Mehmet Özer, 030070050, 2nd Week Answers (03.03.2012)

1.Closed-loop Control (control)

Previous Answer:

There are two different types of circuits to control an operation of a NC machine. One of them is closed-loop system which is equipped with various transducers, sensors and counters that accurately measure the position of the work table. Through feedback control, the position of the work table is compared against the signal and the table movements terminate when the proper coordinates are reached.

(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, pg 1156)

New Answer: (better)

In some automated processes, the work cycle program must contain instructions for making decisions or reacting to unexpected events during the work cycle. Examples of situations requiring this kind of capability include (1) variations in raw materials that require adjusting certain process parameters to compensate, (2) interactions and communications with human such as responding to requests for system status information, (3) safety monitoring requirements, and (4) equipment malfunctions.

 The program of instructions is executed by a control system, the third basic component of an automated system. Two types of control system can be distinguished: closed loop and open loop.Aclosed loop system, also known as a feedback control system, is one in which the process variable of interest (output of the process) is compared with the corresponding process parameter (input to the process), and any difference between them is used to drive the output value into agreement with the input. Figure 38.3(a) shows the six elements of a closed loop system: (1) input parameter, (2) process, (3) output variable, (4) feedback sensor, (5) controller, and (6) actuator. The input parameter represents the desired value of the output variable. The process is the operation or activity being controlled; more specifically, the output variable is being controlled by the system. A sensor is used to measure the output variable and feed back its value to the controller, which compares output with input and makes the required adjustment to reduce any difference. The adjustment is made by means of one or more actuators, which are hardware devices that physically accomplish the control actions.

(M. P. Groover, Fundamentals Modern Manufacturing 4^th Edition , pp.888-889)

2.Material Handling (organization – setting order)

Previous Answer:

Material Handling is defined as the functions and systems associated with the transportation, storage and control of materials and parts in the total manufacturing cycle of the product. Several factors have to be considered in selecting a suitable material - handling method for a particular manufacturing operation:

1- Shape, weight and characteristics of the parts

2- Types and distances of movements, and the position and orientation of the parts during movement and at their final destination.

3- Conditions of the path along which the parts are to be transported.

4- Degree of automation, the level of control desired, and integration with other systems and equipment.

5- Operator skill required

6- Economic considerations

 (Manufacturing Engineering and Technology, S. Kalpakjian, S.R. Schmid, 5th Edition Pages: 1163 - 1164)

New Answer: (better)

Material handling is defined as ‘‘the movement, storage, protection and control of materials throughout the manufacturing and distribution process’’1 The term is usually associated with activities that occur inside a facility, as contrasted with transportation between facilities that involves rail, truck, air, or waterway delivery of goods. Materials must be moved during the sequence of manufacturing operations that convert them into final product.

Materialhandling functions inmanufacturing include (1) loading and positioning work units at each workstation, (2) unloading work units from the station, and (3) transporting work units between workstations. Loading involves moving the work units into the production machine from a location in close proximity to or within the workstation. Positioning means locating the work units in a fixed orientation relative to the processing or assembly operation. At the end of the operation, the work units are unloaded or removed from the station. Loading and unloading are accomplished manually or by automated devices such as industrial robots. If the manufacturing operations require multiple workstations, then the units must be transported from one station to the next in the sequence. In many cases, a temporary storage function must also be provided by the material handling system, as work units await their turn at each workstation.The purpose of storage in this instance is to make sure that work is always present at each station, so that idle time of workers and equipment is avoided.

Material handling equipment and methods used in manufacturing can be divided into the following general categories: (1) material transport, (2) storage, and (3) unitizing.

(M. P. Groover, Fundamentals Modern Manufacturing 4^th Edition , pp.918-919)




3.Sensor Fusion (control)

Previous Answer:

Sensor fusion basically involves the integration of mutiple sensors in such a manner that the individual data from each of the sensors (such as force, vibration, temperature, and dimensions) are combined to provide a higher level of information and reliability. A common application of sensor fusion occurs when someone drinks from a cup of hot coffee. Although we take such an everyday event for granted, it readily can be seen that this process involves data input from the person's eryes, lips , tongue, and hands. Though our basic senses of sight, hearing, smell taste, and touch, there is real-time monitoring of relative movements , positions, and temperatures. Thus if the coffee is too hot, the hand movement of the cup toward the lip is controlled and adjusted accordingly. (Kalpakjian, Smith; Manufacturing Engineering and Technology, 5th edition, p. 1175)

New Answer: (better)
There is some confusion in the terminology for fusion systems. The terms “sensor fusion”, “data fusion”, “information fusion”, “multi-sensor data fusion”, and “multi-sensor integration” have been widely used in the technical literature to refer to a variety of techniques, technologies, systems, and applications that use data derived from multiple information sources. Fusion applications range from real-time sensor fusion for the navigation of mobile robots to the off-line fusion of human or technical strategic intelligence data [Rot91].

Sensor Fusion is the combining of sensory data or data derived from sensory data such that the resulting information is in some sense better than would be possible when these sources were used individually.

The data sources for a fusion process are not specified to originate from identical sensors. McKee distinguishes direct fusion, indirect fusion and fusion of the outputs of the former two [McK93]. Direct fusion means the fusion of sensor data from a set of heterogeneous or homogeneous sensors, soft sensors, and history values of sensor data, while indirect fusion uses information sources like a priori knowledge about the environment and human input. Therefore, sensor fusion describes direct fusion systems, while information fusion also encompasses indirect fusion processes.

(Elmenreich, W. Sensor Fusion in Time-Triggered Systems, PhD Thesis, pp.7-9)




4.Counter sinking (manufacturing method)

Previous Answer: (better)

Countersinking is the shaping of a hole or depression to conform to the shape and thickness of a flat or oval screwhead; it is done with a cone-shaped cutter called a countersink. The angle at which the depression is cut is standard, being controlled by the countersink, which in turn is made to conform with the angle of the underside of the screwhead. The purpose of countersinking is to permit the head of a flathead screw to set flush with or slightly below the surface of the wood. A hole that is to receive a flathead or ovalhead screw is first bored, then it is countersunk on the surface which the screw enters. The depth to which a hole is countersunk will depend on the thickness of the screwhesd. This thickness is measured from the point where the body of the screw ends and the head starts, to the widest part of the head.

(Fundamentals of shopwork, p. 169)

New Answer:

countersinking - is an operation that adds a chamfer at the entry end of a hole. A rotating cutting tool, with the edge set to the angle of chamfer desired, is fed into the hole and removes material at the edge. The tool is centered by the hole; therefore the chamfer is concentric with the hole's axis. The operation is typically used to remove burrs or a sharp edge at the end of a hole, or to provide space for a tapered screw head or other tapered object.

(Bralla, J. G., Handbook of Manufacturing Processes, How Products, Components and Materials Are Made, p.94)




5.Notching (manufacturing method)

Previous Answer:

To obtain the desired outline of a blank, portion of the sheet metal are often removed by notching and seminotching.Notching involves cutting out a portion of metal from the side of the sheet or strip.Seminotching removes a portion of metal from the interior sheet.

(Mikell P.Groover "Fundamentals of modern manufacturing" Second edition,page 441)

New Answer: (better)

notching - is punching or piercing performed at the edge of the work piece. The edge of the strip or blank becomes part of the perimeter of the piece that is removed. The operation is performed when the shape of a blank is too complex to fully incorporate in a blanking die, for low-quantity work when complex tools are not justifiable, to free material for a subsequent forming or drawing operation, or to remove material that would otherwise be distorted in a subsequent operation. A work piece with several notching operations performed is illustrated in Fig. 2C5b.

(Bralla, J. G., Handbook of Manufacturing Processes, How Products, Components and Materials Are Made, p.45)