Smooth Product Flow is a Sure Bet with High Tech Control System

International Gaming Technologies (IGT) is the largest "slot machine" manufacturer in the world. With total revenues approaching 1 billion dollars and nearly 70% of the U.S. market share, they are the undisputed king of the gaming machine business.

To become this big and stay on top requires a good product and excellent customer service, as well as the ability to make whatever adjustments are necessary to meet the demands of an ever-changing, fast moving industry.

In the last 13 years, IGT has increased the number of gaming machine units sold by a magnitude of nearly 20. It has moved from shipments of slightly less than 5,000 units per year to nearly 100,000 units. And during the last two decades, the industry in general has seen a tremendous change in the look and feel of the product being offered. Old electromechanical machines that go "clank, clank" with little more than spinning drums and levered arms exist only as nostalgic illusions. Much of this change is directly attributable to the newer microprocessor based hardware and highly sophisticated software available. These changes have spurred tremendous growth in the gaming industry.

Customization is also a growth factor. Customers for the gaming equipment virtually write their own specs. The graphics on the machines, the payoff ratios, the types of games….it differs from casino to casino, from order to order. A manufacturer’s success depends on the responsiveness to these custom needs and the ability to meet the high tech requirements. Sometimes the specs can change at a moments notice.

Such demands have seen the transition from low tech assembly areas in what was essentially "job shops" to totally integrated and automated flexible manufacturing systems. Such was the case, when IGT decided to consolidate 17 of their small low tech manufacturing facilities into one "super facility" located in the South Meadows Industrial Park just outside Reno, Nevada. This facility, spanning nearly 77 acres, would have a 550,000 sq. ft. manufacturing area, utilizing the latest control and communications equipment to assure optimum production flow. Today, this nearly 86 million dollar investment, with 4.5 million devoted to the manufacturing area has become a reality.

The task of supplying and installing the automated conveyor system was awarded to the systems integrator, FloStor Engineering, Inc. The control system that manages the production flow and controls the conveyor was subcontracted by FloStor to Serra Systems. The electrical design and installation was subcontracted to CC Electrical based in Pleasanton, CA.

The control system divides the manufacturing process into 4 functional areas:

Each area has one or more workstation computers associated with it and at least one programmable logic controller (PLC). Figure 1 shows the control system architecture relating these components. There are a total of 7 Siemens SIMATIC 95U PLCs. The PLCs, together with the 12 PC-based workstations, provide the bottom two levels of the control system hierarchy. The third level is IGT’s AS/400 computer. The AS/400 exchanges data with the control system via a Host Interface Computer. This comprehensive approach provides data flow from the factory flow up to IGT’s business systems and back again thus providing a totally integrated solution.

Rather than have one big and powerful PLC, there was a preference to design the PLC system around a distributed control concept. That is, by distributing small PLCs throughout the manufacturing process, a facility is able to reduce wiring costs and improve the modularity. Distributed systems are nothing new in manufacturing certainly, but a spin-off of that concept is very new. It’s called AS-I bus. Each PLC is responsible for the control and monitoring of all field devices in its proximity. Normally this would entail separate wiring between the field devices (i.e. solenoids, starters, photo-eyes, RF scanners, etc.) and the PLC. This represents what can become miles of confusing, individual wires, requiring lots of man-hours that have to be devoted to cutting and connecting the wires, splicing, and troubleshooting. A number of "two-wire" systems have been introduced in recent years for control engineers and system integrators that simplifies the process. AS-I bus is one such system.

Rich Stein, Project Engineer for FloStor Engineering realized early on the need to try an innovative solution in order to meet IGT’s tight time-line. AS-I seemed a natural to help meet the schedule.

AS-I (Actuator-Sensor-Interface) is the result of a German consortium comprised of sensor manufacturers and some big-name manufacturing companies such as Siemens. It has gained rapid popularity for several reasons. It requires virtually little from the sensor manufacturers, because it works readily with any PnP-type field component. It is also a very fast system that can provide 5 millisecond updates compared to other two-wire schemes that might require 5 times that much time. But most of all, it is popular because of how neat and clean it is to setup or change. The field devices are attached to receptacles on AS-I slave modules which, in turn, connect to a flat flexible yellow two-wire cable (distinctive to AS-I). The slaves have front and back plates that screw together, sandwiching the AS-I rubberized sheath, and making an electrical connection via pointed prongs. They are self-sealing connections too. So, if you make a mistake in placement of one of the slaves or you later want to move it, there is no splicing or rewiring required.

Each of the slaves can be ordered in a variety of configurations. They can be all input or all output nodes, or they can be a combination of inputs and outputs. Each slave is programmed with a node address using a handheld programmer that plugs into the slave. The master for the slaves resides back at the PLC rack. One master can control up to 248 binary elements when using bi-directional slaves. The master takes up two slots in the PLC rack and it has its own intelligence. It scans the slave addresses for slave I/O updates and makes the information available inside the four 16-bit addresses assigned to each of the two Siemens PLC slots.

Jeff King, Industrial Engineer for IGT, explains the installation benefits. "This system really accelerated the installation process. Serra Systems pre-programmed all of the slaves and marked the nodes so that the CC Electrical installers knew exactly what field devices to connect where. It only took about two hours per each assembly line to connect all the field devices to the nodes and install the masters in the PLC racks. With tight deadlines, this was a wonderful time-saver. There was also no troubleshooting time lost to wires being crossed or being accidentally connected wrong."

According to Dean Mueller, President of CC Electrical, "Our biggest problem was supplying pre-cabled field devices to our installers on-site. They could install them quicker than we could make them up".

All of the PLC’s are able to talk to each other in the system by using the Siemens-supplied PROFIBUS twisted pair communications bus. Not only is PROFIBUS a very fast (up to 1.5 Mbits/s transfer rate) fieldbus system, it provides (like AS-I) lower wiring costs because of the twisted pair concept.

The Manufacturing Process

As mentioned earlier, the manufacturing process involves 4 functional areas. Let’s now take a closer look at each of those areas and their respective functions.

Product Induction and Staging—

Currently, the custom cabinets (there are 4 basic styles) are received at the manufacturing facility from a separate location. Each cabinet has a unique serial number associated with it, and a bar-code readable decal is attached at several places on the cabinet at the cabinet making facility so that a scanner can readily establish the number. Palettes located at the entry end of the manufacturing process also have a distinctive identification in the form of readable RF tags that are affixed to underneath side. The cabinets are placed one by one on individual palettes, that are in turn placed on the conveyor rollers. Scanners along the process are able to read this palette number when it passes designated locations. Upon induction into the work process, these two identification numbers are "married" to a work order number supplied from the IGT main computer. This is viewed on the workstation computer screen with easy-to-use Windows based software. Once the marriage of these three pieces of information takes place, the product is moved via power conveyor rollers to the kitting area.

Kitting and Kitted Cabinet Storage--

There are two types of kits associated with each cabinet. Once is referred to as the "glass" kit, and the other is referred to as the "unique parts" kit. These kits are fed to the conveyor via automated vertical carousels. The kits have already been prepackaged from the main parts area. The prepackaging takes place in prep area that is adjacent to the powered conveyor rollers and the carousels that house the packaged kits. There are two vertical carousels used to group the parts into the various kits. Information associated with the work orders "picks" the parts from the main storage area for a given manufacturing day or period. When a workorder is pulled up on the screen of the workstation at the prep area, the computer tells the carousel which parts to dispense for each kit. As the computer directs the carousel to rotate into position for the required part, a worker at that station removes the parts from the bin and places them into a special box. Then the operator attaches a computer generated bar code I.D. to the outside of the kit package.

Two more vertical automated carousels house the packaged kits. Two workstations will direct the operator to pick the appropriate kit when a cabinet arrives at the workstation juncture. The operator scans the decal on the kit packages and they are checked against the specs of the work order that was married to the palette and cabinet earlier. This eliminates the possibility of the wrong kits being placed in the empty cabinet. The cabinets are then released to a staging area where they await the proper queue that will direct the cabinet to the proper manufacturing cell, based on work load and type of work order.

Outside at the manufacturing cells, the PLCs are tracking the I/O information on the manufacturing lines. This is a purely transactional function with the overall process flow being conducted by the AS/400 computer and the host interface supervision gateway. When the PLC in the kitting area receives the information from one or more manufacturing cells PLCs that tell it to release another cabinet from the queue area, the rollers in the staging area are activated. Photo-eyes are located on the in-bound conveyor line that notify the PLCs that another cabinet is heading their way.

Assembly and Test Spurs—

When the cabinet reaches the proper manufacturing cell, it diverts into the assembly cell and proceeds along a progressive build conveyor. Along this route, operators install the various kits along with other special parts that are supplied to the lines via a Kanban system. Along this process a traveling document is updated as to status of the manufacturing for each machine unit.

As the machines are completed by the assembly lines, they are released back to the main line again. Here they reach a "Queue Induction Station". The palette is identified at this point with an RF reader, and an operator scans a status code master sheet, selecting the code that matches what is read on the traveling document. After the status is selected, the operator then scans the machine’s bar-coded serial number. Of course, since the machine’s bar-coded serial number was married with the work order and palette number earlier on, the main computer now knows the status of each work order from start to finish. From this point, the units can be sent to burn-in and testing; sent to a staging area for shipment, or sent to another area for rework. For finished goods, transactions are automatically generated for IGT AS/400 to release the items for shipment.

Conclusions