Sebastian Klug

Design and Control Mechanisms for a 3 DOF Bionic Manipulator

Functionality and design of a bionic robot arm consisting of three joints driven by elastic and compliant actuators derived from biologically inspired principles are presented. In the first design standard springs with linear characteristics are utilized in combination with electrical drives. Different control approaches for the bionic robot arm are presented, discussed and evaluated by numerical simulations and experiments with regards to the long-term goal of a nature-like control performance

Biologically Inspired Reflex Based Stabilization Control of a Humanoid Robot with Artificial SMA Muscles

Suddenly occurring collisions or unintentional motions represent a high safety risk in robotics and must be prevented. Especially for humanoid robots, the influence of disturbances that occur unexpectedly during bipedal locomotion are difficult to compensate. A model based online control approach for stabilization of a humanoid robot with many degrees of freedom may require too much time for computing and implementing an adequate compensating motion. In addition, such a control approach usually requires accurate sensor information about the type and magnitude of the disturbance. The goal of the present paper is a reflex based online stabilization control of a humanoid robot actuator based on artificial SMA muscles. The design of a humanoid robot actuated with SMA muscles allows a lightweight robot design and simplifies the direct implementation of reflexes. The reflex that is integrated into the robot depends on an evaluation of the pressure distribution of the feet. An instable position of the center of mass of the robot leads to a known specific pressure disturbance that should be avoided. The experiments show that the implementation of a reflex for the actuators in the calf leads to a stabilization of the entire robot. Additional reflexes are required when the strength or speed of disturbances are increased, such as in the upper leg or arms.

The Use of Time-of-Flight Camera for Navigating Robots in Computer-Aided Surgery: Monitoring the Soft Tissue Envelope of Minimally Invasive Hip Approach in a Cadaver Study

Background. Time-of-flight (TOF) cameras can guide surgical robots or provide soft tissue information for augmented reality in the medical field. In this study, a method to automatically track the soft tissue envelope of a minimally invasive hip approach in a cadaver study is described. Methods. An algorithm for the TOF camera was developed and 30 measurements on 8 surgical situs (direct anterior approach) were carried out. The results were compared to a manual measurement of the soft tissue envelope. Results. The TOF camera showed an overall recognition rate of the soft tissue envelope of 75%. On comparing the results from the algorithm with the manual measurements, a significant difference was found (P > .005). Conclusions. In this preliminary study, we have presented a method for automatically recognizing the soft tissue envelope of the surgical field in a real-time application. Further improvements could result in a robotic navigation device for minimally invasive hip surgery.

How deep can straight instruments be inserted into the femoral canal: a simulation study based on cadaveric femora*

Abstract Determining how deep instruments can be inserted into the femoral canal without touching adjacent structures is a fundamental necessity for navigating instruments in primary and revision total hip arthroplasty. The aim of the study was to determine the reachable depth of a straight instrument inserted into the femur canal during primary and revision total hip arthroplasty. Based on the three-dimensional data of twenty-six femurs, obtained from a CT scan, the insertion depth of a virtual, straight instrument was accessed by a simulation. The effect of the diameter of the virtual instrument and the extension of the osteotomy were evaluated. Without extending the osteotomy, 100% of the femoral canal was reachable to a depth of 5.1–6.3 cm for instruments with a diameter of 10 mm. The depth was measured from the lower edge of the osteotomy. A maximum lateral extension of the osteotomy by 1 cm enlarges the access to a depth of 8.8 cm. The results provide a theoretical basis for the limitations of guiding instruments used for the preparation of the femoral canal. Bone preserving methods need the development of angulated instruments to reach deep areas in the femoral canal.

Retracting Soft Tissue in Minimally Invasive Hip Arthroplasty Using a Robotic Arm: A Comparison Between a Semiactive Retractor Holder and Human Assistants in a Cadaver Study

Background. All surgical procedures in orthopedics involve the retraction of soft tissue. In this study, the performance of 3 assistants holding the medial retractor during minimally invasive hip arthroplasty was compared with a semiactive retractor holder in a cadaver setup. Methods. A total of 40 measurements on 3 cadavers were carried out with each subject (3 human, 1 robot) measuring each cadaver 10 times. The retractor was equipped with a sensor array on both sides, to measure variations of the retracting pressures over a 2-minute interval. Results. The semiactive retractor holder showed an almost constant performance compared with the test subjects. There was no significant reduction of the applied pressure and almost no variation during the 2-minute interval and across all measurements. Conclusions. The performance of the semiactive retractor holder was more stable than that of a human assistant, making it suitable for intraoperative usage.

The musculoskeletal system of the human arm — More than the sum of its parts

Biological systems show outstanding performance in the control of highly redundant and nonlinear systems. The complexity of these systems has raised questions about sufficient strategies of planning and controlling movements. Although many aspects of the musculoskeletal system, like nonlinear muscle properties, redundant actuation, and mechanically coupled joints, seem to make things more complicate from a purely technical point of view, this complexity has positive influence on the control. In this paper we show first aspects on how the nonlinear characteristics of the musculoskeletal system of the human arm may influence and even support the control of movements.