Elevator Encoder

Elevator Encoder

Elevator encoders are a key component of elevator control systems. They provide reliable and accurate position and speed feedback to a computer that controls and adjusts the motor speed of an elevator.

Encoders are used in many different types of motion control machines. These devices convert motion into an electrical signal that can be read by a control device for feedback.

Speed Feedback

An elevator encoder provides speed feedback to the control system for the hoist motor of an elevator. The feedback can be used for both open and closed loop control of the motor.

In order to provide speed feedback, an elevator encoder typically uses incremental signals. Incremental encoders can be magnetic or optical and provide both an indication that the shaft has moved and a signal to indicate the absolute position of the motor.

Optical sensors are the most common type of encoder that provides speed feedback. They also provide a clear signal, making them ideally suited for use in an elevator application where a high resolution is needed.

Absolute encoders are also available for elevator applications and can be used for both speed and position feedback, but they do not provide a signal to indicate the exact position of the motor.

One of the most common causes of encoder slippage is improper mounting. For example, if an encoder is mounted on the stub shaft of a motor and the mounting screw has become bottomed out or caught. This may cause the encoder to rotate in the wrong direction, which can cause a high current draw or not turn the motor.

Another reason for slippage is if the stub end of the motor shaft has excessive runout (e.g., 0.003 in). Excess runout can cause the encoder to not turn properly, which can lead to premature motor failure or damage to the bearing.

Encoders are also susceptible to slipping when they are mounted in different hoistway positions or directions, such as if the motor is rotated out of the way. This can occur due to grease on the shaft, broken mounting tabs, or other factors that cause the encoder to become displaced from its optimum position.

To prevent this, encoders must be carefully mounted on the motor shaft without slippage. This can be done with a special tool that creates a flat surface on the shaft for the encoder to be mounted. It can also be done manually by holding the encoder on the shaft.

Position Feedback

Elevator encoders provide elevator encoder accurate and reliable position feedback to elevator controllers so they can control and adjust the motor speed. This ensures a comfortable and smooth ride for passengers.

Encoders can be of two types: linear and rotary. Linear encoders detect the position of a load or shaft directly while rotary encoders monitor the motion of an elevator motor by detecting the rotational speed of the shaft.

Both types are typically used in elevator applications, but the rotary type is often more robust and durable than a linear encoder. It also offers greater flexibility in design compared to linear encoders, which are typically only designed for use with a single load and motor.

Unlike linear encoders, rotary encoders report feedback on the rotational speed of the shaft by measuring the magnetic field around the rotating encoder wheel. These encoders are able to operate in harsher environments than linear encoders and can work with both permanent-magnet (PM) and reluctance motors.

In addition to determining the rotor’s position, an elevator encoder can provide feedback on the axial motion of the rotor and brake. This can be useful for monitoring the brake’s release and engagement as well as for evaluating the amount of brake wear.

For this reason, HEIDENHAIN offers an absolute rotary encoder for elevators: the KCI 419 Dplus. It provides not only feedback on the rotor’s position but also meaningful temperature data.

Another benefit of an absolute rotary encoder is that it will never lose its value even if power is interrupted. Unlike incremental feedback, which can be affected by voltage interruptions, an absolute rotary encoder will never lose its position and report it to the controller once power is restored.

Absolute rotary encoders generally feature two incremental speed channels: channel A is a square wave that’s square-wave pulsed in response to the rotational movement of the shaft, and channel B is a continuous square wave with a 90 degree phase shift. The A-B phasing of the encoder can be swapped physically at the interface or with a software parameter setting based on drive type.

Brake Feedback

In addition to speed and position feedback, elevator encoders can also provide brake feedback. When the elevator moves, the encoder can detect if the motor is moving too far and will trigger a fault to prevent further operation until the condition has been fixed.

This is helpful for many applications, such as safety and compliance to national regulations or standards. If a motor is too far from the load, it can cause an elevator to move in an unintended way and may result in a shear cut to the door.

The elevator encoder can also be used to monitor the motor commutation angle for proper stator field alignment. If the rotor shaft is not aligned properly, the motor will need to draw extra current to generate the needed torque. This can result in an increase in commutation time, which can be costly to the elevator manufacturer or building owner.

For this reason, most modern elevators have an encoder that provides a position value and a speed value for the motor. These encoders can be positioned directly on the motor shaft, or they can be incorporated into a microswitch.

Alternatively, the encoder can be fitted in series with the winding of the brake and then connected to one end of the winding by means of a controllable switch. This allows for the winding to be isolated from the electricity supply and to be controlled by the switch.

In this case, the switching device can be used to connect the winding of the brake to an intermediate circuit, wherein the regulating loop makes use of the difference between the reference for the brake current and the measured movement signal. elevator encoder If the difference exceeds a difference threshold magnitude, a brake difference indication is provided.

The encoder can be adjusted to respond quickly to the rotor slippage so that the motor is stopped before it goes too far. This helps ensure that the system is safe, and it prevents nuisance faults.

This type of brake feedback can be useful for preventing a motor from overheating or short-circuiting during emergency stops. The feedback can be provided from the encoder in real-time to a sensor such as a relay, which is then connected to an output contactor, allowing for an automated shutdown when the motor is overheating or short-circuiting.

Door Feedback

In an elevator, the doors need to open and close fully so that passengers can board and exit without being caught between the door. This requires a robust motor, a powerful drive and feedback that allows the elevator controller to track the door position.

Servo-controlled door motors are an excellent choice for this application, delivering precise speed and position control at low power consumption. They can also operate in a variety of environments and are available in hollow-bore designs for compact installation.

A new microprocessor controlled closed-loop elevator door controller from Encore provides accurate door position and velocity sensing by utilizing an encoder. It’s easy to install and works with 90-120 VAC input nominal or 130 VDC input commonly used in older OTIS machines. It also has auto-learning with pre-defined door profiles that make for quick adjustment.

This system is a full retrofit kit including a motor/encoder assembly that can easily replace the PM motor and encoder in an OTIS 6970 machine or GAL MOD, MOM or MOH operator. It also features a built-in digital keypad for quick operation controls.

Encoders are a great way to monitor the movement of an elevator’s doors, helping to ensure that the cars are always in the right position and level with the floor. They can also help to minimize callbacks, the number of times that an elevator must be serviced because of a door-related problem.

To get the best door feedback, you need to choose a high-quality encoder with a good signal quality and high resolution. This is particularly important in an environment that has a lot of high-power cables.

One such device is the rotary encoder, which delivers a true position value in an absolute sense. It uses an optical, magnetic or capacitive sensor to read a unique code from a disc that revolves with the shaft.

This information is then communicated to the driver of the elevator motor. The result is a smooth and quiet ride for all who use the elevator.