office: 2008

2008年12月11日星期四

Mezzanine

Overview
The floor often projects itself from the walls and does not completely close the view of the ceiling from ground floor. In short, the Mezzanine Floor and the ground floor share the same ceiling. There is a belief that a mezzanine floor is always located between the ground floor and the first floor but it is not unusual to have mezzanine floors in the upper floors of a building.
In Palladian architecture the mezzanine is a low upper floor, usually for servants and/or storage.
In stadiums, the "mezzanine" level is a term often used for premium or "club level" seating, typically just a few rows deep and hanging from the upper tier, affording an unobstructed view of the playing field.

Industrial Mezzanines
In industrial applications, mezzanine floor systems are semi-permanent floor systems typically installed within buildings, built between two permanent original stories. These structures are usually free standing and in most cases can be dismantled and relocated. Commercially sold mezzanine structures are generally constructed of three main materials; steel, aluminum, and fiberglass. The decking or flooring of a mezzanine will vary by application but is generally composed of b-deck underlayment and wood product finished floor or a heavy duty steel, aluminum or fiberglass grating.
The mezzanine is often used in shops and similar spaces for storage of tools or materials. The high roof of the shop is ideal for a mezzanine, and offices can be put either below or above it. Mezzanines are frequently used in industrial operations such as warehousing, distribution or manufacturing. These facilities have high ceilings, allowing unused space to be utilized within the vertical cube. Industrial mezzanine structures are typically either structural, roll formed, rack-supported, or shelf-supported, allowing high density storage within the mezzanine structure.

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Unit load

Function
Most consumer and industrial products move through the supply chain in unitized or unit load form for at least part of their distribution cycle. Unit loads make handling, storage, and distribution more efficient. They help reduce handling costs and damage by reducing individual handling.
A typical unit load might consist of corrugated fiberboard boxes stacked on a pallet and stabilized with stretch wrap, straps or other materials. About 2 billion unit loads are in daily use in the United States (Ward 1993).

Unit Load Design
There are three kinds of unit load design: Component based, systems based, and standards compliant. These have different applications.

Component Based Design
Component based design is the outmoded ad-hoc method of unit load design. Components are sometimes over specified to get assured performance, or tested to get inexpensive economic performance.
Unit load storage and distribution systems consist of several interacting parts:
Packaging and labeling (with product),
Pallet, and
Handling/Storage Equipment
The distribution environment (shock, vibration, humidity, temperature, etc)
Considerable knowledge exists regarding the design of each of these components: their interactions have more recently been studied. When packaging, pallet, and handling systems are designed separately at different locations by different teams, the result might be inefficient unit load systems.
The consequences of independent component based design in the supply chain can include:
Unsafe WorkplacesProduct DamageHigh Packaging CostsReduced Handling EfficiencyWasted Natural ResourcesReduction of Environmental Quality

Systems Based Design
Systems Based Design is a proven process of unit load component cost optimization based on an understanding of how the pallet, packaging and material handling equipment interact during product distribution and storage to design the unit load component parts.
Very often a few inexpensive additions to the packaging can stabilize or stiffen a critical part and give good unit-load performance at a low cost.
Factors considered in unit load systems based design include:
Distribution Vibration and ResonanceLoad Bridging and DeformationUnit Load DeflectionsInterfacial friction and load stabilityCompression stress and product protectionVertical and horizontal stabilization

Standards-Compliant Design
Standards permit a unit load to be designed and tested to meet a written specification or test method. A unit load can be verified to comply with a standard and validated to determine that the unit load is indeed effective.
Unit loads move by an unpredictable mix of many types of vehicles and storage areas, the exact set is difficult to predict. Therefore, unit loads must be designed to travel by any such vehicles, and be stored in a wide variety of places. There are therefore many similarities in the requirements for long term storage and long distance transportation of unit loads.
Standards provide institutional memory of the many conditions in real logistic trains, and collect the best practices for design and testing unit loads. Standards also describe load requirements, so that logistic providers can plan to meet them.
Material based standards describe proven designs for particular circumstances. These are often used to describe unit load components such as pallets, strapping, seals, caps, retaining rings and battens.
Performance testing standards describe needs and allow flexibility in the choice of matierials. These are applied to particular unit load designs.
ASTM D4169 has standard test protocols for unit loads. These vary based on the value of the load, the expected hazards, and the distribution environment. This is a performance based standard.
Another standard for unit loads is MIL-STD-1660, a standard for ammunition unit loads. DOD unit loads generally use 40x48" pallets, which pack efficiently into ISO containers. They weigh less than 4000lbs (1800kg) to limit the stresses on handling equipment. They are weatherproof, and stack 16' (4.9m) high. They often use steel pallets, steel straps with notched seals, outdoor plywood, and plastic film. Interestingly, MIL-STD-1660 mandates that loads must never be less than the width of a pallet, while permitting some overhang. The markings are logmars bar codes and standard inventory numbers. The standard describes major parts of the logistic path, including storage, ship, air, truck, forklift and sling (i.e. ship-to-ship and parachute). There are auxiliary standards for ship-to-ship transfers, and amphibious transfers. There are tests for stacking, transport, sling, forklift and pallet jack, impact, drop tests, tip, water-retention (i.e. weather), and safe disassembly.
MIL-STD-1660 at first looks like ridiculous overdesign to commercial unit-load designers. However, similar marking standards, safety, stability, volumetric efficiency, weight limits and impact resistance are routinely needed in commercial logistics. Sling handling is routine for small ports and noncontainer transports. Weatherproofness could be optional. It's sometimes valuable, and the baggies are cheap. High, standardized stacking could be optional as well. It's expensive, but sometimes valuable for rackless and military customers.

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Pallet jack

A pallet jack, also known as a pallet truck or pump truck, is a tool used to lift and move pallets.
The front wheels are mounted inside the end of the forks, and as the hydraulic jack is raised, the forks are separated vertically from the front wheels, forcing the load upward until it clears the floor. The pallet is only lifted enough to clear the floor for subsequent travel.

Types

Manual pallet jack
A manual pallet jack is a hand-powered jack.

Powered pallet jack
Powered pallet jacks are motorized to allow lifting and moving of heavier and stacked pallets. These generally contain a platform for the user to stand while hauling pallets around a warehouse or loading/unloading trucks. The powered pallet jack is generally moved by a throttle on the handle to move forward or in reverse and steered by swinging the handle in the intended direction. Some contain a type of dead man's switch rather than a brake to stop the machine should the user need to stop quickly or leave the machine while it is in use.

Operational limitations
Reversible pallets cannot be used.
Double-faced nonreversible pallets cannot have deckboards where the front wheels extend to the floor.
Enables only two-way entry into a four-way notched-stringer pallet, because the forks cannot be inserted into the notches

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Packaging and labeling

The purposes of packaging and package labels
Packaging and package labeling have several objectives:
Physical protection - The objects enclosed in the package may require protection from, among other things, shock, vibration, compression, temperature, etc.
Barrier protection - A barrier from oxygen, water vapor, dust, etc., is often required. Permeation is a critical factor in design. Some packages contain desiccants or Oxygen absorbers to help extend shelf life. Modified atmospheres or controlled atmospheres are also maintained in some food packages. Keeping the contents clean, fresh, sterile and safe for the intended shelf life is a primary function.
Containment or agglomeration - Small objects are typically grouped together in one package for reasons of efficiency. For example, a single box of 1000 pencils requires less physical handling than 1000 single pencils. Liquids, powders, and granular materials need containment.
Information transmission - Packages and labels communicate how to use, transport, recycle, or dispose of the package or product. With pharmaceuticals, food, medical, and chemical products, some types of information are required by governments.
Marketing - The packaging and labels can be used by marketers to encourage potential buyers to purchase the product. Package design has been an important and constantly evolving phenomenon for several decades. Marketing communications and graphic design are applied to the surface of the package and (in many cases) the point of sale display.
Security - Packaging can play an important role in reducing the security risks of shipment. Packages can be made with improved tamper resistance to deter tampering and also can have tamper-evident features to help indicate tampering. Packages can be engineered to help reduce the risks of package pilferage: Some package constructions are more resistant to pilferage and some have pilfer indicating seals. Packages may include authentication seals to help indicate that the package and contents are not counterfeit. Packages also can include anti-theft devices, such as dye-packs, RFID tags, or electronic article surveillance tags, that can be activated or detected by devices at exit points and require specialized tools to deactivate. Using packaging in this way is a means of loss prevention.
Convenience - Packages can have features which add convenience in distribution, handling, stacking, display, sale, opening, reclosing, use, and reuse.
Portion control - Single serving or single dosage packaging has a precise amount of contents to control usage. Bulk commodities (such as salt) can be divided into packages that are a more suitable size for individual households. It is also aids the control of inventory: selling sealed one-liter-bottles of milk, rather than having people bring their own bottles to fill themselves.

Packaging types

Various household packaging types for foods
Packaging may be looked at as several different types. For example a transport package or distribution package is the package form used to ship, store, and handle the product or inner packages. Some identify a consumer package as one which is directed toward a consumer or household.
Packaging may discussed in relation to the type of product being packaged: medical device packaging, bulk chemical packaging, over-the-counter drug packaging, retail food packaging, military materiel packaging, pharmaceutical packaging, etc.

Pull open aluminum can
It is sometimes convenient to categorize packages by layer or function: "primary", "secondary", etc.
Primary packaging is the material that first envelops the product and holds it. This usually is the smallest unit of distribution or use and is the package which is in direct contact with the contents.
Secondary packaging is outside the primary packaging – perhaps used to group primary packages together.
Tertiary packaging is used for bulk handling, warehouse storage and transport shipping. The most common form is a palletized unit load that packs tightly into containers.
These broad categories can be somewhat arbitrary. For example, depending on the use, a shrink wrap can be primary packaging when applied directly to the product, secondary packaging when combining smaller packages, and tertiary packaging on some distribution packs.

Symbols used on packages and labels
Many types of symbols for package labeling are nationally and internationally standardized. For consumer packaging, symbols exist for product certifications, trademarks, proof of purchase, etc. Some requirements and symbols exist to communicate aspects of consumer use and safety. Recycling directions, Resin identification code (below), and package environmental claims have special codes and symbols.

Bar codes (below), Universal Product Codes, and RFID labels are common to allow automated information management.

"Wikipedia" encoded in Code 128
Shipments of hazardous materials or dangerous goods have special information and symbols (labels, plackards, etc) as required by UN, country, and specific carrier requirements.

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Forklift truck

History
The middle 19th century through the early 20th century saw the developments that led to today's modern forklifts. The Pennsylvania Railroad in 1906 introduced battery powered platform trucks for moving luggage at their Altoona, Pennsylvania train station. World War I saw the development of different types of material handling equipment in the United Kingdom by Ransomes, Sims and Jeffries of Ipswich. This was in part due to the labor shortages caused by the war. In 1917 Clark in the United States began developing and using powered tractor and powered lift tractors in their factories. In 1919 the Towmotor Company and Yale & Towne Manufacturing in 1920 entered the lift truck market in the United States.
Continuing development and expanded use of the forklift continued through the 1920s and 1930s. World War II, like World War I before, spurred the use of forklift trucks in the war effort. Following the war, more efficient methods for storing products in warehouses were being implemented. Warehouses needed more maneuverable forklift trucks that could reach greater heights. New forklift models were made that filled this need.

Design types

The following is a list of the more common lift truck types. It is arranged from the smallest type of lift to largest:
Hand pallet truck
Walkie low lift truck (powered pallet truck, usually electrically powered)
Rider low lift truck
Towing tractor
Walkie stacker
Rider stacker
Reach truck (small forklift, designed for small aisles, usually electrically powered)
Electric counterbalanced truck
IC counterbalanced truck
Sideloader
Telescopic handler
Slip Sheet machine
Walkie Order Picking truck
Rider Order Picking truck (commonly called an "Order Picker"; like a small forklift, except the operator rides up to the load and transfers it article by article)
Articulated Very Narrow Aisle Counterbalanced trucks (commonly called "Flexi Truck")
Guided Very Narrow Aisle truck - 'Man Down' (a type of reach truck designed for aisles less than five feet wide) and 'Man Riser' Combination pickcle Picker/ Stacker truck
Truck Mounted Forklift / Sod Loader

Specialty trucks
At the other end of the spectrum from the counterbalanced forklift trucks are more 'high end' specialty trucks:
Articulated Counterbalance Trucks
These are, unlike most other lift trucks, front wheel steer, and are a hybrid VNA (Very Narrow Aisle) truck designed to be both able to offload trailers and place the load in narrow aisle racking. Increasingly these trucks are able to compete in terms of pallet storage density, lift heights and pallet throughput with Guided Very Narrow Aisle trucks.
Guided Very Narrow Aisle Trucks
These are rail or wide guided and available with lift heights up to 40' non top-tied and 98' top-tied. Two forms are available; 'man-down' and 'man-riser' where the operator elevates with the load for increased visibility or for multilevel 'break bulk' order picking. This type of truck, unlike Articulated Narrow Aisle Trucks, requires a high standard of floor flatness.
U.S. Military 10K-AT "Adverse Terrain"

Counterbalanced forklift components

Image of an electric forklift with component descriptions
A typical counterbalanced forklift contains the following components
The Truck Frame - is the base of the machine to which the mast, axles, wheels, counterweight, overhead guard and power source are attached. The frame may have fuel and hydraulic fluid tanks constructed as part of the frame assembly.
The Counterweight - is a heavy cast iron mass attached to the rear of the forklift truck frame. The purpose of the counterweight is to counterbalance the load being lifted. In an electric forklift the large lead-acid battery itself may serve as part of the counterweight.
The Cab - is the area that contains a seat for the operator along with the control pedals, steering wheel, levers, switches and a dashboard containing operator readouts. The cab area may be open air or enclosed, but it is covered by the cage-like overhead guard assembly.
The Overhead Guard - is a metal roof supported by posts at each corner of the cab that helps protect the operator from any falling objects. On some forklifts, the overhead guard is part of the frame assembly
The Power Source - may consist of an internal combustion engine that can be powered by LP gas, CNG gas, gasoline or diesel fuel. Electric forklifts are powered by either a battery or fuel cells that provide power to electric motors. The motors may be either DC or AC types.
Tilt Cylinders - are hydraulic cylinders that are mounted to the truck frame and the mast. The tilt cylinders pivot the mast to assist in engaging a load.
The Mast - is the vertical assembly that does the work of raising and lowering the load. It is made up of interlocking rails that also provide lateral stability. The interlocking rails may either have rollers or bushings as guides. The mast is either hydraulically operated by one or more hydraulic cylinders or it may be chain operated with a hydraulic motor providing motive power. It may be mounted to the front axle or the frame of the forklift.
The Carriage - is the component to which the forks or other attachments mount. It is mounted into and moves up and down the mast rails by means of chains or by being directly attached to the hydraulic cylinder. Like the mast, the carriage may have either rollers or bushings to guide it in the interlocking mast rails.
The Load Back Rest - is a rack-like extension that is either bolted or welded to the carriage in order to prevent the load from shifting backward when the carriage is lifted to full height.
Attachments - may consist of forks or tines that are the L-shaped members that engage the load. A variety of other types of material handling attachments are available. These include sideshifters, slipsheet attachments, carton clamps, multipurpose clamps, rotators, fork positioners, carpet poles, pole handlers, container handlers, roll clamps and many others.

Attachments
Below is a list of common forklift attachments:
Sideshifter - is a hydraulic attachment that allows the operator to move the tines (forks) and backrest laterally. This allows easier placement of a load without having to reposition the truck
Rotator - To aid the handling of skids that may have become excessively tilted and other specialty material handling needs some forklifts are fitted with an attachment that allows the tines to be rotated. This type of attachment may also be used for dumping containers for quick unloading.
Fork Positioner - is a hydraulic attachment that moves the tines (forks) together or apart. This removes the need for the operator to get out of the cab to manually adjust the tines for different sized loads.
Roll and Barrel Clamp Attachment - A mechanical or hydraulic attachment that is used for handling barrels, kegs, or paper rolls. This type of attachment also usually have a rotate function so that a vertically stored paper roll can be inserted into the horizontal intake of a printing press.
Pole Attachments - In some locations, such as carpet warehouses, a long metal pole is used instead of forks to lift carpet rolls. Similar devices, though much larger, are used to pick up metal coils.
Carton and Multipurpose Clamp Attachments - are hydraulic attachments that allow the operator to open and close around a load, squeezing it to pick it up. Products like cartons, boxes and bales can be moved with this type attachment. With these attachments in use, the forklift truck is sometimes referred to as a clamp truck.
Slip Sheet Attachment (Push - Pull) - is a hydraulic attachment that reaches forward, clamps onto a slipsheet and draws the slipsheet onto wide and thin metal forks for transport. The attachment will push the slip sheet and load off the forks for placement.
Drum Handler Attachment - is a mechanical attachment that slides onto the tines (forks). It usually has a spring loaded jaw that grips the top lip edge of a drum for transport. Another type grabs around the drum in a manner similar to the roll or barrel attachments.
Man Basket - a lift platform that slides onto the tines (forks); meant for hoisting workers. The man basket has railings and brackets for attaching safety harnesses.
Telescopic Forks - are hydraulic attachments that allow the operator to operate in warehouse design for "double-deep stacking", which means that two pallet shelves are placed behind each other without any aisle between them.

Forklift control and capabilities

a typical load capacity chart
‎
Forklift trucks are available in many variations and load capacities. In a typical warehouse setting most forklifts used have load capacities between one to five tons. Larger machines, up to 50 tons lift capacity are used for lifting heavier loads, including loaded shipping containers. [7]
In addition to a control to raise and lower the forks (also known as blades or tines), the operator can tilt the mast to compensate for a load's tendency to angle the blades toward the ground and risk slipping off the forks. Tilt also provides a limited ability to operate on non-level ground. Skilled forklift operators annually compete in obstacle and timed challenges at regional forklift rodeos.

General operations

A forklift transporting a pallet of potted plants in Durham, North Carolina.
Forklifts are rated for loads at a specified maximum weight and a specified forward centre of gravity. This information is located on a nameplate provided by the manufacturer, and loads must not exceed these specifications(In Canada it is 24" Load Center). In many jurisdictions it is illegal to remove or tamper with the nameplate without the permission of the forklift manufacturer.
An important aspect of forklift operation is that many have rear-wheel steering. While this increases maneuverability in tight cornering situations, it differs from a driver’s traditional experience with other wheeled vehicles. While steering, as there is no caster action, it is unnecessary to apply steering force to maintain a constant rate of turn.
Another critical characteristic of the forklift is its instability. The forklift and load must be considered a unit with a continually varying centre of gravity with every movement of the load. A forklift must never negotiate a turn at speed with a raised load, where centrifugal and gravitational forces may combine to cause a disastrous tip-over accident. The forklift are designed with a load limit for the forks which is decreased with fork elevation and undercutting of the load (i.e. load does not butt against the fork "L"). A loading plate for loading reference is usually located on the forklift. A forklift should not be used as a personnel lift without the fitting of specific safety equipment, such as a "cherry picker" or "cage".

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Pallet

Overview
Containerization for transport has spurred the use of pallets because the containers have the clean, level surfaces needed for easy pallet movement. Most pallets can easily carry a load of 1,000 kg (about 2,000 lb). Today, over half a billion pallets are manufactured each year and about two billion pallets are in use across the United States alone.
Pallets make it easy to move heavy stacks. Loads with pallets under them can be hauled by forklift trucks of different sizes, or even by hand-pumped and hand-drawn pallet jacks. Movement is easy on a wide, strong, flat floor: concrete is excellent. A forklift truck can cost the same as a luxury automobile, but a good reconditioned hand-drawn pallet jack costs only a few hundred dollars. The greatest investment is thus in the construction of commercial or industrial buildings where the use of pallets could be economical. Passage through doors and buildings must be possible. To help this issue, some later pallet standards (the europallet and the U.S. Military 35x45.5") are designed to pass through standard doorways.
Organizations using standard pallets for loading and unloading can have much lower costs for handling and storage, with faster material movement than businesses that do not. The exceptions are establishments that move small items such as jewelry or large items such as cars. But even they can be improved. For instance, the distributors of costume jewelry normally use pallets in their warehouses and car manufacturers use pallets to move components and spare parts.
The lack of a single international standard for pallets causes substantial continuing expense in international trade. A single standard is difficult because of the wide variety of needs a standard pallet would have to satisfy: passing doorways, fitting in standard containers, and bringing low labor costs. For example, organizations already handling large pallets often see no reason to pay the higher handling cost of using smaller pallets that can fit through doors.

History

Development of commercial transport packaging

Pallets stacked for loading onto barges in North London
Skids and pallets were slowly introduced throughout the early 20th century; wooden boxes, crates, barrels and kegs were much more commonly used to unitize, protect, store and transport goods. The predecessor of the modern wooden pallet was a simple skid that consisted only of stringers fastened to a top deck. It first appeared in American factories in conjunction with the low lift truck. A crude low lift hand truck was invented in 1887 and a more durable, all-steel low lift truck design was introduced in 1909.
The high lift fork truck first appeared in 1915. With further modification in 1919, the truck could lift loads several feet high while other improvements included cantilever design and forks. The emergence of forks as well during the same period enabled lift trucks to handle a much greater range of materials.
Another development was the new capability of the mast of the fork lift to tilt both forward and back, independent of the lifting mechanism. These developments, along with the emergence of the double-faced pallet during the same time period, allowed for tiering of unit loads. As early as 1926, the essence of the modern lift truck had been developed. Now, pallets no longer were simply a means of moving materials within the plant. High lift trucks made possible vertical stacking of unit loads and a resulting dramatic improvement of warehouse and plant storage efficiencies.

Development of the pallet
The pallet was developed in stages. Spacers were used between loads to allow fork entry, progressing to the placement of boards atop stringers to make skids. Eventually boards were fastened to the bottom to create the pallet. The addition of bottom boards on the skid, which appeared by 1925, resulted in the modern form of the pallet. With the bottom deck, several problems common to the single faced skid were addressed. For example, the bottom boards provided better weight distribution and reduced product damage; they also provided better stacking strength and rigidity. Lift truck manufacturers promoted the idea of using more vertical area of a plant for stock storage.
In size, skids started narrow in order to pass through ordinary doors. As facilities were rebuilt, many organizations optimized their buildings for larger pallets in order to reduce labor costs.
The earliest referenced U.S. patent on a skid is Hallowell's 1924 "Lift Truck Platform." In 1939, Carl Clark patented a recognizably modern pallet, although with steel stringers.In World War II, palleted material handling was rapidly perfected in order to transfer Allied war materials. The patent activity picked up again after the war, as inventors claimed items they improvised for the war effort. The first four direction pallet was claimed in 1945 by Robert Braun.At the end of 1948, Sullivan Stemple claimed the basic idea of a pallet designed to be used with a fork lift; the pallet was to be stamped from steel During World War II, to reduce the resupply time of warships, the first modern disposable four-way block pallet was developed, and patented in early 1949 by Norman Cahners, a U.S. Navy Supply Officer in the ordnance depot at Hingham, Massachusetts. The first completely modern 2-direction stringer pallet was described in 1949 by Darling Graeme.

Impact of pallet on rail transport
Pallets and forklifts also provided much quicker turnaround of rail cars and ships. In 1931, three days were required to unload a boxcar containing 13,000 cases of unpalletized canned goods. When the same amount of goods were loaded into the railway trucks on pallets or skids, the identical task took only four hours. With the entry of the U.S. into World War II, the urgency for material handling reform changed almost overnight. Palletization was regarded as an enormous opportunity to help the U.S. armed forces do more with less. Palletized loads could handle more goods with fewer people, freeing up men for military duty; it also could increase warehouse storage capacity and throughput, reducing the need for additional warehouse capacity. Pallets were used somewhat in the European theater, but they were put to work extensively in the Pacific.

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Material handling equipment

Storage and Handling Equipment
Storage and handling equipment is a category within the material handling industry. The equipment that falls under this description is usually non-automated storage equipment. Products such as Pallet rack, shelving, carts, etc. belong to storage and handling. Many of these products are often referred to as "catalog" items because they generally have globally accepted standards and are often sold as stock materials out of Material handling catalogs.

Engineered Systems
Engineered systems are typically custom engineered material handling systems. Conveyors, AS/RS, AGV and most other automated material handling systems fall into this category. Engineered systems are often a combination of products integrated to one system. Many distribution centers will optimize storage and picking by utilizing engineered systems such as pick modules and sortation systems.

Industrial Trucks
Industrial trucks usually refer to operator driven motorized warehouse vehicles. Industrial trucks assist the material handling system with versatility; they can go where engineered systems cannot. Forklift trucks are the most common example of industrial trucks but certainly aren't the extent of the category. Tow tractors and stock chasers are additional examples of industrial trucks.

Bulk Material Handling
Bulk material handling equipment is used to move and store bulk materials such as ore, liquids, and cereals. This equipment is often seen on farms, mines, shipyards and refineries. This category is also explained in Bulk material handling.

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Doorstop

Usage

Holding Doors Open
A door may be held open by a door stop which is simply a heavy solid object, such as a brick, placed in the path of the door. These stops are predominantly improvised. Historically, lead bricks have been popular choices when available. However, as the toxic nature of lead has been revealed, this use has been strongly discouraged.
Another method is to use a door stop which is a small wedge of wood, rubber, plastic, cotton or another material. Manufactured wedges of these materials are commonly available. The wedge is kicked into position and the downward force of the door, now jammed upwards, onto the door stop provides enough static friction to keep it motionless.
A third strategy is to equip the door itself with a stopping mechanism. In this case, a short metal bar capped with rubber, or another high friction material, is attached to a hinge near the bottom of the door opposite the door hinge and on the side of the door which is in the direction that it closes. When the door is to be kept open, the bar is swung down so that the rubber end touches the floor. In this configuration, further movement of the door towards being closed increases the force on the rubber end, thereby increasing the frictional force which opposes the movement. When the door is to be closed, the stop is released by pushing the door slightly more open which releases the stop and allows it to be flipped upwards. A newer version of equipping the door with the stopping mechanism is to attach a magnet to the bottom of the door on the side which opens outward which then latches onto another magnet or magnetic material on the wall or a small hub on the floor. The magnet must be strong enough to hold the weight of the door, but weak enough to be easily detached from the wall or hub.

Preventing Damage by Doors
Another type of door stop is used to prevent doors from opening too far and damaging nearby walls. In this case a short length of rubber-tipped wood or metal is screwed into either the wall or the floor in the path of the door. If it is attached to the wall, it may be either a few inches above the ground, or at such a height as to meet the doorknob.
On occasion, stops are used that are fitted at the midpoint of the door, as part of the central door-hinge. Such a stop is known as a "hinge pin".

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Wide-angle lens

Wide-angle lenses for 35 mm format
For a full-frame 35 mm camera with a 36 mm by 24 mm format, the diagonal measures 43.3 mm and by custom, the normal lens adopted by most manufacturers is 50 mm. Also by custom, a lens of focal length 35 mm or less is considered wide-angle.
Common wide-angle lenses for a full-frame 35 mm camera are 35, 28, 24, 21, 18 and 14 mm. Many of the lenses in this range will produce a more or less rectilinear image at the film plane (though some degree of barrel distortion is not uncommon here).
Extreme wide-angle lenses that do not produce a rectilinear image are called fisheye lenses. Common focal lengths for these in a 35 mm camera are 6 to 8 mm (which produce a circular image). Lenses with focal lengths of 14 to 16 mm may be either rectilinear or fisheye designs.
Wide-angle lenses come in both fixed-focal-length and zoom varieties. For 35 mm cameras, lenses producing rectilinear images can be found at focal lengths as short as 12 mm, including zoom lenses with ranges of 2:1 that also begin at 12 mm. .

Digital camera considerations

Apparent focal length in APS-sized digital cameras is increased by a crop factor.
As of 2007 most interchangeable-lens digital cameras have photosensors that are smaller than the film format of full-frame 35 mm camerasFor the most part, the dimensions of these photosensors are similar to the APS-C image frame size, i.e., approximately 24 mm x 16 mm. Therefore, the angle of view for any given focal length lens will be narrower than it would be in a full-frame camera because the smaller sensor "sees" less of the image projected by the lens. The camera manufacturers provide a crop factor (sometimes called a field-of-view factor or a focal-length multiplier) to show how much smaller the sensor is than a full 35 mm film frame. For example, one common factor is 1.5 (Nikon DX format and some others), although many cameras have crop factors of 1.6 (most Canon DSLRs), 1.7 (the Sigma DSLRs) and 2 (the Four-thirds-format cameras). The 1.5 indicates that the angle of view of a lens on the camera is the same as a 35 mm full-frame camera with a focal length of 1.5 times the focal length, which explains why the crop factor is also known as a focal-length multiplier. As examples, a 28 mm lens would produce on the DSLR the angle of view of a 42 mm lens (given a crop factor of 1.5) on a full-frame camera. So, to determine the focal length of a lens for a digital camera that will give the equivalent angle of view as one on a full-frame camera, the full-frame lens focal length must be divided by the crop factor. For example, to get the equivalent angle of view of a 28 mm lens on a full-frame 35 mm camera, from a digital camera with a 1.5 crop factor, one would use an 18 mm lens.
Lens manufacturers have responded to this problem by making wide-angle lenses of much shorter focal lengths for these cameras. In doing this, they limit the diameter of the image projected to slightly more than the diagonal measurement of the photosensor. This gives the designers more flexibility in providing the optical corrections necessary to economically produce high quality images at these short focal lengths, especially when the lenses are zoom lenses. Examples are 10 mm minimum focal length zoom lenses from several manufacturers. At 10 mm, these lenses provide the angle of view of a 15 mm lens on a full-frame camera when the crop factor is 1.5.
Construction

Cross-section of a typical short-focus wide-angle lens.

Cross-section of a typical retrofocus wide-angle lens.
There are two different varieties of wide-angle lens: short-focus lenses and retrofocus lenses.
Short-focus lenses are generally made up of multiple glass elements whose shapes are more or less symmetrical in front of and behind the diaphragm. As the focal length decreases, the distance of the rear element of the lens from the film plane or digital sensor also decreases. This makes short-focus wide-angle lenses undesirable for single-lens reflex cameras unless they are used with the reflex mirrors locked up. Short-focus lenses are widely used on large format view cameras.
The retrofocus lens solves this proximity problem through an asymmetrical design that allows the rear element to be further away from the film plane than its effective focal length would suggest. (See Angenieux retrofocus.) For example, it is not uncommon for the rear element of a retrofocus lens of 18 mm to be more than 25 mm from the film plane. This makes it possible to design wide-angle lenses for single-lens reflex cameras.

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Crash bar

A crash bar is a mechanism for unlatching a door, consisting of a metal bar fixed horizontally to the front of the door and hinged. It is operated by pushing on it, which unlatches and opens the door. Many countries' building codes require them on all fire and emergency exits. They are so named because they can be operated by someone "crashing" into them; the alternate term "panic bar" implies a similar meaning.
Crash bars also refers to motorcycle engine guards. They are commonly made of tubular steel bent into a "U" shape and mounted to the sides of a motorcycle's lower frame. They primarily protect the bike's engine and body panels during slides or tipovers but also serve as a mount point for accessories like highway pegs, lights and, on police motorcycles, sirens, cameras and radar guns.

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2008年12月9日星期二

Welding

Processes

Arc
Main article: Arc welding
These processes use a welding power supply to create and maintain an electric arc between an electrode and the base material to melt metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is sometimes protected by some type of inert or semi-inert gas, known as a shielding gas, and filler material is sometimes used as well.

Power supplies
To supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common welding power supplies are constant current power supplies and constant voltage power supplies. In arc welding, the length of the arc is directly related to the voltage, and the amount of heat input is related to the current. Constant current power supplies are most often used for manual welding processes such as gas tungsten arc welding and shielded metal arc welding, because they maintain a relatively constant current even as the voltage varies. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. Constant voltage power supplies hold the voltage constant and vary the current, and as a result, are most often used for automated welding processes such as gas metal arc welding, flux cored arc welding, and submerged arc welding. In these processes, arc length is kept constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. For example, if the wire and the base material get too close, the current will rapidly increase, which in turn causes the heat to increase and the tip of the wire to melt, returning it to its original separation distance.
The type of current used in arc welding also plays an important role in welding. Consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. In welding, the positively charged anode will have a greater heat concentration, and as a result, changing the polarity of the electrode has an impact on weld properties. If the electrode is positively charged, the base metal will be hotter, increasing weld penetration and welding speed. Alternatively, a negatively charged electrode results in more shallow welds.Nonconsumable electrode processes, such as gas tungsten arc welding, can use either type of direct current, as well as alternating current. However, with direct current, because the electrode only creates the arc and does not provide filler material, a positively charged electrode causes shallow welds, while a negatively charged electrode makes deeper welds. Alternating current rapidly moves between these two, resulting in medium-penetration welds. One disadvantage of AC, the fact that the arc must be re-ignited after every zero crossing, has been addressed with the invention of special power units that produce a square wave pattern instead of the normal sine wave, making rapid zero crossings possible and minimizing the effects of the problem.
Processes

Shielded metal arc welding
One of the most common types of arc welding is shielded metal arc welding (SMAW), which is also known as manual metal arc welding (MMA) or stick welding. Electric current is used to strike an arc between the base material and consumable electrode rod, which is made of steel and is covered with a flux that protects the weld area from oxidation and contamination by producing CO2 gas during the welding process. The electrode core itself acts as filler material, making a separate filler unnecessary.
The process is versatile and can be performed with relatively inexpensive equipment, making it well suited to shop jobs and field work An operator can become reasonably proficient with a modest amount of training and can achieve mastery with experience. Weld times are rather slow, since the consumable electrodes must be frequently replaced and because slag, the residue from the flux, must be chipped away after welding Furthermore, the process is generally limited to welding ferrous materials, though special electrodes have made possible the welding of cast iron, nickel, aluminium, copper, and other metals. Inexperienced operators may find it difficult to make good out-of-position welds with this process.
Gas metal arc welding (GMAW), also known as metal inert gas or MIG welding, is a semi-automatic or automatic process that uses a continuous wire feed as an electrode and an inert or semi-inert gas mixture to protect the weld from contamination. As with SMAW, reasonable operator proficiency can be achieved with modest training. Since the electrode is continuous, welding speeds are greater for GMAW than for SMAW. Also, the smaller arc size compared to the shielded metal arc welding process makes it easier to make out-of-position welds (e.g., overhead joints, as would be welded underneath a structure).
The equipment required to perform the GMAW process is more complex and expensive than that required for SMAW, and requires a more complex setup procedure. Therefore, GMAW is less portable and versatile, and due to the use of a separate shielding gas, is not particularly suitable for outdoor work. However, owing to the higher average rate at which welds can be completed, GMAW is well suited to production welding. The process can be applied to a wide variety of metals, both ferrous and non-ferrous.
A related process, flux-cored arc welding (FCAW), uses similar equipment but uses wire consisting of a steel electrode surrounding a powder fill material. This cored wire is more expensive than the standard solid wire and can generate fumes and/or slag, but it permits even higher welding speed and greater metal penetration.
Gas tungsten arc welding (GTAW), or tungsten inert gas (TIG) welding (also sometimes erroneously referred to as heliarc welding), is a manual welding process that uses a nonconsumable tungsten electrode, an inert or semi-inert gas mixture, and a separate filler material. Especially useful for welding thin materials, this method is characterized by a stable arc and high quality welds, but it requires significant operator skill and can only be accomplished at relatively low speeds.
GTAW can be used on nearly all weldable metals, though it is most often applied to stainless steel and light metals. It is often used when quality welds are extremely important, such as in bicycle, aircraft and naval applications.A related process, plasma arc welding, also uses a tungsten electrode but uses plasma gas to make the arc. The arc is more concentrated than the GTAW arc, making transverse control more critical and thus generally restricting the technique to a mechanized process. Because of its stable current, the method can be used on a wider range of material thicknesses than can the GTAW process, and furthermore, it is much faster. It can be applied to all of the same materials as GTAW except magnesium, and automated welding of stainless steel is one important application of the process. A variation of the process is plasma cutting, an efficient steel cutting process.
Submerged arc welding (SAW) is a high-productivity welding method in which the arc is struck beneath a covering layer of flux. This increases arc quality, since contaminants in the atmosphere are blocked by the flux. The slag that forms on the weld generally comes off by itself, and combined with the use of a continuous wire feed, the weld deposition rate is high. Working conditions are much improved over other arc welding processes, since the flux hides the arc and almost no smoke is produced. The process is commonly used in industry, especially for large products and in the manufacture of welded pressure vessels. Other arc welding processes include atomic hydrogen welding, carbon arc welding, electroslag welding, electrogas welding, and stud arc welding.

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Steelmaking

Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required.
The materials used in modern steelmaking are:
The iron produced in a blast furnace, either as molten iron or as pig iron.
Scrap steel.
Alloying elements.
The electric arc furnace is used to remelt scrap steel so that it can be used again for producing steel products by forging or rolling. This is the difference with a blast furnace where new steel is produced from iron ore.
The original methods of producing steel were labour-intensive and highly skilled arts involving open crucibles, see finery forge, puddling, blister steel, crucible steel.
An important aspect of the industrial revolution was the development of large-scale methods of producing forgeable metal (bar iron or steel). The puddling furnace was initially a means of producing wrought iron, but was later applied to steel production. The Bessemer converter was the first successful mass steelmaking process, followed by the open hearth furnace.

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Radar gun

How radar guns work
Radar guns are, in their most simple form, radio transmitters and receivers. They send out a radio signal, then receive the same signal back as it bounces off the objects. However, the radar frequency is different when it comes back, and from that difference the radar gun can calculate vehicle speed.
A radar beam is similar to the beam of a flashlight as it spreads out as the distance from the signal origin increases. The signal then bounces off objects in the path of the beam and are reflected back to the gun. The gun uses the doppler effect to calculate the speed of the object in the beam's path. Using a comparison of frequency shift between received images instead of the frequency shift between sent and received frequencies creates what is known as moving radar, the radar must be stationary to measure speed.
All bands of radar work the same way; they simply operate on different frequencies. X band guns are becoming less common due to the fact the beam is strong and easily detectable. Also, most automatic doors utilize radio waves on X band and can possibly affect the readings of police radar. As a result K band and Ka band are most commonly used by police agencies.
Traffic radar comes in many models. There are hand held, stationary and moving radar instruments. Hand held units are mostly battery powered, and for the most part are used as stationary speed enforcement tools. Stationary radar is mounted in police vehicles, and may have one or two antennas. These are employed when the vehicle is parked. Moving radar is employed, as the name implies, when the police vehicle is in motion. These devices are very sophisticated, able to track vehicles approaching and receding both in front of and behind the patrol vehicle. They can also track the fastest vehicle in the selected radar beam, front or rear.

Problems with radar guns
Although radar is an effective tool to acquire an object's speed, there are problems with it. Today's technology is relatively effective and error free so most inaccurate speed measurements are caused by the user.
For speed to be accurately calculated, the object whose speed is desired ideally should be the only moving object in the beam of the radar. If this is not the case, as in a police officer monitoring speed on a stretch of busy road, more articulation is needed in testifying to a particular vehicle's speed.
The National Highway Traffic Safety Administration (NHTSA), in cooperation with the International Association of Chiefs of Police (IACP) has developed a training program for the operation of police traffic radar. This curriculum provides radar instrument operators with the skills required to properly set up, test, and operate to identify targets. It also provides the operators with information regarding state and local laws and ordinances which apply to the user's jurisdiction. This training, while strongly recommended, is not mandatory in some states. Other states require the successful completion of this training and issue a certificate of completion.
Police officers are also trained in the practice of visual estimation of speed and distance, and the radar is thus used as a verification of the visual estimation. In addition, it is easy enough to testify that the vehicle in the offside lane was passing vehicles in the nearside lane, and is therefore the vehicle whose speed is showing on the readout as traveling above the posted limit.
The angle in which the object is in relation to the radar source can also affect the reading. This phenomenon includes angles on a horizontal and vertical plane and is known as the Cosine Effect. It is suggested that interference in the RADAR band by cellular phones, transmitters of other kinds, power wires, high tension wires, signs and even stationary walls can create erroneous readings. This is not taken into account when a photo RADAR is used and numerous discrepancies can creep in.

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Radar detector

Description
One of the technologies that law enforcement agencies can use to measure the speed of a moving vehicle uses doppler radar to beam a radio wave at the vehicle, and then infer the vehicle's speed by measuring the Doppler effect-moderated change in the reflected wave's frequency. Radar guns can be hand-held, vehicle mounted or statically mounted.
Radar detectors use a superheterodyne receiver to detect these electromagnetic emissions from the radar gun, and raise an alarm to notify the motorist when a transmission is detected. False alarms can occur however due to the large number of devices, such as automatic door openers, that operate in the same part of the electromagnetic spectrum as radar guns.

Counter technology
Radar guns and detectors have evolved alternately over time to counter each other's technology in a form of civilian electronic "warfare". For example, as new frequencies have been introduced, radar detectors have initially been "blind" to them until their technology too has been updated. Similarly, the length of time and strength of the transmissions have been lowered to reduce the chance of detection, which in turn has resulted in more sensitive receivers and more sophisticated software counter technology. Lastly, radar detectors may combine other technologies, such as GPS-based technology with a point of interest database of known speed trapping locations, into a single device to improve their chances of success.

Radar Detector Detectors
Main article: Radar detector detector
The superheterodyne receiver in radar detectors have a local oscillator that radiates slightly, so it is possible to build a radar-detector detector, which detects such emissions (usually the frequency of the radar type being detected, plus about 10 MHz). The VG-2 Interceptor was the first device developed for this purpose, but has since been eclipsed by the Spectre III. This form of "electronic warfare" cuts both ways - since detector-detectors use a similar superheterodyne receiver, many early "stealth" radar detectors were equipped with a radar-detector-detector-detector circuit, which shuts down the main radar receiver when the detector-detector's signal is sensed, thus preventing detection by such equipment. This technique borrows from ELINT surveillance countermeasures. In the early 1990s, BEL-Tronics, Inc. of Ontario, Canada (where radar detector use is prohibited) found that the local oscillator frequency of the detector could be altered to be out of the range of the VG-2 Interceptor. This resulted in detector manufacturers responding by changing their local oscillator frequency. Today, practically every radar detector on the market is immune to the VG-2 Interceptor.

Radar Scrambling
Although some companies advertise that their radar detectors can passively 'scramble' or 'absorb' radar (such as Rocky Mountain Radar), many or all of their products do not affect radar and laser equipment due to the low power intake from the device versus the high power that bounces off a vehicle.
It is illegal in many countries to sell or possess any products that actively transmit radar signals intended to jam radar equipment.Actively transmitting on an FCC licensed frequency without a license is a violation of FCC regulations and a felony in the USA.

LIDAR Detection
Main article: LIDAR detector
Newer speed detection devices use pulsed laser light, commonly referred to as LIDAR, rather than radio waves. Radar detectors, which detect radio transmissions, are therefore unable to detect the infrared light emitted by LIDAR guns so a different type of device called a LIDAR detector is required. LIDAR detection, however, is not nearly as effective as radar detection because the output beam is very focused. While radar's radio waves can expand to 85 feet (26 m) across at 1,000 feet (300 m) from their source, LIDAR's light beam diffuses to only about 6 feet (1.8 m). Also, a police officer targeting a car will most likely aim for the center mass or headlight of the vehicle and, because radar detectors are mounted on the windshield away from the beam's aim, they may not alert at all. Lastly, with such a focused beam, an officer using a LIDAR gun can target a single car in close proximity to others at ranges of up to 3,000 feet (910 m).
Despite the advent of LIDAR speed detection, radar remains more prevalent because of its lower price relative to LIDAR equipment and the amount of radar equipment already in service.