Challenges of extreme load hexapod design and modularization for large ground-based telescopes

Radiotherapy (RT) enables a selective destruction of tumor cells, although the treatment area is limited to the irradiated volume. Any RT technique comes along with multiple sources of error, which can lead to a deviation of the dose that is applied to the patient. Phantoms—structures that replicate a human and include measurement technology to assess the applied dosage—are used to make such errors observable. Past RT-technologies assumed static tumors. Correspondingly, most existing phantoms comprise only static components. Nowadays, RT is at a transition stage toward techniques which explicitly account for physiological motion. These techniques require phantoms generating such motion. Consequentially, a demand for new kinds of manipulators, which operate with a RT-phantom, has come up and will further increase in the future. Key demands of such manipulators are among others, the generation of full rigid body motion, high acceleration, high stiffness, compactness, little weight, and easy portability. Another indispensable feature is the spatial separation of mechatronic components and phantom structure to ensure human equivalency of the latter. In this work, a new kind of parallel kinematic manipulator (PKM), which is tailored to the requirements of RT-phantom technology, is presented. The PKM consists of low cost standardized mechanical components and sets the target structures, which are located inside a human-equivalent area, into translational and rotational motion in three degrees-of-freedom (DOFs). Only a part of the end-effector is located within the human-equivalent area. All the remaining parts of the PKM are located outside that area. Two versions of the manipulator are presented in detail: their kinematics are derived and their kinetostatic properties are compared. This includes a workspace analysis and the analysis of the transmission behavior in general, meaning the influence of the most important design parameters on the performance. It can be shown that practical differences of both kinematics are negligible, while the modified version provides significant mechanical advantages. In conclusion, a first special purpose manipulator for application in the evolving field of RT-phantom technology is presented. The PKM, which employs a novel kinematic structure, provides higher suitability for its purpose than any other robotic system employed so far for the same purpose.

Dynamics simulation of parallel kinematic manipulators (PKM) and non-linear control methods require a precisely identified dynamics model and explicit generalized mass matrix. Standard methods, which identify so-called dynamic base-parameters, are not sufficient to this end. Algorithms for identifying the complete set of dynamic parameters were proposed for serial manipulators. A dedicated identification method for PKM does not exist, however. Such a method is introduced here for the large class of Delta-like PKM exploiting the parallel structure and making use of model simplifications specific to this class. The proposed method guarantees physical consistency of the identified parameters, and in particular a positive definite generalized mass matrix. The method is applied to a simulated model with exactly known parameters, which allows for verification of the obtained dynamic parameters. The results show that the generalized mass matrix, the acceleration, and the Coriolis, gravitation and friction terms in the equations of motion (EOM) are well approximated. The second example is a real 4-DOF industrial Delta robot ABB IRB 360-6/1600. For this robot, a physically consistent set of inertia and friction parameters is identified from measurements. The method allows prescribing estimated parameters, but does not rely on such data, e.g. from manufacturer or CAD.

This paper presents optimizations of a parallel kinematic manipulator used for a machine tool in terms of its workspace and stiffness. The system stiffness and workspace of the parallel manipulator are conducted in the paper. In order to locate the maximum system stiffness and workspace, single and multi-objective optimizations are performed in terms of rotation angles in x and y axes and translation displacement in z axis with genetic algorithms. By optimizing the design variables including geometric dimensions of the manipulator, the system stiffness and workspace of the proposed parallel kinematic manipulator has been greatly improved.

Reconfiguration of a parallel kinematic manipulator with 2T2R motions for avoiding singularities through minimizing actuator forces

This article examines Genetic Algorithms to solve the forward kinematics problem applied to planar parallel manipulators. Most of these manipulators can be modeled by the tripod 3-RPR. The conversion of an equation system solving problem into an optimization one is investigated. Parallel manipulator kinematics are formulated using the explicit Inverse Kinematics Model (IKM). From the displacement based equation systems, the objective function is formulated specifically for the FKP using one squared error performance criteria. The proposed approach implements an elitist selection process where a new mutation operator for Real-Coded GA is analyzed. Experiments on a typical manipulator example shows the fast convergence of the proposed method.

This paper presents the design and analysis of a novel five degrees-of- freedom (DOF) parallel kinematic manipulator (PKM) for part-handling, sorting, general positioning, and robotic machining applications. The 2- R(Pa-IQ)RR, R(Pa-IQ)R manipulator has two rotational DOFs, one parasitic rotation, and three translational DOFs. In comparison with other 5- and 6- DOF PKMs, this PKM possesses three pairs of coplanar legs that contain nested kinematic chains, and it makes exclusive use of revolute and prismatic joints. The inverse kinematic analysis is a novel extension of the geometric (vector) method with the analysis of inner and outer kinematic chains. The forward kinematic analysis was solved using the Newton Raphson (NR) method. The results of the forward and inverse kinematic analyses were validated with SolidWorks ® and MATLAB ® simulations.

This paper presents the geometric, discretization and Monte Carlo method to generate the workspace for Parallel Kinematic Manipulators (PKMs). The geometric method does not require the solution to the inverse kinematics as opposed to the Monte Carlo and discretization methods. Each method possesses advantages and drawbacks concerning accuracy, time and ease of implementation. A case study concerning constant orientation workspace of a planar 3RRR PKM showed that the most efficient and accurate method was the geometric method but it also possessed the most limitations. The discretization and Monte Carlo methods produced the workspace with an accuracy of 92.49% and 95.67% respectively.

The motivation for this chapter is twofold. On the one hand, the determination of the angular velocity and angular acceleration of a rigid body from point-velocity measurements is a fundamental problem in kinematics. On the other hand, the solution of this problem is becoming increasingly relevant in the kinematics of parallel manipulators, to be studied in Chap. 10. Moreover, the estimation of the attitude of a rigid body from knowledge of the Cartesian coordinates of some of its points is sometimes accomplished by time-integration of the velocity data. Likewise, the use of accelerometers in the area of motion control readily leads to estimates of the acceleration of a sample of points of a rigid body, which can be used to estimate the angular acceleration of the body, and hence, to better control its motion.

Laser welding application for car body manufacturing has many advantages in the stiffness and the lightness of vehicle, the productivity of assembly line, and the degree of freedom in design. This presentation will express the innovation of car body manufacturing including parameter optimization, process modeling, and system integration. In this application the investment for systems was cut down dramatically by real time switching over the laser path between two welding stations. Points of technical discussion are as follows: optimization of parameters such as laser power, robot speed and trajectory, compact and useful design of jig & fixture to assure welding quality for 3 sheet-layer zinc-coated steel, system integration between 4kW Nd:YAG laser device and the other systems, on-line real time welding quality monitoring system, perfect safety standards for high power laser, minimization of consumption costs such as arc lamp, protective glass for optic, etc.Laser welding has found a place on Hyundai’s production plant in conjunction with the startup of mass production of new sports car, and this production system is the result of a collaboration of its engineers. Outer side sheets are joined to inner side sheets by 122 stitch welds totally. And the length is about 2.4meter.Laser welding application for car body manufacturing has many advantages in the stiffness and the lightness of vehicle, the productivity of assembly line, and the degree of freedom in design. This presentation will express the innovation of car body manufacturing including parameter optimization, process modeling, and system integration. In this application the investment for systems was cut down dramatically by real time switching over the laser path between two welding stations. Points of technical discussion are as follows: optimization of parameters such as laser power, robot speed and trajectory, compact and useful design of jig & fixture to assure welding quality for 3 sheet-layer zinc-coated steel, system integration between 4kW Nd:YAG laser device and the other systems, on-line real time welding quality monitoring system, perfect safety standards for high power laser, minimization of consumption cos...

This paper examines the symbolic kinematic modeling of a general 6-P-U-S (prismatic-universal-spherical) parallel kinematic manipulator (PKM). The base location of actuators has been previously shown to lead to: (i) reduction of the (motor) weight carried by the legs; (ii) elimination of the actuation transmission requirement (through intermediary joints as in the case of the Stewart-Gough platform); and (iii) most-importantly absorption of reaction-forces by the ground. We focus on using the symbolic equations to derive the conditions for type I and II singularities of this class of parallel manipulators. Based on these conditions, this system of equations is specialized to a specific configuration of the platform that has superior structural design and comparatively minimal singularities within its workspace. A series of studies were conducted to investigate the quality of workspace as well as estimate the actuation requirements for a unit payload carried over their workspace using the symbolic Jacobian model for this specialized configuration.

Very large telescopes will be needed for the future of space science, space laser-com, and other interstellar or interplanetary applications. However, as telescopes' diameters increase, their weight and cost increase dramatically. An approximation for ground-based observatories is that their cost increases to the power of 2.7 of its diameter [SAO, Special Report #385 (1979), p. 9]. Large space-based telescopes become limited by the rocket size and power. Multiple telescopes are also needed for very long baseline interferometry (VLBI), which further increases cost. A solution to overcome these issues is the use of inflatable telescopes. A thin mirror material clearly has much lower mass; however, controlling its surface error or wavefront can be a challenge. Intensity interferometry is an imaging method that has a much looser sensitivity to wavefront error (WFE), and thus is an ideal match for very large inflatable telescopes. A spherical inflatable mirror is the most practical; however, it suffers from spherical aberration. This paper presents new optical designs and simulations for intensity interferometry in support of large inflatable spherical telescopes. The optical system design includes a novel five-mirror off-axis, free-form, spherical aberration corrector. The system design shown is a 10 m diameter f/1 spherical primary mirror with 1.2 arcmin (0.02°) field of view (FOV). MATLAB simulations of intensity interferometry combine signal with noise and WFE. Visibility-based VLBI image simulations are shown based on various telescope arrays. Simulations show that with a 1 GHz detector, a 1 cm RMS WFE is tolerable. So the challenge of the optical design is then more about gathering and concentrating the light down to a reasonable size detector. Further simulations of signal combined with noise indicate that the signal rate must be about 100 times higher than the noise rate for an adequate intensity interferometry measurement. Visibility-based image simulations reveal that many telescopes (5-20 per axis) are needed in a 2D array out to the first visibility minimum to adequately resolve unknown features of a distant object.

Next Generation Telescope (NGT) No sooner had the 200 inch (5.0 m) Palomar Telescope been completed in 1948, than some astronomers started to consider whether it would be possible to build an even larger instrument. One of the most determined was Aden Meinel who, in the early 1950s, produced the outline design of an optical reflector of about 500 inch (~12.5 m) diameter. In this the primary mirror was not to be made of one piece of glass, but of several hundred smaller mirrors. But he received little support for his ideas, particularly when the question of funding was raised. It was also not clear at that time whether it was feasible to build such a machine. Twenty years later, the design of a very large telescope was readdressed by Leo Goldberg the director of KPNO. Telescope design had moved on since Meinel's work, and by 1974 the main building phase of telescopes at KPNO had been completed, leaving a number of talented engineers with relatively little to do.(1) So Goldberg asked these engineers to examine possible designs of an optical telescope with a collecting area equivalent to a 25 m (~1000 inch) diameter mirror. KPNO's first design concept for this very large telescope, called PALANTIR or rotating shoe telescope, consisted of a 75 m long by 25 m wide segment of the primary mirror which could be rotated in azimuth. This primary was composed of hundreds of polished aluminium segments. The secondary mirror assembly, which included a 3 m secondary mirror, was mounted on the elevation axle, which was parallel to the shortest side of the primary. By moving about this axle, the secondary could view the sky from the zenith down to about 30° above the horizontal. The main advantage of this design, over a conventional one, was that the primary mirror could be rigidly held and did not suffer from variable gravitational forces as the telescope looked at various parts of the sky. Unfortunately, the proposed resolution of PALANTIR was rather poor, its secondary mirror could only see a fraction of its primary at any one time, and its capital cost of about $160 million was completely out of the question at that time.

Ferrofluids have been used in development of active dampers due to their controllable magnetic and mechanical properties. However, design and control of these actuators are far from exhausted. The fluid nature of volumetric energy converters using ferrofluids provides additional degrees of freedom in design and operation, yet numerical analysis of such devices includes inherent multi-physics computations that can be complex. Control of a three-dimensional motion can result in substantial reduction in cost and design of electro mechanic actuators. In this paper, a ferrofluid valve is proposed. Ferrofluid is used as an actuator to open and close water flow through a channel. By changing the distribution of ferrofluid, the cross-section area of the open passage in the flow channel is controlled. To reduce the deterioration of ferrofluid in the presence of water, the ferrofluid and the controlled flow are separated by a nitrile rubber film. By varying the strength of magnetic field, the ferrofluid valve can be fully closed and opened. A multi-physics numerical simulation of the valve has been carried out to determine the opening and closing time of the valve, maximum cut off flow rate, pressure drop and resolution. The valve closing time is simulated to be 125ms in a 4 inches by 2 inches prototype. This prototype has been built to validate the simulation results.

摘要： 面对日益增长的射电望远镜口径和工作频率，如何满足复杂环境载荷下的望远镜性能，是大型全可动射电望远镜结构设计的难点。首先对射电望远镜的结构设计进行了概述，接着，回顾了国内外典型大型全可动射电望远镜的结构设计特点，展示了等刚度思想下保型设计，以及机电一体化设计所取得的成功，最后，针对下一代大型亚毫米波射电望远镜所面临的超高精度挑战，结合研究现状，概述了保型拓扑优化设计、多组件耦合设计、光机电一体化设计、可靠性设计、机/结构创新设计以及精准建模等方向的研究趋势。

The Southern African Large Telescope (SALT) is a 10-m class optical/IR segmented mirror telescope based on the groundbreaking, low cost, Hobby-Eberly Telescope (HET) design. Approval to construct and operate SALT, which will be the largest single optical telescope in the Southern Hemisphere, was given by the South African Government in November 1999, after sufficient guarantees of matching funding from international partners were secured. Facility construction started in January 2001, and SALT is due to start operations by December 2004. SALT will enable a quantum leap in astronomical research capability in Southern Africa, and indeed the continent, where currently the largest telescope is a modest 1.9-m, dating to the 1940s. A substantial amount of design work for SALT has been completed, sourced from multiple suppliers, with ~60% South African content. South African industry is well equipped to handle the construction of most of the telescope, the exceptions being the glass ceramic mirror blanks (from LZOS in Russia), the polishing and ion figuring of these (Eastman Kodak in the USA), and fabrication of the four-element spherical aberration corrector (SAGEM in France). This paper will present (1) the scientific requirements, (2) the specified performance of SALT, (3) the basic design, with emphasis on the innovative modifications to the HET design that enable significantly improved performance, (4) the progress and status of the project, currently in its construction phase, (5) the first generation instrument suite, (6) the management and organisation of the project and (7) the international partnership in SALT.