Analysis of the design and application of sensors on CNC machine tools

Due to the characteristics of high precision, high speed, high efficiency, safety and reliability, CNC machine tools are rapidly becoming popular in enterprises in the upgrading of manufacturing technology equipment. CNC machine tools are automated machine tools with a program control system that can operate and machine parts based on programmed programs. It combines the latest technologies in machinery, automation, computer, measurement, microelectronics, etc., using a variety of sensors. This article describes the application of various sensors on CNC machine tools.

2 Introduction to the sensor

A sensor is a device or device that can sense a specified measurement and convert it into an available output signal according to a certain rule. The input signal (measured) is often non-electrical, and the output signal is often a power that is easy to handle, such as voltage.

There are many types of sensors, different classification standards, and different methods. Commonly used are resistance sensors, inductive sensors, capacitive sensors, temperature sensors, piezoelectric sensors, Hall sensors, thermocouple sensors, photoelectric sensors, digital Position sensor, etc. The sensors applied on CNC machine tools mainly include photoelectric encoders, linear encoders, proximity switches, temperature sensors, Hall sensors, current sensors, voltage sensors, pressure sensors, liquid level sensors, resolvers, inductosyns, speed sensors, etc. Mainly used to detect position, linear displacement and angular displacement, speed, pressure, temperature, etc.

3 CNC machine tool requirements for sensors

(1) High reliability and strong anti-interference;

(2) meet the requirements of accuracy and speed;

(3) Easy to use and maintain, suitable for machine tool operating environment;

(4) Low cost.

Different types of CNC machine tools have different requirements for sensors. Generally speaking, large machine tools require high speed response, and medium and high precision CNC machine tools are mainly required.

4 displacement detection

The sensors for displacement detection mainly include pulse encoders, linear gratings, resolvers, and inductosyns.

4.1 Application of pulse encoder

A pulse encoder is an angular displacement (speed) sensor that turns a mechanical angle into an electrical pulse. Pulse encoders can be divided into three types: photoelectric, contact and electromagnetic. Among them, photoelectric applications are More.

In Fig. 1, the X-axis and Z-axis ends are respectively equipped with photoelectric encoders for angular displacement measurement and digital speed measurement, and the angular displacement can indirectly reflect the linear displacement of the carriage or the tool holder through the screw pitch.

4.2 Application of linear grating

Linear grating is made by the phenomenon of transmission and reflection of light. It is often used for displacement measurement. The resolution is higher, the measurement accuracy is higher than that of photoelectric encoder, and it is suitable for dynamic measurement.

In the feed drive, the scale is fixed on the bed, and the pulse signal generated directly reflects the actual position of the carriage. The servo system that uses the grating to detect the position of the table is a full closed loop control system.

4.3 Application of resolver

A resolver is an inductive micromotor with a continuous relationship between output voltage and angular displacement. The resolver consists of a stator and a rotor. Specifically, it consists of a core, two stator windings and two rotor windings. The primary and secondary windings are placed on the stator and rotor respectively, and the electromagnetic coupling between the primary and secondary windings. The degree is related to the angle of rotation of the rotor.

4.4 Application of Inductive Synchronizer

Inductive synchronizers are made using the principle that the mutual inductance of two planar windings varies with position. Its function is to convert the angular or linear displacement into the phase or amplitude of the induced electromotive force, which can be used to measure the linear or angular displacement. According to its structure, it can be divided into two types: linear and rotary. The linear induction synchronizer consists of a fixed length and a slider. The fixed length is mounted on the machine bed. The slide is mounted on the moving part and moves with the table. The rotary induction synchronizer stator is a fixed disc, and the rotor For rotating discs. The inductive synchronizer has the advantages of high precision and resolution, strong anti-interference ability, long service life, simple maintenance, long-distance displacement measurement, good processability and low cost. Linear induction synchronizers are widely used in large displacement static and dynamic measurement, such as three-coordinate measuring machine, program-controlled CNC machine tool, high-precision heavy-duty machine tool and machining center measuring device. Rotary Inductosyn is widely used in turntables for machine tools and instruments as well as in various rotary servo control systems.