Fixed Processing Time Research Articles

EFFICIENT FPGA ARCHITECTURE OF GREY-SCALE SOFT MORPHOLOGICAL FILTERS FOR IMAGE AND VIDEO RESTORATION

Recently, Soft Morphological Filters have shown excellent performance in restoring noisy images. To add soft morphological filters in image processing chains and also to process image sequences in real time, it became a necessity to implement soft morphological operations in hardware. In this paper, FPGA architecture of grey-scale soft morphological filters is proposed. The architecture is based on a stack filter expression with some modification. The design can calculate soft morphological operations of greyscale soft morphological filters with structuring functions of any size and shape inside the structuring function's overall support. The filter architecture guarantees fixed processing time independent of the size and shape of the structuring function of the filter. Implementation results showed that the proposed filter architecture is suitable for real time applications.

A multi-stage stochastic programming approach in master production scheduling

Master Production Schedules (MPS) are widely used in industry, especially within Enterprise Resource Planning (ERP) software. The classical approach for generating MPS assumes infinite capacity, fixed processing times, and a single scenario for demand forecasts. In this paper, we question these assumptions and consider a problem with finite capacity, controllable processing times, and several demand scenarios instead of just one. We use a multi-stage stochastic programming approach in order to come up with the maximum expected profit given the demand scenarios. Controllable processing times enlarge the solution space so that the limited capacity of production resources are utilized more effectively. We propose an effective formulation that enables an extensive computational study. Our computational results clearly indicate that instead of relying on relatively simple heuristic methods, multi-stage stochastic programming can be used effectively to solve MPS problems, and that controllability increases the performance of multi-stage solutions.

Single CNC machine scheduling with controllable processing times to minimize total weighted tardiness

Advanced manufacturing technologies, such as CNC machines, require significant investments, but also offer new capabilities to the manufacturers. One of the important capabilities of a CNC machine is the controllable processing times. By using this capability, the due date requirements of customers can be satisfied much more effectively. Processing times of the jobs on a CNC machine can be easily controlled via machining conditions such that they can be increased or decreased at the expense of tooling cost. Since scheduling decisions are very sensitive to the processing times, we solve the process planning and scheduling problems simultaneously. In this study, we consider the problem of scheduling a set of jobs on a single CNC machine to minimize the sum of total weighted tardiness, tooling and machining costs. We formulated the joint problem, which is NP-hard since the total weighted tardiness problem (with fixed processing times) is strongly NP-hard alone, as a nonlinear mixed integer program. We proposed a DP-based heuristic to solve the problem for a given sequence and designed a local search algorithm that uses it as a base heuristic.

A fast multi-reference frame motion estimation algorithm

This paper proposes a new fast multi-reference frame motion estimation algorithm for efficient hardware implementation. The proposed algorithm reduces the search areas of motion estimation using a linear relationship between the motion vector and the distances from the current frame to the reference frames. First of all, it executes a full search area motion estimation in reference frames 0 and 1. After that, the search areas of motion estimation in reference frames 2, 3 and 4 are minimized by a linear relationship between the motion vector and distances from the current frame to the reference frames. The proposed algorithm does not use an early termination which gives us a fixed processing time schedule and a small size area of hardware. Simulation results show that PSNR drop and bit-rate increase are lower than those of previous fast multi-reference frame motion estimation algorithms. The number of computations of the new algorithm is reduced by 52.5% and the sequence quality of the simulation results is almost the same as with a full search area motion estimation which uses 5 reference frames.

An efficient ILP formulation for the single machine scheduling problem

This paper considers the problem of scheduling n jobs on a single machine. A fixed processing time and an execution interval are associated with each job. Preemption is not allowed. On the basis of analytical and numerical dominance conditions, an efficient integer linear programming formulation is proposed for this problem, aiming at minimizing the maximum lateness (L max). Experiments have been performed by means of a commercial solver that show that this formulation is effective on large problem instances. A comparison with the branch-and-bound procedure of Carlier is provided.

A branch and bound algorithm for optimal cyclic scheduling in a robotic cell with processing time windows

A branch and bound algorithm is described for optimal cyclic scheduling in a robotic cell with processing time windows. The objective is to minimise the cycle time by determining the exact processing time on each machine which is limited within a time window. The problem is formulated as a set of prohibited intervals of the cycle time, which is usually applied in the robotic cyclic scheduling problem with fixed processing times. Since both bounds of these prohibited intervals are linear expressions of the processing times, we divide these prohibited intervals into a series of the subsets and transform the problem into enumerating the non-prohibited intervals of cycle time in each subset. This enumeration procedure is completed by an efficient branch and bound algorithm, which could find an optimal solution by enumerating partial non-prohibited intervals. Computational results on the benchmark instances and randomly generated test instances indicate that the algorithm is effective.

Parallel machine match-up scheduling with manufacturing cost considerations

Many scheduling problems in practice involve rescheduling of disrupted schedules. In this study, we show that in contrast to fixed processing times, if we have the flexibility to control the processing times of the jobs, we can generate alternative reactive schedules considering the manufacturing cost implications in response to disruptions. We consider a non-identical parallel machining environment where processing times of the jobs are compressible at a certain manufacturing cost, which is a convex function of the compression on the processing time. In rescheduling it is highly desirable to catch up the original schedule as soon as possible by reassigning the jobs to the machines and compressing their processing times. On the other hand, one must also keep the manufacturing cost due to compression of the jobs low. Thus, one is faced with a tradeoff between match-up time and manufacturing cost criteria. We introduce alternative match-up scheduling problems for finding schedules on the efficient frontier of this time/cost tradeoff. We employ the recent advances in conic mixed-integer programming to model these problems effectively. We further provide a fast heuristic algorithm driven by dual prices of convex subproblems for generating approximate efficient schedules.

Optimal cyclic scheduling of a hoist and multi-type parts with fixed processing times

This paper proposes an exact algorithm to solve a cyclic hoist scheduling problem in a printed circuit board (PCB) electroplating facility, where multi-type parts with fixed processing times are processed in the same time and the parts are not allowed to wait in the tanks or on the hoist. Finding an optimal schedule in such a production line is equivalent to finding two types of related sequences: part input sequence and hoist move sequence. We show that the entering times of the parts are the decision variables of the problem. We formulate our problem using the notion of prohibited intervals and solve it by enumerating the non-prohibited intervals of the decision variables. This enumeration is accomplished more efficiently with a dynamic branch and bound procedure, which utilises relaxed solutions to eliminate redundant non-prohibited intervals in the search process. The proposed algorithm is polynomial in the number of tanks if the number of part types is fixed, but exponential if it is arbitrary. Computational results on randomly generated test instances indicate that the algorithm is effective.

An efficient algorithm for multi-hoist cyclic scheduling with fixed processing times

We consider no-wait production processes, where identical products are processed sequentially on n machines and transported by programmable hoists. We present an O ( n 5 ) algorithm that determines the minimum number of hoists required for all possible cycle-times; given the number of hoists, it also finds the minimum-time cyclic hoist-schedule.

Preparation of Carbon Molecular Sieves by Pyrolytic Carbon Deposition

The effect of different preparation parameters (pyrolysis temperature, process time, benzene concentration and residence time) on the properties of carbon molecular sieves obtained by pyrolytic carbon deposition from benzene on a microporous activated carbon, has been studied. For a fixed process time of 2 h, the increase of the pyrolysis temperature from 525 to 700∘C produced a strong increase of the CO2/CH4 selectivity, reaching a maximum value of 13 for pyrolysis at 700∘C. Selectivity also increased with process time (up to 5 h, with the pyrolysis temperature fixed at 650 and 675∘C), yielding values as high as 28. The obtained results have allowed to find the optimal preparation parameters for the preparation of CMS with high selectivity.

Approximation schemes for parallel machine scheduling problems with controllable processing times

We consider the problem of scheduling n independent jobs on m identical machines that operate in parallel. Each job has a controllable processing time. The fact that the jobs have a controllable processing time means that it is allowed to compress (a part of) the processing time of the job, in return for compression cost. We present the first known polynomial time approximation schemes for the non-preemptive case of several identical parallel machines scheduling problems with controllable processing times. Moreover, we study the problem when preemption is allowed and describe efficient exact and approximation algorithms. Scope and purpose Most classical scheduling models assume fixed processing times for the jobs. However, in real-life applications the processing time of a job often depends on the amount of resources such as facilities, manpower, funds, etc. allocated to it, and so the processing time can be reduced when additional resources are given to the job. This speed up of the processing time of a job comes at a certain cost. A scheduling problem in which the processing times of the jobs can be reduced at some expense is called a scheduling problem with controllable processing times. We contribute by presenting new approximation algorithms for this kind of problems.

On Not-First/Not-Last conditions in disjunctive scheduling

This paper is concerned with the development of constraint propagation techniques for the characterization of feasible solutions in disjunctive scheduling. In disjunctive scheduling, a set of uninterruptible tasks is to be performed on a set of resources. Each task has a release date, a deadline, and a fixed processing time; each resource can handle only one task at a time. Some of these propagation techniques are implemented by rules that deduce either mandatory or forbidden sequences between tasks or sets of tasks. For instance, certain rules indicate whether a given task must or cannot be performed before or after a set of other competing tasks. We focus our attention on the latter problem, known as the “Not-First/Not-Last” (NF/NL) problem.The genericity of propagation rules is a question of major importance. It induces that the result of the overall propagation must not depend on the order in which the inference rules are applied. Hence, one must search for completeness in the time-windows narrowing, in order to ensure the convergence of the propagation towards a unique fix-point.An efficient algorithm is proposed. It guarantees the completeness of time-windows narrowing due to NF/NL conditions. It has been integrated in a branch and bound procedure to solve job-shop instances. It has also been tested within several lower bounding procedures. Computational results are reported and the power and complementarity of NF/NL rules with other classical inference rules are discussed.

Experimental observation of dip-coating phenomena and the prospect of using motion control to minimize fluid retention

A computer controlled dip-coating apparatus was constructed to investigate physical aspects of transient coating processes and the feasibility of minimizing fluid retention during such operations. Electrobalance measurement of mass retention and drainage has elucidated a number of features which have not received prior notice. Relaxation processes were observed when the substrate motion was halted: the long-time behavior agreed with a combination of Landau–Levich and Jeffreys theories. However, short-time meniscus relaxation produced significant departures which are not fully understood. Comparisons of fluid retention were made for variable draw lengths: good agreement between Landau–Levich theory and experiment was observed even for very short withdrawal lengths, indicating the rapid transition to the steady-state regime. Computer-controlled substrate motion was performed to acquire preliminary information of its effect on mass retention. We investigated constant acceleration and constant speed withdrawal segments over a fixed process time. Experiments involving constant speed withdrawal periods interrupted by drainage periods revealed that more interruptions produced less fluid retention overall; in the limit of an infinite number of interruptions, the retention reached a minimum — equivalent to withdrawing the plate at the time-averaged speed. In addition, ramped speed experiments indicated very little difference over the accessible motion range. As a whole, the study revealed no procedures which could reduce mass retention below that which would be obtained with the slowest allowable constant speed withdrawal.

A decomposition approach for the single—machine scheduling problem

ABSTRACT This paper presents a temporal decomposition approach for the one—machine scheduling problem, with ready times, due dates and fixed processing times. We aim at characterizing feasible schedules of the problem and deriving benefit from the temporal properties pointed out, in order to generate a solution which minimizes the maximum lateness. The set of feasible schedules is characterized by means of constraint—based analysis rules. They permit the determination of the feasible locations of each task in a sequence, represented by the rank interval. A solving heuristic procedure is described; it decomposes the set of tasks according to their rank intervals and applicates upon each subproblem a priority rule. Computational results are reported, so that the characterization method as well as the solving procedure can be evaluated.

Nitriding of austenitic stainless steel by plasma immersion ion implantation

Plasma immersion ion implantation (PI 3™), in which the diffusion of nitrogen from a low pressure r.f. plasma is combined with the implantation of nitrogen ions at energies up to 45 kV, is an effective means of nitriding austenitic stainless steel. At temperatures up to 450 °C, tribological properties can be improved without loss of corrosion resistance. In common with other nitriding processes in this temperature range, a supersaturated f.c.c. phase is formed, sometimes described as expanded austenite, which is maintained to very high nitrogen concentrations. At higher temperatures, chromium nitride is precipitated and the expanded austenite decomposes, leading to a reduction in corrosion resistance. Glancing-angle X-ray diffraction (XRD) of PI 3-treated AISI 316 stainless steel at temperatures between 350 and 450 °C suggests that a highly homogeneous layer of expanded austenite is produced. The expansion increases with increasing process time, but decomposition of the supersaturated phase occurs after several hours of treatment if the temperature is too close to 450 °C. For a fixed process time, the expansion appears to be greatest at the lower temperatures (350 °C), although it can also be influenced by other processing parameters such as plasma density. Microstructural examination by cross-sectional transmission electron microscopy (TEM) has challenged the identification of the supersaturated phase as expanded austenite and reveals the complexity of the modified layer not seen by glancing-angle XRD. Most striking is the formation of a thick (2–3 μm) amorphous zone which may contain nanocrystalline precipitates of CrN and α-ferrite. A highly defective layer (up to 2 μm thick) of expanded austenite has been observed to underlie the amorphous zone where nitrogen diffusion is facilitated by the high defect density. Only partial reconciliation of the TEM results with the XRD observations has been possible to date.

A hodoscope made of resistive plate chambers to identify muons in a fixed targed beauty hadroproduction experiment

We have built a large area hodoscope to identify muons from semileptonic decays of beauty particles produced in the WA92 experiment at the CERN Super-Proton-Synchrotron. The hodoscope is made of resistive electrode chambers read out with strips of 3 cm pitch. The hodoscope has a fast response with a time resolution of 5 ns and a space resolution of 1 cm. A fast trigger processor selects straight tracks pointing to the interaction vertex in a fixed processing time of 90 ns.

Control strategies in directing the hand to moving targets.

We have evaluated the use of visual information about the movement of a target in two tasks--tracking and interceptions--involving multi-joint reaching movements with the arm. Target velocity was either varied in a pseudorandom order (random condition) or was kept constant (predictable condition) across trials. Response latency decreased as target velocity increased in each condition. A simple model that assumes that latency is the sum of two components--the time taken for target motion to be detected, and a fixed processing time--provides a good fit to the data. Results from a step-ramp experiment, in which the target stepped a small distance immediately preceding the onset of the ramp motion, were consistent with this model. The characteristics of the first 100 ms of the response depended on the amount of information about target motion available to the subject. In the tracking task with randomly varied target velocities, the initial changes in hand velocity were largely independent of target velocity. In contrast, when the velocity was predictable the initial hand velocity depended on target velocity. Analogously, the initial changes in the direction of hand motion in the interception task were independent of target velocity in the random condition, but depended on target velocity in the predictable condition. The time course for development of response dependence was estimated by controlling the amount of visual information about target velocity available to the subject before the onset of limb movement. The results suggest that when target velocity was random, hand movement started before visual motion processing was complete. The response was subsequently adjusted after target velocity was computed. Subjects displayed idiosyncratic strategies during the catch-up phase in the tracking task. The peak hand velocity depended on target velocity and was similar for all subjects. The time at which the peak occurred, in contrast, varied substantially among subjects. In the interception task the hand paths were straighter in the predictable than in the random condition. This appeared to be the result of making adjustments in movement direction in the former condition to correct for initially inappropriate responses.

A fast tracking muon trigger for experiment WA92

The WA92 experiment at CERN aims to study the hadroproduction and decay of beauty particles. To get a good signal-over-background ratio, the trigger identifies secondary vertices, large transverse momentum tracks and leptons. We report on the design of the muon detectors and of the first level tracking muon trigger. The muon filter has two planes of resistive plate chambers of area 2×6 m 2 placedbehind an iron absorber. For the readout of the two coordinates 3 cm pitch strips are used. The fast identification of muon tracks coming from the decay detector is done in a fixed processing time of about 100 ns by roads defined with programmable logic arrays and is used to send early signals to other detectors of the experiment.

Solvable Cases of the No-Wait Flow-Shop Scheduling Problem

The no-wait flow-shop scheduling problem (NWFSSP) with a makespan objective function is considered. As is well known, this problem is 𝒩𝒫-hard for three or more machines. Therefore, it is interesting to consider special cases, i.e. special structured processing time matrices, that allow polynomial time solution algorithms. Furthermore, it is well known that the NWFSSP with a makespan objective function can be formulated as a travelling salesman problem (TSP). It is observed that special structured processing time matrices for the NWFSSP lead to special structured distance matrices for which the TSP is polynomially solvable. Using this observation, it is shown that some NWFSSPs with fixed processing times on all except two machines are well solvable while the others are conjectured to be 𝒩𝒫-hard. Also, it is shown that NWFSSPs with a mean completion time objective function restricted to semi-ordered processing time matrices are easily solvable.

Copolymer composition control during the seeded emulsion copolymerization of vinyl acetate and methyl acrylate

AbstractThe effect of various monomer addition policies on the copolymer composition during the seeded copolymerization of methyl acrylate and vinyl acetate in a semicontinuous reactor was investigated. Four policies were considered. In the first, which is called optimal policy, the reactor was initially charged with all of the less reactive monomer (vinyl acetate) plus the amount of the more reactive monomer (methyl acrylate) needed to initially form a copolymer of the desired composition. Then, the addition of the remaining methyl acrylate was made at a flow rate that ensured the formation of a copolymer of the desired composition. In the second, the initial charge is the same as in the previous case but the time dependent addition rate of methyl acrylate was decomposed into three periods of constant feed rate. In the third, the initial charge is the same as in the previous policies but the remaining methyl acrylate was added at a constant feed rate. In the forth, both monomers were added under starved conditions. In order to calculate the optimal addition policy, the time evolution of the average number of radicals per particle, ñ, is required. The calculation of ñ involves rate parameters which values are usually unknown. Therefore, a semi‐empirical method for the calculation of the time evolution of ñ was developed. It was found that ñ was always greater than 2. For the experimental conditions used in this work, this result suggested that termination in the polymer particles was affected by gel effect. A gel effect function was estimated and then the optimal addition policy was calculated. Comparison between the different processes showed that, for a fixed process time, the copolymer obtained through the optimal addition policy was more homogeneous than that formed when the methyl acrylate was fed in three periods of constant feed rate and even better than the one obtained using a constant feed rate throughout the process. The copolymer quality of the later process is similar to that of the copolymer formed by means of the starved process. Nevertheless, a more homogeneous copolymer composition can be obtained through the starved process when longer process times are used.