Research On Object Hardness Measurement System Based On Resonant Tactile Sensor

With the further application of robot technology in the industrial field,medical field and other fields,the requirements of robot intelligence based on multi-source information perception are more and more urgent.Besides visual perception,tactile perception has received more and more attention in intelligent robot technology.For example,in the industrial field,in order to complete the safe and reliable grasping task of objects with different hardness,the robot can determine the hardness of objects through tactile perception,to exert the appropriate grasping force;In the medical field,robots can improve the success rate of surgery by simulating doctors’ palpation through tactile perception.Therefore,the development of tactile sensor system to improve the tactile perception performance of the robot is of great significance to the realization of robot intelligence.In this paper,the resonance frequency of the traditional resonant tactile sensor system is reduced by adding a soft silica gel disc between the driving element and the contact head,aiming at the problem of high resonance frequency and large mass effect when measuring the hardness of the object.In order to analyze the working principle of the resonant sensor system,the theoretical model of the whole sensor is derived according to the electromechanical model,including the model of the sensor structure and the contact impedance when the sensor contacts with the object.The correctness of the theoretical model of the sensor is preliminally verified after the calculation of the theoretical model with MATLAB.In order to further verify the correctness of the theoretical model and optimize the structural size of the sensor system,the finite element analysis of the sensor is carried out by using ABAQUS software.On the one hand,the structural size of the tactile sensor is determined by comparing the natural frequency of the sensor obtained from theoretical calculation and simulation analysis.At the same time,the small error between the two indicates the correctness of the theoretical model of the sensor.When in contact with the object,on the other hand,hardness measurement,the theory of calculation model is compared with the finite element simulation results,shows the smaller error,when joining contact impedance is verified the correctness of the theoretical model,at the same time,according to the frequency change trend under different hardness shows the difference between the sensor soft objects,the feasibility of hardness,It is also proved that it is necessary to reduce the resonance frequency of sensor to measure soft objects.It provides a strong theoretical support for the tactile sensor to identify object hardness.Based on the design scheme and theoretical analysis results,the tactile perception system of resonant object hardness is built.On the hardware,the resonant tactile sensor model is made,and the sensor driver and acquisition circuit are designed.On the software,Lab VIEW is used to design the human-computer interaction interface of the sensor system,and realize the real-time acquisition and processing operation of the sensor signal.Through the hardness test experiment,under the silica gel which simulates the biological tissue with different hardness,the tactile sensor has carried on the obvious distinction,indicating that the tactile sensor has the good object hardness identification ability in the range of 200～1000k Pa.The hardness tactile sensor has great potential in the application of surgical palpation and hardness identification of objects to be grasped.