HUBO

HUBO is a humanoid robot originally developed at the Korea Advanced Institute of Science and Technology and currently undergoing joint research by Korean and American universities. The first HUBO, KHR-3, was the culmination of four years of research based on three earlier prototypes, and it was officially unveiled to the public on January 6, 2005. The name HUBO is short for "HUmanoid roBOt".

Development history
The first HUBO (KHR-3) was developed by mechanical engineering professor Oh Junho and his Ph.D. student teams over the course of about 20 years. During much of this time, the technologies relevant to HUBO were acquired at a steady pace with contributions from within KAIST. This informal approach resulted in a very low development cost of around $500,000 by the time of KHR3's completion. (In comparison, Honda is believed to have spent $300 million on ASIMO between 1986 and 2000.)

Prototypes
The first prototype was the KHR-0 (KAIST Humanoid Robot), consisting of two legs without an upper body. It was built in 2001 with the purpose of investigating the specifications of the actuators (devices that receive electric signals and perform mechanical actions) and the optimal design parameters of the humanoid robot.

The second prototype, the KHR-1, was completed by January 2002. The KHR-1 was humanoid in form, but without the head and hand components that are nonessential for walking. Its purpose was to demonstrate autonomous walking that involves real-time motion control through sensory feedback. (This involves constant adjustments that are absent in playback walking from an offline learning process and partially adjusted walking.) It could walk at speeds up to 0.8 km/hr and change its direction.

The project was continued with the development of KHR-2 from 2003 to 2004. The KHR-2 was built as a complete humanoid and featured improved sensoring with the addition of CCD cameras, inertia sensors, and tilt sensors. It was used as a platform for simulating vision-guided dynamic walking, in which the robot maintains focus on a moving red light.

KHR-3 HUBO
Work on the KHR-3 HUBO was begun in September 2004. The internal components were covered with metallic grey plastic, and modifications were made to the joints and and the skeleton for greater stiffness and minimal mechanical uncertainty. The KHR-3's physical specifications, such as height, weight, and the number of DOFs (degrees of freedom), were similar to Honda's ASIMO, which served as the benchmark for the project. In terms of AI and movements, HUBO fell short of the "next-gen ASIMO," which was unveiled three months later. While HUBO could only walk at 1.25 km/h, the ASIMO could walk at 2.5 km/h and also run at 3 km/h. The ASIMO was also capable of walking up and down stairs, which was a temporary shortcoming for HUBO needing further development. The unnerved KAIST researchers noted, however, that HUBO could play rock-paper-scissors, which was impossible for ASIMO since its fingers could not move independently of each other.

International collaboration
HUBO's development became increasingly international with participation from the United States. The first collaboration involved Hanson Robotics in creating the Albert HUBO, completed in November 2005. Albert HUBO was a derived version of the KHR-3 HUBO, but with a distinctive head resembling Albert Einstein. The head, which was made by the Hanson Lab, featured a Frubber skin (often used in movie productions) and 35 joints underneath it to make realistic facial expressions. Like its predecessors, Albert HUBO contained 2 CCD cameras for vision recognition.

The subsequent collaboration on the Jaemi HUBO (also known as KHR-4 and HUBO 2; "Jaemi" (재미) can mean "in the United States" in Chinese characters or "fun" in colloquial Korean) was a more extensive and strategic effort to combine Korea's expertise in humanoid design with the US's strength in cognition, perception, navigation, and networking. It involved participation of KAIST, Korea University, and the Seoul National University in South Korea, and the Bryn Mawr College, Colby College, Drexel University, the University of Pennsylvania, and Virginia Tech in the United States under a $5 million dollar, 5-year program funded by the National Science Foundation.

The Jaemi HUBO's initial development concerning the mechanical aspect was done at KAIST from 2008 to 2009. The Jaemi HUBO was given a slimmer design with an aluminum endoskeleton and a polycarbonate frame, resulting in a slightly taller height but a 20% lighter weight than its predecessors. Its movements were more realistic since the arms made quicker and more natural motions, and the legs could stretch to imitate human walking, which also consumes less energy than the traditional humanoid walking based on ZMP trajectory (see below). Its walking speed was improved to 1.4 km/h, and it also acquired the ability to run at 3.6 km/h (which is still much slower than the new ASIMO's 6 km/h by comparison).

Design and engineering principles
Central to HUBO's successful development was its focus on simpler and feasible design and movements. For HUBO to be light and efficient, its height was set similar to a child's, and the body was made with special materials (Jaemi HUBO). Its autonomous design lacking external connections helps to both simulate realistic walking and reduce its exposure to outside factors that would increase chances of error.

All models were built with harmonic drives in order to avoid backlash in the gears and to achieve a light, compact design. The DOFs of the different axes in the joints of shoulders, waist, hips, and ankles were merged into intersections in order to attain a simple, closed-form solution (that is, comprised of well-known mathematical functions) of inverse kinematics (the computation of the robot's movements).

Walking from KHR-1 to KHR-3 was based on the Zero Moment Point trajectory, which consists of points on the ground where the total moment of inertia of the active forces equals to zero when one leg is in contact. The trajectory was calculated with a simple model to form a repetitive pattern, in which the robot is always in touch with the ground, and the initial and end phases of its legs' movements are identical. Biped walking speed is naturally restricted, however, due to the limited range of the hip joint (which makes the forward movement of the leg).

Jaemi HUBO is able to move more quickly by running, which includes a flying phase when both its feet are off the ground. Running is not as structurally limited as walking because the robot continues to move forward midair even as its hip joint reverses motion. By rotating its upper body against the one-sided thrusting motion of its legs, the robot is able to maintain a periodic running pattern based on a trajectory of the angular momentum of its center of mass.