Modeling planar slider-crank mechanisms with clearance joints in RecurDyn

Revolute joints in applications always show clearance between pin and bushing due to manufacturing tolerances, the need of relative motion or progressing wear. Many researchers developed and investigated methodologies to calculate the dynamic behavior of mechanisms with such imperfect joints. Very often they use a simple slider-crank mechanism to test or demonstrate the capability of their approaches. In this paper, a methodology for simulating a slider-crank mechanism with an imperfect revolute joint in RecurDyn, a commercial multibody simulation tool, is presented. Therefore, a thorough investigation of existing contact, damping and friction force models as well as different ways of modeling revolute joints in RecurDyn was conducted. For the investigation of the damping models, a special program for calculating the model parameters for a given coefficient of restitution was developed. Only one damping model was capable of reproducing the experimental results, which were found in literature. Some characteristic results of the slider-crank mechanism are presented in a way that they can be compared to results in other papers. Thereby. a good correlation was achieved, demonstrating the capabilities of the methodology.     

MAS动态协作任务求解模型与算法

针对网格环境的自治性、动态性、分布性和异构性等特征.提出基于多智能体系统(mutil agent system, MAS) 博弈协作的资源动态分配和任务调度模型,建立了能够反映供求关系的网格资源调度动态任务求解算法,证明了资源分配博弈中Nash均衡点的存在性、惟一性和Nash均衡解.该方法能够利用消费者Agent的学习和协商能力,引入消费者的心理行为,使消费者的资源申请和任务调度具有较高的合理性和有效性.实验结果表明,该方法在响应时间的平滑性、吞吐率及任务求解效率方面比传统算法要好,从而使得整个资源供需合理、满足用户QoS要求.     

Modeling the behavior of users who are confronted with security mechanisms

In this paper, we describe a new approach to analyze the trade-off between usability and security frequently found in security-related user interfaces. The approach involves the simulation of potential user interaction behavior by a mixed probabilistic and rule-driven state machine. On the basis of the simulations, user behavior in security-relevant situations can be predicted and user interfaces optimizing intended behavior can be designed. The approach is evaluated in an artificial microworld setting which provides good control over the experimental factors guiding the behavior. A comparison of empirical and simulated behavior in this microworld shows that the approach is already able to accurately predict important aspects of user behavior toward security interfaces, but also identifies future work necessary to better cover all relevant aspects guiding this behavior in a real-world setting.     

Modeling of maximum endurance time for one‐handed carrying tasks

The objective of this study was to establish models to predict maximum endurance time (MET) for one‐handed carrying tasks. A one‐handed carrying experiment, under three loads and two walking speeds, was performed. The participant carried a dumbbell on the side using either dominant or nondominant hand. His or her arm was straight‐down. The MET values were collected. Both power and exponential functions were adopted in establishing simplified MET models considering the relative force (f_MVC) applied. The simplified models were further expanded to full models where body weight and walking speed were also included. It was found that the power models provided better estimates than the exponential models when the f_MVC was lower than approximately 0.17 for both the simplified and full models. Considering the effects of the walking speed, the full models are recommended when the f_MVC is 0.3 or lower.     

Modeling analysis of ant system with multiple tasks and its application to spatially adjacent cell state estimate

The problem of multi-cell tracking plays an important role in studying dynamic cell cycle behaviors. In this paper, a novel ant system with multiple tasks is modeled for jointly estimating the number of cells and individual states in cell image sequences. In our ant system, in addition to pure cooperative mechanism used in traditional ant colony optimization algorithm, we model and investigate another two types of ant working modes, namely, dual competitive mode and interactive mode with cooperation and competition to evaluate the tracking performance on spatially adjacent cells. For adjacent ant colonies, dual competitive mode encourages ant colonies with different tasks to work independently, whereas the interactive mode introduces a trade-off between cooperation and competition. In simulations of real cell image sequences, the multi-tasking ant system integrated with interactive mode yielded better tracking results than systems adopting pure cooperation or dual competition alone, both of which cause tracking failures by under-estimating and over-estimating the number of cells, respectively. Furthermore, the results suggest that our algorithm can automatically and accurately track numerous cells in various scenarios, and is competitive with state-of-the-art multi-cell tracking methods.     

On the advantages of foveal mechanisms for active stereo systems in visual search tasks

In this work we study how information provided by foveated images sampled according to the log-polar transformation can be integrated over time in order to build accurate world representations and accomplish visual search tasks in an efficient manner. We focus on a specific visual information modality depth and on how to store it in a flexible memory structure. We propose a probabilistic observational model for a stereo system that relies on the Unscented Transform in order to propagate uncertainty in stereo matching, due to spatial quantization in the retina, to the 3D Cartesian domain. Probabilistic depth measurements are integrated in a novel Sensory Ego-Sphere whose topology can be biased with foveal-like distributions, according to the autonomous agent short-term tasks and goals. Furthermore, we investigate an Upper Confidence Bound algorithm for the task of simultaneously finding the closest object to the observer (visual search) and learning the surrounding environment 3D map (mapping). The performance of task execution is assessed both with a foveated log-polar sensor and a classical uniform one. The advantage of foveal vision and custom ego-sphere representations are illustrated in a series of experiments with a realistic simulator.     

Two-arm manipulation tasks with friction-assisted grasping

—The main objective of this paper is to study human dual-arm manipulation tasks and to develop a computational model that predicts the trajectories and force distribution for the coordination of two arms moving an object between two given positions and orientations in a horizontal plane. Our ultimate goal is to understand the dynamics of human dual-arm coordination in order to develop better robot control algorithms. We propose a computational model based on the hypothesis proposed by Uno et al. that suggests that human movements minimize the integral of the norm of the rate of change of actuator torques. We compare the experimental trajectories and force distributions with those obtained from the computational model. The observed trajectories show a significant degree of repeatability across trials and across subjects. We show that the computational model predicts the trajectories and the distribution of forces (torques) for a certain class of trajectories. However, the trajectories in the sagittal and frontal plane are characterized by asymmetric features that are hard to model using any integral cost function. Finally, we show that the computational model can be used to generate smooth trajectories and actuator forces for cooperating robots and discuss the advantages of such an approach to motion planning.     

Scheduling multiprocessor tasks with genetic algorithms

In the multiprocessor scheduling problem, a given program is to be scheduled in a given multiprocessor system such that the program's execution time is minimized. This problem being very hard to solve exactly, many heuristic methods for finding a suboptimal schedule exist. We propose a new combined approach, where a genetic algorithm is improved with the introduction of some knowledge about the scheduling problem represented by the use of a list heuristic in the crossover and mutation genetic operations. This knowledge-augmented genetic approach is empirically compared with a “pure” genetic algorithm and with a “pure” list heuristic, both from the literature. Results of the experiments carried out with synthetic instances of the scheduling problem show that our knowledge-augmented algorithm produces much better results in terms of quality of solutions, although being slower in terms of execution time     

Developing real-time tasks with predictable timing

A prototype development environment for the Mars maintainable real-time system is described. The Mars design environment supports the implementation of critical real-time tasks with time editing. It uses an experimental real-time language, Modula-R, which is based on Modula-2. The Mars real-time architecture, which is the target architecture of the Mars environment, is described. To illustrate the environment, the development of a simple real-time algorithm that implements insertion sort for an array is presented     

On tasks synchronization with the MMS protocol

The MMS protocol is a powerful tool for communication as well as for synchronization between manufacturing equipment such as robots, programmable logic controllers, etc. This paper shows how the MMS services can be used to handle tasks synchronization in a distributed environment. The MMS weaknesses regarding temporal aspects and possible directions to alleviate these weaknesses are also presented.     

Improving load balance with flexibly assignable tasks

In many applications of parallel computing, distribution of the data unambiguously implies distribution of work among processors. But, there are exceptions where some tasks can be assigned to one of several processors without altering the total volume of communication. In this paper, we study the problem of exploiting this flexibility in assignment of tasks to improve load balance. We first model the problem in terms of network flow and use combinatorial techniques for its solution. Our parametric search algorithms use maximum flow algorithms for probing on a candidate optimal solution value. We describe two algorithms to solve the assignment problem with log W/sub T/ and |P| probe calls, where W/sub T/ and |P|, respectively, denote the total workload and number of processors. We also define augmenting paths and cuts for this problem, and show that any algorithm based on augmenting paths can be used to find an optimal solution for the task assignment problem. We then consider a continuous version of the problem and formulate it as a linearly constrained optimization problem, i.e., min /spl par/Ax/spl par//spl infin/, s.t. Bx=d. To avoid solving an intractable /spl infin/-norm optimization problem, we show that, in this case, minimizing the 2-norm is sufficient to minimize the /spl infin/-norm, which reduces the problem to the well-studied linearly constrained least squares problem. The continuous version of the problem has the advantage of being easily amenable to parallelization. Our experiments with molecular dynamics and overlapped domain decomposition applications proved the effectiveness of our methods with significant improvements in load balance. We also discuss how our techniques can be extended to heterogeneous parallel computers.     

Scheduling of coupled tasks with unit processing times

The coupled tasks scheduling problem was originally introduced for modeling complex radar devices. It is still used for controlling such devices and applied in similar applications. This paper considers a problem of coupled tasks scheduling on a single processor, under the assumptions that all processing times are equal to 1, the gap has exact integer length L and the precedence constraints are strict. We prove that the general problem, when L is part of the input and the precedence constraints graph is a general graph, is NP-hard in the strong sense. We also show that the special case when L=2 and the precedence constraints graph is an in-tree or an out-tree, can be solved in O(n) time.     

Physiological stresses associated with television camera operators' tasks

This study was undertaken to evaluate the physiological stresses experienced by news media cameramen on their jobs. The tasks performed by the cameramen were simulated, based on the results of monitoring the field performance of these camera operators for a two-week period. Four male professional camera operators volunteered to participate in this study. Heart rate and oxygen consumption were selected to measure the physiological stresses associated with the camera operator's jobs. The results clearly show that jobs performed by the news media camera operators working for small television stations include very demanding physical tasks. The camera operator's job could be classified, based on physiological costs, as heavy work. A detailed discussion of the results and their implications in the process of camera operator's job redesign is given.     

Energy-efficient scheduling of real-time tasks with shared resources

This paper explores the energy-efficient scheduling of real-time tasks on a non-ideal DVS processor in the presence of resource sharing. We assume that tasks are periodic, preemptive and may access to shared resources. When dynamic-priority and fixed-priority scheduling are considered, we use the earliest deadline first (EDF) algorithm and the rate monotonic (RM) algorithm to schedule the given set of tasks. Based on the stack resource policy (SRP), we propose an approach, called blocking-aware two-speed (BATS) algorithm, to synchronize the tasks with shared resources and to calculate appropriate execution speeds so that the shared resources can be accessed in a mutual exclusive manner and the energy consumption can be reduced. Particularly, BATS uses a static low speed to execute tasks initially, and then it switches to a high speed dynamically whenever a task blocks a higher priority task. More specifically, the processor runs at the high speed from the beginning of the blocking until the deadline of the blocked task or the processor becomes idle. In order to guarantee that the deadlines of tasks are met, the static low speed and the dynamic high speeds are derived based on the theoretical analysis of the schedulability of tasks. Compared with existing work, BATS achieves more energy saving because its dynamic high speeds are lower than that of existing work and the processor has less chance to execute tasks at the high speeds. The schedulability analysis and the properties of our proposed BATS are provided in this paper. We also evaluated the capabilities of BATS by a series of experiments, for which we have some encouraging results.