The Research On Coupling Characteristics, Kinematics Modeling And Bionic Application Of Mole Cricket (Gryllotalpa Orientalis)

The mole cricket is a typical soil-dwelling insect which has excellent abilities of digging and excavation. As mole cricket has high degree of adaptability in soil-environment, meanwhile, it has capabilities of moving on ground, flying and swimming, which shows a typical triphibian features. The studies of the habits and characteristics on triphibian insects are hotspots not only in academe, but also can provide the bionic theory foundation for the design of compatibility of the multi-environmental robot. The researches on the mechanism and pattern of the excavating motion and terrestrial locomotion can serve as a prototype for the design of multi-legged excavating robot. Moreover, the fore leg of mole cricket has developed into an effective digging organ, the study of that can offer a new insight into the design and improvement on excavating machinery.By taking the theory of biological coupling as theoretical guidance, this study applied quantitative, qualitative and semi-quantitative analysis methods to investigate the dynamic and static coupling characteristics of mole cricket, and made relatively comprehensive analysis to the reasons of why mole crickets have the unique adaptability to the soil-environment, wearable body surface and the ability of excavation. The kinematics-based physical model and the location-gesture equation were established based on the kinematics experiment results. Moreover, with the purpose of engineering applications, the geometrical configuration of fore leg claw was studied, which has excellent excavating performance.The biology information, which include microstructure, tissue structure, and material composition, of mole crickets' main soil-engaging components (fore leg, prothorax, and fore wing) were acquired by using the stereo microscope, scanning electron microscope, transmission electron microscope, and inductively coupled plasma atomic emission spectrometer. By using this information, the implementing mechanism of wearable ability in excavating motion, i.e. the static coupling characteristics, was analyzed. The results show that the fore leg, prothorax and fore wing of mole cricket can be respectively considered as independent coupling system which has different interaction with soil. In the coupling system of mole cricket, these three subsystem assembled by direction and position relationship, and the implementing pattern of wearable ability is'combined parallel implementation of incomplete equilibrium'.By using the high speed camera and combining with homemade experimental facility and soil's resemblance, the movement course of fore leg in mole crickets were acquired. The results show that the movements of fore leg are composed of a series of stretch and fold actions in digging process. In a specific cycle, the motion trajectories of a stretch and a fold action form a closed loop which area depends on the extent amplitude of the fold action. In majority of sequential cycles, the areas of the loops are alternately changed, which has the relationship with the swing of thorax-abdomen joint. In excavation, motion frequencies of fore legs are bigger than that of middle and the hind legs, the movements of hind legs depend on the distance body moved forward, and the function of the middle leg is to help the body roll so as to switch the working face.In the coupling system of a digging mole cricket, the interactions between the three pair of legs and soil are diverse from each other. The implementing pattern of digging function is 'compound parallel implementation of incomplete equilibrium'. In conclusion, the static coupling is the material foundation of dynamic coupling which can greatly influence the implementation of digging function.By using a high speed 3D video recording system, a series of kinematics tests on terrestrial walking mole crickets were carried out, in which the three-dimensional kinematics information and parameters of healthy and disabled mole cricket were recorded and analyzed respectively, including amputated fore leg, amputated middle leg and amputated hind leg. According to the kinematics parameters, the joint angles of three pair of legs and the pitch, yaw, and roll angle of body were calculated respectively. The change patterns of these angles were discussed. By comparing the kinematics parameters of mole cricket with amputated legs and integrity one, the differences on gait pattern, duty factor, joint angles and body angles were investigated. The results shown that the terrestrial locomotion of mole cricket contains two discrete parts:appendage movement and trunk movement, i.e. the cooperation between three pair of legs and body rotation (pitch, yaw and roll), respectively.According to the results, we can conclude that, during terrestrial locomotion, the fore legs of mole cricket only have the small function of dragging and bracing instead of direction control in contrast with common hexapod insects. The results show that the middle legs of mole cricket do play a more important role than common hexapod insects in guiding direction. When terrestrial walking and turning, the middle legs and body joint act more effective in direction control and body support which compensate the function of fore legs partly, and the hind leg play the roles of pushing body forward and supporting the trunk.Generally, the amputation of a pair of leg has certain influence on movement of the adjoining leg, especially on angular variation of the femur-tibia joints. The results show that the amputation of fore leg has minor influence on stride frequency and forward velocity, has less influence on the gait sequence of middle and hind leg, which indirectly proved that the main role of fore leg is not walking. After the amputation of fore legs, the extent of stretch of middle legs were decreased, meanwhile the range of joint angular was increased. After the amputation of middle legs, the motions of fore and hind legs were affected simultaneously, in which the movement range of fore legs increase in order to produce more drag force, and the movement pattern of hind legs was disturbed due to the instability of trunk. After the amputation of hind legs, by comparing with the healthy mole crickets, the parameters of joint angle change little in fore legs, and change a lot in middle legs which because the middle legs partly compensate for the function of hind legs. In conclusion, comparing with other common terrestrial insects, the middle and hind legs of mole cricket compensate some functions of fore legs which can relieve the fore legs from walking for digging or excavating.The kinematics-based physical model was established based on the results of kinematics study, in which every leg has three rotational degrees of freedom and head-abdomen part has two rotational degrees of freedom. By reference to the D-H method, the center of mass was chosen as original point of the global coordinate system, and the location-gesture of the end point of each leg equation was established, which provide the theoretical foundation for the design of bionic digging robot in kinematics and mechanics.Mole cricket's claws have good characteristics in digging soil. By applying the geometrical shape of the claw of mole cricket to a conventional scale of JL80 excavator bucket teeth, bionic excavator tooth was designed. The models of bionic teeth and JL80 teeth were manufactured by using FDM-Dimension rapid molding system. The results of excavating test show that the resistance of bionic teeth is smaller than JL80 conventional teeth when the wedge angles are 90°and 60°. The internal stress of tooth and soil was simulated and analyzed by using finite element method with ANSYS software. The simulating results are in consistent with the practical experimental results. According to the stress contour, we know that bionic tooth can change the stress concentration place from the tip of tooth to the surface of soil, which can disperse the stress of the soil in order to decrease the resistance of wedging. By analyzing and comparing the stress of JL80 and bionic tooth in wedging process, it is clear that the bionic tooth can decrease the wedge angle by not change the design of excavator machine and the working condition. The horizontal component of the total resistance acting in bionic tooth can be reduced by decreasing the wedge angle, which devote to the decreasing of wedge resistance.