In a previous investigation, the minimum energy and power requirements for earthworm locomotion over flexible surfaces were analyzed. The optimum conditions of locomotion were obtained as a function of the number of cells, friction coefficients, stroke length, energy recovery factor, and tangential compliance. In this paper we focus on the energy requirements of inchworms which, unlike earthworms, consume energy both during the locomotion of the cells and the clamping. In order to estimate the energy requirements, an experiment was performed on the aorta of a bull in which the normal and tangential compliances were obtained. The analysis allows us to compare between inchworms, regular earthworms and earthworms with lower forward coefficient of friction, and determine which of the devices is more efficient with given environment conditions. We also propose a new gait of locomotion for inchworms which reduces the energy consumption.

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.

Recent attempts at designing untethered devices for locomotion inside compliant biological vessels, highlighted the requirements for energy efficiency for prolonged duration inside living bodies. Quite a number of studies considered the design and construction of crawling robots but very few focused on the interaction between the robots and the flexible environment. In previous studies, we derived the efficiency, defined as the actual advance divided by the optimal advance, of worm locomotion. In this paper, we analyze the force, minimum energy and power requirements for worm locomotion over flexible surfaces. More importantly, we determine the optimum conditions of locomotion as a function of the number of cells, friction coefficients, stroke length, energy recovery factor, and tangential compliance. Optimality is defined with respect to energy and power requirements. The analytical results are obtained by integrating the force over the actuator motion and alternatively by summing up the overall energy losses due to friction and elastic losses with the surface and the efficient work performed by the robot. The theoretical predictions are compared to numerical simulations modeling worm robots crawling over flexible surfaces and are found in perfect match.

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.

Parallel mechanisms usually have several direct kinematic solutions that are attributed to different assembly modes (AMs) or postures. The present investigation deals with AM changing, and shows that beside the known cusp points, it is possible to change AM by moving on a path like a ramp, while encircling an alpha-curve in the joint space. For micromechanisms, where clearances at the mechanism joints are relatively large, AM changing may also occur when approaching a direct kinematic singularity.

This paper introduces a new architecture of a six degrees-of-freedom parallel robot suitable for microelectromechanical systems (MEMS) fabrication. The robot consists of only revolute joints for the passive joints, and linear actuators located at the base for the active ones, both of which are easier to manufacture in MEMS technology. The hybrid kinematic structure contains three single-loop submechanisms connected in parallel to the moving platform. The solutions of the inverse and direct kinematics problems are presented

This paper presents a robotic system for steering under real-time fluoroscopic guidance a flexible needle in soft tissue. Given a target and possible obstacle locations, the computer calculates the flexible needle-tip trajectory that avoids the obstacle and hits the target. Using an inverse kinematics algorithm, the needle base maneuvers required for a tip to follow this trajectory are calculated, enabling a robot to perform controlled needle insertion. Assuming small displacements, the flexible needle is modeled as a linear beam supported by virtual springs, where the stiffness coefficients of the springs can vary along the needle. Using this simplified model, the forward and inverse kinematics of the needle are solved analytically, enabling both path planning and path correction in real time. The needle shape is detected in real time from fluoroscopic images, and the controller commands the needle base motion that minimizes the needle tip error. This approach was verified experimentally using a robot to maneuver the base of a flexible needle inserted into a muscle tissue. Along the 40-mm trajectory that avoids the obstacle and hits the target, the error stayed below the 0.5-mm level. This study demonstrates the ability to perform closed-loop control and steering of a flexible needle by maneuvering the needle base so that its tip achieves a planned trajectory.

This paper presents a novel swimming method mediated by traveling waves in elastic tails. The propulsion method is potentially appropriate for maneuvering microrobots inside the human body. The swimming action relies on the creation of a traveling wave along a piezoelectric layered beam divided into several segments. This requires that a voltage with the same frequency, but different phases and amplitudes, be applied to each segment. The swimming pattern was analyzed theoretically by solving the coupled electric-elastic-fluidic problem, and was optimized to attain reasonable thrust. It was found that despite extreme size limitations, a tail manufactured by current microelectromechanical-devices technology, using piezoelectric material, is able to swim in water at a speed of several centimeters per second. The swimming theory was verified experimentally using an upscaled model that produced propulsion of 0.04 mN, which matches closely the theoretically predicted propulsion.

This paper addresses the singularity condition of a broad class of six-degree-of-freedom three-legged parallel robots that have one spherical joint somewhere along each leg. First, the actuator screws for each leg-chain are determined. Then Grassmann-Cayley algebra and the associated superbracket decomposition are used to find the condition for which the Jacobian (or rigidity matrix) containing these screws is rank-deficient. These tools are advantageous since they facilitate manipulation of coordinate-free expressions representing geometric entities, thus enabling the geometrical interpretation of the singularity condition to be obtained more easily. Using these tools, the singularity condition of (at least) 144 combinations of this class is delineated to be the intersection of four planes at one point. These four planes are defined by the locations of the spherical joints and the directions of the zero-pitch screws.

Medical doctors use radiology, endoscopy and smart pills to inspect the human body's inner content. Nowadays, self-propelled micro robots are developed to fulfill these tasks which use types of crawling techniques to advance. This paper suggests a novel swimming method, which creates a traveling wave in an elastic tail made of piezo-electric actuators, for propulsion of a micro-robot in the body. The novel swimming method was analyzed and optimized analytically by solving the coupled elastic/fluidic problem. It was found that under the extreme size limitations a tail manufactured by current MEMS technology is able to swim at the order of several mm/sec in water.

This paper deals with the difficulties that arise in the realization of micro-mechanisms by MEMS fabrication technique e.g.: fabrication of joints and actuators, joints clearance, lifting the structure from the 2D silicon wafer plane. It then introduces a new structure of a six degrees-of-freedom parallel robot that is suitable for MEMS fabrication. The robot consists of linear actuators located at the base and only revolute joints, both of which are easier to manufacture in MEMS technology. The hybrid kinematic structure contains three single loop sub-mechanisms connected in parallel to the moving platform, and the solution of its inverse kinematics which yields 4,096 solutions is presented.

This paper presents a new approach to robot-assisted spine and trauma surgery in which a miniature robot is directly mounted on the patient's bony structure near the surgical site. The robot is designed to operate in a semiactive mode to precisely position and orient a drill or a needle in various surgical procedures. Since the robot forms a single rigid body with the anatomy, there is no need for immobilization or motion tracking, which greatly enhances and simplifies the robot's registration to the target anatomy. To demonstrate this concept, we developed the MiniAture Robot for Surgical procedures (MARS), a cylindrical 5/spl times/7 cm/sup 3/, 200-g, six-degree-of-freedom parallel manipulator. We are currently developing two clinical applications to demonstrate the concept: 1) surgical tools guiding for spinal pedicle screws placement; and 2) drill guiding for distal locking screws in intramedullary nailing. In both cases, a tool guide attached to the robot is positioned at a planned location with a few intraoperative fluoroscopic X-ray images. Preliminary in-vitro experiments demonstrate the feasibility of this concept.

This paper presents a novel design for a mobile robot based on the kinematics of parallel mechanisms. The robot consists of 3 legs, each equipped with an asynchronous driving unit. The legs are connected to the driving units with spherical joints and to the upper plate with a revolute joint. Three additional encoders, attached to the upper revolute joints provide redundant data. This data is used by a kinematic model for accurate estimation of the robot's configuration and position in space, even in rough terrains, where conventional odometry fails. Simulation results show the advantages of the design, and suggest a method for detection of irregularities of surfaces in unknown environments.

This paper presents the singularity analysis of a family of 14 composite serial in-parallel six degree-of-freedom robots, having a common parallel sub-mechanism. The singular configurations of this class of robots are obtained by applying line geometry methods to a single, augmented Jacobian matrix whose rows are Plucker coordinates of the lines governing the sub-mechanism motion. It is shown that this family of robots possesses three general parallel singularities that are attributed to the general complex singularity. The results were verified experimentally on a prototype of a composite serial in-parallel robot that was synthesized and constructed for use in medical applications.

This paper describes the structure of three types of parallel robots and compares their performances in the sense of size and static forces. The motivation for this investigation is to construct a robot that best fits a given medical application. The requirements are to cover a given work volume with a given orientation and to maintain the robot within the smallest cube possible. Among the structures examined, three are presented since two are modifications of known structures and the third is a new one.

Manipulation of objects utilizing gravity and using general equilibrium grasps, which are not necessarily force-closure, is discussed. Examining the controllability of the object's dynamics, in the presence of gravity, leads to the conclusion that almost all equilibrium grasps are locally controllable. This fact is used to show that manipulation from any one equilibrium point, to any other, is possible if there is a continuity of equilibrium points between them. In addition, the equilibrium grasps can be used for changing grasps with walking finger manipulation. The system controllability matrix is also used to test grasp quality, depending not only on kinematic values but also on object orientation and dynamic properties.

The experimental model described exhibits the simple parallel robot design due to very few moving parts. The simple structure does not diminish its performances. On the contrary, it increases considerably its work volume, simplifies the kinematic solution and makes the robot very simple to construct. The robot has been tested in two applications: high-precision grinding of micro-pipette and manipulation of surgical tool in laparoscopic operations. We believe that this type of parallel robot is very attractive for several industrial (e.g. assembly) applications as well as and non-industrial (e.g. medical) applications due to its unique combination of large work volume with high accuracy.

A method for constructively approximating functions in the uniform (i.e., maximal error) norm by successive changes in the weights and number of neurons in a neural network is developed. This is a realization of the approximation results of Cybenko, Hecht-Nielsen, Hornik, Stinchcombe, White, Gallant, Funahashi, Leshno et al., and others. The constructive approximation in the uniform norm is more appropriate for a number of examples, such as robotic arm motion, and stands in contrast with more standard methods, such as back-propagation, which approximate only in the average error norm. Copyright 1996 Elsevier Science Ltd