Motion Control Resources
Servos Drive Automotive Manufacturing/Automation for Auto Motion
by Kristin Lewotsky, Contributing Editor
Motion Control & Motor Association Posted 09/24/2007
Improvements to reliability, diagnostics and speed make servos a smart choice for automotive manufacturing applications.
Automation and motion control have been at the heart of the automotive industry for decades. Today’s automotive manufacturers are upgrading systems, adding inspection and networking capabilities, and taking advantage of integration to produce a better, cheaper product in less time.
Doing all of that, of course, means minimizing downtime. In part, that is a benefit of the robust systems available today. Some of it is also savvy design. Tim Walker, president of systems integrator Churchill Technologies LLC (Grand Haven, Michigan), knows all about that.
Walker’s company focuses on inspection applications for subassembly manufacturers, for example using a vision system integrated with robotics to be sure a piece is in the correct orientation before it is picked up, or to ensure that the piece in question is defect free.
In one application, a manufacturer had an intermittent fault in which the ceiling grooves of a component would collect debris. Not such a big problem when you’re producing one part an hour, but for a manufacturer delivering a part every 10 seconds on a line operating 24/7, it was a serious issue. By combining motion control and vision, Walker’s group was able to automatically inspect the parts at the required rate -- faster, actually. “Our system would actually run at 5 seconds [per part] if the line could run that fast,” he says. They have since built another nine systems for the customer, installing the last in a mere four hours.
Walker credits simplicity of design with reliability. In many cases, that means sticking with a four-axis SCARA robot, which takes up less space than a six-axis design and often less than a dedicated gantry-type load/unload unit. The approach offers other advantages as well. The controllers the team uses, for example, are based on integrated PLCs, which allow them to control certain auxiliary functions without adding a separate PLC.
Working the Network
For Jim Schindler, sales engineer at automation specialist C.A. Litzler Co. (Cleveland, Ohio), the integration is all about data. Many of Litzler’s recent automotive plant installations have involved plant floor data collection, often using existing PLCs. The data is mined for process intelligence and product history, allowing manufacturers to obtain product information and monitor in-process products in real time. The database can also include birth history applications in which the manufacturer tracks data for individual products and their actual assembly so it can be used to address quality concerns in the future.
It’s a significant change, he says. “Ten years ago, very little of that data collection was being done. Today in some cases the entire project is, ‘Get me the data.’ I think the flexibility of the networks that are available to us today gives us that capability,” he adds. “It would have been a lot more difficult to do 10 years ago. Today, it’s very straightforward.”
Of course, networking and data mining isn’t just about product monitoring. Motion control can benefit, as well. “The difference between what was done previously and what’s being done today is that today a lot of the servo drives are networked,” he says. “Because that network often brings along with it more information from the servo drive, we now have more diagnostic capabilities we can offer the customer at very little additional cost.”
In particular, the quality of the data that they get for that investment is different. “On a traditional analog-driven ?10-V command servo, it used to be that you would get a couple of status contacts back that would tell you whether you faulted or not,” he says. “Today we can do much, much more. You can look at the torque of the motor; you can look at the actual speed. Things of that nature weren’t even available years ago.”
More sophisticated information means better troubleshooting capabilities, which in turn mean reduced maintenance costs. “You can be a little bit predictive about where the issues are if you choose. Look at the actual torque load on the motor compared to the historical averages to see if you’re getting some mechanical issues developing.” It doesn’t come for free, of course. Taking advantage of the diagnostics means writing extra code, but the capabilities do exist for the interested customer. “You can provide value because you can actually start to pinpoint the problem for the maintenance guy when there’s an issue and tell him much more specifically where the problem is than you could previously.”
Living in the Auto World
In general, Walker and Schindler agree, the automotive customer tends to be servo savvy, driven perhaps by high overhead costs that ensure return on investment in a fairly short timeframe. The large corporations tend to be fans of servo technology; the holdouts tend to be smaller operations with limited resources. “You’re typically talking about a small shop that doesn’t have any technical expertise,” says Schindler. “Their approach is, ‘Give me a bang bang [in/out, two position] cylinder for my pick-and-place because I can’t handle the servo.’ That’s only because they don’t have anybody technical to fall back on.”
Contrary to perception, a machine based on servo motors doesn’t have to be hard to maintain and operate. Walker has proof of that. “We’ve had [the ceiling-groove inspection] system now running for three and a half years and we’ve never had a service call on it,” he says. “That’s millions of cycles for a very, very low investment.” The key is keeping the system as simple as possible. “You can design complex systems that the end customer is going to need a lot of capabilities to keep running, or you can design a simple system with motion control, which is designed to run repeatably.”
By giving up the servos under the mistaken impression that they create a more difficult system, end users give up not just advantages of diagnostics, but also mechanical benefits. Consider using a servo for pick-and-place. Overkill? Not necessarily. “By having a servo there I can make the movement smooth and accurate,” says Schindler. “If I’m doing bang bang control on a cylinder that’s bottoming out, the physical vibration and stress that that bang bang operation creates tends to wear out the machine and create maintenance issues. By taking away the cylinder and putting in a servo drive, we’ve made a much more mechanically reliable application and minimized downtime. We’ve increased the sophistication of the application but we’ve gained something significant by doing that.”
Going forward, Walker sees linear servo motor technology making vast inroads in industries as varied as grinding and machine tooling. “Manufacturers are tending to move away from ball screws and servo motors to linear motors. They’re very, very accurate and very, very high speed, with fewer mechanical parts,” he says. “There’s less to go wrong. Some of the technology is quite phenomenal compared to where it was even five years ago.”
As for Schindler, he remains a big fan of networked systems. “The biggest trend is the move toward networked products. The more sophisticated the product -- such as a servo -- the more benefit you gain.”