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ОглавлениеIntroduction to Programmable Automation
Contents
1.1 Introduction to Programmable Automation
1.4 Manufacturing PerformanceMeasures
Objective
The objective of this chapter is to introduce the reader to programmable automation, define automation in general, and to introduce the ideas of when and where automation is applied.
1.1 Introduction to Programmable Automation
Programmable automation technology is a remarkably useful tool for manufacturing engineers/technologists who seek to improve manufacturing systems of their respective industries. It combines mechanical, electrical, and computer technologies that have been developed for very specific automation capabilities. The term “programmable automation technology” actually refers to three individually distinct technologies that have a common thread: programmability. These technologies are computer numerical control (CNC) technology, robotics technology, and programmable logic control (PLC). Each, in some form, either directly or indirectly, is used in almost all modern automation systems—one is unlikely to walk into a modern manufacturing facility without observing one of these technologies in action. This, however, has not always been the case.
Initial migration to programmable automation was gradual, hampered by the complexity, expense, and, in some cases, poor reliability of early systems. Additionally, utilization of the technology required that companies retain technical experts specifically devoted to the implementation, programming, and maintenance of the systems. However, over the last 25 years programmable automation technology has greatly matured: Modern systems are standardized, substantially less complicated and expensive, and extremely reliable. Whereas use of this technology was initially the domain of specialists—particularly engineers—now virtually every member of an engineering or maintenance staff is expected to use the technology at some level. In fact, it is now imperative that mechanical engineers and technologists—who used to avoid “electrical stuff”—have a solid foundation in it. Hence, the goal of this text: to instruct any member of an engineering team so he or she may comfortably delve into the automation arena.
Before we properly define “programmable automation” and develop a full description of its capabilities, we first must present an understandable picture of manufacturing in general. In the following section we explore manufacturing and define some of its key terms. Subsequent sections define automation in general and programmable automation in particular. The concept of productivity will be introduced, and the last few sections will address reasons for automation, corresponding benefits of it, and ways automation can be implemented.
1.2.1 Manufacturing overview
Manufacturing, regardless of the industry under consideration, is a conversion process. Some form of raw material is brought into a manufacturing facility and converted into a more useful finished product. The conversion is accomplished by applying a series of manufacturing steps, or manufacturing processes, to the raw material. Manufacturing processes alter the raw material’s shape, appearance, physical and mechanical properties, and/or assemble it with other components into a desired finished product. This is achieved through the use of equipment, tools, and supplies combined with the application of labor, time, and energy.
The way that manufacturing operations are organized within the facility defines plant layout. The term “manufacturing system” of the facility refers to the plant layout and worker execution of the operations. The manufacturing system used is determined by the product(s) characteristics. Figure 1-0 shows the plant layout of an imaginary facility, the XYZ Company. XYZ Company manufactures widgets. As the layout indicates, bar stock is processed into a widget through a series of manufacturing processes, which include sawing, turning, milling, and painting. Each manufacturing process executes a systematic sequence of operations called a program of instructions. When a program of instructions is complete for one manufacturing process, the product is routed to the next process.
Figure 1-0 XYZ Company plant layout
Note that the factory must perform operations in addition to manufacturing processes to create the product. The product must be moved between the manufacturing processes. It must also be inspected at some point to ensure that it satisfies the customer’s requirement. Additionally, someone must optimize the processes, schedule the operations, monitor labor usage, schedule maintenance, coordinate material handling, control inventory, and make sure the product is shipped on time. These activities do not contribute to the conversion process of the product per se. However, they are critically important to the manufacture of the product. The manufacturing processes and other activities combined are called manufacturing operations. Typical manufacturing operations found in factories include:
• Manufacturing processes
• Material handling
• Quality control
• Manufacturing support.
Each manufacturing process is designed to accomplish a very specific raw material conversion step. Thus, the number of manufacturing processes and the way they are organized within the facility are determined by the product(s) made. Manufacturing processes might include shaping processes such as molding or machining, property-enhancing processes such as the heat treating of steel, surface processes such as cleaning, coating, or painting, and various types of assembly processes. Assembly processes can be permanent, as in the case of welding, soldering, brazing, or adhesive bonding. However, some assembly processes are considered semi-permanent. Semi-permanent assembly processes typically include various types of mechanical joining, such as what is accomplished with the use of threaded fasteners, rivets, and expansion fits. All manufacturing processes are said to add value to the product; but, the other three operations—material handling, quality control, and manufacturing support—do not add value and are often the first targets for automation.
The way manufacturing operations are organized within a facility defines its plant layout. The term “manufacturing system” refers to both plant layout and worker execution of operations.
1.2.2 Defining the product
A given manufacturing facility may turn out only one product, a variety of models of one product, or many different products. Products may be as simple as a paper clip or as complex as a photocopier. Additionally, the facility might make only one product per year, or it might turn out millions of products. A product is either continuous, such as a liquid like gasoline, or it is discrete, like an automobile. (This text focuses on programmable automation of manufacturing processes and systems for discrete products only; continuous product manufacturing processes and systems will not be addressed.) Taken together, these distinctions make up the product definition and are naturally related to the manufacturing system(s) used within the facility.
The choice of manufacturing system employed for a discrete product is a function of the manufacturing product definition, which encompasses three main factors:
• Product complexity
• Product variety
• Product quantity.
These factors provide the most complete picture of the type of manufacturing system(s) needed to make a product economically.
The level of a product’s complexity is tied to the level of difficulty in the manufacture of that product. In general, product complexity is an indication of whether the product is a small, simple, single component, as is the case with the widget made by the XYZ Company, or a large and complex product, like a nuclear submarine, which has numerous complex individual components. Obviously, the manufacturing systems that would produce these two products would be vastly different. This product complexity is further illustrated in Figure 1-1.
Figure 1-1 Product complexity example
Product variety refers to the number of different product designs, versions, or models to be produced within a facility. If a facility made just a single product, such as a toothbrush, it would use a manufacturing system conducive to efficient production of that one product. Conversely, if the facility were to manufacture, say, hairbrushes in addition to toothbrushes, it might have multiple manufacturing systems or a single system designed to accommodate this product variety.
In addition to this factor, there are different levels of product variety. Soft product variety indicates that product difference within the operation is small. Hard product variety means the products are vastly different. The best way to differentiate soft from hard product variety for assembled products is to consider the number of common parts each product uses. A high percentage of common parts indicates soft product variety, whereas a low percentage points to hard product variety. The case of the toothbrushes and hairbrushes represents hard product variety. Soft product variety might exist in the production of different models or styles of toothbrushes (color, bristle density, and so on). An illustration of this case of hard versus soft product variety is shown in Figure 1-2.
Figure 1-2 Hard versus soft product variety
Product quantity, naturally, specifies the number of products that are to be turned out over a given time period. This is more often referred to as product volume. As will be seen in subsequent sections, high volume product requirements dictate the use of automated high speed manufacturing systems. Low volume manufacturing systems are typically less automated with more worker involvement.
Observe that product definition and manufacturing system are interdependent. High volume manufacturing systems are typically less capable of accommodating product variety. Conversely, manufacturing systems capable of handling a great deal of product variety cannot produce as high a volume. Complex products dictate a complex manufacturing system; simple products will typically be turned out by a relatively simple manufacturing system. Thus, once a manufacturing system is established within the facility it will dictate the type of future products that can be produced, unless, of course, capital is allocated to add other manufacturing systems to the facility.
1.2.3 Manufacturing system
As mentioned already, the manufacturing system is the combination of manufacturing processes and the organization of workers, designed so as to efficiently and effectively create the desired product. There are essentially four standard systems, with numerous variations, that have evolved over time. Each system is geared to produce a fairly specific product definition. The four standard manufacturing systems are:
1. Fixed-position
2. Process
3. Quantity manufacturing system
4. Flow-line.
(Refer to Figure 1-3.) Because of the narrowness of product definition relating to each system, an individual facility may employ one or more of these systems.
Fixed-position manufacturing systems (Figure 1-3(a)) are used for making large, complex products. Because such products are not easily moved, the manufacturing processes are taken to the product; the product remains in a fixed position throughout manufacture. This system produces items that are highly complex, relatively large and immobile, with low volume production requirements, and of soft product variety. Submarines, ships, and large aircraft are examples of products that use this system.
The process manufacturing system is used when product complexity is relatively low and there is hard product variety. Accordingly, production quantities range from low to moderate. This system is also called a job shop system because it can accommodate a wide variety of products or jobs. The manufacturing processes are grouped together according to function or process. Products are routed though the facility to the required manufacturing processes in groups called lots or batches. The size of the lot, or lot size, is the number of products in the group. The use of lots is necessary because of the variety of products the system must accommodate. In a process manufacturing system each manufacturing process to which a product is routed will have to be set up, or prepared, to process that particular product. Consequently, it is economically desirable to run a specific number of products through the process each time it is set up. Some factors that influence lot size include variety of the products made in the facility, setup times, order sizes, and manufacturing lead-time. This system is shown in Figures 1-0 and 1-3(b).
Figure 1-3 Standard manufacturing systems
The quantity and the flow-line manufacturing systems are often combined into one category, called the product manufacturing system. These systems produce mass quantities of products and are thus mass production systems. However, both product complexity and product variety of mass-produced items dictate the division of the product manufacturing system into the quantity and flow-line manufacturing systems.
The quantity manufacturing system is used with low product complexity and hard product variety. These products are produced on a single standard machine, like a plastic injection molding machine with exchangeable tooling. (Refer to Figure 1-3(c).) Other examples of products manufactured with this system include metal stampings and blow molded plastic products, like water bottles.
Flow-line manufacturing is for products with high product complexity and soft product variety. For assembled products, flow-line is more commonly called assembly line manufacturing system. Raw material flows down a line of manufacturing processes, in the end to be converted into a finished product. Henry Ford is often credited with perfecting this system. He produced the Model T using the flow-line manufacturing system to reduce cost so that the average American could afford his automobile. Because of the nature of the flow-line manufacturing system, product variety was essentially nonexistent. All Model T cars had the same body shape and were made in one color. The early flow-line system evolved to a modern form that accommodates soft product variety. Figure 1-3(d) illustrates the flow-line manufacturing system.
The manufacturing systems discussed above are summarized in the table of Figure 1-4 as shown on page 9 according to product complexity, variety, and volume. Also, it cannot be emphasized enough that many manufacturing facilities will have more than one of these systems and/or a variation of some system as dictated by the product definition. Consider Figure 1-6. This figure demonstrates how some manufacturing systems feed into other manufacturing systems to produce the finished product. In this example a flow-line manufacturing system in the form of an assembly line produces the finished product. The components of the finished products are produced on various other manufacturing systems as shown. This is typical of most, if not all, assembled products.
Figure 1-4 Manufacturing systems versus product complexity, variety, and volume
Figure 1-5 Manufacturing support systems
Figure 1-6 Multiple manufacturing processes used to make a product
1.2.4 Manufacturing Support Systems
Another key ingredient to the conversion process is the manufacturing support system. Manufacturing support systems provide the management of the business operations of the facility and the manufacturing system. Thus, the success of a facility, in terms of productivity and thus profitability, is dictated by how well its manufacturing support systems manage its manufacturing system.
A manufacturing support system utilizes people and procedures to manage the manufacturing system and the overall facility. Whereas the manufacturing system processes the raw material, the manufacturing support system processes information necessary to accomplish the conversion of the raw material into the finished product. Accounting, customer service, marketing, human resources, product design, manufacturing engineering, materials engineering, quality control, production planning, and shop floor control are all good examples of manufacturing support systems. Figure 1-5 as shown on page 9 demonstrates how manufacturing support systems interact with the manufacturing system.
Through understanding the different manufacturing systems and manufacturing support systems, as well as how the systems interact, the seeds for automation are sown. The next section will define automation in more precise terms and identify specific types of automation.
Webster’s Online Dictionary (http://www.websters-online-dictionary.org/definition/ automation) defines automation as “a highly technical implementation; usually involving electronic hardware; automation replaces human workers by machines.” In his first book Automation, Production Systems and Computer-Integrated Manufacturing, 2nd ed. (2001), M.P. Groover defined automation, when directed strictly toward the manufacturing environment, as “...technology concerned with the application of mechanical, electronic and computer-based systems to operate and control production” (p. 9).
Each of these definitions provides some key terms and phrases. However, Webster’s definition implies that automation replaces or eliminates workers and that automation is accomplished only with machines—statements that are misleading. Automation does not always replace the worker; it more often displaces the worker to other tasks. Additionally, automation can be implemented in many forms. Often it is with a machine, but it can also be a device or software added to an existing process.
For example, consider the automation of the manual drafting process. The implementation of computer-aided drafting (CAD) is a great example of the automation of a manufacturing support system. CAD automates the creation of engineering drawings, a key component in the manufacturing material conversion process. Prior to the implementation of CAD, engineering drawings were created by hand with paper and pencil at drafting tables. The combination of computer hardware (the machine) and CAD software automated this process. Early CAD systems were two-dimensional and essentially duplicated the manual drawing process, but were much more accurate and faster than manual drafting. Human intervention was still required to operate the software, but to a lesser degree. Hence, manual drafters (the workers) were not replaced. The author observed in the plants with which he was associated that most of the drafters were trained to operate the CAD system. Since the CAD system is more productive than manual drafting, most excess drafters (workers) were displaced to other activities or other companies, and eventually an entire new generation of drafters trained primarily in CAD.
When companies first switched to CAD from manual drafting, a machine, the computer, was required. Computers have since become standard pieces of equipment in the engineering department. Hence, subsequent automation of the CAD process was accomplished only with software, an example of how automation does not always entail insertion of a machine into the process. Consider another example, solid modeling software. Solid modeling software automates the product development process, including the two-dimensional CAD drafting process. It models products as three-dimensional solid objects in the virtual world of a computer. The model enables better visualization of the product. Additionally, rapid prototypes, computer numerical control programs, and engineering drawings can all be created directly from this model.
The definitions above imply that automation only occurs in a production environment. However, automation can occur anywhere people are performing tasks. Consider a grocery store. Modern grocery stores have electronic barcode scanners to determine the price of goods purchased during checkout. The barcode scanners automated the task of a cashier manually entering the price of each item into the cash register. Now, many stores have added automated checkout, which allows the consumer to swipe the purchased goods and pay a machine directly, further reducing the level of cashier involvement. Often this allows more checkout lines than the store would normally be able to payroll. However, a worker is still needed to supervise the automated checkouts and assist shoppers as needed.
Machines and or systems that perform tasks automatically inevitably consist of some combination of mechanical technology (gears, cams, bearings...), electrical technology, and/or computer technology. Early automated machines were mostly mechanical. More modern automated equipment utilizes electrical and computer technology to a greater extent. Additionally, many automated machines or systems are combinations of many smaller automated machines. Thus, automated machines can be further automated with the application of even more technology.
The preceding discussion highlights the fact that a more encompassing definition of automation is needed than is typically found in the literature. So, the author defines automation here as follows:
Automation is the application of mechanical, electrical, and/or computer technology to reduce the level of human participation in task performance.
Note that in this definition “task” is an intentionally vague term. Tasks are not limited to work-related activities. They can be related to any activity requiring human participation. Consider the television remote control, for example. It automated the task of manually changing the television channel, a purely entertainment-related activity. The definition also makes clear that humans are not necessarily replaced. Their level of participation may be greatly reduced, typically displacing them to other activities. This point is important because often great fear exists in the workforce when system automation is considered. Workers inevitably assume that such automation will eliminate jobs, which, as discussed, does not always occur, particularly in a company that values its workforce. Thus, the distinction between “displacing” workers and “replacing” them needs to be emphasized. The other notable aspect of the definition is that it emphasizes that automation can be implemented with various forms and combinations of technology.
Now that a clear definition of automation has been established, the different automation types that have evolved in manufacturing are discussed.
1.3.1 Types of Automation
Automation in a manufacturing facility can occur in the manufacturing support systems and/or in manufacturing systems. Automation in manufacturing support systems is primarily accomplished through the use of computer technology to automate the business operations of the facility. Computer-aided design (CAD) software and computer-aided manufacturing (CAM) software have dramatically impacted the way products are designed and engineered. Shop floor control systems combined with material resource planning systems provide management with a very fast and accurate picture of a facility’s current status. Computer-integrated manufacturing (CIM) takes the automation of the manufacturing support systems a step further. CIM is intended to integrate and thereby automate the entire manufacturing enterprise. In other words, CIM links the automation in the manufacturing support systems directly with automation in the manufacturing systems, resulting in a completely integrated manufacturing facility. However, the focus of this text is not on the automation of manufacturing support systems. Rather, it is on a specific type of automation of manufacturing systems.
Automation in manufacturing systems is centered on reducing the level of human participation in manufacturing processes. Three standard types of automation can be defined. Each type has very specific capabilities relating to the sequence of the processing steps and the definition of the product being processed. The three types are:
• Fixed automation
• Programmable automation
• Flexible automation.
Fixed automation equipment typically consists of processing stations linked together with some form of material handling, which progressively moves the workpiece through the processing steps. Fixed automation can be considered special purpose automation because it is designed to automate a specific process or series of processes. Therefore, the processing sequence is fixed by the organization of the processing stations. In general, it is relatively inflexible in accommodating any type of product variety. However, if it is capable of handling soft product variety, conversion of the machine allowing it to run the variation may be time-consuming. The time to make this change is often termed “changeover time” or “setup time.” Fixed automation can handle a wide variety of product complexity from simple to very complex products; but, the cost of creating such a specialized machine is often quite high. Consequently, fixed automation is typically only used with extremely high volume products. To accommodate the volume, these systems operate at very high rates. Hence, fixed automation equipment is most often associated with flow-line manufacturing systems, often as assembly lines. Early fixed automation was created using mostly mechanical technology combined with electrical technology to drive its mechanical components. Current systems make extensive use of computer technology and often integrate programmable automation into the machine, as well.
Whereas fixed automation is “fixed” to a specific operation progression, programmable automation has the capability to alter both the type of operation to be performed and the order in which it is to be executed. Thus, it can adjust the process to accommodate the product, which makes it capable of handling hard product variety. Programmable automation equipment is multipurpose equipment that can be programmed, and repeatedly reprogrammed, to perform a wide variety of processing operations. However, each programmable automation machine is limited to a specific type of manufacturing process such as machining material removal, metal forming, or material handling. Reprogramming and changing tooling is necessary to accommodate the different products, creating long setup times between products. This combination of versatility, hard product variety, and long setup times would appear to limit programmable automation to use in the process manufacturing system. It is interesting to note that this is in fact the manufacturing system for which programmable automation was developed and where it is still primarily used. However, programmable automation equipment has proven to be so very capable and reliable that it is also used in the quantity and flow line manufacturing systems, either outside of or integrated into fixed and flexible automated equipment.
Flexible automation possesses some of the features of both fixed and programmable automation, with an added characteristic of no time lost for changeover between products. It utilizes, essentially, a fixed automation machine that can process soft product variety with no setup. The elimination of the setup is achieved with the versatility of programmable automation integrated directly into the machine. The machine recognizes or identifies different product configurations and automatically adjusts the operation sequence. The exorbitant cost of such a system limits its use to high volume applications typical of the flow-line manufacturing system. However, this added versatility means reduced production rates when compared with what is possible by a fixed automation machine.
Figure 1-7 summarizes the capabilities of each of the automation types.
Figure 1-7 Automation types
It should be noted that the lines of distinction between these three types of automation and the manufacturing systems in which they appear are often blurred. What should become clear is that programmable automation is at the core of both fixed and flexible automation. In fact, it has become a primary building block of almost all automated machines. Additionally, it is unlikely that a person would walk into any modern manufacturing facility and not encounter programmable automation, as it is found in practically every manufacturing system.
1.3.2 Programmable Automation
Improved productivity is the primary focus of global competition in the world economy. As will be shown in subsequent sections and chapters, automation is a key ingredient to improving productivity. Programmable automation, in some form, is found in almost all automation systems. It is used individually in process manufacturing systems, or it can be fully integrated into fixed automation machines in flow-line manufacturing systems. Flexible automation machines were not even possible prior to the development and maturation of programmable automation. Hence, it is imperative that manufacturing engineers and technologists understand the capabilities of this technology and how it may be used effectively.
Programmable automation, as is shown in Figure 1-8, has evolved into three distinct technologies:
• Computer numerical control (CNC) technology
• Robotic technology
• Programmable logic control (PLC) technology.
Computer numerical control (CNC) technology utilizes a combination of mechanical, electrical, and computer technology to move a tool relative to a workpiece to perform some type of processing. It is most often related to the machining processes, such as milling, turning, and grinding. However, it can be used in any process that requires precise control of a tool relative to a workpiece. Non-material removal examples include wire-bending machines and pen plotters. Some CNC technology examples are shown in Figure 1-9.
Figure 1-8 Programmable automation
Robotic technology is very similar to CNC technology in that it utilizes mechanical, electrical, and computer technology to move a manipulator in three-dimensional space. Also, in many applications it uses a tool to perform processing on a workpiece, an example of which is a welding robot: the robot moves the welding tool through a specific path over the workpiece. However, in many other applications the robot does not use a tool. It merely provides material handling capabilities such as moving a workpiece from one machine to another and/or stacking the workpiece in a specific pattern on a pallet. In either case, the robot is performing a task that could also be performed by a human. In fact, the origin of the term “robot” is credited to a play, which premiered in 1921, about a factory that made artificial people devoid of feelings. These artificial people were called robots. The word was derived from the Czech word robota, meaning serf labor, thereby implying servitude and hard work. Thus, robots are often distinguishable from other types of automation in that they possess humanlike characteristics (e.g., a robot arm) and perform tasks often completed by humans. Robotic technology examples are shown in Figures 1-10 and 1-13.
Figure 1-9 CNC technology
Figure 1-10 Robotic technology
Whereas CNC and robotic technologies provide motion control, programmable logic control (PLC) technology imparts automatic control over tasks or events through the use of electrical and computer technology. This is accomplished by monitoring the status of a given system through sensors that input information to the PLC. Based on the status of these inputs, the PLC will make decisions and take appropriate action on the system by outputting information to actuators. The output to the system is based solely on the status of the inputs. This is called a discrete process control system. A discrete system has inputs and outputs that are binary with two possible values: on or off. The status of these inputs and outputs change at discrete moments in time. Thus, PLC technology provides control over event-driven changes to the system. As events occur that change the status of the inputs, the outputs automatically change. Figure 1-11 shows an example of a PLC.
Figure 1-11 PLC technology
These three technologies are the foundation upon which modern automation is built. The automation system shown in Figure 1-12 makes good use of all three technologies. The figure depicts a typical manufacturing cell. A manufacturing cell is defined as an interconnected group of manufacturing processes tended by a material handling system. In this particular case, the manufacturing processes consist of a CNC lathe and a CNC mill. These two machines are tended by a robot, which loads raw material into one machine, transfers it to the next, and then unloads and stacks the processed material. A programmable logic controller (PLC) controls and coordinates activities between the CNC machines and robot. (Note that PLC is the acronym for both programmable logic control and programmable logic controller.)
Figure 1-12 Manufacturing cell
The CNC equipment, robot, and PLC must possess intelligence in order for the cell to function properly. The intelligence is expressed in terms of decision-making ability. Each machine in the cell must be able to accept input, make a decision based on that input, and implement the decision. For example, consider the CNC lathe. When it is time to process material, it must first recognize that it is ready to process more material and then prepare itself to receive material by opening safety gates, moving tooling out of the way, and opening the lathe chuck. Next, it must inform the PLC that it is ready to accept material for processing. Once the material is loaded, the CNC lathe must recognize that it is loaded and then process the material. When the processing is complete, it must prepare itself to be unloaded. Finally, it will inform the PLC that it is ready to be unloaded. The robot functions similarly. It receives input from the PLC that the lathe is ready to be loaded. It then executes a sequence of movements to pick up the raw material and load it into the lathe. It will then inform the PLC that it has loaded the material and is ready for the next instruction. Thus, the PLC is, essentially, the brain of the cell. It controls the timing and sequence of all events that occur within the cell. It monitors the status of the cell and informs each piece of equipment when and where actions are to be performed.
Figure 1-13 depicts another manufacturing cell. This cell consists of a hydraulically actuated press, a shuttle system, and a robot. In this cell, products (round disks) are molded inside the press then moved outside the press (with the shuttle system), where the robot unloads and finishes the product. A PLC controls the cell. Note that even though a CNC machine was not part of this particular cell, CNC technology had an impact on the cell. A CNC machine was used to produce the mold in the press and the gripper on the end of the robot arm.
Figure 1-13 Press manufacturing cell
Thus, as shown in these two examples, it is easy to envision how programmable automation is present, either directly or indirectly, in almost all modern automation systems.
1.4 Manufacturing Performance Measures
In order to understand when and where to apply automation in general and programmable automation in particular, it is essential to comprehend how manufacturing production performance is measured. From these performance measures one can evaluate and justify the use of automation. As will be seen in the next chapter, the performance measures used most often to quantify production include:
Production rate—measure of products per hour (pc/hr).
Setup time—measure of the amount of time to prepare a machine or process to make a product (hrs).
Production capacity—measure of the maximum amount of product that can be produced by a manufacturing facility, system, cell, or process in a specified period of time (output units/time period).
Utilization—ratio of the actual amount of output from a manufacturing facility, system, cell, or process in a specified period of time to the production capacity over the same time period (%).
Manufacturing lead time—total time to process a product through a manufacturing facility, system, cell, or process.
Each of these measures provides a picture of how certain individual aspects of the manufacturing process and system are performing. These are vital and critical measures to be evaluated when one considers automation. However, each only provides a small segment of the overall picture. Thus, the measures need to be evaluated collectively to effectively evaluate and justify the use of automation. There are other factors as well that should be considered, including burden rates of equipment and labor costs. Thus, it may be difficult to get a clear comprehensive picture of the performance of a process or system. However, there is one measure that effectively combines and summarizes many of the individual measures into one all-encompassing metric: That measure is productivity.
1.4.1 Productivity
The term “productivity” is often cited in the news media as an important economic indicator of the health of the nation’s economy. The U.S. Department of Labor, Bureau of Labor Statistics, collects and publishes productivity data for many elements of the U.S. economy. Per the Bureau of Labor Statistics website (www.bls.gov/bls/productivity.htm):
Productivity and related cost measures are designed for use in economic analysis and public and private policy planning. The data are used to forecast and analyze changes in prices, wages, and technology. (p. 1)
Thus, the measure plays an important role in the development of private sector and government economic policies. The interaction of productivity measurements on price changes, wages, and technology may be complicated, but the definition of productivity is not. While the term may have a slightly different connotation to an economist compared to an industrial engineer/technologist, the basic definition is clear. This simple definition is why this measurement, used as a means of quantifying manufacturing production, can be used in all levels of manufacturing. It is the author’s contention that the productivity measure is perhaps the best indicator of when and where to utilize automation.
As David J. Sumanth observed in Productivity Engineering and Management:
Productivity is concerned with the efficient utilization of resources (inputs) in producing goods and/or services (output.) (p. 4)
Note that “inputs” refer to all the resources (labor, material, capital, etc.) that go into producing the goods or service, and “output” is whatever is produced by the system under consideration. Thus, the productivity of a manufacturing system can be determined simply by the ratio:
productivity = output/input
For the purposes of this text, output will be expressed in units of parts/hr and input in terms of $/hr.
In order for the productivity ratio to rise, either the output must increase (more parts/ hour) or input must decline (amount of product remains the same with less resources). Productivity increases are positively viewed because they indicate that more is produced with less dollar input to the system. Therefore, if the selling price of the product does not change, the producer realizes an increase in profit. Conversely, a decrease in productivity occurs when not as much product is being produced and/or the input cost increases. Typically, all inputs (labor, raw materials, and energy costs) will increase over time. To prevent these increases in inputs from being passed along to the consumer as a price increase, more products must be produced. Note that this is the link of productivity to inflation. Therefore, it is obvious that improving productivity is of vital importance to manufacturing. Equally as obvious is how automation can improve productivity by allowing more products (output) to be made or by reducing the cost (input) of production.
The way a company can use productivity and the other manufacturing measures to justify automation will be addressed in detail in Chapter 2.
Specific reasons to automate one process may be very different from the reasons to automate another. However, the goal of any automation is to produce a tangible benefit. Common to all automation is the benefit of productivity improvement. Listed below are seven common reasons to automate:
Increase labor output
Increasing labor output has a direct effect on increasing productivity. If, through automation, the amount of product is increased, the productivity also increases. Essentially, automation focused on improving the effectiveness of the labor, thereby increasing the amount of product made over a specific time period, will lead to increases in labor output and, thus, productivity improvements. Examples include addition of a robot to handle material or use of a PLC to control a manual process. Each is intended to “free up” the worker from a task, thereby enabling him or her to produce more.
Reduce labor cost
Reducing labor cost also has a direct effect on increasing productivity. Because labor cost is an input in the productivity formula, reducing it increases productivity. In fact, from a productivity viewpoint it is difficult to distinguish reducing labor cost from increasing labor output because the net effect is the same. However, it is listed as separate to emphasize that some automation strategies focus on improving the amount of output produced from the current number of workers whereas others specifically target reducing labor costs. Examples of labor cost reduction include any type of automation that reduces the number of workers or the time each worker spends in production.
Reduce or eliminate effects of labor shortages
Depending on the state of the local economy, a plant may have an abundance of available workers or a severe shortage. If the manufacturing process is particularly labor intensive, lack of workers can result in machine down time, less product, and overtime for the current workforce, each of which can have a detrimental effect on productivity. Making the process less labor intensive through automation allows it to better withstand periods of labor shortages. Thus, automation strategies geared to increase labor productivity and/or reduce labor costs should be considered.
Reduce or eliminate routine manual and clerical tasks
Reduction or elimination of routine tasks is often the first avenue to improving a process’s productivity. Automating these types of tasks, once again, frees up the worker to perform more value-added tasks. This inevitably leads to productivity improvements through reduced labor costs and/or improved worker productivity. A good example is the automation of the engineering drawing process with computer-aided drafting (CAD).
Improve worker safety
Any opportunity to provide a safer worker environment is a worthwhile investment in any process, not only from the obvious benefit of worker protection—management’s ethical responsibility—but also from a productivity standpoint. Down time due to accidents also decreases productivity by limiting output from the process. Yet, physical safeguards intended to protect the worker might also hamper output. A better approach would be to utilize automation and completely remove the worker from the dangerous work environment. This should be attempted even if a productivity gain is realized or not. An example of such precautionary automation might be utilization of a robot to remove parts from an injection press. For a worker to remove parts from the mold, the press door must be opened, which activates mechanical interlocks that prevent the mold from closing as the worker removes the parts. But, if a robot removes the parts, the worker is no longer required to reach in the press, thus removing him from the dangerous environment. Additionally, the press cycle time improves because opening and closing the door is removed from the process since the robot typically accesses the mold from the top of the machine.
Improve product quality
Improving a product’s quality yields many benefits to the manufacturer, including reduced waste—a plus for both the business and the environment, which makes for better brand image and higher sales. The impact on productivity is equally impressive. Reduced waste reduces material costs, which decreases inputs to the process, thus increasing productivity.
Reduce manufacturing lead time
Manufacturing lead time is a measure of how long it takes to create a product from the time the order is received by a manufacturer until the product is shipped. If through automation the manufacturing lead time is reduced for a process or a series of processes, output will increase over a given time period. If all other inputs remain unchanged, productivity will increase.
Some other reasons for automation often referenced in the literature, which are tied indirectly to productivity, include: (1) the high cost of not automating and (2) the existence of processes that simply cannot be done manually. The first is a somewhat obvious statement, regarding which the above list makes a strong case. In today’s economy productivity improvements are perhaps the only way to remain competitive. If a company is not competitive, it will not survive. Therefore, the cost of not automating will be in terms of lost customers and profits.
Consider the second of these, performing processes that cannot be done manually. Some processes may require too high of a degree of precision or be too small for the human hand to effect or have too complex a geometry. Ponder the manufacture of computer chips. Arun Radhakrishnan, writing in http://blogs.techrepublic.com.com/tech-news/?p=2050), pointed out that in 2008 Intel announced a new computer chip containing 2 billion transistors. Obviously, this can only be produced with the aid of automated machines; without the automation to manufacture it, the product could not be made and thus productivity would be zero.
Thus, there may be many reasons to automate, but the primary benefit to automating is improved productivity. When a company continuously improves productivity it is better able to absorb raw material cost increases, labor cost increases, increased energy prices, and other inflationary types of cost pressures—without passing those increases along to the customer. Thus, by improving productivity the company may realize other benefits including higher sales, better customer relations, and a larger market share. Although automation is not the only method to improve productivity, it is often a very effective method and should therefore be strongly investigated.
The why and where of automation are listed in the preceding section. We now turn to the how of automation. Typically, how a plant would automate is one of the more challenging aspects of the automation implementation process. One example was given already, that of employing a robot to perform material handling or adding a PLC to control the process. It is the intent of this section to provide some strategies that can be used to determine how a particular process might be automated.
In the aforementioned Automation, Production Systems, and Computer-Aided Manufacturing, 2nd ed. Groover introduced 10 strategies concerning how automation can be applied to manufacturing processes. Based on this list, five condensed “how to” strategies, geared specifically for programmable automation, are given here:
Minimize manufacturing process steps
As explained, a series of manufacturing process steps convert raw materials into some other higher value form. This strategy seeks to minimize the number of process steps. It does so by combining process steps, as might be done by the performance of more than one process on a single machine. Once operations are combined, it may then be possible to perform processes simultaneously. If processes cannot be combined, it may be possible to integrate several processes into a single machine or work cell. The integration could be in the form of several machines linked together with automated material handling devices. Thus, the cell will have the appearance of a single machine. Whichever method is used the result is the same: manufacturing process steps are minimized. Minimizing process steps can lead to large productivity gains by reducing input to the process and perhaps improving output rates from the minimized process.
Increase process flexibility
Improving process flexibility enables a machine or operation to process more product variety. The flexibility is achieved by minimizing or eliminating setup time typically required in changing a machine over to another product line. This is the essence of flexible automation systems. When a particular machine is able to process more product variety, the machine’s utilization increases, manufacturing lead time decreases and work in process is reduced. This can result in a substantial increase in productivity because inputs (time, labor, ...) are reduced, assuming of course that system output remains the same or increases. This strategy will also likely involve use of the all three programmable automation technologies.
Optimize material handling
Material handling is a non-value-added component of the material conversion process and thus should be optimized. Machines can often move material more consistently, accurately, and reliably than manual labor. Additionally, labor, freed up from performing material handling tasks can be displaced to perform value-added tasks. Thus, the increase in productivity may come from reduced labor costs, increased production rates, and reduction in scrap and rework. Optimizing material handling may involve a combination of mechanical technology systems, including conveyor systems, indexing units, and pick-n-place units, with robotic and PLC technologies.
Automate inspection
Product inspection determines if a product is within specifications. Often performed offline or outside of the process, inspection gives feedback about how a process is performing, and information gathered from inspection is typically used to adjust a process as needed. The feedback loop—make a part, inspect it, adjust process—can be rather long. Hence, products outside of specification (“off spec”) could be completed before the process that made them is adjusted. Automatic inspection is an attempt to minimize the feedback loop and thereby reduce scrap and rework. And, of course, a more consistent, higher quality product is produced. To sum up, raw material usage is reduced and output is increased, resulting in substantial productivity improvements. Automatic inspection systems may utilize material handling technology, including robotics, electronic vision systems, electronic sensors, actuators, and PLC technology.
Implement process control
To produce a high quality product it is necessary to have a consistent, repeatable, and reliable process. To achieve this, a process must be rigorously controlled. Programmable logic controllers are capable of providing this level of control, providing it over event-driven changes to the process. Based on the status of these events, the PLC will make decisions and take appropriate action on the system. This enables fast, reliable control of the process and greatly improves its efficiency. In addition to greater efficiency, process output and product quality are also improved.
Note that a particular automation project may focus on only one strategy or include all five. Keep in mind that not all processes can or should be automated. Some processes may be too technologically difficult to economically automate. For others, the product life cycle is so short that automation cannot be justified. In some cases it may appear that the cost of the automation is completely justified based on the anticipated productivity improvements, but later it may be discovered that is simply not the case. Thus, it is imperative one have a sound method of justifying where and when to use automation. The next chapter deals with this subject in detail.
Programmable automation technology is the combination of mechanical, electrical, and computer technology developed to have very specific automation capabilities. Programmable automation consists of three individual technologies that are linked together by their capacity to be programmed. These technologies include computer numerical control (CNC) technology, robotics technology, and programmable logic control (PLC) technology. These technologies are in use in almost all modern manufacturing facilities and together make up the technological foundation of automation.
Manufacturing converts a raw material into a more useful product that can be sold for a profit. The manufacturing operations that are necessary to produce a particular product include manufacturing processes, material handling, quality control, and manufacturing support. Manufacturing processes are the manufacturing steps that perform the actual physical conversion. They can be classified as shaping processes, property-enhancing processes, and assembly processes. A particular manufacturing process will follow a systematic sequence of operations called a program of instructions. The way in which the manufacturing operations and workers are organized defines the manufacturing system used by the facility.
The manufacturing system in use in a facility is dictated by the finished product’s product definition, which is determined by its complexity, variety, and quantity. Product complexity relates to the difficulty of its production process. Product variety refers to how many different product designs, versions, or models are to be produced within the facility. Product variety can be either hard or soft. Soft product variety indicates there are only subtle differences between product models. Hard product variety indicates vastly different products are to be produced.
The four standard manufacturing systems include fixed-position, process, quantity, and flow-line. Fixed-position manufacturing systems are used to produce large complex products. The process manufacturing system is used when product complexity is relatively low and there is hard product variety. The quantity manufacturing system and the flow-line manufacturing system produce mass quantities of products and are thus called “mass production systems.” The quantity manufacturing system is used with low product complexity and hard product variety. Flow-line manufacturing is for products with high product complexity and soft product variety.
Manufacturing support systems provide the management of the business operations of the facility and of the manufacturing system; they process information necessary to accomplish the conversion of the raw material into the finished product.
Automation is defined as the application of mechanical, electrical and/or computer technology to reduce the level of human participation in performing tasks. Fixed automation, programmable automation, and flexible automation are the three automation types. Fixed automation equipment typically consists of processing stations linked together with some form of material handling, which progressively moves the workpiece through the processing steps. Whereas fixed automation is “fixed” to a specific operation progression, programmable automation has the capability to alter both the type of operation to be performed and the order in which it is to be executed. Flexible automation possesses some of the features of both fixed and programmable automation with an added characteristic of no lost time for changeover between products. It is essentially a fixed automation machine that can process soft product variety with no setup.
CNC technology is one of the three distinct types of programmable automation that utilize a combination of mechanical, electrical, and computer technology to move a tool relative to a workpiece to perform some type of processing. Robotic technology is very similar to CNC technology in that it utilizes mechanical, electrical, and computer technology to move a manipulator in three-dimensional space. Whereas CNC and robotic technology provide motion control, PLC technology imparts automatic control over tasks and events through the use of electrical and computer technology. These three technologies are the foundation upon which modern automation is built.
The benefits of implementing automation come in many forms, each of which can almost certainly be expressed in terms of productivity improvement. The productivity of a manufacturing system is expressed as a ratio (%) of system output to system inputs. Productivity measure is perhaps the best indicator of when and where to use automation. Methods of improving productivity include increasing labor output, reducing labor input, reducing or eliminating labor shortages, reducing or eliminating routine manual and clerical tasks, improving worker safety, improving product quality, and reducing manufacturing lead time.
Some strategies to consider for implementing automation include minimizing manufacturing process steps, increasing process flexibility, optimizing material handling, automating inspection, and implementing process control.
assembly line manufacturing system
automation
batches
computer numerical control (CNC) technology
continuous products
conversion process
discrete process control system
discrete products
fixed automation
fixed position manufacturing system
flexible automation
flow-line manufacturing system
hard product variety
job shop manufacturing system
lead time
lot size
manufacturing
manufacturing cell
manufacturing lead time
manufacturing operations
manufacturing processes
manufacturing setup
manufacturing support systems
manufacturing systems
process manufacturing system
product complexity
product definition
product quantity
product variety
product volume
production capacity
production rate
productivity
program of instructions
programmable automation
programmable logic control (PLC) technology
quantity manufacturing system
robotic technology
soft product variety
utilization
1. Define programmable automation.
2. What hampered programmable automation’s initial use?
3. What member of the engineering staff is best suited to implement programmable automation?
4. Discuss how a manufacturing facility takes raw material and transforms it into a finished product.
5. Define the term “program of instructions.”
6. List and discuss the four typical manufacturing operations.
7. List and explain the factors that determine a finished product’s product definition.
8. Define and discuss the four standard manufacturing systems. Focus your explanation on the type of products produced by each system.
9. What is the difference between a manufacturing system and a manufacturing support system?
10. Define automation and the three major types.
11. What technologies fall under the programmable automation category? Include a definition of each.
12. Discuss the five performance measures of manufacturing.
13. What manufacturing performance measure combines and summarizes many of the individual measures into one all-encompassing metric?
14. Define productivity and provide three examples of how to improve it.
15. Discuss the five automation strategies defined in the chapter.
1. http://www.websters-online-dictionary.org/definition/automation Groover, M.P. (2001) Automation, Production Systems and Computer-Integrated
2. Manufacturing, 2nd ed., Prentice Hall, Upper Saddle River, New Jersey
3. Sumanth, David J. (1994). Productivity Engineering and Management, McGraw-Hill
4. Kandray, Daniel E. (2004). Comparison of fixed automation and flexible automation from a productivity standpoint, Society of Manufacturing Engineers Technical Paper TP04PUB206
5. Machinery’s Handbook, 25th ed. (1996). Industrial Press, Inc., New York, New York
6. http://www.websters-online-dictionary.org/definition/productivity
7. Radhakrishnan, Arun (2008). Intel Announces Two Billion Transistor Computer Chip, IT News Digest, February
