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In this paper, we report real-time measurement results of various contact forces exerted on a new flexible capacitive three-axis tactile sensor array based on polydimethylsiloxane (PDMS).A unit sensor consists of two thick PDMS layers with embedded copper electrodes, a spacer layer, an insulation layer and a bump layer.There are four capacitors in a unit sensor to decompose a contact force into its normal and shear components.They are separated by a wall-type spacer to improve the mechanical response time.Four capacitors are arranged in a square form.The whole sensor is an 8 × 8 array of unit sensors and each unit sensor responds to forces in all three axes.Measurement results show that the full-scale range of detectable force is around 0-20 mN (250 kPa) for all three axes.The estimated sensitivities of a unit sensor with the current setup are 1.3, 1.2 and 1.2%/mN for the x-, y-and z-axes, respectively.A simple mechanical model has been established to calculate each axial force component from the measured capacitance value.Normal and shear force distribution images are captured from the fabricated sensor using a real-time measurement system.The mechanical response time of a unit sensor has been estimated to be less than 160 ms.The flexibility of the sensor has also been demonstrated by operating the sensor on a curved surface of 4 mm radius of curvature.
Lee et al. (Tue,) studied this question.