Vibro-impact Capsule Research Articles

Exploiting reprogrammable nonlinear structural springs for enhancing the manoeuvrability of a vibro-impact capsule robot

Vibro-impact capsule robots, propelled by rhythmic collisions of an internal mass triggered by an external magnetic field, are emerging as promising tools for minimally invasive surgery. This innovative actuation mechanism allows for delicate interaction with tissues, making them ideal candidates for navigating confined surgical spaces. However, their limited manoeuvrability and controllability remain significant hurdles, restricting their ability to navigate complex anatomies and perform precise interventions, ultimately hindering their broader clinical applications. This paper investigates the integration of reprogrammable structural springs in capsule robots, demonstrating how dynamic tuning can tailor the interaction between the inner mass and the capsule, thereby unlocking enhanced manoeuvrability and precise control of the capsule robot. A mathematical model describing the dynamic response of a vibro-impact capsule robot integrated with von Mises trusses (VMT), which are used to tailor the interaction between the inner mass and the capsule, is developed and verified using finite element modelling. Using the verified mathematical model, we explore how the transition between mono-stability and bi-stability of VMTs affects the capsule robot’s propelling performance. Our findings demonstrate that this state switch enables four distinct propulsion modes of the capsule robot. This work paves the way for a new paradigm in small-scale robot design by incorporating reprogrammable nonlinear structures. These structures empower the robots with unprecedented manoeuvrability and controllability within a compact, deployable form factor.

Utilisation of a wrinkled film-based structure for the sensing measurement of a vibro-impact capsule robot

Utilisation of a wrinkled film-based structure for the sensing measurement of a vibro-impact capsule robot

Dynamics of a self-propelled capsule robot in contact with different folds in the small intestine

Considering the anatomy of small intestine involving lesions, circular folds and tumours are the major sources resisting the locomotion of capsule robots. By mimicking the small-bowel tumours as cone folds, this paper presents a comparative study on the dynamics of a vibro-impact capsule robot in contact with different circular and cone folds. With the aid of GPU parallel computing and path-following techniques, extensive bifurcation and basin stability analyses are performed to identify different capsule-fold interactions and unravel the parametric influences on the robot, such as fold shape, Young’s modulus and robot’s control parameters (e.g., excitation period and amplitude). It is found that fold shape and Young’s modulus may only affect capsule’s dynamics significantly when robot’s excitation period is large. Two essential locomotion modes, a period-one motion with capsule-fold contact in the small region of excitation amplitude and a fold crossing motion in the large region of excitation amplitude, dominating the dynamics of the robot regardless of fold shape and Young’s modulus are observed. In addition, the instability mechanism of this period-one motion is revealed in detail. The numerical study presented in this work will provide a solid basis for the locomotion control of the robot when encountering different types of circular folds and small-bowel tumours. It also offers the potential of utilising robot’s dynamics for bowel cancer detection.

Numerical analysis of a multistable capsule system under the delayed feedback control with a constant delay

The vibro-impact capsule system is a self-propelled mechanism that has abundant coexisting attractors and moves rectilinearly under periodic excitation when overcoming environmental resistance. In this paper, we study the control of coexisting attractors in this system by using a delayed feedback controller (DFC) with a constant delay. The aim of our control is to steer this complex system toward an attractor with preferable performance characteristics among multiple coexisting attractors, e.g., a periodically fast forward progression. For this purpose, we give an example of a feedback-controlled transition from a period-3 motion with low progression speed to a period-1 motion with high progression speed at the system parameters where both responses coexist. The effectiveness of this controller is investigated numerically by considering its convergence time and the required control energy input to achieve transition. We combine pseudo-spectral approximation of the delay, event detection for the discontinuities and path-following (continuation) techniques for non-smooth delay dynamical systems to carry out bifurcation analysis. We systematically study the dynamical performance of the controlled system when varying its control gain and delay time. Our numerical simulations show the effectiveness of DFC under a wide range of system parameters. We find that the desired period-1 motion is achievable in a range of control delays between a period-doubling and a grazing bifurcation. Therefore, two-parameter continuation of these two bifurcations with respect to the control delay and control gain is conducted to identify the delay-gain parameter region where the period-1 motion is stable. The findings of this work can be used for tuning control parameters in experiments, and similar analysis can be carried out for other non-smooth dynamical systems with a constant delay term.

Design and Experimental Investigation of a Vibro-Impact Capsule Robot for Colonoscopy

Uptake of capsule endoscopy in the large intestine has been very limited due to both the risk of missed lesions and the often prolonged transit time, making it an unviable alternative to standard colonoscopy. In this letter, we presented a controllable and easy-to-use diagnostic tool, equipping a novel vibration module inside a capsule robot for colonoscopy. The capsule's motion was controlled by applying an external alternating electromagnetic field to the capsule's inner magnet to generate vibrations and impacts on the main body of the capsule. To optimise its motion, we provided a numerical solution for calculating its electromagnetic force and used it to guide a hand-held control panel for navigating the robot. The robot was firstly examined in a large intestine simulator modelled based on the colon-rectal morphometrics, and then tested in an ex vivo environment using porcine intestines. We verified the performance of the robot travelling through the entire intestine with the maximum speeds of 54 mm/s and 40 mm/s in the simulator and the ex vivo environment, respectively. It was found that altering the control frequency of the panel can help the robot to pass through various morphometrics, in particular the sharp turnings at the segment junctions.

Optimising the locomotion of a vibro-impact capsule robot self-propelling in the small intestine

Circular fold is one of the biggest barriers for resisting endoscopic robots moving in the small intestine. Overcoming such a resistance force for progression during endoscopic procedure may significantly improve diagnostic efficiency. This paper studies the locomotion of a vibro-impact capsule robot self-propelled on a small intestine substrate when encounters various types of circular folds. A new capsule-fold model is developed to understand capsule-fold interaction and determine the optimum control parameters (the frequency and amplitude of excitation) for a successful crossing motion. Extensive bifurcation analyses show that the geometry and mechanical properties of the circular folds do not have a significant influence on capsule’s bifurcation patterns but affect its progression in terms of fold crossing. To this end, numerical studies using path-following techniques implemented via the software COCO are performed. In this way, parameter-dependent families of periodic solutions of the capsule-fold model are studied, and critical points are detected to allow to develop control strategies for the capsule motion, in particular in order to cross certain types of circular folds by suitably varying its control parameters.

Simulation and experimental studies of a vibro-impact capsule system driven by an external magnetic field

This paper studies the electromagnetic field used for driving a vibro-impact capsule prototype for small bowel endoscopy. Mathematical models of the electromagnetic field and the capsule system are introduced, and analytical solution of the magnetic force applied on the capsule is derived and verified by experiment. The impact force between the inner mass of the capsule and the capsule body is also compared via numerical simulation and experimental testing. By comparing the capsule’s progressions under different control parameters (e.g. the excitation frequency and duty cycle), the merits of using the vibro-impact propulsion are revealed. Based on the experimental results, the optimised speed of the prototype can achieve up to 3.85 mm/s. It is therefore that the potential feasibility of using the external electromagnetic field for propelling the vibro-impact capsule system is validated.

Dynamics of a vibro-impact self-propelled capsule encountering a circular fold in the small intestine

Given the anatomy of the small intestine, this paper investigates the dynamics of a vibro-impact capsule moving on an intestinal substrate with the consideration of a circular fold which provides the main resistance for the capsule’s progression. To this end, a new mathematical model of the capsule-fold contact that can depict the entire procedure of fold crossing is proposed. Our bifurcation analyses suggest that the capsule always performs period-1 motion when the driving force is small, and fold crossing requires a large excitation amplitude, especially when the duty cycle ratio is small. By contrast, the excitation period of the capsule does not have a strong influence on fold crossing. It is found that the inner mass, capsule mass, frictional coefficient and fold’s height have a significant influence on capsule’s crossing motion. We also realise that Young’s modulus of the tissue has a critical influence on the bifurcation pattern of the capsule, where a stiffer tissue may lead to the co-existence of three stable attractors. On the contrary, the capsule’s length and stiffness of the impact springs have less influence on the capsule’s dynamics. The findings of this study can help with the optimisation and control of capsule’s locomotion in the small intestine.

Dynamic response of vibro-impact capsule moving on the inclined track and stochastic slope

Dynamic response of vibro-impact capsule moving on the inclined track and stochastic slope

The vibro-impact capsule system in millimetre scale: numerical optimisation and experimental verification

The vibro-impact capsule system has been studied extensively in the past decade because of its research challenges as a piecewise-smooth dynamical system and broad applications in engineering and healthcare technologies. This paper reports our team’s first attempt to scale down the prototype of the vibro-impact capsule to millimetre size, which is 26 mm in length and 11 mm in diameter, aiming for small-bowel endoscopy. Firstly, an existing mathematical model of the prototype and its mathematical formulation as a piecewise-smooth dynamical system are reviewed in order to carry out numerical optimisation for the prototype by means of path-following techniques. Our numerical analysis shows that the prototype can achieve a high progression speed up to 14.4 mm/s while avoiding the collision between the inner mass and the capsule which could lead to less propulsive force on the capsule so causing less discomfort on the patient. Secondly, the experimental rig and procedure for testing the prototype are introduced, and some preliminary experimental results are presented. Finally, experimental results are compared with the numerical results to validate the optimisation as well as the feasibility of the vibro-impact technique for the potential of a controllable endoscopic procedure.

Three-dimensional map for a piecewise-linear capsule system with bidirectional drifts

Abstract A three-dimensional map is studied in this paper to provide a fundamental understanding for the vibro-impact capsule system, which is a non-autonomous two degrees-of-freedom non-smooth dynamical system consisting of soft impact and dry friction with forward and backward drifts. By using the map, one can investigate the global and local dynamics of the system and construct all possible local mappings for a wide range of parameter variation. An example study by varying the amplitude of external excitation of the system is presented. Our results show that the proposed map can effectively explain the occurrence of the boundary-intersection crossing and the sliding bifurcations observed in the system.

Optimization and experimental verification of the vibro-impact capsule system in fluid pipeline

This paper studies the prototype development of the vibro-impact capsule system aiming for autonomous mobile sensing for pipeline inspection. Self-propelled progression of the system is obtained by employing a vibro-impact oscillator encapsuled in the capsule without the requirement of any external mechanisms, such as wheels, arms, or legs. A dummy capsule prototype is designed, and the best geometric parameters, capsule and cap arc lengths, for minimizing fluid resistance forces are obtained through two-dimensional and three-dimensional computational fluid dynamics analyses, which are confirmed by wind tunnel tests. In order to verify the concept of self-propulsion, both original and optimized capsule prototypes are tested in a fluid pipe. Experimental results are compared with computational fluid dynamics simulations to confirm the efficacy of the vibro-impact self-propelled driving.

Dynamical analysis of vibro-impact capsule system with Hertzian contact model and random perturbation excitations

In this paper, the modeling and dynamical response of a vibro-impact capsule system with Hertzian contact and random environmental perturbation is studied. The capsule system is modeled as a two-degree-of-freedom dynamical system composed of a rigid capsule and a movable internal mass. The random environmental perturbation is incorporated in the models of the capsule system, which is more realistic working condition of capsule robotic system. The impact between the rigid capsule and the internal mass will occur when the relative displacement is larger than the gap between them. The impact interaction is described by using the Hertzian contact model. The resistance force between the capsule and the sliding face is described by Coulomb friction model. The response of the vibro-impact capsule system is obtained through Monte Carlo simulation. A kind of random stick–slip phenomena can be found in the response of the proposed model, which is consistent with the actual behavior of capsule system. At last, it is worthy noting that stochastic P-bifurcation occurs when the parameters of the system vary.

Optimization of the Vibro-Impact Capsule System for Promoting Progression Speed

This paper studies the dynamics of vibro-impact capsule systems with one-sided and double-sided constraints under variations of control parameters, including frequency of excitation, mass ratio, and stiffness ratio. The aim of this study is to optimize the progression speed of the capsule system. Extensive comparisons reveal that the capsule system with one-sided constraint is better than the one with double-sided constraints in terms of progression speed. Moreover, the system’s period-one one-right-impact motion is proved as the ideal vibration condition due to its lowest energy consumption for impacts. According to the dynamic analyses of control parameters, an inner mass with its weight similar as the weight of capsule and a right constraint with a relative weak stiffness are beneficial for further accelerating the capsule system forwards.

A comparative study of the vibro-impact capsule systems with one-sided and two-sided constraints

This paper studies the dynamics of the vibro-impact capsule systems with one-sided and two-sided soft constraints under variations of various system and control parameters, including mass ratio, stiffness ratio, gap of contact, and amplitude and frequency of external excitation. The aim of this study is to optimise the progression speed and energy consumption of the capsule and minimise the required cabin length for prototype design used for engineering pipeline inspection. Our studies focus on three systems: the capsule with a right constraint, the capsule with a right and a weak left constraints, and the capsule with a right and a strong left constraints. Bifurcation analyses show that the behaviour of the capsule with one-sided constraint is mainly periodic, and the dynamic responses of the other two capsules with two-sided constraints become complex when the stiffness of the left constraint increases. Based on our extensive comparisons, the following optimisation strategies are recommended. When the capsule speed is paramount, one can employ the two-sided capsule with a weak left constraint under large amplitude of excitation. When energy consumption is taken into account, the one-sided capsule is preferable. When a miniaturized prototype is needed, the two-sided capsule with a strong left constraint is the best choice.

Controlling multistability in a vibro-impact capsule system

This work concerns the control of multistability in a vibro-impact capsule system driven by a harmonic excitation. The capsule is able to move forward and backward in a rectilinear direction, and the main objective of this work is to control such motion in the presence of multiple coexisting periodic solutions. A position feedback controller is employed in this study, and our numerical investigation demonstrates that the proposed control method gives rise to a dynamical scenario with two coexisting solutions, corresponding to forward and backward progression. Therefore, the motion direction of the system can be controlled by suitably perturbing its initial conditions, without altering the system parameters. To study the robustness of this control method, we apply numerical continuation methods in order to identify a region in the parameter space in which the proposed controller can be applied. For this purpose, we employ the MATLAB-based numerical platform COCO, which supports the continuation and bifurcation detection of periodic orbits of non-smooth dynamical systems.

Experimental Investigation of the Vibro-impact Capsule System

This paper presents an experimental investigation of the vibro-impact capsule system, which has potential applications in capsule endoscopy and engineering pipeline inspection. The experimental results obtained using novel test rig are used to verify the modelling approach where non-smooth multibody dynamics is applied to describe the motion of the system, and comparisons between numerical simulations and experiments are given. After an appropriate re-scaling, the findings of this work could provide a better insight into the behaviour of such systems which are subject to harmonic excitation.

Optimization of the Vibro-Impact Capsule System

Optimization of the vibro-impact capsule system for the best progression is considered in this paper focusing on the choice of the excitation parameters and the shape of the capsule. Firstly, the fastest and the most efficient progressions are obtained through experimental investigations on a novel test bed. Control parameters, the amplitude and the frequency of harmonic excitation, and one of the system parameter, namely the stiffness ratio, are optimized. The experimental results confirm that the control parameters for the fastest progression are not the same as those for the most efficient progression from the energy consumption point of view. Therefore, the capsule system can be controlled either in a speedy mode or in an energy-saving mode depending on the operational requirements. In the second part of the paper, optimization of the capsule shape is studied using computational fluid dynamics (CFD) simulations. Here the aim of achieving the best progression is addressed through minimizing the drag and the lift forces acting on a stationary capsule positioned in the pipe within a fluid flow. The CFD results indicate that both drag and lift forces are dependent on capsule and arc lengths, and finally, an optimized shape of the capsule is obtained.

Experimental verification of the vibro-impact capsule model

In this paper, an experimental verification of the vibro-impact capsule model proposed by Liu et al. in (Int. J. Mech. Sci, 66:2–11; 2013a, Int. J. Mech. Sci, 72:39–54; 2013b, Int. J. Non-Linear Mech., 70, 30–46; 2015) is presented. The capsule dynamics is investigated experimentally by varying the stiffness of the support spring, and the frequency and the amplitude of excitation. The novel design of the experimental set-up is discussed, and comparisons between the experiments and numerical simulations are presented showing a good agreement. The conducted bifurcation analysis indicates that the behaviour of the system is mainly periodic and that a fine tuning of the control parameters can significantly improve the performance of the system. The main findings provide a better insight into the vibro-impact systems subject to nonlinear friction, and the experimental rig can be used to predict the dynamic behaviour of these systems.

Forward and backward motion control of a vibro-impact capsule system

A capsule system driven by a harmonic force applied to its inner mass is considered in this study. Four various friction models are employed to describe motion of the capsule in different environments taking into account Coulomb friction, viscous damping, Stribeck effect, pre-sliding, and frictional memory. The non-linear dynamics analysis has been conducted to identify the optimal amplitude and frequency of the applied force in order to achieve the motion in the required direction and to maximize its speed. In addition, a position feedback control method suitable for dealing with chaos control and coexisting attractors is applied for enhancing the desirable forward and backward capsule motion. The evolution of basins of attraction under control gain variation is presented and it is shown that the basin of the desired attractors could be significantly enlarged by slight adjustment of the control gain improving the probability of reaching such an attractor.