FLEXMIN - Enhancement of Flexibility of Minimally Invasive Surgery

Project description

Flexmin User Console
Manipulation Instruments
Flexmin Slave Robot
User Interface with Haptic Feedback
Slave Robot Detail (Picture: Katrin Binner)

Project Term: September 2011 to August 2018

The FLEXMIN project, funded by German Research Foundation (DFG), aims at the extension of the flexibility of minimally invasive instruments for soft tissue interventions. This is done by the integration of robotic positioning systems and haptic feedback. Scientific goals of the project include strategies and concepts of intracorporal micro manipulation devices as well as the construction and evaluation of a telerobotic master-slave-system. Project partners are the Departments of Microtechnology and Electromechanic Systems (Prof. Helmut F. Schlaak), and Measurement and Sensor Technology (Prof. Roland Werthschützky, Prof. Mario Kupnik), both from Technical University of Darmstadt, and the working group for Surgical Technology and Training (PD Dr. med. Andreas Kirschniak) of University Hospital in Tübingen.

Medical Relevance: Our surgical robot is designed as single incision system for use in laparoscopic abdominal as well as transanal surgery. Its primary aim is to enable a tissue-conserving performance which results in less postoperative risk for wound healing disorders, infections and prolonged period of reconvalescence. Additionally, the robot-assisted technique increases precision of movements and generates haptic feedback. We analyze the influence of these robotic features on the surgical procedure (subjectively experienced by the surgeon) and its outcome (objectively assessed by follow-up examinations and standardised interviews).

Slave Unit: The mechanical setup of the intracorporal robot consists of camera, retractor and two manipulators with five degrees of freedom (dof) each (cartesian positioning, rotation, gripping). Manipulators are driven by a parallel kinematic structure that uses translation and rotation to transmit mechanical energy. Three BLDC motors are used for translation and two motors are used for rotation in each manipulator, thus providing five independent degrees of freedom. Current realizations of the manipulators can cover cylindrical workspaces with a diameter of 60 mm, and a length up to 85 mm. Forces up to five N, and velocities up to 327 mm/s are achieved in the workspace. All motors are integrated in a drive unit (see figure above) with a mass of 6 kg and a size of 260 mm × Ø 170 mm. Current instruments adapted to the manipulators include grippers, needle holders and HF instruments.

Haptic Feedback: Several sensor configurations are currently investigated to provide signals for haptic feedback to the surgeon. This includes dedicated sensors for different frequencies, different measurement locations in the slave robot and the usage of pseudo-haptic effects. In addition to cost aspects, the work also aims at sensor signal redundancy and limitation to low bandwidth closed-control-loops.

Master Unit: The slave robot is operated by two delta kinematic structures, one for each manipulator, which also provide haptic feedback to the surgeon. A kinematic extension to the delta mechanism is used to match the master to the slave kinematic structure, thus limiting the master movements to the possible movements of the slave. Grips adapted to the endeffectors allow feedback of gripping forces and rotating torques. The master workspace is adapted for a position scaling up to a factor of two for cartesian dof and higher for rotational dof in order to increase dexterity and precision as well as work sequences.

Evaluation: Preliminary tests show a significant higher precision of movement and lower interaction forces in artificial test scenarios. User tests with medical mockups for hernia reparation and gall bladder removal show positive feedback in terms of the system’s dexterity. Haptic feedback has not been tested in medical training scenarios yet.

Current Activities: Integration of different sensors, realization of haptic feedback, realistic test scenarios and an experimental proof of the benefits of the system are currently pursued.

Media Coverage

Selected Publications

  • Matich S, Neupert C, Kirschniak A, Schlaak HF, Pott PP, "3-D force measurement using single axis force sensors in a new single port parallel kinematics surgical manipulator," IEEE/RSJ IROS, Daejeon, 2016, pp. 3665-3670.
  • Neupert C, Matich S, Scherping N, Kupnik M, Werthschützky R, Hatzfeld, C: "Pseudo-Haptic Feedback in Teleoperation", IEEE Trans. on Haptics, vol. 9, no. 3, pp. 397-408, July-Sept. 1 2016.
  • Matich S, Neupert C, Kirschniak A, Schlaak HF, Pott PP, A new Single-Port Robotic System based on a Parallel Kinematic Structure for Transanal Rectum Resection, IEEE IROS, Hamburg, 2015
  • Matich S, Neupert C, Schlaak HF, Pott PP, Drive Unit for a Single Port Surgical Robot with 12 Degrees of Freedom, Innovative Klein- und Mikroantriebstechnik, Köln, 2015
  • Neupert C, Matich S, Klug F, Pott PP, Kirschniak A, Schlaak HF, Werthschützky R, User Interface for a Teleoperation System with Matching Kinematic Structures, 9th IFAC Symposium on Biological and Medical Systems, Berlin, 2015
  • Matich S, Neupert C, Kirschniak A, Werthschützky R, Schlaak HF, Pott PP, Teleoperation System with Haptic Feedback for Single-Incision Surgery - Concept and System Design, CARS, Heidelberg, 2015


  • Neupert C, Matich S, Hatzfeld C: Teleoperationssystem mit intrinsischem haptischen Feedback durch dynamische Kennlinienanpassung für Greifkraft und Endeffektorkoordinaten, Application PCT/EP2016/050901, priority Jan 19, 2015
  • Matich S, Albrecht, W: Sensoranordnung zur Kraft- oder Drehmomentmessung und ein Verfahren zur Herstellung derselben, Application DE 10 2017 102 343.7, priority Feb 07, 2017
  • Wismath, S, Hatzfeld, C, Matich, S, Fröse, V: Integriertes medizinisches Instrument zur Messung von Kräften im distalen Bereich eines Stabes und Herstellungsverfahren desselben, application DE 10 2017 105 053.1, priority Mar 09, 2017


  • Fachgebiet MuST, TU Darmstadt (Prof. Werthschützky, Prof. Kupnik) – Design of the haptic interface, haptic feedback modalities
  • Fachgebiet M+EMS, TU Darmstadt (Prof. Schlaak) – Parallel kinematic structure, sensory concepts
  • Sektion Minimalinvasive Chirurgie, Universitätsklinik für Allgemeine, Viszeral und Transplantationschirurgie, Universitätsklinikum Tübingen, PD Dr. med. Andreas Kirschniak – Medical specifications, task performance and new instruments

Research Staff at TU Darmstadt

Johannes Bilz, M.Sc.

Dr.-Ing. Christian Hatzfeld

Nach oben

Demonstration of pick and place tasks


Technische Universität Darmstadt

Fachgebiet Mikrotechnik und Elektromechanische Systeme (M+EMS)


Johannes Bilz, M.Sc.

S3/06 110
Merckstr. 25
64283 Darmstadt

+49 6151 16-23881
+49 6151 16-23873


Prof. Dr.-Ing. Helmut F. Schlaak

S3/06 128
Merckstraße 25
64283 Darmstadt

+49 6151 16-23851
+49 6151 16-23852

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