Material flow is an important aspect of lean manufacturing. Getting parts to the assembly line without wasted motion is essential. Unfortunately, material handling often creates bottlenecks and ergonomic risks. To solve the problem, assemblers can turn to automated material handling equipment, such as driverless carts, robotic parts bins and autonomous tuggers.
The basic concept behind automated guided vehicles (AGVs) has been around for decades. However, advanced technology is creating demand for a new generation of driverless vehicles that are cost-effective, reliable and flexible.
“Today’s AGVs are simpler, cheaper and more robust than their predecessors,” says Jim Caie, vice president of ARC Advisory Group (Dedham, MA). Caie formerly served as director of controls, conveyors, robotics and welding at General Motors Corp. (GM, Detroit), where he was responsible for early wide-scale application of driverless technology in an assembly environment.
Traditionally, AGVs operate in a loop and are used to transport parts, components and subassemblies from a storeroom or warehouse to an assembly line. But, new technology also allows the devices to automatically load and unload delivery trucks. For instance, at Chrysler’s Belvidere, IL, assembly plant, AGVs interact with robots to unload racks of instrument panels from semitrailers and then return the racks when they’re empty.
Although AGVs were often touted as a panacea in the 1970s and 1980s, the industry is now grappling with a tarnished image. “Most manufacturing engineers are simply more comfortable with conveyor technology,” says Caie.
“That’s one of the biggest hurdles that AGV vendors have faced,” adds Caie. “Traditionally, AGVs have been approximately the same price as a cheap conveyor system. Engineers also know that a conveyor is something that will definitely work, whereas AGVs have been prone to reliability problems in the past. That’s why many manufacturers have shied away from AGVs until now.”
Caie says AGVs are still perceived to be more expensive to deploy, operate and maintain than conveyors. But, as more manufacturers push for flexible assembly lines and lean production processes, the latest generation of AGVs have become more appealing to many engineers.
According to the Material Handling Industry of America (MHIA, Charlotte, NC), an AGV system consists of one or more computer-controlled, wheel-based load carriers. The battery-powered devices operate without a driver and come in a wide variety of sizes, shapes and styles, including tuggers that pull a string of carts or trailers in a train; unit load carriers that move work-in-process from one assembly workstation to another; forked pallet trucks that interface with pickup and dropoff points on the plant floor; and automated guided carts that are smaller, cheaper and easier to install than traditional AGVs.
Not Your Father's AGVWhen the first unmanned systems appeared in the late 1950s, they were simple devices that followed a wire embedded in the floor instead of the rigid rail of a conveyor. Today, AGVs use state-of the-art technology to navigate complex routes. And, a variety of onboard electronic devices allow them to communicate to other production equipment, such as machine tools and robots.
The latest generation of AGVs differ from what was available a decade ago, says Yves Gavin, vice president of engineering at Egemin Automation Inc. (Holland, MI). “The major difference is the jump in technology we have seen in the last 10 years,” he explains. “That [has allowed us] to introduce new components, such as sensors and computers, with greatly improved functionality at decreasing costs, making AGVs much more reliable.”
For instance, most AGVs carry an onboard programmable logic controller (PLC). “More computing power has allowed driverless vehicles to incorporate more complex software in a user-friendly format,” notes Mark Longacre, marketing manager at JBT Corp. (Chalfont, PA), which recently changed its name from FMC Technologies. “In addition, more robust sensors have improved reliability.”
Electronic equipment is getting smaller, more powerful and easier to work with, especially when used in conjunction with radio frequency identification (RFID) technology and wireless communication devices. Many vehicles are also equipped with large flat-screen monitors, touchscreens and 3D graphics that make programming, maintenance and troubleshooting easier than ever. In addition, new software packages are well-suited to AGV position monitoring, which improves visibility, routing and traffic control.
Automated material handling appeals to manufacturers in a wide variety of industries because it helps reduce labor costs while improving operating efficiency through greater consistency. Driverless vehicles are also widely used in warehouses, distribution centers, newspaper printing plants, breweries and beverage bottling plants, in addition to large hospitals.
However, most manufacturing engineers associate AGVs with automotive assembly plants. In fact, some of the very first applications occurred in the auto industry. In the mid-1970s, engineers at AB Volvo (Gothenburg, Sweden) implemented driverless systems at the company’s assembly plants in Gothenburg and Kalmar. During the mid-1980s, GM engineers used the technology with mixed results to automate factories in Detroit, Oshawa, ON, and Saginaw, MI.
When mass-producing automobiles, there is “an incredible quantity of parts moving through the plant,” says Longacre. “Movement of these parts is predictable and repeatable. Automakers want to reduce the amount of labor it takes to build a car and only use people where it is absolutely required. AGV systems fill those needs very well.”
Unfortunately, some gee-whiz applications in the auto industry gave driverless devices a black eye. In the past, AGVs developed a reputation for being expensive, unreliable and inflexible. Many customers felt that their big investment in the technology never delivered the promised ROI.
“During the 1980s and 1990s, AGV systems were typically touted to be, and sold as, the complete solution to almost any material handling need,” notes Neville Croft, vice president of AutoMotion Systems Inc. (St. Augustine, FL). “Also, when an AGV was sold during the early days, it was essentially a black box with a support umbilical firmly attached between the provider and the end user.
“If any issues occurred, and they did, the end user had little or no choice other than being forced into working with the provider,” adds Croft. End users had their hands tied; when something didn’t work, they had to call the vendor for help. “This was potentially disruptive and expensive,” Croft points out. “The supplier had the upper hand. That’s what gave AGVs a bad name.”
Today, manufacturers want material handling automation that meets their unique needs, rather than a generic, one-size-fits-all solution. “Customers are operating leaner and leaner these days, so they must deal with limited manpower,” says Keith Soderlund, vice president of sales at Creform Corp. (Greer, SC). “Recognizing that material movement adds no value to their products, manufacturers are re-evaluating their material handling needs. They see that the process can be automated to free up people for value-adding activities.”
Robust MarketResearchers at the Freedonia Group Inc. (Cleveland) predict there will be a healthy demand for automated material handling equipment, such as AGVs, during the next decade. In fact, they claim that the worldwide market will grow 6 percent annually between now and 2017. “These types of products can enhance the productivity of the material handling function, and are amenable to integration into larger-scale factory automation environments,” says Mike Deneen, a senior analyst.
Driverless systems are gaining popularity in midsized companies in various industries, and many auto parts suppliers are now using the technology-not just OEMs. Manufacturers in nonautomotive industries, such as aerospace and agricultural equipment, are also turning to AGVs as part of their lean initiatives. For instance, both Boeing Commercial Airplanes (Renton, WA) and Deere & Co. (Moline, IL) have invested in automated material handling systems.
Whether they’re big or small, manufacturers want low-end AGVs that are cheaper, less complex, and easier to install and use. “They don’t want all the bells and whistles,” notes Jay Yale, managing director of Frog AGV Systems Inc. (Auburn Hills, MI). “Because everyone’s looking for a cost-effective solution to their material handling needs, they want a scaled-down version of traditional AGVs.”
The material handling industry has come up with a solution. It’s a device called an automated guided cart (AGC), which excels in applications where lighter loads and flexibility is required.
“These low-end vehicles are the most flexible AGVs and are often the easiest to install,” says Soderlund. “Another characteristic of these vehicles is their small size, which permits them to navigate in space-restrictive areas.”
“People find that keeping their systems and vehicles as simple as possible helps reduce investment and makes maintenance easier,” adds Soderlund. “The competition in this segment is strong, so customers are ensured of good value in their vehicle system.”
Flexibility is another benefits of using AGCs. They allow manufacturing engineers to change the vehicle system regularly to compliment ever-changing assembly processes.
“Vehicles and guidepaths can be easily upgraded and changed,” explains Brian Stewart, chief operating officer of Jervis B. Webb Co. (Farmington Hills, MI). “Because the system is neat and compact, it’s also easy to troubleshoot and replace boards.
“Simply by adding or removing AGCs from the line, assembly production rates can be increased or decreased on demand,” concludes Stewart. “Because of their flexibility, AGCs are an excellent choice for companies adhering to continuous improvement initiatives.” A
Beware of Navigational Hazards
When choosing an automated guided vehicle system, end users now have more guidance options to choose from than in the past. But, there are shortcomings with all the navigation processes offered today. For instance, narrow aisles and false reflections create challenges with some systems. Each of the following technologies has pros and cons that engineers must carefully evaluate:
Wire. Traditionally, AGVs have used wire guidance systems. With this technology, an electronic frequency is induced in a wire that is buried in the floor. Another wire is used for communication. Driverless material handling vehicles are equipped with a sensor and an antenna that seek out a low-voltage, low-frequency signal that guides the vehicle along a fixed path. To change paths, the vehicle switches to a different frequency. “This simple guidance system is widely used because of its accuracy and dependability,” says Brian Stewart, chief operating officer of Jervis B. Webb Co. (Farmington Hills, MI). However, wire-guided systems can be expensive to install, because plant floors need to be dug up or cut to embed the wire.
Tape. As an alternative to wire, many AGV users create a guidepath on the plant floor with tape. Surface-mounted magnetic tape or optical strips are typically much cheaper than other guidance methods and offer a greater amount of flexibility. Additional pieces of tape, placed perpendicular to the guidepath, are used to signal commands such as speed changes, directional changes or stops. “This method is the most cost-effective and flexible, allowing guidepath changes to be made in hours vs. days,” notes Stewart. However, tape tends to deteriorate over time and damaged tape can create a maintenance or safety issue in some applications.
Laser. Approximately 50 percent of today’s AGVs use laser measurement systems to detect reflector marks within an operating environment. The lasers measure distance and provide onboard computers with precise information for absolute vehicle positioning. Vehicles navigate by using a laser scanner that measures angles and distances to reflectors that are mounted on walls and machines throughout a plant. “Laser solutions allow the vehicle’s path to be more flexible,” says Steve Aamodt, mobile vehicle market manager at SICK Inc. (Minneapolis). “This type of solution gives users the ability to change routes easily without the capital expenditures that would be typical with a wire-guided system. Laser solutions also open up a wider range of applications, such as truck loading and unloading, where it is difficult to place wire or tape.”
Inertial. An inertial guidance system uses technology that is similar to the way military missiles operate. Automated material handling devices use a solid-state gyro vehicle control computer to accurately maintain the intended path and speed needed to perform a task. Transponders embedded in the plant floor are sensed by the vehicle to confirm its specific location. “Inertial systems can operate in nearly any environment, including tight aisles or extreme temperatures, and have a longer lifespan than other guidance options,” claims Stewart.
Vision. The latest generation of AGVs use machine vision technology to operate without a defined pathway on the plant floor. By using inexpensive onboard cameras and intelligent software, these devices are taught to follow paths and navigate independently. “This technology relies much more on internal software than the more proprietary hardware-centric approach of even laser-guided AGVs,” claims Greg Cronin, executive vice president of Seegrid Corp. (Pittsburgh). “[Vision-guided mobile] robots literally see their environment and learn from it. As a result, they can react much more dynamically to changing needs or real-time activities on the floor.” The technology was recently deployed at a Freightliner assembly plant in Gastonia, NC.
To learn more about automated material handling, search for these articles on ASSEMBLY’s Web site:
AGVs vs. Conveyors.
Next-Generation AGV Technology.
The Lean Side of AGVs.