Development Of Bionic Artificial Joint Thin Film Measuring Device Based On Optical Interference Technology

Professor Dowson proposed a “compliant”article joint or "Cushion bearing" for complete joint replacement for the first time,in which a cartilage-like cushion is introduced on the surface of the artificial rigid joint.Since then,scientists have prepared much bionic lubricating materials and carried out research into their tribological properties,focusing on the measurement and evaluation of friction and wear properties.However,to date there is still no consensus on the complex lubrication mechanisms of joint contact surfaces.Based on this,from the perspective of in-situ observation of the lubrication behaviour on the bionic joint material surface and measurement of its lubricant film thickness,a film measurement device based on optical interferometry was developed on the basis of the point contact optical interferometric lubricant film measurement device developed by our research group,focusing on its motion actuator,loading mechanism,contact sub-materials and ambient temperature control,et al,in order to achieve in-situ observation of the film formation process on the surface of the bionic joint and accurate measurement of the lubricant film thickness,and to evaluate the tribological performance of the bionic lubricant material under realistic conditions of joint motion,the main research work is as follows:(1)Followed by studying the movement forms of human joints and the specific requirements of various artificial joint friction and wear performance of devices,the main design objectives and design requirements of the bionic artificial joint film measurement device were clarified in order to simulate the actual working environment of the in vivo joints as far as possible,specifically including the setting up of a reciprocating oscillating motion actuators,a loading actuators providing various loading,an ambient temperature control actuators,which were redesigned based on the bionic principle.The specific parameters for the test conditions,such as the applied load,the oscillation frequency and angle of the ceramic ball head,the selection of the lubricant,was also confirmed.(2)The mechanical part of the measuring device is designed: firstly,the design principle and real-time strategy of how to control the ceramic ball head to achieve reciprocating oscillating motion are elaborated,including the execution of continuous reciprocating oscillating motion under the control of servo motor in different angular range and frequency;secondly,the loading mechanism is designed by using the lever principle,which can provide fixed load and impact load for the joint contacting subsets to simulate the load on the joints when standing,sitting,walking,going down and other activities.The loading mechanism is designed to provide fixed load and impact load to the joint contacting subassemblies to simulate the load on the joint when standing,sitting,walking,downstairs,etc.The original ceramic sphere-glass disc was redesigned,i.e.,a PDMS cushion layer with low elastic modulus was introduced into the glass disc to simulate the joint cartilage,and a set of bionic artificial joint contact substrate was constructed to meet the requirements of optical measurement;a simple temperature control system was designed to ensure that the optical measurement experiments were conducted at an ambient temperature of 37°±1°.(3)The software and hardware parts of the measurement control system were designed.The motion control system was selected with ECI2608 motion control board and servo motor as the core hardware,and the relevant motion control program was written and the human-machine interface was designed by using C# language;considering the bionic soft cushion layer PDMS,the optical measurement system of the original ceramic sphere-glass disk oil film measurement system was re-corrected and the parameters of the magnifying lens head were re-corrected.The motion control system and the optical interferometry system are organically combined together to complete the automatic acquisition of the optical interferogram for the whole measurement process.(4)Preliminary experiments were carried out on a constructed bionic artificial joint film measurement device.Optical measurement experiments were conducted mainly for the lubrication behavior in the bionic artificial joints under the common states in human lower limb locomotor joints: sitting,standing,descending and walking movements.Silicone oil and deionized water were selected as lubricants,and the changes of the extruded film with time under the application of fixed and impact loads were compared between hard-hard and soft-hard contact subsets,and it was confirmed that the surface deformation of the bionic soft cushion layer was beneficial to promote the generation of lubricating films.The complex lubrication behavior of the PDMS surface was observed in situ during the reciprocating oscillating motion of the ceramic ball head,and the oscillating speed was found to play an important role in the joint lubrication.In this study,we designed and built a reciprocating oscillating bionic joint lubrication film measurement device from a concept of observing the lubrication behavior of the surface of bionic joint lubrication material,and verified that the film formation characteristics between the ceramic ball head and the surface of bionic cartilage material can be studied and the lubrication mechanism can be further revealed under the real working conditions of joint motion by using this device.The measurement system provides a new technical means to evaluate the tribological properties of bionic lubricant materials,and is also of great importance to guide the design of bionic lubricant materials.