In this article, we investigate the characteristics of a collaborative hybrid parallel robot. A comparison between this robot and other collaborative robots regarding the Cartesian inertia is ...presented to highlight the very low inertia of the hybrid parallel robot. A task space stiffness-damping control is also proposed. In order to improve the performance of macro--mini systems in the interaction context, an active macro-active mini system consisting of the hybrid parallel robot mounted on a three degrees of freedom (3-DOF) gantry translational robot is introduced. A control strategy for physical human-robot interaction is applied to the macro--mini arrangement. The stability of this method is analyzed and it is shown that the macro-mini combination is more stable than the mini alone. An experimental validation is then carried out. The results obtained with the hybrid parallel robot show that the desired interaction force can be tracked at high speed and that prescribed impedance parameters can be precisely rendered to the human operator without using any additional sensor. Also, it is pointed out that the bandwidth of interaction of the hybrid parallel robot, as well as of the macro--mini system is much higher than that of other commercial collaborative robots. In addition, other tests are realized on the macro-mini system in order to verify the performance and to demonstrate potential applications. The macro-mini robot introduced in this work yields a very intuitive human-robot interaction, which makes it ideal for many applications in which direct physical teaching or assistance is needed.
A novel backdrivable 3- R ( R R- R RR)SR kinematically redundant (6+3)-degree-of-freedom (DOF) spatial hybrid parallel robot with revolute actuators is proposed for low-impedance physical human-robot ...interaction. The kinematic model is developed based on the constraint conditions of the robot. It is shown that the type II (parallel) singularities can be completely avoided, thereby yielding a very large translational and orientational workspace. A workspace analysis is presented in order to demonstrate the capabilities of the robot. Mechanisms are then introduced to use the redundant DOF of the robot to operate a gripper with the robot actuators, which are mounted on or close to the base, thus reducing the inertia of the moving parts. The architecture of the robot makes it possible to use direct drive motors, thereby making the robot easily backdrivable and allowing the use of a very simple and effective controller. A prototype of the robot is then designed and built and the large workspace of the robot as well as the effortless physical human-robot interaction are demonstrated. The controller of the robot is then described, including a position control mode and a control mode for physical interaction, which does not require the use of a force/torque sensor or joint torque sensors. Because of its backdrivability and low moving inertia, the robot is particularly well-suited for physical human-robot interaction, as demonstrated in the accompanying videos.
This paper addresses the stability of macro–mini robotic systems in a context of physical human–robot interaction (pHRI). A simple model including a one-degree-of-freedom (one-dof) macro robot and a ...one-dof mini robot is investigated using a state-space representation in order to assess the controllability and stability of the system. In this work, the stability of the system is analysed in more detail regarding two perspectives of the interaction process, namely the human force input and the human position input. Moreover, physical limits and the frequency response of the macro–mini system are also examined. Therefrom, this study derives a general formula for the constraints of the virtual mass and the virtual damping. Possible choices of these parameters in certain ranges are graphically and visually demonstrated. Simulations are carried out in order to demonstrate the stability and the behaviour of the system with different input signals. The conclusions of the analysis can be used in the design of multi-dof macro–mini systems. An example of a 12-dof macro–mini system is briefly described to illustrate potential applications.
•The dynamic modelling of macro–mini robotic systems.•A stability analysis of macro–mini robotic systems.•Proposed controller design for macro–mini robotic systems.•Simulation results that demonstrate the stability.•Design guidelines for the selection of the rendered mass and damping.
Recent advances in acquisition and display technologies have led to an enormous amount of visual data, which requires appropriate storage and management tools. One of the fundamental needs is the ...design of efficient image classification and recognition solutions. In this paper, we propose a wavelet neural network approach for sparse representation-based object classification. The proposed approach aims to exploit the advantages of sparse coding, multi-scale wavelet representation as well as neural networks. More precisely, a wavelet transform is firstly applied to the image datasets. The generated approximation and detail wavelet subbands are then fed into a multi-branch neural network architecture. This architecture produces multiple sparse codes that are efficiently combined during the classification stage. Extensive experiments, carried out on various types of standard object datasets, have shown the efficiency of the proposed method compared to the existing sparse coding and deep learning-based methods.
This paper discusses the motion control problem of kinematically redundant hybrid parallel robots that were recently proposed. The kinematic and dynamic models are firstly reviewed. It is pointed out ...that the robot can be decomposed into two parts and that each part can be analysed independently. A new hybrid approach is proposed based on this property of the robot. This approach includes an adapted computed-torque control scheme for the legs that operates in the joint space as well as a compensation of the errors of the platform applied in the Cartesian space. The convergence of this proposed approach is also verified using the Lyapunov stability theory. Two example architectures of kinematically redundant robots are built and experiments are conducted. Finally, the results are compared and analysed in order to validate the improvements provided by the proposed control method. It is shown that the proposed control scheme significantly reduces the position error. Potential extensions of this work are also discussed.
A frequent degradation in video-guided surgery and especially laparoscopic and endoscopic surgery is uneven illumination, due in large part to physical limitations of the sensors and uncontrolled ...lighting conditions in the internal structure of the digestive tract and particularly at the level of the intestines. Surgical as well as postoperative task accuracy can be seriously affected by the perceptual quality of the acquired images or videos. In this respect, a No-Reference Image Quality Assessment (NR-IQA) metric dedicated to uneven illumination is proposed in this paper. The key idea is to analyze the effect of contrast enhancement on the spatial distribution of the luminance component of the signal. The results obtained through extensive experiments, performed on a challenging dedicated database, have shown that the proposed metric significantly improves the state-of-the-art NR-IQA metrics when applied to this type of video content and distortion.
Robots need to adapt their behaviour while physically interacting with an operator to guarantee safety and provide intuitiveness. Inferring the intentions of the operator is a challenging problem ...that can be addressed by introducing sensors, in addition to motor encoders. Also, kinematic redundancy can be used to avoid issues such as singularities or mechanical interference, and the redundant coordinates can be controlled freely. In this work, we propose to use the redundant degrees of freedom to infer the intentions of an operator interacting with a backdrivable kinematically redundant parallel robot, without introducing any additional sensors. The proposed approach is based on the fact that, in mechanically backdrivable robots, the operator can control the redundant degrees of freedom, and this can be sensed using solely motor encoders through the solution of the forward kinematics. This approach is implemented to switch between a position controller and a controller that allows the operator to guide the robot freely thanks to gravity compensation. Experiments are carried out to compare this approach with an existing one and show that it improves intuitiveness during interaction by reducing false mode change detections.
Alternate wetting and drying (AWD) irrigation is projected to replace continuous flooding (CF) irrigation for rice production in parts of the Mekong delta area during the dry season. A dry season ...field experiment was conducted in Mekong delta alluvial soil to compare N cycle processes and agronomic parameters under AWD and CF water management schemes. 15N-labeled urea was applied in microplots to follow the fate of fertilizer N. The major loss of fertilizer N occurred through ammonia volatilization amounting to 21% and 13% of the applied N in the AWD and CF treatments, respectively. Ammonia volatilization was largely controlled by soil and floodwater pH which determined the NH3/NH4+ ratio. Irrespective of water management, 10–12% of the fertilizer N could be recovered from the top soil (0–15 cm) after harvest, whereas 10% of fertilizer N accumulated in deeper soil horizons (15–50 cm). Even though the loss of fertilizer N through nitrification-denitrification was 6 fold higher under AWD than CF (0.22 versus 0.04 g N m−2) it only removed 2.5% of the applied fertilizer and was thus quantitatively insignificant. Overall, net N mineralization and potential nitrification in the top soil were stimulated by the AWD treatment, whereas the difference in water management practice did not affect N uptake by the plants, aboveground biomass, or grain yield. Fertilizer N contributed only around 20% of the N uptake by the plants probably because the soil was rich in N, which was deposited during the preceding flooding season. Although based on data from one dry season crop only, our study indicates that future implementation of AWD irrigation is unlikely to adversely affect crop yields by loss of fertilizer N in intensive rice production systems in the Mekong delta.
► NH3 volatilization was responsible for the major gaseous N loss of fertilizer N. ► Denitrification was increased six-fold by AWD, but was still quantitatively insignificant. ► Approx. 10% of fertilizer N accumulated in deeper soil horizons (15–50 cm). ► AWD did not affect rice yield or fertilizer N loss.
This paper presents an improved indoor localization system based on radio frequency (RF) and ultrasonic signals, which we named the SNSH system. This system is composed of a transmitter mounted in a ...mobile target and a series of receiver nodes that are managed by a coordinator. By measuring the Time Delay of Arrival (TDoA) of RF and ultrasonic signals from the transmitter, the distance from the target to each receiver node is calculated and sent to the coordinator through the CAN network, then all the information is gathered in a PC to estimate the 3D position of the target. A sine wave detector and dynamic threshold filter are applied to provide excellent accuracy in measuring the range from the TDoA results before multilateration algorithms are realized to optimize the accuracy of coordinate determination. Specifically, Linear Least Square (LLS) and Nonlinear Least Square (NLS) techniques are implemented to contrast their performances in target coordinate estimation. RF signal encoding/decoding time, time delay in CAN network and math calculation time are carefully considered to ensure optimal system performance and prepare for field application. Experiments show that the sine wave detector algorithm has greatly improved the accuracy of range measurement, with a mean error of 2.2 mm and maximum error of 6.7 mm for distances below 5 m. In addition, 3D position accuracy is greatly enhanced by multilateration methods, with the mean error in position remaining under 15 mm. Furthermore, there are 90% confidence error values of 23 mm for LLS and 20 mm for NLS. The update in the overall system has been verified in real system operations, with a maximum rate of 25 ms, which is a better result than many other existing studies.
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