Programmable Automation Technologies. Daniel Kandray
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,