What are the types of commonly used position detection devices for CNC machine tools?
The detection device in CNC system is divided into three types: Displacement, speed and current. According to the installation position and coupling right type, it is divided into direct measurement and indirect measurement; according to measurement method, it is divided into incremental measurement and absolute measurement; According to the motion mode, the detection devices are divided into rotary type and linear type, and the prototype of signal conversion can be divided into photoelectric effect, grating effect, electromagnetic induction principle, voltage effect, resistance effect and magnetoresistance effect, etc. . CNC machine tools used in the position detection device is basically divided into linear and rotary two categories. The linear position detection device is used to detect the linear displacement of the moving parts, and the rotary position detection device is used to detect the rotational displacement of the rotating parts.
(1) digital and analog detection. From the type of detection signal, detection elements can be divided into digital and analog. The same kind of detection element can be made either digital or analog, depending on the way of use and the measuring circuit. The so-called digital refers to the mechanical displacement into digital pulse measuring device, and analog refers to the mechanical displacement into voltage amplitude or phase measuring device.
(2) incremental and absolute detection. From the way of measurement, detection elements can be divided into incremental and absolute. Incremental Detection is the relative displacement, that is, the displacement of the incremental value, the distance of the table is measured by counting the signal given. Therefore, it is often given a fixed reference point on CNC machine tools, and the incremental detection element is to reflect the relative incremental value of the reference point. The incremental device is relatively simple and widely used.
Absolute detection is the absolute position of the displacement, each measured point has a corresponding signal as the measurement value. There is no accumulated error in the detection, and the position information is not lost once the power is cut off, but the structure is complex.
(3) Rotary and linear. On the detection element itself can be divided into rotary type and linear type. The rotary type is also called indirect detection, because the linear displacement of the machine tool table has a fixed proportion relationship with the rotation angle of the driving motor, therefore, the displacement of the table can be indirectly measured by detecting the rotation angle of the driving motor, the position detection system is a semi-closed-loop control system. The rotary type has no limitation of detection length and is convenient and reliable to use. But the measurement accuracy is a little lower when the linear motion is added into the error of the transmission chain.
Linear type is also called direct detection, that is, direct detection is used for the straight line movement of the machine tool worktable, which directly reflects its displacement, and its position detection system is a full closed-loop control system. For large CNC machine tools, subject to certain restrictions, often used in the precision requirements of small and medium CNC machine tools.
