I. What is a motor encoder?
A motor encoder is a device that records position data for automated control systems or any machine containing a motor that requires position data. They are ubiquitous, from robotic arms to 3D printers. Encoders play a crucial role in enabling autonomous machines to function properly. They allow for the precise measurement of moving parts within a system.
Motor encoders offer several advantages. For example, linear encoders are commonly used in rail applications and allow CNC machines and 3D printers to create parts with precision, while rotary encoders enable robotic arms in manufacturing. They send signals to activate different outputs of a controller or PLC at the correct time.
II. How does a motor encoder work?
Encoders operate by providing electrical information to control devices based on one of the two different systems mentioned above (rotary or linear). Several other mechanisms exist within encoders for converting physical changes into electrical data: resistive, mechanical, magnetic, and optical, with optical encoders being the most common in manufacturing. An optical encoder contains at least one light transmitter and one light receiver to convert physical motion into electrical signals for the controller to process. Regardless of the conversion method used, an encoder is always either a linear encoder or a rotary encoder.
In optical encoders, both rotary and linear encoders use "windows" cut from a solid surface, allowing light to enter the receiving unit only incrementally. Linear encoders use sensors to detect different patterns in a strip along the path length, while rotary encoders consist of a disk with slots that sends signals back to the control system.
In an optical system, the transmitting unit emits a constant beam of light, which gradually dims as the system moves. Whenever the receiving unit detects light from the transmitting unit, it sends an electrical signal to the controller. Depending on the application, various disk or track configurations are used to block/receive light. These include absolute position encoders and incremental encoders.
III. Absolute encoders and incremental encoders: What are the differences?
Absolute encoders use multiple optical sensors to send binary codes to the controller. These sensors have different slots corresponding to optical transmitter/receiver pairs. For a single-turn absolute encoder, these slots create a binary code that tells the motor its angular position within one revolution.
In applications requiring higher accuracy and a wider range, multi-turn encoders use gear reducers and two encoder discs to achieve a greater range of known positions. Absolute encoders are better suited for situations where position data is needed after a power outage, most commonly in safety circuits. Incremental encoders have evenly spaced slots to send pulses to the controller. These encoders rely on pulses counting from zero position, so having a known position to restart counting is crucial in the event of a power outage for any reason.
If only motor speed is required, an analog signal can be sent to the controller, enabling it to process this data for a useful application. If the process requires position data, the encoder can send electrical pulses to the controller to decipher the motor's position within its boundary area.
IV. Where are linear encoders used?
Linear encoders use "notches" on sensors or scales to send electrical pulse signals to a controller. These pulse signals can be decrypted by a PLC and converted into instructions that the device must follow.
Linear encoders are better suited for applications with sliding positioners, such as 3D printers or CNC machines. They are ideal for processes that require accurate, high-speed data transmission to the controller. Some linear encoders, if not absolute encoders, require a reference position to zero after a power outage or PLC/controller restart.
Absolute encoders use binary to represent position, while incremental encoders can only send pulses counted by the controller after startup. Limit switches or sensors can be used to provide a reference point when position data must be restarted.
Linear encoders based on absolute codes are able to find their positions without moving or using reference points. They use binary code from multiple scales to determine location. This provides greater flexibility in application processes and opens up more opportunities in areas involving post-reboot security.
V. Use of Rotary Encoders
A rotary encoder consists of a circular scale attached to the motor shaft. When the motor rotates, a light sensor that reads a pattern on the scale sends a pulse count or binary code to the PLC. Rotary encoders are very useful in applications requiring motor speed or where distance measurement is difficult without motor rotation, such as in servo motors in robotic arms. Applications requiring motor speed control use incremental encoders that generate pulse counts to measure motor speed.
The encoder scale has a certain number of slots, and the PLC calculates the number of slots as the motor rotates. This can then be converted to RPM. One example where this might be useful is on a conveyor belt motor. Certain parameters may require different belt speeds, and the PLC can adjust accordingly based on the motor's RPM. They are also useful in applications where accuracy is critical because they produce more accurate data than absolute rotary encoders. Although they are more accurate, they cannot read the position without movement and may require a reference position if communication with the PLC is lost.
Absolute encoders can also be used with rotary motor encoders. These are better suited for applications requiring angular data. They also allow for position recall after a loss of communication or power between the encoder and controller, unlike incremental rotary control which requires movement to transmit data.
