The measurement accuracy depends on the accuracy of the detection element and the machine tool feed transmission chain. CNC machining accuracy of closed loop CNC machine tools is largely determined by the accuracy of position detection devices. CNC machine tools have very strict requirements for position detection elements, and the resolution is usually 0.001~0.01 mm or less.
1. Requirements of feed servo system for position measuring device
The feed servo system has high requirements for the position measuring device:
1) It is less affected by temperature and humidity, works reliably, has good accuracy retention and strong anti-interference ability.
2) It can meet the requirements of precision, speed and measurement range.
3) It is easy to use and maintain and adapt to the working environment of the machine tool.
4) Low cost.
5) It is easy to realize high-speed dynamic measurement and processing and automation.
Position detection devices can be divided into different categories according to different classification methods. CNC machining can be classified into digital and analog according to the form of output signal; It can be classified into incremental and absolute according to the type of measuring base point; According to the motion form of position measuring elements, they can be classified into rotary type and linear type.
CNC machining
2. Diagnosis and troubleshooting of detection device
The failure probability of the detection element is relatively high compared with that of the numerical control device, and the phenomena of cable damage, element contamination, collision and deformation often occur. If it is suspected that the fault is caused by the detection element, first check whether the wireless cable is broken, dirty, deformed, etc. You can also determine the quality of the detection element by measuring its output, which requires that you must master the working principle and output signal of the CNC processing detection element. The following is an example of SIEMENS system.
(1) Output signal. Connection between SIEMENS CNC system position control module and position detection device.
The output signal of incremental rotary measuring device or linear device has two forms: the first is voltage or current sinusoidal signal, where EXE is pulse shaping interpolator; The second is TTL level signal. Take HEIDENHA1N sinusoidal current output grating ruler as an example. The grating consists of grating ruler, pulse shaping interpolator (EXE), cable and connector.
During CNC machining movement, the machine tool outputs three groups of signals from the scanning unit: two groups of incremental signals are generated by four photocells, and two photocells with a difference of 180 ° are connected together. Their push-pull forms a phase difference of 90 ° and an amplitude of 11 μ Two groups of Ie1 and Ie2 at the left and right sides of A are approximate sine waves. A group of reference signals are also connected by two photocells with a difference of 180 ° into a push-pull form. The output is a spike signal Ie0, with an effective component of about 5.5 μ A. This signal is generated only when passing the reference mark. The so-called reference mark is that a magnet is installed on the housing of the grating ruler and a reed tube is installed on the scanning unit. When approaching the magnet, the reed tube is connected and the reference signal can be output.
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