What are the tools (instruments) for measuring smaller lengths?

Length measuring tool Length measuring tool refers to a tool that compares the measured length with the known length to obtain the measurement result, which is called measuring tool for short. Length measuring tools include gauges, measuring tools and gauges. Traditionally, measuring tools that cannot indicate the magnitude are called gauges; A measuring tool that can represent numerical values and is used in hands is called a measuring tool; A measuring tool that can indicate size is called a meter.

Some mechanical measuring tools, such as square and caliper, were first used in mechanical manufacturing. /kloc-in the 0/6th century, smooth gauges have been used in gun manufacturing; In 1772 and 1805, Watt and Modsley et al. Britain has successively produced Watt micrometer and measuring machine which uses the principle of screw pair to calibrate the length. /kloc-After the mid-9th century, measuring tools similar to modern mechanical micrometer and vernier caliper appeared. At the end of19th century, a complete set of measuring blocks appeared.

After mechanical measuring tools, there are some optical measuring tools. At the end of 19, the vertical length measuring instrument first appeared; At the beginning of the 20th century, the length measuring machine appeared. By the 1920s, projectors, tool microscopes and optical micrometers had been used in machinery manufacturing. Pneumatic measuring instrument appeared in 1928, which is a measuring tool suitable for mass production.

Electrical measuring tools appeared in the 1930s. Firstly, the limit gauge and profiler made of inductive length sensor are used. At the end of 1950s, a coordinate measuring machine with digital display of measurement results appeared. In the mid-1960 s, coordinate measuring machines with computer-aided measurement were applied to machinery manufacturing; In the early 1970s, the gear measuring instrument controlled by computer appeared again. At this time, the measuring tool has entered the stage of applying electronic computer.

Measuring tools are usually divided into general measuring tools, special measuring tools and special measuring tools according to their uses. According to the working principle, it can be divided into mechanical, optical, pneumatic, electric and photoelectric. This classification method is formed by the development history of measuring tools. Many modern measuring tools have developed into measuring tools that combine the principles of precision machinery, optics and electricity with computer technology. Therefore, this classification method is only suitable for measuring tools with single working principle.

Universal measuring tool refers to a measuring tool that can measure the length or angle of various types of workpieces. This kind of measuring tools have the most varieties and specifications, and are widely used, including measuring blocks, angle measuring blocks, polygonal prisms, sine gauges, caliper micrometers, dial indicators, multi-tooth indexing tables, comparators, laser interferometers, tool microscopes, coordinate measuring machines and so on.

Special measuring tools refer to measuring tools used to measure some geometric parameters, shapes and position errors. There are mainly straightness and flatness measuring tools, such as straightedge, spirit level, flat crystal level, autocollimator and so on. Surface roughness measuring tools, such as surface roughness sample block, light cutting microscope, interference microscope, surface roughness measuring instrument, etc. Roundness and cylindricity measuring tools, such as roundness instrument and cylindricity measuring instrument; Gear measuring tools, such as gear comprehensive inspection instrument, involute measuring instrument, pitch measuring instrument, lead instrument, etc. Thread measuring tools, etc.

Special measuring tools refer to measuring tools that are only suitable for measuring the size, surface roughness, shape and position errors of specific workpieces. There are common automatic inspection machines, automatic sorting machines, single-size and multi-size inspection devices, etc.

The structure of the length measuring tool mainly includes known length, positioning and aiming, amplification and subdivision, display and recording, etc. The gauge basically has only a part of known length. In some measuring tools and instruments, these parts are not completely separated, and some amplification, subdivision and display are actually one part, such as dial gauge; Some parts, such as aiming, magnifying, subdividing and displaying, are one part, such as reading microscope.

The positioning and aiming part is a mechanism used to determine the relative position of the measured length and the known length, so that the two can be compared correctly and accurate values can be obtained. There are two ways of positioning and aiming: contact and non-contact.

The magnifying subdivision part is a mechanism that magnifies and subdivides the smallest unit length in the known length, so that it can accurately distinguish the tiny difference between the known length and the measured length, mainly including mechanical, optical, pneumatic, electrical and photoelectric.

The display and recording part is the mechanism to display and record the measurement results. Common display and recording methods include scale indication, recording display, digital display and image display.

When designing measuring tools, Abbe principle should be observed as much as possible. It was put forward by German Abbe in the 65438+60s. He believes that in length measurement, the measured length should be located on the extension line of the center line of the line ruler. In the measuring tool designed according to this principle, the measurement error caused by the straightness error of the guide rail is a second-order error, which can generally be ignored, so that accurate measurement results can be obtained.

In the design of measuring tools, the Ebenstein parallel optical system can also be used to compensate the measuring error caused by the guide rail error, or the electronic computer can automatically correct the measuring error caused by the guide rail error and the incorrect positioning of the measured length. Besides Abbe's principle, the shortest measuring chain principle and unified base plane principle should also be considered in design.

Measuring tools must be qualified according to the verification regulations before they can be used. Generally, the length standard is used for verification, such as measuring micrometer and caliper with block gauge; Use standard line ruler to verify length gauge and length measuring machine, etc.

Compare two or more measuring tools with the same accuracy level to determine their accuracy. This method is suitable for evaluating some high-precision measuring tools, such as laser interferometer and laser interferometer length measuring instrument, because there is no suitable length standard for the verification of such high-precision measuring tools.