What Are Elevator Encoders Used For?
Elevator encoders provide feedback to an elevator controller that ensures the doors open level with the floor. In addition, they provide motion feedback on automated assembly lines that help robots do their jobs correctly.
Encoders also play a key role in preventing the elevator car from going over speed. This is accomplished by an elevator governor system that requires encoder feedback to detect when the car exceeds a predetermined threshold and trip the safety mechanism.
Position Feedback
In elevators, position feedback is a key part of the system that ensures smooth operation. Whether an elevator runs on hydraulic, traction, machine-less or vacuum principles, a wide variety of sensors are used to monitor the lift’s performance and the environment within the shaft. The types of sensors range from current, level, load and infra-red to hall-effect and limit switches which all work together to ensure smooth operation and reliable service.
One of the most common types of feedback encoders is the absolute encoder that gives feedback in the form of a unique value instead of pulses. This type of encoder is able to provide accurate feedback about the position of an elevator shaft.
The feedback signal from an absolute encoder can then be fed to a controller to perform various actions like elevator start and stop on the arrival of a floor or when the desired floor is reached. This can be useful in a number of applications that require accurate position control such as automated manufacturing, robotics and more.
Elevator feedback encoders can be integrated into motors or loads to communicate their position, velocity, acceleration or current. Depending on the encoder type, this feedback can be given as either an incremental pulse or an absolute value.
For PM motors, the rotor position of the motor is critical to proper stator field commutation in the VFD. Unlike a DC motor, the rotor of a PM motor is magnetic and thus requires the VFD to know its rotor position to modulate at the correct commutation angle to generate maximum torque output.
Because of this, the VFD must be able to accurately determine the rotor position from an absolute encoder. This can be done by physically mounting the encoder on the motor shaft.
Alternatively, the encoder can be mounted on a separate plate that sits on top of the motor. This allows the encoder to be secured to elevator encoder the motor shaft while maintaining a square and tight fit to prevent slipping.
If an encoder is not properly secured to the motor shaft, it can cause problems such as slipping or a misaligned position value convention. This can be fixed by ensuring that all set screws are securely fastened to the motor shaft and that all mounting points are clean and free of dirt and debris. Also, make sure the encoder is mounted squarely on the motor shaft to avoid a misalignment in the position value incrementing and decrementing convention.
Speed Feedback
A common application of elevator encoders is to provide speed feedback to the control system. They can also be used for monitoring and commutation of motors. This can be particularly useful on gearless traction motor elevators, where the motor must be able to achieve maximum torque while maintaining speed and position.
Elevator encoders can be found in a number of different configurations, depending on the specific application and desired output signals. For example, an absolute encoder provides a unique signal at each point of rotation, while incremental encoders send a series of pulses that indicate movement.
Absolute encoders typically use an incremental speed channel consisting of sine and cosine waves, phase-shifted by 90 deg for the A and B channels, to signal the shaft rotation direction. This output signal is then sent to the VFD, allowing it to measure the shaft speed and provide feedback to the control system.
Incremental encoders use a glass disc that contains a black/clear etching pattern for through-beam LEDs that become on/off pulses as the encoder rotates. Each of these pulses represents a certain number of revolutions, and the encoder can deliver a maximum number of signals per revolution.
Often, the output from an incremental encoder is combined with the input from a motor speed sensor (typically a hall effect or current sensor) to determine the speed of the motor. The combined output can be used for commutation of the motor, reducing energy consumption and maintenance time.
It’s also important to make sure the encoder is properly mounted on the motor shaft. Encoders can slip if not secured properly, and this can cause a large loss of motor torque. For example, one deg of error on the motor shaft for a 20 pole motor translates 1,820 counts of electrical error, which is a significant amount of lost motor torque.
Other factors that can cause encoders to slip include dirt or debris in the motor shaft and untightened set screws on the encoder. This can also result in mis-orientation of the encoder, and can lead to a high current draw.
Acceleration Feedback
The highest requirements for elevator transport comfort are to achieve smooth acceleration and deceleration, while avoiding unnecessary vibrations or reverberations. Accuracy and repeatability of encoder signals are also crucial factors in achieving these goals.
High-resolution rotary encoders are essential for accurate position and speed feedback in motors of all designs. elevator encoder They require a high-quality design to minimize radial and axial run-out, pitch and sensor interpolation errors. These errors can cause a significant degradation of the signal and, in turn, affect the control quality of the elevator drive system.
In addition, encoders must be able to withstand the environmental conditions of elevator shafts, such as concrete dust or the noise generated by forklifts. These factors can lead to damage to the encoder and may negatively impact safety and service life.
HEIDENHAIN offers a broad range of encoder products that are optimized for elevator use. These include the ERN 487 and ECN 413, which are rotary encoders specifically optimized for use in servo motors. These are also available with non-wearing, bearingless technology and magnetic scanning to deliver the longest possible service life.
To increase the efficiency of elevators, it is necessary to control synchronous or torque motors with high-resolution rotary encoders. This requires a highly reliable encoder with a long lifetime and zero defect tolerance.
The ERN 487 is a rotatable incremental encoder with a symmetrical design that ensures absolute value output. Its compact size makes it an ideal choice for space-saving integration in elevator motors.
Additionally, it has a robust, durable housing to withstand harsh environments and maintain its accuracy over time. This makes it a good option for elevators that are operated in extremely challenging conditions.
For a long time, the highest demands for the quality of rotary encoder signals have been related to accuracy and repeatability. In addition to these, the sensor must be able to withstand high rotational speeds, mounting positions and harsh environmental conditions.
This is a major challenge in the elevator industry. Several approaches have been developed for fault diagnosis using time-series data. Some have been based on neural networks [5,6,7,8,9], which can extract features from multiple signals and can self-learn to capture the relevant ones. Others have been based on deep learning methods, such as autoencoders and random forest. These methodologies have been successfully applied in fault detection of machines and robotics, and have proven powerful as feature extractors.
Door Feedback
A rotary encoder is a good choice for providing the speed and position feedback needed to operate an elevator door with a high degree of accuracy. They are also useful in detecting the direction of travel as well as providing the required power to the motor.
A particularly good one from HEIDENHAIN is the EQN 400 which comes in a variety of variants and sizes, including an extremely compact model that features a hollow-bore design. It is a worthy contender in the speed control competition for best in class.
Its most impressive feature is its ability to deliver the highest number of input signals. It accomplishes this by utilizing a dual-mode IC. The first mode, the IC’s most basic function, provides pulse outputs to the input terminals. The second mode is a more sophisticated version that uses an array of discrete ICs to produce phase-Z signals. The resulting signal is sent via an interface to an electronic PCB (VVVF drive) for further processing.
In a nutshell, the aforementioned EQN 400 can be considered the most important part of any modern elevator control system. It is able to perform the most challenging tasks with unparalleled precision. It is the best all-around device for providing dependable control over an elevator’s major systems: motor, brakes and shaft copying. It is the star of the show and the envy of many an engineer.
