Elevators


Overview

This tutorial describes how to use elevators in Gazebo. An elevator in Gazebo consists of a car, that moves up and down, with a door. Primatic joints control the car and door.

Functionality

The elevator functionality is implemented through an ElevatorPlugin. This plugin controls two prismatic joints:

  1. lift joint: used to raise and lower the elevator,
  2. door joint: used to open and close the elevator door.

During the plugin's update cycle, the lift joint will move the elevator to the requested floor, and the door joint will open or close the door depending on the elevator's current state. Movement to a particular floor can be requested by sending a string message with the floor number to the elevator's topic. Specification of these parameters is described in the following section.

The elevator's control logic is:

  1. Wait for a floor request.
  2. Close door.
  3. Move to requested floor.
  4. Open door.
  5. Wait for five seconds.
  6. Close the door.
  7. Go to #1.

Floor requests are not queued, and the elevator will complete its movement before responding to a new request.

Parameters

The lift joint, door joint, floor height, and control topic are all specified in SDF. The following is an example:

<plugin filename="libElevatorPlugin.so" name="elevator_plugin">
  <lift_joint>elevator::lift</lift_joint>
  <door_joint>elevator::door</door_joint>
  <floor_height>3.075</floor_height>
  <topic>~/elevator</topic>
</plugin>

In this example, an elevator model exists elsewhere in the SDF file with a joint for lifting called lift, and a joint for the door called door. The height of each floor is 3.075 meters, and the elevator plugin listens for floor requests on the ~/elevator topic.

Example

A complete example world is distributed with Gazebo. You can run this world using the following command:

gazebo worlds/elevator.world

This world has two floors and a single elevator. Place a simple shape on the landing in front of the elevator to trigger a floor request. This floor request takes place thanks to the Occupied Region Event, described next.

Occupied Region Event

The elevator plugin works well the OccupiedEvent component of the SimEventPlugin. The OccupiedEvent sends a message whenever a 3D region becomes occupied with a model. Refer to the OccupiedEvent tutorial for more information.