Real-time estimation algorithm for the center of mass of a bipedal robot with flexible inverted pendulum model (original) (raw)

Center of Mass States and Disturbance Estimation for a Walking Biped

IEEE International Conference on Mechatronics, ICM 2013, , 2013

An on-line assessment of the balance of the robot requires information of the state variables of the robot dynamics and measurement data about the environmental interaction forces. However, modeling errors, external forces and hard to measure states pose difficulties to the control systems. This paper presents a method of using the motion information to estimate the center of mass (CoM) states and the disturbance of walking humanoid robot. The motion is acquired from the inertial measurement unit (IMU) and forward kinematics only. Kalman filter and disturbance observer are employed, Kalman filter is used for the states and disturbance estimation, and the disturbance observer is used to decompose the disturbance into modeling error and acceleration error based on the frequency band. The disturbance is modeled mathematically in terms of previous CoM and Zero moment point (ZMP) states rather than augmenting it in the system states. The ZMP is estimated using the quadratic programming method to solve the constraint dynamic equations of the humanoid robot in translational motion. A biped robot model of 12-degrees-of-freedom (DOF) is used in the full-dynamics 3-D simulations for the estimation validation. The results indicate that the presented estimation method is successful and promising.

Online Center of Mass Estimation for a Humanoid Wheeled Inverted Pendulum Robot

ArXiv, 2018

We present a novel application of robust control and online learning for the balancing of a n Degree of Freedom (DoF), Wheeled Inverted Pendulum (WIP) humanoid robot. Our technique condenses the inaccuracies of a mass model into a Center of Mass (CoM) error, balances despite this error, and uses online learning to update the mass model for a better CoM estimate. Using a simulated model of our robot, we meta-learn a set of excitory joint poses that makes our gradient descent algorithm quickly converge to an accurate (CoM) estimate. This simulated pipeline executes in a fully online fashion, using active disturbance rejection to address the mass errors that result from a steadily evolving mass model. Experiments were performed on a 19 DoF WIP, in which we manually acquired the data for the learned set of poses and show that the mass model produced by a gradient descent produces a CoM estimate that improves overall control and efficiency. This work contributes to a greater corpus of wh...

Estimation of Absolute Orientation for a Bipedal Robot: Experimental Results

IEEE Transactions on Robotics, 2000

This paper deals with a planar biped. The aim of this paper is the estimation, during the imbalance phases of a walking cyclic gait, of its absolute orientation by only using the measurement of the actuated joint variables. The main contribution is the experimental evaluation of an original finite-time convergent-posture observer.

Biped walking stabilization based on linear inverted pendulum tracking

Intelligent Robots and …

A novel framework of biped walking stabilization control is introduced. The target robot is a 42 DOF humanoid robot HRP-4C which has a body dimensions close to the average Japanese female. We develop a body posture controller and foot force controllers on the joint position servo of the robot. By applying this posture/force control, we can regard the robot system as a simple linear inverted pendulum with ZMP delay. After a preliminary experiment to confirm the linear dynamics, we design a tracking controller for walking stabilization. It is evaluated in the experiments of HRP-4C walking and turning on a lab floor. The robot can also perform an outdoor walk on an uneven pavement.

Considerations on Dynamic and Static Stability of a Biped Robot

This paper describes the control of a biped robot, that uses an inverted pendulum for its balance. A control method that consists of the balance of the gaits, through the correction of the lateral and longitudinal angles of the pendulum is proposed in this work. This method p resents three phases: first t he trajectory of the foot i n movement is defined, applying the inverse kinematics to calculate the robot's internal angles, and the direct kinematics is used to ob tain the positions and o rientations of the robot's joints; then the linear and angular accelerations are obtained; l ast, the zero moment point (ZMP) is calculated as a verification parameter of the requested margin of stability. Simulation of the robot gaits to walk in horizontal, sloping plans, and up and down stairs is also made. In order to decrease the calculation time of the dynamic stability, the impact of using zero pendulum angles as starting points for the interactive process of achieving the desire...

An inverted pendulum based approach to biped trajectory generation with swing leg dynamics

2007 7th IEEE-RAS International Conference on Humanoid Robots, 2007

Reference trajectory generation is one of the key problems in biped walking robot research. The linear inverted pendulum model (LIPM) is employed widely as a useful model which simplifies trajectory generation task. Many reference generation algorithms use the Zero Moment Point (ZMP) Criterion for the LIPM in order to achieve stable walking trajectories. However, LIMP ignores the dynamics of the swing leg. This can lead to tracking problems, especially when the legs are heavy. This paper uses a two-mass LIPM and proposes a fifth order state space description for the dynamics of the robot body and the swing leg in the swing phase. The body center of mass (CMB) reference trajectory is obtained for given foot placement references and the desired ZMP trajectory. An inverse kinematics based position controller is then employed for locomotion. The walking performances with the one-mass and one-mass-two-mass switching linear inverted pendulum models are finally compared via 3D full-dynamics simulations of a 12 degrees of freedom (DOF) biped robot. The results indicate that the proposed model switching between one-mass and two-mass models is useful in improving the stability of the walk.

A Walking Bipedal Robot Using a Position Control Algorithm Based on Center of Mass Criterion

2019

A position control algorithm based on inverse kinematics and a control strategy utilizing the Center of Mass criterion are implemented to yield a walking bipedal robot. The bipedal robot has no upper body, stands approximately 50 cm and weighs about four kg. Each leg of the robot has five degrees of freedom: two at the hip, two at the ankles, and one at the knee. The closed form solution of each joint angle is derived by using inverse kinematics, following the DenavitHartenberg guidelines to determine the structural parameters of the biped. Such closed form equations determine the value of the joint angle to achieve an instance needed to complete the walking activity. Bipedal locomotion is verified by both simulation and experiments. Simulation results provide desired joint angle trajectories and will serve as benchmark for the actual experiments. Experimental results show that actual step length, foot clearance and hip height gait parameters do not exceed one centimeter from the ta...

A method for the calculation of the effective Center of Mass of humanoid robots

2011

In this paper we present a general strategy for the calculation of the effective Center of Mass (CoM) of humanoid robots, allowing the reduction of the error between the virtual robot model and the real platform. The method is based on an algorithm that calculates the real position of the CoM of a biped humanoid robot using only 2 force/torque sensors located on the feet of the robot. By means of this algorithm, it is possible to reduce the gap between the real and the virtual posture of the robot and consequently the errors between the ZMP trajectory calculated by the offline pattern generator and the ZMP trajectory calculated by the real-time pattern generator of the humanoid robot. Thus, the influence of the real-time control in the static and dynamic balance of a humanoid platform is minimized. Experimental results using SABIAN platform are provided to validate the proposed method. The results support the applicability of the method to more complex systems.

Calculation of the Center of Mass Position of Each Link of Multibody Biped Robots

Applied Sciences

In this paper, a novel method to determine the center of mass position of each link of human-like multibody biped robots is proposed. A first formulation to determine the total center of mass position has been tested in other works on a biped platform with human-like dimensions. In this paper, the formulation is optimized and extended, and it is able to give as output the center of mass positions of each link of the platform. The calculation can be applied to different types of robots. The optimized formulation is validated using a simulated biped robot in MATLAB.