February 9, 2012
A Penton Media Publication
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ANALYZING TRADEOFFS
BETWEEN SERVOS AND
STEPPER MOTORS,
page 42
TAMING ELECTRICAL NOISE
IN MOTION SYSTEMS, page 50
MORE MANUFACTURERS WANT
TO “MAKE IT IN AMERICA,”
page 64
HOW TO USE THINWALLED
BUSHINGS THE RIGHT WAY, page 72
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VOLUME 84
ISSUE 2
FEBRUARY 9, 2012
MOTION CONTROL
MOTION CONTROL
How
Thermograms of a stepper and an
equivalent servomotor show a difference
in temperature after 10 min of repeatedly
executing a move profile lasting a bit less
than 3 sec. The servomotor maintains a
relatively low 30°C temperature while the
stepper motor reaches 70°C.
SERVOS
and
STEPPERS
stack up
FEATURES
Speed and torque needs are often the
factors that determine whether servos
or steppers are the best approach.
servos and
42 How
steppers stack up
Sometimes the extra expense of
servomotors pays dividends that
stepper motors just can’t provide.
50
Engineers who work in motion control often start out using a relatively simple approach involving stepper motors to synthesize moves.
Steppers are appealing in that their controllers can be simple and inexpensive, at least for undemanding tasks. And most steppers run open
loop, needing no position or velocity feedback to hit their targets.
The problem comes when the application demands appreciable
torque and relatively fast speeds. Stepper motors can handle a range of
torques and speeds that overlap those of more-expensive servomotors,
but the economics for the stepper approach often don’t work out.
It is useful to examine some of the key differences between stepper
and servomotors as a means of understanding which applications each
type of motor fits. Steppers and servos are both synchronous motors. In
both cases, the rotation period exactly equals an integral number of ac
cycles. Both motor technologies employ a rotor with permanent magnets and a stator with coiled windings. Both systems operate by applying a dc voltage to the stator windings in a specific pattern that results
in movement of the rotor, and both technologies are capable of position
and speed control.
Two key differentiators between stepper and servo systems involve
the use of a feedback device and the complexity of the amplifier electronics. Servos, by definition, are closed-loop systems utilizing a feedback device. Steppers are open-loop systems with no feedback.
Authored by:
Scott Carlberg
Yaskawa America Inc.
Waukegan, Ill.
Edited by Leland Teschler
[email protected]
Key points:
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that can give servomotors an
advantage over similar steppers.
Resources:
Yaskawa America Inc., www.yaskawa.
com
Basics of servos, http://www.
electricmotors.machinedesign.com/
guiEdits/Content/bdeee4a/bdeee4a_1.
aspx
Thermal safety margins for
servos, http://machinedesign.com/
article/thermal-safety-margins-forservomotors-0622
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code or go to:
http://www.
electricmotors.
machinedesign.
com/guiEdits/
SiteMap_Articles.
aspx
The amplifier electronics in a servosystem are typically much more
complex than those of a stepper system. While a stepper amplifier simply sends full-rated current to each
winding set, a servoamplifier regulates the current levels it delivers to
the motor windings. In other words,
a servosystem produces only the current the application needs.
Because current is proportional to
torque, the control loop in the servoamplifier that regulates current is called the torque loop.
The servoamplifier typically also employs velocity and
position-control loops. The point of these feedback loops
is to handle loads that vary within the design parameters.
The servosystem might boost the torque supplied, say,
if necessary to keep the servosystem moving at its programmed velocity. In contrast, a stepper system has no
feedback and no control loops. So the stepper motor will
stall when torque demand exceeds available torque at any
given speed.
Stepper and servosystems also perform differently because of variations in their motor designs. Stepper motors
have a large number of poles and a winding inductance exceeding that of servomotors. As a result, the torque available from a stepper motor drops off much more quickly
with rising speed than with a servomotor, given the same
dc-bus voltage. This behavior can be seen in graphs comparing typical stepper and servosystems. In the nearby
example, both motors are of similar size, about 2.3-in.
square. The servo is slightly longer because of the added
feedback device.
Another inherent disadvantage of stepper motors is
that they exhibit two distinct regions of instability because
the motor behaves as a spring-mass system. One is at low
speeds, typically between 100 and 300 full steps/sec or
30 to 90 rpm. It results from excitation at the natural frequency of the motor. When the motor operates in this region, there will be a large velocity ripple, a potential for lost
steps, and a significant error in the system’s final position.
There is also a midrange instability that results from
interactions between the drive electronics and the motor.
This instability typically arises at the speed where motor
output torque is half its full running torque. Midrange
instability can lead to a stalled motor and, like low-speed
instability, velocity ripple and loss of steps that cause inaccurate positioning.
A technique called microstepping can minimize lowspeed instability by dividing each step into smaller incre-
42
Eliminating EMI in
motion systems
A logical approach to EMI/RFI
elimination offers the best chance of
getting it right the first time.
MOTION CONTROL
All factory equipment requires some degree of maintenance, monitoring, and replacement, but some need
much more than others. One group of high-maintenance
components are gearboxes. They are traditionally high
wear items, thanks to their usual task: converting highspeed, low-torque power from electric motors into the
low-speed, high-torque power needed by machinery.
Still, gearboxes remain widespread and
popular because, as one
of the tried and
true rules of
thumb
in the
the most
58 Getting
out of gearboxes
Here are some of the basics engineers
should know before specifying
gearboxes.
power-transmission industry says, “Speed is cheap, torque
is expensive.” And relying on motors to generate the torque
required by many loads (called direct-drive technology) is
usually more expensive than generating the torque with
a motor/gear reducer combination. So most engineers
specify gearboxes in their designs. Plus, gearboxes can
eliminate other mechanical components, such as bearings,
belts, chains, and pulleys, thus simplifying and bringing
down the cost of motion-control applications.
Engineers should also use the most-efficient
gearbox that meets their application’s needs.
Such gearboxes use less energy, which
saves money and the environment. It also
One of Stober’s largest helical gears
is 295 mm in diameter and is used for
high-speed stages. Stober’s smallest,
less than 200 mm in diameter, are used
in planetary gearboxes.
Authored by:
Adam Mellenkamp
Product Manager
Stober Drives Inc.
Maysville, Ky.
Edited by Stephen J. Mraz
[email protected]
Resources:
64
Why it makes sense to
manufacture in the U. S.
Manufacturing in the U.S. on an uptick
for good reason.
truth about thin72 The
walled bushings
Thicker isn’t necessarily better. Here are
some common misconceptions about
thin-walled bushings.
Getting
the
most
out of
Stober Drives Inc., www.stober.com
For info on another
planetary-gear drive unit,
scan this code or go to:
http://machinedesign.com/
article/small-light-rackand-pinion-drive-savesenergy-1208
Engineers should know
some gearing basics before
specifying gearboxes.
GEARBOXES
58
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MACHINE DESIGN.com
FEBRUARY 9, 2012
The SureServo family of brushless servo systems
from AutomationDirect is fully digital and offers a rich
set of features at dynamite prices. Beginners to
experienced users can take advantage of this
easy-to-use family for as little as $978*
(100W system). * All components sold separately.
Agency
Approvals
for Drives:
Agency
Approvals
for Systems:
9 (&'212 ,# 0#
systems from
100 W to 3 kW
9 1$5(2'
DirectLOGIC
PLCs or any other
host control
9 0(4$1%$ 230$
on-board indexer
and adaptive
tuning modes
9 0$$1$23.
software
Agency
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for Motors:
9
7$ 05 00 ,27
Servo Systems
9
9
9
9
3(*2(,+-2(-,"-,20-**$05(2'.0$1$2.-1(2(-,
velocity or torque select presets with switch inputs
and/or the multi-drop Modbus serial interface
-1(2(-,"-++ ,#15(2'8.3*1$#(0$"2(-,:-0
8"-3,23.#-5,:%-0+ 2
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For configuration, tuning and diagnostics, use the drive’s
integrated keypad/display or take advantage of the
free SureServo Pro™ PC-based software.
www.automationdirect.com/servos or www.sureservo.com
AutomationDirect
Price/Part Number
Allen-Bradley
Price/Part Number
$484.00
$1,050.40
SVA-2040
2098-DSD-005
100W Servo Motor
with connectorized Leads
$322.00
$536.31
SVL-201
TLY-A130T-HK62AA
Breakout Board Kit for
CN1 Control Interface
$93.00
$211.09
ASD-BM-50A
2090-U3BK-D4401
10’ Motor
Feedback Cable
$49.50
$83.22
SVC-EFL-010
2090-CFBM6DF-CBAA03
10’ Motor
Power Cable
$29.50
$93.62
SVC-PFL-010
2090-CPBM6DF-16AA03
Configuration Software
FREE
$78.07
SV-PRO*
2098-UWCPRG
Digital Servo Drive
*SureServo Pro software is FREE when downloaded and is also available for $9 on a CD
Complete 1-axis 100W System
$978.00
$2,052.71
All prices are U.S. list prices, AutomationDirect prices are from October 2011 Price List. The Allen-Bradley 100W system
consists of part numbers shown in table above with prices from www.rockwellautomation.com/en/e-tools 8/31/11.
www.automationdirect.com
Go online or call to get complete information,
request your free catalog, or place an order.
RS# 103
ON THE COVER
A 295-mm helical gear and
a 20-mm version, both from
Stober Drives Inc.
DEPARTMENTS
8 EDITORIAL
More manufacturing jobs, but no renaissance
10 EDITORIAL STAFF
12 LETTERS
16 SCANNING FOR IDEAS
Rugged hollow-shaft encoder can be user programmed
Fingerprint-activated switch provides biometric protection
20 REPORTER’S NOTEBOOK
30 LOOKING BACK
36 COMMENTARY
Mandating innovation
38 VANTAGE POINT
Death knell for lead-acid batteries— Dr. Peter Harrop
40 INVENTOR’S CORNER
Technique molds large, hollow, monolithic composites
78 BERKE ON SAFETY
Lessons of hospital accidents
80 FE UPDATE
CFD software calculates underwater speed for a small sub
84 SOFTWARE PRODUCTS
86 PRODUCT SPOTLIGHT
Gears & mechanical drives
93
106
107
108
110
110
111
4
PRODUCTS
BUSINESS INDEX
AD INDEX
DATA FILES
CLASSIFIEDS
BUSINESS STAFF
BACKTALK
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FEBRUARY 9, 2012
POSTMASTER: Send change of address notice to
Customer Service, MACHINE DESIGN, P.O. Box 2100, Skokie,
IL 60076-7800.
Super Ion Air Knife™
Produces a laminar sheet of airÀow
that Àoods an area or surface with
static eliminating ions.
Super Ion Air Wipe™
The uniform 360° ionized
airstream neutralizes and cleans
continuously moving surfaces.
Prevent Shocks, Jamming, Tearing and Static Cling!
When the humidity is low, static electricity problems will happen.
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Ion Air Gun™
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Ideal for hard to reach spaces
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Delivers a concentrated blast of
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What’s new online machinedesign.com
Free Webcast: February 23, 2:00 p.m. EST
Today’s additive manufacturing: Injection
molding, living hinges, overmolding, and more
Objet will discuss advances in rapid prototyping, and how it lets
engineers quickly transform CAD designs into functional prototypes
that are virtually identical to the end products — including finished
assemblies with moving joints and parts. Models are suitable for design
reviews, focus groups, and any situation that demands precise look, feel,
and function. Get more details and register at http://machinedesign.com.
Mercedes E-Cell Plus
Lee Teschler talks with an engineer from Daimler
about the powertrain, NVH, and safety in the
Mercedes B-Class E-Cell Plus. It has pure-electric
range of 70 miles, and a combustion-engine Range
Extender permits journeys of up to
500 miles. View the episode at www.
engineeringtv.com/video/MercedesB-Class-E-CELL-PLUS-El;2012-NAIAS.
EDITOR’S WEB PICKS
Cutting compressedair costs
6
Many manufacturers don’t realize
that energy accounts for 75% of
the cost of buying and running a
compressor. Norgren’s “Guide to
Saving Energy in Compressed Air
Systems” pinpoints problems such
as leaks, misuse, overpressurization,
and flow restrictions; and explains
how to devise an action plan to
boost efficiency. Download a copy
at http://apps.usa.norgren.com/
MyNorgren/pdf/NA-211Rev3.pdf.
Energy-saving
calculators
A new tool from Rockwell
Automation calculates potential
savings from powering pumps and
fans with variable-frequency drives.
Users enter flow rates, operating
hours, cost per kilowatt, and other
info to see cost savings versus
conventional control methods.
The online calculator is available
at www.rockwellenergycalc.com,
or engineers can download the
free mobile app to iPad, iPhone,
Blackberry, and Android systems.
MACHINE DESIGN.com
O-ring calculator app
Trelleborg Sealing Solutions has
released the O-ring Calculator, a
new app that determines required
O-ring dimensions and products.
Users enter bore or rod/shaft
diameter and get O-ring and
housing dimensions according
to ISO 3601. It also searches
for nominal sizes, calculates
recommended tolerances, and
determines materials compatible
with the specified media. Get the
free app from iTunes or the Apple
App Store. Learn more at www.tss.
trelleborg.com.
Hose product catalog
A new catalog from Parker
Hannifin has product and
installation information on
hydraulic hoses, fittings,
equipment, and accessories. It
includes specs, dimensional data,
chemical compatibility charts, and
fitting identification data. QR codes
link users to additional content
such as training videos. Learn more
at www.parkerhose.com.
FEBRUARY 9, 2012
Free Webinars
on Pneumatics
and PLCs
Take 30 to 45 min and watch free
Webinars on industrial controls
topics. See equipment in action,
and take advantage of the
question and answer period at the
end of each session.
PNEUMATICS
This 40-min session covers the
NITRA pneumatic products
AutomationDirect offers. The
line now includes stainless-steel
cylinders, filters, regulators,
lubricators, solenoid valves,
position switches, tubing, and
fittings. See working demos and
customer examples.
February 22, 2012, 2:00 p.m. EST
CLICK PLC OVERVIEW
In this 30-min show, we cover
all aspects of the powerful
Click micro brick PLC, including
hardware features, specifications,
expandability, and installation. See
a demo of the free programming
software, and learn where you can
download the package.
March 14, 2012, 2:00 p.m. EST
Visit www.automationtalk.com to
check the schedule and register
for upcoming presentations.
Recordings of past Webinars are
also available to view at your
convenience.
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RS# 106
EDITORIAL
More manufacturing
jobs, but no renaissance
Employment on the American factory floor is growing, up by 334,000 jobs
over the past two years. Journalists have taken note of the trend. The tenor of
the recent headlines on the subject echo that in the New York Times, which
claimed that, “U. S. Manufacturing is a Bright Spot for the Economy.”
But growth in jobs is a case of good news/bad news. The good news is that
reports show the economy is now producing the same amount of goods and
services it did in 2007. The bad news: It is doing so with 6.3 million fewer
workers, despite an unemployment rate that is falling. The fact is that industries that include construction, transportation, warehousing, waste management, and even manufacturing, were still shedding workers at least through
2010.
Growing businesses are the ones most likely to hire workers. And unfortunately, the industries that are now growing are typically not the blue-collar employers that lost the most workers during the recession. Figures from the U. S.
Bureau of Economic Analysis show where the real growth in the economy has
been over the last few years. It is not in manufacturing. Areas adding workers
include agriculture, forestry, fishing and hunting, mining, retail trade, finance
and insurance, health care, educational services, IT, and government.
Most of these are not what you would call blue-collar industries. U. S. employers in the blue-collar category are in the minority; the blue-collar industries adding jobs over the past few years can be counted on your fingers. They
consist of mining and utilities, each accounting for a miniscule 0.5% of total
U. S. employment.
Government figures show that a lot of the areas of expanding employment in the past few years are those associated with paper pushing. Finance
and insurance have grown to account for about 4.6% of the workforce. The
largest-growing employment area, unfortunately, is government, accounting
for 16.9% of the U. S. workforce in 2010.
But economists say any job vacancies in these growing areas are more
than offset by the joblessness stemming from still-struggling construction
and manufacturing industries. This is distressing for unemployed blue-collar
workers in that the few expanding areas of the economy, such as education
and health care, typically are not fertile ground for workers with industrial
skills.
All in all, the recent upturn in manufacturing jobs pales in comparison
with the 2.3 million decline in factory payrolls over the past two years. Put
another way, manufacturing employs 2 million fewer workers than it did just
four years ago. This though the output of U. S. factories is up about 3% since
2001. The well-chronicled reason is that worker output/hour has climbed over
40% since that time, thanks to automation and adoption of new technologies.
It isn’t just the manufacturing industry that has become more productive.
Economists tell us the economy in general has become more efficient at using
labor. As brick-and-mortar bookstores put out of business by Amazon.com
will attest, nearly all industries use fewer workers to generate the same amount
of goods and services.
And that’s the rub. Productivity gains are just one more reason we are likely
to see persistent unemployment, and why we shouldn’t expect to soon see
headlines about a real boom in blue-collar jobs.
— Leland Teschler, Editor
8
RS# 107
MACHINE DESIGN.com
FEBRUARY 9, 2012
The round thing has to go into
the rectangular thing.
#OMPACT'#ENTRIFUGAL'-ODULES'WITH'THE'NEW'RadiCal'IMPELLERS
s'3PACE'SAVING'PACKAGED'AIR'MOVERS'WITH'IMPELLER'(''MM 'TO''MM
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s RadiCal'IMPELLER'DESIGN'IMPROVES'AERODYNAMIC'EFlCIENCY'AND'ACOUSTICS
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The engineer’s choice
RS# 108
EDITORIAL STAFF
Leland E. Teschler, Editor,
[email protected]
Kenneth J. Korane, Managing Editor,
[email protected]
SENIOR EDITORS
Leslie Gordon,
Stephen J. Mraz
AUTOMOTIVE &
NEWS FEATURES
Stephen J. Mraz,
[email protected]
CAD/CAM
Leslie Gordon,
[email protected]
ELECTRICAL, ELECTRONICS
Robert J. Repas, Jr.,
[email protected]
RS# 109
FASTENING, JOINING
OUR ANGLE IS…YOUR GEAR
SHIPPED IN 24 HOURS
OR IT’S
FREE.*
Jessica Shapiro,
[email protected]
MITRPAK right angle,
three-way, and counterrotating spiral bevel drives
are interchangeable with
Boston Gear, Hub City, Browning…
and we guarantee 24-hour shipment.
Jessica Shapiro,
[email protected]
FLUID POWER
Kenneth J. Korane,
[email protected]
MANUFACTURING
Leslie Gordon,
[email protected]
Kenneth J. Korane,
[email protected]
MATERIALS
MECHANICAL
Kenneth J. Korane,
[email protected]
Jessica Shapiro,
[email protected]
For complete specifications and
CAD files, log onto www.mitrpak.com,
EDITORIAL PRODUCTION
Denise Greco,
Editorial Production Manager
Randall L. Rubenking, Art Director
or call us at 800-648-7725. Learn
how MITRPAK minimizes backlash by
using locknuts, rather than conventional
spacers and rings.
RS# 110
* Contact us for details.
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MACHINE DESIGN.com
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FEBRUARY 9, 2012
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RS# 111
LETTERS
Deregulate engineering?
The recent editorial (“Why Finance
Majors Make More than Engineers,”
Oct. 20) was interesting, but my
takeaway was different than yours.
You make the point that deregulation of the financial industry led
to higher salaries and more innovation in that field. Your proposed
solution is for government to increase regulation on the financial
industry, thus depressing salaries
there to bring them more in line
with engineering. That’s quite a
pessimistic approach.
The correct answer is to deregulate engineering/manufacturing
industries so as to encourage innovation and let salaries rise there as
well. Let the free market determine
the value of engineers.
The problem with your analysis is an incorrect assumption that
deregulation was the cause. In
fact, the real culprit was political
interference in the lending process in the name of increasing
home ownership. Congressional
pressure, combined with assurances that the federal government would back these loans,
led financial institutions to make
risky loans. This, in turn, skewed
demand in the real-estate market, sparking the housing boom.
It was only a matter of time before
individuals began to default on
loans they could not afford. Housing prices plummeted and more
people defaulted as they suddenly
found themselves underwater.
The whole house of cards began
to tumble down as the financial industry looked to Washington to make
good on their earlier promises.
If you are looking to government intervention to fix a problem,
you had better check first to be certain that it wasn’t the cause of the
problem in the first place.
Allen Heindel
Basically, I say there is never any
free lunch. If someone goes into
engineering, he’s providing a real
ser vice of value, and that can
never be reduced. The free-lunch
seekers, i.e., the financial people,
12
MACHINE DESIGN.com
What
are
the
RULES?
often end up getting their free
lunches in prison. Personally, I
would send these white-collar
criminals to the same prisons
populated with axe murderers,
not some Club Fed facility.
Jane Alstott
A very informative editorial on finance majors. Everything makes
sense, except for the last phrase.
If deregulation triggers ingenuity, productivity, and higher
rewards, why would you suggest
more regulation on the financial
industry?
There is a better way: deregulate other industries. Yes, they will
go up and down, But left unregulated, they will self-stabilize on a
much higher level than “regulated”
ones. Regulating everything only
makes funnel money and power to
our “Legal Industry”.
Ilya Feygin
The point is that salaries in the financial industry dropped relative to
those in other industries during the
1930s and 1940s because, according to the two economists doing the
study, the financial industry was
increasingly regulated during that
time period. — Leland Teschler
Do no harm
I appreciated your article on unsafe
guards (“Beware of Unsafe Machine
Guarding,” Sept. 28). I once was
forced to add a safety device to a
machine that used an air cylinder to
bring a guard up when the operator
activated palm buttons. Although
the guard was raised with a low-
FEBRUARY 9, 2012
pressure cylinder, the operator could
get whacked in the face if he or she
leaned too far forward and was not
paying attention. I’ve also seen machines using the same method to
bring a guard down like a guillotine.
People often design safety
methods like these with the idea
that they are at least making an attempt to keep workers safe without realizing the device they have
installed is actually what will most
likely hurt the operator.
In that vein, I’ve seen machines
powered by pneumatic cylinders that
have a long stroke. When that stroke
was interrupted by a light curtain or
e-stop in the middle of its travel and
then reenergized, it would slam into
position because the pressurized air
on the opposing side of the cylinder
had drained off during the stop condition. Adding flow controls didn’t
help because there was enough
empty volume in the opposite side of
the cylinder to let it compress, which
also let the moving components slam
into position. I’m not by any means a
pneumatic expert. So, with that being said, what is the best solution to
prevent this?
Rich Whitford
One of the basic concepts when adding a guard is to make sure that by
adding the guard you are not adding
another hazard. Therefore, whenever a machine is altered or modified, perform a preliminary hazard
analysis to ensure all hazards of the
current machine are addressed. —
Lanny Berke
Name
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RS# 112
©2011 National Instruments. All rights reserved. LabVIEW, National Instruments, NI, and ni.com are trademarks of National Instruments.
Other product and company names listed are trademarks or trade names of their respective companies. 01197
800 453 6202
LETTERS
Job shortage or
worker shortage?
I bought into the lies about impending engineering shortages and went
to an engineering school in the 80s.
Unfortunately, after I graduated engineering salaries were consistently
decimated by offshoring both manufacturing and design work, and by
importing cheap engineers (H-1B and
L1). Now, 25 years later I am sending
my daughter to an ivy-league school
(which is costing me a fortune) to
study engineering, but with explicit
instructions that she is not to become
an engineer. Post-graduate business,
law, or medicine will do nicely. Engineering is her fallback. I am not the
only parent doing this. Who knows; if
this keeps up, maybe someday there
really will be a shortage of engineers.
But I doubt it.
Ray White
I agree with your disdain for graduates who have pursued their
Zero backlash
dream without regard to a viable
livelihood (“Advice for Occupy Wall
Streeters,” Nov. 17). But why is it that
“...43% of those [STEM] graduates
do not work in STEM jobs immediately after graduation”? Were there
no jobs, or did they find something
else more attractive?
I believe the reasons are to be
found in Ruark and Graham’s report, Jobs Americans Can’t Do?: The
Myth of a Skilled Labor Shortage,
which can be found on the Web.
Here are two of their findings:
t5IFHMVUPGTDJFODFBOEFOHJOFFS
ing (S&E) degree holders in the
U. S. has caused many S&E graduates to seek work in other fields.
Less than one-third of S&E degree
holders work in a field closely
related to their degree, while 65%
are either employed in or training
for a career in another field within
two years of graduating.
t8BHFTJOTDJFODF
UFDIOPMPHZ
engineering, and mathematics
occupations have not kept pace
with those of other college graduates, and in some occupations
have actually decreased.”
In a free market, a shortfall of
STEM workers would have raised
compensation, but instead, wages
have lagged or stagnated. This
leads me to conclude it is a manipulated market, created by domestic
businesses that benefit from lower
cost immigrant labor.
There is also a complementary
“diversity” campaign to recruit minorities, who are upwardly ambitious, but economically naive, and
may be lured by comparatively attractive starting salaries.
Robert Rung
We have written about STEM students who take non-STEM jobs
back on May 3, 2010, “Engineering
Students Who Don’t Go Into Engineering.” Here’s a link: http://tinyurl.
com/2eqjrf9
Put some teeth
in your motion control
Accuracy to ±30 μm
(±0.0018")
Unlimited run lengths
Speed up to
36 ft. per sec.
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Low-friction,
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RPS tackles your toughest motion applications.
The innovative, new Precision Roller Pinion System (RPS)
from Nexen handles your most demanding linear motion
control applications. Simply put, no other motion system
offers the combination of speed, positional accuracy, stroke
length, load capacity and zero backlash performance. Not to
mention it’s also extremely quiet, 99% efficient, and so
refined it can run without lubrication. Replace inferior rack
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higher performance and lower maintenance solution.
RS# 113
Learn more at www.nexengroup.com
Call 800.843.7445
# ' "$ + % #$%"*"
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RS# 114
SCANNING FOR IDEAS
Edited by Stephen J. Mraz
Rugged hollow-shaft encoder
can be user programmed
The HS35 incremental hollow-shaft encoder from Baumer Ltd., Southington, Conn.
(www.baumer.com/hs35), combines heavy-duty design with a precise optical scanner
to provide reliable, closed-loop control with accuracies of 60 arc-sec.
The heavy-duty
castings and sturdy
Seals provide IP67 rating,
walls add durability
protecting encoder from wash
downs and contamination.
and stiffness. The
Flexible aluminum
large diameter
shaft adapters
between ABEC 5
bearings, together
with a precise
steel spacer ring,
lets the encoder
handle relatively high
mechanical loads. Dual
ABEC 5 bearings
seals protect against
resist runout and
contaminants and
wobble
leaks. A powder coating
prevents the housing
from corroding, despite
long-term exposure in harsh environments. And
reinforced shaft inserts electrically isolate against
shaft currents of up to 2.5 kV. The inserts also let the
encoders be mounted on smaller shafts.
There are three versions of the encoder. HS35P is
a programmable square-wave encoder. Resolutions
range from 1 to 8,192 in increments of 1. Programming
outputs include HTL and TTL. Users can program
pulse per revolution, index pulse length and position,
rotation direction, and output voltages. Users can also
choose independent A and B counts.
HS35F is an industrial square-wave encoder with
16
MACHINE DESIGN.com
FEBRUARY 9, 2012
Shaft isolated
against shaft
currents
Powder coating
protects housing
against corrosion.
Durable
housing
Precision glass
disc can withstand
200-g shocks.
TTL, HTL, and OC (open-collector) outputs. Direct
read resolution can be up to 56,000 ppr, but internal
interpolation can boost that to 80,000 ppr. And signal
quality is good, even at low speeds. The HS35S sinewave encoder provides good signal quality at all
speeds and prevents drive overheating while saving
energy.
The encoders operate in temperatures from –40 to
212°F, and are available with shaft diameters from 0.5
to 1 in.
RS# 401
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SIMPLE. Starts here.
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HOW MAY WE HELP YOU TODAY?
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RS# 115
SCANNING FOR IDEAS
Fingerprint-activated switch
provides biometric protection
User light
Administrator light
The Harmony XB5
Biometric Switch from
Blue LEDs
Schneider Electric
USA, Palatine, Ill.
(www.schneiderelectric.us), could
be the ultimate in
security for industrial
applications, using
fingerprints to
identify authorized
technicians and
workers. And
authorized users
would never have
to worry about
losing their key
card or forgetting
a password, which
reduces costs
and delays for the
company.
The stand-alone
Output
switch is housed in a
status
shock and vibrationlight
Touchscreen
resistant housing that
meets EMC, IP65, and
NEMA-123 protection
Error light
Reset light
standards. The device
stores and identifies
up to 200 fingerprints,
including prints from
different fingers of the
same person. The unit
records fingerprints as well. It takes less than a second for a
person to be approved or denied access. The false acceptance
rate is less than 0.1%.
The switch installs in a standard 22-mm cutout and is
secured using a single nut. Electrical connections to the power
supply and control output (a relay or PLC) are made using a
2-meter cable or an M12 connector. There are two versions
of the switch. One provides two output states or responses,
while the other, a momentary switch, supplies pulse control. It
operates on 23 Vdc, and in temperatures from –5 to 50°C.
r
formation via ou
Request free in Web site at
The biometric switch can mount horizontally or vertically.
ice
rv
Se
er
Read
An optional hinged cover protects the face of the sensing
sign.com/rsc
w.machinede
ww
screen, and a stainless-steel guard is also available to prevent
vandalism and weather damage if mounted outdoors.
RS# 402
18
MACHINE DESIGN.com
FEBRUARY 9, 2012
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