Elevator Encoder
Elevator encoders help traction elevators start gently, stop at just the right height, rapidly open and close doors, and smoothly speed off again. They also deliver the data needed for operational monitoring.
In a permanent magnet (PM) motor elevator, the variable frequency drive (VFD) requires a precise rotor position to modulate at the correct commutation angle for maximum torque output. This requires an absolute encoder mounted on the stub end of the motor shaft to provide a position signal that can be read by the VFD.
Speed Feedback
An elevator encoder provides speed feedback to a controller in an elevator drive system. It does this by sensing the speed of a hoist motor and providing feedback to the controller that the hoist motor has reached a certain velocity. This speed feedback is important in controlling a drive system in an elevator because it ensures that the hoist car moves up and down in a manner that is level with the floor.
Encoders provide motion feedback to a controller in a number of applications, including drug delivery systems, automated assembly lines, and robots. Depending on the application, encoders may produce incremental signals or absolute signals that indicate that a certain position has changed.
For synchronous motor elevator machines that use permanent magnet (PM) motors, the rotor position needs to be known in order for the variable frequency drive to commutate the PM motor at the proper commutation angle to achieve maximum torque output. To determine this position, an encoder is connected to the motor shaft.
As the rotor position changes, the motor requires more current to generate the desired torque output. The commutation angle of the PM motor can vary by several degrees due to the angular position of the rotor relative to the stator pole windings.
When a malfunction occurs in an elevator encoder, such as a power failure, it can cause the speed feedback to drop to zero or close to zero. This can result in uncontrolled or unintended motion of the hoist car.
To prevent this from happening, a fault threshold time is set in the elevator controller that allows the controller to quickly detect a malfunction of the elevator encoder so that it can disable the elevator drive system and engage the brake to minimize unintended motion of the elevator car.
Steps in the process include a controller sampling the encoder signal provided by the encoder to compare it with a commanded velocity (step 60). If the commanded velocity is greater than zero, but the velocity feedback from the encoder is less than a minimum velocity threshold (step 62), a fault bit is set in the elevator controller.
Position Feedback
An elevator encoder converts motion to an electrical signal that is sent to a controller. The signal tells the controller what position the elevator is in. It can also be used in other applications, such as a printer or an observatory.
In elevators, the position feedback provided by an elevator encoder ensures that doors open fully and level with the floor. This can help reduce noise and vibrations in the elevator, and can be beneficial for safety.
Elevator rotary encoders from companies like Heidenhain offer more than just transmission of rotational position values. They can also measure axial motion, which is important for detecting the brake’s stroke and determining whether it is engaged or released.
This kind of feedback can significantly increase the availability and safety of an elevator. Additionally, elevator encoder it can reduce the cost of installing and maintaining microswitches.
For example, if an encoder on a motor shaft is mounted 1deg incorrectly (electrically), that would be a loss of 1.52% of the motor’s torque. If the encoder is mounted 2deg incorrectly, that would be a loss of 6.0% of the motor’s torque, and so on.
The encoder can slip if the encoder mount is not secure to the motor shaft, or if grease accumulates on the encoder. This can be particularly a problem with PM motors, which require more accuracy than other types of motors.
When a rotary encoder is not properly secured to the motor, it can sway or move in different directions, causing inaccurate information to be transmitted. To prevent this from occurring, the encoder must be secured to the motor shaft using a set screw.
This type of feedback can be very helpful in elevators, as it allows for faster, more accurate installation and provides a reliable means to detect malfunctions. It can also save money by reducing the number of switches needed in an elevator.
In addition to providing a range of different types of feedback, elevator encoders can also provide temperature monitoring data. This can be useful for identifying issues with the motor and brake, such as hot spots or excessive wear.
Door Feedback
Elevator manufacturers have a plethora of technologies at their disposal to ensure passenger safety. This includes infrared sensors and a load sensor that monitors the weight of each door. There are also limit switches that set a maximum and minimum height for the elevator car, which is essential for maintaining safety and keeping passengers from being caught in between doors.
Encoders are also an important part of the puzzle to ensure that elevator doors open and close in a smooth and controlled manner. They provide feedback to the motors in the door to ensure that they operate smoothly and efficiently.
The best encoders are small, lightweight and low-profile enough to fit inside a typical elevator car. This helps reduce vibration and noise for the passengers inside. They also offer elevator encoder a wide range of inputs and outputs for the controller or control electronics.
One of the coolest features is the ability to sense temperature. This is useful for detecting wear and tear, planning maintenance, and for predicting malfunctions before they occur.
For this purpose, HEIDENHAIN offers a number of rotary encoders designed to perform the task. Some of these are even rated to handle high shaft loads up to 150 N axially and 350 N radially, which is more than enough to keep the occupants of an elevator safe from the evils of overloading. The KCI 419 Dplus is an example of this type of encoder. It is the first encoder in this class to offer a comprehensive online self-diagnosis that is as easy to use as a smart phone app.
Motor Feedback
The motor feedback provided by an elevator encoder is critical to controlling the motion of an elevator. It helps a controller determine the speed and direction of movement of an elevator car, which in turn influences the lift’s safety systems. In addition, it monitors automatic doors in an elevator car, ensuring that they fully open and close.
Encoders in an elevator provide a number of benefits, including efficiency gains that increase load capacity, reduce installation space requirements, shorten maintenance intervals, and cut energy costs. These benefits, in turn, help building owners realize new designs and save on construction expenses.
An elevator encoder also provides a valuable feedback signal that is used to control the commutation of a gearless traction motor. This enables the drive to maintain proper motor phasing, a critical requirement for permanent-magnet synchronous motors, also known as torque motors.
In these applications, absolute position feedback is required to accurately synchronize the UVW phasing of the three-phase AC voltage applied to the motor stator winding with the PM magnetic field on the rotor. Absolute encoders that are mounted directly to the motor shaft ensure that the rotor rotation is electrically commutated to the stator phasing in exactly the right direction.
This requires a reference procedure that is performed during startup. It is recommended to phase the drive and motor together such that U-U, V-V, and W-W are swapped physically at the interface or via a software parameter setting based on the type of drive being used.
Depending on the mounting configuration of the encoder, this may cause a discrepancy in the incrementing and decrementing convention for position values coinciding with the direction of the motor stator field. This can result in inaccurate commutation or a reduced motor output.
Another important function of an elevator encoder is to provide a feedback signal that is used to detect when an elevator car’s speed has exceeded a threshold value and to trip the safety mechanism. In this way, the elevator governor can be quickly engaged to limit the motion of the car.
A fault bit is set in the controller when the commanded velocity of an elevator car exceeds a minimum threshold value, and this is detected by the feedback signal from encoder 36. If the commanded velocity remains greater than zero, the fault bit is cleared and the feedback signal is processed again.
