Research On Flexible Drive Unit And Its Application In Humanoid Biped Robot

Research of biped robot started in the1960s, which has become a major field ofrobotics research after more than50years of development. Impact force of humanwalking at a normal speed is3.5times of body weight, which is5times when running,even7times. Human muscle can buffer shock to protect the joints, while humanoidrobot mostly uses reducer drive which lacks for flexibility of human tendon. Humanoidrobot cannot afford such a large impact load, thus the robot walk speed is limited. Inaddition, humanoid robot need to be more similar to people from a biologicalperspective, a light small, easy installation, flexible output’s drive unit is needed forwalk robot research. A humanoid biped walk robot with two flexible drive units makesthe biped walk similar to people. Although flexible drive unit can buffer shock, steelrope’s viscoelastic will make the joint of the drive unit occor backlash and hysteresis,which is difficult to achieve robot walk. Research based on flexible drive unit ofhumanoid biped walk has important practical significance.In this paper, flexible drive unit and its application on the biped robot will bestudied in depth and systematic. The main study are following:A dynamic model of flexible drive unit is established based on viscoelasticdynamics. Steel rope of flexible drive unit is modeled as a viscoelastic by a number ofsprings and damper under the microscopic view. The relationship between the outputand input angle of flexible drive unit and tension on both sides of the joint is derived,which is used for tension control and the example shows the accuracy of dynamicmodel. The simulation model about steel rope and movable pulley is set up based on3Dvariable polylines. It’s easy and convenient using macro command to establish thesimulation system. This method solves a problem that it’s difficult to use discretemethod to establish steel rope and movable pulley model under the following dynamicssoftware, While contact between steel rope and object is omitted.It’s difficult to control for flexible drive unit due to the presence of backlash andhysteresis, and control research will be finished based on viscoelastic dynamic model.Joint position and joint velocity feedback is through the viscoelastic dynamic model,and joint velocity and acceleration feedforward is through the elastic deformation ofsteel rope. Joint position error and velocity error feedback is that joint position loop andspeed loop is based on the motor position loop and speed loop. Steel rope elongationcan be obtained by elastic deformation formula, and speed and acceleration feedforwardwill be obtained by the elongation. Real time modification of velocity feedforward andacceleration feedforward coefficient can achieve the purpose of compensating steel ropeelongation. Flexible drive unit controller is designed according to the above control strategy, which error compensation is achieved for flexible drive unit. Developprototype of flexible drive unit and set up its control system. The performance testprove the effectiveness of the proposed control strategy and its drive ability.The flexibility of steel rope have effects on gait stabilityfor robot, so it is necessaryto research on the stability of the robot. For the problem that constraints of existingrobot walking stability criterion are too strict, supplement sliding and rotationalconstraints are finished, and the effect of robot’s sliding and rotation on walkingstability criterion is analyzed. The backlash and hysteresis of flexible drive joints arecaused by the viscoelastic properties of steel rope, which have certain influence tobipedal robot gait. Hysteresis and walking foot landing phase of biped robot withflexible drive unit is discussed. The biped robot with flexible drive unit simulation canverify the stability theory. Walk sample generation method is researched, and aparametric surface vehicle table model used for robot dynamics analysis is proposed.walking sample generating method of biped robot by the vehicle table model isproposed too. B-spline surfaces is seen as bipedal robot centroid motion surface, andNewton iteration method is used to solve the robot COG motion to get walking samples.Robot COG motion is a regular3D robot in accordance with the walk cycle, whicheffectively increases the walk step and reduce the landing impact. A3D robot trajectorycan be planned without changing the model coordinate system, and the simulationresults show the correctness of the theory.A humanoid biped robot with flexible drive unit is developed, and the biped robotsystem is built. Biped robot walk experiments will be finished, and the robot can reach aspeed of0.1km/h. The robot can be buffered and damped due to the flexible drive unit.Based on the flexible drive unit and its applications and related theory on bipedrobot research, part joints of biped robot have achieved flexible driving, which verifiesthat the flexible drive unit has drive capability and buffer effort for biped robot. Thisresearch is a theoretical and experimental basis for full flexible drive unit of the bipedrobot.