Plantar Interface Stress Measurement System Based On Flexible Three-dimensional Interfaicial Stress Sensor

The stress distribution at the plantar interface can reflect the body’s gait characteristics,balance posture and other information,and it is one of the important biomechanical parameters of the human body.The detection of plantar interfacial stress provides an assessment method for the prevention and rehabilitation of clinical disease such as hallux valgus and diabetes,and has a role in promoting the research and development of clinical medicine,biomechanics,and physical training.Therefore,it is of great significance to study a measurement system that can detect the plantar interfacial stress.At present,the foot interface stress detection system can be divided into two categories,one is to install the rigid sensor array on the measurement platform,this method provides quantitative and repeatable results for the measurement of early plantar interfacial stress,but the bulky disadvantages of the measurement platform make it limited to laboratory research and cannot meet the demand for real-time plantar interface stress measurement over long distances.The other is embedding multiple micro-interface stress sensors into the insole to detect the stress distribution at the inter-plantar interface by measuring the force applied to each sensor when the sole is in contact with the support surface.This can be achieved without affecting the environment.Long-distance,long-distance,real-time measurements of foot interface stress,but the interfacial stress consists of the positive pressure perpendicular to the surface and the shear stress tangent to the surface.This type of measurement method is still insufficient for the study of three-dimensional force detection.In view of the above problems,this paper presents a flexible three-dimensional force interface stress sensor based on parallel plate capacitance and a three-dimensional interface stress distribution measurement system based on this sensor,it can realize long-distance and long-distance real-time measurement of the three-dimensional interfacial stress on the sole of the foot,which has the advantages of high sensitivity and flexibility and portability.This paper analyzes the working principle of the sensor to detect the positive pressure and the shear force,determines the measuring range and production materials of the sensor,designs the structure,size,and electrode coupling of the sensor,studies the manufacturing process of sensors and prepares sensor samples,designs a flexible three-dimensional force sensor experimental measuring device to analyze the static characteristics of the sensor.The results show that the sensor can detect 0-250 k Pa positive pressure,the sensitivity reaches 1.28 f F /N,the linearity reaches 3.40%,the maximum hysteresis citation error is9.37%,and the repeatability error is 2.50%.The sensor can detect 0-250 k Pa shear force,the sensitivity reaches 0.8f F/N,the linearity reaches 4.30%,the maximum hysteresis citation error is 2.73%,and the repeatability error is1.60%.In this paper,the flexible three-dimensional interface stress sensor is embedded in the insole,and a flexible foot three-dimensional interface stress distribution measurement system is designed.This paper analyzes the principle of detecting the stress distribution at the plantar interfacial through this system,determines the size of the measuring shoe and the position of the sensor unit embedded in the measuring shoe,studies the manufacturing process and the selection of production materials for measuring shoe soles,studies the preparation process of the plantar interface stress measurement system and make a measurement system prototype.In this paper,the stress distribution at the plantar interfacial surface of the normal adult male left heel followed by the ground period,the foot relaxation period and the heel-to-heel.This paper plots the positive pressure and shears force distribution on the plantar surface,and analyzes the distribution of positive pressure and shear force on the sole of the foot.The plantar interface stress measurement system designed in this paper has the advantages of flexibility,high spatial resolution and portability,and it can achieve real-time measurement of positive pressure and shear force distribution on the plantar surface.Through the research of this paper,the three-dimensional force measurement theory is enriched and perfected,which provides a new method for the measurement of stress distribution in the three-dimensional interface of the plantar foot,and provides a new idea for the flexibility of the traditional rigid sensor.The research results have great practical value and application prospects in the neighborhood of clinical medicine and biomechanics.