What is an anchor shaft sensor?

Encoders are in two categories: rotary and linear. The category of rotary encoders includes absolute encoders and incremental encoders. Shaft Encode sensor is a type of sensor with optical transmitter and receiver that is used to measure the rotation angle and rotation speed in industrial systems. The encoder shaft has two types, incremental and absolute.

Incremental encoder shaft

An incremental encoder is a rotating plate filled with a cavity or slit around it in front of which a light source is located. By moving this screen, every time the light passes through the slit, it hits the light sensor and as a result, the encoder notices the movement.

The accuracy of this encoder depends on the number of holes or cavities, and although it determines the amount of movement change, it can not determine the position.

Incremental type produces pulse per rotation of the encoder with a certain angle, the number of pulses produced depends on the accuracy and resolution of the sensor.

Usually a minimum of 200 pulses and a maximum of 300 pulses are produced per cycle. With this sensor, in addition to the angle of rotation, the direction of rotation is also obtained.

In this type of encoder, there is a point called the zero point where the encoder gives a pulse on one of its bases at this point. The main use of the encoder is in measuring the angle of rotation, but it can also be used to measure length.

To determine the direction of rotation in the incremental encoder, two rows of grooves are installed on a circular plate, which are 90 degrees apart in phase (phases A and B) if the output in A is pre-phase compared to B, ie The encoder rotates to the left.

In a row, there is only one groove called the Z phase. It gives a pulse in each round that marks the zero point. Using PLC or IC 4017, the output can be displayed on the screen.

The big disadvantage of this type of encoder is that they can not detect their position when the power is cut off and they have to be in the zero position again to determine the number of turns or the right or left direction.

Pulse signal waveforms of phases A and B in incremental encoder clockwise

Pulse signal waveforms of phases A and B in incremental encoder counterclockwise

The encoder has high torque. If any mechanical system connects to a servo, its accuracy decreases, which is why a gearbox is used to connect them.

Absolute encoder shaft

This type of encoder has a rotating screen consisting of several networks. Each grid consists of several segments and has its own color pattern. Position and angle detection in the absolute encoder is based on which pattern the indicator is placed on.

In absolute encoder, output pulses are generated according to the position of the screen. This type of encoder appears as binary, gray and… at the output. When preparing this type of encoder, you should pay attention to the code created by it. Its main application is in servo motors, which is used as position and speed feedback.

The cost of this type of encoder is very high and more expensive than the increase. The main advantage of this type of encoder is that it is absolute, ie it produces a special pulse at any specific point from which its exact position can be determined.

In Absolute Encoder, there is a way to output binary code as a digital signal and a method to convert binary code to an analog voltage and its output.

In addition, for digital signals, there is a parallel output that outputs a binary code that is obtained from multiple slots through multiple signal lines. There is also a serial output that simultaneously switches several signal lines from parallel output, one at a time, outputting one signal line.

Relationship between angle information, binary code, digital output signal and analog output voltage in absolute encoder:

Parallel output signal and serial conversion output signal in absolute encoder:

Magnetic encoder

The magnetic encoder is operated by the effect of magnetic resistivity (MR) and variable reluctance. What is common with all types of magnetic encoders is that they all have a ring magnet on one shaft, or a gear instead that is made of ferromagnetic material.

But the difference in magnetic encoders is related to the storage of changes. This section will either use effect sensors or AMR sensors or will use variable reluctance. The change storage section in magnetic encoders, variable reluctance, consists of a coil housed in the magnetic field of a permanent magnet. As the gear teeth pass in front of it, the permeability coefficient changes and as a result, the change in magnetic density causes voltage to be generated at the winding terminals.

Types of magnetic encoders

There are two types of magnetic encoders: absolute and incremental. In the incremental type, the same method of optical encoders is used, and in the absolute type, similar to the absolute optical encoders, the binary code is used and to increase the reliability, the encoding (Gray) is used, in each position change, only one change in its bits. It happens. These encoders are used in motor feedback, robotics, pedal feedback, tooth positioning, multiaxial positioning, medical GPS antenna positioning: X-ray position sensor, CATSCAN position sensor and MRI device.

Features of magnetic encoders

1- The cost of magnetic encoders is 10 to 20% less than optical encoders.

2- Long life

3- About 50% less components are included.

4- The flexibility of their construction makes the preparation of machines to be done at a low cost.

5- Ability to be placed in integrated parts