Comparison of Inverse Kinematics Algorithms for Multi-Section Continuum Robots

Continuum robots are a unique type of robots that move due to the elastic deformation of their own body. Their flexible design allows them to bend at any point along their body, thus making them usable in workspaces with complex geometry and many obstacles. Continuum robots are used in industry for non-destructive testing and in medicine for minimally invasive procedures and examinations. The kinematics of continuum robots consisting of a single bending section are well known, as is the forward kinematics for multi-section continuum robots. There exist efficient algorithms for them. However, the problem of inverse kinematics for multi-section continuum robots is still relevant. The complexity of the inverse kinematics for multi-section continuum robots is quite high due to the nonlinearities of the robots’ motion. The article discusses in detail the modification of the FABRIK algorithm proposed by the authors, as well as a Jacobian-based iterative algorithm. A comparison of inverse kinematics algorithms for multi-section continuum robots with constant section length is given and the results of the experiment are described.

Uniqueness results for bodies of constant width in the hyperbolic plane

Following Santaló’s approach, we prove several characterizations of a disc among bodies of constant width, constant projection lengths, or constant section lengths on given families of geodesics.

Investigation on the Performance of a Solar Hybrid Refrigeration System Using Environmentally Friendly Fluids

In order to evaluate the performance of a hybrid compression / ejection refrigeration system using solar energy at low or medium temperature, a simulation model of its behavior based on those of its various components has been developed. It includes in particular for the ejector, a 1-D model of the "constant section mixing" type developed in optimal transition regime. The refrigerants tested are steam for the ejector loop and the R1234yf (replacing the R134a) for the mechanical compression loop. The behavior of the H2O vapor flowing in the ejector is considered that of the perfect gas. The properties of refrigerants are calculated using REFPROP® software, everywhere else. For a cooling capacity of 10 kW and air conditioning operating conditions, the model allows to determine the main parameters of the ejector and its entrainment ratio, the thermal and mechanical COP of the whole refrigeration system as well as the necessary surface of the solar collector. Furthermore, the influence of the temperature of the boiler, the condenser, the intercooler as well as that of the evaporator on the mechanical COP of the hybrid system and the solar collection surface in particular, were examined. The results highlight that the solar refrigeration system with hybrid cycle compression/ejection using the refrigerants H2O/R1234yf allows an increase of the mechanical COP higher than 50% compared to that of the conventional refrigeration system and thus constitutes an acceptable ecologically system that can compete with the latter.

Estimated closeness of optimum piecewise constant section width in I-rods with stability or first eigen-frequency limits to the predicted minimum material consumption with regard to strength requirements

The previous research described estimated closeness of optimum piecewise constant section width in I-rods with stability or first eigen-frequency limits to the predicted minimum material consumption with regard to strength requirements in continuous change in variable rod parameters. It is however known that in construction, rods are generally designed with piecewise constant change in the section parameters. Besides, in another work, the criterion was formulated for assessment of optimum solutions of piecewise constant sections of I-rods with stability or the first eigen-frequency limits, without considering the strength requirements. This paper focuses on a more general problem of estimated closeness of optimum piecewise constant section width in I-rods with stability or first eigen-frequency limits to the predicted minimum material consumption with regard to strength requirements.

INVESTIGATION OF RELIABILITY OF THE SCREW UNIT OF THE COAL-ROLL PRESS BТ-3М

In the article we propose the method of calculation of parameters of stress state and rigidity of screw blade at bending in one plane, screw-piston press of BТ-3М grade for production of coal briquettes is simultaneously mixing, transporting and pressing unit. The blade is regarded as a thin axially endless helicoid shell rigidly attached to the shaft along an internal helical boundary. Considering that the presence of the blade does not affect the deformation of the constant-section shaft during bending, we examine the effect of the presence of the blade on the bending stiffness of the screw. Invention covers the problem of screw blade deformations at preset displacements at inner boundary caused by shaft bending considering that its axis has curvature. In the second stage of calculation we construct a compensating solution, which eliminates inconsistencies in differential equilibrium equations and static boundary conditions, and on the inner contour of the shell we set conditions of rigid pinching. As a result, the screw was calculated using the developed method. Blade is calculated with parameters r1 = 0.04 m, r2 = 0.1 m, r3 = 0.03 m, screw blade thickness d = 0.005 m, L = 0.2 m, total length of hollow shaft 1, 2 m. Calculations have shown that at such screw parameters and created specific pressure of material on the screw Ore = 8.5 · 105 Pa, the rigidity of the blade is the stiffness 11% of the tubular shaft. Keywords: screw, press, calculation, briquette, extras, equations.

Energy-shaping control of soft continuum manipulators with in-plane disturbances

Soft continuum manipulators offer levels of compliance and inherent safety that can render them a superior alternative to conventional rigid robots for a variety of tasks, such as medical interventions or human–robot interaction. However, the ability of soft continuum manipulators to compensate for external disturbances needs to be further enhanced to meet the stringent requirements of many practical applications. In this paper, we investigate the control problem for soft continuum manipulators that consist of one inextensible segment of constant section, which bends under the effect of the internal pressure and is subject to unknown disturbances acting in the plane of bending. A rigid-link model of the manipulator with a single input pressure is employed for control purposes and an energy-shaping approach is proposed to derive the control law. A method for the adaptive estimation of disturbances is detailed and a disturbance compensation strategy is proposed. Finally, the effectiveness of the controller is demonstrated with simulations and with experiments on an inextensible soft continuum manipulator that employs pneumatic actuation.

ДО РОЗРАХУНКУ ГЕОМЕТРИЧНИХ ПАРАМЕТРІВ ПОДАТЛИВИХ ГРАНЕЙ КЛИНІВ

Development of recommendations for calculating the geometry of cams with flexibility facet, which have console beams with variable moment of section resistance along their length for provide strength conditions and specified deflections. Method of search, description, analogous and information analysis is used to audit the many possible decisions regarding the subject of research, the experience in the field of knitting machines of automatic half-hose machine and methods of cross and longitudinal sections from the classical position of resistance of materials. Mathematical support for the complex approach of working out of cams of various designs with flexibility working facets according to the criteria of strength, flexibility and minimization of geometric dimensions using the beam shape coefficient of deflections is presented. The advantages of beams with equal resistance along its length in comparison with homogeneous beams having constant section sizes are shown. The dependences are given, which advisable to determine the dimensions of the root and final sections of a trapezoidal beam with a free end load of concentrated force, and also formulas for calculating the shape coefficient by deflection with sufficient accuracy and convenience in engineering calculations. Further development of the theory and methodology of designing elements of knitting systems of automatic half-hose machine based on load modes, dimensions restrictions and technological process requirements. Questions are presented that contribute to a comprehensive approach to the improvement of cams designs with flexibility facet based on calculated recommendations, taking into account their specificity. The information helps to improve the quality and efficiency of cam design solutions to meet the requirements for strength and flexibility using the economic index of section.