Introduction to the expansion of multi-turn absolute encoder

Eltra eltra multi-turn absolute encoder has mechanical gear set absolute lap counting and electronic incremental lap counting, etc. The internal mechanical gear set rotates absolute lap counting, no matter the position of each lap is absolute, and the number of laps is also absolute. The value is called the absolute value really multi-cycle. It is similar to a clock. With 60 minutes, the internal gear meter has a position at 1 o'clock, so that it can have a range of 12 hours X 60 minutes. However, in this case, the number of turns has a range (12 hours), such as 4096 turns and 65536 turns in the current multi-turn encoder. In this way, some people have suggested that exceeding the number of turns is not absolute? It is of course absolute that it does not exceed the number of laps in one processing, or does not exceed the number of ½ laps in power failure.

Electronic incremental lap counting, memory laps through the battery, in fact, single lap absolute, multi-lap increments, the advantage is that a set of mechanical gears are omitted, economical, small in size and no lap limit, it seems to be good, but it After all, it is multi-turn increments and cannot be regarded as the absolute value in the true sense. What is the absolute value in the true sense? It does not rely on the direct reading of the previous history. After a power failure, due to the low power consumption requirements of the battery, the speed and range of movement are actually limited. In addition, the factor of the battery is still doubtful in terms of reliability, such as leakage loops in high speeds and interference. Wrong circle, jitter wrong circle exactly at 12 o'clock, wrong circle of battery failure. Especially if you make a mistake in lap counting, you cannot find the original absolute position.

In fact, many people understand that the absolute value is a problem of moving after a power failure, but they don’t understand the real intention of the Germans using the absolute value of the mechanical real multi-turn in the motion control, because the real absolute value does not depend on the previous history. In high speed, you don’t have to worry about losing data. In motion control, you don’t need to keep reading the encoder value. Coupled with EnDat and other fast communication, you can save a lot of time to complete. Other calculations can solve the problems of high-speed synchronization and multi-axis linkage.

In addition, as mentioned above, the absolute value of the mechanical multi-turn, the movable position after a power failure is 1/2 turn, for example, 2048 turns out of 4096 turns instead of 4096 turns, because the movement after a power failure may be forward or reverse Considering the uniqueness of the absolute value, the movable position is actually 2048 circles.

　　Multi-turn absolute encoder signal output has parallel output, serial output, bus type output, transmission integrated output

1. Parallel output:

The output of the multi-turn absolute encoder is multi-digit digital (Gray code or pure binary code). Parallel output means that there are multiple high and low level outputs on the interface to represent digital 1 or 0. For absolute numbers with low digits Encoders generally output digital directly in this form, and can directly enter the I/O interface of the PLC or upper computer, the output is instant, and the connection is simple.

　　 But parallel output has the following problems:

　　1) It must be a Gray code, because if it is a pure binary code, there may be multiple bit changes when the data is refreshed, and the reading will cause a code error in a short time.

　　2) All interfaces must be properly connected, because if there is a poor connection point, the potential of this point is always 0, which causes an error code and cannot be judged.

　　3) The transmission distance cannot be far, generally one or two meters. For complex environments, isolation is best. 4) For a large number of digits, many core cables are required, and good connections must be ensured, which brings engineering difficulties. Similarly, for encoders, there must be many node outputs at the same time, which increases the failure rate of the encoder.

2. Serial SSI output:

　　Serial output is through an appointment, there is a sequential data output in time, this agreement is called a communication protocol, the physical form of its connection is RS232, RS422 (TTL), RS485, etc. Since the good manufacturers of multi-turn absolute encoders are all in Germany, most of the serial output is matched with Siemens in Germany, such as SSI synchronous serial output.

　　SSI interface (RS422 mode), connected by two data lines and two clock lines, the receiving device sends interrupted clock pulses to the encoder, and the absolute position value is output to the receiving device by the encoder and the clock pulse in synchronization. Triggered by the clock signal sent by the receiving device, the encoder starts outputting a serial signal synchronized with the clock signal from the high bit (MSB).

　　 The serial output connection line is few, the transmission distance is long, the protection and reliability of the encoder are greatly improved.

　　 Generally, high-digit absolute encoders use serial output.

　　3. Fieldbus type output:

　　 Fieldbus type encoder is that multiple encoders are connected together with a pair of signal wires. By setting the address, the signal is transmitted by communication. The signal receiving device only needs one interface to read multiple encoder signals. The bus-type encoder can save connection cables and receiving device interfaces, and has a long transmission distance. In the case of centralized control of multiple encoders, it can also greatly save costs.