Making automated systems run better than ever

Many automated storage and retrieval systems (AS/RS) installed before 1990, and even some newer ones, can benefit from modernization in the areas of control equipment, communication devices and operator interfaces. If they are properly specified and installed, state-of-the-art replacement products and software can contribute to improved functionality, reliability and performance.

Often, users of an AS/RS don’t realize just how much their system can be improved. That’s where an astute maintenance team can put them right.

Most users have seen little change in the physical appearance of AS/RS technology in general over the years and detect little deterioration in their own system’s performance, so why upgrade? Even increased maintenance needs and occasional errors on existing systems tend to get shrugged off as being inevitable after several years’ operation.

Those users might be surprised to learn that modifications and improvements to an AS/RS can enable it to perform better than ever and probably as well as any new system currently on the market. It might, for example, be programmed to perform differently through flow-path changes or new storage algorithms. Or it might be made easier to use, through improved controls and graphically based communications devices, to help achieve faster, more accurate operation. System upgrades also offer new communication networks incorporating the latest developments in wireless technology.

The net result of all these technological advances when applied to existing AS/RS installations is far greater efficiency, reliability and ease of use. Maintenance costs can drop dramatically, too.

An AS/RS upgrade also presents the opportunity to cut the strings from the OEM. In the past, many AS/RS manufacturers equipped their machines with proprietary devices and software, making the user a captive customer. It doesn’t have to be that way any more. Today, universal off-the-shelf devices can transform the AS/RS into a machine that is easily changed, reconfigured and reprogrammed — now and at anytime in the future — without having to spend the sort of money associated with being ‘factory rebuilt.’

Another important aspect of modernizing or upgrading the AS/RS is the appreciation of how efficient that process itself has become. It can often be completed in a matter of days thanks to the quality and universality of today’s electronic devices, transparent software, and the project expertise of the installer.

Not surprisingly, the engineers at United Technologies Corporation’s Pratt & Whitney plant in Middletown, Conn., knew more about possible benefits of AS/RS upgrades than the average user before commissioning work at their plant. After all, the plant manufactures and tests advanced jet engines, including the F119 engine that powers the Lockheed Martin F/A-22 Raptor air dominance fighter. In other words, Pratt & Whitney engineers are among the most knowledgeable in the land.

The plant, consisting of 25 buildings occupying over 2.3 million sq ft, is located on a 1,100-acre site on the Connecticut River. Some of the parts machined at the plant are huge too, measuring as much as 12 ft in diameter or more. Production involves many machine tools, including milling centres and broaching machines, some of them incorporating the latest in CNC technology, to help produce critical components that meet the highest aeronautical standards.

Needless to say, these machines must be continually supplied with cutting tools, broaches, taps, dies, coolants and more to support them. Unscheduled downtime is not an option, so the tooling must be stored in an automated storage system that combines speed, accuracy and total reliability. To do the job day-in, day-out, with minimal intervention, the plant relies on three Eaton-Kenway Mini-Load 750 AS/RS machines.

Most of the parts that are required for the dayshift — which is when the machine tools are active — are picked overnight according to an electronic shopping list. The parts are then distributed to buffer storage units. They look somewhat similar to snack dispensers and are located strategically on the shop floor. Of course, individual rush orders may be picked from the AS/RS at any time during the day.

Each stacker runs in a dedicated aisle under individual computer control. It picks and stores from 700 locations on each side of the aisle (25 columns high by 28 rows deep), for a total of 4,200 order-pick locations. One operator can control all three stackers and they can function simultaneously.

As well as being extremely efficient in their primary function of storage and retrieval, the AS/RS machines help achieve good housekeeping, safety and security. They also ensure that valuable parts and supplies are tracked and controlled more closely than in a manual or semi-automated system. The AS/RS can handle a much wider range of sizes and heavier weights than other automated systems can, and there is no need to worry about load balancing.

Reliability issues

Over the years, it became necessary to fix and adjust the machines more frequently than could reasonably be expected, creating time-consuming maintenance issues and hindering the smooth operation of the shop floor. Physical errors were caused not so much by picking the wrong part, but through such incidents as tray jams, extractor pin jams and misalignments. As for software, this was still resident on a pre-Pentium computer, which imposed severe limitations on the system’s capabilities.

“The need to improve reliability was the main impetus for the upgrade,” says Bob Hand, manager, machine tools services group, and project engineer. “At the same time, we wanted to make sure that any upgrades would use ‘over-the-counter’ hardware and that the source code for software would be readily available. As well, replacement on-board components would have to be specified and fitted in a way that would simplify all future maintenance and troubleshooting needs.”

Following a competitive bidding process, the selected project integrator for the upgrade was Retrotech Inc. of Fishers, N.Y., who brought to the job many years’ experience in modernizing and upgrading AS/RS, beginning with its first North American system in 1985.

“We determined that the technologies used by Retrotech in its upgrades and retrofits are standard field-tested and proven, which is key to delivering highly reliable operating results,” Hand says. “They include both on-board and off-board controls as well as operations software and the appropriate interfaces. We were most comfortable with their proposal and understanding of what needed to be done.”

Another important factor was related to many of the existing components on the AS/RS, such as enclosures, certain sensors, and some mechanical components. They were perfectly serviceable, so why pay to replace them?

“Since we have upgraded many similar systems, we were able to readily identify which components needed to be replaced and which could continue to perform satisfactorily,” says Tom Goetz, a technical sales representative for Retrotech. “Another important aspect of the Pratt & Whitney project with which we were perfectly comfortable was the integration of new physical components, not just among themselves and with existing components, but with the communications and control network.”

Timeliness was also an important factor, as Bob Hand recalls. “We had to get the first one done quickly so as to remain fully operational. Retrotech actually used two crews for it, one working days, the other nights. They did it in a timely and professional way, with a very cooperative approach. One of our technicians, Charlie Perreault, has lived with the system for many years and was able to make suggestions along the way as to what would suit our needs best.”

The on-board controller for each of the three stacker machines was replaced with an Allen-Bradley SLC-5/04 PLC (programmable logic controller) with Model 1746 input/output modules. It is the primary con
troller in auto, auto local and manual modes. Having the PLC control all modes of operation provides reliable, safe performance and protects against any potential hazards. PLC memory capacity is sufficient to support retrofits and possible future system enhancements.

“Retrotech developed new software for the SLC-5/04 controller that fully replicated the original system, and then added some enhancements based on the input of our technicians and operators,” Hand says. “The software operates the mechanical system, while the material inventory system is run by other software on a mainframe application. Retrotech had to interface its software with the mainframe software but were not allowed to affect or change the mainframe application.”

The system uses DeviceNet, an open, low-level communication link that provides connections between simple industrial devices such as sensors and actuators to high-level devices such as the controller. The network also provides inter-operability based on standard Controller Area Network (CAN) technology, allowing devices from multiple vendors to be interchangeable, as long as they meet DeviceNet standards.

DeviceNet permits more diagnostics for improved data collection and fault detection, with reduced startup time compared with traditional, hard-wired systems. The open network provides common end-user solutions and reduces the need to support a wide variety of device networks.

One wire supplies communications and 24V DC power, and devices may be replaced without disrupting other devices, for ease of maintenance.

The existing control sub-panel was removed and replaced with a new one. All new electronic components were supplied, including fusing, relays, motor starters, terminal strips and wiring.

Laser measuring cuts motor wear

The horizontal positioning system saw a latest technology SICK-Optic DME 5000 optical laser distance-measuring device replace an encoder/sync bar system. It provides absolute position measurement of the horizontal axis (aisle length) for control within 10 mm (0.4 inches), enabling precise positioning of the stacker. Mounted on the stacker, the measuring device collects position data from a stationary reflective target mounted at the end of the aisle.

Similarly, the vertical-positioning system benefits from installation of a SICK-Optic DME 5000 device for absolute position measurement of the vertical axis, enabling precise control. The measuring device is mounted on the stacker and collects data from a reflective target mounted on the carriage.

Laser distance measuring brings many advantages, most notably the prevention of misaligned positioning errors that cause mechanical damage. It also cuts motor and gearbox wear caused by position-hunting and reduces throughput errors due to imprecise positioning and creep. As well, it provides the ability to adjust for irregularities in the rack.

New gearbox and drives installed

With regard to the lateral extractor, Retrotech installed new proximity sensors for pin-positioning and shift. Working on laser guidance, they are more accurate than previous fibre-optic cabling, which often caused machine errors or required replacement. As well, the gearbox that drives the extractor’s lateral pins has been replaced, as motor input speed is now approximately 4,000 rpm. For gear-reduction purposes, a new gearbox was installed.

Previous CNC servo-drives and motors on the horizontal, vertical and lateral pins have been replaced by Allen-Bradley Powerflex AC variable-frequency drives and AC motors. The replacement motor is mounted to existing horizontal gearboxes and provides performance at least equal to existing servomotors.

The new AC drive and replacement motor have the advantage of being non-proprietary, off-the-shelf components offering easy setup and configuration. All incoming power is filtered using line reactors, and dynamic-breaking (DB) resistors are used for absorbing excess energy generated during drive operation. Replacement drives are mounted inside the existing drive-control enclosure.

As with any system upgrade, the degree of performance improvement at Pratt & Whitney is naturally affected by existing systems and components, such as wheel and rail condition, drive performance and gearmotor condition. As well, actual maximum travel speed remains the same.

Even so, Hand says operators report a significant improvement in overall operational efficiency measured in terms of time to absolute stop and commencement of productive operations. “The operators and the maintenance people like the result, and both groups find the ‘Help’ screens in particular to be a very useful feature.”

In summary, Hand feels that Pratt & Whitney has acquired a modern, high-tech system, at a fraction of the price of new. “The upgrade has added many years of life to the AS/RS, and reliability is absolutely improved.

“Now that it is in good shape both electrically and mechanically, we can get back into a preventive maintenance mode rather than continually addressing failures. This aspect is further enhanced by a software program, also by Retrotech, that records and analyzes any problems, to provide us with uptime data and allow us to identify any recurring failures quickly, which is another feature we did not have before.”

Richard Rix is a business writer based in Toronto and may be reached at richardrix@sympatico.ca. Retrotech is represented in Canada by Liftandmove of Caledon East, Ont., tel. 905-584-1066 or visit www.liftandmove.com.