Optima Design Services, Mansfield, Nottinghamshire, UK

Optima Design Services is a leading provider of design and engineering services, serving some of the world’s top companies, such as Stanley Works, Siemens, BAE SYSTEMS, and Thales.
The Challenge: Design the First-Ever All Plastic Stadium Seat Starting with the stylish and modern Eventa seat, which is marketed by Pel Stadium Seating Limited, Optima’s assignment was to make the seat durable as well as attractive. For instance, part of Optima’s task was to ensure that over-enthusiastic fans couldn’t break the seat off
by jumping on it.

The Solution: Virtual Prototyping with Pro/ENGINEER  Optima engineers were provided with a point cloud created by scanning a clay prototype. Rather than recreating the model in Pro/ENGINEER, they saved time by using Scantools, part of the Pro/ENGINEER Interactive Surface Design module, to fit a surface model onto the
point cloud with minimal manual intervention. The engineers then designed a mechanism to raise and lower the seat, and created load cases based on the customer’s requirements.

 
The finite element analysis (FEA) results from Pro/ENGINEER Mechanica were used to create a series of 15 iterations of the mechanism. Engineers also optimized the design of the seat, backrest,and stanchion to meet strength requirements while minimizing manufacturing costs.

The Results: First Physical Prototype Works Perfectly
After optimizing the design based on the Pro/ENGINEER prototype,Optima then built and tested a physical prototype. Surprisingly, it met all the design requirements, thus eliminating the need to build and test five or six prototypes that would have been required if the seat had been designed using conventional build-and-test methods. The
Eventa seat is being installed in a 90,000 seated National Football Stadium where the 2012 soccer finals will be played.

With Pro/ENGINEER 3D CAD tools, Optima Design was able to design a durable,
all-plastic seat that could withstand the stress of soccer fans jumping on it.

“By taking advantage of the integration between Pro/ENGINEER and Pro/ENGINEER Mechanica, we provided the mechanical design for the Eventa seat in half the time  that would have normally been required. Each time we were ready to evaluate a new design, we simply changed the model and pushed a button to perform the analysis again.” -Darren Forrest,Director,Optima Design Services

The First All-Plastic Stadium Seat
Pel Stadium Seating Limited originally had the idea of taking stadium seating to a new level of style and economy by creating the world’s first all-plastic stadium seat. The company asked the Radar design consultancy for their input and Radar responded by providing a futuristic design with contoured plastic stanchions, which replaced the
boxy metal stanchions that have been used on nearly every seat up to now. Next, Radar turned to Optima Design Services and asked them to make the seat tough enough to stand up in the stadium environment.

New Seat Design Must Meet Tough Structural Requirements
Radar provided Optima with a number of different structural requirements for the Eventa seat. The most difficult challenge was for the seat to withstand large fans jumping in the air and landing on it in an attempt to break it off for who knows what purpose. This challenge proved particularly difficult for an all-plastic seat because dynamic loads applied by the overenthusiastic fan are all directed toward the small plastic mechanism that connects the seat with the stanchion. This mechanism was primarily designed for raising or lowering the seat, making it easy for fans to pass by when the seat is not occupied.

Converting Point Cloud Data to Surface Model
Radar supplied Optima engineers with point cloud data generated by scanning the clay model they created while developing the conceptual design. Using conventional methods, engineers would have had to go through the tedious process of manually defining splines and surfaces by eye to match the point cloud data. Not only is this time consuming,
but it requires a considerable amount of judgment on the part of engineers, running the risk of compromising the design intent.

In this case, however, Optima engineers took advantage of the Scantools functionality of Pro/ENGINEER Interactive Surface Design Extension (ISDX) to automatically fit surfaces to point cloud data. The surfaces that were generated by Scantools represented the design intent so well that only a few manual tweaks were needed. “The new auto-
mated approach saved 60 to 70% of the time that would have been required with the conventional methods,” says Darren Forrest, Director, Optima Design Services. “This helped to substantially reduce the cost of completing the project.”

Generating the Initial Concept Mechanical Design
The next step was to design the mechanism in the stanchion that allows the seat to swivel up and down. The stanchion is designed as a space frame with ribs strategically located to distribute stresses efficiently through the structure. The stanchion part of the mecha-
nism, which consists of two male slots shaped like pie slices with a small cylinder between them, is designed to mate with the seat. The seat part of the mechanism incorporates two female pie-slice-shaped pieces with space between them to provide room for the cylinder. A bolt that passes through the center of this mechanism provides the physical connection. The male and female pie-slices interface with each other to provide positive stops that limit rotation and deliver strength to resist bending moments applied to the seat.

This Pro/ENGINEER graphic shows the amount of stress in the seat when simulating
a person jumping on the end of the seat.

The backrest is fixed to the stanchion, and the seat is weighted by a metal bar, so it automatically flips up when it is not in use. The use of gas injection molding makes it possible to use hollow sections in the seat, which is gas injected and improves the seat to backrest strength-to-weight ratio. The seat and backrest are made of polypropylene while, the stanchion and other components are made of 30% glass-filled nylon.

Moving From Build-and-Test to Software Prototyping In the past, after defining the initial design concept, Optima engineers would build and break a series of prototypes in order to detect and correct structural deficiencies. Five or six prototypes would generally be required to get a design of this complexity right--a process that would
take nearly a year. Engineers estimated that this design would have taken 18 months without Pro/ENGINEER; using Pro/ENGINEER it took only nine months of work from concept to manufacture, and reduced prototyping expenses substantially. Even better, with the integration between Pro/ENGINEER and Pro/ENGINEER Mechanica, Optima has been able to replace its old process with a new, much faster process based on software prototyping.

On the Eventa project, Optima engineers worked in the familiar Pro/ENGINEER environment to define the additional information required to convert it to a virtual prototype. Engineers first applied shell elements to the surface model because shells can be analyzed very quickly. After running through enough design iterations to get the
design close to finalized, they converted the surface model to a solid model to achieve the highest possible analysis accuracy.

The Pro/ENGINEER Mechanism Dynamics Option was also used to define the mechanism, primarily by defining joints and contact points that come into play as the mechanism operates. A variety of load cases was also defined, such as applying a downward force to the seat to represent a person jumping on it.

Integrated Solution Enables Single-Button Analysis
With the mechanism conditions and boundary conditions complete, Optima engineers simply pushed a button to perform the analysis in Pro/ENGINEER Mechanica. And because this simulation software is completely integrated with Pro/ENGINEER, engineers never had to leave Pro/ENGINEER to conduct the analysis. “It is essential to have an integrated solution for CAD/CAE,” Forrest said. “It allows for better
collaboration, higher quality products, and a faster design process.” Within a few hours of starting the process, the engineers received their first results.

As expected, the analysis results highlighted a number of weaknesses in the initial design. The results showed high stresses in the male and female pie-slice-shaped segments, so engineers reinforced the areas highlighted by the analysis. The analysis also showed weaknesses in the body of the stanchions, seat, and backrest that were addressed by
adding and re-positioning ribs. On the other hand, the analysis showed that some areas of these components faced very low stresses, so, in these areas, material was removed in order to reduce manufacturing costs. The use  of Pro/ENGINEER Mechanica enabled Optima to evaluate more design iterations, which resulted in a better quality product designed in less time and at less cost.

The Optimized Design
Optima engineers performed 15 design iterations on the mechanism,and nearly five more on each of the major components. Their goal was to optimize the design by meeting all of the client’s mechanical requirements, while minimizing material costs. Engineers showed their customer the final design, which required only a few tweaks.
At about this time, the materials suppliers said they couldn’t meet the original ultimate tensile strength specification, so Optima engineers went back to the Pro/ENGINEER model, entered the new material specifications, and made a few tweaks to get it working with the new material specifications. In the past, this would have required at least
one, possibly two iterations of building and testing prototypes, which would have taken much longer. Not only was it easy to rerun the analysis, but the associative nature of Pro/ENGINEER made it extremely easy to implement the engineering changes. After making the modifications to the design, all downstream deliverables were updated automatically, saving time and reducing errors.

Getting it Right the First Time Saves Six Months
The very first prototype passed all the demanding physical tests required of a stadium seat, including first and foremost the ‘soccer hooligan’ test described above. Getting the design right the first time made it possible to complete the design process in only six months, half the time of conventional design methods. Without Pro/ENGINEER, such
a design would have required at least four or five physical prototypes, which are not only time consuming, but also expensive.

Ultimately, Optima engineers created a better-performing design than was possible in the past because the speed of the virtual prototyping process—enabled by the integration between Pro/ENGINEER and Pro/ENGINEER Mechanica—made it possible to consider more than twice as many iterations.

The new seat is already being used in the United  Kingdom at Lord's cricket ground and Sheffield Arena, and is being in stalled in a new 90,000 seat national football stadium that will be used during the 2012 Olympics. “Our customer was very impressed that we were able to meet their demanding specifications with the very first prototype,”Forrest concluded.