Elevator Control Systems

Elevator control systems are the mechanisms that manage the movement and operation of elevators in buildings.

They are responsible for controlling various functions, such as motion control,door operation, floor selection, load management, safety features & traffic management.

Source: Wikipedia

Elevator Inputs

Elevator systems use Human-Machine Interface (HMI) to process inputs from users and sensors, interacting with algorithms to ensure smooth operation. Inputs are signals from sensors, buttons, and other user or environmental interactions.

Examples include:

• Floor selection buttons: Pressed by passengers to request a specific floor.
• Weight sensors: Measure the load inside the elevator to prevent overloading.
• Position sensors: Detect the elevator's current position within the shaft.
• Door sensors: Detect whether doors are fully closed or if there's an obstruction.
• Emergency buttons: Trigger alarms or special safety actions when pressed.

ADCs in Elevators

Many sensors in elevators generate analog signals (e.g., from load sensors, temperature sensors). An ADC is required to convert these analog signals into digital data that the elevator's control system can process.

Example

The load sensor might produce an analog voltage proportional to the weight inside the elevator. The ADC converts this voltage to a digital value that can be read by the processor to determine if the elevator is overloaded.

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Processing in Elevators

This is where the system's microcontroller or processor makes decisions based on the input data. The processor is responsible for:

Interpreting inputs

Understanding requests from passengers (which floors to stop at) and feedback from sensors (e.g., elevator position, door status).

Running control algorithms

Deciding the elevator's movement, such as whether to accelerate, decelerate, or stop.

Coordinating traffic

In buildings with multiple elevators, the processor helps optimize the allocation of elevators to handle passenger demand efficiently.

Safety checks

Ensuring the system reacts appropriately in the event of an overload, emergency stop, or other abnormal situations.

Actuators in Elevators

Actuators are the output components that physically carry out the instructions from the processor. In elevators, these include:

Motors

Elevators are driven by motors that control their vertical movement. The processor controls the motor’s speed and direction.

Brake systems

These engage or disengage to stop the elevator at the correct floor.

Door actuators

Motors that open and close the doors.

Indicators and alarms

Lights, screens, and audible alarms provide feedback to passengers.

Example Elevator Control Process

1. A passenger presses a button to go to the 5th floor (input).
   
2. The processor reads the button press and the elevator’s current position from sensors.
3. The ADC converts the signal from a position sensor into a digital signal to determine where the elevator is.
4. The processor instructs the motor (actuator) to move the elevator to the 5th floor, adjusting speed and stopping smoothly.
5. Once the elevator reaches the floor, the processor signals the door actuator to open the doors.

Elevator Sensors

Position Sensors

Detect the elevator's precise position in the shaft, ensuring it stops accurately at each floor.

Load Sensors

Measure the weight inside the elevator to prevent overloading and manage proper acceleration and deceleration.

Speed Sensors (Encoders)

Monitor the speed of the elevator to ensure it is moving at the correct velocity.

Door Sensors

Detect objects or passengers in the doorway to prevent the doors from closing when blocked.

Proximity Sensors

Used to detect the arrival of the elevator at a floor, typically for door operation.

Limit Switches

Mechanical switches that act as backup to stop the elevator if it goes past certain limits within the shaft.

Vibration Sensors

Detect abnormal vibrations in the elevator system, which might indicate maintenance needs.

Elevator algorithms

Elevator dispatching algorithms control the movement of elevators to minimize waiting time and optimize efficiency. Key types include:

First-Come, First-Served

The elevator services requests in the order they arrive, regardless of direction. Simple but inefficient when requests are far apart.

Look (SCAN) Algorithm

The elevator moves in one direction, servicing all requests, then reverses. Reduces direction changes.

Elevator (SSTF) Algorithm

Moves in one direction, servicing requests until the farthest, then reverses. Common in real-world elevators.

C-LOOK Algorithm

Services requests in one direction, then jumps to the first request in the opposite direction, skipping idle floors.

 Priority-Based

Handles high-priority requests (e.g., emergencies) first, even if out of order.