Dynamic Modeling and Simulation of a Rotating Single Link Flexible Robotic Manipulator Subject to Quick Stops

Single link robotic manipulators are extensively used in industry and research operations. The main design requirement of such manipulators is to minimize link dynamic deflection and its active end vibrations, and obtain high position accuracy during its high speed motion. To achieve these requirements, accurate mathematical modeling and simulation of the initial design, to increase system stability and precision and to obtain very small amplitudes of vibration, should be considered. In this paper the modeling of such robotic arm with a rigid guide and a flexible extensible link subject to quick stops after each complete revolution is considered and its dynamical behavior analyzed. The extensible link which rotates with constant angular velocity has one end constrained to a predefined trajectory. The constrained trajectory allows trajectory control and obstacle avoidance for the active end of the robotic arm. The dynamic evolution of the system is investigated and the flexural response of the flexible link analyzed under the combined effect of clearance and flexibility.

How should we assess the mechanical properties of lower-limb prosthesis technology used in elite sport?: An initial investigation

Despite recent controversy, it is not yet formally recognised how lower-limb prosthesis should be assessed for their performance. To assist in this process, experiments are undertaken to investigate the linearity, stiffness and assessment of feet based energy return prosthesis technology typically used for elite level high speed running. Through initial investigations, it is concluded that static load testing would not be recommended to specify or regulate energy return prostheses for athletes with a lower-limb amputation. Furthermore, an assessment of energy return technology when loaded under dynamic conditions demonstrates changes in mechanical stiffness due to bending and effective blade length variation during motion. Such radical changes of boundary conditions due to loading suggest that any assessment of lower-limb prosthesis technology in the future should use methods that do not assume linear mechanical stiffness. The research into such effects warrants further investigation in the future

Evaluation of in-plane shear failure in composite laminate with high percentage of 90o plies

The first step in analysis composite joint is to have a correct and appropriate definition of properties of material used. The effect of fibre orientation and the interaction between them in the laminated composite play a key role in determining the laminate characteristics, the laminate mode of failure as well as the overall mode of joint failure. In order to study the failure of a new generation of composite laminate joints, sets of material properties are needed in three directions. This paper present the study of the in-plane (interlamina) shear properties and the behaviour of a specific Carbon Fibre Reinforced Plastic (CFRP) laminate with a particular balanced lay-up under compression load. This paper presents the continuation of a previous study by the author to study shear in a specific CFRP Ref [1

Non-destructive testing and assessment of a piping system with excessive vibration and recurrence crack issue: An industrial case study

Flow in piping generates random excitation which is non-periodic and that means resonance will not be the key factor to pipe failure. One of the main causes of pipe failure is weak supports. Due to their dissimilar stiffness in the piping system, it leads to low frequency and high amplitude flow induced vibration that causes high cyclic stress resulting in high cycle fatigue failure of the joints. Other contributing factors in pipe failure are poor or inadequate design, poor workmanship during installations or maintenance and inadequate or weak and flexible support. These pipes are usually required to work non-stop for 24 hours a day 7 days a week for weeks, months or years at a time. Regular monitoring and in-service dynamic analysis should ensure continuous and safe operation. This paper presents a case study on monitoring, diagnosis, and maintenance of a piping system. High vibration was observed during routine maintenance, in a 30 m high, 24 inch diameter amine pipes at an oil and gas processing plant in southern Thailand. Amine liquid leakage due to high cycle fatigue crack was reported at the piping bearing and this remained a major concern for the personnel at the plant. A non-destructive testing approach which relies on a combined experimental techniques (i.e. Operating Deflection Shapes (ODS)) and computational mechanics (i.e. Finite Element (FE) modal analysis, Computational Fluid Dynamics (CFD) Analysis, Fluid-Structure Interaction (FSI) Analysis) was used to assess the structural integrity of the piping and in the effort of proposing a suitable recommendation in rectifying the high vibration issue. The analyses concluded that the root cause of high vibration was due to inadequate and weak piping support. As a result, additional supports were proposed to counter the deflection of the piping generated by the flow. The supports were found effective in reducing vibration in which the stress concentration at the new supports and the piping was considered relatively low

Understanding the design variables that contribute to the response of a prosthetic foot: Part I –Rig Design

In this paper the design of a rig capable of replicating the dynamic response of an energy storing and returning composite prosthetic foot during amputee running is considered. It has been assumed that the amputee/prosthesis system can be modelled as a spring/mass system. Therefore the rig has been designed to allow the applied mass, input force frequency and foot contact point of various feet designs to be varied to test this assumption. The rig will allow the design variables that contribute to the response of a prosthetic foot during running to be understood and optimised to improve the foot’s performance

Understanding the design variables that contribute to the response of a prosthetic foot: Part II – Rig Validation

In this paper the validation of a rig capable of replicating the dynamic response of an energy storing and returning composite prosthetic foot during amputee running is considered. It is shown that the rig can effectively replicate the running action of an amputee runner and return the same ground contact time. It has also been shown that if a small input force is applied in a timed and sympathetic manner to the prosthetic spring-mass system the amplitude of oscillation increases which agrees with results of previous research. The rig will allow the design variables that contribute to the response of a prosthetic foot during running to be understood and optimised to improve the foot’s performance

Evaluation of steady flow torques and pressure losses in a rotary flow control valve by means of computational fluid dynamics.

In this paper, a novel design of a rotary hydraulic flow control valve has been presented for high flow rate fluid power systems. High flow rates in these systems account for substantial flow forces acting on the throttling elements of the valves and cause the application of mechanically sophisticated multi-staged servo valves for flow regulation. The suggested design enables utilisation of single-stage valves in power hydraulics operating at high flow rates regimes. A spool driver and auxiliary mechanisms of the proposed valve design were discussed and selection criteria were suggested. Analytical expressions for metering characteristics as well as steady flow torques have been derived. Computational fluid dynamics (CFD) analysis of steady state flow regimes was conducted to evaluate the hydraulic behaviour of the proposed valve. This study represents a special case of an independent metering concept applied to the design of power hydraulic systems with direct proportional valve control operating at flow rates above 150 litres per minute. The result gained using parametric CFD simulations predicted the induced torque and the pressure drops due to a steady flow. Magnitudes of these values prove that by minimising the number of spool’s mobile metering surfaces it is possible to reduce the flow-generated forces in the new generation of hydraulic valves proposed in this study. Calculation of the flow jet angles was analytically verified by measuring the deflection of the velocity vector using flow velocity field distribution, obtained during visualisation of the results of CFD simulations. The derived calculation formulas can predict metering characteristics, values of steady flow torques and jet angles for the specified design and geometry of the suggested valve. The proposed novel structure of the flow control valve promises to attain improved controllability, reliability and efficiency of the hydraulic control units of heavy mobile machinery operating at high flow rates regimes

Enhancement of Impact-Synchronous Modal analysis (ISMA) with number of averages.

A new method, namely Impact-synchronous Modal Analysis (ISMA), utilizing the modal extraction technique commonly used in Experimental Modal Analysis performed in the presence of the ambient forces, is proposed. In ISMA, the extraction is performed while the machine is running, utilized Impact-synchronous Time Averaging prior to performing the Fast Fourier Transform. The number of averages had a very important effect when applying ISMA on structures with dominant periodic responses of cyclic loads and ambient excitation. With a sufficient number of impacts, all the unaccounted forces were diminished, leaving only the response due to the impacts. This study demonstrated the effectiveness of averages taken in the determination of dynamic characteristics of a machine while in different rotating speeds. At low operating speeds that coincided with the lower natural modes, ISMA with a high number of impacts determined the dynamic characteristics of the system successfully. Meanwhile, at operating speeds that were away from any natural modes, ISMA with a moderate number of averages taken was sufficient to extract the modal parameters. Finally for high-speed machines, ISMA with a high number of impacts taken has limitations in extracting natural modes close to the operating speed

Monitoring the suitability of the fit of a lower-limb prosthetic socket using artificial neural network in commonly encountered walking conditions

Prosthetic sockets are still routinely designed without the aid of quantitative measurement, relying instead on the experience and skill of clinicians. Sockets remain the most common cause for complaint regarding the suitability of a prosthesis, and poor pressure distribution is implicated in many forms of unacceptable care outcomes. Monitoring pressure distribution has been effectively restricted to laboratory settings, and only limited work has examined conditions other than flat walking. In this work, a transtibial amputee completed static and dynamic tasks on flat ground, on slopes and with changes to prosthetic materials and alignment. This was achieved using a set of wireless measurement nodes and custom LabView and MATLAB code, using external strain measurements and a neural network to understand the internal pressure distribution. Future work will focus on modifying the software to be more user-friendly for a clinical operator, and in simplifying the required hardware. Although the system in its current form facilitated the desired measurements effectively, it required engineering support to function accurately. Improving the reliability and stability of the system will be necessary before routine use is possible

Friction analysis and modelling of a novel stepped rotary flow control valve

© 15th International Conference on Condition Monitoring and Machinery Failure Prevention Technologies, CM 2018/MFPT 2018. All rights reserved. High flow rate control is very important for different applications ranging from constructional, industrial, military and aerospace. Generally, hydraulic control relies on different types of valves. For example, poppet and spool valves have been implemented in Independent Metering (IM) system which is usually installed in mobile hydraulic machines such as excavators. Recently, a novel rotary flow control orifice has been developed to design a control valve for high flow rate applications, and a stepper motor was selected as the main actuator for this orifice to grant more accuracy and controllability. The coupling between these two main components requires analysis of the internal dynamical interactions and their effect on the performance. Friction torque is an important parameter to be considered in this design. The paper includes analysis and modelling of the friction torque in the orifice which affects the coupling, also it contains a model validation and evaluation resulted from friction practical measurements