Serial Structures Research Articles

Error Analysis of a 3-DOF Parallel Mechanism for Milling Applications

Parallel mechanisms have been investigated during the last two decades, due to the fact that they present some advantages in a comparison with serial structures. This work deals with the error analysis of a 3-dof asymmetric parallel mechanism, purposely conceived for milling applications. In a comparison with the previous proposed concepts, this type of kinematic structure demonstrates a promising behavior. Topologically, the architecture is simpler and lighter than Tricept because it has no central passive limb. In addition, only the constraining active limb needs to satisfy the parallelism and orthogonality conditions. Furthermore, one degree of freedom, associated to the third actuator, is decoupled from the other two. Important issues, related to this type of kinematic structure, such as the mappings of the tool positioning error throughout the available workspace, due to the actuators imprecisions and manufacturing tolerances, are discussed in detail.

Solving the forward kinematics problem in parallel robots using Support Vector Regression

The Stewart platform, a representative of the class of parallel manipulators, has been successfully used in a wide variety of fields and industries, from medicine to automotive. Parallel robots have key benefits over serial structures regarding stability and positioning capability. At the same time, they present challenges and open problems which need to be addressed in order to take full advantage of their utility. In this paper, we propose a new approach for solving one of these key aspects: the solution to the forward kinematics in real-time, an under-defined problem with a high-degree nonlinear formulation, using a popular machine learning method for classification and regression, the Support Vector Machines. Instead of solving a numerical problem, the proposed method involves applying Support Vector Regression to model the behavior of a platform in a given region or partition of the pose space. It consists of two phases, an off-line preprocessing step and a fast on-line evaluation phase. The experiments made have yielded a good approximation to the analytical solution, and have shown its suitability for real-time application.

Self-Similarity and Compositional Strategies in the Music of Milton Babbitt

The unfolding of a compact algebraic group into a larger structure which exhibits an isomorphic relationship with the smaller group is the essence of "self-similarity." Through the use of transformational networks which take advantage of the group properties of the forty-eight canonical operators and through the examination of the hexachordally combinatorial properties of Babbitt's row forms, this paper examines the manner in which Babbitt selects and combines rows to produce maximal diversity on the surface while optimizing internal coherence at the deeper structural levels. This study focuses on three works that cover straightforward serial structures, simple array structures and superarray structures respectively — Babbitt's three main compositional strategies.

Kinematic, workspace and singularity analysis of a new parallel robot used in minimally invasive surgery

In the last ten years, due to development in robotic assisted surgery, the minimally invasive surgery has greatly changed. Until now, the vast majority of robots used in surgery, have serial structures. Due to the orientation parallel module, the structure is able to reduce the pressure exerted on the entrance point in the patient’s abdominal wall. The parallel robot can also handle both a laparoscope as well an active instrument for different surgical procedures. The advantage of this parallel structure is that the geometric model has been obtained through an analytical approach. The kinematic modelling of a new parallel architecture, the inverse and direct geometric model and the inverse and direct kinematic models for velocities and accelerations are being determined. The paper will demonstrate that with this parallel structure, one can obtain the necessary workspace required for a minimally invasive operation. The robot workspace was generated using the inverse geometric model. An indepth study of different types of singularity is performed, allowing the development of safe control algorithms of the experimental model. Some kinematic simulation results and the experimental model of the robot are presented in the paper.

Methods of Identifying the Workspace of Modular Serial Kinematic Structures

The article analyzes the possibility of automatized generation of workspace resulting from random movement of the end module of a serial kinematic chain by means of numerical mathematical analysis. The methodology is applicable to physical structures with various degrees of freedom of movement. The newly proposed concept of a universal rotation modulus with an optimized 90° interface curvature provides the possibility to construct such physical structures, and the referred methodology identifies their main feature - the scope and shape of workspace.

Program Suite for Conceptual Designing of Parallel Mechanism-Based Robots and Machine Tools

In the development of robots and machine tools, in addition to conventional and serial structures, parallel mechanism-based kinematic structures have been used over a longer period of time. Aside from a number of advantages, the irregular shape and relatively small dimensions of the workspace formed by parallel mechanisms rank among the major weaknesses of their application. Accordingly, this fact has to be taken into consideration in the process of designing parallel mechanism-based robots or machine tools. This paper describes the categorization of criteria for the conceptual design of parallel mechanism-based robots or machine tools, resulting from workspace analysis as well as the procedure of their defining. Furthermore, it also presents the designing methodology that was implemented into the program for the creation of a robot or machine tool space model and the optimization of the resulting solution. For verification of the criteria and the programme suite, three common (conceptually different) mechanisms with a similar mechanical structure and kinematic characteristics were used.

Development of a milling parallel robot for educational purposes

Parallel mechanisms have been investigated during the last two decades, due to the fact that they present some advantages in a comparison with serial structures, namely, the ability to perform fast motions, modular construction, lightness and high load capacity. Regarding the utilisation of parallel mechanisms on milling applications, a great number of architectures have been proposed by industry and academia. From the academia viewpoint, we believe that mechanical engineering students should have the contact with these equipments in their course labs. A parallel robot could be part of an experimental test-bed to analyse its behaviour under milling operations. However, due to the fact that available commercial parallel robots for milling are expensive, not affordable to several academic institutions, we decided to design and build one. Basically, the machine had to satisfy the following requirements: only three axis for milling, modular construction and the utilisation of low-cost standard components. In this work, we present the development of a milling parallel robot for educational purposes. The paper sections deal with the conceptual design, the chosen structural synthesis procedure, the kinematic analysis, workspace, static error evaluation and the characteristics of the built prototypes.

Islet1 regulates establishment of the posterior hindlimb field upstream of the Hand2-Shh morphoregulatory gene network in mouse embryos

How divergent genetic systems regulate a common pathway during the development of two serial structures, forelimbs and hindlimbs, is not well understood. Specifically, HAND2 has been shown to regulate Shh directly to initiate its expression in the posterior margin of the limb mesenchyme. Although the Hand2-Shh morphoregulatory system operates in both the forelimb and hindlimb bud, a recent analysis suggested that its upstream regulation is different in the forelimb and hindlimb bud. A combination of all four Hox9 genes is required for Hand2 expression in the forelimb-forming region; however, it remains elusive what genetic system regulates the Hand2-Shh pathway in the hindlimb-forming region. By conditional inactivation of Islet1 in the hindlimb-forming region using the Hoxb6Cre transgene, we show that Islet1 is required for establishing the posterior hindlimb field, but not the forelimb field, upstream of the Hand2-Shh pathway. Inactivation of Islet1 caused the loss of posterior structures in the distal and proximal regions, specifically in the hindlimb. We found that Hand2 expression was downregulated in the hindlimb field and that Shh expression was severely impaired in the hindlimb bud. In the Hoxb6Cre; Islet1 mutant pelvis, the proximal element that is formed in a Shh-independent manner, displayed complementary defects in comparison with Pitx1(-/-) hindlimbs. This suggests that Islet1 and Pitx1 function in parallel during girdle development in hindlimbs, which is in contrast with the known requirement for Tbx5 in girdle development in forelimbs. Our studies have identified a role for Islet1 in hindlimb-specific development and have revealed Islet1 functions in two distinct processes: regulation upstream of the Hand2-Shh pathway and contributions to girdle development.

An efficient metaheuristic for integrated scheduling and staffing IT projects based on a generalized minimum cost flow network

AbstractScheduling IT projects and assigning the project work to human resources are an important and common tasks in almost any IT service company. It is particularly complex because human resources usually have multiple skills. Up to now only little work has considered IT‐specific properties of the project structure and human resources. In this article, we present an optimization model that simultaneously schedules the activities of multiple IT projects with serial network structures and assigns the project work to multiskilled internal and external human resources with different efficiencies. The goal is to minimize costs. We introduce a metaheuristic that decomposes the problem into a binary scheduling problem and a continuous staffing problem where the latter is solved efficiently by exploiting its underlying network structure. For comparison, we solve the mixed–binary linear program with a state–of–the–art commercial solver. The impacts of problem parameters on computation time and solution gaps between the metaheuristic and the solver are assessed in an experimental study. Our results show that the metaheuristic provides very favorable results in considerable less time than the solver for midsize problems. For larger problems, it shows a similar performance while the solver fails to return feasible solutions. © 2012 Wiley Periodicals, Inc. Naval Research Logistics 59: 111–127, 2012

Kinematic modelling of a 5-DOF hybrid parallel robot for laparoscopic surgery

SUMMARYRobotic-assisted surgery is a continuously developing field because robots have demonstrated clear benefits in operating rooms. Until now, vast majority of robots used in surgery had serial structures. This paper presents the kinematic modelling of a 5-degree of freedom hybrid parallel architecture in two slightly different variants. The kinematics of this structure is determined, and following the analysis of singularities, the best variant is chosen. The robot workspace is computed and finally the experimental model and some simulation results are presented.

Dosimetric consequences of rotational errors in radiation therapy of pediatric brain tumor patients

PurposeTo quantify the rotational offsets and estimate the dose effect of rotation on the target volume and normal tissues in children with brain tumor. MethodsTwenty-one pediatric patients with brain tumors were included in this study. Cone-beam CT was performed before each treatment and at the end of every other treatment. Translational offsets were corrected before the treatment. An offline analysis was performed to quantify rotational errors. The treatment plans were altered and recalculated to simulate a rotation of 2° and 4°, and the dose changes were quantified. Results1016 CBCT datasets were analyzed for this report. The mean of the rotations were not meaningfully different from zero. 18.1% of the fractions had rotations with a magnitude ⩾2°, 5.0% had rotations ⩾3° and 0.9% had rotations ⩾4°. For the 2° rotational simulation, the gEUD values of the PTV and critical structures changed by less than 2%. For the 4° simulation, parallel type normal structures had minor changes (<2%), but serial type normal structures and the PTV had changes of 10% and 5%, respectively. ConclusionsThe majority of rotational errors observed were less than 1°. A rotational error of 2° produced negligible changes in the gEUD to critical structures or target volumes. Rotational errors ⩾4° produced undesirable results, therefore, at a minimum, errors >2° should be corrected.

SU-E-T-638: Optimization of Prescription Isodose Selection for Stereotactic Radiation Therapy: Conventional Linac vs. Cyberknife

Purpose: To determine the optimal prescription isodose line that minimizes normal tissue dose for stereotactic irradiation of intracranial targets comparing conventional linear accelerator and robotic (Cyberknife) delivery. Material and Methods: An anthropomorphic head phantom with a centrally located target was scanned using a 16 slice large bore CT simulator. Two concentric 5mm spherical shells of normal tissue, the first from the target surface to 5 mm radically, and the other from 5 mm to 10mm, were identified/contoured around the target. For linac planning, 9 co-planar, non-opposing 3D conformal beams were designed for conformal dose delivery. By manipulating the block margin, varying prescription isodose lines were used to cover exactly 95% of tumor. After linac planning, the same CT images and contours were sent to the Cyberknife for treatment planning. Multiple plans were generated with different prescription isodose lines covering exactly 95% of the target. gEUD (generalized effective uniform dose) was used to evaluate normal tissue irradiation within the shells using different parameters for parallel and serial tissues. Results: For linac plans, the results show that the optimal prescription isodose line yielding maximum normal tissue sparing is located between 50%∼60% of the maximum dose when the organ displays parallel behavior. For serially functioning tissues, the optimal prescription isodose line increases to approximately 80%. The gEUD of normal tissue (predisposing to toxicity) increases greatly when prescription isodose lines lower than 50% or higher than 80% are used. For Cyberknife plans, the optimal prescription isodose line lies near 50% for tissue for both either parallel or serial structures. These results are consistent for different tumor sizes. Conclusion: Both conventional linac and robotic delivery provide conformal tumor coverage with excellent normal tissue sparing. To achieve optimal normal tissue sparing, a lower isodose line should be prescribed for Cyberkinfe® than for a conventional linac.

SU‐E‐T‐656: Are We Ready for Biological Planning? A Dosimetric Study

Purpose: To evaluate the feasibility of using a commercially available IMRT optimization and plan evaluation tool based on radio‐biological models. Methods: A retrospective dose optimization study was performed for 5 lung cases treated using IMRT to evaluate the biological modules available in Pinnacle system. A hybrid objective function consisting of physical dose constraints, for PTVs, and EUD constraints, for organs at risk, was used for optimization. The OARˈs were: spinal cord, esophagus, cardiac ventricle, and both lungs. The “a” value, used in EUD definition, was a variable to allow the optimizer to match the physical dose optimization solution. A biological optimized plan, (BOP) was deemed acceptable if matches or exceeds the quality of a physical dose optimized plan (PDOP). TCP, NTCP, or P+ values were not included in the optimization however; they were used during plan evaluation. The TCP and P+ are based on Poisson model with linear quadratic cell survival for each individual voxel. NTCP module is based on LKB model. For model parameters we choose a combination of published data and our clinical standards. Results: For serial structures the Max EUD constraint was able to bring the dose to levels obtained during physical dose optimization, however it was unable to easily control the magnitude of maximum dose. Values for parameter “a” are 15–20 for serial structures and a=1.0 for parallel structures. Global values for TCP, NTCP, P+ were 56.8% versus 53.4%, 7.4% versus 6.4%, and 49.4% versus 46.9% for BOP and PDOP, respectively. Conclusions: We have performed a retrospective treatment planning study to investigate the feasibility of using biological models for optimization purposes. Although, results between PDOP and BOP plans are comparable it remains to be seen if the clinicians will be willing to accept these concepts in clinical practice without the existence of clinical trials.

Mythical Returns: Televising Thérèse Raquin

Television is not an obvious home for Zola's novels. Its spatially-restrained aesthetic crops Zola's sweeping vistas and the repetitions inherent in its serial structures have led some to query its artistic endeavour. However, France 3's La Liberté de Marie (2002), an adaptation of Zola's Thérèse Raquin (1867), written and directed by Caroline Huppert, counters both assumptions. It underlines the compatibility between Thérèse Raquin and the medium of television in spatial terms. The adaptation does not return to the detail of Zola's text, but, through its exploration of myth, it echoes Zola's belief that originality lies in the innovative re-telling of an age-old story in a new context.

Dose de tolérance à l’irradiation des tissus sains : les nerfs périphériques

Plexopathies and peripheral neuropathies appear progressively and with several years delay after radiotherapy. These lesions are observed principally after three clinical situations: supraclavicular and axillar irradiations for breast cancer, pelvic irradiations for various pathologies and limb irradiations for soft tissue sarcomas. Peripheral nerves and plexus (brachial and lumbosacral) are described as serial structures and are supposed to receive less than a given maximum dose linked to the occurrence of late injury. Literature data, mostly ancient, define the maximum tolerable dose to a threshold of 60 Gy and highlight also a great influence of fractionation and high fraction doses. For peripheral nerves, most frequent late effects are pain with significant differences of occurrence between 50 and 60 Gy. At last, associated pathologies (diabetes, vascular pathology, neuropathy…) and associated treatments have probably to be taken into account as additional factors, which may increase the risk of these late radiation complications.

SU‐GG‐T‐566: VMAT Optimization on MVCT Dose and the Affects on Prostate IMRT Acceptance Criteria

Purpose: Daily image guidance techniques may contribute significant dose to the patient, particularly in the case of megavoltage conebeam CT. Methods to account for this dose include (1) not altering the prescription, (2) subtracting the MVCT dose from the prescription, and (3) including the daily MVCT dose in the optimization process. This work evaluates the aforementioned methods with respect to the plan acceptance criteria for prostate IMRT at Fox Chase Cancer Center. Method and Materials: MVCT dose was measured in phantom for a Siemens' Artiste linear accelerator. The 15MU mode utilized was for a 27.4 × 27.4cm2 field size, 6MV full rotation beam. The dose measured was scaled using TMR ratios to mimic irradiation in an elliptical phantom with major and minor axis lengths of 40cm and 20cm, respectively and was found to be approximately 9.71cGy. The MVCT beam was simulated on patient geometry within the Nucletron Oncentra MasterPlan system. Dual arc VMAT plans were generated to meet our acceptance criteria with respect to the methods above. Results: Method 1 above results in dose increases in high and low dose rectal cut‐points of 5.7% and 11.7%, respectively. Method 2 results in 1.4% and 7.3% increases while method 3 results in 5.1% and 3.9% increases without changing the input parameters from those used for the dual arc plan. Conclusions: Dose from MVCT on a daily basis can adversely affect plan acceptance criteria. Lower MU protocols can be used but may result in decreased image quality. All plans in this study met our clinical acceptance criteria although those optimized on the MVCT dose demonstrated the lowest increase in lower dose regions. As the significance of adverse effects may be amplified for serial vs. parallel critical structures it may be prudent to optimize on the MVCT dose when generating IMRT plans.

Kinematic Analysis of A 3-DOF Parallel Mechanism for Milling Applications

Parallel mechanisms have been studied during the last two decades, due to the fact that they present some potential advantages in a comparison with serial structures. This work presents the kinematic analysis of a novel 3-dof asymmetric parallel mechanism, purposely conceived for milling applications. In a comparison with the previous proposed concepts, this type of kinematic structure shows some advantages. The architecture is simpler and lighter than Tricept because it has no central passive limb. In addition, only the central active limb needs to satisfy the parallelism and orthogonality conditions. Furthermore, one degree of freedom, associated to the third actuator, is decoupled from the other two. Important issues, related to this type of kinematic structure, such as position and velocity analysis, singularity occurrence prediction and workspace evaluation, are discussed in detail.

The Types of Argument Structure Used by Hillary Clinton in the CNN Democratic Presidential Debate

This qualitative research was conducted to examine the types of argument structure by Hillary Clinton in part one of the CNN Democratic Presidential Debate since Hillary, who had a great deal of experiences in political parties, was supposed to be able to construct convincing arguments that had good argument structures. The theories used to analyze were Bierman and Assali’s (1996), King’s (n.d.) and Stanlick’s (2003). The findings showed that there were five types of argument structure used: serial, linked, convergent, divergent, and hybrid argument structures. The linked argument structure was the argument structure used the most frequently in Hillary’s utterances in the debate, while the divergent was the least one. Thus, it could be concluded that Hillary’s speech in the Presidential Debate was quite interesting since she could combine all the five types of argument structure, though the frequency of using them was not the same and it seems that linked argument structure was the most effective strategy for her in arguing about the politic, economy, and social issues.

Causative and facilitative serial verbs in Asian Ibero-romance Creoles – a convergence of substrate and superstrate systems?

This paper surveys the widespread presence of two types of serial verb – the direct causative and the indirect causative – in Portuguese and Spanish lexically-based creole languages of Asia. The discussion addresses the structural nature of these valency increasing constructions, considering the semantic relations involved in their argument sharing, and contemplates the potential roles of substrate and superstrate languages in their development. It is proposed that the geographic distribution of the serial verbs is owed to a convergence of substrate and superstrates. In the case of the Asian Portuguese lexically-based creoles, the convergence would have begun in India. Subsequently, as the Portuguese progressively established their trade network further east, the serial structures received substrate reinforcement in the different settings where creolization and stabilization occurred. Further reinforcement would have occurred by way of population movements between the communities over a longer period.

Development of skeleton elements in juvenile dwarf and small sympatric forms of Salvelinus alpinus complex from Lake Davatchan (Transbaikalia)

The development of skeleton elements was studied in prolarvae, larvae, and fry of two morphologically different forms of the Arctic char Salvelinus alpinus complex—small plankton-eating and dwarf (having a seasonal change of plankton and benthic feeding)—that sympatrically inhabit Lake Davatchan (Transbaikalia). According to genetic data, these forms diverged in this lake from a specialized lacustrine ecotype of char and reached reproductive isolation. Comparative analysis revealed similarity in the shape of anlagen and transitive states of cranial bones. In prolarvae and larvae of the dwarf form, the onset of similar morphological states of skeleton elements occurs at a smaller body length than in fish of the small form. Differences in the development of serial skeleton structures (teeth, gill rakers, fin rays, centra, and scales), heterochronies of timing of appearance and rate of differentiation of skeleton elements were found. It is suggested that these differences resulted from the ecological differentiation of the two forms according to spawning grounds that became local habitats of larvae and fry (sublittoral and hypolimnion). The initial divergence could be caused by the presence in the lake of two (autumn and spring-summer) peaks of numbers of food organisms.