The working principle of incremental encoder_application of incremental encoder

Working principle of incremental encoder

The incremental rotary encoder converts the timing and phase relationship of the angle code disc through two photosensitive receiving tubes, and obtains the increase (positive direction) or decrease (negative direction) of the angular displacement of the angle code disc.

The working principle of incremental rotary encoder is shown in the figure below.

In the figure, the distance between points A and B is S2, corresponding to two photosensitive receiving tubes, and the grating distances of the angle code disc are S0 and S1.

When the angle code wheel rotates at a constant speed, it can be seen that the ratio of S0: S1: S2 in the output waveform diagram is the same as the ratio of S0: S1: S2 in the actual diagram. Similarly, when the angle code disk rotates at a variable speed, the output waveform diagram S0: The S1:S2 ratio is still the same as the S0:S1:S2 ratio of the actual diagram.

　　 Through the output waveform diagram, we can see that the sequence of each motion cycle is:

We save the current A and B output values ​​and compare them with the next A and B output values ​​to get the direction of rotation of the angle code wheel.

If the optical grid S0 is equal to S1, that is, the angle between S0 and S1 radians is the same, and S2 is equal to 1/2 of S0, then the displacement angle of this angular code disc movement can be obtained as 1/2 of the included angle of S0 radians. Divide by the elapsed time to get the angular velocity of this angular code disc movement.

When S0 is equal to S1, and S2 is equal to 1/2 of S0, the movement direction and displacement angle can be obtained in 1/4 of the movement cycle. If S0 is not equal to S1 and S2 is not equal to 1/2 of S0, then 1 The movement direction and displacement angle can be obtained by the movement period.

　　 The scroll wheel of our commonly used mouse is the same principle.

　　The incremental encoder actually used outputs three sets of square wave pulses A, B and Z (some called phase C). The phase difference between A and B pulses is 90º, and the rotation direction and rotation speed can be judged. The Z-phase pulse is also called the zero position pulse (sometimes called the index pulse). It outputs a pulse for each revolution. The Z-phase pulse represents the zero position reference position. Through the zero position pulse, the zero position reference position of the encoder can be obtained. Used for reference point positioning, as shown in the figure below.

When the shaft of the incremental encoder rotates, there is a corresponding pulse output, and its counting starting point can be set arbitrarily, which can realize multi-turn infinite accumulation and measurement. The encoder shaft rotates a circle and outputs a fixed number of pulses. The number of pulses is determined by the number of grating lines on the encoder's code disc. The number of open or dark engraved lines provided by the encoder per 360 degree rotation is called resolution. It is called the resolution division, or the number of lines, generally 5~10000 lines per revolution. When the resolution needs to be improved, the two signals of A and B with a phase difference of 90 degrees can be used for frequency multiplication or replace the high-resolution encoder .

The accuracy of incremental encoders depends on mechanical and electrical factors. These factors include: grating indexing error, disc eccentricity, bearing eccentricity, errors introduced by the electronic reading device, and the inaccuracy of the optical part. Errors exist in any encoder .

　　 The signal output of the encoder has various forms such as sine wave (current or voltage), square wave (TTL, HTL). And all can use differential drive mode, including symmetrical A+/A-, B+/B-, Z+/Z- three-phase signal. Due to the connection with symmetrical negative signal, the electromagnetic field contributed by the current to the cable is 0, and the signal is stable attenuation The smallest, the best anti-interference, and can transmit a long distance, for example: for TTL encoder with symmetrical negative signal output, the signal transmission distance can reach 150 meters. For HTL encoders with symmetrical negative signal output, the signal transmission distance can reach 300 meters.

Application of incremental encoder

　　The characteristic of the incremental photoelectric encoder is that every output pulse signal is corresponding to an incremental displacement, but the increment at which position cannot be distinguished by the output pulse. It can generate a pulse signal equivalent to the displacement increment, and its function is to provide a sensing method for the discretization or increment of the continuous displacement and the displacement change (speed). It is relative to a certain reference point. The position increment cannot directly detect the absolute position information of the axis.

Incremental encoders are mainly used in CNC machine tools and mechanical accessories, robots, automatic assembly machines, automatic production lines, elevators, textile machinery, sewing machinery, packaging machinery (fixed length), printing machinery (synchronous), woodworking machinery, plastic machinery (Fixed number), rubber and plastic machinery, drawing instruments, goniometers, convalescent radars, etc.