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Research On Active Compliance And Trotting Gait Control Of A Quadruped Robot

Posted on:2017-03-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:G T ZhangFull Text:PDF
GTID:1108330485480149Subject:Pattern Recognition and Intelligent Systems
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The quadruped robot is inevitably to interact with the ground while it is moving. And the robot is a multi-link, deep coupling, time varying system. Thus it is quite complicated to control the robot motion. In this dissertation, we will start with the exsiting robot in our laboratory and study the control of the robot joint, the robot leg and finally the robot motion. We work to control the output torque of the robot joint and implement active compliance to the robot leg. And the robot motion is investigated to achieve stable robot trotting. This dissertation mainly includes the following aspects:1. This dissertation elaborated the derivation for the kinematics and dynamics of the hydraulic actuated single-leg platform in the laboratory. Then we built the simplified mathematical model of the hydraulic actuator and managed to control the output torque of the robot joint. On this basis the active compliance of the leg is achieved by virtualizing "spring-damper" model to the toe. Effectiveness of the controller is validated through the experiments on the single-leg platform.2. An approach based on virtual model is presented to control trotting gait of the quadruped robot. The controller mainly consists of two main modules:the support phase virtual model control and the flight phase virtual model control. During the support phase, this dissertation maps the mathematical relationship between the joint torques of diagonal support legs and the virtual forces applied on the torso. And the virtual torso forces are regulated to control the torso attitude, height as well as the forward velocity and yaw angular velocity of the robot. During the flight phase, lateral velocity is introduced into planning the toe trajectory. And virtual spring-damper sections are implemented to drive the flight toes to track the planned trajectories. In addition, while designing the controller a state machine is introduced to monitor the leg states and outputs phase switching commands for trot gait regulation. The simulations show that the robot is able to trot omni-directionally on flat ground, trot over uneven terrains as well as dissipate impacts.3. On the basis of the trotting controller, virtual model control and online learning mechanism is implemented to realize flight trot gait of the quadruped robot. Stiffness of the virtual vertical spring is modified to regulate the hopping height of the robot. The forward velocity is served by controlling the virtual forward force applied to the torso and the torso attitude is adjusted through the virtual torso torques. Levenberg-Marquardt online learning method is involved to obtain the desired touch-down point of the flight toes so as to control the robot’s lateral velocity. Then the swing toe trajectory is designed based on the state of the robot and a state machine is introduced to sequence the motion of legs. Further more, the transition between the trot gait and flight trot gait is investigated. The simulations show that the robot is able to move rapidly on flat ground with flight trot gait and successfully implemented the gait transitions.4. A controller is designed for position-controlled quadrupedal dynamic locomotion, aiming at simple and robust trotting control. A simplified dynamic model of the quadruped robot is built and the relationship between the motion of the robot toes and torso attitude is deduced. The controller takes the torso attitude angles and velocities into planning the foot trajectories. The yaw motion is also involved within the controller and enables the robot with a stable trotting gait. Validation of this method is vertified through experiment in simulation as well as the LittleCalf robot prototype.
Keywords/Search Tags:Quadruped robot, Active compliance, Trot gait, Virtual model
PDF Full Text Request
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