The principle of photoelectric encoder

Photoelectric encoder, it is a kind of through the photoelectric conversion of the output shaft mechanical geometry convert pulse or digital displacement sensor, is the most used sensors. General photoelectric encoder is mainly composed of grating plate and photoelectric detection device. In a servo system, the light code disc coaxial and motor, motor rotates, grating plate with motor rotate speed. The light emitting diode detecting device in the output of electronic components, such as a number of pulse signal, its principle as shown. By calculating the number of photoelectric encoder output pulse per second can reflect current of motor speed. In addition, to judge the direction of rotation, the encoder can also provide the phase difference of 90 ° 2 channel optical code output, according to the change of state two-way light code to determine motor. According to the principle of detection, can be divided into optical encoder type, magnetic type, inductive and capacitive. According to the calibration method and the mode of its output signal, can be divided into incremental and absolute type and hybrid 3 kinds.

Principle of the encoder

Photoelectric encoder, it is a kind of through the photoelectric conversion of the output shaft mechanical geometry convert pulse or digital displacement sensor. This is the most used sensors and photoelectric encoder is composed of grating plate and photoelectric detection device. Grating plate is in a certain diameter of circular plate on equal to open a number of rectangular hole. By coaxial light code disc and motor, motor rotates, grating plate with motor rotate speed, the light emitting diode detecting device in the output of electronic components, such as a number of pulse signal, its principle diagram is shown in figure 1; By calculating the number of photoelectric encoder output pulse per second can reflect current of motor speed.

1.1 the incremental encoder

Incremental encoder is directly using the principle of photoelectric conversion output three square wave pulse phase A, B and Z; A, B two groups of pulse phase difference 90 workers the evil spirit award ash Gu discharge milling is put more novelty 鳽 phase for each turn A pulse, for reference point positioning. It has the advantage of simple principle structure, mechanical life expectancy can be in the tens of thousands of hours, strong anti-jamming capability, high reliability, suitable for long distance transport. The downside is unable to output shaft rotation absolute position information.

1.2 absolute encoder

Absolute encoder is direct digital output of the sensor, on its round encoder, several concentric yards along the radial direction, each consisting of pervious to light and opaque and sector, relationship between adjacent code number of sectors is double, the code number on the encoder is the binary digital digits, in the side of the encoder is a light source, the other side corresponding to every yard a photosensitive element; When the encoder is in different position, the photosensitive element according to the light or not proper level signal conversion, form a binary number. The characteristics of the encoder is not counter, in any position of the rotor can be read out a fixed position and corresponding digital code. Obviously, the more code word, the higher the resolution, has N bit binary for a resolution of the encoder, the encoder must have N barcode. The current domestic existing 16-bit absolute encoder products.

Absolute encoder are using natural binary or circulation binary (gray code) way of photoelectric conversion. Absolute encoder and incremental encoder differed from the disk in pervious to light, opaque line graphics, absolute encoder can have several coding, according to read the code on the encoder, absolute position detection. The design of the code can use binary code, cyclic code, two's complement, etc. Its features are:

1.2.1 can directly read out the absolute value of the Angle coordinate;

1.2.2 no cumulative error;

1.2.3 power source location information will not be lost after resection. But the resolution is determined by the binary digits, i.e. accuracy depends on the figures, there are 10 and 14, etc.

1.3 hybrid absolute value encoder

Hybrid absolute encoder, it outputs two sets of information: a set of information to detect magnetic pole position, with absolute information function; Another group with completely incremental encoder output information.

Photoelectric encoder is a kind of Angle detection device (angular velocity), it will be input to the shaft Angle, using the principle of photoelectric conversion into corresponding electrical pulses or digital quantity, has small volume, high accuracy, reliable operation, the advantages of digital interface. It is widely used in CNC machine tools, rotary table, servo drive and determination of robot, radar, military, etc need to detect Angle of plant and equipment.