Compliant multistable tensegrity structures. - In: Mechanism and machine theory, Bd. 115 (2017), S. 130-148
In this paper, a method to identify compliant tensegrity structures with multiple states of self-equilibrium is described. The considered algorithm is based on the repeated use of a form-finding procedure, using the static Finite-Element-Method. The algorithm can be used in the development process of compliant multistable tensegrity structures with simple topologies, consisting of only few members. As examples four planar tensegrity structures with two or three stable equilibrium configurations are considered and verified experimentally. Furthermore, a specific kind of multistable tensegrity structures, which have identical convex hulls, but differing prestressed states in their equilibrium configurations, is investigated. The potential technical use of the considered structures is discussed in the context of shape-changing locomotion systems using transitions between their equilibrium configurations.
https://doi.org/10.1016/j.mechmachtheory.2017.04.013
Dynamic analysis of a spherical mobile robot based on a tensegrity structure with two curved compressed members. - In: Archive of applied mechanics, ISSN 1432-0681, Bd. 87 (2017), 5, S. 853-864
The use of mechanically compliant tensegrity structures in mobile robotics is an attractive research topic. The mechanical properties and therefore the locomotion performance of mobile robots based on these structures can be adjusted reversibly during locomotion. In the present work, a rolling mobile robot, based on a simple tensegrity structure, consisting of two rigid disconnected curved members connected to a continuous net of eight prestressed tensioned members with pronounced elasticity, is considered. Pure rolling uniaxial locomotion and also planar locomotion can be realized with small control effort, induced by the movement of two internal masses. After kinematic considerations, the nonlinear equations of motion are derived and transient dynamic analyses are performed, to study the system behavior. Also the dependency of the rolling movement behavior on structural and actuation parameters is discussed. The uniaxial and planar locomotion performance of the system are verified experimentally.
https://doi.org/10.1007/s00419-016-1183-z
A multistable tensegrity structure with a gripper application. - In: Mechanism and machine theory, Bd. 114 (2017), S. 204-217
Multistable tensegrity structures are a new interesting class of compliant prestressed structures. Due to their beneficial properties, these structures are attractive for robotic applications. In this paper a gripper is introduced, which is based on a mechanical compliant, multistable tensegrity structure. The underlying tensegrity structure of the considered gripper is investigated in detail. The influence of the member parameters on the existence of multiple states of self-equilibrium and the mechanical compliance is discussed with the help of static geometric nonlinear analyses, based on the Finite Element Method. The dynamical behaviour of the structure, during the change between the equilibrium configurations, is considered. Therefor the dynamical equations of motion are derived. Then gripper arms are added to the tensegrity structure to obtain a gripper. Different actuation principles for the gripper are discussed. Additionally, a prototype of the gripper has been built and is presented, as well as, selected experimental results.
https://doi.org/10.1016/j.mechmachtheory.2017.04.005
Motion behaviour of magneto-sensitive elastomers controlled by an external magnetic field for sensor applications. - In: Journal of magnetism and magnetic materials, ISSN 1873-4766, Bd. 431 (2017), S. 262-265
The development of sensor systems with a complex adaptive regulation of the operating sensitivity and behaviour is an actual scientific and technical challenge. Smart materials like magneto-sensitive elastomers (MSE) are seen as one potential solution for this problem, since their mechanical properties may be controlled by external magnetic fields. The present paper deals with the investigation of elastic and damping properties of MSE containing magnetically soft particles under the influence of a uniform magnetic field. Based on the measurement of the first eigenfrequency of free bending vibrations of a fixed beam, the effective Young's modulus is evaluated theoretically and also numerically using Finite Element Method. It is shown that this parameter, as well as the first eigenfrequency of the beam, increases monotonically with the magnitude of the applied magnetic field. The results are aimed to develop an acceleration sensor with adaptive magnetically controllable sensitivity range for the detection of external mechanical stimuli of the environment.
http://dx.doi.org/10.1016/j.jmmm.2016.10.009
A ferrofluid based artificial tactile sensor with magnetic field control. - In: Journal of magnetism and magnetic materials, ISSN 1873-4766, Bd. 431 (2017), S. 277-280
The paper deals with a tactile sensor inspired by biological hairs of mammals. The working principle is based on the effect of the magnetic force exerted on a paramagnetic body submerged into a ferrofluid volume under the influence of a nonuniform magnetic field. The deflection of the sensor's rod caused by external mechanical stimuli may be unambiguously identified by the distortion of the magnetic field, which occurs due to the motion of the attached body in the ferrofluid. The magnetic force acting on the body is evaluated experimentally and theoretically for the nonuniform magnetic field of a permanent magnet. The controlled oscillations of the rod are realised by applying a nonuniform magnetic field of perodically altering direction.
http://dx.doi.org/10.1016/j.jmmm.2016.09.105
Kinematic response in limb and body posture to sensory feedback from carpal sinus hairs in the rat (Rattus norvegicus). - In: Zoology, ISSN 1873-2720, Bd. 121 (2017), S. 18-34
One of the most challenging adaptations within the therians has been to ensure dynamic stability of the trunk during rapid locomotion in highly structured environments. A reorganization of limb mechanics and development of new sensors has taken place within their stem lineage. Rats, which have a similar lifestyle to the first therians, possess sinus hairs specialized for tactile sensing. It is supposed that carpal sinus hairs have a role in sensing substrate properties and can thus induce adjustments in limb kinematics and body posture according to the different surface diameters and structures detected. This implies a shared sensorimotor control loop of sinus hairs and body posture. To investigate the role of the carpal sinus hairs during locomotion and to explore a possible interaction between limb and spine motion, spatiotemporal and kinematic parameters as well as the contact mechanics of the hairs with regard to the surface were quantified. Locomotion on a treadmill with continuous and discontinuous substrates was compared in the presence/absence of the carpal sinus hairs across a speed range from 0.2 m/s to 0.6 m/s. Recordings were taken synchronously using x-ray fluoroscopy and normal-light high-speed cameras. Our investigation revealed that the three tactile hairs made a triangle-like contact with the ground approximately 30 ms before touchdown of the forelimb. Within that time, it is likely that both the body posture and its oscillation are adjusted according to the different surface textures. The sensory input of the carpal sinus hairs induces a stabilization of the trajectory of the center of mass and, therefore, improves the dynamic stability of the trunk; conversely, the absence of the sensors results in a more crouched frontal body posture, similar to that seen in rats when they are moving in an unknown terrain. The carpal sinus hairs also sense the animal's speed during surface contact. This implicates an adjustment of the limb and spine kinematics, by increasing the speed-dependent effect or by increasing the distance between the trunk and the ground when the rat is walking faster.
http://dx.doi.org/10.1016/j.zool.2017.02.001
General design equations for the rotational stiffness, maximal angular deflection and rotational precision of various notch flexure hinges. - In: Mechanical sciences, ISSN 2191-916X, Bd. 8 (2017), 1, S. 29-49
Notch flexure hinges are often used as revolute joints in high-precise compliant mechanisms, but their contour-dependent deformation and motion behaviour is currently difficult to predict. This paper presents general design equations for the calculation of the rotational stiffness, maximal angular elastic deflection and rotational precision of various notch flexure hinges in dependence of the geometric hinge parameters. The novel equations are obtained on the basis of a non-linear analytical model for a moment and a transverse force loaded beam with a variable contour height. Four flexure hinge contours are investigated, the semi-circular, the corner-filleted, the elliptical, and the recently introduced bi-quadratic polynomial contour. Depending on the contour, the error of the calculated results is in the range of less than 2 % to less than 16 % for the suggested parameter range compared with the analytical solution. Finite elements method (FEM) and experimental results correlate well with the predictions based on the comparatively simple and concise design equations.
https://doi.org/10.5194/ms-8-29-2017
Dynamics and motion control of a chain of particles on a rough surface. - In: Mechanical systems and signal processing, ISSN 1096-1216, Bd. 89 (2017), S. 3-13
In this paper the mechanics and control of the motion of a straight chain of three particles interconnected with kinematical constraints are investigated. The ground contact is described by dry (discontinuous) or viscous (continuous) friction. Here, we understand this model as a methodological basis for the design of worm-like locomotion systems, i.e., non-pedal mobile robots. This kind of robots will prove an efficient form of locomotion in application to inspection of pipes or for rescue missions. In this paper, a number of issues related to the dynamics and control of artificial limbless locomotion systems are discussed. Simplest models of a limbless locomotor are two-body or three-body systems that move along a horizontal straight line. In the first part of the paper, the controls are assumed in the form of periodic functions with zero average, shifted on a phase one concerning each other. Thus, there is a traveling wave along the chain of particles. In the second part, actuator models are discussed. It is supposed that there are unknown actuator data or the worm system parameter are not known or exactly as well. The focus is on adaptive control algorithms for the worm-like locomotion systems in order to track given reference trajectories, like kinematic gaits. Finally, a prototype together with its signal processing and control software is presented. Theoretically (analytically and numerically) calculated results of the dynamical behavior of the mobile system are compared to experimental data.
http://dx.doi.org/10.1016/j.ymssp.2016.11.001
A biologically inspired sensor mechanism for amplification of tactile signals based on parametric resonance. - In: Microactuators and Micromechanisms, (2017), S. 27-38
In this paper, the vibrational motion of an elastic beam under the parametric excitation is investigated theoretically and numerically. The problem is motivated by biological tactile sensors, called vibrissae or whiskers. Mammals use these thin long hairs for exploration of the surrounding area, object localization and texture discrimination. We propose a mechanical model of the vibrissa sweeping across a rough surface as a straight truncated beam stimulated by a periodic following force. The equation of transverse motion of the beam is studied using the Euler-Bernoulli beam theory and asymptotic methods of mechanics. The numerical analysis is performed by means of the finite element method. It is shown that the parametric resonance of the beam occurs at the specific ranges of the excitation frequency, which depend on the parameters of the beam and the amplitude of the applied force. For these frequency values, the vibrations of the beam are unstable with exponentially increasing amplitude. The comparison of the resonance ranges obtained theoretically and numerically is made. Thus, together with the realisation of the viscoelastic support of an artificial tactile sensor, the parametric resonance may be a potentially useful method for amplifying small signals arising from the contact with an object.
http://dx.doi.org/10.1007/978-3-319-45387-3_3
Towards the development of tactile sensors for determination of static friction coefficient to surfaces. - In: Microactuators and Micromechanisms, (2017), S. 39-48
http://dx.doi.org/10.1007/978-3-319-45387-3_4