Once a pallet is loaded, the conveyor portion of the system moves the pallet to the storage area
To make robotic palletizing work in material handling applications, the secret is custom end effectors. This one-of-a-kind design for Maple-Vail Book Manufacturing Co., quickly and deftly handles partially finished books, saving labor costs of $120,000 per year.
It seems like a simple task, removing stacks of unfinished books from one machine and placing them onto a pallet. It should be easy to automate. Until recently, though, manual labor was required to handle the fragile product. Scott Simons, vice president of operations, Maple Press Co., a part of the Maple-Vail Book Manufacturing Group, York, Pa., wanted to eliminate the cost of this labor. The 100-year old company produces 30 million books and related products annually. Automating the bookpalletizing task with robotic palletizers seemed the ideal solution, but it had always been a challenge.
"Other book manufacturers have tried to convert this task to robots, but they have not been successful," says Simons. "We'd been looking for a couple of years for a solution before we discovered Westfalia Technologies (York, Pa.) who made it work for us."
"Robotic palletizing is on the rise," says Daniel Labell, president, Westfalia Technologies, "replacing both manual and layer forming palletizing applications. Asia and Europe have used this technology more regularly than we in North America. The real issue with robotic palletizing is end-effector design. The basic robotic body and control system are commodities; they are standard and require little or no maintenance. The end effector, though, is key and usually must be custom designed. This is where a project can succeed or fail.
"Simplicity is obviously the best solution," says Labell. "However, often an end effector must do multiple functions."
Management at Maple Press wanted to automate a manual, entry-level job and reduce labor costs, which amounted to $120,000 per year. As Simons saw it, the job used resources poorly. Two employees on each of three shifts continually moved stacks of semi-finished books from an automated stacker to a storage pallet.
"We looked at palletizers," adds Simons, "but they were huge, clunky, hard to maintain, expensive, and they took up a lot of floor space. We realized that we wanted something, but that the palletizers were yesterday's technology."
The press prints, binds and puts covers on books. For each book, pages are printed and glued to a spine, then stacked with other books by an automated stacking machine. The hard covers go on at a later process. The glue on the spine takes a while to setup. Proper handling is important, as these copies without covers are delicate. Both human hands and automated equipment can shift the spine from its center, making it virtually impossible to attach a cover.
The automated stacking machine stacks books to heights ranging from six to 13 inches. The height varies depending on the thickness of each book. Once several books have been stacked into a pile, with an end sheet on the top and bottom of that pile, the machine ejects it.
When this application was handled manually, employees would enter at this point to move the piles from the stacker and place them onto a pallet. The production line is set to a speed that requires employees to remove 16 stacks per minute from the automated stacker system. Once a level on the pallet was filled with piles, employees placed a slip-sheet to prepare for the next level of stacks. When the pallet was full, they would move it to a storage area where the books would wait for the next process, cover assembly. Then, the employees would bring in a pallet for the next load.
If there were long production runs, this material handling job could be physically taxing, especially at the end of a shift, or when the stacks consisted of large books. Sometimes the employees would slow the equipment to keep up. If there were short runs, however, there was a lot of downtime.
Searching for a vendor to help automate this task was partly a matter of serendipity. "We began looking on the Internet," says Simons. "But didn't find what we wanted. My maintenance chief, however, ran into a friend who worked at Westfalia and mentioned that they had just taken on a line of robots. Less than two weeks after that, their engineers were at our facility examining the operation with us. And it helped that they were willing to sell us just one."
Westfalia developed automated material handling components that would take over the functions of moving stacks from the stacking machine to storage. The engineers adds a conveyor that joined the stacker system at its ejection point. Now, stacks of books eject onto this conveyor, which accumulates and moves them toward the robot. Components on the conveyor square the stacks to one side and index them until the right number of piles is ready for pickup by the robot.
At the opposite end of the conveyor, Westfalia supplied a pallet dispenser. Now, employees bring in pallets with a lift truck and load them into it. It issues the pallets, indexing them to the spot where the robot will place the books. Three pallets are in various preparation stages for presentation to the robot at all times. A ram on the conveyor precisely positions an empty pallet in front of the robot while the conveyor moves the full pallet to the storage area. Laser based light curtains surround the robotic system, preventing employees from entering when the robot is active.
The robot is a basic Fuji model with a custom end effector. The end effector is a fork tine design that meets several special requirements. Because it's stacking piles of books next to each other, the forks can't stick out too far when placing a row of books on a pallet because they might run into a previously stacked row of books and damage the pages. The tines also had to be thin to pick up rows of books from the conveyor without damaging the bottom end sheets.
And these effectors needed some method of preventing the books from flying off when the robot whirled around from the conveyor to the pallet. "The robot is turning at a quick speed," says Simons. "It has a lot to do as the books come down the line; get the pallet into place and get the slip sheets. Its turning arc is pretty fast, fast enough that there's a lot of pressure on the books to fly out of the grasp of the end effectors."
To address this potential problem, the operators and engineers designed a compression plate to hold the books so that they stayed on the tines and so that their spines did not move during transit. At first this plate was too thin, so the engineers widened it. This change distributed the compression better across the row of books, preventing any damage as well as securely holding the books.
The robot also needed precise position control. A DC servo motor powers the robot and controls is positioning. With this motor, the robot's end effectors are positioned from one-quarter to one-half inch above a pallet or previous layer to deposit the books. Any higher and there's a risk of distorting the books' spines when set down.
Another feature the robot needed was flexibility. "We wanted to minimize changeover and setup time," adds Simons. There are 10 stacking patterns for palletizing. An operator will measure the book and enter a stacking pattern number based on that data. The robot will then position the rows of books accordingly. The robot can pick up one, two, or three stacks simultaneously for placement. "This machine has not increased my make-ready time at all," continues Simons.
In fact, Simons did not need to make any changes to the production processes to accommodate the automation equipment. The robotic palletizing equipment simply and easily took over the tasks previously preformed by six employees over three shifts. Should the production line need it there's extra capacity. "The robot is running at only 60 percent capacity now, and is handling our requirements for movement of 16 stacks per minute easily," adds Simons.
This system was installed in January 2004, during the press's busiest quarter. "It took about three weeks for the hardware," says Simons. "And a bit longer for the programming. But the machine was never out of production during that time because the engineers helped us design a way to run at full speed. We hit all of our production goals, and service levels during that period. If the robot should need to be down for a while, we can exit the books to the other side and keep running. This enables us to fix a problem during a shift if we need to."
The robotic palletizing system runs three shifts a day, five days a week, and occasionally on weekends depending on production needs. Projections were that this system would reach payback 18 months after installation, and so far, it's on track.
"One of the nice features of robotic palletizing," adds Labell, "is that they require less area and power consumption, and can handle multiple products simultaneously. Flexibility is one of its strongest traits."
This robotic palletizing system saved Maple-Vail $120,000 per year in labor costs. The employees were reassigned to less repetitive tasks. And the owners are happy with all the results.