WORK PROCESSES -simplified overview

Post 657 -by Gautam Shah

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Workshops till middle age were craftspeople oriented. A crafts person would occupy a place surrounded by tools and equipments and carry out the ‘Lot’ of work. After that another person took over that lot. For heavy duty jobs mechanical power drives were superior, but one had to shift around to use them. Mechanical devices like gears, leather belt transmission and offered greater productivity. Some degree of task assignment offered standardized products on a massive scale. The power shaft forced organization of workshops on linearity. The line production methods promoted productivity through time management and sequencing of task procedures. In many instances tasks began to be assimilated and handled simultaneously by many crafts-persons in a single time slot.

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power shaft pulley beltsDuring the early part of the 20th C. machines became adjuncts to assembly-line production systems and multi tasking. For this machine became a device to handle a variety of tools, often simultaneously. The machines were operating at a faster speed requiring equally fast control system.

595px-Machine_shop_in_the_Government_Printing_OfficeMechanical power transmission systems were concurrent systems for the entire workshop, but this impediment was removed with the electric power. Electrical power offered local control through an electric motor through horse power rating, speed variation through voltage control and gears, and operational control like start-stop, etc. Independent electric powered machines with faster and multi tasking capabilities, however, were now difficult for human supervision. Control devices were actuators, for process regulation.

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Control devices or systems are of two types: A Feed-forward system has inputs or predicts unusual happening, but would not oversee or govern the actualization of the action. A Feedback system improvises strategy for future actions in many instances oversees actions being taken.

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Feed-forward systems: Jacquard weaving loom uses a feed-forward control as a programmed punched card to weave a pattern, but cannot stop the loom if there is a short feed of thread. Similarly a cutting machine cuts a large sized shape by moving the cutter tracing a small scale pattern through the arm of a pantograph.

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Feedback systems: A wind mill keeps facing the wind with the help of a tail wane. A pressure cooker seals itself with heightened internal pressure of steam. Pressure valves are weight calibrated opening themselves at certain pressure levels only.

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Control devices and systems have led to automation of processes. Automation began in the late 1940s with the development of the mechanical devices for moving and positioning objects on a production line, though observation and manual intervention were necessary. During 1960s digital computers began to offer control systems in three different manners: For supervisory or optimizing control, Direct digital control, and Hierarchy control. In the first instance, for the supervisory control a computer sets parametric levels for optimizing the operations. In the second instance, for the direct-digital control, several devices feed data to a single processor, which then decides a strategy of operation. The advantage here is very fast and objective evaluation of the data. The third system the hierarchy control applies to all the plant-control situations concurrently, often with the actuation of the control mechanisms.

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MACHINE TOOLS and MACHINES

Post 297 – by Gautam Shah

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Machine tools are power driven utilities, and are of two basic types: Hand held or mobile tools and Stationary tools. Hand-held tools are apparently small, and lightweight. Whereas stationary tools often called, Machine tools, are large, fixed to a position. The large size requires stationary positioning. Both types of machine tools are classifiable into home or hobby machine tools and Industrial or Engineering machine tools.

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Machines and machine tools both are automated entities, and so have slightly overlapping categorization. A machine is a specific product entity which can be conducting several sequential or concurrent processes. A machine tool is a multi-purpose entity, and used for several processes. It can have attachments of (non-machine) tools, or it may be part of a machine. All machine-tools are a type of machine, but conversely all machines may not be called machine tools. To use a tool or machine tools some form adaptation, recognized as craftsmanship is required. Machines do not need personal creativity or craftsmanship except basic technical knowledge.

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Machines and machine tools are powered by human, animal, kinetic, hydraulic and pneumatic power, wind mills, steam and electric power. Machine tools need to be manipulated or the feed-stock requires positioning, adjustment, etc. When this input processes are guided or automated, a machine tool becomes a machine. The guidance or automation may be to free the hands, other limbs and sensory nodes. So, in this sense a machine can have several machine tools, each of which has time-space feeds mechanisms. Advance machines have feed-forward and feed back systems to reduce or correct errors.

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A machine-tool can take up various types of tools. Such as a drill can take different types of bits or a potter uses different shapes of spatulas to shape and finish the turned-clay item. A CNC machine, has predefined set of feed-guide processes controlled by the computer input. A machine tool that is handy will have to be very quite and vibration free. Very fine work tools like a dentist or orthopaedic surgical drills are operated through pneumatic or compressed air, rather then electric motors. The pneumatic technology offers vibration free and noiseless movement at very high speeds. Similarly Air-jet looms working on suction reduce the nominal noise associated with yarn bobbin shuttles.

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Machines were stationary entities due to the robust size, stability and power needs. This created batch production system, creating lots of cross traffic within the plant. Batch production with fixed machines required power locally. This was difficult proposition when steam or a large electric motor generated power was transferred through shafts and belts to the machine. Batch based products tended to be holistic in nature. The need for faster production forced rethinking of product design into component-based entities. Components were produced by machine tools or machines and brought to the assembly line. The assembly line was operated through handy machine tools.

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Assembly lines had many grey areas. A slowdown or stoppage affected the entire production systems. Processes, tasks, etc., were carefully apportioned in terms duration, speed and space. All these studies provided opportunities for automation of assembly processes. The automation allowed multiple operation at a station which drastically reduced the length of assembly lines. The automation is now seen in use of robots handling several processes at a station. A human assembler cannot go into narrow spaces, take difficult body postures and require rest or diversion, but a robot is beyond these difficulties. A robot is a machine with several machine tools.

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