Absolute encoder

Absolute encoders are similar in overall structure to incremental ones, both consisting of five parts: photoelectric code disk, light source, lens, light-receiving element and signal conversion circuit. However, the specific code disk structure and the meaning of the output signal are different. The code disk of an absolute encoder has many coil grooves, which are called code channels. The number and length of the grooves inside each code channel are different. Together, they form a binary code, with one barcode channel corresponding to one bit of the binary number. Usually, the outermost channel of the code disk represents the least significant bit, and the innermost channel represents the most significant bit. The number of code channels determines the number of bits in binary encoding. If an absolute encoder has N code channels, it can output N binary digits, and the total number of binary digits output is 2 times N. These binary numbers are fixed to the mechanical position of the rotating shaft and have nothing to do with external factors of the encoder, so they are called absolute encoders. After the receiving device is powered off and restarted, the absolute encoder does not need to search for the reference zero point.

Principle: When the code disk is at different positions (angles), the photosensitive element converts the corresponding level signal according to whether it is exposed to light or not, and finally converts it into a binary number for output.

Absolute encoders are further classified into single-turn absolute encoders and multi-turn absolute encoders. The two examples mentioned above are both for single-turn, that is, within 360°. When the code disk rotates more than 360°, the output code will be repeated, which does not meet the requirement of data uniqueness for absolute encoders. Therefore, multi-turn absolute encoders emerged. The range of multi-turn absolute encoders can exceed 360°, and usually by a large margin. Their internal structure is also more complex than that of single-turn ones, but the basic principle is the same.

To measure rotation exceeding 360 degrees, multi-turn absolute value encoders are used. The production of encoders applies the mechanical principle of clock gears. When the central code disk rotates, it drives another set of code disks (or multiple sets of gears and code disks) through gear transmission. On the basis of single-turn encoding, the encoding of the number of turns is added to expand the measurement range of the encoder. Such an absolute encoder is called a multi-turn absolute encoder. It is also determined by mechanical position for encoding, and the encoding at each position does not repeat without the need for memory.

Another advantage of multi-turn encoders is that due to their large measurement range, there is often a considerable surplus in use. Therefore, during installation, there is no need to struggle to find the zero point; a certain intermediate position can be used as the starting point, which greatly simplifies the difficulty of installation and debugging.