Servorobots help Polaroid change its modular manufacturing cells - in an instant

Polaroid Corp. may very well be the highest-volume producer of high-precision optical lenses in the world today. In the NI building at its sprawling Norwood, MA "campus-like facilities," as we called them after visiting there the first time (see August 1994 IMM, p. 32), Polaroid molds lenses with optical tolerances pressed between pluses and minuses in the millionths-of-an-inch range. And they do it in price-busting high-cavitation tooling - up to 16 and 24 cavities in many cases - making many millions of lenses each year.

Polaroid has used the same kind of process engineering savvy that makes this kind of world-class production possible to create truly flexible manufacturing cells. These manufacturing cells allow Polaroid to make even better quality lenses today, with better labor efficiencies.

Theodore A. Parker is a principal engineer in Polaroid Camera Div.'s Optics Group: "We have a large number of active products, well over 100. And we run them in 24 molding machines. But we don't believe in large inventories, so we do lots of mold changes. That's why flexibility is a key operating principle around here."

Manual . . .

Not too long ago, flexibility involved higher labor costs and lower lens quality. Parts were removed, degated, inspected, and packaged manually, with an operator opening and closing a safety gate, interrupting the cycle, and potentially contaminating the high-precision lenses simply by handling them. Parker says his group decided early on to automate parts removal and handling. But they wanted to do it with true, closed loop, all-electric servodriven robots. "We had a couple of pneumatic robots with electric traverse strokes. They did the job, but they were not very easy to set up. Setup involved a lot of tweaking and trial and error, all manual, and they offered little programming flexibility." He had learned from prior experience that ease of programmability in robots is extremely important. "We did not want anything with ladder logic. We wanted any of our engineers to be able to program the robots."

. . . or Automatic?

Smarter robots were needed because Polaroid had gotten smarter. It planned to fully automate lens manufacturing. Robots would hand lenses off to Polaroid's own servoautomated beside-the-press product-handling stations. There, automatically, the lenses would be ultrasonically degated, oriented, and transferred to PVC packaging tubes or vacuum-formed trays or palletized in fixtures for special optical coating in high-vacuum coaters. So the robots had to be able to interface and communicate fluently with the molding machines and with the secondary automated handling stations, as well as with the operator. Better control over the quality of the process would eliminate the need to do 100 percent inspection for product quality. One person could handle the output of two or three workcells at a time.

But remember, Parker says Polaroid does lots of mold changes. Production efficiencies could be improved if the secondary stations were mobile self-contained modules that could be plugged in and out of manufacturing cells, like a camera's film cartridges. Such cells could travel with molds from machine to machine as business warranted. And new cells could easily be plugged in with existing injection machines and robots running new projects in new molds. Nothing would be hard-wired.

There would be no single host supercomputer running everything. Control would be decentralized among the discrete controllers of the units in the cell, requiring only a "handshake" communications protocol to share safety, timing, and sequencing routines between themselves. And individual cell units could be serviced off-line. Manufacturing would truly be flexible.

Robots would have to be smart enough, not only to remember detailed choreographed parts removal and handling routines for molds, but also to remember parts-handling programs for the parts-handling modules. In addition, robots would need a fourth closed loop servodriven axis, a wrist rotation, to accurately place lenses removed from vertical multicavity mold faces in differing pattern layouts into different horizontal holding fixtures in different secondary stations. Some pattern layouts are radial and some are rectangular. The latter requires the robot end-of-arm tool to deposit, say, eight parts in a row in a pallet, then flip around and deposit the other eight.

Polaroid's ideas were ahead of its time. Servorobots like the ones they wanted weren't around when they started their project earlier in the '90s. After a few outright refusals to quote, false starts, and time-consuming setbacks, the company found a servorobot supplier it could work with that was a 3-hour drive away - Wittmann Robot & Automation Systems (Torrington, CT).

Polaroid is used to working with its capital equipment suppliers, and working on their equipment. It modifies almost everything that comes in the door. For example, the majority of its 26 hydraulic molding machines are from Shinwa Seiki (50 to 300 tons). Polaroid used its process engineering savvy to come up with a number of improvements to the machines for its own purposes in-house, mostly improvements in machine control software. The OEM has incorporated Polaroid's suggestions into its latest series of closed loop machines.

Polaroid worked with Wittmann to customize the robots to the "plug-and-play" flexible manufacturing cells it uses today, particularly in adapting its controller to accept its redundant safeties, its standardized interface cable connectors, and its software protocols. These are shared by the robot, the molding machine, and the product-handling peripheral.

There are 128 I/Os in the robot controllers for auxiliaries. Wittmann Robot CAN-BUS control-area-network architecture also came in handy. If necessary, robot controllers have the intelligence to control the entire product-handling workcell. In palletizing workcells, the robot controller coordinates pallet filling. The number and arrangement of slots in a pallet are not consistent with the number of parts in a shot, so the robot tells the pallet when to index when the time is right.

Polaroid builds its own end-of-arm tooling and grippers. It has even developed its own positive-contact and digital part sensors for different types of grippers. Of critical importance, Parker and his associates find programming the robots to be intuitive, thanks to their easy-to-use interface. "I don't think we've yet found everything a Wittmann robot can do," Parker admits.

Wittmann provided training for all three shifts. The robots are clean enough to work in Polaroid's Class 10,000 cleanroom molding area. Polaroid has eight Wittmanns now. In about two years of operation only one cable had to be replaced on one robot. Other service problems were equally minor. There's only one pneumatic robot left in the shop.

So far, the capital investment in machines, robots, and secondaries in the project has been between $2 million and $3 million. Cycles are rock steady and stabilized, and manual handling has been all but eliminated, so lens quality has improved. There is still a way to go to fully automate the entire plant, but the hard part is over. "We're fortunate that the company over the years has been willing to invest in new technology. To compete in the marketplace, we have to continuously improve our production efficiencies," Parker concludes. But it took savvy to make production capabilities flexible enough to adapt to change. For more information on servorobots and automation solutions from Wittmann, circle 237. - Carl Kirkland

At its facilities in Norwood, MA, Polaroid molds lenses with optical tolerances pressed between pluses and minuses in the millionths-of-an-inch range.

A Flexible Polaroid Cell In Action

Here's how it works with a radial-pattern multicavity mold: A parts-handling module safety enclosed in clear plastic is rolled up and docked into place on a docking plate beside the press after a mold is changed. Since the module is enclosed, there's no need for permanent, floorspace-wasting guards around the back of the molding machine's clamp. Saved setup programs are loaded into the controllers. As programmed, the Wittmann robot automatically discards a predetermined number of parts after a cold start-up. Gripping the runner, the robot removes the lenses, moves up and over the safety gate, then precisely places them into a holding fixture on the parts-handling module. Suspect parts detected by the Shinwa Seiki's process controller are automatically discarded.

Empty PVC packaging tubes are indexed into position around the circumference of the holding fixture under guide chutes. Like a Scara robot, a servodriven ultrasonic welder rotates into position over the fixture and degates the parts. Lenses are transferred through guide chutes into the PVC tubes, separated by cavity, while sprues and runners are automatically discharged into waste containers.

After the proper number of lenses has filled a tube, the tube is automatically packaged, and is automatically replaced with an empty tube. This automatic degating/ packing system is a three-axis servodriven machine in and of itself, providing closed loop control over the positioning of the welder, the shot, and the tubes. Magnetic safety locks on access doorways on the modules are automatically engaged while the robot is in motion.