What is the function of the encoder on the CNC lathe

It is a rotary sensor that converts rotational displacement into a series of digital pulse signals. These pulses can be used to control angular displacement. If the encoder is combined with a gear rack or screw screw, it can also be used to measure linear displacement.

The photoelectric encoder is a sensor that converts the mechanical geometric displacement on the output shaft into a pulse or a digital amount through photoelectric conversion. It is composed of a grating disc and a photoelectric detection device. The grating disk is a circular plate with a certain diameter that opens several rectangular holes separately.

Since the photoelectric encoder is coaxial with the motor, when the motor rotates, the grating plate rotates at the same speed as the motor, and a detection device composed of electronic components such as light-emitting diodes detects and outputs several pulse signals. By calculating the number of pulses output by the photoelectric encoder per second It can reflect the current speed of the motor.

In addition, in order to judge the rotation direction, the code disc can also provide two pulse signals with a phase difference of 90º. According to the detection principle, the encoder can be divided into optical, magnetic, inductive and capacitive. According to its scale and signal output form, it can be divided into three types: incremental type, type and hybrid type.

The function of the encoder on the CNC lathe is to logically process the program specified by the control code or other symbolic instructions, and decode it, so as to make the machine tool move and process the parts.

The encoder consists of a photoelectric code disc with a shaft in the center, on which there are ring-shaped and dark scribe lines, read by photoelectric emitting and receiving devices, and obtain four groups of sine wave signals combined into A, B, C, D, each The sine wave has a phase difference of 90 degrees (360 degrees relative to one cycle), reverse the C and D signals and superimpose them on the A and B phases to enhance the stable signal; in addition, a Z-phase pulse is output for each revolution to represent zero Bit reference bit.

Since the phase A and B differ by 90 degrees, the forward rotation and reverse rotation of the encoder can be judged by comparing the phase A or phase B before, and the zero reference position of the encoder can be obtained through the zero pulse.

The material of the encoder code disc is glass, metal, plastic. The glass code disc is a thin engraved line deposited on the glass, which has good thermal stability and high precision. However, due to the certain thickness of metal, the accuracy is limited, and its thermal stability is an order of magnitude worse than that of glass. The plastic code disc is economical and its cost is low, but its accuracy, thermal stability, and life are worse. .

Resolution - The number of pass or dark lines provided by the encoder per 360 degrees of rotation is called resolution, also called resolution division, or directly called how many lines, generally 5 to 10,000 lines per rotation.

Briefly describe the spindle control principle of CNC lathes The spindle performance of CNC machine tools is continuously adjustable in a wide range of speed and a wide range of constant power.

When the machine tool is required to have functions such as thread processing, accurate stop and constant surface speed processing, it is necessary to control the feed and position of the spindle. At this time, the spindle drive system can also be called a spindle servo system, and the spindle motor is equipped with an encoder or an external encoder is installed on the spindle to detect the spindle position. At present, there are two main forms of spindle drive speed change: one is that the spindle motor has gear shifting, the purpose is to reduce the spindle speed and increase the transmission ratio to meet the needs of cutting; the other is that the spindle motor drives the spindle through a synchronous toothed belt or a v-belt. , This type of spindle motor is also called wide-range motor or strong cutting motor, and has the characteristics of constant power and wide range. Since there is no need for mechanical shifting, gears and clutches are eliminated in the headstock, and the headstock actually becomes the main shaft bracket, which simplifies the main drive system and improves the reliability of the drive chain. Because the AC drive system maintains the advantages of the DC drive system, and the AC motor does not require maintenance, is easy to manufacture, and is not affected by harsh environments, the current DC drive system has been replaced by the AC drive system. In the early days, the analog AC servo system was used, and now the mainstream of the servo system is the digital AC servo system. The AC servo drive system is moving towards digitalization. The feedback control of the current loop and speed loop in the drive system has been fully digitalized. The control model and dynamic compensation of the system are processed in real time by high-speed microprocessors, which enhances the system's self-diagnosis capability and improves the system's performance. Speed and precision.

1. The large and medium-sized CNC machine tools with main transmission gears adopt this speed change method. By reducing the speed of a few pairs of gears, the output torque is expanded to meet the requirements of the output torque characteristics at low speed of the main shaft

2. The main drive through the belt drive is mainly used in machine tools with high speed and small speed change range. The speed regulation of the motor itself can meet the requirements, which can avoid vibration and noise caused by gear transmission

3. Use two motors to drive the main shaft respectively. The hybrid transmission of the above two methods, the pulley directly drives the main shaft at high speed, and the other motor drives the main shaft after deceleration through gears at low speed. It can effectively improve the rigidity of the spindle components, but the output torque of the spindle is small, and the heating of the motor has a great influence on the spindle. The electrical simulation of the spindle is given by the CNC to give an analog voltage of 0---+10V to control the stepless speed regulation of the inverter. . The servo spindle is controlled by the CNC to control the spindle drive by issuing the speed command to realize the speed or position control. It is not a spindle with stepless speed regulation, and the M code is issued by the CNC to control the spindle motor, and the clutch or gear shifting