Hun-ok Lim

Development of a new humanoid robot WABIAN-2

A new humanoid robot-WABIAN-2- that can be used as a human motion simulator is proposed in this paper. Its trunk is designed in order to permit rotation, and forward, backward, and sideway movement. Further, its arms are designed to support its complete weight when pushing a walk-assist machine. Moreover, it can lean on a walk-assist machine by forearm control using trunk motion. Basic walking experiments with WABIAN-2 are conducted with and without a walk-assist machine, thereby confirming its effectiveness

Realization of dynamic biped walking stabilized by trunk motion on a sagittally uneven surface

The authors introduce a control method for dynamic biped walking stabilized by trunk motion on a sagitally uneven surface, that is for a biped walking robot which has a trunk to stabilize its walking, and its effectiveness as supported by walking experiments using a biped walking robot. This control method is based on the introduction of a new concept called a virtual surface, to consider the ZMP (zero moment point) on an uneven surface, and the main algorithm for computing the trunk motion which compensates for lower-limbs motion and time trajectory of the arbitrarily planned ZMP on the virtual surfaces. Using this control method in a number of experiments, the biped walking robot WL-12RIII (Waseda Leg-12 Refined III) which has a trunk, realized dynamic biped walking on stairs with a step height of 0.1 m and a trapezoidal terrain with an inclination of +or-10 deg. The walking period was 2.6 sec/step on the stairs, and 1.6 sec/step on the trapezoidal terrain. So that, the effectiveness of this control method was experimentally supported.<<ETX>>

Human Safety Mechanisms of Human-Friendly Robots: Passive Viscoelastic Trunk and Passively Movable Base

We would like to give robots the ability to secure human safety in human-robot collisions capable of arising in our living and working environments. However, unfortunately, not much attention has been paid to the technologies of human robot symbiosis to date because almost all robots have been designed and constructed on the assumption that the robots are physically separated from humans. A robot with a new concept will be required to deal with human-robot contact. In this article, we propose a passively movable human-friendly robot that consists of an elastic material-covered manipulator, passive compliant trunk, and passively movable base. The compliant trunk is equipped with springs and dampers, and the passively movable base is constrained by friction developed between the contact surface of the base and the ground. During unexpected collisions, the trunk and base passively move in response to the produced collision force. We describe the validity of the movable base and compliant trunk for collision force suppression, and it is demonstrated in several collision situations.

Collision-tolerant control of human-friendly robot with viscoelastic trunk

A human-friendly robot (HFR) is described to realize human safety, and a collision-tolerant control method is also proposed to achieve task performance. The HFR consists of an arm covered with viscoelastic materials and a trunk with mechanical elements, such as springs and dampers. In an unexpected or expected collision with a human, the passive viscoelastic trunk of the HFR passively deforms in response to the collision/contact forces. It is difficult, however, for the end effector to perform a desired task owing to the deformation of the passive trunk. In order to deal with this problem, the joint configurations of the arm are directly calculated according to the passive trunk deformation. The HFR with the passive viscoelastic trunk is compared with a conventional industrial robot with a rigid trunk for evaluation. Simulation and experimental results confirm that the proposed control method is useful for the end-effector position control and the passive viscoelastic trunk suitable for the suppression of collision/contact forces.

Biped walking robots created at Waseda University: WL and WABIAN family

This paper proposes the mechanism and control of the biped humanoid robots WABIAN-RIV and WL-16. WABIAN-RIV has 43 mechanical degrees of freedom (d.f.): 6 d.f. in each leg, 7 d.f. in each arm, 3 d.f. in each hand, 2 d.f. in each eye, 4 d.f. in the neck and 3 d.f. in the waist. Its height is about 1.89 m and its total weight is 127 kg. It has a vision system and a voice recognition system to mimic some of the capabilities of the human senses. WL-16 consists of a pelvis and two legs having six 1 d.f. active linear actuators. An aluminium chair is mounted on two sets of its telescopic poles. To reduce the large support forces during the support phase, a support torque reduction mechanism is developed, which is composed of two compression gas springs with different stiffness. For the stability of the robots, a compensatory motion control algorithm is developed. This control compensates for moments generated by the motion of the lower limbs, using the motion of the trunk and the waist that is obtained by the zero moment point concept and fast Fourier transform. WABIAN-RIV is able to walk forwards, backwards and sideways, dance, carry heavy goods and express emotion, etc. WL-16 can move forwards, backwards and sideways while carrying an adult weighing up to 60 kg.

A study of function of foot's medial longitudinal arch using biped humanoid robot

The humanoid robot, WABIAN-2R, has achieved human-like walking with knee-stretched, heel contact and toe off motions by using a foot mechanism with a passive toe joint. However, the foot structure is different from a humans. In this paper, we describe a new foot mechanism capable of mimicking the humans foot arch structure to figure out the function of the arch structure. Especially, the developed foot mimics the elastic properties of the arch of the humans foot and the change of the arch height during walking. The foot mechanism consists of a passive joint in the internal toe, a passive joint in the external toe, and a joint in the foot arch. We conducted several walking experiments by using WABIAN-2R, and the function of the arch structure is clarified quantitatively. As a result, we confirmed that the arch elasticity could absorb a foot-landing force at the plantar contact phase and the change of the arch height contributed to a strong thrust at the push-off phase.

Biped landing pattern modification method with nonlinear compliance control

Many researchers have been studied on acceleration control algorithms for biped robots to deal with uneven terrain. However, the control algorithms are difficult to be used for human-carrying biped walking robots because of modeling errors. In this paper, a landing pattern modification method is proposed which based on nonlinear compliance control. Theoretical compliance displacements calculated from a walking pattern are compared with the actual compliance displacements, while a robots foot touches slightly uneven terrain. In result, the height of landing terrain is detected, and the preset walking pattern is modified. Using this method, a human-carrying biped robot would be able to walk stably on uneven terrain. This pattern modification method does not need any special sensors except force sensors. Through various walking experiments, the effectiveness of the method is confirmed

Realization of biped walking on uneven terrain by new foot mechanism capable of detecting ground surface

We have developed a new biped foot mechanism capable of detecting ground surface to realize stable walking on uneven terrain. The size of the foot mechanism is 160 mm × 277 mm and its weight is 1.5 kg. The foot system consists of four spikes each of which has an optical sensor to detect ground height. The foot makes a support polygon on uneven terrain by using three or four spikes. We have conducted several experiments on the outdoor ground surface that has a slope of 7.0 degrees and a maximum height of 15 mm bumps, and the effectiveness of the foot mechanism is confirmed.

Waseda biped humanoid robots realizing human-like motion

To explore issue of developmental structure and human-like motion, we have constructed a human-like biped robot called WABIAN-RII (Waseda biped humanoid robot-revised II) that has a total of forty-three mechanical degrees of freedom (DOF); two 6-DOF legs, two 10-DOF arms, a 4-DOF neck, four DOF in the eyes and a torso with a 3-DOF waist. We present a follow-walking control with a switching pattern technique for the biped robot to follow human motion. Also, emotional walking of the biped robot is described, which expresses emotions by parameterizing its motion. The follow-walking and emotion expression can be realized by the compensation of moment by the combined motion, of the waist and trunk.

Interactive biped locomotion based on visual/auditory information

This paper describes an interactive locomotion method for a biped humanoid robot. The method consists of two main parts: a pattern generator and a human-robot interface. The human robot interface is used to achieve real-time interactive locomotion. In particular, visual information and voice instructions are employed to determine locomotion parameters such as step length, step direction, and the number of steps. The motion of the lower-limbs is generated by the online pattern generator based on the locomotion parameters. Continuous locomotion experiments are carried out in real time using WABIAN-RV. The experimental results show the feasibility of the proposed interactive locomotion method.