their control systems using Simulink’s Stateflow technology. With several sensors and switches onboard the device, harmonizing their interactions with the motor was key to making a responsive tool. While the ultimate test of whether their design would be a success would come at the hands of surgeons, modeling the electronic interactions of the ECHELON were important if Ethicon’s engineers were going to rapidly iterate how their tool behaved.

With Stateflow technology, Ethicon could create a visual map of their control system and use it to modulate the way that their motor was being driven by the ECHELON’s sensors. Because of Stateflow’s intuitive design, engineers could update their control systems quickly and easily.

With their ECHELON FLEX prototype nearly complete, it was time to turn the design over to the surgeons to see how the instrument would hold up in the hands of its users. Within moments of using the micro-controlled stapler, surgeons were giving Ethicon’s engineers valuable feedback about the speed and latency of the stapler’s actions. For the engineers, this was excellent. With several models of their design already built inside Simulink software, the Ethicon team could update their model, upload it to the stapler and fine-tune the tool’s abilities on the fly.

According to Ethicon, by using MBD principles, the company was able to develop the ECHELON FLEX in three months. In the past, similar products took up to 18 months to develop, underscoring the value of having a strong model for rapid design iteration.