Reliability technology in medical instrument application

1 Introduction

Reliability study originated from the weapon system, after nearly half a century of development, has become a covering various subjects from various sectors of engineering and technical disciplines, from electronic product reliability to mechanical and non-electronic product reliability, reliability from hardware to software reliability, reliability from the attention to the development of statistical test emphasized reliability engineering test, by environmental stress screening and ret to expose product failure, increase the reliability of the product.

From the 1970s began to practical application in the medical device industry. Reliability in the application of the medical device with some particularity. First, the medical equipment is based on medical, health, health care, used for diagnosis, treatment, prevention, research, testing of instruments and devices, the accuracy of the results of more sophisticated, the therapy equipment and requires its uninterrupted nature; the second involved a more comprehensive knowledge of the subjects, optical, mechanical, electronic, computer, materials, chemical and biological, nuclear physics, and so on; with automation, increased miniaturization allows device structure more complex, with a wide variety of used devices, which constitute a system of equipment complex systems larger, the system environment is diverse, system failure, the greater the chance of the operation and maintenance personnel, the higher the requirements, design and manufacture of the greater difficulty of nature, reliability of the problem has to be more on reliability, technical requirements, the more urgent.

But the reliability of medical equipment in the country is far from mature.

Medical equipment technician generally feel reliability prediction, reliability, allocation, evaluation, and more on reliability are statistics, operations research, and as electrical, software, materials, professional engineers, professional differences make the reliability and expertise into two layers of skin. Medical device product features a small-batch, there is no strength particularly powerful institutions, SME, no conditions at a larger data statistics and reliability growth tests, and no national investment professional research institutions engaged in the research and findings to the community sharing; most typical domestic equipment manufacturing enterprises seldom stand-alone established reliability engineer positions, thus reliability of one of spots. Breakdown of domestic medical equipment industry is poor, very small enterprises are engaged in the whole production, everything myself, so limited technical resources are distributed within the company, even if you want to carry out reliable, realistic start, parts, components, the machine must be reliable, human resources and knowledge would conflict with the development cycle. It concluded that a fundamental conclusions: reliability on domestic manufacturer of medical equipment and medical institutions in Device Manager, it is necessary, but need a rooted in reality, realistic, solving practical problems in specific ways, this is the focus of this discussion. This article from reliability management, reliability, design and analysis, reliability test three aspects on medical device product reliability study on the work carried out.

2 reliability management

Reliability is the management, which is the industry's technical staff and managers have established a concept.

Management of the object is a development and reliability of all activities related to the focus on reliability design and reliability testing activities. Design, test, production process is a unified whole, and the failure of any one link will result in overall are lost; therefore, its management to run through the whole process of development, beginning from the development, and to have a comprehensive plan. The reliability of the product depends on its weak points, so the planning, implementation and management is to seize a few key, highlight the key points to improve the effectiveness of reliability.

Reliability of the work's main task is to prevent failures, the probability of a failure to control, correct the malfunction has occurred; therefore need to establish fault reporting, analysis and corrective action systems (FRACAS), from the management procedures and the organizational structure to ensure genuine failure review to ensure the development of all the fault of timely reports, careful analysis, the proper remedy, prevent reappearance, thereby achieving reliability growth.

From big ways, is in the medical device industry realization fault control the entire process, from raw materials procurement, design, registered forensics, production quality control and after-sales service, delivery, acceptance and use of tracking, usage, maintenance and management needs to control every aspect of the problem must have operational processes to ensure that the information is timely feedback to the design of production units forming a loop.

But now the industry characteristics in delivery acceptance, use, tracking, use process maintenance management link in the acute shortage of reliability data, some manufacturers have done relatively well, pay attention to service tracking, collection of data to improve some of the weaker enterprises collected is very poor, even the large enterprises collected many also is limited to its own products, industry representatives were not far from similar products in the reliability of data, similar to the industry to improve the reliability of the product is far from enough.

In terms of childhood is the design and production internal fault control, fault analysis, reliability, design, production control, service tracing, these regulatory aspects of the industry in recent years to strengthen the ISO9001 system review system on product reliability in design and production services for the request, the YY/T0316-2003 medical device-risk management-risk management applied to medical device law implementation also provides a basis for technical regulations standards.

3 reliability design and analysis

Product design determines the product reliability, if in the design phase did not seriously consider reliability design and analysis, regardless of how careful manufacture, strict management, rational use, are difficult to achieve high reliability requirements.

Reliability design and analysis aimed at mining and determine the potential hazards of products and the weak link, through in the design process improvement measures taken to prevent and effectively eliminate risks, and vulnerabilities; therefore, the design of product performance, reliability and design should be conducted and analytical work, focusing on prevention.

3.1 reliability modeling, estimated and distribution

Reliability model is established reliability diagram and mathematical models, through quantitative and qualitative assessment of the reliability of the model

The reliability of the links of the weak points and product design structure of the system.

Reliability prediction based composition system components, components and subsystems of reliability to speculate about the reliability of the system, this is a local to global, growing, bottom-up integrated process.

Reliability prediction as a design tool, to provide a basis for design decisions, and advance found weaknesses in the design, be improved.

Reliability of distribution means the requirement of reliability index, assigned to the system of subsystems, units, until the product level, this is a whole-to-local, from big to small, top-down process of decomposition.

Reliability of the distribution is intended to make clear at all levels of design personnel reliability design requirements, upon request, at an estimated manpower, time and resources, and to study the possibility of implementing the requirements and procedures.

Knowledge of the reliability is not so straightforward mechanism to implement reliability in the most simple way is to implement reliability modeling is expected and the allocation of basic concepts, the simplest method for a reliability analysis in advance.

To my actual work, for example, a machine of mask button has a "confirm" button, the workflow is like this: press the power switch — post-set parameters — sets the end of the "confirm" key-entering the working state. This process to work properly on the machine, confirm that the key is a key link, it will be taken seriously for reliability, the mask buttons processing mode, processing factory became the fatal impact reliability. This is an in-line system (as),

From here we can see, not just power some of the most critical, if you have a backup power supply and backup power supply always online, then power on the importance of reliability rather than the "confirm" button (shown below).

Because of the net power supply and battery two paths to power, this is a parallel structure, the "confirm" button is the only path, so its reliability should be strengthened.

The author as an electronic engineer, after analyses suddenly realized that not only the LCD, drives, sensors, power supply is the key part.

Through the analysis from the reliability of thinking on help we found many similar problems.

3.2 reliability data collection

Reliability analysis for statistical data, the reality is sample is relatively small.

So how to maximize the number of statistical sample and sample the symptom of practical value, you need a more complex work.

A is accomplished through the reliability test, you can determine medical products in a variety of environmental conditions or storing reliability features, product design, production, use, provide useful data and test fully exposed products in design, materials, components, processes, and other aspects of the problem.

And then through failure analysis, quality control, and a series of feedback, problems gradually resolved, thereby improving product reliability level.

The second is conducting a site survey on medical device product site usage survey, broadly speaking, any medical device product usage, failure or failure of the investigation, an investigation may be considered to be reliable.

Compared with the reliability test, in human and material resources, you can save a lot. If you are careful, you can achieve meaningful information, and even more realistic. This means that you can pass on the results of the statistical summaries and failure analysis, medical device product reliability assessment, identify weaknesses, reliability improvement measures to improve their reliability. Therefore, the reliability of the scene is medical equipment reliability important elements of the work. Field investigation of the first task is to collect the relevant medical device product reliability of data used on site, its contents have observation in General, working conditions, the failure condition, maintenance, failure phenomenon and the reliability of the data. It should be noted that the reliability of data not only fail, you must also include data without fail. Be aware that the investigation is tracking memory, data provided by the medical staff, easily lead to the exact fault description is insufficient, the data is not accurate ills; field investigations are resources limitations, restrictions on the number of samples, due to extensive medical field, can only rely on repair sector records and statistics, there are still some limitations.

Third, the survey in hospitals, clinical use and maintenance of two aspects, in order to get closer to the actual results, not just collect clinical application, but also collect medical worker sector repair maintenance evaluation.

The first part of the production units to resolve itself, the second and third parts as an industry organization can carry out academic work, utilization of society members work to facilitate, complete data, such as collection of x-ray machine fault and the reasons why the classification in order to design, environmental causes, users causes, production control, lack of training in the use, as an open data to enterprises, research institutions, evaluation of the Agency, the user provides information.

3.3 failure modes, effects and hazard analysis (FMECA) and fault tree analysis (FTA)

Failure modes, effects and dangers of the product design process, through to product constituent unit potential various failure modes and their effect on product features and analysis of each potential failure modes, press it's harsh degree classification, quantification of each failure mode and effect of fatal degree, you can take preventive measures to improve the reliability of the product.

It is a systematic failures expected technology, using inductive methods to systematically analyze product design can exist in each failure modes and their consequences and hazards, through comprehensive analysis to identify weaknesses in the design, implementation of focus to improve and control.

Fault tree analysis is in the system design process, through to may cause system failure by various factors (including hardware, software, environment, human factors, etc.) for the analysis, draw the logical diagrams, from

And determine the system failure causes various possible combinations and their occurrence probability, to calculate the probability of system failure, by taking the appropriate corrective measures to improve the reliability of the system. It is a system of detailed failure investigation methods, using deductive method of finding causes the system to a failure of the basic reasons to construct a connection failure causal logic chart, through failure analysis of the relationship between the logic to find the failure of all the paths and the critical path to take corrective action or control methods.

FMECA is single factors in the analysis unit failure mode effect on the system, it is assumed that all other conditions without fault as a unit; whereas the FTA is traced the root cause of system failure to failure combines in depth.

FMECA and FTA must go hand in hand with the design work, the results of the FMECA as improved design reference, through FTA, locate the system vulnerabilities, provide improved method. FMECA is a ready to FTA, the FTA is the development of the FMECA and supplements are mutually complementary. By FMECA and FTA, the product maintenance manual provides a wealth of material and basis.

3.3 reliability design method

By reliability analysis to identify the product weaknesses and vulnerabilities that only through the project take reliability design technology that can really enhance the reliability of the product.

The following according to the characteristics of the medical equipment, medicine in some instances, the introduction of some widely used reliability design technology.

3.3.1 resistance to environmental design

Resistance to environmental design refers to the product in shock, vibration, humidity, temperature, salt, mold, nuclear radiation, electromagnetic, and other harsh environments, as some of the units was difficult to withstand the impact of these environmental stress arising from failure by taking environmental protection design measures to reduce the environmental impact of stress on the product, improve product's service life and reliability.

For example: medical equipment often used LSI, COMS, CCD, in the event of an electrostatic shock, easily destroyed, so the design time consideration should be given to measures against static electricity.

In a humid environment (South of the rainy season), some medical devices if stored for a longer time, easy moisture short circuit, on the one hand, strengthen product moisture-proof design, on the other hand a clear product use environment requiring maintenance requirements. For sophisticated medical devices, due to adsorption dust, moisture and at the same time the adsorption of harmful gases, accelerates the corrosion rust, thermal performance, possibly due to reduced insulation strength short circuit leakage phenomenon, so you should do a whole dust, air filtration and other measures. By aerospace system reliability and technical experts to prepare for reliability design criteria class books on specific design method for explicit demands, such as inlet air filter must be added, the cooling air in-the-box access must be guaranteed by the high temperature low temperature module to module flows, and so on, you can reference a reference for designers.

3.3.2 components, spare part selection and control

Components are electronic, electrical system of basic products, parts and components is a mechanical system of basic products, their performance, reliability, cost, and other parameters directly affect the entire system (final product) for performance, reliability and cost.

If early in the development stage, the selection of components, parts and control attention and establish corresponding control bodies, develop preferred directory and listings, will greatly enhance the system's optimization level.

For example: for some medical devices, because of the long-running, with mechanical parts wear, the cause of medical equipment in mechanical movement is not in place.

Over time, some components will gradually aging, insulation condition declined, rubber sealing devices are also aging; easy to produce circuit faulty, the pressure is not up to standard. Therefore, in the selection of components, parts, you should consider the product's use frequency, life, environmental and reliability index; for the moment not meet design requirements, components, spare parts, you can consider backup replace fragile parts, strengthen maintenance strategy.

3.3.3 redundancy design

Redundancy design refers to product design, use a set of devices (devices, circuits, energy, etc.) to complete the assigned task.

Redundancy design can improve product reliability of tasks, but due to the increased complexity of the system, volume, weight, so that the system of basic reliability decreases, so depending on the product development goals and constraints for comprehensive trade-offs.

For example: for some relations of human life, if the medical equipment in use, because the product failure, leading to personal security, will not be tolerated.

Therefore, in a number of important medical device, the design-time to take redundancy measures to fully take into account a variety of emergency situations, ensuring that the safety during use.

3.3.4 take full account of the human influence on system reliability

No matter what kind of health system development, production and use are accomplished by people.

Human failure accounts for a significant proportion, according to 303 Central Hospital Yuan-ping of research data, medical electrical equipment 2800 cases fails statistical classification, environmental system fault 1176 cases, representing 42%, operating system failure 829 patients, 29.6%, instrument system fault 795 cases, 28.4%. Thus, environment/equipment failure/operations constitute the three core failure factors. With medical equipment of accuracy and intelligent level, human impact on the system. Study on medical equipment reliability problems is essentially human reliability issues. Human effects on different devices according to time and from place to place, human factors including personnel lack systematic training, environmental conditions, technical information is not comprehensive, management are not in place; Similarly, operation errors, Assembly errors, design errors, repair errors, installation error can also result in medical device does not function properly or is damaged.

4 reliability testing and evaluation

Product reliability is the design, manufacture and management, also must have a verification link constitutes a closed loop.

Through the reliability testFound products in design, materials and techniques of various defects, confirm compliance with the quantitative reliability requirements, in order to improve product reliability, reduce maintenance costs. Reliability test is divided into engineering tests and statistical test two broad categories: reliability engineering test is designed to expose weaknesses and product defects, and take corrective measures to exclude; reliability statistics the main purpose of the test is to verify the product's reliability indices. Reliability engineering test including environmental stress screening, reliability growth tests, reliability, development and testing, etc. Reliability of statistical tests including reliability evaluation test, reliability and life testing acceptance test. According to medical equipment development, to facilitate early exposure to product design, manufacturing defects, to take measures to improve product reliability, reliability engineering test should be strengthened, auxiliary conducting reliability test statistics.

At present, practically broader application of reliability engineering is environmental stress screening test.

Environmental stress screening is through the imposition of specific mechanical stress, stress, heat stress, environmental stress, make components, processes and accelerate the development of latent defects as early failure and to exclude, thereby improving product reliability. Environmental stress screening is a knockout product potential defects of the means, is a test process for electronics, optical, mechanical and electrical products, should carry out this work.

Reliability evaluation contains project evaluation and statistical assessment in two parts.

In order to determine the reliability of the product must be quantitative indicators for the development and use phase, actively gather reliability data, while appropriate conduct reliability evaluation test and life testing, provides data for statistical evaluation.

5. concluding remarks

This article from the engineering point of view, in reliability management, reliability, design and analysis, reliability test three aspects, a preliminary discussion on the development of medical device reliability work, hope can cause medical device developers pay attention to the reliability of medical equipment to provide a reference.