1)EWMA Charting: (Statistic)
An exponentially weighted moving average chart is a control chart for variables data. ıt plots weighted moving -average values. A weighting factor is chosen by the user to determine the relative impact of older data to more recent data on the calculated moving average value. Because the EMWA chart uses information from all samples, it detects much smaller process shifts than a normal control chart.
An exponentially weighted moving average chart is a control chart for variables data. ıt plots weighted moving -average values. A weighting factor is chosen by the user to determine the relative impact of older data to more recent data on the calculated moving average value. Because the EMWA chart uses information from all samples, it detects much smaller process shifts than a normal control chart.
(Six Sigma Demystified, Keller P, Page: 247)
EWMA Charting:(new) (better)
Each point on an Exponentially Weighted Moving Average (EWMA) Chart, also referred to as a Geometric Moving Average (GMA) chart, is the weighted average of all the previous subgroup means, including the mean of the present subgroup sample. The weights decrease exponantially going backward in time. The weight (0 < weight ≤ 1) assigned to the present subgroup sample means is a parameter of the EWMA chart. Small values of weight are used to guard againist small shifts.
(JMP 8 Statistics and Graphics Guide,SAS Publishing,p.1002)
2)Emergency Stop (new) (Safety)
An emergcy stop is manually operated hardware (e.g. palm buttons, trip wires) which can be easily used when needed to quickly put the systems into a safe state and maintain this state until a safe, intentional restart is accomplished.
Optimally, emergency stop devices are located where most likely needed. An emergency stop on the teach pendant accomplishes this for personel using the teach pendant. Pressure-actuated pads mounted on a surfaces in the work envelope are another alternative. A cable attached to a circuit-breaking switch provides many points along its length at which an emergency stop can be initiated. Convenience and ease of reach are important considerations in locating the emergency stop devices.
A periodic verification will ensure that the emergcy stop work as intented. An effective emergency stop will be capable of interrupting the drive circuits even when energy to robot control circuits needs to be maintained.
In some factories it has been suggested that hitting an emergency stop leads to an extented period of time for restart due to the need to move the robot and other equipment to a home home position. In other cases this stop is used as a normal maintanance stop. Training which emphasizes immediate use of the emergency stop when needed will diminish workers natural reluctance to use it due to time lost in restarting system.
As a matter of practice, emergency stops are use infrequently. Jones and Dawson report that 2170 stops recorded at robotized workstations, there were only 11 cases in which the emergency stop wwas used while performing corrective maintenance.
(Safe Maintenance Guide for Robotic Workstations,John R. Etherton,p.13)
3)Age Hardening (Heat process)
Age hardening or precipitation hardening produces a uniform dispersion of a fine, hard coherent precipitate in a softer, more ductile matrix. The Al %4 Cu alloy is a classical example of an age-hardenable alloy. There are three stages in the age hardening treatment.
Step1: Solution treatment: In the solution treatment the alloy is first heated above the solvus temperature and held until a homogenous solid solution alfa is produced. The step dissolves the teta precipitate and reduces any segregation present in the original alloy.
Step2: Quench: After solution treatment the alloy which contains only alfa in is structure is rapidly cooled or quenched. The atoms do not have time to diffuse the potential nucleation sites, so the teta does not form. After the quench the structure still contains only alfa. The alfa is a super saturated solid solution.
Step 3: Age: Finally the supersaturated alfa is heated below the solvus temperature. At this ageing temperature, atoms diffuse only short distances. Because the supersaturated alfa is not stable, the extra copper atoms diffuse to numerous nucleation sites and precipitates grow. Eventually if we hold the alloy for a sufficient time at the ageing temperature, the equilibrium alfa+teta structure is produced. This however is not always desirable as higher strenght may be achieved by stopping the ageing process before an equilibrium structure is produced.
(Donald R. Askeland, The Science and Engineering of Materials, Third S.I Edition, page 322)
AGE HARDENING (new) (Better)
To be a candidate for precipitation hardening, an alloy system must exhibit solubility that decreases with decreasing temperature, such as the aluminum-rich portion of the alumium-copper system shown in Figure 5-3 and enlarged in Figurc 5-4. Consider the alloy with 4% copper,and use the phase diagram to determine its equilibrium structure, Liquid metal solidifies In to a single-phase solid (α phase). At 1OOO°F, the full 4% of copper isdissolved and distributed th roughout the alpha crysta1s. Ast he temperature drops, the maximum solubility of copper in aluminum decreases Irom 5.65% at 1018°F to less than 0.2% at room temperature. Upon cooling through the solvus (or solubility limit) line at 930°F, the 4% copper alloy centers a two-phase region, and copper-rich theta phase precipitates form and grow (Note:T heta-phase is actually a hard, brittle intermetallic compound with th e chemical formula of CuAI,.) The equilibriums structure, therefore, would be an aluminum-rich alpha-phase structure will coarse theta-phase precipitates, generally lying along alpha-phase grain boundaries where the nucleation of second-phase particles can benefit from the existing interfacial surface.
Whenever two or more phases are present, the material exhibits dispersion strengthening. Dislocations are confined to thelr own crystal and cannot cross interfacial boundaries.Therefore, each interface between alpha-phase and the theta-phase preapitate is a strengthening boundary.Take a particle of theta precipitate and cut it into two halves. Forming the two half-size precipitates has just added two additional interfaces, corresponding to both sides of the cut. If the particle were to be further cut Into quarters, eighths, and sixteenths, we would expect strength to increase as we continually add interfacial surface. Ideally, we would like to have millions of ultra-small particles dilspersed throughout the alpha-phase structure. When we try to form this more desirable nonequilibnum configuration, however, we gain an unexpected benefit that adds significant strength. This new nonequillbrium treatment is known as age hardening or precipitation hardening.
(DeGarmo's Materials and Processes in Manufacturing,E. Paul DeGarmo,p.93)
4)ESPI Electronic Speckle Pattern Interferometry (Measurement)
An extended laser beam is used to provide coherent illumination of a test sample which is viewed with a CCD camera or other electronic image sensor. Coherent light scattered from an optically rough test surface impresser a laser speckle pattern on the image of the test object, and the spatial characteristics of the speckle pattern are determined primarily by the finite resolution of the imaging lens. The interferometer optics, might be one of many configurations depending on the measurement objectives. The basic function of interferometer is to deliver two dinstint coherent wavefronts to the imaging system.
(Donald O. Thompson,Dale E. Chimenti, Review of progress in quantitative nondestructive evaluation, page 373)
ESPI Electronic Speckle Pattern Interferometry(new)(better)
Displacements well below a micron can be dedected by interferometric methods.This is achieved by phase-sensitiverecording ofthe specle light with the aid of a reference wave in a setup for video-holography, mostly called Electronic Speckle Pattern Interfferometry (ESPI). Here, too, the object under investigation is illuminated by laser light and imaged by a CCD-camera. Now, however, a spherical reference wave is superimposed via a beamsplitter producing an interference image (image plane hologram) available for further processing in a computer. Substraction of successive images, for example, yields a system of so-called correlation fringes. These are contour lines of constant displacement in the direction of sensitivity vector k that is determined by the difference in illumination and observation directions. For normal illumination and viewing, for example k points into the out-of-plane direction. In combining several optical setups of different geometry all three spatial components of a displacement vector can thus be determined. The interpreation of a single fringe system is ambiguous- it does not tell us the sign of the displacement. Furthermore, jumps in the fringes that occur when discontinuties in the displacement field are involved impede evaluation. To handle these problems several images need to be recorded for each of which the reference wave has undergone a set phase shift. Often three or four images at regular phase intervals are collected- a strategy known from classical interferometry as phase shifting. Such a series of images allows automated evaluation by a procedure called spatial phase unwrapping and provides unambiguous deformation data
(Oscillations, waves and interactions,Kurz, Thomas, p.262)
4)Programmable Automation: (automation) (better)
In programable automation, the production equipment is designed with capability to change the sequence of operations to accomodate different product configurations. The operation sequence is controlled by a program, which is a set insturctions coded so that they can be read and interpreted by the system. New programs can be prepared and entered into the equipment to produce new products. Some of the features characterize programmable automation include, 1) high investment in general purpose equipment, 2) lower production rates than fixed automation, 3) flexibly to deal with the variations and chages in product configuration, and 4) high suitability for batch operations. Programmable automated production systems are used in low- and medium- volume production. The parts or products are typically made in batches. To produce each new batch of a different product, system must be reprogrammed with the set of machine instructions that correspond to the new product. The physical set up of the machine must also be changed: Tools must be loaded, fixtures must be attached to the machine table and the required machine settings must be entered. This changeover procedure takes time. Consequently, the typical cycle for a given product includes a period during which the setup and reprogramming takes place, followed by a period in which the parts in the batch are produced. Examples of programmable automation include numerically controlled machine tools, industrial robots, and programmable logic controllers.
(M.P. Groover, Automation, production systems, and computer-integrated manufacturing, 3rd Edition, p. 10-11)
Programmable Automation: (new)
The concept of programmable automation was introduced later. These were electrically
controlled systems and programs were stored in punched cards and punched tapes. Typical
examples of programmable automation are:
i. Electrical programme controlled milling machines
ii. Hydraulically operated Automatic lathes with programmable control drum
iii. Sequencing machines with punched card control /plug board control
Development of digital computers, microelectronics and microprocessors significantly
altered the automation scenario during 1950-1990. Machine control systems are now
designed around microprocessors and microelectronics is part and parcel of industrial
drives and control. The significant advances in miniaturization through integration of large
number of components into small integrated chips and the consequent improvement in
reliability and performance have increased the popularity of microelectronics. This has
resulted in the availability of high performance desktop computing machines as well as
file servers which can be used for industrial control with the help of application software
packages.
(CAD/CAM/CIM 3.edition, P. Radhakrishnan, S. Subrahmanyan, V. Raju, p.4)
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