LECTURE 1: Intro, Systems Overview;
Course Objectives
In this course, we shall learn about the different aspects of factory automation and its components. At the lowest level, we study sensors and actuators that control the physical process. At the highest level, we learn high level programming languages, and write software which shall ultimately drive the actuators. We study the structure of the control logic, and its implementation. It is by complete understanding of each element of this interface that we can design automated factories for any particular application. The most significant element of automation in modern industry is the growing use of computers and electronic controls. In keeping with this, the course shall concentrate on computers and computer applications.
History of Automation:
The concept of automated factories is not old historically. The first organized automation is believed to have sprung out of the industrial revolution in England in the latter half of the 18th century. Some of the landmark events in these 200 years of rapid industrialization include:
• Outburst of mechanization due to the Industrial revolution, 1770.
• Henry Ford and the development of hard automation and transfer lines, 1900.
• Machine tools with automatic controls; e.g. copying machines with a stylus to traverse the master copy in order to generate an electrical signal for the servomotor drive.
• Numerically Controlled (NC) machine tools, 1952 (US Air Force, MIT).
• Rapid development of microchip computers, late 1960's.
• CNC (computer numerical controlled) machine tools.
• Industrial Robots (1970's).
• Computer networks (1970's).
• Factory of the future: fully automated, Flexible Manufacturing Systems (FMS) for high flexibility, 1990's.
Industrial automation can be at any level of operation of the factory:
• equipment level
• MRP and mps
• databases
• inventory
• automatic order processing (communications)
• personnel and other record-keeping
Why Automate?
• Improved quality: Interchangeability, increased life
• Precise control with Shorter response time
• Shorter processing time: low lead-time, lower work-in-progress time, lower inventory
• Safer work-place: hazardous substance handling, chemicals handling, heavy/unwieldy materials handling
Less waste: repeatability
Figure 1.1. Basic Structure of an Automatic Control System
Open Loop Vs Closed Loop Systems
Control structures can basically be looked upon as open loop or feedback systems.
Figure 1.2. Open Loop Control
Figure 1.3. Closed Loop (feedback) Control
Although open-loop systems are easier to implement and also cheaper, they cannot, in general, match the performance of closed loop systems. Closed loop systems monitor the actual output, and modify the input automatically according to the current output. In this way, the final condition of the output device can be brought arbitrarily close to the desired value. Accuracy as well as repeatability of closed loop systems are at least equal to (and usually better than) open-loop systems. Open-loop systems, however, are cheaper, and usually lighter (since there is no sensor to be mounted on the operated device).
The use of computers in Industry provides one thing: automation. What is industrial automation ? Any activity that is controlled by some means other than human can be said to be automated. Automation can be achieved without computers, by purely mechanical devices, or electro-mechanical devices, or even chemical means. In this course, we learn about those methods of automation that either directly, or indirectly, involve the potential use of computers.
At the outset, let us look at a hypothetical scenario to display the versatility of computerized automation of factories.
Mr. Co runs a small shop building garden tables. He purchases pre-fabricated plastic table-tops from a manufacturer Pi_Co; and aluminum tubes from Ai_Co; screws from Si_Co. In his shop he has a saw, a tube bending machine, and a drill. The aluminum tubes are cut to the right length, bent, and holes drilled into them to allow fixing them to the table-top. He supplies tables to two shops in MongKok, who place orders with him once a month.
Figure 1.4 The physical, communications, and processing structure
His tables become popular, and many other shops, some even in TST, place orders with him. Orders come in at random time intervals.
Too much paperwork, keeping track of all orders. He decides to buy a small computer to maintain the order information. He buys Microsoft™ Access, a database program, and creates a database of all orders. Each time a new order is placed, he enters a new record in the database with information of incoming time, due date, quantity, address of shop.
Figure 1.5 Improved processing and communications
Now he can check in an instant, which is the earliest due order; where to send a delivery; how many tables he needs to manufacture each week to fulfill demands; how much total demand he has at the moment, etc.
Business is very good! Next month he needs to manufacture 5000 tables. But the tube supplier can only provide enough tubes to make 3000. So he goes to Aj_Co to purchase the remainder of tubes. Similar problems in supply of other components make him to go to different suppliers Sj_Co, Sk_Co, Pj_Co for extra supplies. Now he has to keep track of supply-orders he places with each company. Since they charge different prices, he would always like to buy as much as he can from the cheapest source.
He enters all supplier information in another database, including supplier addresses, orders placed with them, promised delivery dates, price quoted, and maximum supply quantity per month.
Then he gets a brilliant idea: why not automatically generate demand required using the computer also ? He knows that each table requires:
1 table top;
8 screws;
4 m of aluminum tube on the average;
He purchases a spreadsheet software called Microsoft™ Excel. Each time a new order is placed with him, the spreadsheet automatically calculates how much of each input he needs. By looking at the supplier database, he can easily find which supplier quoted him the least cost for each input, and how much he has already ordered for this month. If this amount is less than the maximum supply volume, he places the order for the new quantities.
Figure 1.6. Further improvements
But now a new problem arises. His workers are running the drill, bending machines and saw continuously, and still cannot produce all his demands. So he thinks of purchasing more machines. He discovers that most machine tool makers are now making sophisticated, Numerically Controlled machines. These machines are expensive, but the automatic saw can be programmed in such a way that he can load hundred uncut tubes in the holder, and it feeds and cuts them automatically. The production rate of the machine is twice as fast as the one he has. Now he is equipped with some more machines, and can manufacture much higher volumes.
Figure 1.7. Automating the shop floor
He had to expand the shop floor to accommodate the new machines.
Since he has excess capacity, he decides to diversify. So he begins making chairs, and also different sizes, shapes, and colors of tables. He purchases more machine tools, and hires more workers. The chair bodies are ordered from vendors. The tubes have to be cut and bent to different sizes depending upon which type of table/chair they will be used in. He has to:
- create and maintain databases for each new supplier
- update all databases to include additional information, like table-top color, order requests for different product lines, etc.
- maintain NC programs for different products.
Now he is producing different products in batches. There is a lot of traffic on the shop floor, with workers carrying pipes and other materials between machines. To facilitate the material flow, he installs a material handling conveyor.
He purchases another PC, on which he runs software to control the shop floor activities. His new PC can also directly communicate with the NC machines. This way, he can keep operating the machines, and simultaneously be writing programs for machining different parts. The PCs and machine controllers are connected to form a network.
Figure 1.8. Towards sophisticated automation
Business improves: He decides to open another factory in Guangzhou. Since the main office is still in HongKong, all the order processing and mps is controlled from there. The automated factory in Guangzhou has its own shop-floor controlling LAN (local area network), and inventory planning. The computers in the two factories can connect any time, using phone lines, to communicate.