ASSEMBLY has been keeping engineers up to speed on the latest conveyor technology since it debuted. Fifty years ago, most conveyors consisted of belts, chains and rollers. Modular conveyors, skillet conveyors, self-propelled conveyors, automated guided vehicles and other material handling technology commonly found on plant floors today did not exist.
Automated assembly lines and conveyors go hand in hand. It’s hard to have one without the other. No matter what type of product is being assembled, conveyors are an essential element of mass production.
When ASSEMBLY magazine debuted in the late 1950s, modular conveyors, skillet conveyors, self-propelled conveyors, automated guided vehicles and other material handling technology commonly found on plant floors today did not exist. Fifty years ago, most conveyors consisted of belts, chains and rollers.
ASSEMBLY has been keeping engineers up to speed on the latest conveyor technology since it debuted. For instance, an article in the September 1960 issue explained how McCulloch Corp. (Los Angeles) assembled small gasoline engines using state-of-the-art conveyors. Operators built 10 different two-cycle engines that were used to power chain saws and go karts.
The article explained how “major assembly work is accomplished on three oval-shaped, bench-height conveyorized assembly lines. Each of these lines consists of a continuous conveyor threading the edge of a bench-height work table approximately 50 feet long and 6 feet wide.
“The ends of each table are rounded to facilitate conveyor travel. Ball-and socket adjustable fixtures, which in turn mount special holding fixtures, are attached to the conveyor at 36-inch intervals.” Up to 40 engines could be assembled at one time on each table. An overhead conveyor crossed each of the three assembly lines and transported engines to test and inspection, painting and final assembly workstations located in other parts of the factory.
Traditionally, conveyors were used to improve the efficiency of manual or semiautomated assembly processes. But, by the mid-1960s, conveyors were also part of fully automated systems. An article in the June 1965 issue discussed a new system used at the Polaroid Corp. plant in Waltham, MA. Engineers from the instant-camera company and Link-Belt Co. spent 5 years developing the conveyor system, which handled “the complete fabrication and assembly of packs for both color and black and white film.”
Conveyors routed parts from fabricating machines on the first floor of the factory that made plastic box bottoms, metal box covers and metal pressure plates. The parts were conveyed to automatic assembly machines located on the second floor. The machines assembled the parts and joined them with film and developing materials to form a finished pack. Once assembled, conveyors transferred the packs to automatic packaging machines. According to the article, “the parts go untouched by human hands until the user puts the film pack into his camera.”
Power-and-free conveyors were introduced in the 1960s and became popular with manufacturers of large, heavy objects, such as engines and transmissions. Many plants adopted the technology in an overhead arrangement, which allowed operators to access all sides of the assembly.
Despite improvements such as rivetless conveyor chain, flexible plastic chain and nylon trolley wheels, the basic concept behind conveyors has not changed in the last 50 years. “In most cases, a majority of conveyors used in today’s plants are similar in concept to what has been used for the past 40 to 50 years,” says Richard Shore, president of Automation & Modular Components Inc. (Davisburg, MI). “The only difference is what they are manufactured from. Aluminum and plastic are now used more often than steel.”
Demands on conveyors are also much greater than they were in the past. “A conveyor today is expected to run at high speeds 24 hours a day, 7 days a week, but cost much less than 40 years ago,” notes Shore.
Contemporary assembly lines typically contain more conveyors. And, the ongoing miniaturization of electronics, medical devices and other products have forced conveyors to become smaller and more accurate.
“New features, such as clean room compatibility, electrostatic discharge, high temperatures, [humidity control] and higher positioning accuracy, had to be designed into conveyors due to greater product and assembly requirements,” explains Stefan Reitmeier, manager of material flow systems at Bosch Rexroth AG (Stuttgart, Germany). For instance, he says contact lenses, hearing aids, pacemakers, video games and solar panels are just a few types of products that did not exist in the late 1950s.
“Smaller and more modular units of conveyors have created new options in flexibility,” says Dave Helgerson, chief technology officer at MagStar Technologies Inc. (Hopkins, MN). “Conveyor functionality has expanded into diverting and accumulating products. Integrated intelligence and control in the assembly process has allowed for a higher level of automation than previously experienced.”
According to Paul Jarossy, director of marketing at FlexLink Systems Inc. (Allentown, PA), plant floors today typically have more conveyors that are shorter and feature more sophisticated controls than their predecessors. “Assembly lines tend to have a cleaner, yet compact layout as demands on total efficiency increase,” he points out.
“With the [continuous] advancement in electronic components, computers, cell phones [and other high-tech devices], new applications for conveyors exist now that certainly weren’t needed 50 years ago,” adds Ray Johnson, lead engineer at Automated Conveying Systems Inc. (Bloomington, MN). “Medical products and the pharmaceutical field have created a need for specialty conveyors that continues to expand. The common thread in all of these markets has been the development of clean room conveyors.”
The concept of modular assembly lines is often associated with today’s lean manufacturing initiatives. However, it’s been around a lot longer. For instance, an article extolling the benefits of modular workstations and conveyors appeared in the February 1967 issue of ASSEMBLY. The author explained how this “building block approach” was brought about by “the growing need for flexibility in work surface design and layout to cope with changing manufacturing requirements.”
The introduction of extruded aluminum structural profiles in the late 1970s had a major impact on modular conveyors. They allow engineers to bolt-together components that can be reconfigured in response to changes in product mix or production volume.
“Modular, reconfigurable conveyors allow for layout changes,” notes Helgerson. “Flexibility is essential to manufacturers to allow layout changes and product changes while using the same equipment. Conveyors today are more integrated into the application; automation and integration allows conveyors to contribute more to an automated process.”
“Quicker cycle times and smaller companies have brought about a demand for conveyors that are quickly delivered in standard configurations and customized by the end user,” says Gregory Ferguson, vice president of SmartMove Conveyors (Fall River, MA). “Modular conveyors allow customers to quickly and inexpensively modify their existing equipment to meet changes in material flow.”
“Everything today is about modularity and flexibility,” adds Michael Scott, vice president of sales and marketing at Logomat Automation Systems (Hebron, KY). In the past, conveyors were made for a particular product or application.
“Systems now are flexible solutions,” explains Scott. “Today, people want to place any module on the same conveyor instead of making the conveyor fit the part,” explains Scott. “Conveyor companies now provide the pallets; the pallet design never used to consider the conveyor supplier.”
Traditionally, conveyors were primarily used to assemble products. But, in the 1960s, growing demand for electronic devices spurred new applications. For instance, more manufacturers began using conveyors to deliver parts directly to operators.
An article in the December 1967 issue of ASSEMBLY explained how Westinghouse Electric Corp. (Pittsburgh) used a conveyorized parts handling system to assemble electronic modules for industrial control systems. The company’s plant in Buffalo, NY, was originally laid out with island-type assembly stations where operators would manually attach transistors, diodes, resistors, capacitors and other components to printed circuit boards.
However, that production method was inefficient, because assemblers were wasting too much valuable time moving materials back and forth. That excessive handling also increased the risk of damaging parts.
A dual-conveyor system solved the problem by allowing continuous assembly of the circuit board modules. “The longer of the two, a 23 station system, forms the backbone of the printed circuit assembly line,” explained a manufacturing engineer. “After the circuit boards have been assembled and tested, they are returned to a central dispatching area, and then sent to workstations on a 15 station line where they are integrated into complete modules.”
According to the engineer, “the objective of providing the shortest possible cycle time from the time an order is received to the time it is shipped is well on its way to becoming a reality. The combination straight-line systems have made it possible to accommodate a substantial increase in production. At the same time, the floor space, parts handling requirements and man-hours per assembly have been reduced.”
After OSHA was created in the early 1970s, many manufacturers were forced to invest in conveyor technology to conform with new regulations that demanded safer workplaces. The industry responded by offering low-profile, low-power conveyors with easy human access and safeguards, such as covers over chains, rollers, sprockets and other moving parts.
“The early 1970s was the beginning of a major trend toward the use of low-profile conveyors,” says Anthony Mitchell, vice president of Conveyor Technologies Ltd. (Milford, OH). “These smaller, more compact conveyors allowed them to be easily adapted into many new industries. Belt development, as well as improved drives, also contributed to increases in flexibility and performance.”
Some engineers believed that the ultimate form of safety involved floating on air. Indeed, an article in the June 1972 issue of ASSEMBLY described how heavy-duty compressors weighing up to 6,500 pounds were easily moved down an assembly line while riding on air cushions. Engineers at Joy Manufacturing Co. (Michigan City, IN) wanted a material handling system that could raise and lower fixtures to a height that would make assembly operations more efficient and less fatiguing.
The air cushions operated when shop air was introduced into a large cushion in the form of a flexible, torus-shaped bag. “As the bag inflates, air is also introduced into a plenum chamber that is formed by the inside diameter of the torus, the underside of the platform and the shop floor,” explained one of the company’s manufacturing engineers. “When the total air pressure acting over the support area exceeds the total weight of the support and load, the system is lifted off the floor about 0.005 inch and hovers in position ready to be moved.”
In the early 1990s, self-powered conveyors were developed. Traditional palletized systems used belts or chains to move pallets. But, new technology made it possible to put motors in the pallets and made the conveyor a static rail.
“It completely flipped the way palletized transport systems work,” claims Will Hunter, general manager of Montech LLC (Huntersville, NC). “Because the rail does not have any continuously moving parts, it is inexpensive, easy to modify and can be configured to any layout. Most importantly, it does not have the heavy-wear belts and chains that can break and cause a shutdown.”
During the past decade, conveyor suppliers have been developing individually controllable pallets powered by linear motors, which can achieve fast speeds and high accuracy. Engineers can control the direction, acceleration, speed and position of each pallet at any point in the system. This eliminates hard stops and pallet-to-pallet contact. In addition, there’s no need to track pallets with bar codes or radio frequency identification (RFID) systems.
“The general availability of microprocessors and microcontrollers led to the creation of self-propelled conveyors, as well as conveyor modules and components with integrated controls,” says Bosch Rexroth’s Reitmeier. New technology, such as PLCs, field buses and RFID, have helped make conveyors more intelligent and allowed them to carry different product variants on the same line.
The increasing use of robots today has also created new applications for conveyors. For instance, low-profile, open-center conveyors make it easier to integrate robotic workcells, sensors and machine vision systems. As more robots are used for assembly and material handling applications, conveyor manufacturers have placed a new emphasis on controls.
“High-efficiency motors that deliver variable speeds and constant torques help conveyors be much more flexible,” explains SmartMove’s Ferguson. “Plug-and-play sensors allow customers to start and stop conveyors without expensive wiring or logic controls.”
“Mechanical [components] used to be 70 percent of the cost and controls were 30 percent,” says Logomat’s Scott. “Today, mechanical is 40 percent of the cost and controls are 60 percent.”
For instance, pneumatic components, such as stop-start devices, are now solenoid and servo-actuated, eliminating the need to plumb valves and wire motors. With the ability to efficiently control and vary line speed, various types of work can now be accomplished while products are in motion, such as inspection, labeling and packaging.
“Miniaturization of electronics lets us use custom circuit boards, allowing for a high-tech queuing conveyor without computer or PLC supervision,” notes MagStar’s Helgerson. “DC brushless and stepper motor technology allows us to use safe, low-power conveyor drives with an almost unlimited life.”
Traditionally, the motors and controls that drive conveyors have been tethered to a complex array of cable and wiring. But, recent advances in industrial wireless technology are allowing engineers to finally cut the cord. Wireless proximity switches and other controls hold many potential advantages over wired solutions, such as increased flexibility, improved monitoring, and lower installation and maintenance cost.
“I suspect [that future] improvements will be driven by products that are only being dreamed of now,” says Automated Conveying Systems’ Johnson. “[However], future conveyors will continue to be modifications of conveying principles that have existed for the past 50 years and longer.”
And, one day in the near future, some conveyors may be totally invisible, at least to the human eye. Scientists at Lawrence Berkeley National Laboratory (Berkeley, CA) have already transformed carbon nanotubes into conveyor belts capable of ferrying atom-sized particles to microscopic worksites.
By applying a small electrical current to a carbon nanotube, they moved indium particles along the tube “like auto parts on an assembly line,” says Chris Regan, a researcher in the laboratory’s materials sciences division. “It lays the groundwork for the high-throughput construction of atomic-scale optical, electronic and mechanical devices that will power the burgeoning field of nanotechnology.”
Conveyors Remain a Vital Link to Efficiency
August 31, 2007