Control Engineering Motors, Drives, & Motion Control Newsletter for February 2002
In this issue:
Linear pneumatic actuator emulates muscle motion
Are you looking for an alternative to pneumatic cylinders? Check out a novel method to obtain precise, repeatable linear motion using material flexure and deformation similar to that of human muscles.
New MAS Fluidic Muscle from Festo Corp. (Hauppauge, N.Y.; Esslingen, Germany) claims advantages of size, weight, and output force compared to standard pneumatic cylinders. It offers as much as 10 times the force, but has only about 13% the weight of a metal cylinder of equal inner diameter, according to the company.
Fluidic Muscle is based on membrane-contraction-a concept that 'involves the wrapping of a watertight, flexible hose with nonelastic fibers arranged in a rhomboidal fashion.' The resulting 3-D grid pattern deforms when actuated by compressed air. As internal pressure is increased, an axial pulling force develops to cause the tubular unit to contract, turning it into a linear actuator.
Fluidic Muscle has models with tubing inner diameters of 10, 20, and 40 mm, and overall lengths of 40-9,000 mm (nearly 30 ft), including end connectors. Typical actuator stroke is about 25% of the unit's physical length.
More motion control trends survey results; care to comment?
Recently, I was involved in generating the questionnaire to an extensive 'Motion Control Trends Survey' of readers of Control Engineering and Design News magazines, conducted by Cahners Research. The collaborative survey explored the views of users and specifiers of motion technology. I shared some of the results with you, along with my analysis, in last month's newsletter. Here's a bit more of results.
Users have more choices available today in the types of electronic drives available to power their motors. Among trends indicated in the drives portion of the survey are:
Nearly all those surveyed (94.9%) use 'off-the-shelf' drives versus 26.3% for 'custom-engineered' drives. (More than one answer allowed.)
A majority of respondents (63.9%) say they currently use or would consider using so-called 'universal drives.' These units enable control of several types of motors in the same drive package by maximizing common hardware, relying on software and microprocessor advances to provide various motor control functions.
By a margin of nearly two-to-one, users prefer to purchase the drive and motor as matched units, rather than separately (66.1% vs. 35.7%).
Simple set-up/control, convenient operator interface, and programmability in software were the most important drive selection features noted, reflecting software's large influence.
Do you have comments on these findings? E-mail me at email@example.com
Sintered magnet material advances high-performance motors, actuators
Stacks of traditional steel motor laminations perform fine in most applications. But in high-frequency actuators or high-speed rotary motors, heat generated by eddy currents produce core losses that can lower magnetic strength of the material. Where do you need to be concerned about this effect? Typically in high-frequency applications, such as automotive fuel-injection valve actuators (2-5 microsec response) or motors required to run above 10,000-20,000 rpm.
To attack this problem, Sumitomo Electric Industries Ltd. (SEI, Tokyo) has developed a sintered soft-magnetic material that's heat resistant yet magnetically stable at high frequencies. The new material has a base of fine magnetic iron powder (tens of micrometers in diameter), which receives an insulating layer (several hundred nanometers thick) and a minute amount of heat-resistant binder before the powder is compressed into a solid material. The insulating layer helps reduce core losses.
'The material has magnetic flux density of 1.6 tesla at a magnetic field strength of 125 oersted, up to a 30% improvement over standard sintered soft magnetic material,' according to SEI. Its heat-resistant property targets hot 'under hood' automotive applications, among others.
SEI's sintered soft-magnetic material offers other cost savings in areas of design, production, and eventual recycling. Material samples are available now, with mass production scheduled for later this year.
A twist on drive and motor integration
Integration of ac induction motors and drives in one package has not received overwhelming uptake by users, after the splashy commercial introduction of the technology some years ago. A new drive development may add life to this slowly growing sector.
Rockwell Automation (Mequon, Wis.) has just introduced Bulletin 160Z AC Drive for three-phase ac motors in the 0.37-3.7 kW (0.5-5 hp) range at 200-240 and 380-460 V input. On a recent Control Engineering visit to Rockwell's Mequon facility, product line manager Stan Ho explained to me that the drive's multi-use design makes it unusual. 160Z AC Drive is intended for distributed, stand-alone applications as well as for direct mounting on most standard ac motors. For stand-alone use, four configurations are available, ranging from open style to a sealed, washdown housing. In addition, the drive includes adapter plates for wall and flange mounting.
Mr. Ho believes that applications will likely split around 35% for standalone drives and 65% for motor-mounted mounted. For the latter case, Rockwell Automation supplies interface plates that mate the drive to motors of numerous manufacturers. This should add to the volume of integrated motor drives. 'It will definitely aid retrofit applications because the user does not have to bring in another make or type of motor to gain benefits from an integrated drive, using existing motors' he says.
160Z AC Drive includes communication modules for DeviceNet, RS-232, Profibus-DP, and Interbus-S.
Enhancements to simulation software
Integrated Engineering Software (Winnipeg, Canada) and Simulation Research (Alphen aan den Rijn, Netherlands) have announced Release II of Caspoc 2001, a design and simulation software for Power Electronics and Electrical Drives modeling. Originally developed by Simulation Research, Caspoc allows the combination of multiple models (electric circuit, mechanical system, and control/component) in one schematic-along with showing simulation results right in the schematic. Of special interest to motion system users are models for power-switching semiconductor devices, such as diodes, GTOs, MOSFETs, IGBTs, and SCRs.
Developers of power electronic systems (including drives) will find enhancements in the new release that further shorten design time and reduce the need to build physical prototypes. Specific Release II upgrades include ability to model in Microsoft Visual C++ or Borland C++, and to generate reports automatically from multiple simulations.
Just before the end of 2001, Ansoft Corp. (Pittsburgh, Pa.) released Simplorer 5.0 simulation software for automotive electrical and electromechanical systems. Targeted at power-electronic and drives applications, software tools in Simplorer 5.0 focus on specific technology areas, such as circuit simulation, block diagrams, and machine models-including 'state machines for digital and discontinuous systems.' Users have a choice of modeling languages that can be used simultaneously. This eliminates extra mathematical transformations, allowing development of each system element through the most efficient language.
New and enhanced motor products continue to hit the market. Here is a recent sampling of the 'small and miniature' side of motors.
Portescap (Amherst, N.Y.), a Danaher Motion company, has announced new 16G88 Series miniature dc ironless-rotor (coreless) motors with 'typical maximum continuous output torque of 5 mNm (0.71 oz-in.) and maximum speed of 12,000 rpm. At 4.5 W continuous power rating, these 16-mm diameter motors are said to provide performance equal to 22-mm OD motors, in many applications. Matching planetary and spur gearheads are available with a wide range of gear ratios.
New brushless dc motors with 1.4 to 5.8-in. diameters and slotless stator windings have been introduced by EADmotors (Dover, N.H.). 'Zero cogging torque,' elimination of vibrations, and reduced audible noise are attributed to the patented stator design. These motors offer torque constant values up to more than 600 oz-in./A, and can reach speeds up to 50,000 rpm. Numerous options, such as number of poles, magnetic densities, feedback devices, and mountings are available.
Pittman (Harleysville, Pa.) has recently added a longer length model to its Lo-Cog 22 mm iron-core brush dc motor family. The 1.900-in. long motor delivers up to 2 oz-in. continuous torque, which is up to 40% more than the 1.256 in. and 1.556 models in the family. Custom options include ball bearings, gearheads, and encoders.
Control Engineering in February
Look for additional motors, drives, and motion control items each month in CE's print issue.
February's News section describes new large-frame contactors (115-500 amp range) and overload relays from Siemens Energy & Automation Inc. (Alpharetta, Ga.). Just 13 coil ranges cover motor control voltages of 24-600 V ac and dc.
More detail is also available at www.controleng.com/archives/news/2002/January/fb0124a.htm or visit online News Archives at / .
In the Products and Software section, Harmonic Drive Technologies (Peabody, Mass.) presents its new servo actuators in two styles: flange output and shaft output. PS Series actuators have better than 1 arc min positioning accuracy. Bosch Rexroth (Hoffman Estates, Ill.) has added SERCOS interface to System200 REFUdrive that targets applications in the 1.5 to 600 kW power range. Profibus, Interbus, and CANbus are other interface options available.
Courses, other learning sources
Are you looking to expand your knowledge? Here are some recent possibilities.
Siemens Energy & Automation (Alpharetta, Ga.) makes available free of charge to distributors and customers several 'basics of technology' Internet-based training programs. Among the courses are 'Basics of AC Motors' and 'Basics of Electricity,' while the latest program addresses 'Basics of Power Monitoring.' These online courses are electronic versions of the company's in-print training programs.
The Material Handling Industry of America (MHIA, Charlotte, N.C.) and its Material Handling Institute division have recently introduced a series of e-Lessons on 'Material Handling and Logistics.' The free, online lessons range over topics in material handling basics, associated equipment, justifying the investment, and automatic guided-vehicle systems. Each lesson is self-contained and takes 20-45 minutes to complete. However, the overall series can be used to prepare for the national certification exam administered by the Institute.
A recent, notable reference for electric motor developers is 'The Induction Machine Handbook' by Ion Boldea and Syed A. Nasar. This so-called 'bible' of ac induction motors covers analysis, design optimization, thermal modeling, testing methods, monitoring, and other pertinent topics. Variable-frequency operation and single-phase motors are also covered. ISBN: 0-8493-0004-5, CRC Press.
The book can be ordered from CRC Press.
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