What Is a Rotary Encoder?

Rotary encoder is a device that can measure speed and cooperate with PWM technology to achieve fast speed regulation. The photoelectric rotary encoder can convert mechanical quantities such as angular displacement and angular velocity of the output shaft into corresponding electrical pulses through digital conversion through photoelectric conversion. Output (REP).

According to the output type of the signal, it is divided into: voltage output, open collector output, push-pull complementary output, and long-line drive output ^[1]

Shaft type: Shaft type can be divided into clamping flange type, synchronous flange type and servo mounting type.

Shaft sleeve type: Shaft sleeve type can be divided into half-empty type, full-empty type and large-caliber type.

Photocell

Rotary encoder is a speed and displacement sensor integrating optical-mechanical and electrical technology.

Signal output has sine wave (current or voltage), square wave (TTL, HTL), open collector (PNP, NPN), push-pull type, of which TTL is long-line differential drive (symmetric A, A-; B, B -; Z, Z-), HTL is also called push-pull, push-pull output. The signal receiving device interface of the encoder should correspond to the encoder.

Signal connection-encoder

installation

Do not apply direct impact to the shaft during installation.

For connecting the encoder shaft to the machine, use a flexible connector. When mounting the connector on the shaft, do not press it hard. Even if a connector is used, due to poor installation, a load larger than the allowable load may be added to the shaft, or a core shifting phenomenon may be caused. Therefore, pay special attention.

Bearing life is related to the use conditions, and is particularly affected by bearing load. If the bearing load is less than the specified load, the bearing life can be greatly extended.

Do not disassemble the rotary encoder. Doing so will impair oil and drip resistance. Anti-drip products should not be immersed in water or oil for a long time. Wipe clean when there is water or oil on the surface.

vibration

The vibration added to the rotary encoder often becomes the cause of false pulses. Therefore, pay attention to the installation place and installation place. The greater the number of pulses per revolution, the narrower the slot spacing of the rotating grooved disc, and the more susceptible it is to vibration. When rotating or stopping at low speed, the vibration added to the shaft or the body will shake the rotary groove disk, and false pulses may occur.

About wiring and connection

Miswiring may damage the internal circuit, so pay full attention when wiring:

Wiring should be performed when the power is off. If the output line contacts the power when the power is on, the output circuit may be damaged.

If the wiring is incorrect, the internal circuit may be damaged, so pay attention to the polarity of the power supply when wiring.

If it is wired in parallel with the high-voltage line and power line, it may be damaged due to induction and malfunction. Therefore, separate the wiring.

When extending the wire, it should be less than 10m. And because of the distribution capacity of the wire, the rise and fall time of the waveform will be longer.

Rotary encoder is a speed and displacement sensor integrating optical-mechanical and electrical technology.

Incremental

When the incremental encoder shaft rotates, there is a corresponding phase output. The determination of the rotation direction and the increase or decrease of the number of pulses need to be realized by means of a rearward direction determining circuit and a counter. The counting starting point can be set arbitrarily, and infinite accumulation and measurement of multiple turns can be realized. You can also use the Z signal for each pulse as a reference mechanical zero. When the pulses are fixed and the resolution needs to be improved, the two signals with a 90-degree phase difference A and B can be used to multiply the original pulse number.

Absolute value

For absolute encoder shaft rotators, codes (binary, BCD code, etc.) corresponding to the position are output. From the change of the code size, the position of the forward and reverse directions and the displacement can be determined without the need for a direction circuit. It has an absolute zero code. When power is off or turned off and then re-measured, it can still accurately read the code of the power outage or shutdown position and find the zero code accurately. In general, the absolute encoder's measurement range is 0 to 360 degrees, but special models can also achieve multi-turn measurement.

Sine wave

A sine wave encoder is also an incremental encoder. The main difference is that the output signal is a sine wave analog signal, not a digital signal. It appeared mainly to meet the needs of the electrical field-as a feedback detection element for electric motors. On the basis of comparison with other systems, this encoder can be used when people need to improve the dynamic characteristics.

In order to ensure good motor control performance, the feedback signal of the encoder must be able to provide a large number of pulses, especially when the speed is very low, using a traditional incremental encoder to generate a large number of pulses, which is problematic in many ways When the motor rotates at a high speed (6000rpm), it is difficult to transmit and process digital signals.

In this case, the bandwidth required to process the signal to the servo motor (for example, the encoder has 10,000 pulses per revolution) will easily exceed the MHz threshold; on the other hand, the use of analog signals greatly reduces the above troubles and has the ability to simulate A large number of pulses from the encoder. This is thanks to the interpolation of the sine and cosine signals, which provides a calculation method for the rotation angle. This method can obtain a high multiplication of basic sine, for example, from 1024 sine wave encoders per revolution, more than 1,000,000 pulses per revolution can be obtained. The bandwidth required to accept this signal is sufficient as long as it is slightly larger than 100KHz. Interpolation multiplication needs to be completed by the secondary system ^[1]

Signal sequence

In general, the encoder output signal is in addition to the two phases of A and B (the phase difference of the signal sequence of the two channels of A and B is 90 degrees), and a zero pulse Z is output for each revolution.

When the spindle rotates clockwise, the pulse is output as shown in the figure below, and the signal of channel A is located before channel B; when the spindle rotates counterclockwise, the signal of channel A is located after channel B. Thereby, it is judged whether the main shaft is forward or reverse.

Output pulse number / revolution

The number of pulses output by one rotation of the rotary encoder. For optical rotary encoders, it is usually the same as the number of slots of the grating inside the rotary encoder (you can also increase the number of output pulses to twice the number of slots on the circuit. 4 Times).

Resolution

The resolution indicates the maximum equal fraction of the position data when the spindle of the rotary encoder rotates for one revolution. The absolute value type does not output in pulse form, but represents the current spindle position (angle) in code form. Different from the incremental type, it is equivalent to the "output pulse / revolution" of the incremental type.

Grating

Optical rotary encoders have metal and glass gratings. If it is made of metal, there is a light-through slot; if it is made of glass, a light-shielding film is coated on the glass surface, and there are no transparent lines (slots) on it. In the case of a small number of slots, the metal disc can be slotted with a punch or an etching method. Metal encoders are used in impact-resistant encoders, which are less impact-resistant than metal encoders, so be careful not to apply impact directly to the encoder.

The maximum response frequency is the maximum number of pulses that can be responded in 1 second (for example: the maximum response frequency is 2KHz, that is, it can respond to 2000 pulses in 1 second)

The formula is as follows:

Maximum response speed (rpm) / 60 × (number of pulses / revolution) = output frequency Hz

The maximum response speed is the highest speed that can be responded to. The pulse response formula at this speed is as follows:

Maximum response frequency (Hz) / (number of pulses / revolution) × 60 = shaft speed rpm

Output Waveform Outputs the waveform of a pulse (signal).

Output signal phase difference

For two-phase output, the relative time difference between the two output pulse waveforms.

The output voltage

Refers to the voltage of the output pulse. The output voltage will vary depending on the output current. Please refer to the output current characteristic chart for the output voltage of each series

Starting torque

Necessary torque for rotating the encoder shaft at rest. In general, the torque during operation is smaller than the starting torque.

Allowable shaft load

It indicates the maximum load that can be added to the shaft. There are two types of radial and axial loads. The radial load is vertical to the shaft, and the force is related to the eccentricity and eccentricity. The axial load is horizontal to the shaft, and the force is related to the force of the push-pull shaft. The magnitude of these two forces affects the mechanical life of the shaft

Shaft moment of inertia

This value indicates the inertia of the rotating shaft and resistance to changes in speed

Rotating speed

This speed indicates the mechanical load limit of the encoder. Exceeding this limit will have a negative effect on bearing life and the signal may be interrupted.

Gray code

Gray codes are high-level data and are safe because they are cell distance and cyclic codes. There is only one change per step. During data processing, Gray codes must be converted into binary codes.

Working current

Refers to the load current allowed by the channel.

Operating temperature

The data and tolerances mentioned in the parameter table are guaranteed in this temperature range. If it's slightly higher or lower,

To avoid rigid connection to the encoder, a leaf spring should be used.
When installing, the encoder should be gently pushed into the shaft of the quilt. It is forbidden to hit it with a hammer to avoid damaging the shaft system and the code disk.
For long-term use, please check whether the leaf spring is loose with respect to the encoder; whether the screws holding the Been encoder are loose.
The solid shaft encoder uses an elastic soft connection between the encoder shaft and the user-side output shaft to avoid damage to the BEN encoder shaft system and code disk due to the series and runout of the user shaft.
Please pay attention to the allowable shaft load during installation.
Should ensure that the encoder shaft and the user output shaft have a different axiality of <0.20mm and an off-angle of less than 1.5 ° from the axis.
Knocking and knocking are strictly prohibited during installation, so as not to damage the shaft system and the code disc.
The grounding wire of the electrical equipment should be as thick as possible, and should generally be larger than 3.
Do not connect the signal line of the encoder to the DC power supply or the AC current to avoid damaging the output circuit.
Do not overlap the output lines of the encoder to avoid damaging the BEN encoder output circuit.
Motors and other equipment connected to the encoder should be well grounded and free of static electricity.
Before starting up, you should check carefully whether the product manual matches the BEN encoder model and whether the wiring is correct.
Use shielded cables for wiring.
When transmitting over long distances, the signal attenuation factor should be considered, and the output mode with low output impedance and strong anti-interference ability should be selected.
Avoid using in strong electromagnetic wave environment.
The encoder is a precision instrument in terms of environment. When using it, pay attention to whether there are vibration sources and interference sources around it.
Please pay attention to whether the ambient temperature and humidity are within the requirements of the instrument.
Encoders that are not leak-proof should not be splashed with water, oil, etc. If necessary, a protective cover is definitely relative to the increment. As the name implies, the so-called absolute is the process in which the output signal of the encoder runs in one or more weeks. In the output code corresponding to each position and angle, there is a unique correspondence, so that it has the function of power-down memory.
Each position of the absolute encoder determined by the mechanical position is unique, it does not need to memorize, does not need to find a reference point, and does not need to keep counting, when it is necessary to know the position, and when to read its position. In this way, the anti-interference characteristics of the encoder and the reliability of the data are greatly improved ^[2]

This system uses relative counting method for position measurement. Before running, the pulse number corresponding to each signal, such as the position of the speed change point, the leveling point, and the position of the braking stop, is stored into the corresponding memory units by programming. During the elevator operation, the rotary encoder is used. The detection and software calculate the following signals in real time: the position of the floor where the elevator is located, the position of the speed change point, and the position of the leveling point, so as to count the floors, send out speed change signals and flat floor signals.
The displacement calculation during elevator operation is as follows: H = SI
Where S: pulse equivalent I: cumulative pulse number H: elevator displacement S = D / P
D: Traction wheel diameter : Frequency division ratio of PG card : Deceleration ratio of reducer P: Number of pulses corresponding to each revolution of rotary encoder In this system = 1/32 D = 580mm
Ned = 1450r / min P = 1024 = 1/18
Substitute S = D / P to get S = 1.00 mm / pulse. Set the height of the floor to 4m, then the number of pulses at each floor level point is: 0 on the first floor; 4000 on the second floor; 8000 on the third floor; .
Assuming that the speed change point is 1.6 meters from the floor, the pulse number of the speed change point on each floor is: rise: 2400 from the first floor to the second floor, 6400 from the second floor to the third floor, and 10400 from the third to the fourth floor; drop: 4 9600 from the third to the third floor, 5600 from the third to the second floor, and 1600 from the second to the first floor. ^[1]