Cornelius Schilling

Structural Characterization of the Whisker System of the Rat

Vibrissae or tactile hairs, commonly known as whiskers, are the mechanical gates of special mechano-sensitive organs. In terrestrial mammals, they carry various functions, especially object determination and texture discrimination. We hypothesise that the characteristic morphology and structure of whiskers is a primary morphological condition for their mechano-sensitive functions. To constitute mathematical models on the systematic but different mechanical behavior of the main types of whisker hairs (micro vibrissae, macro vibrissae, straddlers), information is lacking on the distribution of properties in a field of all three types of hairs, taken from one and the same animal. Referring to sets taken from five individuals, geometry data is provided as one complete set for a female rat (Rattus norvegicus). Due to measurements of diameters along the length, the shape of whiskers in rats is confirmed to resemble a cone, which may be overlaid by some convexity or concavity. Additionally, the surface and internal structure of different vibrissae were examined by scanning electron microscopy. The cuticle of the rat whisker consists of flat scales, overlapping like roofing slates. A cross section reveals up to 20 superposed layers of cuticular scales. The longitudinal dimension of one scale is shorter in whiskers compared with body hairs. A hollow medulla is observed from the base to approximately half of the overall length, which is then partially filled by compact tissue, until it disappears completely near the tip. An extraordinarily thick cortex probably rules the characteristic bending features, and the multilayer cuticle probably has a mainly protective function.

Biomimetic robotics should be based on functional morphology

Due to technological improvements made during the last decade, bipedal robots today present a surprisingly high level of humanoid skill. Autonomy, with respect to the processing of information, is realized to a relatively high degree. What is mainly lacking in robotics, moving from purely anthropomorphic robots to ‘anthropofunctional’ machines, is energetic autonomy. In a previously published analysis, we showed that closer attention to the functional morphology of human walking could give robotic engineers the experiences of an at least 6 Myr beta test period on minimization of power requirements for biped locomotion. From our point of view, there are two main features that facilitate sustained walking in modern humans. The first main feature is the existence of ‘energetically optimal velocities’ provided by the systematic use of various resonance mechanisms: (a) suspended pendula (involving arms as well as legs in the swing phase of the gait cycle) and matching of the pendular length of the upper and lower limbs; (b) inverted pendula (involving the legs in the stance phase), driven by torsional springs around the ankle joints; and (c) torsional springs in the trunk. The second main feature is compensation for undesirable torques induced by the inertial properties of the swinging extremities: (a) mass distribution in the trunk characterized by maximized mass moments of inertia; (b) lever arms of joint forces at the hip and shoulder, which are inversely proportional to their amplitude; and (c) twisting of the trunk, especially torsion. Our qualitative conclusions are three‐fold. (1) Human walking is an interplay between masses, gravity and elasticity, which is modulated by musculature. Rigid body mechanics is insufficient to describe human walking. Thus anthropomorphic robots completely following the rules of rigid body mechanics cannot be functionally humanoid. (2) Humans are vertebrates. Thus, anthropomorphic robots that do not use the trunk for purposes of motion are not truly humanoid. (3) The occurrence of a waist, especially characteristic of humans, implies the existence of rotations between the upper trunk (head, neck, pectoral girdle and thorax) and the lower trunk (pelvic girdle) via an elastic joint (spine, paravertebral and abdominal musculature). A torsional twist around longitudinal axes seems to be the most important.

Characterization of Statical Properties of Rat's Whisker System

This contribution describes mechanical properties of the whisker system of rats. The motivation for the work was to achieve a better understanding of the functionality of this remarkable sense organ by defining structure-function-correlations. Special features of the different types of whisker are interpreted in terms of their morphological background, e.g., object recognition and texture discrimination. The whiskers are found to be conical in shape. Theoretical considerations of rod types reveal certain advantages of conically shaped rods over cylindrical rods. There is a difference in deformation, with the higher values applying to conical rods. Whiskers have a very flexible tip which is sensitive to very small forces. Uniaxial bending tests using actual whiskers were performed to characterize the static parameters. From experimental data obtained, the spring constant, the Youngs modulus and the flexural stiffness are calculated. Youngs modulus is one standard parameter for the characterization of materials. It was found that this can be regarded as constant along the whiskers with an average value of 7.36 GPa. Flexural stiffness was found to depend on the hair diameter and decrease from base to tip. The short vibrissae exhibit the lowest flexural stiffness, which means they are sensitive to very small forces. The experimental results obtained might well be used as a basis for the optimization or the construction of bioinspired technical sensor systems.

On technomorphic modelling and classification of biological joints

Biological motion systems are of particular interest to engineers in robotics, prosthetics and micromechanics. Since biological motion systems show a high degree of mobility, smooth movements and minimal deployment of material, the analysis of such systems might help to invent or optimize technical motion systems. To enable the transfer of explanatory techniques, biomechanics and engineering need a shared terminology. Generally, a reference limb, muscles, tendons, a joint and a driven limb are forming two closed mechanisms with different transfer functions. The direction of the forces applied to links is influenced by guiding structures. Movable connections can be constructed by form closure, force closure, and compliance of an anisotropic segment between two rigid segments. Eleven different basic variants of rigid-body joint structures can be classified by the possible relative translatory and rotatory movements in orthogonal co-ordinates. If classified by the form of their rigid parts, biological rigid-body joints (diarthroses) show some similarities to technical joints, but occur in fewer basic variants. The functioning of exoskeletal joints can involve hydrostatic forces, depending on the structure of the rigid elements and the type of linkage between them.

A modular robot climbing on pipe-like structures

“Raupi” is a prototype of a climbing robot. The robot is designed modularly, with the demands to climb on a pipe-like substrate and to change to another bar for avoiding. Research on biological climbers shows us, that the locomotion is driven by the trunk, not only by the limbs. So a trunk-driven concept is chosen as a base for the design process. The request by climbing locomotion to the mechanics of the system is very strong. The robot is build by only two different module types. The substrate contact has to be established and broken actively. A sensor concept a schematic was developed, with allow to determinate relevant sensor ranges depending on the desired type of control. It detects the relative position between gripping module and substrate by tactile sensors. The control of the robot is realized with four different modes. It is possible to switch between the modes. So it is possible to use the optimal control strategy for the actual situation.

A Modular Concept for a Biologically Inspired Robot

Many climbing robots are specialized for a certain substrate like glass-like Stickybot [20] (suction mechanisms or adhesive mechanisms) or porous substrates like Spinybot [21] (claw-like mechanisms). Thus, these robots are often expensive mechatronical systems. One possibility to gain more flexibility in application and to reduce costs is to modularize such systems. On the one hand we have to achieve high flexibility in application, but on the other hand we need a high performance robotic system. A major challenge is to do the step from specialists to generalists in climbing robots.

Biomechatronics is not just biomimetics

The idea of biomechatronics is based on the observation, that for mechatronic as well as for living systems a high degree of functional integration is characteristic. This allows biomimetic approaches without logical constraints. On the other hand, modularization is a major strength of mechatronics, while in life sciences “module” is a functional abstraction (e.g. the columns in the visual cortices of brains) with mostly diffuse structural boundaries. In practice, those contradictions turn out to be only of theoretical relevance, since biomechatronics is a strategy to gain better technical solutions, which has to be evaluated by its results, it is no ideology. For bio-robotics, the biomimetic principles of intensive use of compliance and of massive under-actuation may well be embodied in modular structures, providing integrated functions.

Energy harvesting for active implants: powering a ruminal pH-monitoring system

Abstract Energy harvesting is a feasible method to prolong service life of implanted devices. We present a thermal energy harvesting approach for a ruminal pH-monitoring probe in cattle. Thermoelectric generators utilize the temperature gradient between the probe and the ruminal fluid during water intake. The in vivo experiment yielded a maximum electric power of 32 μW.

Biomechatronics: how much biology does the engineer need?

Biomechatronics is the development and optimization of mechatronic systems using biological and medical knowledge. This strategy may be exemplified by bionically inspired robotics: identification of biological principles and their transfer into technical solutions extends the engineers toolbox. This modified kind of constructive thinking needs an adapted foundation in academic education.