Special Purpose Machines, by definition, are built for a specific purpose. Design of such machines creates special challenges which, while not always unique for SPMs, may require unique solutions.
The top challenges faced by a designer of a Special Purpose Machine are:
The most important aspect of the design of any Special Purpose Machine is to understand the process that is to be carried out by the machine or system. Any process, no matter how complex it is, should be broken down into smaller subcategory processes. This will help in the understanding of the desired working of the SPM and therefore is the critical first step in the design of the machine.
As we already know, an SPM is built for a specific purpose. Some examples of such purposes are:
Insufficient knowledge of the SPM’s process could directly lead to failure in achieving the core purpose of the SPM.
An additional downstream effect of the insufficient understanding of the process is Cost Overrun. The overrun of cost is almost always a major setback for any project as the investment already made usually cannot be easily recovered and the machine is still unusable because it isn’t complete yet and/or isn’t fully functional. Which means additional investment may be required.
Since the whole design of the SPM is based on the knowledge of the process for which the SPM is being built and the details of this process, insufficient understanding of the same will lead to design errors which in turn will lead to rework and cost overruns. Even the tiniest of errors with parameters like temperature, pressure and orientation can give undesirable outcomes and end in a failed product.
Any of the following aspects can be variables for a Special Purpose Machine.
Apart from the above there can be other variables which may need to be considered during the design of an SPM and which can be dependent upon the process that is intended to be carried out by the machine.
Based just on the names of the variables listed above, we can imagine that failure can be caused simply because of ignorance of one or more variables, which in turn can trigger a domino-effect leading to a catastrophic failure of the machine.
Furthermore, many of the variables or parameters 3 need to be controlled to produce an efficient system. Or they may be required to be modified to achieve different types of results under different conditions. Many a times variables can get introduced into the process due to the process itself or due to the machine. These need to be carefully estimated and monitored as early as possible and as exactly as possible. Failing to do so could lead to failure of the process or failure of the machine.
All Special Purpose Machines have to be designed taking into account all types of constraints caused because of the core purpose of the machine. These constraints can come from parameters which directly affect the functioning of the SPM as well as from the output of the SPM.
Here are examples of parameters which can constrain the design of an SPM:
From the point of view of the personnel who will work on the SPM, it is important to ensure that the machine’s operating position is ergonomically well-placed, well-ventilated, well-lit, etc.
As per the company’s safety norms / rules or International safety norms / rules some conditions may be imposed on the machine for which the machine should be qualified. In some processes hazardous working conditions for the personnel as well as for the machine’s internal components need to be properly considered to achieve a functional machine which follows rules and regulations.
Other functional or geometrical requirements can pose restrictions with respect to availability of space on the work floor or with respect to ventilation, availability of power and so on.
All the above factors have a combined effect not only on the working of the SPM but also on its design and orientation. 4
A very important aspect of designing any Special Purpose Machine is having a proper understanding of the expectations of the customer. The designer needs to ask: Can these expectations be met – both theoretically and practically? Building an SPM can be a costly affair and so we need to understand how these expectations impact the needed investment. What are the trade-offs between achieving the customer’s expectations and, at the same time, keeping costs under control? It is always preferable to have realistic expectations rather than dream scenarios or wishes. In this respect, the designer needs to manage the customer’s expectations well.
And, it isn’t only the engineering department’s expectations which need to be managed but also those of the production department, the quality department, stores department, purchase department and in some particular cases the electrical or electronics department as well as the IT department.
The maintenance department also plays a vital role in the performance of the SPM as the reliability of the machine and its functionality and accuracy are very dependent on how well the machine is being maintained.
Understanding (and taking into account) the expectations in terms of quality, regulations, production rate, communication types, etc. helps realize a well-designed machine producing the expected results. On the other hand, insufficient understanding or not taking into consideration the expectations of all stakeholders can lead to unsatisfactory performance of the machine, higher breakdown time, excessive tooling cost, etc. In some cases, ignorance may lead to failure of the machine itself.
So, to fulfil the purpose (and the promise) of the machine, customer expectations must be carefully studied, set, managed and then implemented to the maximum extent possible.
1‘Flexibility of use’ refers to the ability to handle various types of tooling, various types of work pieces, operate in different modes of operational sequences, etc.
²‘Types and ways of communication’ refers to different types of indications – eg Tower lamps, Hexadecimal displays, LCD displays – as well as Computer Interfaces, Wired or wireless communication, interfacing of the communication within the components of the SPM, etc.
³‘Parameters are characteristics or set of characteristics that define the final output objective – eg. Surface finish. Variables, unlike Parameters, can change over time (eg. Tool feed in mm required to achieve the specified Parameter like Surface Finish)
4‘Orientation’ refers to the outer shape of the machine in terms of dimensions and structure (eg. “L shaped”, “Straight line”, “U shaped” etc.)