Human–Robot Cooperative Strength Training Based on Robust Admittance Control Strategy

With global aging people and patients with lower-limb dysfunction growing, motion control of the omnidirectional lower-limb rehabilitation robot during centre-of-gravity shift is becoming more and more important. This paper proposes a robust trajectory tracking control strategy for omnidirectional lower-limb rehabilitation robot during centre-of-gravity shift. The main contents of this paper consist of three parts: 1) The kinematic and dynamic model that considered centre-of-gravity shift are presented firstly. 2) A robust control strategy with H ∞ tracking performance is developed and used to achieve the desired trajectories. 3) Simulation tests are performed and demonstrate the feasibility and efficacy of the proposed approach.

In this paper, robust adaptive control strategies are designed for Underwater Remotely Operated Vehicles (ROVs) with velocity constraints. First, robust control strategies are investigated for under-water ROVs, and then adaptive robust control strategies are further developed with online parameter estimation. To prevent the velocity constraint violation, the Barrier Lyapunov Function (BLF) is employed in Lyapunov synthesis. By ensuring the boundedness of the BLF, we also guarantee that the velocity constraints are not transgressed. The stability analysis of the closed-loop system is provided and all closed-loop signals are ensured to be bounded. Simulation results for 5 degree-of-freedom (DOF) underwater ROV demonstrate the effectiveness of the proposed approach.

Archosaurs (crocodylians, birds and their extinct relatives) underwent numerous evolutionary transitions in limb morphology and body size, reflecting a diverse suite of postural and behavioral adaptations. Among archosaurs, saurischians (sauropodomorph and theropod dinosaurs) evolved a wide diversity of hip joint morphology and locomotor postures, as well as spanning seven orders of magnitude in body size. The very largest saurischians possessed incongruent hip joints, in which the bony ends of the femur and the acetabulum (hip socket) differ in shape and size. This observation has led to the suggestion that gigantic saurischians built their joints using large volumes of soft tissues. Nevertheless, the lack of hip joint anatomical data in extant archosaurs and the general poor preservation of joint soft tissues in fossils hinder functional inferences of archosaur hip joints, thus complicating our attempts to understand the posture, locomotor behavior, ecology, and evolution of this diverse clade. This thesis investigates the anatomy and homology of articular soft tissue in the archosaur hip joint, reconstructs the evolutionary transition of hip joints in Saurischia, and infers the correlated evolution of hip joints and body size in the sauropod and theropod lineages. In the first study, I described the soft tissue anatomies and their osteological correlates in the hip joint of archosaurs and their sauropsid outgroups, and infer structural homology across extant sauropsids using dissection, imaging, and histology. This study provides new insight into soft tissue structures and their osteological correlates in the archosaur hip joint, allowing anatomical inferences of once-present joint soft tissues in fossil archosaurs. In the second study, I used maximum likelihood ancestral state reconstruction and osteological correlates to infer major trends in hip joint soft tissue transitions within sauropodomorphs and theropods, and tested the integration between femoral and acetabular structures. Results of this study indicate that sauropodomorph hip joints underwent few concerted transitions, followed by subsequent stasis in soft tissue anatomy throughout Sauropoda. In contrast, the theropod hip joint is characterized by mosaic evolution within the stem lineage, such that bird-like hip joints independently evolved in multiple theropod clades. In the final study, I used 3D imaging techniques and phylogenetically correlated correlations to test the relationship among hip joint dimensions, morphological characters, and body size of saurischian dinosaurs. Giant theropods and sauropods convergently evolved highly incongruent bony hip joints. In sauropods, the femoral head was capped a thick layer of hyaline cartilage, which functioned to resist massive axial compressive loads. In contrast, theropods covered their femoral head and neck with thinner hyaline cartilage, and maintained the femoral neck-antitrochanter articulation to accommodate shear forces during femoral abduction and axial rotation. These results indicate that the archosaur hip joint underwent divergent transformations in soft tissue morphology reflective of body size, locomotor posture, and joint loading. Moreover, these studies provides the basis for reconstructing hip joint function, hindlimb posture, and locomotor evolution of archosaurs, as well as expanding the body of comparative knowledge on vertebrate joint and cartilage biology.

Connected and Autonomous Vehicles (CAVs) in a platoon can exchange real-time information using Vehicle-to-Vehicle (V2V) communication technology to enhance platoon control performance. However, the V2V communication technology also provides opportunities for cyber-attacks, where falsified information can be injected into vehicle controllers to disrupt the platoon operation and even induce vehicle collisions. To address this problem, this study proposes a robust platoon control strategy for CAVs to mitigate the impacts of the falsified information to maneuver the CAV platoon to achieve consensus safely. The proposed control strategy consists of three components: (i) a robust control law, which consistently negates the disturbance induced by falsified information; (ii) a state observer which estimates the vehicle states and disturbance induced by falsified information and inputs the estimated results into the robust control law to compute a synthesized control decision; and (iii) a control decision regulator which applies a Control Barrier Function-based Quadratic Programming (CBF-QP) to regulate the control decision computed by the robust control law to avoid actuator saturation issue and ensure safe spacing for each vehicle in the platoon. Numerical experiments demonstrate that the proposed control strategy can effectively drive the CAV platoon to the desired consensus safely and efficiently under the impacts of falsified information injection.

The objective is to control a web transport system with winder and unwinder for elastic material. A physical modeling of this plant is made based on the general laws of physics. For this type of control problem, it is extremely important to prevent the occurrence of web break or fold by decoupling the web tension and the web velocity. Due to the wide-range variation of the radius and inertia of the rollers the system dynamics change considerably during the winding/unwinding process. Different strategies for web tension control and linear transport velocity control are presented. First, an H/sub /spl infin// robust control strategy which reduces the coupling between tension and velocity, is compared to the decentralized control strategy with proportional integral derivative (PID) controllers commonly used in the industry. Second, an H/sub /spl infin// robust control strategy with varying gains is shown to render the control more robust to the radius variations. Then, a linear parameter varying (LPV) control strategy with smooth scheduling of controllers is synthesized for different operating points and compared to the previous methods. Finally, this LPV control and the H/sub /spl infin// robust control strategy with varying gains are combined to give the best results on an experimental setup, for the rejection of the disturbances introduced by velocity variations and for the robustness to radius and inertia changes.

In this paper, an integrated tube robust iterative learning model predictive control (Tube‐RILMPC) strategy based on the dynamic partial least squares (DyPLS) identified algorithm is proposed. The problems of large amount of online data calculation and input and output variable dimensions disaster in the original variable space are solved. This integrated Tube‐RILMPC strategy enhances the tracking performance and robustness of two‐dimensional (2D) control system. The output trajectories of system are located in the tube the nominal trajectory, which reduces the modelling error caused by the uncertain model. Based on the worst‐case performance index of ellipsoidal uncertainty and polytopic uncertainty, a robust iterative learning control (ILC) strategy is designed. Finally, the superiority of the proposed control algorithm is verified by comparative simulation.

The purpose of this chapter is to redesign the standard adaptive control schemes by using hybrid structure composed by Model Reference Adaptive Control (MRAC) or Adaptive Pole Placement Control (APPC) strategies, associated to Variable Structure (VS) schemes for achieving non-standard robust adaptive control strategies. The both control strategies is now on named VS-MRAC and VS-APPC. We start with the theoretical base of standard control strategies APPC and MRAC, discussing their structures, as how their parameters are identified by adaptive observers and their robustness properties for guaranteeing their stability. After that, we introduce the sliding mode control (variable structure) in each control scheme for simplifying their design procedure. These design procedure are based on stability analysis of each hybrid robust control scheme. With the definition of both hybrid control strategies, it is analyzed their behavior when controlling system plants with unmodeled disturbances and parameter variation. It is established how the adaptive laws compensates these unmodeled dynamics. Furthermore, by using simple systems examples it is realized a comparison study between the hybrid structures VS-APPC and VSMRAC and the standard schemes APPC and MRAC. As the hybrid structures use switching laws due to the sliding mode scheme, the effect of chattering is analyzed on the implementation and consequently effects on the digital control hardware where sampling times are limiting factor. For reducing these drawbacks it is also discussed possibilities which kind of modifications can employ. Finally, some practical considerations are discussed on an implementation on motor drive systems.

Background/Problem: Standard neurorehabilitation and gait training has not proved effective in restoring normal gait coordination for many stroke survivors. Rather, persistent gait dyscoordination occurs, with associated poor function, and progressively deteriorating quality of life. One difficulty is the array of symptoms exhibited by stroke survivors with gait deficits. Some researchers have addressed lower limb weakness following stroke with exercises designed to strengthen muscles, with the expectation of improving gait. However, gait dyscoordination in many stroke survivors appears to result from more than straightforward muscle weakness. Purpose: Thus, the purpose of this case study is to report results of long-duration gait coordination training in an individual with initial good strength, but poor gait swing phase hip/knee and ankle coordination. Methods: Mr. X was enrolled at >6 months after a left hemisphere ischemic stroke. Gait deficits included a ‘stiff-legged gait’ characterized by the absence of hip and knee flexion during right mid-swing, despite the fact that he showed good initial strength in right lower limb quadriceps, hamstrings, and ankle dorsiflexors. Treatment was provided 4 times/week for 1.5 h, for 12 weeks. The combined treatment included the following: motor learning exercises designed for coordination training of the lower limb; functional electrical stimulation (FES) assisted practice; weight-supported coordination practice; and over-ground and treadmill walking. The FES was used as an adjunct to enhance muscle response during motor learning and prior to volitional recovery of motor control. Weight-supported treadmill training was administered to titrate weight and pressure applied at the joints and to the plantar foot surface during stance phase and pre-swing phase of the involved limb. Later in the protocol, treadmill training was administered to improve speed of movement during the gait cycle. Response to treatment was assessed through an array of impairment, functional mobility, and life role participation measures. Results: At post-treatment, Mr. X exhibited some recovery of hip, knee, and ankle coordination during swing phase according to kinematic measures, and the stiff-legged gait was resolved. Muscle strength measures remained essentially constant throughout the study. The modified Ashworth scale showed improved knee extensor tone from baseline of 1 to normal (0) at post-treatment. Gait coordination overall improved by 12 points according to the Gait Assessment and Intervention Tool, Six Minute Walk Test improved by 532′, and the Stroke Impact Scale improved by 12 points, including changes in daily activities; mobility; and meaningful activities. Discussion: Through the combined use of motor learning exercises, FES, weight-support, and treadmill training, coordination of the right lower limb improved sufficiently to exhibit a more normal swing phase, reducing the probability of falls, and subsequent downwardly spiraling dysfunction. The recovery of lower limb coordination during swing phase illustrates what is possible when strength is sufficient and when coordination training is targeted in a carefully titrated, highly incrementalized manner. Conclusions/Contribution to the Field: This case study contributes to the literature in several ways: (1) illustrates combined interventions for gait training and response to treatment; (2) provides supporting case evidence of relationships among knee flexion coordination, swing phase coordination, functional mobility, and quality of life; (3) illustrates that strength is necessary, but not sufficient to restore coordinated gait swing phase after stroke in some stroke survivors; and (4) provides details regarding coordination training and progression of gait training treatment for stroke survivors.

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Stroke is a significant cause of disability worldwide, and stroke survivors often experience severe motor impairments. Lower limb rehabilitation exoskeleton robots provide support and balance for stroke survivors and assist them in performing rehabilitation training tasks, which can effectively improve their quality of life during the later stages of stroke recovery. Lower limb rehabilitation exoskeleton robots have become a hot topic in rehabilitation therapy research. This review introduces traditional rehabilitation assessment methods, explores the possibility of lower limb exoskeleton robots combining sensors and electrophysiological signals to assess stroke survivors' rehabilitation objectively, summarizes standard human-robot coupling models of lower limb rehabilitation exoskeleton robots in recent years, and critically introduces adaptive control models based on motion intent recognition for lower limb exoskeleton robots. This provides new design ideas for the future combination of lower limb rehabilitation exoskeleton robots with rehabilitation assessment, motion assistance, rehabilitation treatment, and adaptive control, making the rehabilitation assessment process more objective and addressing the shortage of rehabilitation therapists to some extent. Finally, the article discusses the current limitations of adaptive control of lower limb rehabilitation exoskeleton robots for stroke survivors and proposes new research directions.

User perspectives on the design and setup of lower limb mirror therapy equipment after stroke: a technical report

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