Elevator Encoder
Elevators are designed to transport passengers safely and quickly to their destination. To do this, the car needs to be able to start gently, stop at just the right height, rapidly open and close its doors, and smoothly speed off again.
Encoders provide feedback to motors and brakes to help elevator cars achieve these goals. They also deliver the data needed for operational monitoring.
Positioning
In a motion control system, an encoder is a detection device that converts motion into an electrical signal to be read by some type of controller. Encoders are used in many applications, including elevators and robotic assembly lines.
In an elevator, the encoder tells the controller when a car has reached its correct floor, and in the correct position. It ensures that elevator doors open level with the floor, so you don’t have to climb in or out.
Similarly, in a crane application, the encoder feedback tells the crane when to pick up or release its load. In an automated assembly line, it can be used to give the robots information on where they should weld.
Since permanent-magnet (PM) motors have become more popular options in elevator applications, the rotor positions on these motors must be known by the variable-frequency drive to modulate the motor at the proper commutation angle to produce maximum torque output. Consequently, the VFD needs an absolute position encoder on the motor shaft to determine the rotor position.
If the encoder position values increment or decrement in the wrong direction, the VFD must use more current to generate the desired torque and the motor may not turn as it should. This can lead to higher maintenance costs and decreased performance, as well as potentially dangerous consequences for people inside the building.
Absolute encoders typically feature an A-B channel to determine whether the position values are incrementing or decrementing. Depending on the A-B phasing and the manufacturer’s established position incrementing and decrementing convention, the encoder may “lead” channel A or “lag” channel B.
These encoders are available in a variety of form factors, resolutions and output interfaces to meet the stringent requirements of precise positioning and velocity sensing in a wide range of industrial machines, robotic arms, lifts, elevators, light detection and ranging (LiDAR), automated guided vehicle (AGV), solar panel tracking, medical devices and factory automation.
The Lika Electronic SC shaft copy system is a complete belt / cord measuring system that includes mechanical components, pulleys, toothed belt or stretched cord and a choice of incremental and absolute encoders to fit almost any application (DSP 417 CANLift protocol encoders included). It offers an “all-in-one” solution with all parts needed for installation preassembled in one box.
Speed
The speed of an elevator car is a critical element for the safety and comfort of passengers. In addition, elevators have to be able to withstand the environmental conditions in an elevator shaft which may include concrete dust or other elements that can cause damage to the mechanical parts of the vehicle.
To meet this need, a variety of sensors are used in elevator systems including current, level, load, infra-red, and hall-effect sensors. The sensors communicate this information to a control device that controls and changes the speed of an elevator motor.
In the case of an elevator powered by a gearless traction motor, an encoder is used to monitor the speed and position of the elevator car. In this application, the encoder may be a hollow-bore encoder that mounts directly to the non-drive end of the shaft.
One type of encoder uses alternating openings and masked regions to provide electrical signals related to the motion of elevator encoder elevator car 26. The order and rate of signals received from the masked regions can be converted to determine the linear distance traveled by elevator car 26.
Another type of elevator encoder is an absolute encoder that is mounted on a measuring wheel to provide feedback to the elevator control system that can accurately position the elevator car. Absolute encoders are available with various mechanical interfaces and electrical contacting options to meet a wide range of applications.
An elevator encoder may also be used to prevent the car from going over a threshold speed. This is achieved by a separate assembly that runs over sheaves and connects to a safety-trip mechanism.
The elevator car is stopped when the elevator encoder detects that it is traveling over a pre-determined threshold speed and a switch is actuated. The safety switch can be a manual or a hydraulic system that will lock the sheaves and stop the elevator.
In a typical installation, an elevator drive system includes controller 18, inverter 22, and hoist motor 12. Controller 18 compares velocity and motion feedback from encoder 36 to a commanded velocity and direction of motion for elevator 14. The commanded velocity and direction of motion is based on efficient dispatching of elevator car 26 based on elevator demands. When the actual velocity and direction of motion of elevator 14 does not match the commanded velocity and direction of motion, controller 18 operates inverter 22 to drive hoist motor 12 such that the desired velocity and direction of motion of elevator 14 is obtained.
Door opening/closing
Door opening and closing speed is a significant factor in elevator operation, which can affect stopping times and passenger transport volumes. This requires precise and fast servo-controlled door motors that deliver accurate and dynamic position feedback.
Compact rotary encoders deliver this needed position feedback in an efficient and robust design. They are well suited for applications with high shaft loads such as up to 150 N axially and 350 N radially.
In addition to providing rotational speed and position feedback, the HEIDENHAIN EQN 400 also includes a bearing assembly that decouples the encoder from the axial and radial forces. This eliminates the risk of overloading the rotary encoder and ensures maximum accuracy and reliability.
The HEIDENHAIN EQN 400 is particularly suitable for applications with high axial and radial shaft loads. In addition, the encoder’s hollow-bore design is very space-saving and allows for optimal placement in the elevator car.
New elevators must meet new code requirements for a device that automatically reverses the direction of the hoist way doors when they are obstructed. This feature can save lives by alerting passengers to an incoming elevator or an obstruction in the entrance area that could cause them to fall into the elevator.
Some elevator manufacturers provide a 2D door detector with flashing-colored LEDs that signal the doors are in the closing phase (Figure 2). These devices offer additional passenger protection from stray doors.
Many elevators also provide a safety ray or multi-beam door sensor that detects passengers boarding or exiting. These sensors are located in the bottom and top corners of the elevator car, ensuring that the doors open at the correct time to prevent accidents.
Elevators also have a feature that automatically reverses the direction of the closing car door when it encounters an object in the doorway. This function is elevator encoder required under the New York City Safety Code for elevators and escalators.
Whether or not this function is present, property managers can test it by standing in front of the hoistway door for a few seconds while it is fully open and not obstructing the 2D car-door device (Figure 1). If the audible nudging door-closing signal occurs, no further action is required.
Fault detection
An elevator encoder is a small sensor that measures the movement of an elevator car and transmits it to a control system. It can be either an incremental or absolute encoder, depending on the application. An absolute encoder is ideal for shaft copying applications that require jerk-free braking and precise positioning of the elevator car, while an incremental encoder is more cost-effective in speed control.
Many types of faults occur in rotatory machines such as elevators, and there are several methods that can be used to detect them. Typically, fault detection algorithms use features extracted from accelerometer or magnetic signals, and these features are classified with a random forest algorithm to determine whether the fault is real or not.
Faults in the elevator can have severe consequences if not detected quickly enough. For example, if an elevator encoder fails, the position of the hoist motor can no longer be determined. This can cause the elevator to move uncontrolledly, which is not safe for passengers and can lead to injury.
The encoder also provides temperature monitoring data, which can help to pinpoint wear and plan maintenance. This helps to maximize equipment uptime and improve reliability.
This is a valuable advantage over other systems, which often require additional sensors and cabling to provide this kind of information. In addition to enhancing availability and safety, this technology can significantly reduce maintenance costs for elevator manufacturers.
Another advantage of an elevator encoder is its ability to detect multiple zones in an elevator. This can be particularly useful in cases where there is a possibility of a passenger contact or door strike.
Detectable zones can be divided into outer door zone, inner door zone and dead zone. These zones are usually characterized by the occludement of one or more sensors during a rise in an elevator.
When an elevator starts to rise, its optical unit 10 begins to surround the vane 16. As the optical unit continues to rise upwardly, it will continue to occlude sensors A and D. Eventually, only sensors B and C will remain occluded.
