Control Engineering eNewsletter for Motors, Drives, & Motion Control for July 2003



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Unwinder applications ''get a brake''

AC motor braking is key to ABB's integrated web speed and tension control system.

Throughput improvements in machinery often make the news, yet advances for the back-end of processes deserve attention, as well. Tension control and braking are functions vital to web handling processes like paper, packaging film, and foil production. Braking torque is necessary to keep constant tension on the rolls as material unwinds into the process so that stretching, wrinkling, print registration changes, and other material variations are minimized.

These processes traditionally employ air-powered mechanical (disk) brakes, but not without the problems of wear/aging, inconsistent tension control accuracy, and attendant maintenance costs. Electric motors powered in generator mode produce braking torque, and thus provide an alternative solution. This method has been used in high-power applications, for example, controlling huge rolls used in papermaking. Typically, a dc motor, gearbox and drive control are involved—according to ABB Inc., Automation Technologies (New Berlin, WI)—along with a way to dissipate the energy generated or return it to the plant or line. However, returning power to the plant is limited to motor brakes above 25 hp (less than 20 kW), says ABB.

Printing, coating, film, foil, flexographic, wire/cable, and textile machines are said to benefit from ac motor-based brake control.

With dramatic advancements made by modern ac variable-frequency drive (VFD) technology, there is a new alternative, which also extends to cost-conscious lower power applications. ''The ac drive/motor solution now provides performance and control superior to traditional dc installations,'' says Chuck Hollis, ABB, Inc., drives manager.

In one recent application, ABB has installed a lower power drive/motor brake solution at IR Industries, a processor of plastic film located in Brewster, N.Y. The new system consists of a 5-hp ac induction motor, 4:1 gear reducer, load cells, and ACS 800 drive with direct torque control (DTC) and built-in flux control. It replaces a two-roll unwinder with two 10-year-old, air-operated mechanical brakes.

ACS 800 drive operates in torque mode via DTC, providing precise tension control with a 4-20 mA reference signal going from the setpoint controller directly to the drive and motor. DTC, with its 25-microsecond scan rate that calculates torque and flux, eliminates the need for tachometer feedback used in a dc drive. ABB considers ac motor brakes to be ''a natural part of the evolution to more precise and electronic control.''

EPRI's new, comprehensive 2nd edition ASD Guide

Need a comprehensive, one-source guide to adjustable-speed drive (ASD) technology? If so, the recently released 2nd edition of the Electric Power Research Institute 's (Palo Alto, CA) EPRI ASD Applications Guide published on CD ROM belongs among your references. EPRI ASD Applications Guide covers electronic ASDs exclusively—excluding fluid-coupling and eddy-current drives.

The 2nd edition fulfills the main intent to supply basic information on ASD usage for ''user-side'' and ''supplier-side'' professionals. Fundamental topics include:

ASD Application Guide from EPRI comes highly recommended by industry experts and can be previewed online.


  • How to calculate horsepower or kW and speed;

  • How to calculate acceleration rate;

  • Control of harmonics;

  • ASD reliability engineering;

  • Torsional analysis;

  • The engineering and construction package; and

  • Sample specifications.

However, the Guide goes into deeper issues, upgrading drive and motor technologies and application methods that reflect new knowledge gained since the original publication in 1992, which distributed 100,000 copies.

Direct-torque control and vector control are among newer technologies explained. New material highlights torque from the perspective of ASD and motor combinations and presents load torques applicable to 70 types of driven equipment. Electromagnetic interference (EMI) receives updated treatment, including ways to control EMI for ASD applications.

New material also has been added on calculating the performance of pumps and fans with ASD control, application of ASDs to utility usage—for example, forced draft and induced draft fans, and use of ASDs on natural gas pipelines, showing techniques to increase pipeline capacity. A new appendix adds application of ASDs to reactor recirculation pumps for boiling-water reactor units in nuclear power plants.

Other expanded coverage areas are EPAct (Energy Policy Act) motors, cycloconverters, and 18-, 24-, and 30-pulse ASD topologies. While focus is on advantages of squirrel-cage induction motors, uses of synchronous, wound-rotor induction, and dc motors are also briefly discussed.

EPRI ASD Applications Guide is published by Jarsco Publishing Co. (Corona, CA) and can be purchased for $120 from the publisher. Click here to preview the CD-ROM and for purchase information .

How small can ''pancake'' motors get?

The immediate answer to how small comes from Maxon Precision Motors (Burlingame, CA; Sachseln, Switzerland), which offers a ''pancake'' motor at 6-mm diameter by 3.75-mm long. That's a dimension of just 0.24 x 0.15 inch, not including the tiny shaft!....This is just a bit larger than candy sprinkles on your ice cream sundae.

Maxon's EC 06 pancake motor weighs in at a diminutive 0.32 g (0.01 oz).

Long life accompanies miniscule size in new EC 06 brushless, pancake motors due to electronic commutation, without mechanical brushes to wear out, and a ruby bearing. Performance features of the tiny motor include maximum continuous torque output of 0.019 mNm (0.003 oz-in.), maximum speed of 20,000 rpm, and ambient temperature rating of -40 to 80 °C (-40 to 176 ° F).

What are some applications you ask? Extremely small size makes these pancake motors particularly suitable for optical, laser, and biomedical applications, as well as for test/measurement devices and miniature robotics. Control electronics complement the tiny motor.

This ''cool'' product is a further example that innovation remains strong in electric motor development.

Seminars, educational opportunities, related events

Professionals in the Motors, Drives & Motion Control arena need periodic updating of their skills. Here is a sampling of upcoming events for learning.

Fall 2003 seminar schedule of the Electrical Apparatus Service Association (EASA, St. Louis, MO) includes:

''Root Cause Failure Analysis'' (Sept. 12-13, 2003, in Newark, N.J.) examines common and unusual causes of electric motor failures. The seminar presents a methodology to identify the most probable cause of failure.

''Fundamentals of DC Operation and Repair Tips'' (Oct. 3-4, in Cleveland, OH) covers the theory of dc motor operation on a basic level, while the course as a whole can benefit experienced users. The seminar reaffirms the longevity of dc motor technology.

EASA is an international trade organization with more than 2,200 electromechanical (motors, generators, drives, controls) sales and service firms in 59 countries. For enrolment or other information, call +1 314/993-2220 or visit the web site .

SMMA—The Motor & Motion Association (S. Dartmouth, MA)—will hold its 2003 Fall Technical Conference in Nashville, TN, Nov. 5-7. Wide ranging presentations about new technologies for electric motors and drives will be grouped by the following categories:

  • Design

  • Efficiency

  • Materials

  • Software

  • Manufacturing

  • International standards

Two special educational sessions are scheduled. An SMMA Motor & Motion College course, ''Basics of Brushless DC Motors'' and a discussion of ''EMERF 2nd Edition Lamination Steels CD-ROM,'' which is a compendium of steel alloys used for electric motor laminations, will take place prior to the conference on Nov. 5, 2003. Each session requires separate registration.

For more information about the conference, call +1 508/979-5935 or click here to visit the web site .

By the way, EMERF stands for the Electric Motor Education and Research Foundation; additional background about the CD-ROM can be found in my December 2001 Newsletter .

Also, it's not too early to think about a major related event in Europe. SPS/IPC/Drives 2003, the electronic automation exhibition and conference will be held in Nuremberg, Germany, during Nov. 25-27, 2003. This growing fall event ranges over systems and components needed to implement integrated automation solutions.

Exhibit sectors cover controls (PLCs, industrial PCs), electric drives, fieldbus technology, networks and industrial communication, visualization, software, industrial sensors, intelligent vision sensors, and safety technology. Last year, this event drew some 790 exhibitors and nearly 23,000 visitors. The conference portion of the show consists of lectures, tutorials, and special presentations (mostly in German), which consisted of more than 116 sessions in 2002.

For more information about SPS/IPC/Drives 2003, call + 49 711 61946-0 or visit the web site .

More on dynamometers

An optical speed sensor and torque measurement device integrated into Magtrol's WB dyno obtains typical system accuracy of 0.3% full scale.

My May E-newsletter included coverage of a compact dynamometer for teaching purposes and for conveniently demonstrating characteristics of various motors. This month the topic turns to an example of a high-speed dynamometer for formal testing of electric motors.

A new generation eddy-current dynamometer has recently been introduced by Magtrol Inc. (Buffalo, N.Y.) to accommodate higher speed requirements of miniature motors now more frequently integrated into tools, medical/dental equipment, and commercial and consumer products. Magtrol's High-Speed WB dynamometers provide motor testing speeds up to 70,000 rpm at very low torque rating of 150 mNm (21.2 oz-in.). Other options allow higher torque ratings up to 20 Nm (167 lb-in.) and speed capability of up to 65,000 rpm.

With Magtrol's TM torque sensor mounted inline with the dynamometer, higher system accuracy of 0.1% full scale and speeds up to 50,000 rpm can be obtained. High-Speed WB dynamometer, combined with Magtrol's High-Speed Programmable Dynamometer Controller, Power Analyzer, and M-Test 4.0 software forms a complete system for online production testing of motors.

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