KISS techniques for reliable machine performance

In the June cover story for CONTROL DESIGN, Senior Technical Editor Rich Merritt asks machine builders and automation suppliers about the steps they take toward building a better running machine. The answer he got? Keep it simple, stupid.

By Rich Merritt, Senior Technical Editor

THE PERFECT MACHINE requires no maintenance, no repairs, and no aftermarket service of any kind. Once it goes out the door, you forget about it. Because that’s not possible with any machine more complex than a bench vise, the next best thing is a machine that requires the absolute minimum of changeover effort, maintenance, repairs and service. How do you build such a machine? We asked machine builders and automation suppliers what they do towards that goal, and got some interesting answers. Basically, they say to keep it simple, monitor it, and fix it before it breaks.

Kiss Your Troubles Away
Mechanical devices cause most of the problems in most machines. Traditional motors, gearboxes, line shafts, belts and chains require endless adjustments and maintenance, and are prone to failure after prolonged use. Parts changeovers often are tedious and time consuming for your customers. The better solution would be to look for a way to keep it simple, stupid (KISS).

R. A. Jones & Co. in Covington, Ky., has made packaging machines for 100 years, and they’ve kept up with technology all the way. “Manufacturers that use carton machines are in an extremely competitive mode,” says Darren Elliott, chief engineer at R.A. Jones. “They need to run products faster and more efficiently.” In 2000, R.A. Jones began implementing what is known in the industry as Generation 3 (Gen3) machines, using Rockwell Automation’s Kinetix motion control system, servo drives, a digital SERCOS network, and MP-Series motors and actuators.

FIGURE 1: DRIVE, HE SAID

R.A. Jones has been building cartoner packaging machines for 100 years. In its new cartoner machines, the company changed over to servo drives to reduce the number of mechanical components and increase reliability.

Its new Criterion 2000 cartoner machines (See Figure 1) now rely less on mechanical components and more on digital, all-servo-driven technologies. By using servos, R.A. Jones reduced its engineering costs and built a flexible, high-reliability cartoner that compresses installation time and reduces maintenance by eliminating belts, drive chains, line shafts, pulleys, sprockets and torque tubes.

Tom Matyas, product manager for drives, motors and motion at AutomationDirect, says lineshafts work well, but require too much service. “Due to their mechanical nature they rely a great deal on correct machine setup, such as synchronization and mechanical connections, plus proper maintenance,” he says. “This usually means longer setup between cycles on machines that run several different products. Improper setup and/or mechanical wear at a single station may have a ripple effect on any station connected, thereby affecting the efficiency and performance of the entire system.”

Servos, direct-drive technology, linear drives and variable-speed motors all seem to be K-I-S-S solutions for machine builders.

“Converting rotary motion into linear motion requires, at minimum, a rotary motor, gearbox, two pulleys, a belt, couplings, a ballscrew and zero-backlash nut, and linear bearings and races,” explains Matyas.

“A linear motor makes the same movement as the rotary solution without the additional mechanical components, thereby greatly reducing the chance of system failure.” Obviously, the more moving parts, the more wear and higher the maintenance.

“The move to servos and integrated control technology has the potential to replace up to 60% of the mechanical parts in a machine,” explains Mike Wagner, business development team leader, Global OEM Team, Rockwell Automation.

“The benefits of this reduction include lower costs, increased reliability and maintainability, as well as improving machine performance by up to 75%. For example, in the past it took several hours to change over a machine to run a new part, and the machine could only run a few product variations. Today, servo-driven machines complete changeovers in less than two hours, and now you can run hundreds of product variations on a single machine.”

Servos make a key difference. “I use servos as much as possible,” says Archie Jacobs, engineer at Manufacturing Automation LLC, a system integrator in Orangeburg, S.C. “I mostly use them for flexibility and feedback, such as for current load. It also eliminates contactor replacement due to arcing when full voltage starting. The acceleration and deceleration reduces mechanical system shock at startup extending the life of mechanical components.”

Tom England, marketing manager of the direct-drive motors business unit at Danaher Motion, says direct-drive technology also simplifies operations. “Machine control using direct-drive technology provides significant improvements in machine uptime due to the elimination of the mechanical transmissions, gearboxes, and timing belts,” he says. “Machine simplification also is greatly enhanced by the elimination of all the components needed, such as brackets, mounting parts, and tensioning components. Most high-speed pick-and-place machines employ direct-drive technology today due to the speed performance and reliability improvements.”

Matyas agrees. “Regardless of the high-speed motion bus being used, electronic drive trains provide reliable coordinated motion between stations and allow for on-the-fly adjustments, such as changing gearing ratios, altering phase relationships, etc.,” he says. “Product changeover now can be done by simply loading a recipe in the system, which takes seconds, not hours. This virtually eliminates the risk of mechanical setup problems. Further, any stations that experience a problem effectively are isolated and, therefore, do not directly affect the performance of the other stations on the machine.”
What about cost? That’s always a factor for machine builders. As you might expect, the cost of servos and similar systems--all of which require controls--is more expensive than traditional mechanical systems.

Curtis-Toledo, manufacturer of air compressors in St. Louis, found a way around the extra cost of controls by using an ABB ACS800 variable-speed drive (VSD), which has built-in controls for the drive and the compressor. Jerry Elson, national sales manager for C-T, says it makes the company’s design more reliable than competitive compressors, because one major component--the PLC or board-level controller--is eliminated, and it lowers the cost. “Having a variable-speed drive integrated into our compressors is precipitated by industry demand,” says Ellson. The drive software also regulates and changes speed to match the exact air demands from the plant, thus saving energy. “VSDs are coming into play where energy costs are higher, such as in California,” adds Elson.

Fortunately, prices are coming down for motors of all sizes as well. “Servo technology prices have dropped as much as 40% in the last four years, while the cost to implement the technology has been reduced by at least 50%,” says Wagner.

“There are more products and application developers available today which, by nature, reduces price,” says Matyas. “In addition, offshore products and manufacturing have been driving down the price of products domestically. The price and availability of the hardware and software make it more feasible to incorporate today than years past. However, specifiers have to weigh the cost of these enhancements against the system’s increased performance and flexibility. Simply stated, we don’t want to complicate and add cost to the basic mousetrap to still catch only one mouse a day.”

Hardware cost seems to be coming down, especially from the industry giants due to competition from the lower cost brands, such as Automation Direct, adds Jacobs.

“Direct linear control comes at a cost,” says Wagner. “However, it does allow for further reductions in mechanical parts.”

R.A. Jones, for example, builds its new machines with 30% fewer parts than previous models. “With fewer mechanical parts, the Criterion 2000 has exceptional reliability and efficiency, compared to its mechanical counterparts, and runs at higher speeds,” says Elliott. The company also reduced its programming time by more than one-third, thanks to integrated motion and sequential control, reduced number of I/O points, and ladder logic.

Does this technology give you a competitive advantage? “I would like to think that it does,” notes Jacobs. “My experience shows that customers tend to rule ‘out’ machine builders as a result of bad end products more than ruling them ‘in’ for good products. Bad machines are always at the forefront of attention; good ones disappear and are not much thought about.”

What Condition Is Your Condition In?
Simplifying the machinery is just one step. Determining when a problem is going to happen is the next step. This calls for condition monitoring and analysis. Essentially, you install condition monitors such as vibration and temperature sensors on the machine, acquire all the data in real time, and compare the data to a baseline signature to determine if a problem is getting severe enough to require maintenance.
“Mechanical failures are wonderfully predictable,” argues Mike Fahrion, president of B&B Electronics.

“The predictive-failure indicators are generally well-known. A motor manufacture can supply a control chart for temperature, vibration, current and other parameters. From there it's simply a matter of instrumenting, data logging and analysis.”

FIGURE 2:
GRAPHIC RESULTS
When a bearing starts to go bad, it creates a signal that an accelerometer can detect. If maintenance or the machine builder react fast enough to the warning, a catastrophic failure can be prevented. Source: PCB Piezotronics
For example, an accelerometer mounted on the input shaft of a roller mill gearbox can establish the baseline signature of a new system. Then, using data from the gearbox manufacturer, bearing manufacturer, or plain old-fashioned run-to-failure testing, it is possible to set limits at which to sound an alert and then set a fault (See Figure 2). The big spike in the graph indicates a major inner race bearing fault (See Figure 3 below). If this was a real plant, a maintenance technician or the machine builder’s service department could respond to the first alert, in time to shut the roller mill down before a catastrophic failure occurred.

The illustration comes from a series of tests conducted by PCB Piezotronics with Emerson Process Management, IMI Sensors and NSK. Tests were conducted at an NSK bearing test facility, using a machinery fault detector from PCB Piezotronics. The device provides a 4-20 mA output signal that can be monitored by conventional data acquisition devices such as a DCS, PLC or SCADA system.

In addition to the roller mill gearbox, they also tested a pinion stand gearbox and a large machine running at 10 rpm. Their results showed that an accelerometer is a reliable detector of a fault, and a reliable indicator of the severity of the fault. In other words, simple accelerometers and simple data acquisition might be all you really need to detect faults in time.

SKF, a bearing manufacturer headquartered in Sweden, has a vested interest in condition monitoring, because bearings are a major source of machine failures. It created its own internal group -- SKF Condition Monitoring -- to keep an eye on customers’ machines. As part of their maintenance program, SKF customers use an online surveillance system with hardware and software that monitors machines around the clock. The first version, the Local Monitoring Unit, was released ten years ago, so they have been at this for a while.

The newest version, Multilog Condition Monitoring Unit (CMU), connects to the plant network via Ethernet. Ethernet makes it easier to instrument big machines. A paper machine, for example, can be as long as a football field and as tall as a three-story structure, but the Ethernet network can daisy-chain to all sensors, thus simplifying wiring. Host PCs to run condition monitoring software can be positioned anywhere on the network.

Wayne Weir, manager of the applications engineering group at SKF, says condition monitoring is especially good for machine customers that have downsized, because remote monitoring means that nobody has to walk out into the plant and retrieve data by hand. “A single online system with 32 channels can save up to four hours a day in data-collection labor costs. It also can collect data in extremely hot or dangerous areas.” These are good selling points for a machine builder that might want to offer a condition monitoring option.

Condition monitoring rapidly is replacing old-fashioned preventive maintenance (PM) programs, he says. “If you manage PM programs based on hours-run, or worse, a purely calendar-driven schedule, you're likely wasting resources,” he says. “With proper instrumentation, you could schedule PM based on control chart data. It's not unreasonable to think that PM expense could be reduced by two to three times.”

Jim Ephraim, vibration monitoring product manager at Hardy Instruments, says condition monitoring helps the machine builder as well as the end user. “Maintenance managers at the end user no longer need to live in a reactive mode, but rather can use trending to plan for equipment repair, and eliminate excessive costs due to overtime, expedited parts ordering, and lost product,” he explains. “Monitoring the vibration signal through a PLC will allow automatic initiation of protective actions such as reduction in feed rate, a pause in the process or a basic alarm. By using remote monitoring capabilities, a machine builder not only can ensure its equipment is continuously monitored, but they also can access the health information from a remote location, or be alerted of an issue via a cell phone or pager.”

Make Money From Monitoring
Jack Bernard, business development manager, Rockwell Automation Integrated Condition Monitoring, offers a financial reason for machine builders to use condition monitoring. “Machine builders benefit by reducing their post-sales support to the end-user,” he explains. “Specifying a condition monitoring system and condition-based maintenance program, as well as a parts management agreement, phone support contract, and a preventive maintenance contract, allows the machine builder to do what it does best--build machines, not support them. Further, they can avoid or lower the costs of warranty repairs.”

Although many condition monitoring systems running today were installed by the end user, this is not something that customers really want to do any more, says Chris DeFilippo, product engineer at National Instruments. Now it’s a job for the machine builder. And it’s profitable. “In general, end-users do not want to develop their own PM systems because of real or perceived problems associated with high cost or the difficulty of implementation,” he says.

“Machine builders have the opportunity to build extra value into their products by incorporating condition monitoring into the control systems using programmable automation controllers (PACs). With built-in memory and performance-grade processors, PACs can provide continuous, on-line machine monitoring and diagnostics, while performing complex control. One of the ways machine builders use PM systems to differentiate themselves is by guaranteeing equipment uptime and offering extended warrantees on machines with condition monitoring. Customers benefit from more reliable equipment and are willing to pay a premium for this advantage.” 

Fahrion agrees that the machine builder can benefit greatly. “It could create an entirely new value proposition,” he notes. “Who better to analyze sensor data than the builder? The technology already is in place so this data could be piped back to a server at the manufacturer. They now could sell a PM scheduling service that would save the end-user money. Warranty claims should drop to near zero.

Warranties could be extended to ‘lifetime’ when the service contract is purchased, since the machine builder would have complete insight into failure prevention for each installation. The machine builder also would now have access to a phenomenal amount of data about its own equipment. Analyzing that data should allow them to further refine their equipment at a design and manufacturing level. This could drive an entire new level of QA.”

Of course, nobody said condition monitoring is easy. It requires expensive sensors, data acquisition equipment, and analysis software. Then, the machine builder has to run baseline tests, so it knows what failure conditions look like in the various systems in the machine.

“Computer power and software analysis tools are not expensive,” says Fahrion, “but the cost of instrumenting the system can be too high.” He says wireless is one way to avoid high wiring costs. “The perfect solution is for condition sensor data to flow into analysis software via wireless connections. No data cables, no power cables. IEEE 802.15.4 is poised to pull this off.”

FIGURE 3: GRAPHIC FAILURE
The graph in Figure 1 was caused by a major inner race bearing fault on the input shaft of a roller mill gearbox. Source PCB Piezotronics







 

 

 

 

 

 

 

 

 

How Much is “Not Expensive?”

Many of the contributors to this article suggest that the cost of predictive maintenance for machine builder and/or customer is not prohibitive. Our research estimates that it costs somewhere between $4,000-7,500 to instrument a machine and acquire the data. The cost of the condition monitoring, asset management and maintenance management software needed to analyze the data and make predictions ranges from economical to astronomical.

These costs might be coming down rapidly, because some of the “big guns” in the control industry are stepping into the condition monitoring business. For example, Emerson Process Management now sells a machinery health monitor for motor-pump trains. It includes vibration and temperature sensors, a machine-mounted analyzer, and a network link, all for $5,000-$7,000. This is just might be the beginning of a trend that will shake the condition monitoring industry to its core, and result in falling prices across the board. Competition has a way of doing that.

For the moment, a machine builder has to decide: Is it worth adding $5,000-$7,000 to the cost of each machine to obtain all the benefits noted? Should they make condition monitoring available to customers as an extra-cost option? Will it sell? Or can they make the investment back on reduced service and warranty costs?

In any case, simplifying the machinery and then using condition monitoring to check for potential faults seems to be the wave of the future for machine builders.
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