A servo motor encoder is a sensor installed on a servo motor to measure the position of the magnetic poles and the rotation angle and speed of the servo motor. Based on the different physical media, servo motor encoders can be divided into photoelectric encoders and magnetoelectric encoders. In addition, a rotary transformer is also considered a special type of servo encoder. The market mainly uses photoelectric encoders, but magnetoelectric encoders, as a rising star, have the characteristics of reliability, low price, and resistance to pollution, and are trending towards surpassing photoelectric encoders.
The basic functions of a servo encoder are the same as those of a regular encoder. For example, absolute encoders have signals such as A , A -inverse , B , B -inverse, Z , Z -inverse, etc. However, servo encoders differ from regular encoders in that most servo motors are synchronous motors. When a synchronous motor starts, the position of the rotor's magnetic poles needs to be known in order to start the servo motor with high torque. This requires several additional signals to detect the rotor's current position. For example, incremental encoders have signals such as UVW . Because of these signals for detecting the rotor position, servo encoders appear somewhat complex, making them difficult for the average person to understand. In addition, some manufacturers deliberately conceal certain signals, and related information is incomplete, further adding to the mystique surrounding servo motor encoders.
Since phases A and B are 90 degrees out of phase, the forward and reverse rotation of the encoder can be determined by comparing whether phase A or phase B comes first. The zero-position reference position of the encoder can be obtained through the zero-position pulse.
Encoder disks are made of glass, metal, or plastic. Glass disks have very thin lines deposited on glass, resulting in good thermal stability and high precision. Metal disks have lines directly engraved with both through and non-through surfaces, making them less prone to breakage. However, due to the thickness of the metal, their precision is limited, and their thermal stability is an order of magnitude worse than that of glass. Plastic disks are economical, with low cost, but their precision, thermal stability, and lifespan are all inferior.
Resolution —The number of through or dark lines provided by an encoder per 360 degrees of rotation is called resolution, also known as resolution scale or simply the number of lines. It is generally 5 to 10,000 lines per revolution .
Types of servo motor encoders
With the development of industrial production technology, advanced production equipment is used in production. An important component of this equipment is the servo motor encoder. An encoder is an instrument that encodes and converts signals. So what are the main classifications of servo motor encoders? The following is a detailed introduction.
Servo motor encoders are classified according to the different engraving methods of the code disk: (There are many classification methods for encoders nowadays, only the commonly used classifications are mentioned)
1. Absolute encoder: Its circular code disk has several concentric code disks along the radial direction. Each track consists of alternating light-transmitting and light-blocking sector areas. The number of sectors in adjacent code tracks is double. The number of code tracks on the code disk is the number of bits in its binary code. There is a light source on one side of the code disk, and a photosensitive element on the other side corresponding to each code track. When the code disk is in different positions, each photosensitive element converts the corresponding level signal according to whether it is illuminated or not, forming a binary number.
2. Incremental encoder principle: The shaft emits a pulse signal after rotating through a specified unit angle (some emit a sine signal, which is then subdivided and chopped to produce a higher pulse). It is usually a three-phase output of A , B and C. The A and B phases are pulse outputs with a mutual delay of 4 cycles. The forward and reverse directions can be determined based on the delay relationship. By using the rising and falling edges of the A and B phases, frequency multiplication of 2 and 4 times can be performed . The Z phase is a single-turn pulse, that is, one pulse is emitted per revolution.
