Research In Compliant Bionic Joint Based On The Loading And Motion Characteristics Of Ostrich Intertarsal Joint

The joints in the middle of the mechanical leg play a vital role in the loading and movement of the robot.Conventional design simplifies joint into an articulated rotary motion,with power source at the joint,which would cause many problems such as an increase in the moment of inertia of the leg,deterioration in flexibility,and poor stability.In order to optimize the joint design,this paper simulated the high-speed movement of the African ostrich's intertarsal joint in the complex terrain as a biomimetic prototype,combined with the special planter surface as the ground condition perception feedback.Finally,a rope-driven bionic flexible ball joints was designed.Through the outdoor field experiment,the movement data of the ostrich intertarsal joint and the corresponding plantar pressure were collected.The motion analysis system Simi Motion and the foot pressure analysis system Footscan were used to analyze the exercise parameters and the plantar pressure data of the ostrich on the hard/soft ground during walking and running.The results show that there is a distinct peak in the touchdown period on the hard ground relative to the soft ground during running.At the same time,through the analysis of plantar pressure,the 3rd and4 th toe touch the ground synchronizely,then the 4th toe first leaves the ground before the 3rd when the ostrich moves on the hard ground.When the ostrich moves on the soft ground,the middle of the 3rd toe first touches the ground,then the 4th toe touches and leaves the ground subsequently,and the 3rd toe finally leaves the ground.The size and mechanical parameters of the ostrich intertarsal joint were tested by gross anatomy,CT scan and nanoindentation.The results showed that there was a meniscus on the lateral of the joint,the shape was parallel to the sagittal plane.There was no meniscus on the medial,which was at an angle of 15° to the sagittal plane.The thickness of the distal tibia cartilage was relatively uniform,with a mean value of0.54 mm,and the thickness on both sides was significantly larger than the middle at the proximal tarsometatarsus.There were two nutrient foramen in the proximal tarsometatarsus,which were arranged at an angle of 43°.The mechanical properties around the nutrient foramen are unevenly distributed.The calculation formula of the density and elastic modulus around the nutrient foramen was obtained by the Hu value of the CT data.The nanoindentation measurement data proves that the formulacould accurately estimate the mechanical properties of the bone material around the nutrient foramen.The 3-D model of the ostrich intertarsal joint was reconstructed by CT scanning and reverse engineering techniques.The loading characteristics of the joint and the influencing factors of the stress concentration of the nutrient foramen were analyzed.Through the static pressure analysis of the joints,the tibia epiphysis and the tibial fossa were the main loading areas of the joint.The front side load was significantly larger than the back side load,and the outer was significantly larger than the inner.With the load biased to the posterior,the spine at the posterior aspect of the tarsometatarsus epiphysis and the lateral posterior sesamoid could effectively prevent excessive extension.With the load biased to the lateral,it was beneficial to increase the distance of the fulcrum and increase the stability of the static standing of the ostrich.According to the dynamic analysis,the joint surface load gradually shifted from the inner side to the middle and outer,and from the front to the back,during the process of touching the ground.Finally,numerical simulations of the effects of the two-hole shape,the orientation of the pores,the shape of the ostium,the non-uniform material around the nutrient foramen and the load position on the stress distribution of the nourishing pores of the ostrich intertarsal joints indicated that these factors prevent the mechanical properties from weakening by transferring the stress region to the area around the hole..Through the optimization and simplification of the key structural factors of the ostrich intertarsal joint,a rope-driven flexible ball robot joint was designed by engineering bionics technology.At the same time,a set of plantar perception feedback adjustment system was designed combined on the planter surface.The results showed that the bionic joint moved on the ground with larger particle size and hardness,and the range of angle change of the touchdown period was larger.That is,the greater the impact of joint movement on the ground with higher hardness.Finally,the effectiveness of the plantar perception auxiliary support system was verified by the motion of the bionic joint on different hardness grounds.This paper designed a rope-driven bionic ball joint,which could achieve stable movement of various grounds,effectively reduced the moment of inertia of the joint and increase the flexibility of the joint through the sliding of the ball joint and the contraction of the rope.In addition,the plantar sensing system could effectively judge the hardness of the ground environment,thereby driving the auxiliary toe to achieve the effect of auxiliary support.The research in this paper had important referencevalue and enlightenment significance for joint design,driving form and motion optimization of foot robot.