Motion Control Resources
by Kristin Lewotsky, Contributing Editor
Motion Control & Motor Association Posted 10/02/2009
Judicious use of motion control, along with integration and modular design, helps drive down machine costs.
The economy. It’s the phrase on everyone’s lips. Economists might maintain the recession is over but manufacturers are still wary of spending. At the same time, to remain competitive, they need to upgrade their packaging lines. How do they justify expenditures? Using motion control and careful design, component vendors, OEM machine builders, and end users can drive down equipment costs and speed return on investment. Let’s take a look at how.
Less Is More
“What end-users are looking for is higher throughput and less downtime, in a machine that’s easy to maintain," says Bill Faber; senior manager, application engineering; Yaskawa Electric America (Waukegan, Illinois). Motion control is a solution with a lot to offer, including fast, easy changeover; rapid diagnostics; plug-and-play operation for replacements; increased efficiency; and decreased noise. That doesn’t necessarily mean that more is better when it comes to servo axes, however. Motion control should be used intelligently, not merely as comprehensively as possible (see figure 1). After all, that enhanced performance comes at a price, and even the best-designed machine in the world is useless if the cost justification can’t be made to purchase it.
Although motion-control-enabled packaging machines boast enormous capabilities, a one-size-fits-all approach can ultimately morph into one-size-fits-none. In part, it's a question of knowing the market. OEM machine builder Colborne Foodbotics makes manufacturing lines that can produce and pack pies at a rate of 1200 per minute. It might seem a natural move to develop a machine that can produce and package a range of desserts but doing so ignores an important fact of life in the food industry: Different types of foods -- for example fruit pies and meat pies, or even cream pies - are governed by different sets of standards. As a result, they are typically manufactured in different plants. Although one machine could be designed and manufactured to make them all, it would carry a higher price tag and yet no one product line would leverage all of its capabilities. A smaller, less complex machine tailored to produce each individual type of pie would be more easily justified on a cost basis and more rapidly achieve return on investment (see figure 2).
In general, the route to success lies with smarter, not greater use of servo motors, says Rich Hoskins, Director of Operations at Colborne Foodbotics. “It's the process and the overall system design that really create the best economies,” he observes. “In the motion control area, we’re looking for ways to cut cost by requiring fewer mechanisms to drive our equipment, doing things in a more streamlined way.” Often, upstream processes can create registration errors in the product that, in turn, require additional servo axes in the packaging line to compensate. The problem tends to manifest particularly in the case of retrofits, so the Colborne Foodbotics engineering team goes to work. "We try to figure out what we can do to help the customer correct some of the things they've done further upstream," says Hoskins. “You can create a problem downstream with the first thing you do on a line. It might be 300 ft upstream and you're creating a huge issue for the rest of the line.” The better the registration, the simpler - and more economical - the packaging line will be. Proper control of upstream product can improve infeed consistency and operation for a downstream machine, making it more efficient, less prone to downtime, and more cost effective.
Wire To Wire
Distributed control architectures provide an important avenue to cost cutting. Traditional centralized control involves connecting each motor via power and feedback cables to drives and controllers housed in a central electrical cabinet. Distributed control leverages motors that integrate drives directly into the package. They can be daisy-chained together for power supply and control purposes, eliminating the need to wire them back to the electrical cabinet. This can reduce wiring by 85%, not only cutting cost but decreasing points of failure.
The approach offers other benefits. With fewer components in the cabinet, the enclosure can be as much as 30% smaller, reducing footprint and price (see figure 3). The streamlined cabinet is easier to design and install from an electrical perspective, and doesn’t require active cooling. “The machine builder saves not just in terms of hardware costs but in engineering time,” says Rick Rey; Business Development Manager, packaging industry; Bosch Rexroth (Hoffman Estates, Illinois). “If they need to add a couple more axes, all they have to do is reprogram the controller and daisy chain the two extra motors to the rest, provided the power supply is able to handle the power.”
End users not only benefit from OEM savings on hardware and development, they also benefit from reduced cost of ownership. Smart components provide enhanced diagnostics and plug-and-play operation, speeding maintenance and reducing costly downtime. Added up, the various economies of distributed control bring a 30% to 40% cost reduction over traditional designs.
Another important aspect is energy efficiency and sustainability. It’s a long-term benefit that can be important for return on investment. Rey cites the example of an OEM customer that produces beverage palletizers. The machines initially used hydraulics but converted to electromechanical motion courtesy of a 20-hp DC motor. The next retrofit brought in 10 hp servo motors for dramatically increased efficiency in a smaller package.
The design also uses a regenerating power supply so that when the motor lowers a heavy pallet, it becomes a generator (see figure 4). The energy can be put back on the bus so that other servomotors in a system can use it. Alternatively, it can be returned to the regenerating power supply. “It becomes a reverse inverter," says Rey. "You're taking DC power, converting it to AC, and feeding it back to the power company on the line. The average power consumed by the machine drops. That's a long-term cost savings.”
Instead of a regenerating power supply, a machine can store energy in a capacitor module. If other servomotors on the system demand power, they can draw it from the capacitor before turning to wallplug power. Again, the net result is lower average power consumption, which can translate to a smaller - and less expensive - power supply. According to Rey, the technique can provide savings of up to 15% over conventional systems.
Improved hardware also has a role to play in today’s machines. Linear motors can be a more efficient way of generating linear motion than the conventional rotary servo motor/actuator combination, which suffers losses due to friction and coupling. “We really believe that a lot of the applications out there for motion control should be linear-type systems," says Hoskins. “Getting rid of a lot of the intermediate transmission stuff like ballscrews and sprocket drives and just going directly to linear motion [makes the system ] operate at close to its maximum potential and gives us throughput that provides much more value to the customer."
The increased efficiency of linear motors can offset the additional cost in certain cases, so long as they are properly stacked up against rotary designs. “You're not just comparing a motor to a motor,” says Rey. “You have to compare the cost of the linear motor with the rotary servo motor and gearbox and ballscrew and rail system.”
Improved performance at the component level offers other economies. A motor has to be able to meet the peak demand requirements of a system, but that peak demand may only last for a matter of seconds. Sizing a motor around peak demand could result in oversizing the motor in terms of RMS value. “If a smaller motor is designed to handle significant overload, for example surviving 350% torque overload for several seconds, it eliminates the need for a larger, more expensive motor," says Farber (see figure 5). Smaller motors mean lower inertia, allowing the machine to accelerate more rapidly.
Integrating machine control also provides benefits. Instead of control architecture featuring a programmable logic controller (PLC), a motion controller, programmable limit switches (PLSs), and so on; a single processor with an integrated programming environment could potentially do it all. "The trend toward mechatronics is expanding the role of the motion controller for many OEM's," says Faber. "Integrating PLC sequence and motion control with other peripherals such as PLSs or temperature control modules can greatly reduce component and installation costs.” The approach also simplifies development, integration, and maintenance while minimizing hardware costs.
Capital equipment always represents an investment, but machines that leverage the techniques and components discussed above give the best possible performance for the money, whatever the economy. “It's all about cost savings,” says Rey. “This kind of technology would make sense in a good economy. It makes even more sense now.”