-
Manufacturing
From Sensor to Transmitter
Robust Industrial Sensors through Integral Electronics A.
Kirchheim, D. Otter, D. Kobler, K. Bräuer, A. Lehmann, G.
SchaffnerKistler Group,Winterthur
ifm2007 –International Mechatronics Forum12 + 13 September
2007Winterthur, Switzerland
Special Print920-361e-05.08
Modelling
Mechatronics
MechanicalEngineering
InformationTechnology
Electrical Engineering
Actuators and Sensors
Computerized Process
Engineering
ElectricEngineer
M
-
2 www.kistler.com
-
www.kistler.com 3
From Sensor to Transmitter
Robust Industrial Sensors through Integral Electronics
A. Kirchheim, D. Otter, D. Kobler, K. Bräuer, A. Lehmann, G.
SchaffnerKistler Group, Eulachstr. 22, 8408 Winterthur,
Switzerland
1 IntroductionThe high resolution, wide measuring range and
substantial overload protection of piezoelectric sensors make them
par-ticularly suitable for monitoring and analyzing manufacturing
processes. New, compact and powerful electronic components are
increasingly allowing integration of the evaluation electron-ics
directly into the sensor. Ongoing miniaturization makes it possible
today to use electronics allowing very flexible pro-gramming in new
force and strain transmitters. This enables the major advantages of
piezoelectric sensors and simple industrial sensors to be
combined.
2 Piezoelectric Measuring ChainPiezoelectric force and strain
sensors are now used not only in very many areas of research but
also increasingly in produc-tion, either directly or as OEM
components in machinery. They capture dynamic changes up to
extremely high frequencies and additionelly allow successful
quasistatic measurement. These multifaceted applications include
measuring the joining forces involved in press fitting, clinching
or riveting.
Such manufacturing applications make use of press force
sen-sors, a common piezoelectric type, as shown in Figure 1a and
1b. The special, patented press force design is characterized by
axial preloading of the sensor. This is required to ensure good
linearity of the output signal, particularly for small compres-sion
forces. The press force sensor contains an annular pair of quartz
washers as an integral sensor element sensitive to pres-sure. The
pressure-sensitive direction of the washers is oriented so that a
charge signal proportional to the magnitude of the compression
force is outputed and converted in a charge meter (charge
amplifier) into a proportional electrical voltage. As a result of
the piezoelectric measuring principle and high rigid-ity of the
press force sensor, measurement is virtually without
deflection.
For ease of mounting e.g. in press plungers the sensor has
adapter flanges and a special mounting thread.
unloaded loaded
Crystal lattice
Crystal elements
Fig. 1a: Longitudinal piezoelectric effect
Mounting thread KInternal centering seats D2Mounting thread
PFree passage D3
Connector protectionPlug connectionPiezo element
Fig. 1b: Design of a preloaded force link (press force
sensor)
-
4 www.kistler.com
unloaded loaded
Principle ofshear effect
Point of application of force
Fig. 2a: Piezoelectric shear effect
10 kN
Fig. 2b: Design of a piezoelectric strain sensor
Like strain gages, strain sensors can measure surface strain
directly proportionally to the load on machine structures. This
strain is transferred by friction to a shear-sensitive sensor
element integral with the body of the sensor. This is achieved by
attaching the sensor to the structure with an M6 screw tightened to
10 kN in order to measure strains up to 800 με in loaded machine
structures.
In the case of the sensors described above, the charge signal
proportional to strain (and hence force) is conditioned in an
external charge amplifier and passed to the measuring PC, PLC or
other control unit. Figure 3 shows the piezoelectric measuring
chain consisting of sensor, cable and industrial charge amplifier
including block diagram.
For use in the industrial manufacturing environment the
multi-channel industrial charge amplifier (ICAM: Industrial Charge
Amplifier Manufacturing) is integrated into a robust, sealed case
(IP65), can be flexibly adapted for different processes and has
sufficiently high accuracy and linearity. Other fea-tures
include:
Wide, adjustable measuring range (±100 ... 1 000 000 pC)•
Integral peak memory with programmable functionality• Robust,
serial communication interface (RS-232C)• Offset, gain and filter
values via setup selectable menu• Automatic zero compensation•
The heart of the charge amplifier (Q/U converter) is
imple-mented as a thick layer ceramic module. The complete PCB is a
multilayer Starrflex manufactured from FR4 on which SMDs are
mounted (Figures 4 and 5). It has an 8-bit microcontroller with
integral 12-bit A/D converter (25 MIPS; 12-bit ADC, 100 ksps;
12-bit DAC; 32 kB flash; TQFP64).
However, the force can also very easily be represented
indi-rectly through the strain in the loaded structure (see Figures
2a and 2b).
Fig. 3: Piezoelectric measuring chain consisting of sensor,
cable and charge amplifier (signal conditioning)
Sensor Cable
Q/U converter
Reset
Q Ct
Ri Cc
Cr
Rt
Uo
Press Force SensorMeasuring range 70 kN
Strain Sensor Connecting Cable Adapter ICAM
-
www.kistler.com 5
Fig. 4: Block diagram of ICAM charge amplifier
Fig. 5: Starrflex PCB of charge amplifier (folded)
3 Miniaturization and Integration of ElectronicsTo meet the
demand for greater integratability and robust design, the
electronic signal conditioning system was incor-porated into the
actual case of the sensor. The result is a homogeneous measuring
system with a high degree of inte-gration with a rugged connecting
cable (M12 connector) for use in tough production environments. The
entire measuring chain is combined and moved to the actual
measuring point and form a system called a transmitter (Strain
transmitter Type 9238A..., press force transmitter Type 9337A...)
as shown in Figure 6.
The electronics of the charge amplifier underwent continu-ous
development to meet the more stringent miniaturization requirements
imposed on transmitter electronics.• The Q/U converter module was
integrated directly onto
the substrate (laminate)• Circuit complexity was reduced to that
necessary (custom-
ized)• The mechanical design was optimized
The transmitter electronics use SMD technology on a rigid
multilayer PCB manufactured from special (highly insulated) FR4
laminate. Here as well the heart of the electronics is an 8-bit
microcontroller with integral 12-bit A/D converter (100 MIPS;
12-bit ADC, 100 ksps; 12-bit DAC; 128 kB flash; TQFP64). All this
is implemented on two PCB surfaces in the form of a disk just 25 mm
in diameter (corresponding to 980 mm2; see Figure 6).
The miniaturization has brought a greater than 3-fold reduc-tion
in the area required for each channel, yet digitization of the
signal (block diagram in Figure 7) has also improved flexibility.
More flexible signal scaling or inversion allowed by the
digitization is achieved at the cost of increased process-ing power
(digital signal processing) requirements, which can however be
provided very cost-effectively these days with more powerful
microcontrollers.
Fig. 6: Standard (piezoelectric) measuring chain in contrast
with transmitter
ICAM inside Strain Transmitter Charge Amplifier
-
6 www.kistler.com
4 Configuration and MeasurementAll of the presented transmitters
can also be configured through an RS-232C interface. Default
settings and adjust-ments can be made using either a terminal
program or the much more user-friendly PC tool "ManuWare".
Fig. 8: Kistler products currently supported by ManuWare
Strain transmitter
Reference measuring chain for force
Fig. 11: The strain at the transmitter corresponds to the force
read off the reference measuring instrument. Scaling is performed
in this case using the teach-in technique.
Charge Amplifier Force Strain Electromechanical ICAM Transmitter
Transmitter NC joining module (piezo)
Setup
Fig. 9: Visualization of measurands and indication of signal
status are im por tant aids whenever commissioning
Fig. 10: Self-explanatory setup procedures lead the user through
the entire process of setting the transmitter. Here the mapping of
the mechanical measurand (force in N) to the electrical output
signal (voltage in mV) is specified.
However, although appropriate for force sensors this method is
scarcely suitable for strain sensors, as the relationship between
force and resultant strain is usually unknown. In this case the
second method, the teach-in technique, leads to the desired outcome
(see Figure 11).
ManuWare basically supports those Kistler products that can be
set up via serial interface and where measurement data can be
transmitted by analog or serial means.
A useful feature of this program is the measurement data
visualization and export function (in Figure 9), which repre-sents
another step along the path of implementing Kistler's measure and
analyze concept. Measurands, for example, can be displayed as a
function of time and saved in common export formats*. A box also
indicates the logical status of all of the control signals to and
from the transmitter.
Different methods of scaling the measuring range are offered.
One is to merely type in the sensor data from the calibration
record. There is no need to introduce forces or other mechanical
variables (shwon in Figure 10) here.
*) In preparation
-
www.kistler.com 7
Displacement sensor
Direct force measurement
Indirect force measurement
Direct force measurementForce shuntmeasurement
Fig. 12: Measurement of press forces (mounting)
A distinction is drawn between direct, indirect and shunt force
measurement. With the direct method, the entire force to be
recorded is passed through the sensor for very sensi-tive
high-resolution measurement. The indirect approach measures the
force through the resultant strain, and the force shunt technique
positions the sensor in the structure so that only part of the
force passes through the sensor. Indirect and force shunt
measurement trade very high resistance to overloading off against
lower sensitivity. As joining processes are usually tracked by
monitoring the joining force through the resultant displacement,
the latter also has to be measured (Figure 13).
The next two figures show typical force curves as generated by
the described force and strain transmitters during press fitting or
resistance welding. The transmitters have electronic systems whose
power, ease of use and flexibility was previ-ously only encountered
in laboratory measurement.
Fig. 13: Press force transmitter mounted in press. Typical press
fitting operation against shoulder.
Fig. 14: Bench machine for resistance welding with mounted
strain sensors on the electrode and strain transmitters on the
frame of the machine; clamping force (quasistatic) and welding
force (dynamic) over a welding cycle.
6 Summary New, compact and powerful electronic components are in
creasingly allowing integration of the evaluation electronics
directly into the sensor. This means that these days electron-ics
allowing very flexible programming can be used in new force and
strain transmitters, making it possible to combine the major
advantages of piezoelectric sensors and simple industrial
sensors.
7 ReferencesBill, B.: Messen mit Kristallen: Grundlagen und
Anwen-• dungen der piezoelektrischen Messtechnik. Moderne
Indus-trie, Landsberg/Lech: 2002Tichy, J.; Gautschi, G.:
"Piezoelektrische Messtechnik" Phy-• sikalische Grundlagen Kraft-,
Druck- und Beschleunigungsaufnehmer, Verstärker, Springer-Verlag,
Berlin Heidelberg, New York, 1980Kirchheim A., Lehmann A.,
Schaffner G., Deuerling, R., • Thommes H.; Hussmann D.: Sichere
Verbindungen durch Überwachung der Fügekräfte, 13th Paderborn
Symposium: Fügetechnik Mechanisches Fügen und Kleben, Paderborn, 29
& 30 November 2006
5 ApplicationsThe high resolution, wide measuring range and
substantial overload protection make piezoelectric sensors ideal
for mon-itoring and analyzing manufacturing processes. However, it
is not enough to rely on the performance of the sensor itself, the
mounting point in the path of the forces through the machine must
also be correct. Figure 12 shows mounting examples in a (C-frame)
press as frequently used in assembly, for example for press
fitting.
Build-up of additional force (re-pressing)
Mechanical stop (shoulder)
Push-in
Sens
or S
igna
l [k
N]
Time [s]
Sens
or S
igna
l [V
]
Strain TransmitterType 9238A...
Strain SensorType 9237A...
Time [s]
-
920-
361e
-05.
08
©20
08, K
istle
r G
roup
FranceKistler FranceZA de Courtabœuf 115, avenue du Hoggar91953
Les Ulis cedexTel. +33 1 69 18 81 [email protected]
GermanyKistler Instrumente GmbHDaimlerstrasse 673760
OstfildernTel. +49 711 34 07 0 [email protected]
ItalyKistler Italia s.r.l.Via Ruggero di Lauria, 12/B20149
MilanoTel. +39 02 481 27 [email protected]
NetherlandsKistler B.V. NederlandLeeghwaterstraat 252811 DT
ReeuwijkTel. +31 182 304 444 [email protected]
Korea, Republic ofKistler Korea Co., Ltd.Gyeonggi Venture
AnyangTechnical College Center 801572-5, Anyang-Dong,
Manan-Gu,Anyang-City, Gyeonggi-Do 430-731Tel. +82 31 465
[email protected]
SingaporeKistler Instruments (Pte) Ltd.50 Bukit Batok Street
23#04-06 Midview BuildingSingapore 659578Tel. +65 6316
[email protected]
TaiwanKistler Representative Office in TaiwanRoom 9, 8F, No. 6,
Lane 180Sec. 6, Mincyuan E. RoadTaipei 114Tel. +886 2 7721
[email protected]
ThailandKistler Instrument (Thailand) Co., Ltd.26/56 TPI Tower,
20th FloorNanglingee Rd., (Chan Tat Mai Rd.)Thungmahamek,
SathornBangkok 10120Tel. +66 2678 6779-80
[email protected]
Europe
AustriaKistler GmbHLemböckgasse 49f1230 WienTel. +43 1 867 48 67
[email protected]
Czech Republic/SlovakiaKistler, s.r.o.Zelený pruh 99/1560140 00
Praha 4Tel. +420 296 374 [email protected]
Denmark/Norway/SwedenKistler Nordic ABAminogatan 34431 53
MölndalTel. +46 31 871 [email protected]
FinlandKistler Nordic ABSärkiniementie 300210 HelsinkiTel. +358
9 612 15 [email protected]
Asia
JapanKistler Japan Co., Ltd.23rd floor, New Pier Takeshiba North
Tower1-11-1, Kaigan, Minato-kuTokyo 105-0022Tel. +81 3 3578
[email protected]
China, People’s Republic ofKistler China Ltd.Room 925, Yuan Chen
Xin BuildingNo. 12 E1, Yuminlu Road DeshengmenwaiBeijing 100029Tel.
+86 10 8225 [email protected]
IndiaKistler Instruments (Pte) Ltd.India Liaison Office2B
Century Plaza560/562 Anna SalaiTeynampet, Chennai 600 018Tel. +91
44 4213 [email protected]
Kistler worldwide
Switzerland/LiechtensteinKistler Instrumente AG Verkauf
SchweizEulachstrasse 228408 WinterthurTel. +41 52 224 12
[email protected]
United KingdomKistler Instruments Ltd.13 Murrell Green Business
ParkLondon RoadHook, Hampshire RG27 9GRTel. +44 1256 74 15
[email protected]
America
USA/Canada/MexicoKistler Instrument Corp.75 John Glenn
DriveAmherst, NY 14228-2171Tel. +1 716 691
[email protected]
Australia
AustraliaKistler Instruments Australia Pty Ltd5 Glenn
CourtRowville, Victoria 3178Tel. +61 3 9755
[email protected]
Other countries
Kistler Instrumente AGExport SalesEulachstrasse 22, 8408
WinterthurSwitzerlandTel. +41 52 224 11
[email protected]
Headquarters
SwitzerlandKistler GroupEulachstrasse 22, 8408 WinterthurTel.
+41 52 224 11 11Fax +41 52 224 14 [email protected]
www.kistler.com
/ColorImageDict > /JPEG2000ColorACSImageDict >
/JPEG2000ColorImageDict > /AntiAliasGrayImages false
/CropGrayImages true /GrayImageMinResolution 300
/GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true
/GrayImageDownsampleType /Bicubic /GrayImageResolution 300
/GrayImageDepth -1 /GrayImageMinDownsampleDepth 2
/GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true
/GrayImageFilter /DCTEncode /AutoFilterGrayImages true
/GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict >
/GrayImageDict > /JPEG2000GrayACSImageDict >
/JPEG2000GrayImageDict > /AntiAliasMonoImages false
/CropMonoImages true /MonoImageMinResolution 1200
/MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true
/MonoImageDownsampleType /Bicubic /MonoImageResolution 1200
/MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000
/EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode
/MonoImageDict > /AllowPSXObjects false /CheckCompliance [ /None
] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false
/PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000
0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true
/PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ]
/PDFXOutputIntentProfile () /PDFXOutputConditionIdentifier ()
/PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped
/False
/CreateJDFFile false /Description > /Namespace [ (Adobe)
(Common) (1.0) ] /OtherNamespaces [ > /FormElements false
/GenerateStructure false /IncludeBookmarks false /IncludeHyperlinks
false /IncludeInteractive false /IncludeLayers false
/IncludeProfiles false /MultimediaHandling /UseObjectSettings
/Namespace [ (Adobe) (CreativeSuite) (2.0) ]
/PDFXOutputIntentProfileSelector /DocumentCMYK /PreserveEditing
true /UntaggedCMYKHandling /LeaveUntagged /UntaggedRGBHandling
/UseDocumentProfile /UseDocumentBleed false >> ]>>
setdistillerparams> setpagedevice