Ill-Woo Park

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.

Online Walking Pattern Generation and Its Application to a Biped Humanoid Robot-KHR-3 (HUBO)

The authors propose a simple on-line method for generating a walking pattern for the biped humanoid robot KHR-3 (HUBO). The problem of realizing a walking action in humanoid robots involves two components: generation of the basic walking pattern and the compensation required to maintain the robots balance. Dynamic walking can be realized by incorporating the real-time stabilizing control algorithm developed for KHR-1, KHR-2 and KHR-3. The walking pattern of KHR-3 has four modes: forward/backward, left/right, curved walking and turning around. In the previous pattern generation of the KHR series, the step time and stride of the robot were fixed, and the walking modes, step time and action of stride without stopping could not be changed. Hence, the flexibility of the walking pattern of the robot needed to be upgraded. The walking pattern in this paper allows variation in the walking mode, step time and stride for each step. The pattern uses a simple mathematical form of trajectory curves, specifically the sine, cosine, linear and third-order polynomial curves, and the superposition of these curves is used to minimize the complexity and burden of the computation. The authors used a third-order polynomial to generate the trajectory of the robots pelvis. With the aid of a simplified zero-moment point (ZMP) equation, the pelvis trajectories have a direct relationship with the ZMP trajectories. An effective means of generating the trajectories is introduced, and the scheme is verified experimentally under various walking conditions that take into account the step time and stride. The experimental platform, which has human-like features and movement, is briefly introduced here. With a simple kinematical structure and distributed control hardware architecture, the platform was designed to consume relatively low levels of energy. Moreover, the scheme for generating the trajectory is realized for variations to flexible walking.

Development of humanoid robot platform KHR-2 (KAIST humanoid robot-2)

We are presenting the mechanical and electrical system design and system integration of controllers including sensory devices of the humanoid, KHR-2 in this paper. The concept and the objective of the design will be described. We have developed KHR-2 since 2003 which has 41 DOF (degree of freedom). Each arm including a hand and a wrist has 11 DOF (5+2 DOF/hand (finger + wrist), 4 DOF/arm) and each leg has 6 DOF. Head and trunk have 6 DOF (2 DOF/eye and 2 DOF/neck) and 1 DOF respectively. The mechanical part of the robot is designed to have human friendly appearance and wide movable angle range. Joint actuators are designed to have negligible uncertainties such as backlash. To control all axes, distributed control architecture is adopted to reduce the computation burden of the main controller (PC) and to expand the devices easily. We developed a sub-controller which is a servo motor controller and sensor interfacing devices using microprocessor. The main controller (PC) attached on the back of the robot communicates with sub-controllers in real-time by using CAN (controller area network). Windows XP is used for OS (operating system) for fast development of main control program. RTX (real time extension) HAL extension software is used to realize the real-time control in Windows XP environment. KHR-2 has several sensor types, which are 3-axis F/T (force/torque) sensors at foot and wrist, inertia sensor system (accelerometer and rate gyro) and CCD camera. The F/T sensor at the foot is the most fundamental sensor for stable walking. The inertia sensor system is essential for determining the inclination between the ground and the robot. Finally, we used the CCD camera for navigation and stabilization of the robot in the future. We described the details of the KHR-2 in this paper.

Online Biped Walking Pattern Generation for Humanoid Robot KHR-3(KAIST Humanoid Robot - 3: HUBO)

This paper describes an algorithm about online walking pattern generation method, sensory feedback controllers for walking of humanoid robot platform KHR-3 (KAIST Humanoid Robot-3: HUBO) and experimental results. The walking pattern trajectories have continuity, smoothness in varying walking period and stride, and it has simple mathematical form which can be implemented easily. The gait trajectory algorithm is composed of two kinds of function trajectory. The first one is cycloid function which is used for ankle position in Cartesian coordinate space. Because this profile is made by superposition of linear and sinusoidal function, which has a property of slow start, fast moving, and slow stop. This characteristics can reduce the over drive at high speed motion of the actuator. The second one is 3rd order polynomial function. It is continuous in the defined time interval, easy to use when the boundary condition is well defined, and has standard values of coefficients when the time scale is normalized. Position and velocity values are used for its boundary condition. F/T (Force and Torque) sensors at the ankles of the robot and accelerometers at soles are used to compensate the input position profiles (in joint angle space and Cartesian coordinate space) for keeping its dynamic balance. They are to reduce unexpected external forces such as landing shock, and vibration induced by compliances of the F/T sensor structures, link frames and reduction gears, because they can affect seriously on the walking stability. We use real-time controllers such as ZMP (zero moment point), vibration reduction, landing orientation, damping, landing timing and landing position controller according to its objectives. This trajectory and control algorithm is implemented for the free-walking of KHR-3

Experiments of vision guided walking of humanoid robot, KHR-2

This paper introduces an integration of vision system and a visual guided walking of humanoid robot as a its application. Two CCD cameras are installed in a head which has 6 DOFs in total. Eyes and neck have the pan and tilt mechanism to move the view direction freely. All joints are driven by DC servo motors. We developed the motor controller to move all joint axes of the head. Each CCD camera transmits the NTSC formatted images to a frame grabber witch is installed on a main computer continuously. And then, the frame grabber captures the image frames in the frequency of 10 ~ 15 Hz. For a basic study, we construct the visual processing algorithm so that the robot can always gaze a red light marker. Besides, we establish the strategy of combining non real-time visual information and real-time walking pattern. Finally, vision guided walking algorithm which enables the robot to follow the red light marker on foot, is tested experimentally by using a humanoid robot, KHR-2

RUNNING PATTERN GENERATION OF HUMANOID BIPED WITH A FIXED POINT AND ITS REALIZATION

This paper discusses the generation of a running pattern for a humanoid biped and verifies the validity of the proposed method of running pattern generation via experiments. Two running patterns are generated independently in the sagittal plane and in the frontal plane and the two patterns are then combined. When a running pattern is created with resolved momentum control in the sagittal plane, the angular momentum of the robot about the Center of Mass (COM) is set to zero, as the angular momentum causes the robot to rotate. However, this also induces unnatural motion of the upper body of the robot. To solve this problem, the biped was set as a virtual under-actuated robot with a free joint at its support ankle, and a fixed point for a virtual under-actuated system was determined. Following this, a periodic running pattern in the sagittal plane was formulated using the fixed point. The fixed point is easily determined in a numerical approach. In this way, a running pattern in the frontal plane was also generated. In an experiment, a humanoid biped known as KHR-2 ran forward using the proposed running pattern generation method. Its maximum velocity was 2.88 km/h.

Development of a Humanoid Robot Platform HUBO FX-1

Many researches about humanoid robot are performed for last decade. There exist outstanding results about hardware platforms and software algorithms and some results become commercial products. Humanoid robot engineering is synthetic study which includes mechanism design, sensor system, control algorithm and so on. But humanoid robot engineering has just symbol of technology, practical usage is very low compare with other robot shapes. Main object of this research is to develop humanoid robot which can be used in industrial or social environment. HUBO FX-1 is humanoid robot which is used for transportation system in social or industrial environment. It can carry luggage or a person according to shape of its upper body