Virtual Target Research Articles

Constancy of Preparatory Postural Adjustments for Reaching to Virtual Targets across Different Postural Configurations

Postural and movement components must be coordinated without significant disturbance to balance when reaching from a standing position. Traditional theories propose that muscle activity prior to movement onset create the mechanics to counteract the internal torques generated by the future limb movement, reducing possible instability via centre of mass (CoM) displacement. However, during goal-directed reach movements executed on a fixed base of support (BoS), preparatory postural adjustments (or pPAs) promote movement of the CoM within the BoS. Considering this dichotomy, the current study investigated if pPAs constitute part of a whole-body strategy that is tied to the efficient execution of movement, rather than the constraints of balance. We reasoned that if pPAs were tied primarily to balance control, they would modulate as a function of perceived instability. Alternatively, if tied to dynamics necessary for movement initiation, they would remain unchanged, with feedback-based changes being sufficient to retain balance following volitional arm movement. Participants executed beyond-arm reaching movements in four different postural configurations that altered the quality of the BoS. Quantification of these changes to stability did not drastically alter the tuning or timing of preparatory muscle activity despite modifications to arm and CoM trajectories necessary to complete the reaching movement. In contrast to traditional views, preparatory postural muscle activity is not always tuned for balance maintenance or even as a calculation of upcoming instability but may reflect a requirement of voluntary movement towards a pre-defined location.

Flexible Assimilation of Human's Target for Versatile Human-Robot Physical Interaction.

Recent studies on the physical interaction between humans have revealed their ability to read the partner's motion plan and use it to improve one's own control. Inspired by these results, we develop an intention assimilation controller (IAC) that enables a contact robot to estimate the human's virtual target from the interaction force, and combine it with its own target to plan motion. While the virtual target depends on the control gains assumed for the human, we show that this does not affect the stability of the human-robot system, and our novel scheme covers a continuum of interaction behaviours from cooperation to competition. Simulations and experiments illustrate how the IAC can assist the human or compete with them to prevent collisions. In this article, we demonstrate the IAC's advantages over related methods, such as faster convergence to a target, guidance with less force, safer obstacle avoidance and a wider range of interaction behaviours.

Grasping Weber’s Law in a Virtual Environment: The Effect of Haptic Feedback

Recent findings suggest that the functional separation between vision-for-action and vision-for-perception does not generalize to situations in which virtual objects are used as targets. For instance, unlike actions toward real objects that violate Weber’s law, a basic law of visual perception, actions toward virtual objects presented on flat-screens, or in remote virtual environments, obey to Weber’s law. These results suggest that actions in virtual environments are performed in an inefficient manner and are subjected to perceptual effects. It is unclear, however, whether this inefficiency reflects extensive variation in the way in which visual information is processed in virtual environments or more local aspects related to the settings of the virtual environment. In the current study, we focused on grasping performance in a state-of-the-art virtual reality system that provides an accurate representation of the 3D space. Within this environment, we tested the effect of haptic feedback on grasping trajectories. Participants were asked to perform bimanual grasping movements toward the edges of virtual targets. In the haptic feedback condition, physical stimuli of matching dimensions were embedded in the virtual environment. Haptic feedback was not provided in the no-feedback condition. The results showed that grasping trajectories in the feedback, but not in the no-feedback condition, could be performed more efficiently, and evade the influence of Weber’s law. These findings are discussed in relevance to previous literature on 2D and 3D grasping.

Administration of mircoRNA-135b-reinforced exosomes derived from MSCs ameliorates glucocorticoid-induced osteonecrosis of femoral head (ONFH) in rats.

Exosomes were found to exert a therapeutic effect in the treatment of osteonecrosis of the femoral head (ONFH), while miR‐135b was shown to play an important role in the development of ONFH. In this study, we investigated the effects of concomitant administration of exosomes and miR‐135b on the treatment of ONFH. A rat mode of ONFH was established. TEM, Western blotting and nanoparticle analysis were used to characterize the exosomes collected from human‐induced pluripotent stem cell–derived mesenchymal stem cells (hiPS‐MSC‐Exos). Micro‐CT was used to observe the trabecular bone structure of the femoral head. Real‐time PCR, Western blot analysis, IHC assay, TUNEL assay, MTT assay and flow cytometry were performed to detect the effect of hiPS‐MSC‐Exos and miR‐135b on cell apoptosis and the expression of PDCD4/caspase‐3/OCN. Moreover, computational analysis and luciferase assay were conducted to identify the regulatory relationship between PDCD4 mRNA and miR‐135b. The hiPS‐MSC‐Exos collected in this study displayed a spheroidal morphology with sizes ranging from 20 to 100 nm and a mean concentration of 1 × 1012 particles/mL. During the treatment of ONFH, the administration of hiPS‐MSC‐Exos and miR‐135b alleviated the magnitude of bone loss. Furthermore, the treatment of MG‐63 and U‐2 cells with hiPS‐MSC‐Exos and miR‐135b could promote cell proliferation and inhibit cell apoptosis. Moreover, PDCD4 mRNA was identified as a virtual target gene of miR‐135b. HiPS‐MSC‐Exos exerted positive effects during the treatment of ONFH, and the administration of miR‐135b could reinforce the effect of hiPS‐MSC‐Exos by inhibiting the expression of PDCD4.

A novel fluorescent lung-marking technique using the photodynamic diagnosis endoscope system and vitamin B2.

For small pulmonary nodules that are unidentifiable by palpation or in endoscopic surgeries wherein palpation is not feasible, visualizing their location is necessary when performing pulmonary sublobar resection procedures, such as wedge resection or segmentectomy. We invented a new transbronchial lung-marking technique using the photodynamic diagnosis endoscope system and vitamin B2 and examined its feasibility and safety via porcine studies. We established the marking procedure in pigs and examined the marking clarity and size, fluorescence intensity and duration and possible complications. In another study, sublobar resection for virtual target lesions was performed in pigs based on the fluorescent markings. The procedure duration, marking visibility, surgical margin from the lesions and technique-related complications were assessed. All 36 markings in 6 pigs were identifiable and were widely distributed over the right lung. The median diameter and fluorescence intensity at 60 min after marking were 6.0 (5.5-6.7) mm and 137.5 (122-168), respectively. All 18 markings for the 6 virtual target lesions (3 markings for each target) were clearly identified, and all target lesions were found in the resected specimens. The median duration per marking was 244 (194-255) seconds. The shortest median surgical margin from a target lesion was 11.5 (9.3-13.5) mm. No procedure-related complications were observed. This novel transbronchial fluorescent lung-marking technique was useful and safe in sublobar resections for small non-palpable pulmonary lesions.

A Novel Double Layered Hybrid Multi-Robot Framework for Guidance and Navigation of Unmanned Surface Vehicles in a Practical Maritime Environment

Formation control and cooperative motion planning are two major research areas currently being used in multi robot motion planning and coordination. The current study proposes a hybrid framework for guidance and navigation of swarm of unmanned surface vehicles (USVs) by combining the key characteristics of formation control and cooperative motion planning. In this framework, two layers of offline planning and online planning are integrated and applied on a practical marine environment. In offline planning, an optimal path is generated from a constrained A* path planning approach, which is later smoothed using a spline. This optimal trajectory is fed as an input for the online planning where virtual target (VT) based multi-agent guidance framework is used to navigate the swarm of USVs. This VT approach combined with a potential theory based swarm aggregation technique provides a robust methodology of global and local collision avoidance based on known positions of the USVs. The combined approach is evaluated with the different number of USVs to understand the effectiveness of the approach from the perspective of practicality, safety and robustness.

Effects of Avatar Perspective on Joint Excursions Used to Play Virtual Dodgeball: Within-Subject Comparative Study.

BackgroundVisual representation of oneself is likely to affect movement patterns. Prior work in virtual dodgeball showed greater excursion of the ankles, knees, hips, spine, and shoulder occurs when presented in the first-person perspective compared to the third-person perspective. However, the mode of presentation differed between the two conditions such that a head-mounted display was used to present the avatar in the first-person perspective, but a 3D television (3DTV) display was used to present the avatar in the third-person. Thus, it is unknown whether changes in joint excursions are driven by the visual display (head-mounted display versus 3DTV) or avatar perspective during virtual gameplay.ObjectiveThis study aimed to determine the influence of avatar perspective on joint excursion in healthy individuals playing virtual dodgeball using a head-mounted display.MethodsParticipants (n=29, 15 male, 14 female) performed full-body movements to intercept launched virtual targets presented in a game of virtual dodgeball using a head-mounted display. Two avatar perspectives were compared during each session of gameplay. A first-person perspective was created by placing the center of the displayed content at the bridge of the participant’s nose, while a third-person perspective was created by placing the camera view at the participant’s eye level but set 1 m behind the participant avatar. During gameplay, virtual dodgeballs were launched at a consistent velocity of 30 m/s to one of nine locations determined by a combination of three different intended impact heights and three different directions (left, center, or right) based on subject anthropometrics. Joint kinematics and angular excursions of the ankles, knees, hips, lumbar spine, elbows, and shoulders were assessed.ResultsThe change in joint excursions from initial posture to the interception of the virtual dodgeball were averaged across trials. Separate repeated-measures ANOVAs revealed greater excursions of the ankle (P=.010), knee (P=.001), hip (P=.0014), spine (P=.001), and shoulder (P=.001) joints while playing virtual dodgeball in the first versus third-person perspective. Aligning with the expectations, there was a significant effect of impact height on joint excursions.ConclusionsAs clinicians develop treatment strategies in virtual reality to shape motion in orthopedic populations, it is important to be aware that changes in avatar perspective can significantly influence motor behavior. These data are important for the development of virtual reality assessment and treatment tools that are becoming increasingly practical for home and clinic-based rehabilitation.

Value-Flow-Based Demand-Driven Pointer Analysis for C and C++

We present Supa, a value-flow-based demand-driven flow- and context-sensitive pointer analysis with strong updates for C and C++ programs. Supa enables computing points-to information via value-flow refinement, in environments with small time and memory budgets. We formulate Supa by solving a graph-reachability problem on an inter-procedural value-flow graph representing a program's def-use chains, which are pre-computed efficiently but over-approximately. To answer a client query (a request for a variable's points-to set), Supa reasons about the flow of values along the pre-computed def-use chains sparsely (rather than across all program points), by performing only the work necessary for the query (rather than analyzing the whole program). In particular, strong updates are performed to filter out spurious def-use chains through value-flow refinement as long as the total budget is not exhausted. We have implemented Supa on top of LLVM (4.0.0) together with a comprehensive micro-benchmark suite after a years-long effort (consisting of around 400 test cases, including hand-written ones and the ones extracted from real programs). We have evaluated Supa by choosing uninitialized pointer detection and C++ virtual table resolution as two major clients, using 24 real-world programs including 18 open-source C programs and 6 large CPU2000/2006 C++ benchmarks. For uninitialized pointer client, Supa achieves improved precision as the analysis budget increases, with its flow-sensitive (context-insensitive) analysis reaching 97.4 percent of that achieved by whole-program Sparse Flow-Sensitive analysis (SFS) by consuming about 0.18 seconds and 65 KB of memory per query, on average (with a budget of at most 10,000 value-flow edges per query). With context-sensitivity also considered, Supa becomes more precise for some programs but also incurs more analysis times. To further demonstrate the effectiveness of Supa, we have also evaluated Supa in resolving C++ virtual tables by querying the function pointers at every virtual callsite. Compared to analysis without strong updates for heap objects, Supa's demand-driven context-sensitive strong update analysis reduces 7.35 percent spurious virtual table targets with only 0.4 secs per query, on average.

Smartphone- versus smartglasses-based augmented reality (AR) for percutaneous needle interventions: system accuracy and feasibility study

To compare the system accuracy and needle placement performance of smartphone- and smartglasses-based augmented reality (AR) for percutaneous needle interventions. An AR platform was developed to enable the superimposition of annotated anatomy and a planned needle trajectory onto a patient in real time. The system accuracy of the AR display on smartphone (iPhone7) and smartglasses (HoloLens1) devices was evaluated on a 3D-printed phantom. The target overlay error was measured as the distance between actual and virtual targets (n = 336) on the AR display, derived from preprocedural CT. The needle overlay angle was measured as the angular difference between actual and virtual needles (n = 12) on the AR display. Three operators each used the iPhone (n = 8), HoloLens (n = 8) and CT-guided freehand (n = 8) to guide needles into targets in a phantom. Needle placement error was measured with post-placement CT. Needle placement time was recorded from needle puncture to navigation completion. The target overlay error of the iPhone was comparable to the HoloLens (1.75 ± 0.59mm, 1.74 ± 0.86mm, respectively, p = 0.9). The needle overlay angle of the iPhone and HoloLens was similar (0.28 ± 0.32°, 0.41 ± 0.23°, respectively, p = 0.26). The iPhone-guided needle placements showed reduced error compared to the HoloLens (2.58 ± 1.04mm, 3.61 ± 2.25mm, respectively, p = 0.05) and increased time (87 ± 17s, 71 ± 27s, respectively, p = 0.02). Both AR devices reduced placement error compared to CT-guided freehand (15.92 ± 8.06mm, both p < 0.001). An augmented reality platform employed on smartphone and smartglasses devices may provide accurate display and navigation guidance for percutaneous needle-based interventions.

An allele of rs619586 polymorphism in MALAT1 alters the invasiveness of meningioma via modulating the expression of collagen type V alpha (COL5A1).

The rs619586 polymorphism has been shown to alter the expression of MALAT1, which act as a competing endogenous RNA (ceRNA) against miR‐145. And miR‐145 was found to target COL5A1, the interaction between which was shown to be involved in the pathogenesis of invasive meningioma. In this study, we aimed to explore the effect of rs619586 polymorphism and its underlying molecular mechanism in invasive meningioma. Real‐time PCR and Western Blot analysis were used to study the differentiated expression of miR‐145, MALAT1 (metastasis‐associated lung adenocarcinoma transcript 1) and COL5A1 (collagen alpha‐1(V) chain) in tumour/serum samples genotyped as rs619586 AA, AG and GG. Computational analysis and luciferase reporter assay were also conducted to identify the regulatory relationship between miR‐145 and MALAT1/COL5A1. Meanwhile, expression of miR‐145 and COL5A1 in different cell treatment groups was measured to validate the results obtained from earlier experiments. As shown by the results and in tumour/serum samples genotyped as AA, AG and GG, the expression of both MALAT1 and COL5A1 was down‐regulated in a stepwise fashion, while the expression of miR‐145 was increased, suggesting a potential negative relationship between MALAT1/COL5A1 and miR‐145. Meanwhile, miR‐145 was shown to bind to MALAT1, while COL5A1 was identified as a virtual target gene of miR‐145. As a consequence, a MALAT1/miR‐145/COL5A1 molecular pathway was established based on the above results. In particular, with the presence of rs619586 A>G polymorphism, the expression of MALAT1 and COL5A1 was both reduced, leading to reduced invasiveness of meningioma.

The role of electromagnetic navigational bronchoscopy in the era of robotics

The advent of the superDimension (Medtronic Corporation, Minneapolis, MN, USA) electromagnetic navigation bronchoscopy (ENB) offers bronchoscopists specialized navigation software to create a 3-dimensional map to target peripheral pulmonary nodules. A pervasive criticism of ENB has centered around the reliance on virtual targets and catheter deflection. The presence of CT-to-body divergence is a critical concern when attempting to ensure that the virtual target truly represents the target lesion. Attempts to make up for the shortcomings of ENB have resulted in development of multiple robotic bronchoscopic platforms. Robotically guided bronchoscopy platforms typically feature smaller scopes that are used to navigate through the small, peripheral airways using automated arms. The ability to successfully biopsy peripheral lung nodules will continue to improve as both the ENB platforms and robotic bronchoscopy platforms evolve. A central question to the future of biopsy platforms is whether one is preferred over the other.

Magnetic resonance imaging/transrectal ultrasonography fusion guided seed placement in a phantom: Accuracy between 2-seed versus 1-seed strategies

PurposeTo investigate whether the 2-seed placement per Magnetic Resonance Imaging (MRI) suspicious lesion yields a higher seed placement accuracy than a 1-seed strategy on a phantom. MethodsEight olives embedded in gelatin, each simulating a prostate, underwent MRI. Three virtual spherical lesions (3, 5, and 8 mm diameters) were marked in each olive on the MRI images and co-registered to the MRI/Transrectal Ultrasonography (TRUS) fusion biopsy system. Two radiologists placed 0.5 mm fiducials, targeting the center of each virtual lesion under fusion image guidance. Half of the 8 olives in each phantom were assigned either to the 1-seed or 2-seeds per lesion strategy. Post-procedure Computed Tomography (CT) images identified each seed and were fused with MR to localize each virtual lesion and collected the seed placement error - distance between the virtual target and the corresponding seed (using the closer seed for the 2-seed strategy). Seed placement success is defined as fiducial placement within a lesion boundary. ResultsEach operator repeated the procedure on three different phantoms, and data from 209 seeds placed for 137 lesions were analyzed, with an overall error of 3.03 ± 1.52 mm. The operator skill, operator phantom procedural experience, lesion size, and number of seeds, were independently associated with the seed placement error. Seed placement success rate was higher for the 2-seed group compared to 1-seed, although the difference was not statistically significant. ConclusionsPlacing 2 seeds per MRI lesion yielded a significantly lower error compared to 1-seed strategy, although seed placement success rate was not significantly different.

Design and Implementation of Web-Based Virtual Mobile Robot Laboratory for Engineering Education

A web-based virtual and remote laboratory environment is developed, realized and proposed for real time control and monitoring of a mobile robot in an indoor environment. In this laboratory, a real time and continuous video stream of indoor laboratory environment is viewed by wireless IP camera mounted to the ceiling. The localization of the robot is also implemented using this IP camera. In this environment, a virtual target and virtual obstacles are located anywhere on the video image taken by the user. The robot is guaranteed to arrive at the virtual target avoiding virtual obstacles using the shortest path. The video stream of the robot’s navigation is monitored through the web environment. The robot is controlled by a BeagleBoard-xM single board computer. The PC web server symmetrically communicates with the other web server on the BeagleBoard-xM, executing developed application software. Since genetic algorithms generate alternative solutions, it is utilized as a path planning algorithm. Parameters such as population size and maximum generation of genetic algorithms applied to get the shortest path for the robot are tuned via the web-based virtual laboratory environment. The robot is also controlled manually through the web environment. At the conclusion of the experiments, the results are monitored on the web-based virtual laboratory environment. A low-cost mobile robot virtual remote laboratory is designed and implemented for engineering education in this paper. Consequently, survey and some experimental works, of the usability and performance of the RRC-Lab (remote robot control-laboratory) system are confirmed by students.

Planar Path Following Control for Wave Glider and Experimental Study

Qi, Z.; Wang, B.; Qin, Y.; Shi, J., and Zhai, J., 2020. Planar path following control for wave glider and experimental study. In: Zheng, C.W.; Wang, Q.; Zhan, C., and Yang, S.B. (eds.), Air-Sea Interaction and Coastal Environments of the Maritime and Polar Silk Roads. Journal of Coastal Research, Special Issue No. 99, pp. 16-20. Coconut Creek (Florida), ISSN 0749-0208.This paper addresses a path following problem of Wave Glider along a predefined path in horizontal plane. The path following controller designing is challenging since Wave Glider is weak maneuvering, underactuated, inaccuracy mathematical model and large environmental disturbances. First, a planar curve path tracking error model is established in the Serret-Frenet coordinate frame. Based on the LOS guidance law and the virtual target method, a planar guidance controller for underactuated Wave Glider is presented to ensure the stability of the path following. And then, according to the classic feedback linearization PID controller and fuzzy controller, a fuzzy adaptive PID controller is developed. Fuzzy controller is used to achieve PID controller parameters online adaptive adjust, in order to improve the robustness of the control system under the influence of environmental disturbances and inaccuracy modeling parameters. Furthermore, analyzing the typical application scenarios of Wave Glider, we set two simulation path in horizontal plane named polyline path and circular path. Numerical simulation results illustrate the proposed control design is effective to deal with planar following problem of Wave Glider. Two sea trails show that the controller can achieve the path following task, however, the speed of Wave Glider is directly related to the accuracy of the path following.

Electromagnetic Navigation Bronchoscopy With Tomosynthesis-based Visualization and Positional Correction: Three-dimensional Accuracy as Confirmed by Cone-Beam Computed Tomography.

Background:Electromagnetic navigation bronchoscopy (ENB) aids in lung lesion biopsy. However, anatomic divergence between the preprocedural computed tomography (CT) and the actual bronchial anatomy during the procedure can limit localization accuracy. An advanced ENB system has been designed to mitigate CT-to-body divergence using a tomosynthesis-based software algorithm that enhances nodule visibility and allows for intraprocedural local registration.Materials and Methods:A prospective, 2-center study was conducted in subjects with single peripheral lung lesions ≥10 mm to assess localization accuracy of the superDimension navigation system with fluoroscopic navigation technology. Three-dimensional accuracy was confirmed by cone-beam computed tomography. Complications were assessed through 7 days.Results:Fifty subjects were enrolled (25 per site). Lesions were <20 mm in 61.2% (30/49). A bronchus sign was present in 53.1% (26/49). Local registration was completed in 95.9% (47/49). Three-dimensional target overlap (primary endpoint) was achieved in 59.6% (28/47) and 83.0% (39/47) before and after location correction, respectively. Excluding subjects with unevaluable video files, target overlap was achieved 68.3% (28/41) and 95.1% (39/41), respectively. Malignant results were obtained in 53.1% (26/49) by rapid on-site evaluation and 61.2% (30/49) by final pathology of the ENB-aided sample. Diagnostic yield was not evaluated. Procedure-related complications were pneumothorax in 1 subject (no chest tube required) and scant hemoptysis in 3 subjects (no interventions required).Conclusion:ENB with tomosynthesis-based fluoroscopic navigation improved the 3-dimensional convergence between the virtual target and actual lung lesion as confirmed by cone-beam computed tomography. Future studies are necessary to understand the impact of this technology on diagnostic yield.

Integral vector field control for three-dimensional path following of autonomous underwater vehicle

A new control method for autonomous underwater vehicle (AUV) is developed to achieve three-dimensional (3D) path following under ocean current disturbances when AUV lacks lateral and vertical driving forces. To make the control system more convenient for practical application and reduce the energy consumption of AUV, the controller is designed with relative velocities. To avoid the singularity problem of curve path following, the Serret–Frenet frame is introduced as virtual target and the error model is defined. The adaptive law of the virtual target and an integral vector field (IVF) guidance law are designed in the kinematic controller. The back-stepping method and adaptive dynamical sliding mode control (BADSMC) technology are applied in the design of dynamic controller. The Lyapunov theory and nonlinear cascade system theory are applied to prove the closed-loop stability. Finally, the performances of the IVF + BADSMC and ILOS + PID algorithm are compared through simulation. Simulation results demonstrate that the proposed controller can realize the path following of AUV under disturbances of ocean current and can improve the following quality.

Understanding Limb Position and External Load Effects on Real-Time Pattern Recognition Control in Amputees.

Limb position is a factor that negatively affects myoelectric pattern recognition classification accuracy. However, prior studies evaluating impact on real-time control for upper-limb amputees have done so without a physical prosthesis on the residual limb. It remains unclear how limb position affects real-time pattern recognition control in amputees when their residual limb is supporting various weights. We used a virtual reality target achievement control test to evaluate the effects of limb position and external load on real-time pattern recognition control in fourteen intact limb subjects and six major upper limb amputee subjects. We also investigated how these effects changed based on different control system training methods. In a static training method, subjects kept their unloaded arm by their side with the elbow bent whereas in the dynamic training method, subjects moved their arm throughout a workspace while supporting a load. When static training was used, limb position significantly affected real-time control in all subjects. However, amputee subjects were still able to adequately complete tasks in all conditions, even in untrained limb positions. Moreover, increasing external loads decreased controller performance, albeit to a lesser extent in amputee subjects. The effects of limb position did not change as load increased, and vice versa. In intact limb subjects, dynamic training significantly reduced the limb position effect but did not completely remove them. In contrast, in amputee subjects, dynamic training eliminated the limb position effect in three out of four outcome measures. However, it did not reduce the effects of load for either subject population. These findings suggest that results obtained from intact limb subjects may not generalize to amputee subjects and that advanced training methods can substantially improve controller robustness to different limb positions regardless of limb loading.

Grasping a 2D virtual target: The influence of target position and movement on gaze and digit placement.

While much has been learned about the visual pursuit and motor strategies used to intercept a moving object, less research has focused on the coordination of gaze and digit placement when grasping moving stimuli. Participants grasped 2D computer generated square targets that either encouraged placement of the index finger and thumb along the horizontal midline (Control targets) or had narrow "notches" in the top and bottom surfaces of the target, intended to discourage digit placement near the midline (Experimental targets). In Experiment 1, targets remained stationary at the left, middle, or right side of the screen. Gaze and digit placement were biased toward the closest side of non-central targets, and toward the midline of center targets. These locations were shifted rightward when grasping Experimental targets, suggesting participants prioritized visibility of the target. In Experiment 2, participants grasped horizontally translating targets at early, middle, or late stages of travel. Average gaze and digit placement were consistently positioned behind the moving target's horizontal midline when grasping. Gaze was directed farther behind the midline of Experimental targets, suggesting the absence of a flat central grasp location pulled participants' gaze toward the trailing edge. Participants placed their digits at positions closer to the horizontal midline of leftward moving targets, suggesting participants were compensating for the added mechanical constraints associated with grasping targets moving in a direction contralateral to the grasping hand. These results suggest participants minimize the effort associated with reaching to non-central targets by grasping the nearest side when the target is stationary, but grasp the trailing side of moving targets, even if this means placing the digits at locations on the far side of the target, potentially limiting visibility of the target.

Distributed target-encirclement guidance law for cooperative attack of multiple missiles

The target-encirclement guidance problem for many-to-one missile-target engagement scenario is studied, where the missiles evenly distribute on a target-centered circle during the homing guidance. The proposed distributed target-encirclement guidance law can achieve simultaneous attack of multiple missiles in different line-of-sight directions. Firstly, the decentralization protocols of desired line-of-sight angles are constructed based on the information of neighboring missiles. Secondly, a biased proportional navigation guidance law that can arbitrarily designate the impact angle is cited. The missiles can achieve all-aspect attack on the target in an encirclement manner by combining the biased proportional navigation guidance law and dynamic virtual targets strategy. Thirdly, the consensus protocol of simultaneous attack is designed, which can guarantee that all missiles’ time-to-go estimates achieve consensus asymptotically, and the convergence of the closed-loop system is proved strictly via the Lyapunov stability theory. Finally, numerical simulation results demonstrate the performance and feasibility of the proposed distributed target-encirclement guidance law in different engagement situations.

Formation flight of fixed-wing UAV swarms: A group-based hierarchical approach

This paper investigates a formation control problem of fixed-wing Unmanned Aerial Vehicle (UAV) swarms. A group-based hierarchical architecture is established among the UAVs, which decomposes all the UAVs into several distinct and non-overlapping groups. In each group, the UAVs form hierarchies with one UAV selected as the group leader. All group leaders execute coordinated path following to cooperatively handle the mission process among different groups, and the remaining followers track their direct leaders to achieve the inner-group coordination. More specifically, for a group leader, a virtual target moving along its desired path is assigned for the UAV, and an updating law is proposed to coordinate all the group leaders’ virtual targets; for a follower UAV, the distributed leader-following formation control law is proposed to make the follower’s heading angle coincide with its direct leader, while keeping the desired relative position with respect to its direct leader. The proposed control law guarantees the globally asymptotic stability of the whole closed-loop swarm system under the control input constraints of fixed-wing UAVs. Theoretical proofs and numerical simulations are provided, which corroborate the effectiveness of the proposed method.