I recently spent some time at a big-box store, an international retailer specializing in home furnishings and décor. Not the type of store where I usually spend a lot of my shopping time, but friends and family rave about it, so I decided to make a quick visit to see what all the fuss is about.
Aisles in this store are somewhat narrow and have a lot of twists and turns. They wander so much in and out of merchandise displays, that one of the first things you see when you enter the store is a map of the shopping floor so you get a rough idea of how to get from Point A to Point B as you shop. Arrows on the floor help you move in the right direction (from entrance to check-out), and there are a couple of shortcuts shown on the map to help you get to certain areas of the store faster.
So there I was wandering through the store following the arrows in the twisting, turning aisles, when I see a dad rolling his son around in a full-size shopping cart, the type of heavy duty metal-framed cart you typically find at a grocery store. Not really that unusual you might think, for a Saturday afternoon shopping trip to a big-box store, except the cart seemed a bit odd. As I watched the dad pushing the cart, it looked like he was doing the shopping cart equivalent of automotive “power slides” around aisle corners – the kind of slide you might see in an automotive drifting race, where drivers negotiate turns by steering out of, rather than into the turn, then accelerating just enough so traction for the rear wheels breaks loose and the back end of the car slides toward the outside of the turn. This combination of steering and sliding move the car smoothly through the turn. If you have never seen a power slide race, it is worth looking one up on your favorite sports channel or Internet search website. I thought this a strange move for a shopping cart, particularly since I did not hear the sound of rubber wheels doing a chattering skid across a linoleum covered floor. Then I saw it, the simple solution for maneuvering clumsy shopping carts around crooked store aisles: four wheel steering. I imagine this solution is neither unique to this retailer, nor even a very recent innovation in shopping cart design. But when I go shopping and need a cart to haul my stuff around the store in, the only option I have is a cart with front wheels that steer, and rear wheels in a fixed, straight ahead position. So seeing a cart with all four wheels that help with steering was new for me. And it made perfect sense for the quick turning, narrow store aisles.
Okay, so adding four wheel steering to a shopping cart is not a very complicated process. In fact, I doubt if there was much, if any, engineering design involved. I can imagine a slow day on the shopping cart assembly floor, with assembly technicians trying to think-up an entertaining activity to break the boredom. One says “Hey! I wonder what would happen if we added a second pair of swivel wheels to one of our carts?” And just as simple as that, the four wheel steering shopping cart was born. In fact, this is how many engineering design solutions are born as well. We keep experimenting, sometimes on paper, sometimes with real hardware in the lab, trying different solutions until we find one that fits. Figuring out “how” sometimes comes first; understanding “why” occasionally waits until the “how” works. If you are like me, this process is usually incremental. I find that letting my brain work on something for a while usually helps me find a workable solution. Sometimes solutions come to mind after only a few minutes or maybe an hour or two. Then there are solutions that take a week or two, or maybe even a couple of months, to figure out. And the end solution is usually pretty simple. My brain may start out thinking in great detail about complicated options, but I usually arrive at a solution that is much simpler than where my thought experiments started. I also find that the magnitude of a problem does not necessarily correlate to the amount of time it takes to find a solution. Sometimes big problems are solved in a flash; sometimes simple problems take a while to figure out. Regardless of the design challenge, however, solution options need to be thoroughly thought through.
As it turns out, modeling and simulation are great ways to think through a design problem. Just trying to model a system is often a great way to figure out what really matters to the design and what is technical fluff. And simulation helps you confirm how your model, and therefore your system, performs. Key to this modeling-to-simulation flow is choosing the right modeling language. There are, of course, many modeling languages to choose from. Some are general purpose, while others are targeted to a specific engineering problem or analysis. Among the most flexible is the class of analog hardware description languages tuned for analyzing systems that contain a mix of engineering domains. Two of the most capable languages are VHDL-AMS, the multi-domain and mixed-signal IEEE standard language, and the proprietary but similarly capable MAST language from Synopsys®, Inc. Both languages are well suited for modeling the complex behavior of mechatronic systems. Choosing which language to use depends on what simulator you have access to. Using MAST means you choose to use the Saber® simulator from Synopsys. Using VHDL-AMS gives you access to a broader range of simulators like SystemVision® from Mentor Graphics®.
Some of our customers are working through this very choice. They have Saber and use MAST, but are looking for the modeling and environment flexibility offered by VHDL-AMS, SystemVision, and other tools in the Mentor Graphics portfolio. The challenge, of course, is migrating their existing MAST-based models and designs to VHDL-AMS. To help with this migration process, the SystemVision Engineering team developed a MAST to VHDL-AMS converter. It does a nice job of converting MAST source code and netlist-based models into standard VHDL-AMS syntax , providing a good starting point for moving designs forward to an IEEE standard modeling language. Just as the simple addition of four-wheel steering to a shopping cart makes it easy to maneuver narrow, twisting shopping center aisles, SystemVision’s MAST to VHDL-AMS converter is a simple solution that eases the transition from a proprietary modeling and simulation environment to a more flexible environment based on proven IEEE standards.