David Zarrouk

Conditions for Worm-Robot Locomotion in a Flexible Environment: Theory and Experiments

Biological vessels are characterized by their substantial compliance and low friction that present a major challenge for crawling robots for minimally invasive medical procedures. Quite a number of studies considered the design and construction of crawling robots; however, very few focused on the interaction between the robots and the flexible environment. In a previous study, we derived the analytical efficiency of worm locomotion as a function of the number of cells, friction coefficients, normal forces, and local (contact) tangential compliance. In this paper, we introduce the structural effects of environment compliance, generalize our previous analysis to include dynamic and static coefficients of friction, determine the conditions of locomotion as function of the external resisting forces, and experimentally validate our previous and newly obtained theoretical results. Our experimental setup consists of worm robot prototypes, flexible interfaces with known compliance and a Vicon motion capture system to measure the robot positioning. Separate experiments were conducted to measure the tangential compliance of the contact interface that is required for computing the analytical efficiency. The validation experiments were performed for both types of compliant conditions, local and structural, and the results are shown to be in clear match with the theoretical predictions. Specifically, the convergence of the tangential deflections to an arithmetic series and the partial and overall loss of locomotion verify the theoretical predictions.

Analysis of Wormlike Robotic Locomotion on Compliant Surfaces

An inherent characteristic of biological vessels and tissues is that they exhibit significant compliance or flexibility, both in the normal and tangential directions. The latter in particular is atypical of standard engineering materials and presents additional challenges for designing robotic mechanisms for navigation inside biological vessels by crawling on the tissue. Several studies aimed at designing and building wormlike robots have been carried out, but little was done on analyzing the interactions between the robots and their flexible environment. In this study, we will analyze the interaction between earthworm robots and biological tissues where contact mechanics is the dominant factor. Specifically, the efficiency of locomotion of earthworm robots is derived as a function of the tangential flexibility, friction coefficients, number of cells in the robot, and external forces.

Analysis of earthworm-like robotic locomotion on compliant surfaces

An inherent characteristic of biological vessels and tissues is that they exhibit significant compliance or flexibility, both in the normal and tangential directions. The latter in particular is atypical of standard engineering materials and presents additional challenges for designing robotic mechanisms for navigation inside biological vessels by crawling on the tissue. Several studies aimed at designing and building such robots have been carried out but little was done on analyzing the interactions between the robots and their flexible environment. In this study, we will analyze the interaction between earthworm robots and biological tissues where contact mechanics is the dominant factor. Specifically, the efficiency of locomotion of earthworm robots is derived as a function of the tangential flexibility, friction coefficients, number of cells in the robot and external forces.

A Note on the Screw Triangle

This paper derives the expressions of an equivalent finite screw of two successive screw motions in a simplified form using purely vectorial analysis. This is achieved by tracing the trajectories of specific points on the moving body, which together with the known axis and angle of combined rotation, yield the expressions of the screw triangle. This paper also gives a short overview of different known expressions of the screw triangle and shows that the one given in this paper reduces the number of arithmetic operations by about a third compared with the most efficient algorithm in the literature.

Experimental validation of locomotion efficiency of worm-like robots and contact compliance

Biological vessels are characterized by their substantial compliance and low friction which present a major challenge for crawling robots for minimally invasive medical procedures. Quite a number of studies considered the design and construction of crawling robots, however, very few focused on the interaction between the robots and the flexible environment. In a previous study, we derived the analytical efficiency of worm locomotion as a function of the number of cells, friction coefficients, normal forces and local (contact) tangential compliance. In this paper, we generalize our previous analysis to include dynamic and static coefficients of friction, determine the conditions of locomotion as function of the external resisting forces and experimentally validate our previous and newly obtained theoretical results. Our experimental setup consists of worm robot prototypes, flexible interfaces with known compliance and a Vicon motion capture system to measure the robot positioning. Separate experiments were conducted to measure the tangential compliance of the contact interface which is required for computing the analytical efficiency. The validation experiments are shown to be in clear match with the theoretical predictions. Specifically, the convergence of the tangential deflections to an arithmetic series and the partial and overall loss of locomotion verify the theoretical predictions.

Worm-Like Robotic Locomotion in Flexible Environment

Miniature crawling robots for medical purposes have been the issue of many studies in the past decade. The main challenge of this type of locomotion is the high flexibility of the tissue of biological vessels combined with the usually low friction coefficients. However, little has been done in the field of analyzing the interaction between the tissue and the robot. In a previous study, we presented the influence of the local compliance effects on the locomotion and developed the efficiency as a function of the number of cells, friction coefficients and tangential compliance. In this study we include the influence of the structural compliance on the locomotion analysis of two-cell worm robot.

Locomotion of One Degree of Freedom Worm Robots

Worm-like robots have been widely designed for applications including maintenance of small pipes and medical procedures in biological vessels such as the lungs, intestines, urethra and blood vessels. The robots must be small, reliable, energy efficient and capable of carrying cargos such as cameras, biosensors, and drugs. Earthworm and inchworm robots have been traditionally designed with three or more cells and clamps and a corresponding number of actuators. The use of multiple actuators complicates the design, makes the system more cumbersome, reduces power efficiency and requires more control for coordination. In the present study, we analyze the worm locomotion, in terms of the distance between the cells and clamping modes, and model it as a cyclic function of the time. That is, the worm locomotion can be represented by a single degree of freedom. Consequently, multi-cells worm-like robots actuated by a single motor were designed. The robots employ a rotating screw-like shaft that mechanically coordinates the sequencing of the cell displacement as well as the clamping modes with no external control for each separate cell. This design allows for significant miniaturization and reduces complexity and cost of the system. Two prototypes of earthworm and inchworm robots for locomotion within 20mm and 70mm wide tubes were manufactured. The robots demonstrated high reliability and strong grip. They can crawl vertically while carrying a payload at a rate of few cm/s for the larger robots and roughly 1cm/s for the smaller ones. Furthermore, the low power consumption enables the robots to crawl wirelessly for hundreds of meters using standard off the shelf batteries.Copyright