What types of encoders are there? What are their respective applications?
An encoder is an instrument that encodes signals or data and converts them into a signal form that can be used for communication, transmission, and storage.
1. Classification by different coding methods of the code disk: (There are many classification methods for encoders nowadays, only the commonly used classifications will be mentioned)
( 1 ) Absolute encoder: There are several concentric code disks along the radial direction on its circular code disk. Each track is composed 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 of 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). Usually, it is a three-phase output of A , B and C. Phases A and B are pulse outputs with a mutual delay of 4 cycles. The forward and reverse directions can be determined based on the delay relationship. By utilizing the rising and falling edges of phases A and B , frequency multiplication of 2 and 4 times can be performed . Phase Z is a single-turn pulse, that is, one pulse is emitted per revolution.
2. Classification by encoder mechanical mounting method: ( 1 ) Shaft type: Shaft type can be further divided into clamping flange type, synchronous flange type, servo mounting type, etc. ( 2 ) Bushing type: Bushing type can be further divided into semi-hollow type, fully hollow type, large diameter type.
Encoder Applications
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 quantity), rubber and plastic machinery, drafting instruments, goniometers, and radar for therapeutic devices, etc.
4. How to implement servo control?
1. Servo motors primarily rely on pulses for positioning. Essentially, a servo motor receives one pulse and rotates by the angle corresponding to that pulse, thus achieving displacement. Because the servo motor itself has the function of generating pulses, it generates a corresponding number of pulses for each rotation angle. This creates a feedback loop, or closed loop, between the pulses sent to and received by the servo motor. In this way, the system knows how many pulses were sent to and received by the servo motor, allowing for very precise control of the motor's rotation and achieving accurate positioning down to 0.001mm . DC servo motors are divided into brushed and brushless motors. Brushed motors are low-cost, simple in structure, have high starting torque, wide speed range, and are easy to control. They require maintenance, but maintenance is convenient (replacing carbon brushes). They generate electromagnetic interference and are subject to environmental requirements. Therefore, they are suitable for cost-sensitive general industrial and civilian applications. Brushless motors are small in size, lightweight, have high output power, fast response, high speed, low inertia, smooth rotation, and stable torque. While complex to control, it is easily made intelligent. Its electronic commutation method is flexible, allowing for either square wave or sine wave commutation. The motor is maintenance-free, highly efficient, operates at low temperatures, emits minimal electromagnetic radiation, has a long lifespan, and can be used in various environments.
2. AC servo motors are also brushless motors, and they are divided into synchronous and asynchronous motors. Currently, synchronous motors are generally used in motion control because they have a wide power range and can achieve very high power. They also have high inertia, low maximum rotational speed, and their speed decreases rapidly as power increases. Therefore, they are suitable for applications requiring low-speed, stable operation.
3. The rotor inside a servo motor is a permanent magnet. The three-phase electricity (U/V/W) controlled by the driver creates an electromagnetic field, causing the rotor to rotate under the influence of this magnetic field. Simultaneously, the motor's built-in encoder feeds back signals to the driver. The driver compares the feedback value with the target value and adjusts the rotor's rotation angle accordingly. The accuracy of a servo motor depends on the accuracy (line count) of the encoder.
