Research On Flexible Sensing System For Multi-information Perception Of Robots

Robots have gradually entered every field of human life with the development of robot intelligence,especially in intelligent manufacturing,health care,family services and other fields.Accurate real-time acquisition of environmental information is an important prerequisite for improving the safety,stability and flexibility of robots,which is of great significance for protecting the safety of humans and robots themselves.The built-in sensors based on multi-dimensional force,moment and angle cannot perceive the external environment information,while the visual sensors are affected by occlusion and the algorithm is complex.Flexible electronic devices have excellent ductility in the past ten years,which can be attached to the objects to perceive the external environment information accurately in real time.These devices used in intelligent sensing of robots are also called flexible electronic skin(e-skin),which can perceive one or more kinds of information such as physical properties,contact force,temperature and humidity.At present,flexible e-skin also has some problems,such as high coupling error between various kinds of information,affected by external environment easily and weak anti-impact ability.As a result,the electrical theoretical model,performance of sensing unit,development of sensing array and experimental verification of multi-information flexible sensing system are studied in this paper.A multi-stage sensitive structure model is proposed for the robot to respond to the long distance approach and wide range of contact forces,which is analyzed theoretically and optimized by simulation.The electrical model of multistage sensitive structure is established based on the basic principle of capacitance and resistance sensing.A physical model of sensor based on the vertical composite structure of coplanar electrode capacitance and flexible film is presented.The material and structural parameters of the flexible sensor unit are optimized for the detection accuracy and range of the sensor based on the theoretical formula derivation and multi-physical field simulation.The numerical optimization solution of the electrical theoretical model of the composite sensor is realized.The theoretical analysis results show that the sensor model can detect the long distance approach(100～0 mm)and the wide range of contact force(0～450 N).The proximity/tactile flexible sensing unit is studied based on the physical model of sensor.Firstly,the preparation technology of flexible composite films is studied.Carbon black is used as conductive filler and PDMS as polymer matrix.According to the change law of resistivity and relative dielectric constant of composite films near the seepage threshold,the filling concentration of carbon black of composite films is optimized as 2.5wt%.The mechanical/electrical properties of composite films at this concentration are studied.The high quality sensitive material is provided for sensor preparation.The preparation technology of sensing unit is studied.The mass preparation of sensor is realized by laser processing,template copying and layer by layer assembly.The proximity distance and contact pressure performance of the sensing unit are studied.The error between the experimental results and the simulation results is less than 4%,which verifies the correctness of the multistage sensitive structure electrical model and the applicability of the flexible sensor manufacturing process.A multi-information flexible sensing unit is developed based on the proximity and tactile function.The temperature-proximity/tactile flexible composite sensing unit is obtained by stacking the temperature-sensitive layer of nickel film vertically.The detection range of temperature module is 20～120 ℃,which has high linearity and sensitivity,low hysteresis error and drift rate.The temperature compensation by polynomial fitting makes the coupling degree of temperature-distance-pressure less than 5%,which improves the quality of sensor`s output signal.,The humidityproximity/tactile flexible composite sensing unit is obtained by stacking PVDF/PVA/Li Cl humidity sensitive layer vertically.The detection range of humidity module is 0～70%,which presents high linearity,sensitivity and low drift rate and hysteresis error.The cross-coupling errors of humidity,distance and pressure in the process of approach and contact are all less than 4.5%.The flexible sensing system is developed and its performance is verified based on the multi-information flexible sensing unit.The distribution design of each sensitive layer in the flexible sensor array is carried out,and the sensor array test system is developed according to this layout.As a result,the development of the multi-information flexible sensing system is completed.The verification platform of sensing system is built,and the layout strategy of sensing array attached to the robot arm is studied.The performance of sensing system on the robot arm is optimized and improved by introducing machine learning algorithm,installing electromagnetic shielding device and other hardware and software means.The effectiveness of the flexible multi-information sensing system is verified by the experiments of motion following and active safety control response of the robot arm.