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
Acoustic testing in production 1. Introduction Electric motors and drives of various sizes and power ratings can be found in practically all devices 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 satisfaction and the data can in addition be used for the documentation of the production and development to improve the product quality. The purchaser always has the last word, however. Through continuous monitoring and documentation 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 electric 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 functioning 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.
2. Requirements With today's high cost pressure, automated mass production with high volume requires computerized control, measurement and testing technology. The reason is not only the number of pieces or the training of the employees, but the documentation of test results and rapid intervention in production, if repeated errors are detected. 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 evaluation 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 objective decision by the testing system. If we cannot rely on the subjective evaluation as a reference, 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 production.
4. Test values The following table shows the typical sizes of a comprehensive drive test: test value high voltage testing protective conductor ground resistance speed torque (load simulation) current noise, vibration electronics testing meaning safety according to VDE 0100 stiffness, mounting errors performance test stiffness, safety assembly defects, component failure, sound quality 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 elastodynamic 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 Table 3: Categories of noise types microphone, ear pressure sensor, hydrophone
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 human examiner because of his feeling (to hear and feel). These perceptions are subject to numerous, 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, individually or combined, constitute the evaluation measure [Ropke, Filbert 1995]. acoustic assessment subjective perception and evaluation (due to experience) by man sense of hearing physical and mental factors objective or metrological signal acquisition, processing and classification by a computer / machine measured values, calculated characteristics technical factors advantages disadvantages recognition of complex noise learning new noise no absolute evaluation 85% reproducibility 85% confidence level no automation individual assessment scale reproducibility documentability automatability standardization known 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.
Conditions Acoustic testing can only be successfully used in industrial environments if the following conditions 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: Test rig: Measuring conditions: robust, industrial, influence-poor vibration-isolated from environment, vibration test optimized test item fixture 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 squeak disharmonious mixture of low frequency, modulated components high frequency signal, low-frequency excitation of a resonant structure high resolution spectrum, modulation spectrum sharpness, spectrum buzz nasal sound in the middle frequency modulation spectrum howl more fluctuating higher engine orders, lowfrequency AM modulation roughness, modulation spectrum 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 meshing, steering racks with welding beads, brush errors, collector errors).
7. Sample applications Tubular drives After assembly, tubular motors for rolling shutters 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 current measurement with the help of acceleration sensors. Electronic parking brakes The "electrical brake", which replaces today's manually operated hand brake, simultaneously meets the ever-increasing demands on comfort, functionality, durability and space in the passenger compartment. The brakes are tested for unwanted vibrations with a test system SONIC TC.NVH in the production line. By evaluating the structureborne noise, a comprehensive assessment of the resonant behavior is carried out. In extensive engineering in collaboration between 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 position on the complex housing structure.
Gear motors Gear motors of different types and designs are examined on compact fixtures for performance and vibration. A magnetic particle brake simulates the load conditions of the subsequent installation situation 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 located close to the driver. In this area, any noise level is very critical.
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 parameters.
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 sequence 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 parameterization 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
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
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 powerful devices and programs of high reliability 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 environments. LC VIBRO is an industrial signal processing system for the acoustic process and product monitoring. LC VIBRO operates autonomously and requires no external 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 monitor 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
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