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Transcript of Drive Testing - rte.de · subjective assessment of noise means the assignment of an evaluation to a...
RTE Akustik + Prüftechnik GmbH Gewerbestr. 26 D-76327 Pfinztal/Germany Tel. +49/721/94650-0 Fax +49/721/94650-50 www.rte.de [email protected]
Drive Testing
Noise and performance test of electric drives in production
Contents
Acoustic testing in production ...................................................................................... 2
1. Introduction .................................................................................................................. 2
2. Requirements .............................................................................................................. 3
3. Quality and quality control ............................................................................................ 3
4. Test values .................................................................................................................. 4
5. Acoustics ..................................................................................................................... 4
6. Types of noise and analysis ......................................................................................... 6
7. Sample applications ..................................................................................................... 7
Tubular drives ..................................................................................................................... 7
Electronic parking brakes .................................................................................................... 7
Gear motors ........................................................................................................................ 8
Convertible top lock ............................................................................................................ 8
8. Testing technology..................................................................................................... 10
Status: March 2010
Doc: RTE APPL NVH drive testers E-100311
RTE Akustik + Prüftechnik GmbH Gewerbestr. 26 D-76327 Pfinztal/Germany Tel. +49/721/94650-0 Fax +49/721/94650-50 www.rte.de [email protected]
Acoustic testing in production
1. Introduction
Electric motors and drives of various sizes and power ratings can be found in practically all de-
vices – beginning with miniature power drives and stepper motors in devices for the household, in
the office, in air conditioning and in cars up to industrial heavy machines.
Even in the private sector, today the customer pays increasing attention to pollution caused by
noise and perceives the noise of a device not only just as disturbing, but even fears a malfunction
or failure due to conspicuous sounds.
Integrated sound and performance testing in production can significantly improve customer satis-
faction and the data can in addition be used for the documentation of the production and devel-
opment to improve the product quality.
The purchaser always has the last word, however. Through continuous monitoring and documen-
tation of production, customer complaints can be reduced to a minimum.
Only a drive?
Today electric motors are no longer used only for the relief of workers with severe physical tasks
(drill, circular saw), but are used to improve the quality of daily life. Think, for example about your
morning routine: After being awoken by your radio alarm clock, you brush your teeth with an elec-
tric tooth brush, you possibly trim your beard with an electric razor, you blow dry your hair and
brew a cup of coffee with freshly ground beans in your new machine.
Now, the noise certainly also includes information needed by man as feedback for a proper func-
tioning of the device. So a mute vacuum cleaner makes us feel it must have low power and must
thus have a low cleaning capacity
So it is not important to create as little noise
as possible, but the right noise. Here one
speaks of “value adequate” noises.
The accompanying chart shows a "noise
corridor", which evaluates the sound as a
whole, both upwards and downwards and
thus showing characteristic distribution of
spectral composition.
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2. Requirements With today's high cost pressure, automated mass pro-
duction with high volume requires computerized control,
measurement and testing technology. The reason is not
only the number of pieces or the training of the em-
ployees, but the documentation of test results and rapid
intervention in production, if repeated errors are de-
tected. Production data must be available for evaluation
at all times and under different aspects.
3. Quality and quality control
Documentation, archiving, verification, traceability - these requirements are applicable also to the
noise and vibration assessment of products. However, practical implementation is more difficult
than, for example, measuring physical quantities such as current, voltage or speed and torque. A
challenge here is less the acquisition than the selection of appropriate procedures and the evalu-
ation of the acoustic signals, since only the subjective perceptions and the assessment of the
investigators are available as a reference. The subjective assessment forms the basis for objec-
tive decision by the testing system.
If we cannot rely on the subjective evaluation as a ref-
erence, the built-in learning mode of the SONIC|TC.NVH
software provides a way of statistically creating limits
based on measurement data, acquired in the produc-
tion.
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4. Test values
The following table shows the typical sizes of a comprehensive drive test:
test value meaning
high voltage testing protective conductor ground resistance
safety according to VDE 0100
speed stiffness, mounting errors
torque (load simulation) performance test
current stiffness, safety
noise, vibration assembly defects, component failure, sound quality
electronics testing e.g. hall sensors, radio controls and much more
Table 1: Test values of a comprehensive test
5. Acoustics
Basics
The acoustics deals with the description of sound fields and their phenomena (see Table 2).
Acoustics
noise generation by shock, friction or other deviations
sound propagation of structure-borne noise
sound radiation of airborne sound
sound recording sensors, ear
Table 2: Categories of acoustics
We can distinguish different types of noise (see Table 3), which are ultimately defined as elasto-
dynamic oscillations and waves in each medium.
noise types
Structure-borne noise Air-borne noise Liquid-borne noise
oscillation, vibration noise Pulsation
acceleration sensor, force sensor, nerves
microphone, ear pressure sensor, hydro-phone
Table 3: Categories of noise types
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For quality control it is particularly important to assess the nature of the sound. In this context the
subjective assessment of noise means the assignment of an evaluation to a product by the hu-
man examiner because of his feeling (to hear and feel). These perceptions are subject to numer-
ous, not exactly determinable factors.
The "objective" assessment is based on acoustic sensors for different types of noise and tries to
minimize the influencing factors respectively to consider them algorithmically.
To perform an evaluation, separable characteristics also have to be found, whose values, indivi-
dually or combined, constitute the evaluation measure [Ropke, Filbert 1995].
acoustic assessment
subjective objective or metrological
• perception and evaluation (due to experience) by man
• sense of hearing
• physical and mental factors
• signal acquisition, processing and classification by a computer / ma-chine
• measured values, calculated cha-racteristics
• technical factors
advantages • recognition of complex noise
• learning new noise
• reproducibility
• documentability
• automatability
• standardization
• known assessment scale
disadvantages • no absolute evaluation
• 85% reproducibility
• 85% confidence level
• no automation
• individual assessment scale
• expenses for small batches
• necessarily identical test conditions
Table 4: Categories of noise evaluation
Noise testing in production means the evaluation of airborne sound, while the vibration analysis
of structure-borne noise signals includes both the vibration of the test piece as well as its coupling
with the surrounding structure.
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Conditions
Acoustic testing can only be successfully used in industrial environments if the following condi-
tions are met and the target direction is clearly defined. This requires an accurate task analysis
and design of the entire inspection system.
For a successful sound assessment under production conditions, the influencing factors must be
minimized, and reproducible conditions have to be established in accordance with Table .
Sensors: robust, industrial, influence-poor
Test rig: vibration-isolated from environment, vibration test optimized test
item fixture
Measuring conditions: reproducible, comparable, use of meaningful values
Characteristics determination: differentiable, manageable number, meaningful
6. Types of noise and analysis
For example, the following failures will be detected with appropriate designed sensors and test
system layout by using the noise and vibration test:
type of noise description possible methods of analysis
knocking Low-frequency, periodic excitation of a structure resonant frequency
frequency band within a spectrum, kurtosis, crest factor
hum disharmonious mixture of low fre-quency, modulated components
high resolution spectrum, modulation spectrum
squeak high frequency signal, low-frequency excitation of a resonant structure
sharpness, spectrum
buzz nasal sound in the middle frequency modulation spectrum
howl fluctuating higher engine orders, low-frequency AM modulation
roughness, modulation spectrum
more…
Table 5: Examples of types of noise and possible methods of analysis
This is due, for example, to faulty installation or the use of defective parts (such as tooth mesh-
ing, steering racks with welding beads, brush errors, collector errors).
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7. Sample applications
Tubular drives
After assembly, tubular motors for rolling shut-
ters and awnings are subjected to automatic
performance and noise testing. The inspection
stations are loaded manually.
A mechanical load unit is used to simulate the
load conditions during operation.
The vibration test is done parallel to the cur-
rent measurement with the help of accelera-
tion sensors.
Electronic parking brakes
The "electrical brake", which replaces today's
manually operated hand brake, simultaneous-
ly meets the ever-increasing demands on
comfort, functionality, durability and space in
the passenger compartment.
The brakes are tested for unwanted vibra-
tions with a test system SONIC|TC.NVH in the
production line. By evaluating the structure-
borne noise, a comprehensive assessment of
the resonant behavior is carried out.
In extensive engineering in collaboration be-
tween OEMs, suppliers and RTE, the basic
conditions for the optimal measurement were
determined. In the run-up, a comprehensive
series of measurements, among others, was
performed to determine the ideal sensor posi-
tion on the complex housing structure.
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Gear motors
Gear motors of different types and designs
are examined on compact fixtures for perfor-
mance and vibration.
A magnetic particle brake simulates the load
conditions of the subsequent installation situ-
ation in the various operating conditions (“up”,
“down”, “open” and “close”).
During the automatic sequence, the worker
produces the next drive.
Through the concept of parallel testing and
production, the worker always has a direct
feedback about his production.
Convertible top lock
The electro-mechanical hook of a convertible
top lock is integrated in the roof and thus lo-
cated close to the driver. In this area, any
noise level is very critical.
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Using a proportional valve and with the help of
a pneumatic cylinder, the load curve of the
closure motion is simulated. The resulting
sounds are recorded and analyzed.
Comparative measurements in the vehicle and
the test system support the set-up of the pa-
rameters.
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8. Testing technology
SONIC|TC - Product diagnosis for production and development
The new generation of test technology with maximum application benefit. The system links the
monitoring level with the field level (“Digital Nerve System” in the context of the Microsoft initiative
“Linking Profit to Production”. The software provides an important module for modern information
and knowledge-orientated enterprises.
SONIC|TC is a powerful PC-based test system that is suitable for many products across different
industries. It is especially used for integrated testing in mass production.
At the same time, both acoustic (frequencies, levels
etc.) as well as performance properties like voltage,
current, force, displacement, etc. are measured and
evaluated. All measured values can be documented in
accordance with ISO 9000.
With its modular, adaptable design SONIC|TC perfectly
meets the requirements of different industries and
working environments. It can be used in manufacturing,
testing and laboratory and can control the test se-
quence of a manual or automatic test station.
SONIC|TC communicates with both the sensors and actuators at the field level as well as with
plant-wide systems. Particular emphasis was placed on SONIC|TC to allow the user a paramete-
rization on a large scale. He formulates and configures his own testing procedures and has all the
tools for application-specific processing available.
Functional properties
Parameter entry for products, test instructions, test processes and documents
Parameter entry for testing different product versions
Measurement values from different test benches can be collected and integrated in one
set
High flexibility through script-based control of test sequence
Calculation of characteristics
Standardized communication and process interfaces via OPC
Analysis and evaluation functions, statistical process control (SPC)
Modular system architecture is easily extendable and adaptable to customer needs
Capability characteristics
Any number of slow measurement categories through the field bus (Profibus, Ethernet...)
Up to eight fast measurement channels e. g. for acoustics
Standard PC with Windows operating system
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Fields of Application
Integrated vibration and function testing of components and systems
Process information collection and interconnection
Production and product documentation
Non-destructive, 100% testing in the production cycle
electric motors
gear boxes
valves
white goods
complex components
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LC|VIBRO - Acoustic signal processing for products and processes
Noise and vibrations are fast-changing signals that describe the condition of a product or process. Inexpensive, yet po-werful devices and programs of high relia-bility are required for a real-time survey and evaluation for damage detection, monitoring and for acoustic quality control, which can be used in harsh industrial en-vironments.
LC|VIBRO is an industrial signal pro-cessing system for the acoustic process and product monitoring.
LC|VIBRO operates autonomously and requires no ex-ternal control. The measurement and evaluation unit can be placed directly at the measuring point or on the mounting plate in the control cabinet. To increase the reliability, moving parts like hard disks have been avoided. The parameters and the software are stored on a Compact Flash memory card.
Parameter data can be written, read and archived by the service application. For service tasks, an external moni-tor and input devices can be directly connected via a service interface. Additional options are accessed via a remote connection.
Functional properties
acoustic signal analysis
noise and vibration monitoring
continuous measurement with monitoring of thresholds
evaluation of alarm conditions and notifications
product testing
comparison of acoustic characteristics
archiving
test data buffering and transfer to a host system
sequencing system
independent flow control and synchronization with host
data acquisition through the field bus (Profibus, Ethernet...)
up to eight fast measurement channels e. g. for acoustics
embedded platform
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Capability characteristics
time domain analysis (RMS, crest factor, kurtosis etc.)
statistical methods (peak counter, threshold peak detection etc.)
frequency domain analysis (frequency spectrum, modulation spectrum)
adjustable frequency bands
equivalent continuous sound pressure level
multiple communication standards (DeviceNet, EtherNet/IP, Profibus, Ethernet (TCP/IP),
EtherCAT, RS232, digital I/O etc.)
others …
Fields of Application
monitoring of assembly operations, machine vibration and process steps
noise and vibration testing of products
condition diagnostics for machine tools and production machinery
force fitting monitoring
others …