Development of circuit solution and design of capacitive pressure sensor array for applied robotics

Abstract

This paper presents development of pressure sensor array with capacitance-type unit sensors, with scalable number of cells. Different assemblies of unit pressure sensors and their arrays were considered, their characteristics and fabrication methods were investigated. The structure of primary pressure transducer (PPT) array was presented; its operating principle of array was illustrated, calculated reference ratios were derived. The interface circuit, allowing to transform the changes in the primary transducer capacitance into voltage level variations, was proposed. A prototype sensor was implemented; the dependency of output signal power from the applied force was empirically obtained. In the range under 30 N it exhibited a linear pattern. The sensitivity of the array cells to the applied pressure is in the range 134.56..160.35. The measured drift of the output signals from the array cells after 10,000 loading cycles was 1.39%. For developed prototype of the pressure sensor array, based on the experimental data, the average signal-to-noise ratio over the cells was calculated, and equaled 63.47 dB. The proposed prototype was fabricated of easily available materials. It is relatively inexpensive and requires no fine-tuning of each individual cell. Capacitance-type operation type, compared to piezoresistive one, ensures greater stability of the output signal. The scalability and adjustability of cell parameters are achieved with layered sensor structure. The pressure sensor array, presented in this paper, can be utilized in various robotic systems.

Algorithm for Controlling Manipulator with Combined Array of Pressure and Proximity Sensors in Gripper

“…Based on previous research, an array with cells of a combined pressure and proximity sensor was developed [19]. The array design corresponds to the structure, given in [20]. For utilization in a gripper of an anthropomorphic robot [21,22], based on the developed circuits and design solutions, experimental prototypes of the sensors were assembled in the layout 2 × 2 (Fig.…”

Signal processing of capacitive force sensors installed in the foot of an anthropomorphic robot

“…The application of the interface scheme proposed in [19] for the matrix required a separate adjustment of each cell, which requires a significant amount of time. In [20], we proposed an interface circuit based on an operational amplifier, which requires tuning one matrix cell, and for the rest, the same component ratings are used. The disadvantage of the interface scheme described in [20] was that after adjusting the sensor the output signal from the interface circuit could change in a small range.…”

“…In [20], we proposed an interface circuit based on an operational amplifier, which requires tuning one matrix cell, and for the rest, the same component ratings are used. The disadvantage of the interface scheme described in [20] was that after adjusting the sensor the output signal from the interface circuit could change in a small range. This feature does not allow using the entire range of ADC values of the microcontroller, which negatively affects the accuracy of force measurement.…”

“…By changing the gain U 2 , it is possible to increase the sensor's sensitivity relative to the value obtained after adjusting the gain U 1 and selecting R 1 . The process of setting up the interface circuit without a differential amplifier and the calculated ratios are presented in detail in [20].…”

“…Experiments with the developed sensor matrix of a similar design described in [20] showed that the levels of the output signals of the cells of the sensor matrix differ from each other. This feature is mainly associated with the imperfect manufacturing of the sensor itself.…”