PC-Based Control in Minimally Invasive Surgery The Miniature Robot Operates PC-Based and Highly Precisely

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Miracle II is the second phase of the Miracle project funded by the Werner Siemens Foundation. The name stands for Minimally Invasive Robot Assisted Computer-guided LaserosteotomE, i.e. a modular laser robot for minimally invasive bone removal that is planned and accompanied in virtual reality. The robotics elements of this system were developed by Prof. Dr. Georg Rauter and his team at the University of Basel, based on Beckhoff control technology and in particular on TwinCAT 3 Target for Simulink.

Miracle II is based at the Department of Biomedical Engineering (DBE) of the Faculty of Medicine at the University of Basel. “There, researchers from the fields of computer science, engineering, robotics, laser physics, surgery and other disciplines are brought together to take bone surgery into the space age,” says Prof. Dr. Georg Rauter, head of the Biromed Lab (Bio-Inspired Robots for Medicine Laboratory) at the DBE. The corresponding miniature robot is to carry out functional cuts with previously unattainable precision for individually adapted implants manufactured directly at the point of care.

PC-Based Control as the Technological Basis

As part of his research, roboticist Prof. Dr. Georg Rauter has been working with Beckhoff’s PC-based control technology since 2008. He describes the starting point as follows: “At the time, we needed communication with several hundred components distributed across a large space. In addition, measurement cards were predominantly based on the PCI bus or PCI Express bus. To avoid the increasing difficulties regarding the number of interfaces and signal line lengths, we looked for a bus-based system and came across EtherCAT as a suitable solution—and thus also Beckhoff as a suitable control supplier.”

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As a doctoral candidate, he began his activities with the development of a rowing simulator at ETH Zurich, based on a cable robot. The focus was on the synchronized control of two cable-based parallel robots, each with five drive strands. The aim of this rowing simulator was to autonomously teach people movements via an intelligent algorithm by providing personalized multimodal feedback on movement execution. Prof. Dr. Georg Rauter explains: “The intention was to investigate motor learning in complex movements in healthy individuals. However, since rowing can generate large forces, e.g. when immersing the oar, which the simulator must also be able to reproduce, safety was a key element of the simulator. Initially, the safety functionality was implemented with a separate safety controller. With TwinCAT 3, we now use the system-integrated safety technology TwinSAFE, which, for example, also enables seamless integration into the HMI. Another advantage of TwinCAT 3 is that we were able to keep the familiar workflow. This means we can continue to use a graphical programming environment as well as programming with MATLAB and Simulink. I really like the workflow with TwinCAT 3 Target for Simulink, which delivers a C++ project that can be integrated directly into TwinCAT and, after compilation, provides the appropriate machine code.” In addition, the TwinCAT workflow also benefits master’s students and new employees: “Every year there is a block course on this—twice in Basel and, due to its great popularity, now also once in Innsbruck. In addition, there are corresponding workshops held in connection with conferences that we organize. In principle, these courses are also open to industry participants who are particularly interested in implementing MATLAB and Simulink in TwinCAT 3.”

Implementation in Surgical Robotics

Prof. Dr. Georg Rauter applied his robotics know-how and experience with PC-based control to surgical robotics within the Miracle II project. The aim is classic orthopedic applications in which, during a minimally invasive procedure, the laser is introduced into the body together with an endoscope through a small opening and then precisely processes the bone or modifies its geometry and thus its stability. Building on this research, work is also moving in the direction of regenerative cartilage medicine. Serving as a platform for this is the miniature robot presented, among other venues, at the 2025 World Expo in Osaka, Japan, which can be used to illustrate interdisciplinary collaboration through a specific application in the knee—laser osteotomy or regenerative cartilage medicine.

Prof. Dr. Georg Rauter explains: “Parallel robotics combined with a laser—that is our core focus here in Basel and is also unique at miniaturized dimensions. Currently, surgical robotics uses large devices placed on the floor with correspondingly large kinematic chains that have to be laboriously stabilized to ensure sufficient precision. Our miniature robot, by contrast, is supported locally on the tissue and also introduces the laser there, which itself exerts no interaction forces. This allows the system to be positioned very precisely without having to compensate for disturbing forces. The required torques are introduced from the outside via flexible spindles. Overall, with a cross-section of 7.5 × 7.5 mm (approx. 0.3 × 0.3 inches), this design results in a very small footprint.”

High-Performance Control Technology in Demand

The drive trains that must be operated in parallel require high-performance control technology for synchronization, as provided by TwinCAT, the embedded PC CX2043, and the EtherCAT and TwinSAFE terminals from Beckhoff. This enables the planar system to reliably utilize its three planar degrees of freedom: forward/backward motion, lateral movements, and rotation. For this purpose, a total of four EtherCAT- and FSoE-capable small servo motors are used, including redundancy, which bring the robot to the desired position via flexible spiral lead screws. Prof. Dr. Georg Rauter describes the special control-engineering aspect as follows: “Due to the redundant drive, the controller does not have to solve a linear system of equations, but rather a real-time optimization problem in order to arrive iteratively—and several times every millisecond—at the best possible result.”

The high functionality of TwinCAT is used very broadly, according to Prof. Dr. Georg Rauter: “A good example is TwinCAT HMI, where I particularly like the data exchange across different logics—from C++ to the PLC or hardware and all the way to safety. In addition, our kinematics can be conveniently integrated into TwinCAT, and you can easily communicate with third-party components via ADS, for example with machine-learning-based vision components. This openness and flexibility are offered by TwinCAT and EtherCAT not least because of their widespread adoption. Therefore, for all requirements there are also components available with the appropriate interfaces.”

Benefits Through Close Collaboration

According to Prof. Dr. Georg Rauter, research at the University of Basel also benefits from the close cooperation with Beckhoff Switzerland. Important aspects in this regard are the very short response times to specific inquiries as well as the possibility of testing hardware at short notice. For example, they were able to test the application potential of the intelligent transport system XPlanar for a year. In addition, their own development suggestions regarding control technology are listened to openly and reviewed.

“Ten years ago, the safe and reliable communication and automation technology from Beckhoff, which we originally used on the rowing simulator at ETH, enabled a technology transfer: in the form of the world’s first cable robot for free, body-weight-supported 3D gait rehabilitation over ground, ‘The FLOAT,’ developed together with Reha-Stim Medtec AG, Schlieren, Switzerland, and the University of Zurich’s Paraplegic Center at Balgrist. We are now looking forward to achieving this step of commercialization—thanks to robust automation technology—in surgical robotics as well, as soon as possible.”