A high resolution traction stress sensor array for use in robotic tactile determination

Abstract

When two solid bodies are brought into physical contact, a stress profile is generated at the interface. This contact stress profile, termed traction stress, has three components: one component oriented normal to the surface (normal stress), and two components oriented tangent to the surface (shear stress). It has long been recognized that processing this contact stress information is important to the formation and maintenance of stable grasp configurations in dexterous robotic manipulation systems. Throughout the past two decades, many contact stress sensor arrays have been developed with the intent of conferring upon robotic manipulators the ability to sense tactile information. Indeed, a broad variety of transduction mechanisms have been harnessed to this end. However, much of the utility of tactile sensors in robotic manipulation has been demonstrated with relatively low spatial resolution arrays that are insensitive to shear stress. In fact, only one array capable of simultaneously measuring both shear and normal stress information has been demonstrated to date. Nonetheless, the successful development of a robust, high resolution, shear sensitive contact stress sensor would most certainly expand the range of manipulation tasks that may be performed by robotic systems. The first tactile sensing array capable of measuring triaxial contact stress profiles at a high spatial resolution has recently been developed at Stanford University. The array, composed of 4,096 (64 x 64) sensor elements, was constructed using VLSI circuit fabrication techniques, thereby allowing a sensor spacing comparable to that of the papillary ridges of the human dermis (300 μm). Digital CMOS circuitry has been integrated on the device substrate to allow sequentially scanning of the 1.92 x 1.92 cm active sensing area. Testing of the device indicates performance which is commensurate with that needed for a useful robotic tactile sensor. Characterization studies revealed that the sensor array was capable of measuring two dimensional contact stress profiles with normal and shear stress measurement resolutions of 0.20 kPa and 1.0 kPa respectively, as well as a two-point spatial resolution of 0.7 mm. In this thesis, the design, construction, fabrication, and characterization of the array are presented.