Lean Machine-Tending Robotics
With flexible mounting and greater reach, tending robots do more in less floor space
By Michael Tolinski
When automotive component shops look to automation to cut costs, future results must justify the initial expense. So to improve the investment case for automated machine-tool tending, machine integrators are trying to incorporate or optimize every possible improvement in robot design. Some enhancements aid labor-costcutting by allowing one robot to tend two or more machines, for example. Or sleeker robots can reduce floor space requirements, opening up a shop for future expansion or additional production. Or zero-footprint robots can be mounted overhead, exploiting the full reach of the robot while de-cluttering the manufacturing cell.
Still, the overall emphasis for robotic machine tending remains greater speed and flexibility. This means robots must load and unload parts faster, allow quicker and easier job changeovers, and perform more automated secondary operations—such as part gaging or deburring. Improvements in these areas are timely for automotive component manufacturers looking to cut labor cost and remain competitive.
Even manufacturers in low-wage regions have turned to machine-tending robots. This year, production is reportedly ramping up at an engine block plant in Chongqing, China, at three cells that include robots from ABB Inc. (Norwalk, CT). In a two-minute cycle, each IRB 6600 robot extracts an engine block part from a casting machine, passes it through a checker, and sends it to a saw for trimming before placing it in a cooling shower bath. These cells for automaker Changan Suzuki were supplied by integrator Müller Weingarten (Erfurt, Germany). "Every robot spares a worker," says Jürgen Lamparter, director of the integrator's die-casting unit.
But an automation upgrade can sometimes be a difficult business case to make. Even with a solid argument showing that a new robot can recover its investment in a reasonable time, there are always concerns about the risks of using unproven technology or of over-investing for an application.
The "unknown factors" of robotics still hold some potential users back, says John Schneider of machine-tool supplier and integrator Arthur Machinery Inc. (Elk Grove Village, IL). User concerns often focus on how machine-tending automation will interfere with job changeovers, complicate maintenance, or reduce—rather than enhance—the flexibility of an operation. "That's the most common fear: they think [the automation] has to be dedicated to a particular part, and it does not."
Robot manufacturers and integrators, at least, have been willing to invest in developing slimmer systems that work faster and more intelligently—even systems that at first may seem too futuristic for the average machine shop. And these integrators argue that more manufacturers are looking to take the plunge into next-generation robotics.
"The increased use of robots for machine tending is a growing trend in the machine tool industry," says Dick Motley, manager, load/unload systems, for Fanuc Robotics America Inc. (Rochester Hills, MI). The reasons are connected to robots' flexibility of configuration, as well as their new vision capabilities, which make them "smart" enough to perform duties of other production or quality equipment. "Intelligent robots provide significant cost-savings advantages by eliminating the need for expensive part-feeding fixtures."
Properly chosen robotics support efficient floor space management around the machine tool. This efficiency depends on how to best handle the flows of material into and out of the machines, adds Fanuc's Mark Handelsman. "It's often surprising to see how much space is taken by conveyors or other part transfer devices, as well as the effective space taken by fork trucks getting material into/out of a line.
Different robot configurations free up different amounts of floor space. The basic case simply places the robot where an operator would stand, encircled by tools and production equipment, Handelsman says. One way to clear the floor is with gantry-mounted articulated robots placed over the cell. The robot can then act both as a means to load/unload machines, and as a way of transferring parts from machine to machine. "It also allows for single-piece work flow, avoiding costly and space-consuming means of queuing up parts and handling rejects."
This overhead "flip-over" concept is used with Fanuc's six-axis M-710iC robot, adds Handelsman. Said to be especially appropriate for machine tending, with a reach of 1360–2050 mm and payload of 50–70 kg, the 70T Toploader version of the robot is mounted upside-down to load/unload parts beneath it. "If you have the ability to lay out the machines," he observes, "then it's probably more common to put them in a line and use a robot like the Toploader," rather than use robots and conveyors for each machine.
Robots mounted in "underslung" or "sideslung" configurations from a rail allow different possible work envelopes. Overhead mounting gives a symmetrical work envelope on both sides under the rail; a sideslung robot provides the maximum vertical reach, useful for tending an injection-molding machine, for example. "For applications such as grinding, deburring, or dispensing, the flipover design provides an extremely large work envelope that would be impossible to reach with a floor-mounted robot," says Handelsman.
Adding to the robot's abilities to handle parts and error-proof a process is Fanuc's iRVision 3D laser vision sensor, now made available with all the company's robots (reportedly driving down its cost). The vision system enables simple tasks like checking part orientation before machining to avoid tool damage, or postprocess checks of critical features to make sure they were machined properly, Handelsman adds. And unlike other vision systems that require a PC or dedicated monitor on the shop floor, this system displays images on the robot's teach pendant.
Smaller robots for machine tending also offer mounting options—outside or inside of the machine tool. Portable mounting concepts give shops additional ways of using and repositioning tending robots. For example, Arthur Machinery integrates robots from Stäubli Corp. (Duncan, SC) on railmounted platforms that can be moved away from the machine tool when necessary. The concept gives personnel access to the machine to change tools or to run prototypes or unusual stock.
"Customers really grasp the concept when they come here, because they think the robot needs to live in front of one machine," says Arthur product specialist Steve Runge. But few operations seek fixed, dedicated robots for machine tending. "Job shops still want to still run bar jobs; the next day they want to run a chucking job by hand; and the next day they want to run with the robot for a longer-running job."
Arthur's clients have demonstrated this concept in specific automotive manufacturing situations. The company's John Schneider points to a "high-end, high-volume automotive airbag manufacturer" whose full identity he could not reveal. The company has used a Stäubli robot mounted on rails to tend two machining centers for about four months while the shop has a new transfer machine built for the job. "When that's done, those two machines will go to do something else, and that robot will be put between two turning centers."
Small tending robots can also be mounted inside the machining or turning center itself. Machines with internal robots are sold as complete systems, or robots can be retrofitted into machines in the field, says Schneider. "We have on our floor right now a Haas Mini Mill with the robot mounted inside the upper-right hand corner. We can do that in any VMC," though he adds that certain models have particularly accessible mounting points.
One of the obvious benefits is saved space on the shop floor. "You're incorporating it into a machine tool, which is already using floor space," says David Arceneaux of Stäubli. And given the dirty internal machine environment, he confirms that the robots used are constructed with IP67-type resistance to lubricants and chips, especially in the robot's wrist area, where these materials might otherwise tend to accumulate.
"The other advantage of it being mounted inside the machine is that your load and unload time is short," adds Schneider. Part conveyors come right inside the machine; the robot picks up raw product and loads it into the workholding. When the machine tool is finished, the robot unloads the part and places it on a conveyor heading out of the machine. "So you don't have to deal with an automatic door opening up and closing." This saves precious seconds.
Other OEMs offer inside-themachine robots. For example, Fanuc's upgraded LR Mate 200iC is reportedly used as a dedicated machine loader mounted on top of, in front of, or inside of a machine tool. And some machine-tool OEMs offer pre-integrated robot tenders; Fuji Machine America Corp. (Vernon Hills, IL), for example, offers a pinion swing-arm robot in its TNW-series twin-spindle lathes. The company's ANW-3500 lathe includes a 7-kg-payload robot, and is said to be ideal for large hubs, small differential cases, and disk brakes and rotors. Recently, two Fuji machines and an integrated robot reportedly were demonstrated producing bearing ring components in 35 sec, with "on-the-fly" spindle loading in 2.5 sec.
Back outside the machine, an extra axis of movement—and the sinuous movements of an unorthodox robot design—makes machine-tending a bit leaner and cleaner, according to Motoman Inc. (West Carrollton, OH). The company's distinctive IA20 multilink robot has made the tradeshow rounds, and has recently been demonstrated tending two machines at the same time, loading and unloading wheel-hub components. The 20-kg-capacity robot uses only about 1 ft2 (0.093 m2) of floor space when offline in its vertical (stored) position, the company says. Yet the robot, 1590-mm tall when stored, still has an 1140-mm horizontal reach.
Tom Sipple, Motoman handling technology leader, points to the IA20's seven-axis design. "The real benefit of the arm is recognized when you consider the position of the axes and the length of the links between the axes." In a traditional robot of similar size, the company's HP20, an axis link is as long as 795 mm. "The IA20's longest link is 267.5 mm. Also, on the IA20 every other axis on the robot is offset 90° from the previous." Compounded across seven links, this multiplies its range of motion and flexibility.
"The IA20 offers many benefits for machine tending," argues Sipple. "The high flexibility of the IA20 will allow—in some cases—the robot to be mounted between the machines rather than in front of the machines." This reduces the floor space required significantly, compared with what a standard robot would need for tending two machines. Motoman offers an example of a layout that shows almost a 60% reduced floor footprint when using one IA20 to tend two machine tools and a typical conveyor, compared with the footprint of a standard robot.
The design also allows the front of each machine tool to stay clear for running prototype parts off-line, or for maintenance, he adds. "It's not unusual to hear concerns from a customer that a robot will be 'in the way' during maintenance, setup, or prototype runs. The IA20, when positioned between the machines, eliminates this concern."
The robot reportedly has a light-weight, hollow-shaft design, reducing its moment of inertia. "This allows the robot to handle tools and parts that are larger and have more mass," says Sipple. Moreover, "the actuator-based design provides a hollow path for electrical wiring and air hoses through the center of the arm," eliminating potential interferences. And, to add more flexibility, the 120-kg robot can be floor, wall, or ceiling-mounted.
But fitting these tending robots between other equipment requires advanced planning. Within a restricted amount of shop-floor space, a robot typically must work in close quarters with machine tools, check fixtures, conveyors, and secondary operation equipment. Thus, major robotics OEMs offer software that helps integrators and manufacturers simulate how a machine-tending robot will perform in service. For example, Fanuc's Roboguide offline software program helps users create part-production programs, showing areas of potential problems that might occur. "Roboguide allows designers to verify in 3-D that the robots will fit without interferences or other problems," says Mark Handelsman.
Likewise, the robotics division of ABB offers software for creating a "virtual robotic cell," reportedly without special training, in less than an hour. The RobotStudio Machine Tending PowerPac allows users to test different configurations and robot position, assessing variables including cycle time, cell footprint, and "reachability." Software modules lay out popular brands of machines and peripheral stations that are represented graphically on screen, or users can import their own CAD models. Though initially focused on cell-building for injection molding, the software is being preloaded with models of Okuma machines for metal cutting, says Erwin DiMalanta, ABB business development manager.
Statistics from simulations are useful if they expose potential bottlenecks that will occur during real production. Or, as Handelsman adds, "It's much less expensive to move robots around and modify tooling in the virtual 3-D world, rather than on the plant floor, when you realize there is a problem."
This article was first published in the September 2007 edition of Manufacturing Engineering magazine.