Laparoscopic surgery is carried out by using long and slender instruments that are inserted through small incisions in the abdominal wall. Visual feedback is provided by an endoscope with a camera. The incision point restricts the degrees of freedom (DOF) of the endoscope from six to four (Fig. 1). As a result, it is impossible to observe organs from different sides while keeping the viewpoint in focus. This reduces the surgeon’s ability to perceive depth.

In close co-operation with the Man-Machine Systems Group of the Delft University of Technology in the Netherlands, a new steerable endoscope for laparoscopy has been developed. The endoscope, called Endo-Periscope, is designed as a spatial parallelogram-mechanism with a miniature camera on the tip (Figs 2,3). The 6 DOF steerable tip can be used to observe organs from different sides. The handgrip contains an arrow that points always in the direction of the camera’s line-of-sight. This provides intuitive control of the tip, showing the surgeon how the camera is oriented in the abdominal cavity.

In order to obtain a very small bending radius, the endoscope tip contains a new kind of spring, called Ring Spring, that is constructed from rings of spring metal (Fig. 4). The outside of the rings is bent and the rings are welded to each other in pairs. The Ring Spring combines very high torsion stiffness with a low, asymmetric bending stiffness. The spring contains holes for guiding two pulling cables. If one of the cables is completely tightened and if the other cable (steering cable) is released, the spring will bend with a very small radius (Fig. 5). In order to realize the parallelogram-behaviour, the steering cable is unrolled along a disc that is connected to the handgrip (Fig. 3). The diameter of the disc is chosen such that the handgrip and the endoscope tip stay always parallel.

The Endo-Periscope and the Ring Spring have been applied for two international patents.

References:

1. Breedveld P. (2000). Endoscope. International Patent application, International Publication Number WO 01/10292 A1, Applicant: Delft University of Technology, Priority date 06/08/1999, 13 p.
2. Breedveld P., Hirose S. (2001). Spring and endoscope equipped with such a spring. International Patent Application, International Application Number PCT/NL01/00552, Applicant: Delft University of Technology, Priority date 24/07/2000, 20 p.
3. Breedveld P., Hirose S. (2001) Development of the Endo-Periscope for improvement of depth perception in laparoscopic surgery. Proc. 2001 ASME Design Engineering Technical Conferences Computers and Information in Engineering Conference, Sept. 9-12, Pittsburgh, PA, USA, Paper DETC2001/DAC-21031, 7 p.
4. Breedveld P., Hirose S. (2001). The Endo-Periscope - a new tool to improve depth perception in laparoscopic surgery. Abstr. 9th International Congress of the European Association for Endoscopic Surgery, June 13-16, MECC, Maastricht, the Netherlands, p.110.
5. Breedveld P., Hirose S (2001). Development of the Endo-Periscope. To be published in Minimally Invasive Therapy and Allied Technologies, Vol. 10, No. 6.