Limbmechanism Robot

Introduction of limb-mechanism robot "ASTERISK"

Limbmechanism Robot

Insects have 6 legs which are generally used to walk with. In case of need, 2 of them can also be used as arms to pick objects. Therefore we call their legs, which can also be used as arms, ''limbs''. The concept of Limb Mechanism Robot is motivated from the concept of limbs. The mechanism enables the 2 following things.

  1. Efficient operation altering limbs properly for manipulation and navigation tasks according to the situations.
  2. Miniaturization of the component by integrating the two functions into one mechanism.

We have developed a new Limb Mechanism Robot named "ASTERISK". ASTERISK has 6 limbs which each has 4DOF. By radially arranging limbs in six directions from the center of the body, ASTERISK achieves both even work space and mobility in every direction. We also design symmetrically the top and bottom of the robot so that there is no distinction between the work area in the upper and lower part of the body.

Therefore, it is possible to move in every direction without alteration of posture, lift an object, and easily return to its standard position after falling up-side-down.

Radially arranged limb Structure of each limb Specifications of robot

ASTERISK has the following 6 kinds of sensors.

  1. Pressure sensors on the tips of all of the limbs, which can detect whether they are being pushed or pulled.
  2. Infrared sensors on the tips of 3 of the limbs.
  3. A gyro sensor and an acceleration sensor on the body.
  4. Wireless cameras on the tips of 3 limbs and 3 CCD cameras on the body.

We displayed ASTERISK at the World Expo 2005 in Aichi, from June 9th to 19th, to show the performance of ASTERISK.

Dynamic Rolling-Walk by Isotropic Robot Design

New dynamic rolling-walk motion for multi-legged robot with Sensory Compensation is proposed. The motion is realized by using the isotropic leg arrangement and the dynamic center of mass control inspired by bipedal robots. By using the Preview Control of Zero Moment Point with cart-table model based on the bipedal robot technique, the robot’s center of mass trajectory is planned for the dynamic motion. The Resolved Momentum Control for manipulating the multi-links robot as a single mass model is also implemented in the system to maintain stability of the robot. In the new dynamic rolling-walk motion, the robot switches between two legs supporting and three legs supporting phases with the Preview Control of Zero Moment Point and Resolved Momentum Control as dynamic motion controllers and Gyro sensor for error compensation to achieve the motion. We analyzed the motion and confirmed the feasibility in the Open Dynamic Engine before implementing the motion in an actual robot.

Result of Dynamic Rolling-walk Motion ODE simulation Result of Dynamic Rolling-walk Motion with Gyro sensor

Stair Recognition with Laser Range Scanning by ASTERISK

Stair recognition with laser range scanning for continuous stair climbing by limb mechanism "ASTERISK" is proposed. In this research, laser range scanning is divided into rough scan for fast scanning, and precise scan for range scanning. We use 2D laser range finder attached with motor for 3D laser range scanning. As a result of the experiment, the robot could recognize a stair position and posture even it is located at the physical limitation of laser range finder which is 4 m and detect the actual stair up to 6 out of 10 steps which the height is about 5 times of "ASTERISK" normal posture standing height. After robot recognized a stair, it will automatically walk toward the stair and climb up while considering its body stability and leg(s) workspace at all time.

actual environment experiment result

Tumbling Operation of Polygonal Prism for "ASTERISK"

tumbling motion

This research objective is to improve the object transportation ability of our Limb Mechanism Robot "ASTERISK". We proposed the tumbling motion of ASTERISK. Generically, "tumbling" is the effective way to transport a heavy and large object with a little load. In our tumbling motion, we control the force which the robot applies to an object. We take friction forces between the limb and the object, the one between the limb and the floor, and the one between the object and the floor into account, so that we can derive the optimal force which does not cause any slip. We control the robot's center of mass position and the angle of each joint in order to perform the tumbling motion without slip. The effectiveness is confirmed through experiments.

Building Monitoring System Using RFID and Mobile Robot

The collaborative monitoring system with RFID sensor tag and the mobile robot is proposed. The proposed system consists of three systems: RFID sensor network system, Remote robot controlsystem and Integration control system. The sensor network continuously monitors the surrounding of sensor tags while the mobile robot moves around for periodic inspection.  When certain sensor tag measured abnormal information, the integrated control system commands the mobile robot to particularly check around the area. We implement the system for Water Leak Detection in a ceiling inside a building. In this research, we equips the mobile robot with a thermography to find heat of evaporation by the detailed temperature distribution. This technique is evaluated in demonstration experiment.

concept of collaborated monitoring experiment result

Obstacle Avoidance Using Collision Detection for ASTERISK

experiment result

An obstacle avoidance method using collision detection is proposed for multi-legged robot. The proposed method employs virtual impedance control so that the swing leg can avoid an obstacle while maintaining its legs' work space. When the leg goes over the preferred operating region, the body avoids an obstacle by the repulsive force from the virtual impedance wall. During an experiment with wall on both sides of the robot, the robot realized the movement along a wall on one-side without changing a commanded direction of a joy-stick. As a result of this experiment, the robot could walk through those walls by only changing its legs' posture on both sides.

Grid wall walking by Limb Mechanism Robot "ASTERISK"

grid wall walking

We set a goal for this research to improve the vertical mobility of our limb mechanism robot "ASTERISK" by proposing the "grid wall walking gait" which is a movement on a grid structure.

With our method, static evaluation determines the stable grid wall walking. At the same time, feedback control discards the position errors and distributes loads on legs while walking.As an experimental result, "ASTERISK" could walk on a vertical and a +/-30-degree inclined walls.

At present, we are searching for an optimal grid wall walking gait on each inclination of wall with our optimization method, which is a genetic algorithm (GA) based on the static evaluation.We aim to apply this method to off-line generator of grid wall walking when there is a change of environment such as grid stroke or hardware of "ASTERISK".

Locomotoin method using swing motion for ASTERISK

The goal of this research is to enhance the mobility of "ASTERISK". A new locomotion method by using swing motion with wire holding leg is proposed. The motion planning employs simple 2-links model and the 2-nd joint is controlled by using cycloid trajectory. The single mass model is realized by using resolved momentum control for multi-link robot. The proposed methods are implemented to“ ASTERISK ”model in dynamic simulator and a real robot and the feasibility is confirmed. We achieve ASTERISK to make swing motion in physical simulation, and affirm swing motion with real robot.

experiment concept experiment result

Hybrid Locomotion of Leg-Wheel ASTERISK H

wheeled and legged locomotion

Leg-wheel hybrid locomotion on rough terrain we propose for a hexapod robot is realized by continuous transition between wheeled and legged locomotion based on sensor feedback. In basic positioning on a flat surface, the robot is supported by three legs andmoves using its wheels. Upon sensing an obstacle, the robot's support and swing legs change to a tripod gait with an oval orbit to cross over the obstacle. The maximum obstacle height depends on the robot's height and the positioning of the foreleg. We analyzed optimal positioning implemented in the hybrid robot ASTERISK H, as confirmed by experimental results.

Research of high resolution NDT Grid Map

The goal of this research is to make a map which enables a small robot like ASTERISK to recognize a narrow environment. Then, we made a high-resolution grid map which can describe details of the environment and keep a data amount. To raise the precision of the map, a method to adapt Normal Distributions Transform (NDT) algorithm for the high-resolution grid map is proposed. But, because of false detections of Laser range finder, we cannot know the real position of small objects. A method which removes the false detections generated around a small objects is proposed, By this method, positional accuracy of small obstacles is improved.

experimental environment experimental result

Running motion generation for Limb Mechanism Robot "ASTERISK"

Running motion

In this research, our goal is to expand ASTERISK's movable area. ASTERISK is small, so it can go through a narrow space where a human cannot enter. Now, we research about the dynamic motion such as jump and run.

First, we made the jumping movement. In addition to the jumping movement, we made ASTERISK move toward the horizontal direction. As the publication of experiment, we succeeded in making ASTERISK run at 0.5 m/s.