Academic literature on the topic 'Stewart platform; biomechanical testing; control'

The article deals with description of design of sensor system for linear actuators. These constitute a part of a parallel kinematic machine based on a structure of a Stewart platform. The machine is intended for testing of bone implants in biomechanical and medical practice. The developed Stewart platform presents a mechatronic system. Hence the design of mechatronic systems known as a V-model was used. The system of sensors has been developed since the middle phase of the Stewart platform development.

Being relatively new to the field, electromechanical actuators of Stewart platform in vibration control and motion simulation applications lack the knowledge base compared to ones accumulated for the other actuator types, especially when it comes to characterization and system identification. This paper focuses in the modeling of an electromechanical linear actuator to be used in a heavy load six-degrees-of-freedom platform application intended for motion control technology. The paper keeps the main kinematic and dynamic parameters unaffected, ignoring others. After obtaining the structure of model, parameters is derived by system identification. Provides a comparison of output of real system and simplified model by same input signal, the experimental result shows that the method is accurate and have good ability.

A multidimensional loading material testing machine (MLMTM) based on Stewart Platform is proposed in this paper. The kinematic and dynamic characteristics of MLMTM are analyzed, including the influence of universal joint in each limb on dynamic modeling. The dynamic model is established via Kane method, and the control system is founded based on classic PID strategy. Four experiments are performed to examine the validity of proposed dynamic model and control system of the MLMTM, including two uniaxial experiments and two biaxial experiments. Results of these experiments are summarized as well as the capacity of force tracking and load errors are analyzed. The experimental results demonstrate the validity of dynamic model via Kane method and illustrate that the proposed MLMTM is capable of performing multidimensional loading tests.

During the integration phase of a system development, we are often concerned as to whether the designed control algorithm could be performed on the selected controller in real-time. One of the tools to test and validate the control scheme is the Hardware-in-the-Loop (HiL) simulation technique, which is a part of a model-based design methodology. This approach requires a simulation model of a controlled system running in a real-time loop with an intended controller and a control algorithm, which are objects of interest in this method. To perform the test, the control algorithm must be deployed to the controller such as a PLC. This paper presents a use case of the HiL technique in the design of the Stewart platform control, where the controller is PLCnext from Phoenix Contact. The control algorithm was first verified in the Model-in-the-Loop simulation (MiL) and then generated as a code from the Matlab/Simulink environment and deployed to the PLCnext, which resulted in a smoother transition from the design to the integration and testing phase. The presented method is also applicable to other controllers that support code generation.

This paper presents the automatic approach procedure of a flying vehicle, attached to an ABB 7600 robot, and a mobile platform, attached to a Stewart platform. Due to a nonlinear dynamic behavior, it is necessary to implement complex control, stabilization and guidance schemes. The proposed solution for this system includes the development of an algorithm based on a backstepping control method, the controller design methodology being based on Lyapunov's stability theory. The proposed command law requires that the states are known, but it is also necessary to introduce a series of state estimators. Tracking a mobile platform is critical in surveillance, reconnaissance and tracking missions, with the control methodology defining a clear distinction between translational and rotational dynamics. The proposed algorithm is developed by separating two types of states involving an inverse kinematics, known as algebraic kinematics, in which the dynamic movements of the two pieces of equipment are used. The dynamics of the ABB 7600 robot involves a movement with seven degrees of freedom, while the Stewart platform can be used with a movement of six degrees of freedom. The proposed algorithm is implemented in both Matlab software and experimental testing. This paper provides results in terms of generating dynamics for both devices that can be used for simulating different scenarios of aerospace missions.

The paper presents a new multi-dimensional loading structure based on parallel mechanism used for testing the materials and components. The mechanics of structure is introduced, kinematics and control model is analyzed, and loadings are simulated. It shows that because various actual forces can be supplied and controlled, static and dynamic performances of components can be evaluated by this structure, with which the capacity of the load-bearing can be ensured accurately. The data obtained by this structure is very important for the design of the materials and the components.

The Air Force Research Laboratory team has been confronted with many unique testing challenges in the Ballistic Missile Defense Organization sponsored Vibration Isolation and Suppression System (VISS) performance test program, VISS incorporates a combination passive/active vibration mitigation technology in a Stewart platform configuration to provide a mechanically quiet platform for a medium-wavelength, infrared camera. VISS actuator stiffnesses, insufficient to support the payload in a l-g field, require a gravity off-load system to simulate the free boundary conditions of space A performance test series characterized the test fixture dynamics, VISS payload dynamics and the open loop control system plant. Passive performance has been characterized and the active performance measured in the laboratory will be verified when VISS is on-orbit. VISS goals include demonstrating good passive-based vibration isolation at high frequencies, augmenting low-frequency isolation with closed loop control, suppressing an on-board disturbance due to a cryocooler, and demonstrating steering capabilities of the payload with a prescribed amplitude and spectral content.

Abstract The article focuses on compressive axial loading experimental testing and simulations of topologically optimized design and additively manufactured cervical implants. The proposed platform design is based on anatomical and biomechanical requirements for application in the cervical area. Thanks to new ways of production, such as additive manufacturing, and new software possibilities in the field of structural analysis, which use the finite element method and analysis, it is possible to execute topological optimization of an implant in construction solution, which would be impossible to make by conventional methods. The contribution of this work lies in investigation of 3D printed PLA cervical implant usage in surgical intervention and creation of a numerical static loading modelling methodics and subsequent experimental confirmation of the modelling correctness.

Lower limb prostheses offer a solution to restore the ambulation and self-esteem of amputees. One key component is the prosthetic socket that serves as the interface between prosthetic device and amputee stump and thereby has a wide range of impacts on efficient fitting, appropriate load transmission, operational stability, and control. For the design and optimization of a prosthetic socket, an understanding of the actual intra-socket operational conditions becomes therefore necessary. This is however a difficult task due to the inherent complexity and restricted observability of socket operation. In this study, an innovative mechatronics-twin framework that integrates advanced biomechanical models and simulations with physical prototyping and dynamic operation testing for effective exploration of operational behaviors of prosthetic sockets with amputees is proposed. Within this framework, a specific Stewart manipulator is developed to enable dynamic operation testing, in particular for a well-managed generation of dynamic intra-socket loads and behaviors that are otherwise difficult to observe or realize with the real amputees. A combination of deep learning and Bayesian Inference algorithms is then employed for analyzing the intra-socket load conditions and revealing possible anomalous.

This thesis investigates the development and application of a robotic system for in-vitro biomechanical testing to study the mechanisms leading to human joint injury and degeneration in an ethical and safe manner. Six degree of freedom (6-DOF) robotic-based systems, in particular Gough-Stewart platform-based systems, have been increasingly used in applications of biomechanical testing where 6-DOF mobility, large load capacity, and high stiffness and positioning accuracy are required from the testing machine. This study proposes a novel Gough-Stewart platform-based manipulator with ultra-high stiffness and accuracy for use in biomechanical testing and investigates its mechanism and control. Not only restricted to biomechanical testing, the proposed manipulator concept can also be applied to other robotic-based applications, particularly those requiring ultra-high accuracy positioning under large external loads (e.g machining). Four main features of the proposed manipulator are individually studied in this thesis: namely, stiffness and control of a non-collocated actuator-sensor mechanism, active preload control using actuation redundancy for backlash elimination, adaptive velocity-based load control of human joints for unconstrained testing, and reproducing the in-vivo measured kinematics on human cadaveric joints. Stiffness and Control of the Non-collocated Actuator-Sensor Mechanism A novel Gough-Stewart platform-based mechanism is proposed with a fully decoupled actuator-sensor arrangement for passively compensating the structural compliance of the manipulator. The stiffness of the robot load frame and the sensing frame are respectively quantified using the robot kinematics error model combined with finite element analysis (FEA) on the top and bottom assemblies. Numerical results demonstrate that the proposed mechanism improves the stiffness of the robotic testing system in excess of an order of magnitude on the translational axes and two orders of magnitude for rotational axes compared to a traditional actuator-sensor collocated design. Control disturbances arising from actuator-sensor non-collocation is addressed using decoupled control. Experimental results show that the proposed decoupled control algorithm improves the dynamic accuracy of the manipulator by approximately 25% on average. Active Preload Control Using Actuation Redundancy for Backlash Elimination This thesis investigates combining the benefits of both active and passive preload control methods, using actuation redundancy to prevent backlash on a general Gough- Stewart platform. Both the mechanical configuration and the dynamics model of the redundant manipulator are investigated for the ease of control. A novel online optimization algorithm combined with a feedback force control scheme is formulated to achieve a real-time method which is robust to both model inaccuracy and load disturbance. Simulation results demonstrate an effective preload efficacy by the redundant arrangement within the workspace of the robot. Simulation results also show that the proposed method can effectively achieve backlash-free positioning of the manipulator under large 6-DOF external loads. Experimental results further prove that the proposed method can eliminate backlash instabilities from control and consequently higher bandwidth control can be achieved by the robot with improved accuracy. Adaptive Velocity-based Load Control of Human Joint for Unconstrained Testing A novel adaptive velocity-based load control method is proposed in this thesis to more effectively achieve pure force or moments on human joints under unconstrained testing compared to existing methods. The force/moment control gains are designed to vary adaptively based on the tracking performance of the force/moment to make a compromise between load following and control stability, which makes the proposed method self-adaptive to unknown joint dynamics. Sheep functional spinal units are used to experimentally validate the method on the custom-built Gough-Stewart platform-based manipulator. Experimental results illustrate the efficiency of the proposed method, which can be further improved when overcoming certain limitations of the system (e.g. load sensor noise, position inaccuracy arising from backlash, etc.) Reproducing the In-vivo Measured Kinematics on Human Cadaveric Joints This thesis develops a method to scientifically reproduce the general in-vivo kinematics measured from a living human on human cadaver joints using the custom-built Gough-Stewart platform-based manipulator. A human wrist is used as a typical example to elaborate the theory of the method and to assess the fidelity of the method. The proposed method uses a 3-D motion capture system to collect the in-vivo wrist kinematics from 12 patients undertaking hammering motion. In parallel, CT scans and static motion capture are undertaken on 8 cadaveric human wrist specimens in an effort to define the locations of the coordinate systems. Consequently the in-vivo measured wrist kinematics is transformed to the kinematics of the robotic testing system, which is used to reproduce the hammering motion. Experimental results show that the accuracy of the reproduced motion on the cadaveric samples is of similar magnitude to the measurement error of the motion capture system. Experimental results also show that the assumption of fixed wrist joint centre of rotation is valid for motion reproduction.
Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2014

A stewart platform type motion simulator[1] has been developed, in order to generate the HMMWV (High Mobility Multipurpose Wheeled Vehicle) motion. The purpose of this simulator is to test the stabilization system of the mobile surveillance robot that is mounted on the HMMWV. For developing this motion simulator, the multibody dynamics model of the motion simulator has been created using the general purpose dynamic analysis program ADAMS to validate the design of the motion simulator. Dynamics and control co-simulation model for the motion simulator has been also established for control performance analyses using ADAMS and MATLAB/Simulink. Actual hardware of the motion simulator has been fabricated. Hardware test of the motion simulator has been tried to validate the design.

The Multi-Axis Ride Simulator (MARS) facility is a versatile testing facility for the evaluation of vehicle motion effects on personnel and devices. It consists of a 6-DOF Stewart platform driven by a computer-controlled actuation system. An off-line strategy is used to correct the amplifier input and drive the table dynamic response to the desired trajectory. The capabilities and performance limits of the facility are described in detail. The off-line control strategy is also described and its performance evaluated with a series of experimental tests. The results are presented and discussed in detail.

A standard biomechanical testing protocol for evaluation of the sub-axial cervical spine is the application of pure bending moments to the free end of the spine (with opposing end fixed) and measurement of its motion response. The pure moment protocol is often used to compare spinal fusion instrumentation and has also been used to evaluate non-fusion instrumentation (e.g. disc arthroplasty devices) [1,2]. A variety of different testing systems have been employed to implement pure moment application. In cases where the loading is applied quasi-statically using a series of weights and pulleys the spine may relax between intermittent loading phases and/or unintended loading may be applied causing experimental artifact. Our objective was to use an existing programmable robotic testing platform (Spine Robot) to develop a novel real time force control strategy to simulate pure moment loading under precisely controlled continuous movement conditions. This would serve to advance robotic testing capabilities with an end goal to simulate different protocols in the same platform, and to potentially minimize fixturing and quasi-static artifacts.

A compound load simulator has drawn increasing attention due to the growing demand for testing of critical components in mechanical devices. However, its development is still limited owning to the shortage of corresponding design principle. Accompanied with the application of parallel mechanisms in a variety of multi-axis machine tools and motion simulators, it brings new inspiration to this field. Although existing six degree-of-freedom (DOF) parallel mechanisms such as Stewart platform can output multi-dimensional loads, it also produces the complexity of force control and inevitable collaborative error. Actually, it is enough to utilize deficient-DOF mechanisms for a majority of load patterns and practical engineering applications. Therefore, this paper mainly focuses on synthesizing deficient-DOF parallel/hybrid compound load simulators. Regular load types are summarized including one-dimensional generalized force and compound of them. Based on characteristics of each load type, DOF of the moving platform connecting to the component to be tested is determined through the mapping between force and displacement in rigid body motion. Current typical deficient-DOF parallel mechanism is enumerated to evaluate its load output characteristics. What is more important, a type synthesis procedure based on the graphic approach is presented to construct the configurations of parallel/hybrid mechanism corresponding to different compound load types, which may lead to useful load simulator configurations. The procedure also verifies that the graphic approach is a concise and effective method to synthesize the load simulators associated with a specified load pattern.

The main objective of the BATMAV project is the development of a biologically-inspired Micro Aerial Vehicle (MAV) with flexible and foldable wings for flapping flight. While flapping flight in MAV has been previously studied and a number of models were realized they usually had unfoldable wings actuated with DC motors and mechanical transmission to provide the flapping motion, a system that brings the disadvantage of a heavy flight platform. This phase of the BATMAV project presents a flight platform that features bat-inspired wings with a number of flexible joints to allow mimicking the kinematics of the real mammalian flyer. The bat was chosen after an extensive analysis of the flight parameters of small birds, bats and large insects characterized by a superior maneuverability and wind gust rejection. Morphological and aerodynamic parameters were collected from existing literature and compared concluding that bat wing present a suitable platform that can be actuated efficiently using artificial muscles. Due to their wing camber variation, the bat species can operate effectively at a large rage of speeds and allow remarkably maneuverable and agile flight. Bat skeleton measurements were taken and modeled in SolidWorks to accurately reproduce bones and body via rapid prototyping machines. Much attention was paid specifically to achieving the comparable strength, elasticity, and range of motion of a naturally occurring bat. Therefore, a desktop model was designed, fabricated and assembled in order to study and optimize the effect of various flapping patterns on thrust and lift forces. As a whole, the BATMAV project consists of four major stages of development: the current phase — design and fabrication of the skeletal structure of the flight platform, selection and testing different materials for the design of a compliant bat-like membrane, analysis of the kinematics and kinetics of bat flight in order to design a biomechanical muscle system for actuation, and design of the electrical control architecture to coordinate the platform flight.