The image measuring instrument is an “optical imaging system (called imaging system) based on imaging on a photoelectric coupling device. It collects data through the photoelectric coupling device, processes the image through software and displays it on the computer screen. The measurement software is used to perform geometric operations to obtain the final result. Non-contact measuring instrument results”. The measuring software extracts the coordinate points on the workpiece surface through digital image processing technology, and then uses coordinate transformation and data processing technology to convert to various geometric elements in the coordinate measurement space, thereby obtaining parameters such as geometric dimensions and geometric tolerances of the measured part.
1. Overview of the development of image measuring instruments
In the late 1970s, especially since Professor David Marr established the theoretical framework of “computational vision”, image processing technology and image sensors developed rapidly. With the increasing development and maturity of coordinate measurement technology, substantial new progress has been made in the development and application of coordinate measurement methods in the field of optical measurement based on optical comparison.
In 1977, the American View Engineering Company invented the world’s first RB-1 image measurement system driven by a motor on the XYZ axis (see Figure 1). This is an automatic image measuring instrument with a control terminal integrating video detection and software measurement. . In addition, Mechanical Technology’s Boice Vista system fully exploits the advantages of coordinate measuring machines and integrates a video image measurement system on the probe of the coordinate measuring machine. This system can compare the measurement data with the pre-programmed nominal dimensions and the tolerances are compared.
These two instruments rely on the coordinate measuring principle of the coordinate measuring machine in different ways and project the image of the measured object into the coordinate system. Its measurement platform inherits the shape of a three-dimensional measuring machine, but its probe is similar to an optical projector. The emergence of these instruments has opened up an important measuring instrument industry, namely the image measuring instrument industry. In the early 1980s, image measurement technology underwent significant developments. In 1981, the ROI company developed an optical imaging probe (see Figure 2), which can replace the contact probe on a coordinate measuring machine for non-contact measurement. Since then, this optical accessory has become one of the basic components of imaging equipment. In the mid-1980s, image measuring instruments equipped with high-magnification microscope eyepieces appeared on the market.
In the 1990s, with the development of CCD technology, computer technology, digital image processing technology, LED lighting technology and DC/AC servo motor technology, instrument products image measurement have undergone considerable development. More and more manufacturers have entered the image measuring instrument product market, jointly promoting the development of image measuring instrument products. After 2000, China’s technical level in this field continued to improve, and the research literature on image measurement technology also continued to appear; companies) Measuring instruments have also been continuously improved and developed in terms of production scale, variety and quality. In 2009, our country formulated the national standard GB/T24762-2009: Geometric Product Specification (GPS) Acceptance Testing and Reinspection of Image Measuring Instruments. It is suitable for image measuring instruments in the rectangular coordinate system of the XY plane, including those. which are perpendicular to the plane at right angles. An image measuring instrument with positioning or measuring functions in the Z direction of the coordinate system.
2. Evaluation of image measuring instruments
We could also evaluate the image measuring instrument products from the perspective of instrument structure, key technical indicators, etc.
(1)Appearance and structure
The appearance and structure of precision measuring instrument products provides an important basis for user selection. Good appearance and structure of a product give people a sense of stability, reliability and precision, and are often important factors that determine the success or failure of a product in the market.
At present, the main structural forms of image measuring instruments include columnar structure, fixed bridge structure and movable bridge structure. Column structure and fixed bridge structure are widely used in small-range image measuring instruments, and each has its own advantages. The movable bridge structure is mainly used in ultra-long range image measuring instruments. The advantage of the column structure is that it has a compact structure, takes up little space, and is convenient for loading and unloading parts; the fixed bridge structure is characterized by a stable and atmospheric product, but it occupies a large space and is not convenient for loading and unloading parts; the structure of the mobile bridge is easy to implement. Large range measurement, the workpiece is fixed during the measurement process.
(2) Light source system
The light source system plays an essential role in the image measuring instrument, which directly determines the performance and operation of an image measuring instrument. A good light source system can help the image probe obtain clear, sharp, uniform and correct images, ensuring measurement accuracy and repeatability. In order to provide effective illumination for parts of different materials, shapes and types and to perform complex measurement tasks, image measuring instruments generally provide three illumination sources: surface light source, light source contour and coaxial light source.
Surface light sources provide illumination for measurements on the top surface of the part. A good surface light source should be able to provide illumination from different incident angles and different incident directions to ensure that different rooms achieve consistent lighting effects.
The contour light source provides illumination for measurements such as the outer contour of the part and through holes. The contour light source is usually installed on the base of the image measuring instrument. When working, the part of the image blocked by the part is imaged in black and the unobstructed part is white, helping the image probe to image the part with it. clear black and white, high contrast and clear boundaries. Under the illumination of a contour light source, the instrument can often achieve the highest measurement accuracy.
The coaxial light source is projected onto the workpiece surface along the optical axis of the lens, which can provide illumination for measuring high reflectivity surfaces and deep holes in the workpiece.
(3) Multi-probe integration
The imaging probe has unparalleled speed advantages in two-dimensional measurement, but the imaging probe also has disadvantages in three-dimensional measurement, the measurement efficiency is not high enough, and the side characteristics of the workpiece cannot be measured. Therefore, multi-probe integration is necessary. The comprehensive use of image probes, contact probes, laser probes, white light probes, etc. can select the most suitable measurement method for different parts and different measurement needs. precision and the best measuring efficiency. When measuring large quantities of two-dimensional dimensions, the image probe can be used; when measuring the side walls of complex parts without high efficiency requirements, contact measurement can be selected in the three-dimensional measurement of complex parts, if applicable; the efficiency is very high, white light probe or laser probe can be used.
(4) Measurement performance
Accuracy is the foundation of measuring instruments, and accuracy is one of the most important indicators for users to choose instruments. The measurement accuracy of the image measuring instrument mainly depends on the quality of the image measuring probe, the performance of the illumination source system, the movement of the instrument and the positioning accuracy of the quality and level of data processing and measurement software and hardware. are also extremely important influencing factors. As an automated measuring instrument, the measuring efficiency of the image measuring instrument is one of the factors that customers value most. High measurement efficiency can reduce equipment investment, improve production efficiency, reduce labor costs, etc.
(5) Measuring function
The basic measurement functions of image measuring instruments generally include: measuring various basic geometric quantities such as points, lines, circles, arcs, etc. In terms of measurement methods, it provides a variety of extraction and construction methods; shape tolerances and position tolerances; Provides a variety of methods for establishing coordinate systems; provides manual measurements and automatic batch measurements; the batch measurement program can record measurement primitives, extraction methods, machine control, light source control, autofocus and other processes; can be imported and exported; The measurement data can be output to generate a report in the specified format. In addition to these basic measurement functions, instrument manufacturers usually offer extended functions such as SPC, drawing comparison, offline programming and custom output reports. Some manufacturers will also develop corresponding special software or hardware to meet the measurement needs of specific user industries, and add instrument measurement functions, such as small module gear measurement, sieve calibration testing, etc.
(6)Other aspects
The ease of use of the product, adaptability to the environment and user-friendliness of the control interface are also important factors in judging the performance of the instrument. The fact that it is convenient to establish measurement tasks, formulate and produce reports, control the machine, etc. affects user acceptance of the instrument.
Long-term stability of the instrument, provision of measurement solutions, customer service response speed, delivery cycle, custom development capabilities, etc. are all important factors that influence customers in choosing image measuring instrument products.
A three-dimensional coordinate measuring instrument is an instrument that can express geometric shape, length and circumferential graduation in hexahedral space. It is also called three-dimensional coordinate measuring machine or three-dimensional measuring machine. The three-dimensional coordinate measuring instrument can also be defined as “a detector movable in three directions and capable of moving on three mutually perpendicular guide rails. This detector transmits signals in a contact or contactless manner. The movement of the three axes The measuring system (like a grating ruler) calculates each point (x, y, z) of the workpiece and measures each feature via a data processor or computer. The measuring functions of the three-dimensional coordinate measuring instrument should include dimensional accuracy, positioning accuracy, geometric accuracy and contour accuracy, etc.
The three axes of the three-dimensional coordinate measuring instrument are equipped with air source brake switches and micro-motion devices, which can realize single-axis precision transmission and adopt precision acquisition system. high performance data. It is used in precision measurement such as product design, casting equipment, gear measurement, blade measuring machine manufacturing, tooling fixtures, steam mold accessories, electronic devices, etc.
The basic structure of the three-dimensional coordinate measuring instrument
1. X-axis beam: using precision inclined beam technology.
2. Y guide rail: adopts unique overall bottom dovetail groove positioning structure directly processed on the workbench.
3. Guide rail method: A four-sided floating hydrostatic guide rail made of preloaded and self-cleaning high-precision air bearings.
4. Drive system: It adopts our high-performance DC servo motor and flexible synchronous toothed belt transmission device. Each axis has limited position and electronic control, which makes the transmission faster and the movement performance better.
5. Z axis spindle: Adjustable pneumatic balancing device improves Z axis positioning accuracy.
6. Control system: adopt special imported three-coordinate dual-computer control system.
7. Machine system: using computer-aided 3D error correction (CAA) technology to ensure the long-term stability and high precision of the system.
8. Measuring software: Use the powerful 3D-DMIS measuring software with comprehensive measuring functions and online functions.
Functional principle of three coordinate tester
In simple terms, a coordinate measuring machine has a guiding mechanism, length measuring components and a digital display device in three mutually perpendicular directions. It has a workbench that can place the workpiece (not necessarily for large and giant workpieces). the measuring head may be a measuring device that moves quickly to the measured point manually or motorized and uses a reading device and a digital display device to display the coordinate value of the measured point. It is obviously the simplest and most primitive measuring machine. With this type of measuring machine, the coordinate value of any point in the measuring volume can be displayed through the reading device and digital display device. The point collection and signaling device of the measuring machine is a measuring head equipped with a grating ruler and a reading head along the three axes X, Y and Z. The measuring process is the following: When the probe contacts the workpiece and sends a point acquisition signal, the control system collects the coordinate values of the current three-axis coordinates of the machine tool relative to the origin of the machine- tool, then the computer system processes the data.
Well-known brands of coordinate testers
1.ZEISS Zeiss
Founded in Germany in 1846, the company is the world’s leading manufacturer of optics, precision engineering and electronic observation, as well as a leading international company in the fields of optics and optoelectronics. In 1973, Zeiss successfully manufactured the world’s first CNC coordinate measuring machine, the UMM500. At the same time, Zeiss continues to develop new technologies and launch new products, and has several international patents so far. ZEISS measuring machines are widely used in many industries, including aviation, aerospace, automotive, electronics, machinery and plastics.
2.HEXAGON Hexagon
Founded in Switzerland in 1975, its probe technology is recognized in the machine tool industry. Hexagon’s measurement technology mainly includes two parts: “Large-scale measurement”, which mainly includes the measurement of mountain surveying, urban surveying and mapping, road lines, tunnels and bridges , as well as other construction projects. “Small Measurement” focuses on more precise dimensional measurement tasks and is geared toward various products supplied by the manufacturing industry, including automotive, aerospace, machine tools, military, processing and manufacturing, as well as daily consumer goods.
3.Mitutoyo Mitutoyo
A famous Japanese brand of measuring instruments, a professional supplier of global measuring solutions and measuring equipment, a global enterprise focused on measuring solutions and measuring equipment, and the leader of the entire measuring tools industry. The main products include: various items of measuring tools industry, including: micrometers, calipers, depth gauges, bore micrometers, dial gauges, lever gauges, height gauges, differential heads, gauge blocks , linear micrometers, grid rulers, roughness instrument, profile measuring instrument, microscope, hardness tester, three-dimensional measuring machine, etc.
4.Wenzel Wenze
The German WENZEL group is a pioneer in innovation in the field of metrology. Wenze’s various products offer unique solutions for multiple industries such as 3D measurement, CT scanning and high-speed optical scanning. Wenze Group’s technical solutions have a large number of applications in many sectors such as automotive, aerospace, power generation and medical. WENZEL has delivered and installed more than 10,000 measuring devices worldwide. Its subsidiaries and business partners sell products in more than 50 countries and provide after-sales services to meet customer needs.
5.NikonNikon
Nikon’s instrument division was founded in Japan in 1917. It is a world-renowned optical instrument brand and one of the first measuring machine brands to adopt industrial ceramic technology. It has a long history and is a world-renowned designer and manufacturer of optical products. has become the most famous brand in the world, firmly occupying a leading position in the optical instrument market. As the only microscope company to produce its own glass, all production activities provide meticulous quality assurance. With more than 90 years of continuous accumulation of specialized knowledge in the field of optical instruments, coupled with the company’s global mission to enhance innovation and integrity, Nikon has always been at the forefront of innovation optical and technological.
6.COORD3 Bosaï
Founded in Italy in 1973, it belongs to the American company Perceptron. It is a global leader in in-line laser measuring technology and a large multinational company dedicated to the design, manufacture and sale of coordinate measuring machines Perceptron Inc. (NASDAQ: PRCP) has was founded in 1981 in the automobile capital of the United States, Detroit, with more than 30 years of measurement experience, is the world leader in online laser measurement technology. Worldwide, more than 900 systems, 12,000 Perceptron measurement sensors and more than 3,000 Coord3 coordinate machines are in use. Headquartered in Plymouth, Michigan, USA, Perceptron operates globally with subsidiaries in Brazil, China, Czech Republic, France, Germany, India, Italy, Japan, Singapore, Spain and in the United Kingdom.
7.Acretech Tokyo Precision
Tose Precision Equipment (Shanghai) Co., Ltd., as a business link of Japanese company Tokyo Precision in China, is responsible for the sales and after-sales service of all products manufactured by Tokyo Precision in China. The Company’s products mainly consist of two parts: measurement and testing equipment and semiconductor manufacturing equipment. Measuring and testing equipment products are mainly used in automobile spare parts, aerospace and other precision machining industries. Semiconductor manufacturing equipment is used in the chip manufacturing, testing and packaging industries.
8.FARO
Originating in the United States and a top ten measuring instrument brand, FARO is the world’s most trusted provider of 3D measurement, imaging and realization technologies. Mainly engaged in the development and sales of computer-aided measurement equipment and software. The company develops and delivers cutting-edge 3D data acquisition, 3D measurement and analysis solutions to a wide range of industries, including manufacturing, construction, engineering and public safety.
9.AEH Edward
Edwards is a large industrial measurement group headquartered in Germany, with R&D and production bases in China, Germany and France, spread across the Eurasian continent. Xi’an Edward Measurement Equipment Co., Ltd. is one of the earliest intelligent enterprises in China engaged in the research and development, production and sales of three-dimensional measuring equipment and continues to promote technological innovation and growth. Since its establishment in 1997, Edward has viewed technological R&D and innovation as the foundation of business survival and the source of growth. With strong technological innovation capabilities, Edward combines advanced design concepts, scientific product manufacturing models, powerful software functions and network technology, and is committed to providing users with professional, efficient measurement solutions. and intelligent.
Daguang focuses on providing solutions such as precision CNC machining services (3-axis, 4-axis, 5-axis machining), CNC milling, 3D printing and rapid prototyping services.
