As for the positioning problem in industrial control, proximity switch, photoelectric switch and other devices are generally adopted. With the continuous development of industrial control, rotary encoder has appeared. Its characteristics are:
1. Informatization: in addition to positioning, the control room can also know its specific location;
2. Flexibility: positioning can be flexibly adjusted in the control room;
3. Convenient installation and safety, long service life.
A rotary encoder can measure distances from several microns to tens of hundreds of meters. Multiple work position, as long as chooses a rotary encoder, can avoid to use the more close to switches, photoelectric switch, solve the mechanical installation trouble, are easy to be damaged and by high temperature, moisture and other issues.
Because of the optical code disk, no mechanical loss, as long as the installation position is accurate, its service life is often very long.
4. Multi-function: in addition to positioning, it can also transmit the current position far away from the current position, and the conversion speed is very important for the application of frequency converter and stepper motor.
5. Economization: for multiple control stations, only one rotary encoder is required, and the cost of installation, maintenance and loss is reduced, and the service life is increased.
In view of the above advantages, rotary encoder has been widely used in various industrial control situations.
Encoder is a device that converts physical signals into signals that can be used for communication, transmission, and storage. A detecting element applied to a speed control or position control system.
An encoder is a device for converting angular displacement or linear displacement into electrical signals. The former becomes a code disk, the latter a yardstick.
A rotary encoder is a device for measuring speed. It is divided into single output and dual output. The technical parameters mainly include each pulse number (dozens to thousands of each), and the power supply voltage, and so on. Single-channel output refers to the output of the rotary encoder is a set of pulses, and dual output rotary encoder output pulse phase difference of 90 degrees, the two groups in the two groups of pulse not only can measure the rotational speed, also can judge the direction of rotation. The incremental encoder (rotating) working principle:
By A central shaft of light code disc, on which there are circular and dark scribed line, have read photoelectric emission and receiving devices, obtain four groups of sine wave signal is combined into A, B, C, D, each sine wave 90 degree phase difference (as opposed to A cycle of 360 degrees), will reverse, C, D signal superimposed on A, B two phase, can strengthen stability of signal; The other output of a Z phase pulse to represent zero reference bits.
Because of A, B two phase difference of 90 degrees, but only through A phase in the former or B phase in the former, with forward and inversion of discriminant encoder, through the zero pulse, encoder zero reference can be obtained.
Encoder code disc material with glass, metal, plastic, glass encoder is in the deposition of thin scribed line on the glass, its thermal stability, high precision, metal encoder directly to scribe lines and impassability, non-friable, but because has certain thickness of metal, precision is limited, its thermal stability is an order of magnitude worse than glass, plastic encoder is economical, its cost is low, but the accuracy and thermal stability, life is less.
Resolution - the number of pass-through or dark lines provided by the encoder for each rotation of 360 degrees is called resolution, also known as analytical indexing, or directly how many lines, generally between 5~10000 lines per revolution.
The signal output has sinusoidal wave (current or voltage), square wave (TTL, HTL), collector opening (PNP, NPN), and push-pull in various forms, where TTL is the long-term differential drive (symmetric A, A-; B, B -; Z, Z-), HTL is also known as push-pull type, push-pull output, and the signal receiving device interface of the encoder should correspond with the encoder.
Signal connection - the pulse signal of the encoder is generally connected with the counter, PLC, computer, PLC and computer connected module with low speed module and high speed module, and the switching frequency is low and high.
If single - phase join, used for single direction counting, single direction speed measurement.
A.B two - phase connection, for positive and negative counting, positive and negative direction and velocity measurement.
A, B, and Z are connected for the position measurement with reference bit correction.
- A, A, B, B -, Z, Z - links, due to the negative signal connection with symmetry, current electromagnetic field for cable contributions to 0, attenuation minimum, anti-interference, best can transmit far distance.
For TTL encoder with symmetric negative signal output, the signal transmission distance can be up to 150 meters.
For the HTL encoder with symmetric negative signal output, the signal transmission distance can reach 300 meters.
1. According to the readout mode encoder can be divided into contact type and non-contact type.
The contact type adopts the brush output, and one brush contacts the conductive area or the insulation area to indicate whether the state of the code is "1" or "0"; The non-contact sensitive element is photosensitive element or magnetic sensor, and the light sensitive element is used to indicate the state of the code is "1" or "0".
2. According to the working principle encoder can be divided into two types: incremental and absolute.
The incremental encoder converts the displacement into a periodic electrical signal, converts the electrical signal into a counting pulse, and USES the number of pulses to represent the displacement. Each position of an absolute encoder corresponds to a certain number code, so its value is only related to the starting and ending position of the measurement, not the middle process of the measurement.
The rotating incremental encoder outputs pulses at rotation, knowing its location by counting devices, and counting the internal memory of the device to remember the position when the encoder is stationary or without power. So, after the power outage, there cannot be any movement, encoder when calls work, in the process of the encoder output pulse, also can't be a pulse interference and loss, otherwise, the counting device memory of zero offset, and the amount of the offset is don't know, can only know wrong after the production results.
The solution is to increase the reference point, and the encoder corrects the memory location of the counting device for each reference point. The accuracy of the position cannot be guaranteed before reference point. For this reason, in the industrial control, there is a reference point for each operation, and the startup change method.
For example, the printer scanner's location is the incremental encoder principle, and every time we turn it on, we can hear the clatter of the chip, it's looking for reference zero, and then it's working.
This method is troublesome to some industrial control projects, and even does not allow startup change (you need to know the exact location after starting up), so there is an absolute encoder.
Absolute rotary optical encoder, because its every position only, anti-interference, absolutely no power lost memories, already more and more widely used in various industrial Angle, length measuring and positioning control of systems.
There are a lot of lines on the optical disk of the absolute encoder, each of which is followed by two lines, four lines, eight lines and sixteen lines. Arrangement, so, in every position of encoder, by reading each groove and the dark, get a set of zero power from 2 to 2 n - 1 to the power of the only two hexadecimal code (gray code), it is called a n a absolute encoder. Such encoder is determined by the mechanical position of the code disk, and it is not affected by power failure or interference.
Absolute encoder is determined by mechanical position of the uniqueness of each position, it does not need memory, don't need to find a reference point, and don't always count, when you need to know, when to go to read it. In this way, the anti-interference characteristics of encoder and the reliability of data are greatly improved.
Because the absolute encoder is better than the incremental encoder in positioning, it is more and more applied to the position of industrial control. Absolute encoder because of its high precision, output figures, such as still using parallel output, the output signal must ensure that every connection is very good, for more complex conditions and isolation, connecting cable some more, thus bring many inconvenience and reduce the reliability, therefore, absolute encoder in multibit output type, generally selects the serial output or linear output, the German production of absolute encoder is the most commonly used serial output SSI (synchronous serial output).
3. Single coil absolute encoder and multi-loop absolute encoder.
Rotating single ring absolute encoder, to measure the optical encoder in rotation of the scribed line, in order to get the only encoding, when more than 360 degree rotation, code back to the origin, so it doesn't conform to the principle of absolute coding only, the encoder can only be used to rotate 360 degrees within the scope of the measure, known as the single ring absolute encoder.
If you want to measure the rotation over 360 degrees, you need to use a multiloop absolute encoder.
Encoder manufacturers using the principle of gear mechanical clocks and watches, when the rotating center code through gear drive another set of encoder (or multiple sets of gear, multiple sets of encoder), on the basis of the lap coding number of laps to add code, to enlarge the measuring range of the encoder, the absolute encoder is called a coil more absolute encoder, it is also determined by mechanical position coding, each location coding not only repeat, without memory.
Another advantage is more laps encoder, because of the large measurement range actually use often more rich, so unnecessarily difficult find when installation, will be a middle position as a starting point, and greatly simplifies the difficulty of installation and debugging.
The advantages of multi-loop absolute encoder in length positioning are obvious, and more and more are applied to the position of industrial control.
4. Mechanical installation of absolute rotary encoder:
The mechanical installation of absolute rotary encoder has many forms, such as high-speed terminal installation, low-speed installation, auxiliary machinery installation and so on.
1) the client installation: installed on the power of motor shaft end (or gear), advantages of this method is high resolution, because the encoder has 4096 times more, motor coil number within this range, it can fully use the full range and improve the resolution, the disadvantage is that after moving object through the reduction gear, the charges have gear clearance error, generally used for one-way control positioning accuracy, such as rolling roll gap control. In addition, the encoder is installed directly in the high speed terminal, and the motor jitter should be smaller, otherwise it is easy to damage the encoder.
2) low end installation: installed on the reduction gear, such as winding wire rope drum shaft end or the last section reduction gear shaft end, this method has no gear charges of clearance, measurement is more direct, high precision, this method is generally measured positioning for long distances, such as all kinds of lifting equipment, feeding dolly positioning, etc.
3) auxiliary machinery installation:
Common use of gear rack, chain belt, friction wheel, rope, and so on.
5. Features of optical encoder.
Using reflection induction technology surface-mount without pin encapsulation provide two channel analog signal output count rate: 20 KHZ \ adopt single 5.0 V power supply operation working temperature: - 10 to 70 oc coding resolution: 180 lpi comply with RoHS environmental protection standard requirements.