Chakravarthini M. Saaj

Spacecraft Swarm Navigation and Control Using Artificial Potential Field and Sliding Mode Control

The artificial potential field (APF) method provides simple and effective path planners for practical terrestrial robotics control. Sliding mode control (SMC) strategy together with artificial potential field has been used for control of multi-agent systems or swarms. The aim of this work is to examine for the first time the applicability of APF and SMC for spacecraft swarm navigation and control. This paper demonstrates that spacecraft formation flying can be successfully achieved using SMC for closed loop feedback and APF method for path planning.

Measuring and Simulating the Effect of Variations in Soil Properties on Microrover Trafficability

The authors of this paper build on many years of experience in planetary rover locomotion system design and validation at the University of Surrey. One of the key lessons learned from these systems is how little is accurately understood about the deformation of soil under microrover systems. As such, this paper examines some areas of soil mechanics and their effect on traditional vehicle locomotion. Then, moving beyond wheeled and tracked locomotion systems for planetary rovers, the authors evaluate legged locomotion as a viable option for future robotic explorers. As such, a methodology for determining the tractive capability of a legged robot in Martian soil will be presented. Mathematical models developed in MATLAB validate the terramechanic theory behind the soil deformation under each of these experimental conditions and new models for measuring microrover capability in soil are proposed. Finally a legged vehicle is proposed and simulated in the software under Martian soil conditions in order for the vehicle’s performance to be measured.

Evolving legged robots using biologically inspired optimization strategies

When designing a legged robot a small change in one variable can have a significant effect on a number of the robots characteristics, meaning that making tradeoffs can be difficult. The algorithm presented in this paper uses biologically inspired optimization techniques to identify the effects of changing various robot design variables and determine if there are any general rules which can be applied to the design of a legged robot. Designs produced by this simulation are also compared to existing robot designs and biological systems, showing that the algorithm produces results which require less power and torque than similar robots, and which share a number of characteristics with biological systems.

A unified system identification approach for a class of pneumatically-driven soft actuators

The class of Pneumatically-driven Low-pressure Soft Actuators (PLSA) is a popular choice potentially used in the surgical robotic applications. One fundamental problem lying in the PLSA research is the lack of a generally validated model for the complex nonlinear dynamic behaviours. In this paper, a unified identification approach for the general PLSAs is proposed. It is a parameter-independent way directly used to identify the dynamical relation between the actuating pressures and the principal degrees of freedom of a PLSA, the bending and the steering. The approach is based on a modified auxiliary kinematic setting and a newly developed identification model structure, named DIO-PWL-OBF. Following the concluded identification procedure, the implementations for the single chamber bending and the double chamber bending and steering are demonstrated separately. The results show that the proposed approach can accurately capture the nonlinear pressure-shape dynamical relation. The approach is also efficient in real-time applications. It can be further used to improve the current control design for the PLSAs in robotic applications. A unified system identification approach is proposed.The approach is used to identify the nonlinear pressure-shape dynamic relation.The used auxiliary kinematic setting can be implemented by gyroscopic sensors.

Crimped braided sleeves for soft, actuating arm in robotic abdominal surgery.

Abstract Background: This paper investigates different types of crimped, braided sleeve used for a soft arm for robotic abdominal surgery, with the sleeve required to contain balloon expansion in the pneumatically actuating arm while it follows the required bending, elongation and diameter reduction of the arm. Material and methods: Three types of crimped, braided sleeves from PET (BraidPET) or nylon (BraidGreyNylon and BraidNylon, with different monofilament diameters) were fabricated and tested including geometrical and microstructural characterisation of the crimp and braid, mechanical tests and medical scratching tests for organ damage of domestic pigs. Results: BraidPET caused some organ damage, sliding under normal force of 2-5 N; this was attributed to the high roughness of the braid pattern, the higher friction coefficient of polyethylene terephthalate (PET) compared to nylon, and the high frequency of the crimp peaks for this sleeve. No organ damage was observed for the BraidNylon, attributed to both the lower roughness of the braid pattern and the low friction coefficient of nylon. BraidNylon also required the lowest tensile force during its elongation to similar maximum strain as that of BraidPET, translating to low power requirements. Conclusion: BraidNylon is recommended for the crimped sleeve of the arm designed for robotic abdominal surgery.

Trafficability Assessment of Deformable Terrain through Hybrid Wheel-Leg Sinkage Detection

Off-road ground mobile robots are widely used in diverse applications, both in terrestrial and planetary environments. They provide an efficient alternative, with lower risk and cost, to explore or to transport materials through hazardous or challenging terrain. However, nongeometric hazards that cannot be detected remotely pose a serious threat to the mobility of such robots. A prominent example of the negative effects these hazards can have is found on planetary rover exploration missions. They can cause a serious degradation of mission performance at best and complete immobilization and mission failure at worst. To tackle this issue, the work presented in this paper investigates the novel application of an existing enhanced-mobility locomotion concept, a hybrid wheel-leg equipped by a lightweight micro-rover, for in situ characterization of deformable terrain and online detection of nongeometric hazards. This is achieved by combining an improved vision-based approach and a new ranging-based approach to wheel-leg sinkage detection. In addition, the paper proposes an empirical model, and a parametric generalization, to predict terrain trafficability based on wheel-leg sinkage and a well-established semiempirical terramechanics model. The robustness and accuracy of the sinkage detection methods implemented are tested in a variety of conditions, both in the laboratory and in the field, using a single wheel-leg test bed. The sinkage-trafficability model is developed based on experimental data using this test bed and then validated onboard a fully mobile robot through experimentation on a range of dry frictional soils that covers a wide spectrum of macroscopic physical characteristics.

Design optimisation of soft silicone pneumatic actuators using finite element analysis

The current trend in soft robotic solutions is to pneumatically actuate chambers within manipulators that feature elastomeric material. This work describes the development of a repeating module actuator with each module capable of producing 3 degrees of freedom, as well as longitudinal expansion, intended for use as a laparoscopic tool in minimal invasive surgery. The design of the manipulator geometry as well as the choice of suitable material is dependent on the application, range of motion, and the suitable actuation pressure. This work describes the use of finite element analysis to simulate the range of motion of the hyperelastic response of two different soft silicones. Different geometry ratios and channel designs of the actuator are then optimized in terms of bending angle, maximum stress generated, radial expansion due to air pressure, and the amount of free area that the design allows in the actuator for other tools necessary in laparoscopic surgery. The optimum geometries are then selected as candidates for the development of the repeating module design, and the addition of skins to the module is investigated for the optimized module design.

Biorobotics: Innovative and low cost technologies for next generation planetary rovers

This paper details some of the various robotics projects which have been inspired by the natural world, and which the authors believe will have an impact on the future of robotic space exploration. This includes both hardware-centric projects such as RiSE, and projects which concentrate more on software and control such as Swarm-bots. The authors outline two of the biologically inspired planetary explorer robots currently under investigation at the University of Surrey.

A new coefficient-adaptive orthonormal basis function model structure for identifying a class of pneumatic soft actuators

The class of Pneumatically-driven Lower-pressure Soft Actuators (PLSA) is a popular research topic as it can be potentially used in the surgical robotic applications. One fundamental problem lying in the PLSA research is the lack of a generally validated model for the complex nonlinear dynamic behaviours. In this paper, a new coefficient-adaptive orthonormal basis function model structure is specifically developed for the identification of the general PLSAs. It is a parameter-independent way directly used to identify the dynamic relation between the actuating pressures and the principal degrees of freedom of a PLSA, the bending and the steering. The approach is based on a modified auxiliary kinematic setting. Following the discussion of the identification procedure, the implementations for the double chamber bending and steering are demonstrated. The results show that the proposed approach can accurately capture the nonlinear pressure-shape dynamics. The approach is also efficient in the real-time applications. It can be further used to improve the current control design for the PLSAs in robotic applications.

Anubis: Artificial neuromodulation using a bayesian inference system

Gain tuning is a crucial part of controller design and depends not only on an accurate understanding of the system in question, but also on the designers ability to predict what disturbances and other perturbations the system will encounter throughout its operation. This letter presents ANUBIS (artificial neuromodulation using a Bayesian inference system), a novel biologically inspired technique for automatically tuning controller parameters in real time. ANUBIS is based on the Bayesian brain concept and modifies it by incorporating a model of the neuromodulatory system comprising four artificial neuromodulators. It has been applied to the controller of EchinoBot, a prototype walking rover for Martian exploration. ANUBIS has been implemented at three levels of the controller; gait generation, foot trajectory planning using Bézier curves, and foot trajectory tracking using a terminal sliding mode controller. We compare the results to a similar system that has been tuned using a multilayer perceptron. The use of Bayesian inference means that the system retains mathematical interpretability, unlike other intelligent tuning techniques, which use neural networks, fuzzy logic, or evolutionary algorithms. The simulation results show that ANUBIS provides significant improvements in efficiency and adaptability of the three controller components; it allows the robot to react to obstacles and uncertainties faster than the system tuned with the MLP, while maintaining stability and accuracy. As well as advancing rover autonomy, ANUBIS could also be applied to other situations where operating conditions are likely to change or cannot be accurately modeled in advance, such as process control. In addition, it demonstrates one way in which neuromodulation could fit into the Bayesian brain framework.