Elevator Encoder

Encoders provide motion feedback to controllers, telling them when a machine or machine part has reached the correct position. This includes elevators, cranes and automated assembly lines.

Often these encoders are used to control elevator speed, but they can also be used for positioning and acceleration. Absolute encoders are a popular choice for these types of applications.

Positioning

Elevator encoders measure the position of an elevator car and its doors to ensure that they open level with the floor. This information is sent to the elevator controller, which sends a signal to the motor to start and stop the car.

A magnetic-tape-based system enables precise position measurement of an elevator shaft without any contact between the sensor and the car, which is particularly beneficial when measuring in hard, dirty or dusty conditions. Typical measuring errors caused by rope slip or dynamic rope effects (rope expansion) are also avoided.

The magnetic tape technology enables a high measuring precision, even in low-quality elevators or elevator shafts with high contamination. This is a major advantage over optical systems, which have to be adapted to the particular conditions and are prone to degradation under rough handling and in humid environments.

Encoders that provide feedback on the operation of an automatic door in an elevator need to be hollow-bore designs and compact enough to fit in the allotted space, while delivering fast and accurate rotational speed and position information. HEIDENHAIN offers rotary encoders for this application, providing reliable feedback to help minimize jerk-free operation and increase safety in this important transportation system.

Another type of encoder feedback device is an elevator governor, which prevents the elevator car from going too fast. This involves a separate assembly from the motor feedback that monitors the car’s speed and, when it reaches a predetermined threshold, activates a safety-trip mechanism.

Incremental encoders are a common choice for elevator speed control. They are inexpensive and offer an effective solution for this application. However, they cannot be used to commutate the elevator motor because this requires an absolute encoder.

In contrast, absolute encoders have an electrical interface and are typically elevator encoder used for commutation. This makes them ideal for this application.

Absolute encoders also have the ability to provide temperature monitoring data to the control for improved availability and safety. These features are especially useful in the elevator industry, where temperatures can be an indicator of wear and maintenance issues.

Speed

The speed of an elevator encoder can vary based on the type of encoder and application. In elevator applications, the encoder is typically used for monitoring the movement of the elevator car and providing information about its travel. This can be accomplished using a variety of different encoder types, including absolute and incremental encoders. Absolute encoders provide information about the rotational position of the shaft, while incremental encoders offer improved accuracy for measuring position.

An elevator encoder can also be used to monitor the movement of the automatic doors in the elevator car. These doors need to be open and close fully, so an encoder that can provide feedback on these movements is necessary.

Elevator encoders that are designed specifically for this purpose often have high resolution to detect slow openings and closings. These can be a valuable asset in an elevator system, as they can help prevent damage and increase equipment uptime.

Optical encoders are ideal for speed control, as they can accurately track the rotational positions of shafts over a dynamic range. However, ensuring that these devices have an accurate and stable signal can be challenging.

In particular, it is important that these devices have a stable supply voltage. Long cables can cause a significant voltage drop, which can lead to inaccurate sensors signals.

To avoid this, encoders with long cable lengths should be designed with tight tolerances for the supply voltage. They should be able to withstand a minimum of 5V +/-5%.

Additionally, long cable lengths should be insulated with insulation to prevent the wires from contacting each other. This can reduce noise from the circuitry and increase the lifespan of the encoder.

Another common problem with encoders is that they can be difficult to read if they are not located in a well-ventilated area. If this is the case, it may be necessary to add a ventilation fan to the system, which can increase the life of an encoder and improve its accuracy.

In addition to the ability to monitor an elevator’s speed, encoders can be used to provide feedback on the direction of travel of the elevator car and on the position of its wheels. This information can be used to determine whether an over speed situation has occurred and can be used to reduce the speed of the elevator car.

Acceleration

An elevator encoder is an essential component of an elevator’s drive system. It provides feedback signals that are used to control position, acceleration and deceleration. By providing these signals, the elevator encoder ensures that the elevator’s position and speed are accurate, which results in maximum ride comfort for passengers.

For elevators with a brake, start and stop jerks are undesirable because they can be uncomfortable and distracting for riders. Moreover, they can cause a hazard. For this reason, state-of-the-art elevators are designed to provide smooth jerk-free startup and slowdown of an elevator car.

To avoid these jerks, start and stop profiles are extracted from elevator sensor data including acceleration and magnetic signals by a Kalman filter. The algorithm is based on low-pass filtering and peak detection, and is used to fuse acceleration and magnetic sensor data into elevator start and stop events.

The resulting data is then compressed before transmission and analyzed to identify faulty rides. The selected faulty rides are fed to the algorithm for profile extraction separately from healthy rides.

Once the profiles are extracted, they are compared to elevator rated speeds for any over speed conditions. If a speed that is greater than the rated speed is detected, the motion control 34 may trigger a software tripping point and notify a brake 14 to activate via a link 48 within the controller 28.

If the brake is activated, a drive motor 42 may take the information provided by the A&B channels 30 of the encoder 16 and modify the torque and frequency of operation of the drive motor to reduce the speed of the elevator car 4. This is done to bring the elevator car back to its rated speed while maintaining safety requirements.

This technique is cost effective, but it can elevator encoder produce a jerk when the elevator first moves. In order to prevent this jerk, a starting torque profile is used that begins with a high speed. It then decreases to a lower speed until the jerk stops.

In addition, the acceleration profile may be adjusted in a way that it promotes a smooth opening of the brake. This can be accomplished by selecting a starting torque profile that begins with an increasing speed and decreases to a lower speed when the elevator first moves.

Brake

The brake function of an elevator encoder is important for preventing unintended motion of the elevator car, especially during low and high speed elevator runs. This function is also useful for determining if the elevator has been loaded with an overload.

When the current supply to the winding of a brake is disconnected by closing a first and a second controllable switch, the electricity stored in the winding is discharged into an intermediate circuit of the brake control circuit. This reduces the energy that would have been consumed in braking and thereby minimizes the amount of current that is required to operate the safety gear of an elevator car.

If the detected operational nonconformance of the movement control system does not require immediate disconnection, the current supply to the winding is controlled as follows:

In this way the braking force exerted on a moving part of the elevator machine by the brake shoe can be reduced with as little deceleration as possible. In the case of a normal or low speed elevator run, this reduces the amount of current that is required to brake the movement of the elevator car, which may result in the brake shoe pressing against the moving part with more force and thus providing better safety.

However, the braking force exerted on the movement of the elevator car during an emergency stop can be more uncomfortable for passengers. For this reason, an adjustable brake function can be used to provide a braking ramp that varies the amount of deceleration that is applied to the elevator car.

This method is particularly helpful when the brake shoes on the elevator brakes wear. It allows the FB value, which is calculated automatically from the velocity feedback of the encoder, to be adjusted based on the wear and tear of the brake shoes.

For this purpose, an outer and inner track are arranged around the encoder. Each of these tracks includes a light source and a light detector (not shown) that produce electrical signals when encoder 36 rotates through and chops the light beam from the light source.