Error analysis of electromagnetic motion tracking systems is of growing interest to many researchers. Under sensor movement, it is logical to presume that the error in position and orientation measurements will increase due to the linearization used in the algorithms, among other reasons. In this article, we analyze theoretically the error, that results from linearization, in position measurement of the Polhemus tracking system for a moving sensor. We derive formulas to estimate this error in terms of the sensor position and speed. Then, we verify these formulas by numerical simulations.

Accurate continuous glucose monitoring (CGM) is essential for fully automated glucose control in diabetes mellitus type 1. State-of-the-art glucose control systems automatically regulate the basal insulin infusion. Users still need to manually announce meals to dose the prandial insulin boluses. An automated meal detection could release the user and improve the glucose regulation. In this study, patterns in the postprandial CGM data are exploited for meal detection. Binary classifiers are trained to recognize the postprandial pattern in horizons of the estimated glucose rate of appearance and in CGM data. The appearance rate is determined by moving horizon estimation based on a simple model. Linear discriminant analysis (LDA) is used for classification. The proposed method is compared to methods that detect meals when thresholds are violated. Diabetes care data from 12 free-living pediatric patients was downloaded during regular screening. Experts identified meals and their start by retrospective evaluation. The classification was tested by cross-validation. Compared to the threshold-based methods, LDA showed higher sensitivity to meals with a low rate of false alarms. Classifying horizons outperformed the other methods also with respect to time of detection. The onset of meals can be detected by pattern recognition based on estimated model states and consecutive CGM measurements. No individual tuning is necessary. This makes the method easily adopted in the clinical practice.

A method for preprocessing a time series of glucose measurements based on Kalman smoothing is presented. Given a glucose data time series that may be irregularly sampled, the method outputs an interpolated time series of glucose estimates with mean and variance. The method can provide homogenization of glucose data collected from different devices by using separate measurement noise parameters for differing glucose measurement equipment. We establish a link between the ISO 15197 standard and the measurement noise variance used by the Kalman smoother for self-monitoring of blood glucose (SMBG) measurements. The method provides phaseless smoothing, and it can automatically correct errors in the original datasets like small fallouts and erroneous readings when surrounding data allow. The estimated variance can be used for deciding at which times the data are trustworthy. The method can be used as a preprocessing step in many kinds of glucose data processing and analysis tasks, such as computing the mean absolute relative deviation between measurement systems or estimating the plasma-to-interstitial fluid glucose dynamics of continuous glucose monitor or flash glucose monitor (FGM) signals. The method is demonstrated on SMBG and FGM glucose data from a clinical study. A MATLAB implementation of the method is publicly available.

Robot-assisted therapy is an emerging form of rehabilitation treatment for motor recovery of the upper limbs after neurological injuries such as stroke or spinal cord injury. Robotic rehabilitation devices have the potential to reduce the physical strain put on therapists due to the high-effort one-to-one interactions between the therapist and patient involving repetitive high-intensity movements to restore arm and hand functions. Numerous custom robotic devices have been developed in recent years to aid in physical rehabilitation of stroke patients, but most commercially available systems are high-cost devices because of low production volumes and high development costs. In this paper, we analyse the safety and functionality of the UR5 collaborative industrial robot from universal Robots equipped with an external force/torque sensor in a real-time control system for typical rehabilitation exercises. The aim of the paper is to show that a new class of general-purpose industrial robots designed for human-robot collaboration may prove a viable alternative to custom designs. Experiments show that robotic rehabilitation of the upper limbs using a standard industrial robot manipulator UR5 may be feasible. Results have the potential to make robotic rehabilitation more available as a high-quality therapeutic treatment for more patients.

Biological snakes can gracefully traverse a wide range of different and complex environments. Snake robots that can mimic this behaviour could be fitted with sensors and also transport tools to hazardous or confined areas that other robots and humans are unable to access. To carry out such tasks, snake robots must have a high degree of awareness of their surroundings (i.e. perception-driven locomotion) and be capable of efficient obstacle exploitation (i.e. obstacle-aided locomotion) to gain propulsion. These aspects are important to realise the large variety of possible snake robot applications in real-life operations such as fire-fighting, industrial inspection, search-and-rescue and more. In this paper, an elaborate review and discussion of the state-of-the-art, challenges and possibilities of perception-driven obstacle-aided locomotion for snake robots is presented for the first time. Pertinent to snake robots, we focus on current strategies for obstacle avoidance, obstacle accommodation, and obstacle-aided locomotion. Moreover, we put obstacle-aided locomotion into the context of perception and mapping. To this end, we present an overview of relevant key technologies and methods within environment perception, mapping and representation that constitute important aspects of perception-driven obstacle-aided locomotion.

This paper presents a general motion planning framework for body shape control of snake robots. We demonstrate the applicability of the framework for straight line path following control, and for implementing body shape compliance in environments with obstacles. Compliance is achieved by assigning mass-spring-damper dynamics to the shape curve defining the motion of the robot. The performance of the control strategies is illustrated with simulation results.

Snake robots are biomimetic robots highly suited for traversing challenging terrain where traditional robots have difficulty moving. A key aspect is obstacle-aided locomotion, where the snake pushes against the environment to achieve the desired propulsion. The main focus of this work is to optimally determine how to use the motor torque inputs that result in obstacle forces suitable to achieve some user-defined desired path for the snake. To this end, we present a new dynamical snake model, an explicit algebraic relationship between input and obstacle forces, and formulate an optimization problem that seeks to minimize energy consumption while achieving propulsion along the desired path.

This paper presents a motion planning framework for three-dimensional body shape control of snake robots. Whereas conventional motion planning approaches define the body shape of snake robots in terms of their individual joint angles, the proposed framework allows the body shape to be specified in terms of Cartesian coordinates in the environment of the robot. This approach simplifies motion planning since Cartesian coordinates are more intuitively mapped to the overall body shape of the snake robot. The paper demonstrates the applicability of the framework for realizing different types of three-dimensional motion patterns.

This paper presents the snake robot Mamba, which is a modular, reconfigurable, and waterproof experimental platform developed to support the ongoing research on snake robot locomotion, including underwater locomotion. A novel contribution of the snake robot is its ability to measure environment contact forces acting along its body, which is achieved by isolating the actuator inside each joint module with a custom-designed force/torque sensor. The paper describes the design of this sensor and presents experimental results which illustrate its performance.

This paper presents a control framework for shape control of snake robots for the purpose of locomotion. An advantage of the framework is that it allows the macroscopic shape of a snake robot to be controlled explicitly and intuitively. The framework is based on specifying the desired shape of the snake robot as a continuous shape curve defined by a set of shape control points interconnected by Bézier curves. We propose a novel approach for motion generation in which the shape curve is repeatedly extended according to a desired gait pattern while a virtual snake robot is progressed along the shape curve to retrieve joint reference angles for the physical snake robot. Practical applications of the proposed control framework are exemplified along with simulation results.

This paper presents the design of a waterproof and mechanically robust joint module for the snake robot Mamba. The main contribution of the module is a custom-designed force/torque sensor based on strain gauges, which enables the module to measure forces and torques acting on its joint shaft. The ability to measure joint constraint forces and torques enables a snake robot to estimate the external contact forces from its environment, which is important for intelligent and adaptive snake robot locomotion. The paper presents experimental results which illustrate the performance of the force/torque sensor.

As a step towards enabling snake robots to move in unstructured environments, this paper considers control strategies where environment adaptation is combined with directional control of snake robot locomotion. The first contribution of the paper is a general framework for motion control of snake robots, which allows the motion to be specified in terms of a body wave component, an environment adaptation component, and a heading control component. As a second contribution, we employ the controller framework to propose a control law for straight line path following control of snake robots in environments with obstacles. The paper presents simulation results where the path following controller is combined with a waypoint guidance strategy in order to steer the snake robot between waypoints in an obstacle environment.

In a recent paper, the authors have proposed a control strategy for a snake robot during obstacle-aided locomotion. In this paper, experimental results are presented where the controller is shown to successfully maintain the forward propulsion of a physical snake robot in a course with different obstacle configurations.

This paper derives and experimentally investigates fundamental properties of the velocity of a snake robot conducting lateral undulation. In particular, the derived properties state that the average forward velocity of the snake robot 1) is proportional to the squared amplitude of the sinusoidal motion of each joint of the robot, 2) is proportional to the angular frequency of the sinusoidal motion of each joint, 3) is proportional to a particular function of the constant phase shift between the joints, and 4) is maximized by the phase shift between the joints that also maximizes the particular phase shift function. The paper presents an experimental investigation of the validity of these derived properties by measuring the forward velocity of a physical snake robot during lateral undulation. The experimental results support the theoretical findings.

A snake robot can traverse cluttered and irregular environments by using irregularities around its body as push-points to aid the propulsion. This is denoted obstacle-aided locomotion and requires the snake robot to have two features: 1) a smooth exterior surface combined with 2) a contact force sensing system. These two features are characteristic of biological snakes, but have received limited attention in snake robot designs so far. This paper describes the development of a new snake robot aimed at meeting both these requirements. The paper details the design and implementation of the snake robot, presents experimental results that validate the function of the contact force measurement system, and demonstrates some of the motion capabilities of the robot.

A snake can traverse cluttered and irregular environments by using irregularities around its body as push-points to aid the propulsion. This characteristic feature of biological snake locomotion, denoted obstacle-aided locomotion, is investigated for snake robot locomotion purposes in this paper. The paper presents a hybrid model of the dynamics of a planar snake robot interacting with obstacles in its environment. Obstacle contact forces are calculated by formulating and solving a linear complementarity problem (LCP). The existence and uniqueness properties of the state evolution of the hybrid model are investigated. Simulation results validate the hybrid modelling approach.

This paper presents a model of the kinematics and dynamics of a planar, wheelless snake robot aimed at control design and stability analysis purposes. The proposed model is significantly less complex than existing models of planar snake robot locomotion. The paper presents an analysis of an existing complex snake robot model which reveals a set of essential properties that characterize the overall motion of a planar snake robot. The proposed model is developed to capture only these essential properties of snake locomotion, thereby significantly reducing the complexity compared to the original model used in the analysis. The paper presents simulation results that indicate that the qualitative behaviour of the proposed model and the original complex model are similar, and that a quantitative similarity is achieved with a proper choice of numerical values of the friction coefficients in the two models.

This paper presents a set of fundamental properties of the velocity of a snake robot conducting lateral undulation on a planar surface. In particular, the derived properties state that the average forward velocity of the snake robot 1) is proportional to the squared amplitude of the sinusoidal motion of each joint of the robot, 2) is proportional to the angular frequency of the sinusoidal motion of each joint, 3) is proportional to a particular function of the constant phase shift between the joints, and 4) is maximized by the phase shift between the joints that also maximizes the particular phase shift function. The paper presents simulation results that support the validity of the derived properties.

A snake can traverse cluttered and irregular environments by using irregularities around its body as push points to aid the propulsion. This characteristic feature of biological snake locomotion, which is denoted as obstacle-aided locomotion, is investigated for snake robot locomotion purposes in this paper. The paper presents a hybrid model of the dynamics of a planar snake robot interacting with obstacles in its environment. Obstacle contact forces are calculated by formulating and solving a linear complementarity problem (LCP). The existence and uniqueness properties of the state evolution of the hybrid model are investigated. The paper also presents a hybrid control strategy employing measured contact forces to maintain propulsion while simultaneously preventing the snake robot from being jammed between obstacles in its path. The simulation results validate the hybrid modelling approach and the effectiveness of the proposed control strategy.

A snake robot can traverse cluttered and irregular environments by using irregularities around its body as push-points to aid the propulsion. This is denoted obstacle-aided locomotion and requires the snake robot to have two features: (1) a smooth exterior surface combined with (2) a contact force sensing system. These two features are characteristic of biological snakes, but have received limited attention in snake robot designs so far. This paper presents a joint mechanism for a snake robot aimed at meeting both these requirements. The paper details the design and implementation of the joint mechanism and presents experimental results that validate the function of the contact force measurement system.

A snake robot can traverse cluttered and irregular environments by using irregularities around its body as push-points to aid the propulsion. This characteristic feature of snake locomotion, denoted obstacle-aided locomotion, has received limited focus in previous literature. This paper presents a model of this phenomenon and a control strategy employing measured contact forces to maintain propulsion while simultaneously preventing the snake robot from being jammed between obstacles in its path. The simulation results validate the contact modelling approach and the effectiveness of the proposed control strategy.

This paper investigates the controllability properties of planar snake robots influenced by viscous ground friction forces. The paper provides three contributions: 1) A partially feedback linearized model of a planar snake robot is developed. 2) A stabilizability analysis is presented proving that any asymptotically stabilizable control law for a planar snake robot to an equilibrium point must be time-varying. 3) A controllability analysis is presented proving that planar snake robots are not controllable when the viscous ground friction is uniform, but that a snake robot becomes strongly accessible when the viscous ground friction is non-uniform. The analysis also shows that the snake robot does not satisfy sufficient conditions for small-time local controllability (STLC).

This paper presents an analysis of snake locomotion that explains how non-uniform viscous ground friction conditions enable snake robots to locomote forward on a planar surface. The explanation is based on a simple mapping from link velocities normal to the direction of motion into propulsive forces in the direction of motion. From this analysis, a controller for a snake robot is proposed. A Poincare¿ map is employed to prove that all state variables of the snake robot, except for the position in the forward direction, trace out an exponentially stable periodic orbit.

This paper presents the SnakeFighter concept and describes the generic element within this concept in the form of a water hydraulic snake robot. Applications of a SnakeFighter system are presented with focus on fire intervention tasks. The development of a water hydraulic snake robot that demonstrates the concept is described. The robot is the first water hydraulic snake robot ever constructed. The paper identifies design challenges of a complete SnakeFighter system and describes future research on this concept

A preliminary design of a remote palpation instrument for minimally invasive surgery (MIS) is given. The lack of the tactile sense in MIS limits the surgeon's abilities to examine and palpate internal organs. Based on this problem, the aim of this paper is to describe a surgical instrument which can serve as an extension of the surgeon's fingers. A piezoelectric sensor array attached to the instrument's end effector provide tactile information, which is sent to the surgeon's fingers via a tactile display to provide a feeling of the shape and hardness of the tissue. The sensor array is 24 mm /spl times/ 8 mm and consists of 30 piezoelectric sensors, while the tactile display constitutes of 30 micro motors adding up to a total size of 32 mm /spl times/ 18 mm /spl times/ 45 mm.