What Is Quadrature?

In the field of electronics, the word "quadrature" often appears in various scenes, such as quadrature encoder or quadrature signal processing. But what is "quadrature" and what is its function? The following content introduces the meaning of "quadrature" and what quadrature encoder is.

The industrial encoder is a rotary sensor that converts the rotary displacement into a series of digital pulse signals. These pulses can be used to control the angular displacement. If the encoder is combined with the gear strip or screw, it can also be used to measure the linear displacement.

The History Of Quadrature

Although the word "quadrature" is most widely used in the field of electronics, in fact, it is a word originated in ancient Greece. Mathematicians at that time tried to model the curved region with squares. Although this method is quite backward compared with our current integral and PI calculation, all objects in our life can be composed of countless tiny squares, even curved objects. The rotary quadrature encoder can decompose the unknown rotation into square wave pulses when performing tasks.

Rotary And Linear Quadrature Encoder

In the fanuc motor encoder, quadrature means receiving two square wave signals indicating motion and direction in a 90 degree or quarter cycle out of phase mode. Therefore, it is a square wave mode. These signals can be generated by light or physical contact. In rotary optical encoder, some disks with signal windows are arranged at uniform intervals, and light can pass through these windows. When the sensor is exposed in the window area, its output is high level, otherwise it is low level.

In this way, the fanuc spindle encoder can output different signals. When turning clockwise, when one sensor makes a specific conversion, the other sensor will be in a known state. For instance, when sensor A transitions from high to low at 180º, sensor B will read low when traveling clockwise. Alternatively, if sensor A transitions from high to low and sensor B reads as high already, it’s evident that the wheel is in fact spinning counterclockwise.

The rotation distance of the movement can be measured by pulses on a single channel. Fanuc absolute encoders usually use PPR or pulse value per rotation. However, with proper adjustment, the fanuc pulse coder can measure the conversion of two channels from high level to low level and from low level to high level. In this way, the accuracy of single channel pulse measurement can reach four times. 

It should be noted that 360 degrees is not the total rotation angle of the wheel, but many separate on or off modes that usually occur in the whole rotation mode. In addition, the 90 degree offset is important here. If the sensor phase difference is 180 degrees, the two sensors will convert at the same time, which will lead to an uncertain state in the conversion process, resulting in wrong results. 

Alternatively, some original encoders use an offset pattern of windows for the two sensors, instead of the sensor offset arrangement shown here. The structure of the linear quadrature encoder is similar to this method, but the window of the sensor is linear, so as to determine the driving distance to monitor the position of the object.