Jun-Ho Oh

System Design and Dynamic Walking of Humanoid Robot KHR-2

In this paper, we describe the mechanical design, system integration and dynamic walking of the humanoid, KHR-2 (KAIST Humanoid Robot– 2). KHR-2 has 41 DOFs in total, that allows it to imitate various human-like motions. To control all joint axes effectively, the distributed control architecture is used, which reduces computation burden on the main controller, and allows convenient system. A servo motor controller was used as the sub-controller, whereas a 3-axis force/torque sensor and an inertia sensor were used in the sensory system. The main controller attached on the back of KHR-2 communicates with the sub-controllers in real-time through CAN (Controller Area Network) protocol. Windows XP was used as the operation system, whereas RTX HAL extension commercial software was used to realize the real-time control capability in Windows environment. We define the walking pattern and describe several online controllers in each stage. Some of the experimental results of KHR-2 are also presented.

Walking Control Algorithm of Biped Humanoid Robot on Uneven and Inclined Floor

This paper describes walking control algorithm for the stable walking of a biped humanoid robot on an uneven and inclined floor. Many walking control techniques have been developed based on the assumption that the walking surface is perfectly flat with no inclination. Accordingly, most biped humanoid robots have performed dynamic walking on well designed flat floors. In reality, however, a typical room floor that appears to be flat has local and global inclinations of about 2°. It is important to note that even slight unevenness of a floor can cause serious instability in biped walking robots. In this paper, the authors propose an online control algorithm that considers local and global inclinations of the floor by which a biped humanoid robot can adapt to the floor conditions. For walking motions, a suitable walking pattern was designed first. Online controllers were then developed and activated in suitable periods during a walking cycle. The walking control algorithm was successfully tested and proved through walking experiments on an uneven and inclined floor using KHR-2 (KAIST Humanoid robot-2), a test robot platform of our biped humanoid robot, HUBO.

Mechanical design of the humanoid robot platform, HUBO

The Korea Advanced Institute of Science and Technology (KAIST) humanoid robot-1 (KHR-1) was developed for the purpose of researching the walking action of bipeds. KHR-1, which has no hands or head, has 21 d.o.f.: 12 d.o.f. in the legs, 1 d.o.f. in the torso and 8 d.o.f. in the arms. The second version of this humanoid robot, KHR-2 (which has 41 d.o.f.) can walk on a living-room floor; it also moves and looks like a human. The third version, KHR-3 (HUBO), has more human-like features, a greater variety of movements and a more human-friendly character. We present the mechanical design of HUBO, including the design concept, the lower-body design, the upper-body design and the actuator selection of joints. Previously we developed and published details of KHR-1 and KHR-2. The HUBO platform, which is based on KHR-2, has 41 d.o.f., stands 125 cm tall and weighs 55 kg. From a mechanical point of view, HUBO has greater mechanical stiffness and a more detailed frame design than KHR-2. The stiffness of the frame was increased, and the detailed design around the joints and link frame was either modified or fully redesigned. We initially introduced an exterior art design concept for KHR-2 and that concept was implemented in HUBO at the mechanical design stage.

Experimental realization of dynamic walking of the biped humanoid robot KHR-2 using zero moment point feedback and inertial measurement

This paper describes a novel control algorithm for dynamic walking of biped humanoid robots. For the test platform, we developed KHR-2 (KAIST Humanoid Robot-2) according to our design philosophy. KHR-2 has many sensory devices analogous to human sensory organs which are particularly useful for biped walking control. First, for the biped walking motion, the motion control architecture is built and then an appropriate standard walking pattern is designed for the humanoid robots by observing the human walking process. Second, we define walking stages by dividing the walking cycle according to the characteristics of motions. Third, as a walking control strategy, three kinds of control schemes are established. The first scheme is a walking pattern control that modifies the walking pattern periodically based on the sensory information during each walking cycle. The second scheme is a real-time balance control using the sensory feedback. The third scheme is a predicted motion control based on a fast decision from the previous experimental data. In each control scheme, we design online controllers that are capable of maintaining the walking stability with the control objective by using force/torque sensors and an inertial sensor. Finally, we plan the application schedule of online controllers during a walking cycle according to the walking stages, accomplish the walking control algorithm and prove its effectiveness through experiments with KHR-2.

Development of an above knee prosthesis using MR damper and leg simulator

Since conventional above-knee prostheses are passive type devices with constant mechanical properties, the knee joint motions are not similar to that of normal persons. On the other hand, active type prostheses can improve the swing phase gait but these are expensive, heavy and consume large energy. Thus we propose a semi-active prosthesis using the rotary magnetorheological (MR) damper. The torque dissipation in the knee joint can be controlled by the magnetic field induced by the solenoid. A 3-DOF leg simulator has been developed to generate various hip motions and analyze the results of walking motions. The tracking control of knee joint angle was performed with this leg simulator. The experiment shows that the proposed prosthesis system has good performance in swing phase. We applied the repetitive controller in conjunction with the computed control law and PD control law. This algorithm reduces the RMS tracking error as the repetitions of the tracking. Moreover, the proposed prosthesis system is adaptable to walking speed.

Realization of dynamic walking for the humanoid robot platform KHR-1

This paper presents three online controllers for maintaining dynamic stability of a humanoid robot and describes simplified walking patterns for easy tuning in real experiments. The legs of a humanoid robot are relatively long and serially connected with compliant force/torque sensor at the ankle. This architecture has the inherent characteristics of a lightly damped system. Most research on balance control overlook the deterministic vibration caused by structural compliance. In addition, the vibration was not positively considered to improve the characteristics of the system. Therefore, a simple inverted pendulum model with a complaint joint is proposed. The proposed model has an advantage in easy parameter identification by experiment. For this model, the damping controller that increases system damping is proposed as a balance controller. Furthermore, the performance of maintaining balance against external forces is experimentally shown. A landing orientation controller at the ankle joints is presented to manage fast and stable ground contact. A landing position controller is implemented in order to modify the prescribed trajectory of the swing foot and to reduce the landing impact during unexpected landing. The effectiveness of the proposed controllers is confirmed by walking experiments that have been applied on the KAIST humanoid robot platform KHR-1.

Experimental realization of dynamic walking for a human-riding biped robot, HUBO FX-1

This paper describes a control strategy of the stable walking for the human-riding biped robot, HUBO FX-1. HUBO FX-1 largely consists of two legs with 12 d.o.f., a pelvis and a cockpit. A normal adult can easily ride on HUBO FX-1 by means of a foothold, and can change the walking direction and speed continuously through the use of a joystick. Principally, this kind of robot must be able to carry a payload of at least 100 kg in order to carry a person easily. A sufficient payload can be accomplished by two ways. The first is through the choice of a highly efficient actuator. The second is through weight reduction of the robot body frames. As an efficient actuator, a high-power AC servo motor and a backlash-free harmonic drive reduction gear were utilized. Furthermore, the thickness and the size of the aluminum body frames were sufficiently reduced so that the weight of HUBO FX-1 is light enough. The disadvantage of the weight reduction is that HUBO FX-1 was not able to walk stably due to structural vibrations, as the body structures become more flexible due to this procedure. This problem was solved through the use of a simple theoretical model and a vibration reduction controller based on sensory feedback. In order to endow the robot with a stable biped walking capability, a standard walking pattern and online controllers based on the real-time sensory feedback were designed. Finally, the performance of the real-time balance control strategy was experimentally verified and stable dynamic walking of the human-riding biped robot, HUBO FX-1, carrying one passenger was realized.

Improvements on VSS-type self-tuning control for a tracking controller

This paper points out that the VSS-type self-tuning controller of K. Furuta (see ibid., vol.40, p.37-44, 1993) can be improved by modifications of the sector with separate gains and the equivalent control algorithm. The controlled system is stable in the outside of the sector and ultimately bounded in the inside of the sector. The proposed VSS-type self-tuning controller prevents the fluctuation of the estimated parameters that can occur during the parameter adaptation. This controller, having reduced the switching sector, is actually applicable to the tracking control of discrete systems in the presence of parameter uncertainties.

Controllers for running in the humanoid robot, HUBO

This paper discusses the controllers for running in the humanoid robot and verifies the validity of the proposed controllers via experiments. To realize running in a humanoid robot, the overall control structure is composed of an off-line controller and an on-line controller. The main purpose of the online controller is to maintain the dynamic stability while the humanoid robot runs. The on-line controller is composed of the posture balance control in the sagittal plane, the transient balance control in the frontal plane, and the swing ankle pitch compensator in the sagittal plane. These controllers were applied to the humanoid robot, HUBO, and it ran forward stably at a maximum speed of 3.24km/h.

Human-friendly motion control of a wheeled inverted pendulum by reduced-order disturbance observer

This paper introduces a novel approach to control a wheeled inverted pendulum when a disturbance is applied by a human. The interaction between a human and a wheeled inverted pendulum involves a pulling or pushing force. This type of action is a severe disturbance for a wheeled inverted pendulum, as the wheeled inverted pendulum tends to maintain its initial position if there is no desired input. Thus, there are many possibilities for the wheeled inverted pendulum to be unstable as a result of interactions with humans. To solve this problem, the control algorithm of a wheeled inverted pendulum was designed to move in coordination with the external force of a human. This control algorithm is termed human-friendly motion control. It contains an optimal controller using a full-state feedback and a reduce-order disturbance observer. The disturbance torque from a human was estimated, and the estimated disturbance torque was used to generate a position reference for the human-friendly motion. This control algorithm keeps the wheeled inverted pendulum stable even when a severe disturbance is applied.