Servo Motion Spreads Integration, Applications

08/23/2002


This article is an Online Extra to the Electric Servos Go for Ease of Use, Integrate with All the Plant .' Click on the title to read the entire article.

Sidebar: Servo motion applications

Integration of components that comprise an electric servo system is growing, alongside an overall integration of servo motion systems into manufacturing processes. Several complementary factors are helping to expand applications, hence the servo motion market. Software tools for setup and servo tuning have become more effective and easier to use. Also, high-resolution feedback is becoming available at more affordable prices. ( See main article .)

Newer applications areas for electric servo motion control include packaging machinery; conveyor, assembly, and converting systems; and plastics manufacturing machinery, among others. Example applications are given at the end of the article.

"Integrating motion control into complete automation systems is the best approach to meeting customers' expectations for improving efficiency, connectivity and effectiveness," says Bill Kegley, senior product engineer at Rockwell Automation, Allen-Bradley Industrial Motion Control (Eden Prairie, Minn. www.rockwellautomation.com ) The newer crop of capable feedback devices contributes to servo system integration is (see main article). Mr. Kegley notes that incorporating intelligent components into feedback devices adds to their value. Servo system suppliers can then program "personalities" into the devices, creating plug-and-play capabilities for motors, actuators, and entire drive systems. "More information available from feedback devices complements the advances in processor speeds and loop-closure times," he adds.

In related products, ControlLogix controllers support motion functionality in three programming languages of IEC 61131-3 standard: Ladder Logic, Structured Text, and Sequential Function Charts. Rockwell Automation's MP-Series servo motors have a range of 2.5 to 244 Nm (22-2,160 lb-in.) peak output torque.

Importance of software

Software's influence in the servo motion arena is substantial and growing. Mark Crocker, technical director at Baldor UK Ltd. (Bristol, U.K. www.baldor.co.uk ), mentions benefits associated in using modular programming methods. "Multitasking adds more modularity," he states, "allowing multiple programs to execute concurrently. Tasks can be developed to handle different aspects of the machine and can even be called upon when an option is fitted to the machine."

For example, Baldor's high-level motion language-Mint-supports modular programming features, including multitasking. The Basic-like language comes with various Baldor programmable servo drives and motion controllers. Those who wish to program in familiar Visual Basic, C++, or LabView can use Microsoft ActiveX as a simplifying tool. Developed programs pass to Baldor's ActiveX control, which works with various Mint drives/controllers and uses the same application-programming interface as Mint. It simplifies the transition between different program languages, explains Mr. Crocker.

Few standards

Several experts at servo system supplier companies cited the need for more standards. Lack of standards "creates numerous motion control solutions, making it difficult for users to choose the best one," remarks Paul Derstine, motion solutions product manager at GE Fanuc Automation (Charlottesville, Va. www.gefanuc.com ).

Servo motor manufacturers in particular have created their own "proprietary" standards. Baldor Electric's (Fort Smith, Ark. www.baldor.com ) motion control product manager John Mazurkiewicz mentions motor standards developments by the National Electrical Manufacturers Association (NEMA, Rosslyn, Va. www.nema.org ). He predicts users will welcome motor standardization, because of the benefits for interchangeability, second sourcing, and replacements-especially in an emergency. The "Back to Basics" department in CE's July 2002 issue will discuss motion-control standards.

z. "It will be of great assistance to customers in a shutdown, or emergency situation, since a standard stocked item shortens delivery times, and greatly assist when equipment needs fixing," he says.

John Krasnokutsky, product manager for Motion Control Drives at Siemens Energy & Automation (Alpharetta, Ga. www.sea.siemens.com ) refers to ''a lack of industry standards'' in need of attention. He believes that standards such as found in the ''PLC world'' would be useful. Specifically, he looks for standards on flow-chart type languages to help development environments and interoperability of hardware for motion systems.

Drive-to-controller communications

Various communication methods are active in the world of automation; few have sufficient capability for high-performance interaction needed in servo motion control systems. One communication method developed specifically for motion control is SERCOS (SErial Realtime COmmunication System). A number of servo product manufacturers have embraced SERCOS, among them, Bosch Rexroth, Danaher Motion/Pacific Scientific, Industrial Indexing Systems, Parker/Compumotor, Rockwell Automation, Schneider Electric, and Yaskawa Electric America. (These companies appear in the main article.)

A long-time exponent of SERCOS, Bosch Rexroth's Electric Drives and Controls division (Hoffman Estates, IL, www.boschrexroth-us.com ; Lohr, Germany) points to practical benefits of this protocol specific to communication among motion controllers and intelligent drives.

Other communication buses stress high-transmission speeds, but this attribute doesn't address the actual information content of the message. "SERCOS specifies the network language, as well, and can do more with less information flowing over the media," as staff engineer Bill Erickson puts it. "SERCOS has a lot less overhead than competing buses." In short, SERCOS concentrates the most useful data within messages transmitted.

This division of Bosch Rexroth manufactures a broad line of servo drives, controllers, and servo motors, including direct-drive models. Servo drives are available in the range of 100 W to 400 kW, while motors carry torque ratings from 0.3 to 1,200 Nm (2.6 lb-in. to 885 lb-ft).

In a related area, GE Fanuc focuses on PLC-based and standalone controls, however its servo controllers and drives incorporate growing amounts of intelligence. Network buses, such as DeviceNet and Profibus-DP are used for communication, as well as for some motion control tasks-but not for contouring, multiple-axis moves, or other synchronized control, explains Mr. Derstine.

Among GE Fanuc's servo products is the S2K Series servo controller. Its 480-V version comes in two forms: a complete standalone controller or servo amplifier only. S2K Series motion controllers incorporate an all-digital 480-V drive (324 to 528 V ac input); support torque output in the 4-477 lb-in. range; and are available in continuous current ratings of 3-28 A (rms). The controller includes dual processor technology to separate "real-time" operating system and servo-loop tasks, allowing 122-

Market growth?

Original equipment manufacturers (OEMs) have a substantial effect on the growth of servo motion control, according to Rockwell Automation. Migration of servo designs from one generation of machinery to the next takes place in tune with market economics. "Over the last several years, production machine builders have had little opportunity for redesign projects due to their volume of business. Recently, the shift in the economy has builders trimming cost wherever possible to survive the downturn," says Mr. Kegley. "OEMs are extremely customer driven, they will redesign a machine to servo technology (or upgrade to current servo technology) only if the business case warrants the investment," he adds.

As to the question of what's holding back wider usage of servo motion, Don Neumann, product market manager at Danaher Motion, Pacific Scientific (Rockford, Ill. www.danahermotion.com ), points to education as the much-needed missing element. "Many people simply don't realize how cost effective servo technology has become, and how it can benefit their application. Our challenge is to educate designers on the new technologies," he says.


Servo motion applications

Complexities associated with servo motion control in the past are being resolved. More user-friendly hardware and software, combined with newer, lower-cost designs help bring servo motion to a wider audience. Printing and packaging machines have been quite visible in the recent spread of servo motion applications, as the following descriptions show. Especially in packaging machinery, the need for low-cost components is essential for servo motion to have market success. Other growth application areas in the news include semiconductor manufacture, assembly/labeling equipment, and plastics processing machinery.

Interestingly, other parts of the world are way ahead of the U.S. in adopting servo motion systems to industry. In Japan, for example, use of leading technology is more in the forefront. Despite the country's long sojourn into economic doldrums, electric servos are prominent in Japanese industrial robots, and they're making their mark in injection-molding/blow-molding machines and related applications. Higher cost for energy is one factor behind the difference.


Application 1: Servo-drive technolgoy enables short-run, high-speed printing

Digitally generated images and image changes on the fly for corrugated packaging? Yes, it's here-and all without film or printing plates. Packagers are looking at printing in another light these days, thanks to servo-drive technology that enables noncontact digital printing and makes it affordable-even for short runs.

One company taking full advantage of this technology is United Container Machinery (Glen Arm, Md. www.united-container.com ) with its new Jet-Pac, reportedly the first high-speed, fully digital inkjet printing press for corrugated board. Designers of Jet-Pac had cost-effective, extremely short-run printing in mind for this machine, allowing faster time-to-market for new packaging and reducing box inventory in the process.

United Container, a major equipment manufacturer for the corrugated-packaging industry for over 100 years, worked closely with two divisions of Bosch Rexroth (Hoffman Estates, IL; www.boschrexroth-us.com ) -Electric Drives and Controls and Linear Motion and Assembly Technologies-to make this unique application possible.

Servo drives, motors, software all contribute

Rexroth servo drives, motors, linear modules, and software, help Jet-Pac presses deliver high printing accuracy at a continuous speed of 300 fpm, with a capability of 1,000 fpm.

"Our digital printing press design required positioning accuracy while moving a sheet of corrugated board through the system," explains Meyer Ruthenberg, vice president of finishing equipment at United Container, "and Bosch Rexroth had the servo-drive technology we needed for accurate transport of the boards and precise positioning of the print heads."

Jet-Pac employs up to eight position-controlled print heads that provide printing on die-cut corrugated sheets or knockdown boxes ranging in size from 8 x 8 in. to 60 x 60 in. Each head can print a single-color image 4.25-in. wide at 240 dots per inch. Multiple heads can be "stitched" together to print wider images; print heads also can be aligned to print multicolor images.

A combination of Rexroth servo motors and linear modules positions Jet-Pac's inkjet print heads to the accuracy needed. Jet-Pac also includes a servo-driven stream feeder and a vacuum transfer box that transports corrugated board through the machine driven by a separate servo motor. Still another servo motor runs a rubber-coating roll.

All servo drives, motors, and linear modules are networked and coordinated using SERCOS (SErial Real-time COmmunication System) fiber-optic loop and VisualMotion control software. By communicating with the various servo drives, the SERCOS loop can compensate for abnormal conditions, for example, a backlog of cartons in the system.

Position to 0.001 inch in any direction

An operator at a touchscreen loads graphics files and press set-up data into a database from a remote location. Using digital workflow software, this information is downloaded to the drive and motor, which powers the linear module. This module positions the print head laterally across the machine.

According to Vince Staab, electrical engineer at United Container, the print heads can be positioned within 0.001 in. for a specific order, and then saved and restored for future runs. "An operator can make an adjustment of 0.001 in. in any direction. By simply entering the change on the touchscreen, the servo will make the adjustment on the fly," he says.

"The other great advantage of the servo-drive system," adds Mr. Staab, "is that we can do all the programming in-house." Microsoft Windows-based control software is used for machine set-up, parameters, and recipe changes. United Container engineers can dial into the system via modem for troubleshooting or debugging. Drive synchronization and diagnostics are also simplified. In case of a problem, individual drives are easily replaced without revising the control software.

First of its kind


"Jet-Pac is the first of its kind," explains Kin Yung, business manager of Bosch Rexroth's Printing and Converting Group. "Because it's a noncontact, digital system, Jet-Pac offers a faster way to change settings, allowing for quick set-ups that are ideal for short runs."

Accurate positioning at high speeds comes from the servo-driven actuator, which is the combination of a servo motor and linear module. "Precise positioning is essential for digital printing," according to Mr. Yung.

An all-digital system offers economic benefits as well. Costly flexographic printing plates can be eliminated, along with the handling and cleaning they require. Box inventory is reduced because of the ability to print on demand. Changes between production runs are faster, resulting in shorter lead times.

The bottom line is that servo-driven presses offer an affordable alternative to traditional printing on corrugated packaging.


Application 2: Intelligent motion system helps troubleshoot production

Great Dane Trailers (Savannah, Ga. www.greatdanetrailers.com ), a maker of truck trailers and related parts, has implemented a new manufacturing system to expand production capability and reduce downtime in each of its plants located in four states and Canada. The manufacturing up-grade includes Schneider Electric (North Andover, Mass. www.schneiderelectric.com ) motion control modules in a Quantum PLC rack interfacing to Lexium servo drives and motors over SERCOS.

"The transition to an intelligent motion system has even enabled Great Dane to make process improvements and troubleshoot production machinery over the Internet, from its main engineering facility in Savannah," says Robb Dussault, U.S. marketing manager of motion control products at Schneider Electric. A web server built into Quantum PLC enables servo drive diagnostic information to flow over the Internet. It also connects local maintenance staffs with motion system experts at company headquarters.


Application 3: Orchestrated packaging

A conductor is no less essential to a high-speed packaging line than to an orchestra. Kisters Kayat Inc.'s (Edgewater, Fla. www.kkiusa.com ) 320/70 iRT WrapAroundPacker machine represents a case in point. To obtain optimal product flow, the machine's servo-controlled flight bar-a rotating arm that precisely sets the timing of bottles and cardboard into the partition section-must be coordinated with the compression (gluing) section located at the line's end.

Kisters Kayat, a packaging machinery original equipment manufacturer, worked with Rockwell Automation (Eden Prairie, Minn. www.rockwellautomation.com ) to design and build a continuous motion machine with an output of 50 beverage cases a minute to meet an end-user's stringent performance requirements. The resulting product became an integrated robotic technology packaging machine that controls a robotic partition former and inserter, product group loading section, and compression section. It replaces multiple packaging machines that performed separate box erecting, case packing, and case sealing functions, says the company.

One control approach

A single control platform that integrates motion and logic functions was used to meet diverse customer demands. Other design benefits included simpler machine setup and programming, decreased operator training, and inherent modularity for future expansion.

Kisters Kayat selected Kinetix integrated motion system from Rockwell Automation to control various functions of its WrapAroundPacker. By integrating servo and machine controls into one processor, the Kinetix system shortens development time and eliminates separate communication requirements. Servo drives, motors, ControlLogix controller modules, and other Kinetix components perform at various sections of the packer.

An Allen-Bradley 1394 Servo Drive and MP-Series motor handle the flight bar's movements, which drive the cardboard blank incline that positions blanks accurately under a six- or 12-pack of bottles. Two MP-Series servo motors with brakes control the machine's collation section, which goes into action when an incoming cardboard blank is detected by a sensor at the front-end. This machine section selects the correct number of bottles for packaging from an incoming bottle-feed.

A similar servo system controls the back-end partition feed. The brakes serve to hold position when the machine stops or the power is shut off. Seven servo motors, five of them MP-Series, are used overall.

Motion coordination, flexible design


For simplified motion coordination, an A-B 1756-M08SE SERCOS Interface card in the ControlLogix rack communicates with the A-B 1394 drive for all servo drive and motor control. Through absolute feedback, the servo motors can ''talk'' to the processor, transmitting exact position information. There is no need for users to "home" the machine, or move product packages to a sensor, both of which lower machine throughput.

''We chose ControlLogix with SERCOS, 1394 drives, and MP-Series motors because we needed absolute positioning with rollover,'' says Roger Calabrese, manager of electrical engineering at Kisters Kayat. ''When the power goes out and comes back on, the machine remembers where it was. SERCOS was mandatory for that.''

Kisters Kayat designs packing machines in ''function models,'' allowing the coupling of modules to create a variety of machines. This way, designers and operators can disconnect the machine in the center and add a new complete function module, as needed.

''We can sell a machine today for a particular configuration and, later, split that machine or add modules upstream or downstream to reconfigure it to package a completely different type of product,'' adds Gary Hunt, director of engineering for Kisters Kayat. ''The controller is robust enough to accept the demands that future expansions add.''





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