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Purpose This paper aims to present a pipeline to progressively deal with the online external parameter calibration and estimator initialization of the Stereo-inertial measurement unit (IMU) system, which does not require any prior information and is suitable for system initialization in a variety of environments. Design/methodology/approach Before calibration and initialization, a modified stereo tracking method is adopted to obtain a motion pose, which provides prerequisites for the next three steps. Firstly, the authors align the pose obtained with the IMU measurements and linearly calculate the rough external parameters and gravity vector to provide initial values for the next optimization. Secondly, the authors fix the pose obtained by the vision and restore the external and inertial parameters of the system by optimizing the pre-integration of the IMU. Thirdly, the result of the previous step is used to perform visual-inertial joint optimization to further refine the external and inertial parameters. Findings The results of public data set experiments and actual experiments show that this method has better accuracy and robustness compared with the state of-the-art. Originality/value This method improves the accuracy of external parameters calibration and initialization and prevents the system from falling into a local minimum. Different from the traditional method of solving inertial navigation parameters separately, in this paper, all inertial navigation parameters are solved at one time, and the results of the previous step are used as the seed for the next optimization, and gradually solve the external inertial navigation parameters from coarse to fine, which avoids falling into a local minimum, reduces the number of iterations during optimization and improves the efficiency of the system.

Purpose The purpose of this paper is to improve control performance and safety of a real two-wheeled inverted pendulum (TWIP) robot by dealing with model uncertainty and motion restriction simultaneously, which can be extended to other TWIP robotic systems. Design/methodology/approach The inequality of lumped model uncertainty boundary is derived from original TWIP dynamics. Several motion restriction conditions are derived considering zero dynamics, centripedal force, ground friction condition, posture stability, control torque limitation and so on. Sliding-mode control (SMC) and model predictive control (MPC) are separately adopted to design controllers for longitudinal and rotational motion, while taking model uncertainty into account. The reference value of the moving velocity and acceleration, delivered to the designed controller, should be restricted in a specified range, limited by motion restrictions, to keep safe. Findings The cancelation of model uncertainty commonly existing in real system can improve control performance. The motion commands play an important role in maintaining safety and reliability of TWIP, which can be ensured by the proposed motion restriction to avoid potential movement failure, such as slipping, lateral tipping over because of turning and large fluctuation of body. Originality/value An inequation of lumped model uncertainty boundary incorporating comprehensive errors and uncertainties of system is derived and elaborately calculated to determine the switching coefficients of SMC. The motion restrictions for TWIP robot moving in 3D are derived and used to impose constraints on reference trajectory to avoid possible instability or failure of movement.

Purpose One of the development trends of robots is to enable robots to have the ability of anthropomorphic manipulation. Grasping is the first step of manipulation. For mobile manipulator robots, grasping a target during the movement process is extremely challenging, which requires the robots to make rapid motion planning for arms under uncertain dynamic disturbances. However, there are many situations require robots to grasp a target quickly while they move, such as emergency rescue. The purpose of this paper is to propose a method for target dynamic grasping during the movement of a robot. Design/methodology/approach An off-line learning from demonstrations method is applied to learn a basic reach model for arm and a motion model for fingers. An on-line dynamic adjustment method of arm speed for active and passive grasping mode is designed. Findings The experimental results of the robot movement on flat, slope and speed bumps ground show that the proposed method can effectively solve the problem of fast planning under uncertain disturbances caused by robot movement. The method performs well in the task of target dynamic grasping during the robot movement. Originality/value The main contribution of this paper is to propose a method to solve the problem of rapid motion planning of the robot arm under uncertain disturbances while the robot is grasping a target in the process of robot movement. The proposed method significantly improves the grasping efficiency of the robot in emergency situations. Experimental results show that the proposed method can effectively solve the problem.

In this paper, the configuration transformation of Wheel-Legged Robot (WLR) is studied, which can enable the robot to change its multilinks configuration on Inverted Equilibrium Manifold (IEM), while keeping balance with a small location drift on the floor. First of all, the general form of dynamics equation of planar Articulated Wheeled Inverted Pendulum (AWIP) with a wheel and n − 1 rigid links, is derived. The Partial Feedback Linearization (PFL) combined with a Sliding Mode Control (SMC) is used to design the inverse dynamics controller of AWIP, while considering full dynamics terms. The well-known WLR model is used as a simple example of AWIP to accomplish the configuration transformation task. An optimization based configuration transformation algorithm is proposed to realize a comprehensive optimization of the shortest path in joint space and the minimum location drift of WLR on the floor. Finally, the effectiveness of the proposed algorithm is demonstrated through simulation to implement the configuration transformation task.

The rapid increase in volume and types of hazardous waste (HW) due to China's rapid economic development makes it significant to conduct HW safety management. However, due to the information asymmetry between the regularors and regulated institutions,problems such as illegal dumping and statistical fraud are common in hazardous waste transfer (HWT) activities. Moreover, there is a severe problem of information isolated island among waste production companies, transportation companies, and treatment companies in the HW market. Promoting the monitoring and information traceability of the whole process of HWT is the main challenge for HW management. Blockchain provides an ideal solution to overcome the above challenges. This study builds a framework of the blockchain-based HWT management system, enabling government regulators to obtain relevant information in HWT and improve HW's convenience. The system is introduced in detail from the infrastructure, blockchain-service,functions and users, emphasizing six information management functions.Finally, the positive impact and various challenges encountered in implementing blockchain in HWT management were discussed. This study applies blockchain to the research field of HWT management, which expands the application of blockchain in the field of solid waste management with great theoretical and practical significance.

Critical high-tech minerals (CHTMs) are raw materials that are essential for a future clean-energy transition and the manufacture of high-end products. Cellphones, one of the fastest growing electronic products, contain various CHTMs. Since 2019, India has surpassed the United States to become the second largest smartphone market in the world. An increasing and alarming number of excessive waste cellphones will be generated in India in the near future. In this study, the dynamic material flow analysis approach and the Weibull distribution are adopted to analyze the volumes of accumulated waste cellphones and the contained CHTMs based on the differentiation between smartphones and feature phones in India. Moreover, a market supply model is adopted to predict the future trends of CHTMs in waste cellphones. The results show a general upward tendency of waste cellphone volume in India, which indicates that various CHTMs contained in cellphone waste can be properly reused or recycled. Future implications based on the analysis results are provided for efficient cellphone management in India.

Purpose Surgical robot systems have been used in single-port laparoscopy (SPL) surgery to improve patient outcomes. This study aims to develop a vision robot system for SPL surgery to effectively improve the visualization of surgical robot systems for relatively complex surgical procedures. Design/methodology/approach In this paper, a new master-slave magnetic anchoring vision robotic system for SPL surgery was proposed. A lighting distribution analysis for the imaging unit of the vision robot was carried out to guarantee illumination uniformity in the workspace during SPL surgery. Moreover, cleaning force for the lens of the camera was measured to assess safety for an abdominal wall, and performance assessment of the system was performed. Findings Extensive experimental results for illumination, control, cleaning force and functionality test have indicated that the proposed system has an excellent performance in providing the visual feedback. Originality/value The main contribution of this paper lies in the development of a magnetic anchoring vision robot system that successfully improves the ability of cleaning the lens and avoiding the blind area in a field of view.

Uneven terrain is common in natural environment. The TWIP robot has demonstrated its rapid movement ability in even ground in previous works. This paper explores control of the TWIP robot in the continuous uneven ground except the step case. The sinusoidal function and the piece-wise linear function type ground surface are taken as an example to explore motion characteristics of robots on complex terrain. As for the robotic system, continuous or step changes of slope are the main types of disturbance to it. To cope with these disturbance, a Sliding Mode Control (SMC) is used to design the nominal controller due to its insensitivity to uncertainty. Then, the Extended Kalman Filter (EKF) is adopted to estimate the slope of unknown terrain without any ground information from sensors but according to motion state of robot and the Equilibrium Point Estimation (EPE) is then achieved based on the obtained slope angle. In simulation, the TWIP robot moves on these two types of uneven ground surface to track the reference position or velocity trajectory. The comparative experimental results have demonstrated that SMC combined with the EPE method can enable TWIP robot to locomote on some limited uneven ground with higher stability and dynamic performance, compared to the single LQR and the single SMC method. Also, the proposed algorithm has been conduted successfully on the WIP-Bot robot to travel upward and downward slope.

Two-wheeled robots have many advantages over other mobile robots, but they are difficult to self-balance compared with other wheeled robots. Reinforcement learning (RL) is a general framework for sequential decision-making problems. So far, there are many applications of reinforcement learning to solve robot control problems, but most of them are used in simulators because of the large amount of data required. In addition, due to the reality gap, the policy learned in a simulation environment cannot be transferred directly to a real robot. Real robot data often expensive due to the potential damage to the robot. Model-based methods require far fewer robot data than model-free methods, but these methods have the problem of model bias. In this paper, we use a model-based reinforcement learning method to achieve self-balance of a two-wheeled robot. We present a model learning method that can reduce the problem of model bias. Our method combines the simulator and a few real robot data to learn a probabilistic dynamics model of the robot through an iterative way, which requires no expertise and can learn from scratch. Then the control policy is optimized based on the learned model.

As the robot gradually develops from indoor to outdoor, multi-sensor fusion is increasingly being applied to the field of robot perception. Among them, LiDAR and binocular sensors are most widely used. Robots use the complementary and redundant data they provide to perform environmental perception and implement certain functions of the robot, such as SLAM, autonomous obstacle avoidance and so on. However, the data obtained by each sensor are relative to its own coordinate system. Data must be converted to a unified coordinate system before data fusion. Therefore, the calibration of the transformation among sensors is the first problem to be solved in data fusion. Moreover, the accuracy of calibration is directly related to the effect of data fusion. Therefore the calibration between sensors is very important and necessary. In this paper, we propose a novel method to find accurate rigid-body transformation for the extrinsic calibration of a 3D LiDAR and a stereo cameras, using two Aruco calibration boards. Also the validity of the algorithm is demonstrated by some experiments.

This paper presents the force control strategies and a kind of compliance control strategies of the hydraulic- driven unit (HDU) in the legged robots. The model of HDU is established and the transfer function of the HDU force control system is given. The analysis of the force control strategies is introduced according to the characteristic of the HDU system. Based on the force control strategy called velocity feedback control strategy which performs the best, the virtual model control strategy which is a kind of compliance control strategy is presented to enhance the adaptability of the legged robot. Finally, the experiments are taken on the HDU experiment platform to test the performance of the force control strategies and the compliance control strategy. The landing buffer experiments are taken on the single leg robot to verify the effectiveness of the compliance control strategy. In the landing buffer experiments, the impact force of the single leg robot's knee HDU is about 0.33 time of what it is without the compliance control strategy while landing.

The performance of traditional hydraulic robots is often limited by their hoses across moving joints or connecting hydraulic drive units, which would reduce their mobility and impede their ability to operate in complex environment. In response to this deficiency, this paper introduces the WLR-II (the second generation of wheel-legged robot), a novel hydraulic wheel-legged robot developed by using hose-less design approach which is focused on improving the reliability of the hydraulic system and perfecting the appearance of the robot. As its notable features, seven Hydraulic Hose-less Joints (HHJ) that include a pair of high and also low pressure oil pipes based on rotary seal, Cylinder-Valve-Skeleton (CVS) integration thighs and arms which are produced by subtractive manufacturing as well as oscillating cylinders driven by gear rack transmission are included. In addition to a description of its design, experimental characterizations of rough pavement adaptability and payload capability together with the achievement of the reliability of hydraulic system are also demonstrated. As a result, we confirmed effectiveness of the hose-less design by moving on the rugged ground, climbing slope, squatting with load, dragging and picking up a heavy load. To the authors’ best knowledge, this is the first time that the design of a hose-less hydraulic wheel-legged robot has been presented.

The wheeled humanoid robot is such a new type of robot that combines both the humanoid structure and the Wheeled Inverted Pendulum (WIP) base. They are able to move rapidly on flat ground as well as stand still on the slope, which has been well demonstrated on the WLR-II robot in this paper. In order to achieve it, a novel but simplified control framework is designed, which comprises of two main modules, the wheel balance controller and the centroidal adjustment controller. The former controller helps to maintain balance of the robotic system by rotating the wheel to move forward or backward, while the latter controller works by moving the Center of Mass (CoM) of the robot at a distance from the equilibrium point, which will result in a specified acceleration used to drive the first wheel balance controller. In order to design such these two controllers, the dynamic model of the robot in sagittal plane is decoupled into two relatively simplified model. In particular, the coupled dynamics between each other is significantly considered and alleviated. Experiments conducted on the WLR-II robot show that the proposed control framework can make the robot both accurately track the velocity tajectory and steadily stand on the slope.

Linear Parameter Varying (LPV) system shows preferable performance in dealing with NonLinear (NL) systems and systems with time-varying parameters, based on a kind of wheel-legged robot with two-wheel and balance as Inverted Pendulum, this paper proposes a gain scheduling control method for balancing using LPV system on Equivalent model with Center Of Mass (COM). In order to ensure the stability and responsive of the system with possible values for all variable parameters, Higher Order Singular Value Decomposition (HOSVD) is used for constructing polytopic LPV system, then the robust controller is designed for the vertex systems forthputting Linear Matrix Inequality (LMI) approach, and the gain scheduling controller for global system is obtained by convex combination of vertex LTI systems. The simulation results show that the system can achieve the expected indicators.

Two-wheel mobile robot (2WMR) has been widely investigated for its variety of different applications. This paper focuses on a two-wheel robot with a pair of auxiliary arms, aiming at keeping the body of robot upright during acceleration and deceleration. The model dynamic of 2WMR with auxiliary arms has been derived and the relationship between acceleration and center of gravity(COG) is investigated. A controller based on adjusting COG and linear quadratic regulation(LQR) is proposed in this paper. The effectiveness of auxiliary arms and the corresponding controller is confirmed by numerical simulations. By actively rotating the auxiliary arms to adjust the position of COG, the 2WMR accelerates and decelerates rapidly with the body almost upright all the time in simulation.

Vision-based solution is a popular research for 6-DOF state estimation in recent years. All of these algorithms are based on the assumption that surrounding is static. Actually, in a highly dynamic environment, estimated state is mixed, including robot and dynamic objects. To this end, an approach for detecting dynamic objects based on the velocity of feature points is proposed in this paper. Our approach establishes the model of the velocity of feature points and separates dynamic objects motion from the mixed motion by comparing the velocity of IMU (inertial measurement unit) and feature points. Finally, the detection results of dynamic feature points on the left and right cameras’ front and rear frames are fused and verified to eliminate the influence of noise and mismatching. Experimental results prove that our approach can get more accurate state estimation, which shows that this method is effective in high dynamic environments.

This paper presents a vertical jumping trajectory planning and landing buffer control methods that enable a hydraulic driven single legged robot to execute load-bearing take-off and stable landing motions. After a brief description of the robot, the kinematics and dynamics models of HSLR are established based on the actual structure of the robot. Then the paper describes the details of jumping trajectory planning method based on spring loaded inverted pendulum (SLIP) model, which can realize vertical jump control with a desired height. Moreover, landing buffer strategy based on single legged virtual model is presented to protect robots from the impact damage. Finally, the experimental results show that the proposed method for HSLR can achieve vertical jump to 0.2m as well as a stable landing buffer performance.

Compared with the traditional hydraulic humanoid robots, the WLR-II, a novel hydraulic wheel-legged robot developed by using hose-less design, can significantly increase the reliability and maneuverability. The WLR-II combines the rough-terrain capability of legs with the efficiency of wheels. In this paper, a novel framework called rough-terrain adaption framework (RTAF) is presented which allows WLR-II to move on both flat terrains and terrains with unmodeled contact dynamics. RTAF is a hierarchical framework, which has a high-level balance controller and a low-level impedance controller that a high-performance nested torque controller with feed-forward velocity compensation is used. The low-level impedance controller for the hydraulic-driven unit can cancel out the load dynamics influence such as unexpected terrain disturbances and increase the force-tracking performance. With the high-level balance controller, the robot is able to handle unexpected terrain disturbances through wheel-ground force estimation, pitch/roll balance control and impedance parameter regulator. The proposed approach is suitable for a wheel-legged humanoid robot to manage balance through torque control at joints and regulate force-based interaction on rough terrains. The performance of the proposed RTAF is evaluated on variable gradient slopes and grassland which are the typical rough-terrain scenarios for real-world applications. The experimental results reveal that the maximum speed of grassland movement can reach 3 km/h.

BACKGROUND Unlike a manual surgical instrument, a surgical instrument used in robot-assisted minimally invasive surgery (MIS) is configured with a wrist to improve flexibility in surgical operation. However, this configuration has a shortcoming that leads to coupled motion between the wrist and end-effector. METHODS Three methods are presented to eliminate the coupled motion between the wrist and end-effector. The three methods are compared via the decoupled motion characteristic, and the third method is applied to design four surgical instruments. Several experiments are done to validate the effectiveness of these surgical instruments. RESULTS These improved surgical instruments create decoupled motion. The results of experiments on the removal of gall bladder and kidney are excellent, which validates the effectiveness of decoupled surgical instruments. CONCLUSIONS Improved surgical instruments without coupled motion are developed and have a promising clinical application in MIS.

BACKGROUND Surgical robot systems have been used in laparoendoscopic single-site surgery (LESS) to improve patient outcomes. A magnetic anchoring surgical robot system for LESS can effectively extend the operation space. METHODS A robot system based on visual servo control for LESS is proposed. It includes a magnetic anchoring robot and a control subsystem, in which an uncalibrated visual servo control method obtains an accurate positioning capability of the robot for LESS. RESULTS The results of the simulation and the tissue experiment show that the robot system can successfully accomplish the expected control functionalities for LESS. The average positioning error of the proposed system is 1.622 mm. CONCLUSION The magnetic anchoring robot system is able to implement the autonomous positioning of its end-effector through the proposed control approach according to experimental results.

Background Surgical robot systems which can significantly improve surgical procedures have been widely used in laparoendoscopic single-site surgery (LESS). For a relative complex surgical procedure, the development of an in vivo visual robot system for LESS can effectively improve the visualization for surgical robot systems. Methods In this work, an in vivo visual robot system with a new mechanism for LESS was investigated. A finite element method (FEM) analysis was carried out to ensure the safety of the in vivo visual robot during the movement, which was the most important concern for surgical purposes. A master–slave control strategy was adopted, in which the control model was established by off-line experiments. Results The in vivo visual robot system was verified by using a phantom box. The experiment results show that the robot system can successfully realize the expected functionalities and meet the demands of LESS. Conclusion The experiment results indicate that the in vivo visual robot with high manipulability has great potential in clinical application.