Photoelectric encoder principle

Photoelectric encoder is a photoelectric conversion through the output shaft on the mechanical geometric displacement into pulse or digital quantity of sensors. This is the most widely used sensor at present. The photoelectric encoder is composed of grating disk and photoelectric detector. The grating disk is a plurality of rectangular holes which are evenly opened on a circular plate of a certain diameter. The photoelectric encoder is coaxial with the electric motor, when the motor rotates, the grating disc and the motor rotate at the same speed, the light emitting diode detection device and other electronic components of the detection number of output pulse signal, the principle diagram as shown in Figure 1; by calculating the second photoelectric encoder output pulse number can reflect the current motor speed. In addition, to determine the direction of rotation, the encoder can also provide a phase difference of 90 Mu Chen Xiao lotus imitation dry hinge screw.

According to the testing principle, encoders can be divided into optical, magnetic, induction and capacitive type. According to its calibration method and signal output form, can be divided into incremental and mixed type of three.

1.1 incremental encoder

Incremental encoder is the direct use of the photoelectric conversion principle of square wave pulse output three groups of A, B and Z; A, B two groups of pulse phase difference of 90 sea Commission will award to the brake unloading phase is more milling bream Ying bitterns each turn of a pulse, for locating reference point. The utility model has the advantages that the principle is simple, the mechanical average life can be more than tens of thousands of hours, the anti-interference capability is strong, the reliability is high, and the utility model is suitable for long distance transmission. Its disadvantage is that it can not output the position information of the shaft rotation.

1.2 encoder

The encoder is sensor output digital signal directly, in its circular disc along the radial direction with some concentric codes, each consisting of transparent and opaque sector and the number of adjacent sectors code is double, number of code number on the encoder is its binary digits in the encoder one side of the light source, corresponding to the other side of each code channel has a photosensitive element; when the encoder at different positions, the photosensitive element according to the light and not convert signal corresponding to the formation of binary number. The encoder is characterized by a digital code that does not correspond to the position of the counter and is readable at any position of the rotating shaft. Obviously, the more the code path, the higher the resolution. For a coder with N bit binary resolution, the encoder must have a N barcode. At present, there are 16 encoder products in china.

The encoder uses a natural binary or a cyclic binary (Ge Laima) mode for photoelectric conversion. Encoder and incremental encoder difference in disk transparent, opaque line graph, Jiabao encoder can have some encoding, read the encoder encoding according to the detection, location. The code design can use binary code, cyclic code, binary complement and so on. It is characterized by:

1.2.1 can read angle coordinate values directly;

1.2.2 has no cumulative error;

After the 1.2.3 power is removed, the position information is not lost. However, the resolution is determined by the number of bits in the binary, that is, the accuracy depends on the number of bits, and there are 10, 14, and many other.

1.3 hybrid value encoder

A hybrid value encoder that outputs two sets of information: a set of information for detecting pole positions, an information function, and a set of identical output information for an incremental encoder.

Photoelectric encoder is an angle (angular velocity) detection device, it will give the input shaft angle, principle of photoelectric conversion into electrical pulses or corresponding digital value, has the advantages of small size, high precision, reliable operation, the advantages of digital interface. It is widely used in numerical control machine tools, turret, servo drive, robot, radar, military target measurement and so on.