Why Vibration Testing?

1. Design and development stage

1. Analyze the vibration modes of the sample under different vibration states

2. Test the ultimate strength of the product and determine the relevant characteristic specifications

3. Failure analysis and improvement

2. Production stage

Thorough ESS testing is carried out to screen out a large number of potential defects.

(According to the characteristics and vibration scale of the product, the ESS test is put into the effective screening out of potential defective parts, and the residual thermal stress and internal stress during electronic or mechanical processing can effectively eliminate the residual stress effect in the process, and can effectively eliminate the discrete capacitance effect between multilayer circuit boards, which will provide considerable help to product quality.) ）

3. Quality management (QC)

Effectively ensure and manage the quality level of products.

4. Quality Assurance (QA)

The function, specification and reliability of the certified products are the same as those labeled.

5. Miscellaneous

What can I expect from a vibration test?

1. Provide the basis and reference
for engineering development

2. Process control

3. Improvement and promotion
of quality

4. Provide conditions
for the interrelationship related to vibration

5
. Guarantee the quality of the product

6. Reduce maintenance expenses and increase profitability

7. Improve the overall image

Vibration testing can be used to screen out defects

• The fixing is loose

• Poor
  splicing of electronic contacts

• Screen out potentially bad parts
  

• Filter out defective solder joints

• The vibration position and accuracy of the adjustment part are distorted

• Cracking or damage of components

• The circuit is broken and the short circuit is abnormal

• Abnormal wear and tear of the power cord or signal line, or broken wires or loose contacts

• The specimen generates vibration noise

• Abnormal malfunction
  

How to use vibration testing to improve product reliability

• Verification tests in the design phase (qualitative, quantitative tests/fatigue, failure)

• ESS stress screening is carried out comprehensively during the production phase

• Reliability sampling and certification
  in the quality control and quality assurance stages

• Verification testing (quality, specification, characteristics, and function verification)
  at the acceptance stage

Reliability and failure

1. Definition of Reliability:

• THE PROBABILITY THAT THE PRODUCT WILL ACHIEVE THE INTENDED FUNCTION WITHIN A CERTAIN LIFE PERIOD AND UNDER ENVIRONMENTAL CONDITIONS (GENERALPRODUCRT)

• THE PROBABILITY THAT A PRODUCT WILL COMPLETE A TASK WITHIN THE TIME REQUIRED TO BE ACTUATED UNDER CERTAIN CONDITIONS (ONESHOT PRODUCT)

2. Failure analysis - for reliability testing

• Poor development design

• Improper selection of parts

• Poor
  quality parts

• Poor
  production capacity

The reason why the product is unreliable

• The usage environment cannot be accurately estimated and measured

• Failure to adequately meet user needs

• There is a mismatch between reliability requirements and design levels

• Variations in quality levels

• Design errors
  

• Manufacturing errors
  

• Adjustment and maintenance errors

• Errors and negligence

Forms of invalidation kinds

> INDEPENDENTFAILURE 

Failure specimens that do not affect each other within the product

> INDEPENDENTFAILURE

Cascading failures caused by abnormalities or failures of other systems

> INTERMITTENTFAILURE

Occasional functional abnormalities or failures during use

> MULTIPLE FAILURE 

More than two independent failure events occur at the same time

> molding failure

The same part has two or more abnormal failures

How to complete a vibration test report

Instruments and equipment, fixture types and characteristics, test specifications, execution status and steps, fixture and specimen fixing methods, accelerator installation position, specimen before, during and after the test function test records, failure analysis and judgment, test results review, evaluation, improvement and suggestions

How to execute a reliability plan

• Customized product life cycle: refers to the service life under normal functional operation

• Defined environmental requirements: Generally refers to the environment
  under production, storage, transportation and use operations

• Define the configuration of reliability: Define the requirements
  for product reliability

• Configuration of reliability: components, semi-finished products and finished products are equal to the level
  of demand at different stages

• Benefit Evaluation: Analyze the quality cost and define the distribution level of the needs of the brave, including (a) reliability, (b) usability, and (c) functional requirements

• Design analysis (a) functional analysis (b) environmental analysis (c) tolerance analysis (d) failure analysis and defective product effect response analysis

• Customized Test Procedure:

(a) Vibration test plans at different stages

(b) Criteria for determining reliability

(c) Environmental requirements level: single or composite environmental testing

• Comprehensive analysis: Collect the data after testing and analyze the implementation plan

(a) Reasonableness, (b) Economic, and (c) Other benefit impact assessment

• Tracking and control: Establish a product feedback system to find new problems and potential problems

The secret to the success of your Execution Reliability Program

• Improving product reliability is a high indicator for development and production

• Choose high-reliability spare parts and mature related technologies

• The necessary destructive testing and analysis
  is carried out on each newly developed product

• Conduct phased design evaluations and improvement plans

• Conduct environmental impact analysis and assessment of products

• Periodic reliability tests are conducted

• Tracking & Control

Test variables

• Vibration test equipment

1. Controller

2. Amplifier

3. The magnitude and large amount of vibration and thrust

4. The frequency influence range and response spectrum of the vibrating voice coil

• Select the axial direction for the vibration test

• Vibration spectrum and power intensity

• The execution time is long

• How and at which the scan is performed

Types and characteristics of fixtures

• The test piece itself

• Installation skills
  

• The type, quality, and quantity of accelerometers (sensors).

• The installation position and fixing method of the accelerometer

• Specimen status (shutdown/shutdown test, composite test)

• other

Vibration and representation

• Vibration intensity is often expressed in terms of velocity, acceleration, amplitude, and also in terms of changes
  in the magnitude of force

• Acceleration (a), velocity (v), amplitude (d), force (N) are usually expressed in linear units

• The amount of vibration intensity is usually described in the following ways:

A. peak to peak

B. peak level

C. Average level

D. Root meansquare (RMS)

E. Powerspectrum density (PSD)

F. Accelerationspectrumdensity (ASD) 

• The various unit descriptions have their specific timing of use, with vibration intensity notation

Fundamental factors influencing vibration measurements

̈Vibration measurements are usually measured using an accelerometer as a perception, and the acceleration signal is integrated for the velocity or amplitude. Of course, you can also choose a speedometer or displacement gauge for measurement, no matter what kind of sensor is selected as the measurement sensor, you must pay attention to its characteristic specifications, otherwise it will seriously affect the accuracy of the vibration test.

̈The sensor itself is a mechanical system with its own physical characteristics such as resonance frequency and resonance frequency doubling when in contact, and it is usually necessary to select a sensor higher than the test bandwidth before performing vibration measurement.

̈The sensor with the higher measured value must be selected

̈ The way in which the perceptron is mounted

̈Changes in the surrounding environment are also important factors influencing vibration measurements

Types of transducers (perceptrons).

When measuring vibration signals, the longest option is to use a measuring cell that converts mechanical energy into electrical energy, referred to as an energy exchanger or energy converter.

The transducer converts the mechanical motion energy of the specimen into electrical energy, and then analyzes the strength and change of the output signal, such as frequency, acceleration, velocity, displacement and force.

In the actual measurement environment, according to the actual needs, it can be divided into:

1. Contact type

2. Non-contact

Among them, non-contact sensors are commonly used

1. Eddy current type

2. Capacitive type

3. Photoelectric type

A. Photoelastic method

B. Laser photoreflectometry

C. Laser Doppler effect measurement

Characteristics of the use of contactless perceptrons

A. Distance Measurements

B. Measurement in a high/low temperature environment

C. Environments where the perceptron cannot be fixed

D. Disadvantages of no mass effect

How to choose an accelerometer

> frequency influence range, sensitivity, linearity, dynamic range/safety limit values, mass effect, axial and lateral sensitivity, temperature effect, signal line length, and other environmental factors

Types of vibration waveforms

> SINE WAVE

1. SWEEP SINE

A. Linear scan – 1.Linar2.Hz/sec

B. Logarithmic scan – 1.Log2.Octave

2. RESONANCERESEARCH

3. RESONANCE DWELL

4. STEP SINE

5. MULTIRESONANCE DWELL

> RANDOM, SHOCKWAVE

6. HALF SINE1/2SINE

7. SAWTOOTH WAVE

8. SQUARE WAVE

9. SELF DEFINITION

> SINE ON (SOR), RANDOM ONRANDOM (ROR), AND OTHER – COMPOSITE WAVEFORM TESTING

Types of Cycle Scans and When to Use Them (Sweep Sine)

The specimen vibrates with a specific vibrational energy in a predetermined frequency range and time, and its frequency changes continuously.

Purpose: To make the specimen in the set frequency range, from low frequency to high frequency or high frequency to low frequency continuous multiple cycle scanning test, in order to identify whether the product is enough to withstand environmental stress, and early prevention and improvement.

Technique: The vibration intensity, scanning rate and scanning method of sinusoidal scanning have an important impact on the occurrence of resonance. The correct scanning rate must be full enough to make the specimen resonate for the shortest time as the basis for the scan rate setting. It is hoped that enough resonance times can occur in the resonance frequency range to identify the ability of the specimen to tolerate the stress of the vibration environment.

Method: 1. Linear scanning, 2. Logarithmic scanning

RANDOM VIBRATION

Purpose: For most vibration environments, whether natural or man-made, most of the vibration environments are generated by random waves. For example, the vibrations generated by waves, currents, winds, rainfalls, earthquakes, and environments in daily life, such as 、、、 transportation environment, are all classified as random vibrations. The environment in which the solid specimen and the product exist is originally covered by random vibration, if the vibration-related research and analysis of the specimen can be carried out, and the random vibration test that has been studied and planned will be closer to the actual effect. The efficiency of the test is much higher than that of the sinusoidal sweep, and it is not prone to the adverse effects of overstress and stress residue caused by the sinusoidal sweep type.

Resonance search

The specimen is scanned with a low vibration energy, sub-low frequency to high frequency with a fixed energy intensity, continuous frequency, and moderate scanning rate, which is used to stimulate the vibration mode of the specimen, which is an important basis for the resonance residence test.

In general, the frequency range of the search must be moderately widened to better grasp the actual environmental variation and the damage of the specimen due to fatigue or aging, resulting in shrinking of the safety margin.

RESONANCE DWELL

Purpose: The purpose of the test is to test the ability of the specimen to tolerate long-term resonance environments

Steps: Firstly, the resonance frequency and resonance mode found in the resonance search are analyzed, and the frequency distribution that may occur for a long time or is easy to occur in a specific environment or the frequency distribution with high vibration intensity in the vibration environment is selected as the test basis for resonance residence, and whether the specimen can tolerate the ability to withstand the resonance environment for a long time.

Note: A good resonance residence system can track the resonance frequency of drift at any time to achieve the best resonance effect. In general, the resonance dwell is usually used for 107 times or the cumulative time that may be distributed in the effective resonance frequency range during the use period as a reference for the test specimen.

OCNATIVE

The scanning rate of the specimen is doubled for each unit of time

When to use: Test specifications that are better or less intense in the test environment are usually used. (e.g. audio, audio-visual equipment, communication products)

Step-by-step resonance dwelling

（STEP RESONANCE DWELL）

Objective: This paper aims to design and plan a fast and effective test method for the invalid test frequency domain without resonance in the process of performing cyclic scan test, which is easy to use a large amount of test time and equipment.

Timing of use: provincial production line test, quality control sampling test.

Execution skills: Firstly, the specimen is analyzed for the spectrum, the state of resonance and the related physical quantities are recorded, the resonance frequency at the time of resonance occurrence, the effective vibration frequency range, the resonance frequency doubling and the resonance mode are calculated, and the physical strength conditions of the specimen and the reliability design strength of the specimen are considered, and the allowable test time period of the specimen is considered during the test analysis, and all conditions are analyzed and judged, the actual effective test spectrum is determined, and the steps such as tracking frequency estimation and correction are established.

Execution benefit: Save 50%~9% of the time occupied by invalid test bandwidth in cyclic testing on average, and increase the efficiency of equipment use.

Complex resonance dwelling 

（MULTI RESONANCE DWELL）

It is a screening method that has been planned to output multiple sets of specific spectrums of different intensities in the same time domain at the same time, with the purpose of making the components with a high defect rate on the specimen or the components that need to be specially specified for screening, and giving a specific power spectrum to improve the testing efficiency.

The main function is to improve the longer time consumed in the step scan test in the resonance test, which aims to save a lot of test time, and make the test results equivalent to the effect of cyclic scanning and random vibration, so that the defective parts can be screened out in the shortest time.

How to use: SOR. ROR. MULTI SINE.

When to do it: Production line test.

How the ESS test differs from the environmental vibration test

• Strictly speaking, ESS is a screening procedure to improve production quality and environmental test, the basic difference is as follows:

• The spirit of ESS testing requires 100% comprehensive screening of products, and environmental testing only requires a small number of samples to be tested or quantitatively performed or regularly or irregularly sampling.
  

• The main purpose of environmental testing is to test the ability of the test specimen to withstand environmental stress, and the results of the test are undesirable for failure parts.

• During ESS screening, it is hoped that a large number of potential defects in the specimen will be exposed, so the occurrence of failure is expected.
  

• In order to speed up the discovery of latent defects in the product, the specifications of the test are not related to the use environment, and the specifications of the test should not exceed the design strength of the test piece or the physical limit strength range of the components, or due to the characteristics of the components in the product, it is specially designed to avoid opening the frequency domain that is extremely sensitive to vibration, so that the system can be combined to carry out functional tests or other tests.
  

• The specifications of the environmental test are often determined according to the actual environment of the life cycle of the specimen.
  

What are the characteristics of an ESS plan? 

According to the definition of ESS, the effective implementation of an ESS procedure should include the following characteristics:

• It can quickly expose potential defects in the product

• The strength of the environmental stress under the implementation of ESS shall not be greater than the ultimate strength or design strength
  of the product itself

• Performing ESS should not affect the normal service life
  of the product

• Cost-effective
  

What are the benefits of implementing an ESS plan 

• Effectively improve product reliability

• Improve MTBF when using the product

• Process productivity can be increased

• In the R&D stage, it can assist in early detection of design problems, improve engineering reliability, save development time and development costs, and create overall benefits.

Things to look out for in the implementation of the ESS plan 

• Master the stress analysis of different environmental factors

• The impact of different stress levels on the product and the engineering benefits
  

• Analyze the product after screening and the use of the
  product after screening

Establish a pre- and post-screening cost-benefit analysis model

What are the types of vibrating machines (according to power)

Mechanical, pneumatic, hydraulic, electromagnetic

Vibration test equipment

• CONTROLLER

Analogy: digital tape, plug-in card

Open circuit closed circuit

• POWER AMPLIFIER

LINEAR POWERAMPLIFIER(40~60%)，SWITCHINGPOWER AMPLIFIER(96%)

• SHAKER

Mechanical, pneumatic, hydraulic, electromagnetic

• TRANSDUCER, FIXTURE

What are the important properties of the vibrator

• Vibration Thrust Value (Peak/RMS), Frequency Range (FrequencyRange), Frequency Accuracy and Resolution, Voice Coil Quality (Armaturemass), Voice Coil Resonance Frequency and Resonance, Large Displacement, High Velocity (Velocity), Large Acceleration (Acceleration), Large Load Capacity (Loading), Magnetic leakage, durable, H/S protection system, antiresonance

Vibration control mode

Characteristic type

Anloge, digital, tape, ROM/RAM card

Control mode

1. Open Loop Control, Closed Loop Control

What you should pay attention to when choosing a vibration controller

> frequency control range, frequency resolution and accuracy, control point number machine control mode, dynamic compression ratio, scanning rate and scanning method type, safety margin setting value, integrity of software and hardware protection design, accuracy of control value, software and hardware expandability (SINE/RANDOM/SHOCK/FFT), multi-stage programming ability, error-proof, fool-proof design, humanized design of operation

Considerations for power selection amplifiers

> response bandwidth, power factor efficiency, instantaneous power value and continuous power value, noise protection system, over-temperature, over-current, over-voltage protection, and expandability of series and parallel outputs

How to choose the right vibration test system for your needs

> understanding of their own products, determination of future needs (scalability), and awareness of tasks

1. Vibrating equipment

2. Control system

3. Signal analysis, storage and processing

> performance and price, after-sales service

Comparison of the advantages and disadvantages of mechanical vibrators

Merit:

> is cheap, easy to operate, easy to maintain, and has a heavy static load

Shortcoming:

> The frequency response range is small, the actuation frequency is low, basically only a single frequency is produced, the vibration waveform is mainly sine wave mode, the general noise value is high when executing, usually with positioning and shifting output (variable acceleration), the frequency change rate is low, and the control accuracy is low

Comparison of the advantages and disadvantages of electromagnetic vibrators

Merit:

> wide frequency response: DC~20kHz, high control accuracy, can simulate various waveforms: SINE, RANDOM, ROR, SORSHOCK, easy to control, suitable for different testing needs: development, engineering, quality control, stress screening, large expandability, easy maintenance

Shortcoming:

> the cost of equipment for large-scale units is high, and a large power supply is required

Comparison of the advantages and disadvantages of hydraulic vibrators

Merit:

> has a large thrust and can produce a large amount of displacement, which is convenient for multi-axial connection testing

Shortcoming:

The cost of > and maintenance is high, the high-frequency response cannot be achieved, and the large unit is not easy to install and assemble

Comparison of the advantages and disadvantages of pneumatic vibrators

Merit:

> easy to operate, the special model is suitable for fixed screening work, can generate multi-axial vibration spectrum, easy to install and maintain

Shortcoming:

> it is not possible to arbitrarily change the vibration spectrum that has been set, the compressed air needs to be cleaned, the air consumption is large, it is not easy to compress the control vibration waveform, and the weight of the side object is more sensitive, and a large displacement cannot be generated