Research On The Kinematics And Dynamics Of Kangaroo Hopping Robot

Research on HRMK (Hopping Robot Modelled on Kangaroo) is achallenging exploration in the robot area. Faster speed, more stable motion,smaller foothold requirement and lower energy cost are the advantages ofkangaroo hopping model, in which both legs move simultaneously. HRMK can bewidely used in planet detection, military spying, geological detection, forestprotection, emergency and calamity management, anti terrorism because of itssimplicity in configuration and control, lower intellectualized requirements andflexible adaptability under unconstructed and unbeknown working conditions.A bionic mechanism analytical method by video information is firstpresented in this paper. Based on the kangaroo-hopping video, by using thetheoretical analysis and simulation theory the HRMK model has been put forward.The analytical theory and design method have been established by the study onemulational kinematics and dynamics, which reveal the mechanism of kangaroo'shopping motion and provid the theoretical foundations for hopping robot design,hopping momentum etc.Combined with the research achievements in bionics, the proportion of thesize and mass distributing of kangaroo-hopping mechanism, the motion modality,the special functions of pliable foot and tail, are analyzed. Based on theSpring-Mass model, the formulas to calculate the ground force, the law of energychanging and the stiffness coefficients of kangaroo legs, some rules of kangaroo'shopping motion, the important parameters which influencing its motion, and somevaluable bionic research problems are discovered.Grounded on the motion characters of kangaroo, a HRMK model of pliabletoes is first presented, which is divided into touch-down and flying phases. Itoffers the foundation for research on the kinematics and dynamics with this model,motion parameters and its bounds.The kinematics formulas for HRMK are set up. The positive and reversedanalysis of HRMK's configuration are executed by D-H method both intouch-down and flying phases; the velocity analysis method is constructed withthe research on Jacobian matrix and differential motion analysis; a simulation forthe above method is performed through a Matlab program. The results show thatthe configuration and the curve of COWB (the center of whole body) are similarto the result getting from the tests which reveals the law of kangaroo's long jumping, stable motion and low energy cost motion characters.A multi-rigid dynamics research of HRMK in which the impact influences isconsidered when a hopping period has been presented for the first time. Based onthe motion characters of kangaroo, a four parts rigid model is given which isdivided into three phases: touch-down, impact and flying. The dynamics and bodyrotational formulas are formed for the three phases by Lagrange method andangular momentum theorem and then the whole period of trajectories of the jointangles are shaped and some formulas for it are given at the same time. And finally,the model is simulated in Matlab. The results show that, the hopping configurationand motion requirement can be achieved by this model; it can be used to forecastthe robot's configuration of a period, the curve of COWB, the driving torque ofeach joint, the reaction force of ground, and the impact condition. Thedisadvantage of this model is that some errors in accelerations still exist. However,the model formed above is of value for multi-rigid dynamics.For the first time, a heuristic method is applied to the mechanism model ofHRMK to analysis its dynamic characteristics. Based on the analysis of energystorage characteristics of the linear torsional spring, pseudo-rigid-body model forhopping mechanism is presented and the dynamic formulas are established byKane method. Finally, the formulas of input torque at each joint in touch downphase are given too. Through searching on elastic distortion and buffer capacity ofkangaroo's pliable toes by pliable cantilever, dynamic model of kangaroo's toes isprovided, and then the law of effect of point of toe joint by pliable toe of robot,environment dynamic formulas and conditions of hopping off ground aredisplayed. The results show that, pliable joints can effectively reduce the apexvalue of ankle driving torque and makes it more stable which is useful forchoosing driving electromotor. The pliable toe can effectively increase the takeoff time and improves the take off velocity at the same time, which improves theadaptability of the robot and changes the pressure of the foot. The dynamiccharacter of kangaroo's tendon is also revealed through this model. All the resultsshould be a useful foundation for designing and controlling hopping robot.This research project is supported by the National Natural Science Fund ofChina (No. 50375120).