Theoretical Analysis And Experimental Research Of Optical Wave-Guided Three-Axis Force Sensing Method

Recently, the development of intelligent robots requires considerably high-tech sensors. As one of the most important sensing methods, tactile sensing gets more and more attentions. There are many kinds of tactile sensors based on resistance, piezoelectricity effect, pyroelectricity effect, capacitance, magnetic conduction,etc. This paper reviews the current development of tactile sensing technology at home and abroad, and points out their advantages and disadvantages. However, among the numerous tactile sensors, there are no satisfactory solutions when measuring three-axis force directly.On the basis of one-axis tactile sensing technology, this paper brings forward a newly optical wave-guided three-axis tactile sensing technology. This new technology has many advantages such as large-scale force measurement, not affected by electromagnetism, shock proof, high sensitivity and easy to fabricate. Consequently, there is a lot of research being done in this field because of its scientific and practical significance. Moreover, this project gets financial aid from the National Science Foundation of the State.This paper details the principle of the sensor and the corresponding experiment system. It is comprised of a silicone rubber sheet, a wave-guide plate, an apparatus to apply three-axis force and facilities to capture faculae. There is a columnar contact-tip array on one side of the rubber sheet, and on the other side, corresponding to each columnar contact-tip, there is a conical contact-tip array(with 2×2 conical contact-tips) which directly contacts the wave-guide plate. When applying an external force on a columnar contact-tip, the corresponding four conical contact-tips will be pressed to the wave-guide plate, which breaks the condition of full inner reflection in the guided wave, and faculae arise because of the leaking light. The contact areas between the four conical contact-tips and the wave-guide plate are not equal as three components of external force are unequal, and the corresponding faculae areas captured by CCD camera are different from each other. In other words, the three components of the force can be calculated from the four contact areas.Based on the optical theory of planar wave-guide, this paper analyzes the transformation of pattern from symmetrical wave-guide to asymmetrical wave-guide. And the result shows that some patterns will radiate from the wave-guide when applying an external force on the sensor.This paper goes into details on the principle of faculae with Maxwell electromagnetic theory. In conclusion: The planar wave-guide is just like a high pass filter. The faculae arise with change of the cutoff frequency when the wave-guide transforms from symmetry to asymmetry. For each pattern rank of the planar wave-guide, the light with the cutoff frequency change will be leaked out and captured by the CCD camera.Through FEA method, it's suggested that the areas of faculae have a specific relationship with the externally applied force on the sensor. The corresponding mathematical model is deduced from many simulations using the APDL program.Finally, the reliability of the formula is verified by the data collected. Therefore, the component force in any direction can be easily calculated through the faculae captured by CCD camera, which provides a good solution to three-axis tactile sensing technology for intelligent robots.