The Design And Development Of Flexible Capacitive Tactile Sensor

With the outstanding performances of collaborative robots in the fields of flexible manufacturing and human-machine collaboration,more and more robots are completing production tasks with human-beings in the same space,resulting in more frequent interactions.In this unstructured environment,it is an important research direction that enhancing robots' perception abilities so as to guarantee human's as well as robots' safety.This puts forwards the demand for flexible tactile sensors that can be easily installed on the complex robot surfaces to detect 3D contact force.At present,most research are focusing on monitoring human-health signals etc,so there is a great prospect exploring 3D force measurment on robot surfaces.At the same time,most flexible capacitive sensors researchers focus on designing microstructure or dopping conductive particles materials in the dielectric layer,but the combination of the two methods to improve sensitivity has not received sufficient attention.Therefore,this article carries out the development of a flexible 3D force tactile sensor for the robotic arm surfacrs.First,I summarize the published flexible force tactile sensors based on different principles,compare and analyze their advantages and disadvantages.Secondly,this article designs the structure of the sensor through combining two optimization methods.Afterwards,the sensor body was manufacured by photolithography-wet etching technology,and a set of low-cost special packaging equipments was designed.Next,the Pcap chip and STM32 micro-controller were used to collect,measure and transmit the capacitance signal s.Finally,tests of basic performances and the calibration of 3D force measurement are carried out.Based on the principle of parallel plate capacitance,the sensor is divided into three parts.The effects of button in the top-layer are analyzed and its parameters are optinuzed.The shape and size of the microstructure in dielectric layer are determined by the finite element simulation of micro capacitor unit.The theory of doping conductive particles to improve sensitivity is analyzed,and the principle of 3D force measurement based on the arrangement of electrode plates is studied.In manufacturing the sensor body,dielectric layer templates of the pyramid structure and truncated cone structure are prepared by silicon photolithography-wet etching technology and micro-machining technology respectively.The dielectric layer was directly formed on the FPC used as electrode plates by pouring PDMS into the template and covering FPC on it.Limited by lab's equipment,a set of low-cost packaging equipment is designed to encapsulate the sensor layer by layer,and the capacitance signal is led out by FPC.This article uses the Pcap01 AD chip to collect and measure the capacitance signal through SPI communication and tries grounding and floating measurement methods.STM32F103 is used to register configuration,measure capacitance and get data from the Pcap chip.At the same time,the data is sent to the PC terminal for visualization,and the fastest capac itance measurement frequency can reach 100 Hz.Finally,in the experiments,the prepared sensor and others are installed on the assembled 3D force loading platform,and the basic properties such as repeatability,dynamic response and hysteresis are tested.The data fitting method is used to calibrate 3D force measurement and calculate sensitivity.