Moving the mail: Postal Robotics

The United States Postal Service (U.S.P.S.) has emerged as one of the larger end users of robotics in the United States. The needs and challenges of implementing a robotic system to help move more than 200 billion pieces of mail a year present unique challenges over those faced in general industry.

Other countries, such as Great Britain, have chosen a robotic solution to the problem of moving large amounts of mail as well. Some 1,000 robots were installed worldwide in 2000 to sort mail. Early in their robotics development program the U.S.P.S. planned to integrate robotics into both dispatch and receiving operations, as well as machine servicing. It was known that not all existing models were suitable for these applications. To date the U.S.P.S. has deployed approximately 200 cells in dispatch operations only.

'The postal system was not designed for robotics, unlike the automotive industry,' says Michael Van Wormer, Systems Division sales manager of Fanuc Robotics North America, Rochester Hill, MI. The uniformity and predictability of product size and shape as well as the condition of the product that is the norm in manufacturing applications are not present in the postal system. Robot makers have had to conjure up solutions to this and other problems facing postal applications.

Trays and Tubs
'The trays and tubs were not designed for robotic handling so figuring out how to pick them up was a challenge. Also, the trays are used over and over again and as a result can be in less than optimum condition,' remarked John Weller, program manager at the U.S.P.S.

Fanuc's Van Wormer concurs with Weller on the problem of postal trays. 'From a process point of view, postal robotics is not a difficult challenge, one that is quite simple. The main difficulty is the postal cardboard containers, which are used over and over again. They get crushed, broken, and have variations in heights and widths,' Van Wormer said. 'The postal service is looking into new types of tray designs, ones that are more suitable for automation,' Van Wormer added.

To manipulate these cardboard trays, Fanuc chose to use a vacuum cup lifting system. The tray is lifted from a sleeve that covers it. The sleeve is strapped on to the tray with a plastic band so it remains attached while the tray/sleeve assembly is lifted from above. The robot picks one of these sleeved and strapped trays and front-loads them in large rolling wire containers for transport within a postal facility or loading on to trucks or airplanes for distribution throughout the country. The worn condition of some of the trays means that there is a possibility that they will collapse or that their shape will be altered significantly enough to pose difficulties in stacking.

The Fanuc technique of mail management, the Robotic Tray Handling System (R.T.H.S.) has a four axis M-410iw robot at its heart. This pedestal robot has a reach of 3139 mm within a circular work envelope. The R.T.H.S. handles the mail trays at a rate of six transactions per minute. This was the initial specification requirement of the U.S.P.S., but subsequent requirements call for faster tray loading. There are 89 of these robots deployed in the U.S.P.S. system at the moment.

The ABB approach to mail handling, the Robotic Containerization System (R.C.S.), has two gantry robots doing most of the heavy lifting. In 1999, the U.S.P.S. ordered 100 of ABB's R.C.S. with plans to be installed at 51 postal sites nationwide. This system has a rectangular work envelope of five by 30 meters. The R.C.S. is capable of lifting trays or tubs, the latter having a mass of approximately 32 kg when full. The gripper for the R.C.S. is a mechanically operated component that elevates the trays by holding them from beneath.

'The R.C.S. picks up the trays from the bottom with its fingers to place the trays close together. The grippers grab from the bottom to support the open containers because they sag or bow when full,' explained Bruce Meyer of ABB Flexible Automation. Meyer, who is the New Berlin, WI firm's vice president of their Distribution Systems Group, agreed with his colleagues at the U.S.P.S. and Fanuc that the inconsistent shape and size of the trays posed an engineering challenge.

'The trays wiggle, bend and do all sorts of things. We had to be able to pick the trays up and stack them, which is very difficult. The U.S.P.S. specifications did not call for a higher processing rate, in part, because of this complexity. That is just the reality of their system,' observed Meyer. 'For most commercial palletizing and material handling applications, the robots are dealing with boxes that are generally of a uniform shape. Postal trays are used so many times the shape changes quite a bit. We had to accommodate that,' Meyer continued.

The ABB method of postal material handling employs an IRB 840 gantry robot, a system which incorporates two gantry heads in one robot cell. Each gantry head is charged with moving the mail within two zones, for a total of four operations zones. Trays are delivered by an in-fed conveyor and sorted by destination using a bar code reader. With two operating gantry heads, the R.C.S. is capable of filling two containers simultaneously.  These are removed by an operator as each is filled. When a container is full, the system informs the operator who enters the workcell perimeter to remove it.

To maintain safety and efficiency, the R.C.S. stops loading in that zone, while the other three zones are available for operation. Mail that is destined to the zone that has been stopped to allow the operator's safe presence is recirculated through the system until the operator is safely out of the workcell. Then the system keeps filling containers until the next cycle is complete. The R.C.S. is specified to process at least ten trays a minute.

Not all postal trays are sleeved and strapped.

'Some trays are open, some are not. The open trays tend to nest inside one another. In some cases the R.C.S. has to lower the shelf in a container,' pointed out Meyer. Some containers have a hinged horizontal divider to allow two tiers of open trays to be stacked in them. The IRB 840 loads the first tier of trays into the container, and is programmed to lower the shelf automatically. The system then continues loading trays onto the second tier until the container is completely full. The full container is taken out and replaced by an empty one by an operator. The shelf is a necessity when stacking open trays in a container.

Postal Robots Abroad
The U.S.P.S. is not the only postal system to implement a robotic solution.

'We are installing the system right now which will be up and running October of this year,' stated Shaun Roedel, a program manager of Siemens Dematic, Inc. Roedel was referring to the robotic mail sorting system being implemented by Siemens Dematic Corp. in Great Britain. Not all of Britain's mail will be handled roboticly.  This system is for international mail only, coming in or going out.

There are six robots that load trays into the wire cages, similar to the R.C.S. technique. Roedel described the cages as being like that of an airline container.

'There is only one postal facility utilizing robotics, but it is the most advanced one in Britain, perhaps all of Europe,' Roedel said. This is the first robotic postal system in Britain. 'The idea is to take the technology that makes the most sense and export it to smaller facilities,' Roedel continued.

Like the American system, the British robotic mail handling infrastructure had to take in to account the dissimilarity in the size and shape of postal containers.

'The quality of the trays is also an issue. So, we had to design in a larger tolerance for trays that are being loaded. The next tray could be off by a couple of inches, which is fifteen to twenty percent. We had to have the ability to handle that tray without changing the robot's performance. Siemens Dematic designed the equipment to accept a wider range of product. It does not handle it quite as well. You can design it in, but there are always tradeoffs,' Roedel contends.

The end of arm tooling on the Siemens Dematic system reflects the type of tray a particular robot is designed to handle. Vacuum cups lift the trays that have banded lids in a manner comparable to that of Fanuc's R.T.H.S. A mechanical gripper grabs ahold of ridges on the front of the trays.

Another facet of the difficulty in implementing a robotic solution to mail handling challenges is not technical, but rather that of perception.

'A challenge was that Royal Mail had never used robotic tray loading. There was fear of a new product. It would be very good for their business. The labor savings benefits made sense,' Roedel declared.

From the U.S.P.S. perspective the fear of new technology was addressed through training of not only the workers and maintenance personnel, but supervision as well.  Briefings were also held with the unions to explain the operation and plans for robotics within the postal service.  The technology has been well received on the workroom floor.

One quality that all three systems share is that they were designed for envelope-sized letters and 'flats'. The latter consists of magazines, legal size envelopes, and the like. None of these systems were designed to handle packages and parcels robotically due to their wide variety of sizes and shapes.

Another feature of the U.S.P.S. system that differs from robotic manufacturing is the number of sort points within a facility.

'A manufacturer might have four to six sort points or load stations at a time. We, at the U.S.P.S., tried to maximize the number of load stations the robot would access,' commented Weller. This stems from the fact that product is coming in from numerous origins and will be going to many destinations. Maximizing sort points makes sense from an efficiency perspective.   That is not always the case in robotic manufacturing applications.

How much mail is handled robotically? According to John Weller, 'Five or ten percent, approximately. There are pedestal cells in about 40 facilities, and about 51 facilities with gantries, for a total of about 91. That is out of 350 mail processing plants in the U.S.'

Concluded Weller, 'We are just beginning to scratch the surface when it comes to possible uses for robotic-like devices in the postal mail process.  We are looking at handling inbound container unloading, as well as machine tending in the future.'