Jitendra Khatait

Modeling of a Flexible Instrument to Study its Sliding Behavior Inside a Curved Endoscope

Flexible instruments are increasingly used to carry out surgical procedures. The instrument tip is remotely controlled by the surgeon. The flexibility of the instrument and the friction inside the curved endoscope jeopardize the control of the instrument tip. Characterization of the surgical instrument behavior enables the control of the tip motion. A flexible multibody modeling approach was used to study the sliding behavior of the instrument inside a curved endoscope. The surgical instrument was modeled as a series of interconnected planar beam elements. The curved endoscope was modeled as a rigid curved tube. A static friction-based contact model was implemented. The simulations were carried out both for the insertion of the flexible instrument and for fine manipulation. A computer program (SPACAR) was used for the modeling and simulation. The simulation result shows the stick-slip behavior and the motion hysteresis because of the friction. The coefficient of friction has a large influence on the motion hysteresis, whereas the bending rigidity of the instrument has little influence.

Design of an Experimental Set-Up to Study the Behavior of a Flexible Surgical Instrument Inside an Endoscope

The success of flexible instruments in surgery requires high motion and force fidelity and controllability of the tip. However, the friction and the limited stiffness of such instruments limit the motion and force transmission of the instrument. In a previous study, we developed a flexible multibody model of a surgical instrument inside an endoscope in order to study the effect of the friction, bending and rotational stiffness of the instrument and clearance on the motion hysteresis and the force transmission. In this paper, we present the design and evaluation of an experimental setup for the validation of the flexible multibody model and the characterization of the instruments. A modular design was conceived based on three key functionalities: the actuation from the proximal end, the displacement measurement of the distal end, and the measurement of the interaction force. The exactly constrained actuation module achieves independent translation and rotation of the proximal end. The axial displacement and the rotation of the distal end are measured contactless via a specifically designed air bearing guided cam through laser displacement sensors. The errors in the static measurement are 15 μm in translation and 0.15 deg in rotation. Six 1-DOF load cell modules using flexures measure the interaction forces and moments with an error of 0.8% and 2.5%, respectively. The achieved specifications allow for the measurement of the characteristic behavior of the instrument inside a curved rigid tube and the validation of the flexible multibody model.

Flexible multibody modeling of a surgical instrument inside an endoscope

The implementation of flexible instruments in surgery necessitates high motion and force fidelity and good controllability of the tip. However, the positional accuracy and the force transmission of these instruments are jeopardized by the friction, the clearance, and the inherent compliance of the instrument. The surgical instrument is modeled as a series of interconnected spatial beam elements. The endoscope is modeled as a rigid curved tube. The stiffness, damping, and friction are defined in order to calculate the interaction between the instrument and the tube. The effects of various parameters on the motion and force transmission behavior were studied for the axially-loaded and no-load cases. The simulation results showed a deviation of 1.8% in the estimation of input force compared with the analytical capstan equation. The experimental results showed a deviation on the order of 1.0%. The developed flexible multibody model is able to demonstrate the characteristic behavior of the flexible instrument for both the translational and rotational input motion for a given set of parameters. The developed model will help us to study the effects of various parameters on the motion and force transmission of the instrument

3-D multibody modeling of a flexible surgical instrument inside an endoscope

Modern surgical procedures involve flexible instruments for both diagnostic and therapeutic purposes. The implementation of flexible instruments in surgery necessitates high motion and force fidelity, and good controllability of the tip. However, the positional accuracy and the force transmission of these instruments are jeopardized by the friction and clearance inside the endoscope, and the compliance of the instrument. The objective of this paper is to set up a 3-D flexible multibody model for a surgical instrument inside an endoscope to study its translational and rotational behavior. The 3-D model incorporates all the deformations—axial, torsion, and bending— due to its interaction with the surroundings. The interaction due to the contact is defined along the normal and tangential direction at the contact point. The wall stiffness and damping are defined in the normal direction. Friction is defined along the tangential direction. The calculation of the interaction force and moment is explained with an example. Various simulations were performed to study the behavior of the instrument inside a curved rigid tube. The simulations for the insertion into a 3-D tube defined in a plane were compared for both 2-D and 3-D model. The simulation results from the 3-D ∗Address all correspondence to this author. Tel.: +31 53 489 5442. Fax: +31 53 489 3631. Email: j.p.khatait@utwente.nl model give the same results as the 2-D model. A simulation was carried out for the insertion in a 3-D tube using the 3-D model and the total interaction force on the instrument was analyzed. A 3-D multibody model was set up for the simulation of fine rotation. A motion hysteresis of 5◦ was observed for the chosen configuration. The 3-D multibody model is able to demonstrate the characteristic behavior of the flexible instrument under different scenarios. Both translational and rotational behavior of the instrument can be characterized for the given set of parameters. The developed model will help us to study the effect of various parameters on the motion and force transmission of the instrument.

Modelling of an Orifice-type Aerostatic Thrust Bearing

The orifice type of aerostatic bearings have been used for precision machine. However, most of researchers are focus on the dynamic and stability analyses of aerostatic bearings instead of the design and development. This paper provides the basic frame work and the procedure for design and development of aerostatic bearings with the result from the experiment and finite element analysis. The finite element method is employed to obtain the numerical solution of the pressure distribution and the flow speed between the surface of aerostatic bearing and the slide surface. It can provide the information between the input pressure and the output pressure. The experiment includes the physical measurement of the air pressure on the aerostatic bearing and the stiffness and damping characteristics. This result can help the researchers and engineers to further understand the basic characteristics of aerostatic bearings and correct the design the aerostatic bearing for their application

Motion and force transmission of a flexible instrument inside a curved endoscope

Flexible instruments are increasingly used to perform advanced and complex surgical procedures either manually or robotically. The success of flexible instruments in surgery requires high motion and force fidelity, and controllability of the tip. However, the friction and the limited stiffness of such instruments limit their motion and force transmission. The implementation of flexible instruments in surgery necessitates their characterization, the development of proper tools to understand the effect of various mechanical parameters on their overall performance, and an improvement in motion and force fidelity. Therefore, this thesis describes 2-D and 3-D flexible multibody models of a flexible surgical instrument inside a curved endoscope, and covers the design and evaluation of a dedicated experimental set-up. The thesis also includes the evaluation of the models with the analytical and experimental results, and describes the strategy to improve force transmission along the axial direction due to the combined motion input at the proximal end of the instrument.

Design of a Linkage-Based Backdrivable Underactuated Gripper

This paper presents the design of a gripper whose fingers can passively adapt to the shape and size of the object being grasped. Passive shape adaptive behavior of fingers is obtained by implementing underactuation, thus reducing the amount of sensory input required for grasping. The gripper has two identical fingers placed opposite to each other. Each finger has two phalanges and is actuated using a backdrivable electric motor via a linkage mechanism. Thus, the gripper has four degrees of freedom and two degrees of actuation. First, optimization procedure for sizing gripper mechanism and associated variables are explained. Subsequently, learnings from the realization of first two prototypes are presented.

Improved Force Transmission of a Flexible Surgical Instrument by Combining Input Motion

The force transmission of a flexible instrument through an endoscope is considerably deteriorated due to friction between the contacting surfaces. Friction force along the axial direction can be reduced by combining the translational motion input with rotation. A ratio ζ is defined to measure the reduction in the friction force along the axial direction due to the combined motion input at the proximal end of the instrument. An analytical formula is derived that shows the reduction in the friction force for the combined motion input. A flexible multibody model was setup and various simulations were performed with different motion inputs. The simulation result showed a reduction of 80% in the value of ζ in accordance with the analytical result for the given velocity ratio. Several experiments were performed with constant translational motion input combined with constant and sinusoidal rotational motion input. A maximum reduction of 84% is obtained in the value of ζ against a reduction of 89% calculated analytically. The knowledge of force transmission with a combination of motions can be used to increase the force fidelity of a flexible instrument in applications like robotic surgery with a flexible instrument

Effect of combined motion on force transmission of a flexible instrument

The force transmission of a flexible instrument through an endoscope is deteriorated due to friction between the contacting surfaces. Friction force along the axial direction can be reduced by combining the translation motion input with rotational motion input at the proximal end of the instrument. The effect of the combined motion on the force transmission is studied for a flexible instrument through a curved rigid tube. A mathematical formula is derived for the reduction in friction force along the axial direction due to the combined motion input. The force transmission of a flexible instrument through a curved rigid tube is analysed using the capstan equation. The ratio of the input and output forces is compared for the combined motion with that of the translation motion only. A ratioζ is defined to measure the reduction in the friction force along the axial direction due to the combined motion input. The analytical result shows the reduction in the friction force for the combined motion input. A flexible multibody model is set up and various simulations are performed with different motion inputs. The simulation result showed a reduction in the value of ζ in accordance with the analytical result for the given velocity ratio. The results are further validated with the experimental results. The simulation and experimental results show an agreement with the analytical solutions. The knowledge of force transmission with a combination of motions can be used to increase the force fidelity of a flexible instrument in applications like robotic surgery with

Test Set-up to Study the Behavior of a Flexible Instrument in a Bent Tube

The continued involvement of flexible endoscopy in carrying out both diagnostic and therapeutic interventions requires complex manipulation of flexible surgical instrument. The instrument is guided through the endoscope. The motion and force are transmitted to the distal end of the instrument by actuating the proximal end. The friction and the clearance between the instrument and the endoscope, together with the limited stiffness of the instrument, induces non-linear dynamic behavior, which jeopardizes the motion and force fidelity of the instrument. In order to study the dynamic behavior of the instrument, simulations were carried out using a flexible multibody model. The simulation results showed stick-slip behavior and motion hysteresis, which depend on a number of parameters such as the shape of the bent tube, friction, and stiffness of the instrument. This paper will discuss the test set-up which was designed to validate the model and simulation results, and also to characterize the instrument behavior inside a bent tube. The design objectives of the set-up are to actuate the instrument tip from the proximal end, to measure the interaction force between the instrument and the bent tube, and to measure the tip motion.