Understand first, then simplify and only then automate the process.
The USA Principle is a common sense approach to automation projects. Similar procedures have been suggested in the manufacturing and automation trade literature, but none has a more captivating title than this one.
USA stands for:
1. Understand the existing process.
2. Simplify the process.
3. Automate the process.
A statement of the USA principle appeared in an APICS* article. The article was concerned with implementation of enterprise resource planning, but the USA approach is so general that it is applicable to nearly any automation project.
*APICS=American Production and Inventory Control Society
Going through each step of the procedure for an automation project may in fact reveal that simplifying the process is sufficient and automation is not necessary.
Understand the Existing Process.
The obvious purpose of the first step in the USA approach is to comprehend the current process in all of its details. What are the inputs? What are the outputs? What exactly happens to the work unit between input and output? What is the function of the process? How does it add value to the product? What are the upstream and downstream operations in the production sequence, and can they be combined with the process under consideration?
Some of the basic charting tools used in methods analysis are useful in this regard, such as the operation process chart and the flow process chart. Application of these tools to the existing process provides a model of the process that can be analyzed and searched for weaknesses (and strengths). The number of steps in the process, the number and placement of inspections, the number of moves and delays experienced by the work unit, and the time spent in storage can be ascertained by these charting techniques.
Mathematical models of the process may also be useful to indicate relationships between input parameters and output variables. What are the important output variables?
How are these output variables affected by inputs to the process, such as raw material properties, process settings, operating parameters, and environmental conditions? This information may be valuable in identifying what output variables need to be measured for feedback purposes and in formulating algorithms for automatic process control.
Simplify the Process.
Once the existing process is understood, then the search can begin for ways to simplify. This often involves a checklist of questions about the existing process. What is the purpose of this step or this transport? Is this step necessary? Can this step be eliminated? Is the most appropriate technology being used in this step? How can this step be simplified? Are there unnecessary steps in the process that might be eliminated without detracting from function? Can steps be combined? Can steps be performed simultaneously? Can steps be integrated into a manually operated production line?
It helps to consider these questions within the following methodologies:equence of this strategy. Material handling effort and non-operation time are also reduced. Manufacturing lead time is reduced for better customer service.
Specialization of operations.
The first strategy involves the use of specialized equipment designed to perform one operation with the greatest possible efficiency. This is analogous to the concept of labor specialization used to improve productivity.
Production occurs as a sequence of operations. Complex parts may require dozens, or even hundreds, of processing steps. The strategy of combined operations involves reducing the number of distinct production machines or workstations through which the part must be routed. This is accomplished by performing more than one operation at a given machine, thereby reducing the number of separate machines needed. Since each machine typically involves a setup, much of that time can usually be saved as a result. Material handling effort and idle time are also reduced.
A logical extension of the combined operations strategy is to simultaneously perform the operations that are combined at one workstation. In effect, two or more processing (or assembly) operations are being performed simultaneously on the same workpart, thus reducing total processing time.
Integration of operations.
Another strategy is to link several workstations together into a single integrated mechanism, using automated work handling devices to transfer parts between stations. In effect, this reduces the number of separate machines through which the product must be scheduled. With more than one workstation, severprocesss can be processed simultaneously, thereby increasing the overall output of the system.
This strategy attempts to achieve maximum utilization of equipment for job shop and medium volume situations by using the same equipment for a variety of parts or products. Prime objectives are to reduce setup time and programming time for the production machine. This normally translates into lower manufacturing lead time and less work-in-process.
Automate the Process.
Once the process has been reduced to its simplest form, only then should automation be considered. It might turn out that automating the process is unnecessary or cannot be cost-justified after it has been simplified.
If automation then appears to offer a further return on investment, then the following strategies can help to optimize the potential benefits of automation.
Improved material handling and storage.
A great opportunity for reducing nonproductive time exists in the use of automated material handling and storage systems. Typical benefits include reduced work-in-process and shorter manufacturing lead times.
Inspection for quality of work is traditionally performed after the process is completed. This means that any poor quality product has already been produced by the time it is inspected. Incorporating inspection into the manufacturing process permits corrections to the process as the product is being made. This reduces scrap and brings the overall quality of product closer to the nominal specifications intended by the designer.
Process control and optimization.
This includes a wide range of control schemes intended to operate the individual processes and associated equipment more efficiently. Individual process times can be reduced and product quality improved.
Plant operations control.
Whereas the previous strategy was concerned with the control of the individual manufacturing process, this strategy is concerned with control at the plant level. It attempts to manage and coordinate the aggregate operations in the plant more efficiently. Its implementation usually involves a supervisory control and data acquisition (SCADA) system within the factory.
Computer-integrated manufacturing (CIM).
Expanding on the previous strategy, factory operations can be integrated with the engineering and the business functions of the firm. CIM involves extensive use of software solutions such as manufacturing operations management (MOM), manufacturing execution systems (MES), and enterprise resources planning (ERP).
These strategies should provide a starting point for possible improvements to automated production systems. In most cases, multiple strategies can be applied to any single improvement project.
Industrial Automation Course Notes
Universidade do Minho