BIOTACT.org

Artificial vibrissal sensing is a relatively new field. Basic questions concerning the ideal shape, and material properties of artificial whiskers; how best to transduce whisker deflections into sensor signals; and how to actuate the whiskers, either individually or as an array, remain to be answered. We will explore a variety of alternative solutions to those previously tested in order to get closer, in terms of functional properties, accuracy, and size, to the biological models we are trying to emulate. This work will be supported by biological investigations of the whisker, follicle, and early sensory processing stations, and by computational modelling of these components.

Specific issues to be addressed include:

• Material properties of the whisker shaft
• Sensor transduction
• Sensor actuation
• Sensor design
• Early sensory processing
• Technological advancement

Material properties of the whisker shaft

Facial whiskers are delicate, tapered elastic beams that deform easily upon touch, and probably also during whisking in air. Mechanical deformations convey specific sensory information about air currents and external objects via morphological effects such as changes in whisker curvature. The reliability and information content of this kind of “morphological computation”, and its use during active touch, will be investigated in order to optimise the design of this component.

Sensor transduction

Mechanoreceptors in the whisker follicle respond with high acuity to deflections of the whisker. Although several useful prototypes have been developed, the optimal design of transduction mechanisms for artificial whiskers has yet to be determined. Both existing prototypes and novel designs will be tested and their performance compared to that of their biological counterparts.

Sensor actuation

Muscle-like micro-actuators are currently a highly active research field in engineering. The challenge will be to design an actuated sensing device that is reliable, energy efficient, and of sufficiently small in size, but also provides fast and accurate actuation with adequate degrees of freedom of movement to replicate much of the versatility of natural whisking control.

Sensor design

The structure of the BIOTACT sensor will be inspired by the organisation of the rat vibrissae, where the longer, more widely-spaced, actuated macrovibrissae surround a dense array of shorter, non-actuated microvibrissae. Different technological solutions will likely be adopted for these two components. It is anticipated that the final device will be standalone, in the sense that it could be attached to a variety of different robot platforms. Indeed, for the purposes of development and testing, prototypes will mounted as the end-effector of a robot manipulator allowing them to be manoeuvred into any position in 3d space.

Early sensory processing

Each whisker follicle in the rat is innervated by up to 200 sensory fibres. Thus ascending signals are processed first in the trigeminal ganglion, then the trigeminal complex, and via loops involving the cerebellum, before being relayed to further processing stations in the mid- and fore- brain. Building on existing pilot work by consortium partners we will develop biomimetic models of these early sensory processing stations, to determine their effects on relayed signals. For example, sensory information from whisking contains artefacts produced by the animal's own movements. We will therefore employ a model of the adaptive cerebellar loop to test the hypothesis that the cerebellum monitors motor control signals and proprioceptive signals and uses these to remove self-movement artefacts from whisking information. Special purpose hardware in the form of application-specific integrated circuits (ASICs) will also be developed to provide compact, real-time implementation of these signal-processing operations.

Technological enhancements

We believe there are very many useful insights to be mined from the study of natural vibrissal touch systems. However, slavishly copying biology does not necessarily generate the most effective technologies. Therefore, in addition to developing a strongly biomimetic version of the BIOTACT sensor for use as a research tool, in the final year of the project we will look for ways to optimise and streamline the design without further specific regard for biological accuracy. We will then explore the potential of this technologically-enhanced sensor for applications in industrial settings.