Everybody hates an unplanned machine failure. Your customers hate them because any unscheduled shutdown means loss of production, loss of revenue, and maybe even the need to call in the cavalry to fix the machine immediately.
Machine builders hate unplanned failures because they're the cavalry. When your phone rings, it's the unhappy customer on the other end of the line, and he wants your troops to arrive right now and get things running again.
Maintenance and repair people at both the user and machine builder hate unscheduled shutdowns because of all the pressure exerted to get the machine running again.
And, because of the old rule about what runs downhill, it seems like control system designers always take the heat. Everyone understands when a motor or gearbox fails--it's mechanical, and failures are to be expected. But no one understands when a control system sputters, the HMI screen goes blue screen, or the network stops networking.
Fortunately, modern machine control technology is coming to rescue, making it possible for control engineers to build exceptional reliability into their machines, increase uptime, reduce the number of unexpected failures, and become heroes instead of villains.
Here are a few design ideas to discuss with your customers as a means for them to achieve competitive advantage through uptime and reliable operation.
A way to boost uptime is to minimize downtime. Sounds obvious, but many companies discount the time wasted to refixture a tool and reset the machine to run a new part.
"We have seen our customers move away from dedicated machinery that only allows one particular part to be manufactured," notes Jason Munk, controls engineer and project estimator at machine builder QSI Automation. "Now, the majority of our customers have a family of products that are required to run on one automated system."
It's the same everywhere, it seems. "Job changes are frequent in die casting, especially now that many plants are using Lean Manufacturing and holding less inventory," says Dave Woods, product development manager at Rimrock, a builder of machines that make die cast parts.
Running smaller lot sizes puts pressure on a machine and also on the company's ability to process orders. "Historically, manufacturers would regularly receive big orders for 10,000 products," says John Warner, president of Accenture, an asset management software company. "Now, orders require smaller quantities and speedier turnarounds."
Advances in hardware fixturing can cut downtime during changeovers. QSI, for example, uses "family-oriented fixturing" that allows an entire group of products to run using identical tooling. "Another method we use is simply making the fixturing rotational," explains Munk. "When a product is changed, just remove a couple of bolts and rotate the fixture 90 or 180[degrees] to accommodate the new product."
Michigan Custom Machines builds special machinery for assembly and test of diesel fuel systems, such as injectors, pumps, nozzles, and subassemblies. "We have designed our machines to be universal," says Michael Schena, president of MCM. "Injector and nozzle machines accommodate several different products with a 5-min. fixture and component change."
Hardware fixturing is not the only way to accommodate rapid part changes. "We are doing a lot of work in the automotive industry here and in Europe to convert robotic assembly stations from traditional hardtooling part location to visual fixturing," claims Jordan Merhib, vice president of Isra Vision Systems.
Merhib explains that robots are programmed to perform a function along a predefined path. With traditional mechanical fixturing, a vehicle or part must be precisely located at the exact same point every time. For a vehicle, the required accuracy is 1.0 mm. "The tooling to do this is expensive, subject to wear, and model specific," says Merhib.
By using cameras for visual fixturing, the vehicle can be stopped anywhere within 25 mm of the target, a feat easily accomplished with a typical conveyor. "We then use the vision system to provide the required precision," he says. Essentially, position data from four cameras determine the exact X, Y, Z coordinates of the vehicle, and this information is downloaded to robots. "They are then able to perform their function to the 1 mm tolerance required."
Typical time for this process is 2-3 secs., and it can accommodate multiple products coming down the line. Merhib reminds that visual fixturing has been used in circuit board assembly machines for years.
Completely automatic changeovers are possible, too. "We design machines to handle various parts using servos and PLCs to change tooling position," says Edwin Zimmerman, director of technical operations at Apex Automation. "The factory automation industry is using more servos and electronics where there are stringent requirements for frequent product changeovers." But not everywhere, it seems. "There is still a niche market for low-cost, single-product machines," he adds.
"We try to work with components that allow for automatic downloading of software parameters for part changeovers," says Jeff Bell, manager of automated assembly systems at Taylor-Winfield. "The operator pushes one button and the system automatically changes over the weld controller, robot program controllers, laser and impact marking systems, electrical testing systems, and so on."