How to Design and Create a Cardan Shaft for a Single Port Robot by Selective Laser Sintering

Abstract

With the spread of endoscopic interventions the postoperative stress for patients has been reduced clearly. These interventions through natural orifices of the body (Natural orifice transluminal endoscopic surgery: NOTES) need miniaturized instruments with high precision, high range of motion and a high force load transmission. Our aim is to develop a mechatronic, single-port robotic system to guide and move flexible endoscopic instruments and optics inside the body. The system should be adapted to a flexible endoscope and consists of two flexible and actuated end-effectors that carry and manipulate flexible instruments. Due to the flexible end of the structure, laparoscopic single-port surgery through one incision and endoscopic surgery through a natural orifice would be possible. The concepts and prototypes were realized by selective laser sintering (SLS). One way to create flexible structures for a single use robot is to use universal joints assembled together in series. Next, selective laser sintering can now print these parts with the joints already assembled, in one part. There is no need for assembling or adhesive bonding. The final step is to replace the real joints of the cardan shafts with elastic joints. The proposed joints are made by the powder PA 2200 based on nylon. This basic powder is certificated as biocompatible according to ISO 10993-1. The challenge in this new field of printed medical robotics is to define a manufacturing process that enables you to design a part, create it by SLS and get it approved as a medical product.

Interdisciplinary concept of design, actuation, control and vision computing of a laser-sintered single-port robot

“…The applied laser is a CO2 laser with an effective power of 30W (wavelength 10.2 to 10.8 µm). The focused laser spot has a diameter of 0.43-0.45 mm [5]. The powder particle size is in between 56-65 µm.…”

“…Our robot system as proposed in [5] and [6] consists of an overtube frame for a flexible endoscope and a tip with two hollow Multi-Arm Snake-Like Robot kinematics [6]. The kinematics are produced monolithically by selective laser sintering.…”

“…In our previous works we tested the possibilities of SLS and presented some examples of flexible structures, forming a hollow arm to insert endoscopic instruments [5], [6], [9]- [13]. The structure basically consisted of a helical spiral with a hole in its middle to insert endoscopic instruments ( Figure 4).…”

“…One forceps and one cauterizing hook inserted. The third arm in the middle can be used for a second camera or another instrument (Taken from [5], [11]). …”

First pullout strength measurements of threads produced by selective laser sintering

“…The manufacturing of patient specific models and drilling templates have been researched, as well as the development of a complete medical robot designed for additive manufacturing [4], [5], [6], [7]. Especially the use of selective laser sintering (SLS), a process which builds a structure by melting powder layer by layer [8] allows the production of complex shapes with sufficient strength and stiffness to build medical robots.…”