Different Types of Motor Encoders in Industrial Automation

I. What is a Motor Encoder?

Motor encoders are devices used in automation control systems or any machines containing motors that require position data. They can be found everywhere from mechanical arms to 3D printers. Encoders play a critical role in allowing autonomous machines to function properly. They enable precise measurement of moving parts within the system.

Encoders have several advantages, such as linear encoders commonly used in track applications that allow CNC machines and 3D printers to create parts accurately, while rotary encoders make mechanical arms possible in manufacturing. The signals they send are used to activate different outputs of controllers or PLCs at the right time.

II. How Does a Motor Encoder Work?

Encoders work by providing electrical information to a control device based on one of two different systems (rotary or linear). There are several mechanisms within encoders for converting physical changes into electrical data: resistance, mechanical, magnetic, and optical, with optical encoders being the most common in manufacturing. Optical encoders contain at least one light transmitter and one light receiver to convert physical motion into an electrical signal for processing by the controller. Regardless of the conversion method used, encoders are always either linear encoders or rotary encoders.

In optical encoders, both rotary and linear use "windows" cut out of a solid surface that only allow light to enter the receiver in an incremental manner. Linear encoders use sensors to detect different patterns along the length of a strip, while rotary encoders consist of a disk with slots that can send signals back to the control system.

In optical systems, a constant beam of light is emitted from the transmission unit, and as the system moves, the beam is gradually interrupted. Each time the receiver unit detects light from the transmission unit, it sends an electrical signal to the controller. Depending on the application, there are various disk or track configurations to block/receive light. These include absolute position encoders and incremental encoders.

III. Absolute Encoders vs. Incremental Encoders: What's the Difference?

Absolute encoders use multiple light sensors to send binary code to the controller. They have different slots corresponding to each light transmitter/receiver pair. For single-turn absolute encoders, these slots create a binary code that can tell the motor the angular position within one turn.

In applications requiring higher accuracy and a larger range, multi-turn encoders use gear reducers and two encoding disks to achieve a larger range of known positions. Absolute encoders are more suitable for situations where position data is needed after a power outage, commonly found in safety circuits. Incremental encoders have uniformly spaced slots that send pulses to the controller. These encoders rely on counting pulses from a zero position, so having a known position to restart counting is very important if the system loses power for any reason.

In cases where only motor speed is needed, an analog signal can be sent to the controller, allowing it to process this data into useful applications. If position data is required, the encoder can send electrical pulses to the controller to decode the motor's position within its boundary area.

IV. Where are Linear Encoders Used?

Linear encoders use sensors or scales with "cutouts" to send electrical pulse signals to the controller. These pulse signals can be decoded by a PLC and converted into instructions for the device to follow.

Linear encoders are more suitable for applications with sliding positioners, such as 3D printers or CNC machines. They are very suitable for processes that require the precise transfer of high-speed data to the controller. Certain linear encoders, if not absolute encoders, require a reference position to find zero if there is a power outage or PLC/controller restart.

Absolute encoders use binary representation for positioning, while incremental encoders can only send pulses that the controller counts after starting. Limit switches or sensors can be used to provide a reference point when position data needs to be restarted.

Linear encoders based on absolute code can find their position without moving or using a reference point. They use binary code from multiple scales to determine position. This provides greater flexibility in the application process and opens up more opportunities in the field of safety after restart.

V. Uses of Rotary Encoders

Rotary encoders consist of a circular scale connected to the motor shaft. When the motor rotates, the optical sensor reads the pattern in the scale and sends pulse counts or binary code to the PLC. Rotary encoders are very useful in applications that require motor speed or are difficult to measure distance by other means besides motor rotation, such as servos in mechanical arms. Applications requiring motor speed control use incremental encoders that generate pulse counts to measure motor speed.

There are a certain number of slots on the encoder scale, and the PLC calculates the number of slots as the motor rotates. Then it can be converted into RPM. An example of this is on conveyor belt motors. Certain parameters may require different belt speeds, and the PLC can make appropriate adjustments based on the motor's RPM. They are also useful in applications where accuracy is very important because they produce more accurate data than absolute rotary encoders. Although they are more accurate, they cannot read position without moving and may require a reference position if communication is lost with the PLC.

Absolute encoders can also be used for rotary motor encoders. These are more suitable for situations where angle data is needed. They can also recall position if there is a loss of communication or power between the encoder and the controller, unlike incremental rotary encoders that require movement to transmit data.

In conclusion, motor encoders are indispensable components in industrial automation systems, enabling precise positioning and control of motors. Understanding the different types of encoders, such as absolute and incremental, as well as their working principles, is crucial for selecting the appropriate encoder for specific applications. Whether it's a linear or rotary encoder, each type offers unique advantages in terms of accuracy, resolution, and ease of implementation. By carefully considering the requirements of an automation system, engineers can leverage the benefits of motor encoders to improve efficiency, reliability, and safety in industrial processes.