Zero Moment Point Reference Research Articles

A Walking Stabilization Method Based on Environmental Modes on Each Foot for Biped Robot

In this paper, a method that makes biped robots track zero-moment-point (ZMP) reference trajectories is proposed. The biped robots have flat rectangular soles with force sensors at each corner. The sensors detect reaction force from the ground. Sensor information is transformed into useful structure, which is defined as ldquoenvironmental modes.rdquo The environmental modes represent contact states between the ground and the soles and are extracted by the information of four force sensors at each corner of the rectangular soles. The environmental modes consist of the following four modes: 1) heaving; 2) rolling; 3) pitching; and 4) twisting. These modes are related to the ZMP, by which walking stability is evaluated. Therefore, command values of the environmental modes can be derived by the ZMP reference trajectory. By tracking the command values, the walking motion becomes more stable. The conventional study on controlling the environmental modes takes only the rolling and pitching modes into account. However, it is not sufficient to stabilize the walking motion, because the heaving mode has been neglected. The heaving mode is also very important to stabilize the walking motion. Therefore, in this paper, we extend the conventional method for considering the heaving mode to track the ZMP reference trajectory. Validity of the proposed method was confirmed by experimental results.

Natural ZMP Trajectories for Biped Robot Reference Generation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The control of a biped humanoid is a challenging task due to the hard-to-stabilize dynamics. Walking reference trajectory generation is a key problem. Linear Inverted Pendulum Model (LIPM) and Zero Moment Point (ZMP) Criterion-based approaches in stable walking reference generation are reported. In these methods, generally, the ZMP reference during a stepping motion is kept fixed in the middle of the supporting foot sole. This kind of reference generation lacks naturalness, in that the ZMP in the human walk does not stay fixed, but it moves forward under the supporting foot. This paper proposes a reference generation algorithm based on the LIPM and moving support foot ZMP references. The application of Fourier series approximation simplifies the solution, and it generates a smooth ZMP reference. A simple inverse kinematics-based joint space controller is used for the tests of the developed reference trajectory through full-dynamics 3-D simulation. A 12-DOF biped robot model is used in the simulations. Simulation studies suggest that the moving ZMP references are more energy efficient than the ones with fixed ZMP under the supporting foot. The results are promising for implementations. </para>

A novel compound biped locomotion algorithm for humanoid robots to realize biped walking

In this paper, a compound biped locomotion algorithm for a humanoid robot under development is presented. This paper is organized in two main parts. In the first part, it mainly focuses on the structural design for the humanoid. In the second part, the compound biped locomotion algorithm is presented based on the reference motion and reference Zero Moment Point (ZMP). This novel algorithm includes calculation of the upper body motion and trajectory of the Center of Gravity (CoG) of the robot. First, disturbances from the environment are eliminated by the compensational movement of the upper body; then based on the error between a reference ZMP and the real ZMP as well as the relation between ZMP and CoG, the CoG error is calculated, thus leading to the CoG trajectory. Then, the motion of the robot converges to its reference motion, generating stable biped walking. Because the calculation of upper body motion and trajectory of CoG both depend on the reference motion, they can work in parallel, thus providing double insurances against the robot’s collapse. Finally, the algorithm is validated by different kinds of simulation experiments.

Balance control of a biped robot using camera image of reference object

This paper presents a new balance control scheme for a biped robot. Instead of using dynamic sensors to measure the pose of a biped robot, this paper uses only the visual information of a specific reference object in the workspace. The zero moment point (ZMP) of the biped robot can be calculated from the robot’s pose, which is measured from the reference object image acquired by a CCD camera on the robot’s head. For balance control of the biped robot a servo controller uses an error between the reference ZMP and the current ZMP, estimated by Kalman filter. The efficiency of the proposed algorithm has been proven by the experiments performed on both flat and uneven floors with unknown thin obstacles.

2P1-F12 ZMP修正指標マップを用いた不整地歩行(ヒューマノイド)

This paper describes a method of walking on rough terrain for a humanoid robot by using ZMP Criteria Map. ZMP Criteria Map is the criteria of ZMP (Zero Moment Point) trajectory modification made in advance by the walking pattern generation using the model of preview control. We classify the rough terrain into concavity and convexity, and propose a method to enable changing gait to stable walking pattern by modifying reference ZMP trajectory according to the map.