Summary of Research Paper on IE -Optimization of cutting Wood

Optimization of cutting in primary wood transformation industries 

Raïdandi Danwé, Isaac Bindzi, Lucien Meva’a

National Advanced School of Engineering, the University of Yaounde I (CAMEROON)

(JOURNAL OF INDUSTRIAL ENGG. AND MANAGEMENT,2012,VOL-5,115-132)

Introduction:

The Cameroon forest covers about 20 millions of hectares, representing 44% of the national territory. Cameroon possesses one of the most developed primary conversion wood industry. The loss of raw materials in wood cutting industries has reached high proportions (30 to 36% of volume yield).

 Statistical analyses have shown that there exists a considerable difference between the volume of logs bought by primary conversion wood factories in Cameroon and the volume of the cuts leaving the industries. This low efficiency results in the waste of raw material, which is burnt as biomass. In order to tackle this problem, the exploitation and the primary conversion of wood in  Cameroon was studied.  The various methods of cutting and the different products obtained were studied. We then proceeded with the formulation of the log cutting  optimization problem based on a real shape model of the logs. The solution to this problem then led to the design of a software package to be used as a cutting optimizer. The automation of the cutting operation leads to an accelerated work and an increase in the volume of the cuts produced daily.

In this Paper, the work they  studied the optimization of wood production in industries of primary conversion. Primary wood conversion comprises of  the activities of sawing and wood planning, unrolling and trenching, drying, and finally  wood impregnation, in which they  studied the various methods of cutting and the  different products obtained. We then proceeded with the formulation of the log cutting optimization  problem based on a real shape model of the log. Finally  design and the presentation of a software package called cutting optimizer  were done.

Geometrical Modeling and Cutting up

The achievement of a better profit in sawing industries depends mainly on the mathematical representation of the logs of wood during cutting up. Geometric modeling of logs serves as a preliminary stage in the automation of operations in a sawmill .The automation also requires real time simulations. Time required for the analysis of data related to logs should then be reduced. This additional constraint imposes a compromise between the accuracy of the model and the quantity of data to be processed.

It is quite relevant to mention that in modeling  the external shape of the log, swellings (which generally characterize the roughness of logs), should not be taken  in account in the perspective of optimizing  the volume output of logs being cut up. Only smooth logs are considered here.

Cutting

The mode of cutting  depends on the characteristics of the log and the equipment’s of the company. In order to optimize cutting decisions, an automated real-time (i.e. at production speed) evaluation of material dimensions and quality is required. Some requirement for the first cut is to lead to a maximum value yield of a log are a knowledge of the log  geometry (length, diameters, eccentricity, sweep...), the log quality, the  determination of the best orientation and position of the log at the first cut, and  the use of a cutting system that enables to obtain plane surfaces during log  cutting.

Discrete Geometric Model of the log

Products from the first stages of primary conversion of wood

·        Best Opening Face: The BOF uses the principle that the first cut is the key of the sawing strategy for a given sawing pattern, in order to maximize the yield of the saw log. It considers the volume-yield of the saw log, leaving out the effect of internal characteristics.

Production Optimization: The achievement of a better profit in sawing industries depends mainly on the mathematical model of logs during cutting. With respect to the small logs, loss of material can be observed due to the effects of the wood feature, the precision, the method used in cutting, and the thickness of the saw.

Cutting Process and Classification: For local sawing industries, we encounter three major classes. For the first class is made up of cuts presenting no defect (absence of nodes, dimensional conformity according to the functional condition of contract). The second class is made up of cuts having at most one node. For the third one, the number of nodes is greater than or equal to two and in addition, we can also find dimensional defects.

Formulation of Optimization Problem: The optimization model resorts to wide-spread techniques of linear programming or operational research. The above optimization problem can be assimilated to a knapsack problem with non-bounded variables which can be formulated thus: We have N types of object (product from log cutting) in an infinite number for each type.  An object of type k has a positive integer value Ck (its market price) and occupies a volume ak (for a cut cross-section Sk). Let uk be the number of type k objects in the bag. The problem is thus expressed as: Finding the subset of objects of maximum value, whose volume does not exceed the capacity b of the bag.

Resolution of Optimizing Problem: knapsack model is used in following situation

·         When loading ships or planes: all luggage have to be packed without  overloading

·          When cutting materials: to minimize scraps when cutting rods into iron bars.

Optimization software package for log cutting: It aims at determining the number of cuts of type k that we  can extract from a log of wood in a way so as to optimize the material output and maximize its  commercial value.

The Cutting Optimizer: The optimization program provides a cutting schedule. This program calculates the first position and the next positions depending on the memorized log dimensions and the thickness of the blade.

The  optimization software used by these sawmills present some deficiencies which are

·         The software does not take into consideration the ordering list of the  enterprise and the market prices in optimizing of the cutting process.

·         Cutting is done uniquely with one of the cutting methods, whatever the  operator’s order.

·         The software neither takes into account  the real shape of the log, nor does it take into consideration the defects on it. It deals only with the principal cross-section of the log. We run the risk of having much scrap. 

The command principle of the cutting optimizer:

The command principle of the optimizer

The length of each log varies  depending on the order. At the output of our system , we obtain the cuts.

The optimization system for the log carriage semi-modern software (piloting and optimization devices), a decision making block which receives data from the input (characteristic dimensions of each log), analyses them  together with the data from the command computer and then takes a decision on  the cutting method to be implemented. This decision is transmitted to the  automaton that commands the rotational and translational movements of the

carriage. The command computer receives at its input a feedback from the market (database on the prices of the cuts) and the commands received by the enterprise.

Conclusion: The modeling  of the real shape of the log enabled us to identify the input parameters to generate the log in real shape. The formulation of the optimization  problem assimilated to a knapsack problem was solved using the method of dynamic programming. That enabled to set up an algorithm for optimum cutting of the log, alongside a cutting optimizer. This work has led to a possible solution for increasing material output, productivity, and quality of cuts, regardless the type of wood.

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