Design of compliant mechanisms using continuum topology optimization: A review

Kinematic analysis of mechanisms kinematic synthesis of mechanisms simple mechanisms and coupler curves cams spur gears helical, spiral, worm and bevel gears gear trains hydrodynamic lubrication static force analysis inertia force analysis combined static and inertia force analysis turning moment diagram and flywheel balancing of rotating components balancing of reciprocating components gear forces.

Mechanism and machine theory

The maintenance works (e.g. inspection, repair) of aero-engines while still attached on the airframes requires a desirable approach since this can significantly shorten both the time and cost of such interventions as the aerospace industry commonly operates based on the generic concept "power by the hour". However, navigating and performing a multi-axis movement of an end-effector in a very constrained environment such as gas turbine engines is a challenging task. This paper reports on the development of a highly flexible slender (i.e. low diameter-to-length ratios) continuum robot of 25 degrees of freedom capable to uncoil from a drum to provide the feeding motion needed to navigate into crammed environments and then perform, with its last 6 DoF, complex trajectories with a camera equipped machining end-effector for allowing in-situ interventions at a low-pressure compressor of a gas turbine engine. This continuum robot is a compact system and presents a set of innovative mechatronics solutions such as: (i) twin commanding cables to minimise the number of actuators; (ii) twin compliant joints to enable large bending angles (ź90°) arranged on a tapered structure (start from 40mm to 13mm at its end); (iii) feeding motion provided by a rotating drum for coiling/uncoiling the continuum robot; (iv) machining end-effector equipped with vision system. To be able to achieve the in-situ maintenance tasks, a set of innovative control algorithms to enable the navigation and end-effector path generation have been developed and implemented. Finally, the continuum robot has been tested both for navigation and movement of the end-effector against a specified target within a gas turbine engine mock-up proving that: (i) max. deviations in navigation from the desired path (1000mm length with bends between 45° and 90°) are ź10mm; (ii) max. errors in positioning the end-effector against a target situated at the end of navigation path is 1mm. Thus, this paper presents a compact continuum robot that could be considered as a step forward in providing aero-engine manufacturers with a solution to perform complex tasks in an invasive manner. A novel slender continuum robot is introduced for in-situ repair/inspection of jet engines.A new kinematic model is introduced for the new tapered design.Modes of control for the continuum robot were developed, including tip-following, feeding-in/out, Machining commands.Navigation and inspection/machining tests in engine model were introduced.

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Development of a slender continuum robotic system for on-wing inspection/repair of gas turbine engines

A cable-driven hyper-redundant manipulator has superior dexterity for confined space applications. However, the modeling and control considering the cables are very complex. In this paper, we established the kinematics and dynamics models and proposed a dynamics control strategy. The multilevel mapping between the motors, cables, joints, and end-effector was first analyzed. The corresponding kinematics equations were derived and solved by combining analytical and numerical methods. Especially, the cable coupling relationship was established and a decoupling method was addressed to compensate the coupled motion between cables. Furthermore, we derived the dynamics equations including the cable forces and the joint variables. Considering practical control requirements, the cables’ forces were distributed by simplifying the dynamics equations and obtaining the minimal solutions. Then, we presented a dynamics control strategy, which uses the forward and inverse kinematics of multilevel mapping for motion resolution and compensation, and computes the feedforward torques for the motors using recursive dynamics and “cable force–motor torque” relationship. Finally, a prototype and a truss inspection experiment system were developed to verify the corresponding models and methods. Experiment results show that the derived kinematic and the dynamic equations, and the proposed dynamic control strategy are effective.

Kinematics, Dynamics, and Control of a Cable-Driven Hyper-Redundant Manipulator

Cable-driven parallel robots (CDPRs) are categorized as a type of parallel manipulators. In CDPRs, flexible cables are used to take the place of rigid links. The particular property of cables provides CDPRs several advantages, including larger workspaces, higher payload-to-weight ratio and lower manufacturing costs rather than rigid-link robots. In this paper, the history of the development of CDPRs is introduced and several successful latest application cases of CDPRs are presented. The theory development of CDPRs is introduced focusing on design, performance analysis and control theory. Research on CDPRs gains wide attention and is highly motivated by the modern engineering demand for large load capacity and workspace. A number of exciting advances in CDPRs are summarized in this paper since it is proposed in the 1980s, which points to a fruitful future both in theory and application. In order to meet the increasing requirements of robot in different areas, future steps foresee more in-depth research and extension applications of CDPRs including intelligent control, composite materials, integrated and reconfigurable design.

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A Review on Cable-driven Parallel Robots

Design and analysis of a family of snake arm robots connected by compliant joints

Background A twisting problem is identified from the central located flexible backbone snake arm robot. Regarding this problem, a design solution is required to mechanically minimise this twisting angle along the backbone. Further, the error caused by the kinematic assumption of previous works is identified as well, which requires a kinematic solution to minimise. Method of approach The scope of this paper is to introduce, describe and test a novel design of snake arm robot which has a twin-pivot compliant joint construction that minimizes the twisting around its axis. A kinematics model is introduced which can be applied to a wide range of twin-pivot construction with two pairs of cables per section design. And according to this model, the approach for minimising the kinematic error is developed. Furthermore, based on the geometry and material property of compliant joint, the work volumes for single/three-section snake arm robot are presented respectively. Results The kinematic analysis has been verified by a three-section prototype of snake arm and adequate accuracy and repeatability tests carried out. And in the test, the system generates relatively small twisting angles when a range of end loads is applied at the end of the arm. Conclusions Utilising the concept presented in this paper, it is possible to develop a snake arm robot which can minimise the twisting angle and be accurately controlled.

A Novel Continuum Robot Using Twin-Pivot Compliant Joints: Design, Modeling, and Validation

In-situ aeroengine maintenance works are highly beneficial as it can significantly reduce the current maintenance cycle which is extensive and costly due to the disassembly requirement of engines from aircraft. However, navigating in/out via inspection ports and performing multi-axis movements with end-effectors in constrained environments (e.g. combustion chamber) is fairly challenging. A novel extra-slender (diameter-to-length ratio

Xin Dong

Papers

Development of a slender continuum robotic system for on-wing inspection/repair of gas turbine engines

Design and analysis of a family of snake arm robots connected by compliant joints

A Novel Continuum Robot Using Twin-Pivot Compliant Joints: Design, Modeling, and Validation

Design, Modelling and Validation of a Novel Extra Slender Continuum Robot for In-situ Inspection and Repair in Aeroengine

In-situ repair/maintenance with a continuum robotic machine tool in confined space