Views: 0 Author: Site Editor Publish Time: 2022-08-19 Origin: Site
A roundness tester is a precision instrument for measuring the out-of-roundness of a rotating surface (shaft, hole or spherical surface) of a part. There are usually two types:
Small desktop, the workpiece is mounted on the rotary table, and the measuring head is mounted on the fixed column.
Large floor type, the workpiece is mounted on a fixed worktable, and the measuring head is mounted on the rotating spindle.
During measurement, the measuring head is in contact with the surface of the workpiece, and the rotary part of the instrument (table or spindle) rotates once. Due to the extremely high precision of the support bearing of the rotating part, the measuring head will produce a high-precision circular trajectory on the surface to be measured when rotating.
The out-of-roundness of the surface to be measured causes the measuring head to shift, which is converted into an electrical (or gas) signal, which can be automatically recorded on the circular recording paper after being amplified, and the out-of-roundness of each part can be directly read out for evaluating the accuracy and process analysis.
It’s widely used in precision bearings, machine tools and instrument manufacturing industries.
Roundness measurement includes rotary axis method, three-point method, two-point method, projection method and coordinate method.
1. Rotary axis method
By comparing the circular trajectory (ideal circle) formed by the shaft in the precision shaft system with one rotation with the measured circle, the difference between the radii of the two circles of the roundness meter is converted into an electrical signal by the electrical length sensor, which is processed by the circuit and the electronic computer. After the calculation, the roundness error is indicated by the display instrument, or the measured circle outline graph is recorded by the recorder.
The rotary axis method has two forms: sensor rotation and table rotation. The former is suitable for high-precision roundness measurement, while the latter is often used to measure small workpieces. The roundness measuring tool designed according to the rotary axis method is called a roundness meter.
2. Three point method
The workpiece to be measured is often placed in a V-shaped block for measurement. When measuring, make the workpiece to be tested rotate in the V-shaped block for one week, read the value max and min value from the micrometer, and the half of the difference between the two displayed values is the roundness error of the outer circle of the tested workpiece. This method is suitable for measuring the outer or inner circle with odd-numbered edge shape errors. Two V-shaped blocks with two angles of 90°, 120° or 72° and 108° are commonly used to measure respectively.
3. Two-point method
Commonly used micrometers, comparators and other measurements, take half of the difference max between the diameters of a certain section of the measured circle as the roundness error of this section. This method is suitable for measuring outer or inner circles with even-numbered edge shape errors.
4. Projection method
It is often measured in a projector, and the contour image of the measured circle is compared with the two extreme concentric circles drawn on the projection screen, so as to obtain the roundness error of the measured part. This method is suitable for measuring small workpieces with edge-shaped edges.
5. Coordinate method
It is generally measured on a three-coordinate measuring machine with an electronic computer. According to the pre-selected rectangular coordinate system, the coordinate values of several points on the measured circle are measured, and the roundness error of the measured circle is calculated by the electronic computer according to the selected error evaluation method.
The roundness meter adopts the radius measurement method and works in a rotary type. The rotating shaft system of the roundness meter adopts a high-precision air-floating spindle as the measurement reference. The electrical part of the roundness meter is composed of an advanced computer, a precision circular grating sensor, and a precision inductive displacement sensor. The circular grating sensor and the precision inductive displacement sensor measure the angle and radial displacement to ensure the accuracy of measuring the angular displacement and radial value of the workpiece. .
The roundness measurement software adopts the roundness measurement software based on the Chinese version of the WinXP operating system platform to complete data acquisition, processing and measurement data management.
