In 2000, the BIT team got budget for humanoid robot research from the State High-Tech Development Plan (863 Program) of the Ministry of Science and Technology of China and National Natural Science Foundation of China (NSFC). Two years later, the first generation of BHR series robot, BHR-1 was unveiled, which is the first fully integrated humanoid robot capable of dynamic walking without tether in 2002. It marks a significant progress in the field of humanoid robots in China. BHR-1 is 1.58 m tall, weighs 76 kg and has 28 degrees of freedom. It was equipped with gyro and acceleration sensors in the chest, force-torque sensor on each foot, and vision system. It was a testbed for bipedal walking and whole-body motion. The maximum walking speed of BHR-1 was 2 km/h. Some motion planning and balance control methods were validated on BHR-1 robots. At present, the BHR-1 robot is displayed in the History Museum of Beijing Institute of Technology (Figure 2).

In 2005, BHR-2, the second generation of the BHR robot, was unveiled with the support from 863 Program and NSFC. BHR-2 robot is 1.6 m tall, weighs 63 kg and has 32 degrees of freedom. The BHR-2 robot improved the capability of complex motion control based on BHR-1. The BHR-2 can perform the traditional martial arts (Figure 3), such as Tai Chi and broadsword. BHR-2 also showed better balance control capability than BHR-1. In 2005, BHR-2 robots were invited to give live performance on CCTV-1 “Innovation China” TV program (Figure 4). The BHR-2 robots are selected as one of major national scientific and technological achievements of 863 Program of tenth Five-Year Plan and invited to participate in the Major Science and Technology Achievement Exhibition of

National Tenth Five-Year Plan of China in 2005. Many media reported the progress of BHR-2 robots.

The third generation, BHR-3 unveiled in 2007, was designed for museums, for example, China Science and Technology Museum (Figure 5), Guangdong Science and Technology Center and Zhejiang Science and Technology Museum. It was the first time in China that adult-sized humanoid robots were sold as commercial product. BHR-3 was implemented with modular design, which significantly improved the reliability and efficiency of robot. The robots performed twice every day in museums.

The issue of human-robot interaction is important for having humanoid robots serve humans in daily life. A humanoid robot preferably has a humanlike face and makes facial expressions similar to human. In order to achieve this goal, the BIT team developed BHR-4 robot (Figure 6), which was unveiled in 2009. BHR-4 is very similar to the original model, a professor in the BIT team. It is 1.7 m tall, weights 65 kg, and has 46 degrees of freedom. There are 13 active degrees of freedom in the robotic head. BHR-4 is capable of performing human-like facial expressions to express several typical emotions, such as happiness, anger, disgust, fear, sadness, and surprise (Yu et al., 2014a) . Besides performing facial expressions, BHR-4 also has the functions of its previous generations, such as locomotion with two legs.

The BHR-4 was selected as a significant achievement and was exhibited on the 20^th Anniversary Achievement Exhibition of National High-tech Zone Construction in 2012. Many news media reported the research result (Figure 7).

Humanoid robots should not only be able to walk, but also have the ability of manipulation. In order to investigate humanoid manipulation, the BIT team began to develop a new humanoid robot in 2008. The fifth generation of the BHR robot, BHR-5, unveiled in 2011 can fulfill fast manipulation based on vision, such as playing table tennis against human and robotic opponents (Figure 8). Two BHR-5 robot played more than 200 rounds.

In order to play table tennis, BHR-5 first detects initial ball trajectory by stereo vision system at a speed of 125 Hz, then predict the ball’s subsequent trajectory by aerodynamics and bouncing model between the ball and the table, then plan whole body’s motion for hitting the ball to desired landing area, and finally control the robot to accomplish the planned motion. To play table tennis, visual precision, movement speed and balance capability are strict requirements on the robot. If a humanoid robot can play table tennis, it would accomplish many other dynamic tasks.

The BHR-5 was also exhibited on the 20^th Anniversary Achievement Exhibition of National High-tech Zone Construction in 2012 (Figure 9 and Figure 10). The news media praised BHR-5 as one of highlights of the exhibition.

Humanoid robots are expected to assistor replace humans to accomplish tasks in dangerous environments, for examples emergency rescue scenarios. To our experiences on humanoid experiments, although we try our best to keep a humanoid robot balance, the robot might fall down due to unexpected disturbance. It is almost inevitable to avoid falling in real environments. If a humanoid robot suffers from unexpected falling, the damage will be severe and the robot can’t recover and continue to work. To grant a humanoid robot with multi-mode locomotion capability is a feasible way to make humanoid adapt to real environment. For example, if a robot suffers from falling down unexpectedly, it can try to protect itself and recover again. If a robot can’t pass through low and narrow space by walking, it might choose crawling. If a robot can’t pass through by crawling, it might select jumping.

To break through these problems of humanoid robot, the development of BHR-6 was launched in 2013. We conducted joint research with Takanishi Laboratory of Waseda University with the support of NSFC. In order to achieve multi-mode locomotion, the robot should have large range of movement. High strength and light weight mechanism are very critical for the robot. To endure large impact during falling and achieve large range of movement, a parallel differential mechanism consisting of two leadscrew drives was used in waist joints. In order to buffer and absorb impact during falling, some passive buffering material is attached on chest, knees, back, and hips.

In 2017, BHR-6 was unveiled, with the height of 1.65 m, the weight of 55 kg, and 23 degrees of freedom. BHR-6 can walk on outdoor road, crawl, roll and take fall protection (Figure 11 and Figure 12).

BHR-6was exhibited in 2017 in the State Exhibition of Five Years of Great

Achievements (Figure 13). In August 2018, the BHR-6 was exhibited in the exhibition of 2018 World Robotics Conference (Figure 14).

The 2018 IEEE-RAS 18th International Conference on Humanoid Robots (Humanoids 2018) took place in Beijing, China, on November 6 - 9, 2018. BIT hosted the conference and technical tour, and about 200 scholars witnessed the demonstration of BHR-6 humanoid robots during the technical tour (Figure 15).

All these significantly spread the impact of BHR humanoid robots at home and abroad.