A PC-BASED MODEL FOR EVALUATION OF INVESTMENT IN MANUFACTURING EQUIP:MENT

The investment in advanced manufacturing equipment must be evaluated on two levels, ie. a general technical investigation, and an in-depth technical and economical analysis if necessary. This is especially true for a country like South Africa where new technologies like robotics are relatively untried . It is therefore important to choose a suitable framework for both technical and economic analyses. This framework forms the foundation of the discussed evaluation model. For practical use, the evaluation and choice process is programmed for use on a PC. OPSOl\1MlNG: Belegging in toerusting vir gevorderde vervaardiging word gewoonlik op twee vlakke geevalueer, nl. 'n algemene tegniese ondersoek en 'n deeglike tegniese en ekonomiese ontleding, indien vereis. Dit is veral waar in 'n land soos Suid-Afrika waar nuwe ontwikkelings soos robotika nag relatief onbekend is. Dit is dus belangrik om 'n gepaste raamwerk te kies vir beide die tegniese en die ekonomiese ontledings. Hierdie raamwerk is die basis van die ontledingsmodel wat bespreek word. Om toepassing te vergemaklik, word die ontledingsen keuseprosesse geprogrammeer vir 'n mikrorekenaar. http://sajie.journals.ac.za http://sajie.journals.ac.za

-25- 1. INlRODUCIlON Any investment in manufacturing equipment needs to be evaluated on two levels . At first the investor has to do a general technical investigation into the technical feasibility of employing this type of equipment in his particular production facility . Following this evaluation and provided that a positive result was obtained. an in-depth technical and economic analysis is necessary . The investment in industrial robots and related equipment is analyzed along the same lines as normal capital equipment and will be used as a case study to illustrate the concept.
In general, in order to ascertain whether an acquisition is suitable for a given task and will be economical for that task, the potential buyer has to go through seven decision-making stages : a.) Application identification.
g.) Decision and order placement.
Several recommendations exist for the seven different stages in the decision-making process.
However, there is no user-friendly instrument to carry out this task. Obviously the more difficult stages are the technical and the economic analyses . Both of these have to be integrated in-to a software tool for practical usage on a Pc. gives a first orientation of its suitability. However, an application cannot be considered in isolation from the production realities, ie production structure, production equipment, manpower, etc. Therefore, these factors should playa major role in the evaluation process.
For sophisticated and capital intensive technical equipment, the reputation of the equipment supplier is also very important. The quality of his service and financial status can be decisive to the success of the investment.
The user therefore has to strive to find optimal technical equipment, in this particular case an optimal robot configuration, in relation to:

Application suitabilitỹ
Utilization adaptability and Vendor reliability.
It is a basic principle in the industrial engineering field that a manufacturing process has to provide high productivity and good quality under acceptable economic conditions. So, the whole evaluation process from a technical point of view has to be seen critically through the prism of economic viability. Fig.1 illustrates this statement. For evaluation of technical objects , and also for objects of a non-techn ical nature, the Use Value Analysis method has been found to be very powerful [2]. Furthermore, it allows for the execution of the evaluation process on a PC. The first step is to find the significant attributes of the evaluated object which describes it well enough . Starting out from an overall aim, these attributes have to be expressed as aims in the direction which the evaluation is taking . From these aims, evaluation criteria can be derived , which concretise the aims. The evaluation criteria satisfy specific parameters and therefore , in turn, become arguments in the evaluat ion funct ions. The evaluation functions have to mathematically describe the technological reality with maximum truth . The evaluation result V j expresses how the corresponding single aim A j is achieved . This step depends largely on the specialised knowledge of the evaluator regard ing the case under consideration. (Fig. 2). -29-2.2 .2 Aim Hierarchy: The overall aim of the evaluation model will be to choose an optimal robot configuration for a particular application. However, the optimality cannot be discussed in general terms. It always relates to a concrete situation and embodies a defined point of view. Therefore, the defined overall aim must be divided into the following three group aims : Good suitability to the manufacturing task (application) High adaptability to the manufacturing conditions (utilization) High reliability of the potential supplier (vendor) .
Every one of these three group aims can be sub-divided into separate single aims.
To The second group aim concerns the manufacturing conditions of the user, or : "How adaptable is the robot configuration to the workshop environment?" . Here the user has to estimate how the robot behaves regarding flexibility and availability (reliability , safety, manpower) .
Therefore, the user has to ensure a fast change-over to other manufacturing tasks (time flexibility) and also a large application variety (function flexibility) . The function flexibility is directly related to the end-effector, or : how free is the wrist, how wide are the grippers designed, etc . Furthermore, the "communications" feasibilities can playa very important role .
A robot set-up is normally a cap ital intensive investment. Therefore, the user has to strive for a high production availability of the robot. He has to be in a condition to quickly discover the reasons for a fault or failure or he wants his equipment to work a long time without failure.
Finally the user expects a high safety factor from his acquisition regarding itself or other equipment because of the danger of possible collisions and defects, but also regarding othe r operations or people. It therefore follows that the second group aim can be divided into the following single aims: For the weighting in this technical orientated evaluat ion model, the assumption is made that for the user, all three aspects , represented by the three group aims, are equally important.
Ther efore all 17 aims have the same starting points (the same basic conditions). To have the whole evaluation proces s on the same basis as the value funct ions , it is neces sary to define the condition -31given in [3], can be shown by the weights W j of the several aims A j on a 10 point scale system as well as their values under the above sum condition .

SUMMARY AND CONCLUSIONS:
In this paper, possibilities for choice of a robot configuration for a particular applicat ion were discussed . Starting from the chained steps of the decision-making process, an evaluation model for technical analysis of robot configurations was developed. Special attention was given to the building of the aim hierarchy. Therefore related technological realities were thoroughly researched and described mathematically through evaluation functions . A results interpretation provides a connection with the economic model, which was briefly discussed.
A discussion .of the whole evaluation model with regards to work volume and results reliability ends this study. Possible uncertainties are indicated .
The evaluation model discussed in this paper provides the technical manager with a very useful solution to robot installation problems. It allows for "what-if" type testing of many possible scenarios and parameters over a specified planning horizon . An analysis shows that robot installations can be profitable for normal production reasons like scrap reduction and the resulting lower production and inventory requirements, and not only on the basis of the replacement of direct labour. http://sajie.journals.ac.za