Current situation and development trend of the hot

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The current situation and development trend of strain gauge weighing sensor technology

I. the development and technological innovation of strain gauge weighing sensor

in 1938, Professor MMONS (Simmons) of California Institute of technology and Professor Ge (lurch) of Massachusetts Institute of technology developed paper-based wire wound resistance strain gauges at the same time, named SR-4 with their initials and two assistants respectively, which were patented by BLH company of the United States. It lays a theoretical and material foundation for the development of strain load sensor

in 1940, urston, the chief engineer of BLH company and revere company in the United States, developed a strain load sensor with cylindrical structure by using SR-4 resistance strain gauge, which was used for engineering force measurement and weighing measurement, and became the founder of strain load sensor. In 1942, a large number of strain load sensors have been produced in the United States, which has a history of more than 60 years

for more than 30 years, the load sensors of column, tube, ring and beam structures using normal stress (tension, compression and bending stress) dominated the world. During this period, the British scholar Jackson developed the metal foil resistance strain gauge, which provided an ideal conversion element for the load sensor, and created a new process of pasting the resistance strain gauge with thermosetting adhesive. After years of practice, BLH company and revere company in the United States have created the load sensor circuit compensation and adjustment process, which has improved the accuracy and stability of the load sensor, and increased the accuracy from a few percent in the 1940s to 0.05 in the early 1970s. However, the problems in the application process are also very prominent, mainly: the change of the force application point will cause relatively large sensitivity changes; The sensitivity deviation is large when tension and compression cyclic loading are carried out at the same time; Poor resistance to eccentric and lateral loads; Small load measurement is not allowed. The above shortcomings seriously restrict the development of load sensors

in the last 30 years, it has experienced two technological breakthroughs: shear stress load sensor and aluminum alloy small range load sensor in the 1970s; In the 1980s, the weighing sensor was completely separated from the force measuring sensor, and there were two major changes: the formulation of R60 international recommendations and the development of digital intelligent weighing sensors; In the 1990s, high and new technologies were continuously incorporated into structural design and manufacturing process to meet new challenges, which accelerated the development of weighing sensor technology

In 1973, in order to overcome the inherent shortcomings of normal stress load sensor, American scholar hogstrom proposed the theory of designing load sensor by using shear stress independent of bending moment instead of normal stress, and designed a circular I-section cantilever shear beam load sensor. It breaks the rule of normal stress load sensors and forms a new development trend. This is a major breakthrough in the structural design of load sensors

around 1974, American scholar Stein and German scholar erdom respectively proposed to establish a more complex mechanical model of the elastomer, and use the finite element calculation method to analyze the strength, stiffness, stress field and displacement field of the elastomer, so as to obtain the optimal design. It opens up a new way to design and calculate load sensors by using modern analysis and calculation methods

in the Middle School of the 1970s, weighing instrument manufacturing companies in the United States, Japan and other countries began to develop electronic pricing scales for commercial use, which urgently needed small-scale load sensors. Neither the traditional normal stress nor the newly developed shear stress load sensor can measure in the range of several kilograms to tens of kilograms. American scholar chaters proposed to use aluminum alloy with low elastic modulus as elastomer and adopt multi beam structure to solve the contradiction between sensitivity and stiffness. A small range aluminum alloy parallel beam load sensor is designed, and it is pointed out that the parallel beam load sensor is based on the principle of constant bending moment, which makes the normal stress structure using the bending stress on the surface of the parallel beam have the characteristics of shear stress load sensor, which lays a theoretical foundation for the design and calculation of the parallel beam structure load sensor and forms another development trend

creep is a key problem often encountered and must be solved by resistance strain gauges and aluminum alloy load sensors. In 1978, kolokova, a former Soviet scholar, through the analysis of one-dimensional mechanical model and strain transfer coefficient, put forward the theory that the resistance strain gauge with different creep values can be manufactured by controlling the ratio of the gate head width to the gate wire width of the sensitive gate of the resistance strain gauge, and successfully developed a series of creep compensated resistance strain gauges. It plays a vital role in reducing creep error and improving accuracy of low-capacity aluminum alloy load sensors, making it possible to produce aluminum alloy load sensors for electronic pricing scales in multiple varieties and in large quantities

due to the rapid development of electronic weighing technology, the evaluation method of load sensor performance can no longer meet the needs of using stepped tolerance zone to evaluate the accuracy grade of electronic weighing instruments, and there is an urgent need for measurement procedures suitable for the accuracy evaluation method of electronic weighing instruments. In the early 1980s, the quality measurement guidance Secretariat of the international organization for Legal Metrology (OIML) decided to completely separate the sensors used for electronic weighing from the sensors used for force measurement, and the Secretariat of the 8th report, which was in charge of the United States, drafted the weighing sensor measurement procedures. After the written vote of OIML Member States, it was officially approved at the 7th Legal Metrology conference in October 1984, and issued in 1985 as OIML, R60 international recommendations, which were distributed to Member States. At present, countries are implementing the 2000 version of R60. It can be said that R60 "weighing sensor measurement procedures" is the "pass" for weighing sensors of various countries to enter the international market

with the development of digital technology and information technology, there are more and more demands for digital electronic weighing instruments in various industries. The requirement of using digital weighing system to break through the limitations of analog weighing system is put forward, and the analog weighing sensor can do nothing about it. Before that, the research of load cell focused on hardware, such as innovating elastomer structure, improving manufacturing process, improving circuit compensation and adjustment, etc. The analog weighing sensor has the disadvantages of small output signal, poor anti-interference ability, short transmission distance, complex weighing display and control instruments, and long debugging cycle of group weighing. In order to meet the needs of digital electronic weighing instruments, American Toledo, STS and cardinal companies, and German HBM company have successively developed integral and separate digital intelligent weighing sensors. With its characteristics of large output signal, strong anti-interference ability, long signal transmission distance, and easy to realize intelligent control, it has become a necessary product for digital electronic weighing instruments and automatic weighing measurement and control systems, forming a development hotspot

In the 1990s, as the basic technologies such as the design and calculation of weighing sensors became mature, the development of weighing sensors focused on process research and application research, and great progress was made in product standardization, serialization, engineering design and large-scale production process, mainly:

the introduction of computer simulation technology and virtual technology into structure and process design

incorporate flexible manufacturing technology into elastomer processing

adopt computer network technology in production process

the new processes of vibration aging and resonance aging were transplanted in the stabilization treatment

automatic rapid detection and dynamic comparison methods are created in the test and verification

there is also a breakthrough in the research of application technology: a new weighing module is developed on the basis of the traditional weighing module. This is a typical product that applies new technologies to face new challenges. It is characterized by a modular design and has a "plug and play" function, which can reduce the weighing error caused by bias, thermal effect, accidental overload, etc., and can withstand bias caused by vibration, impact, mixing or other external forces. In short, two technological breakthroughs in the 1970s, two major changes in the 1980s, and the introduction of the R & D concept of high and new technologies facing new challenges in the 1990s have greatly promoted the development of weighing sensor technology

II. The current situation of foreign weighing sensor technology and the reasons for its rapid development

weighing sensor technology and manufacturing process for industrial and commercial electronic scales. Famous manufacturing companies in the United States, Germany and other industrial developed countries are in the leading position of international market leaders, and weighing sensor manufacturing companies with a certain scale in China are in the position of market challengers or market followers. The R & D and production center of weighing sensors for household electronic scales is in China and Shenzhen, and the manufacturing technology, process level, product quality and annual output have increased year by year

the competition of weighing sensor technology in today's international market is concentrated in the competition of product accuracy, stability and reliability; Competition between manufacturing technology and manufacturing process; The application of high-tech research and development of new products and independent intellectual property products. All weighing sensor manufacturing enterprises are striving to cultivate their core competitive technologies and build core competitive products

from the products exhibited at the international weighing instrument industry exhibition in recent years and the analysis of the products of many enterprises in the position of market leader, it can be concluded that the common pursuit of these enterprises is: better elastomer material; The technical requirements and environmental stress screening of resistance strain gauges and compensation components are more stringent; More refined manufacturing process; The circuit compensation process is more perfect; The appearance quality is more perfect

the accuracy, stability and reliability of weighing sensors are important quality indicators, and they are also the most concerned problems of users. In this regard, these enterprises have made great progress in structural design, manufacturing technology, circuit compensation and adjustment, stability treatment and other aspects of research and testing, and the main results are:

(1) in the process of structural design and calculation, computer simulation technology is introduced for dynamic simulation and dynamic analysis; In the process of process design, computer virtual technology is introduced to simulate and test the elastomer production process

(2) incorporate advanced manufacturing technology into elastomer processing, and change rigid manufacturing into flexible manufacturing. Machining centers, flexible manufacturing cells and flexible manufacturing systems are widely used

(3) in the whole production process, reduce manual operation and manual control as much as possible, increase semi-automatic and automatic control, automatic inspection processes, and adopt computer network technology in the production process

(4) improve and innovate process equipment, realize efficient intelligent circuit compensation, establish a full-automatic rapid detection system, and improve the success rate of C3 products and the sampling inspection qualification rate of mass-produced products

(5) transplant advanced stability treatment technology and equipment, and implement the new process of vibration aging or resonance aging to improve the long-term stability and working reliability of the load cell

(6) apply high and new technology to develop new products and products with independent intellectual property rights to enhance core competitiveness. Enterprises in the leading position in the international market have their own core competitive technologies, processes and products, such as "O creep" weighing sensors of positive and negative creep bridges; Beryllium bronze dynamic weighing sensor; Integral and separate digital intelligent weighing sensors; High accuracy stainless steel 3-column and 4-column high temperature weighing sensors; "Plug and play" new weighing module with component design, etc

the development characteristics of foreign weighing sensor technology and the reasons for its rapid development:

(1) pay attention to the research of basic technology, basic process and common key technology, so as to achieve the parallel of basic research and pre research; Common key technology research and application technology research are in parallel; Typical product development and product engineering go hand in hand. Ensure that the basic technology and basic process (resistance strain gauge, strain adhesive, compensation components, protection and sealing materials, etc.) have always been in the leading position in the world


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