Episode 10 – Open the door
General description. Doors are ubiquitous in human environments. There are many types of doors, some of which are easier to operate than others for a robot.
Unfortunately, one of the most difficult types of doors is the most frequent of all, especially when considering private environments: the door swinging around hinges defining a vertical axis coincident with one side of the door, with a locking handle. To unlock the door, usually the handle needs to be rotated (around a horizontal axis perpendicular to the surface of the door) while moving, at the same time, the door from its closed position.
Other version of this type of swinging door are used in public spaces: these, while usually lacking the locking mechanism (and therefore the need to rotate the handle to unlock the door) are generally fitted with mechanisms for automatic closure that significantly increase the torque needed to operate the door. The resisting torque (due to the closure mechanism) frequently has a non-linear relation to the opening angle: for instance, it often provides the highest torque values at the extremes of the angular range.
A final difficulty is due to the very dimensions of doors: such dimensions are typically sufficiently large (w.r.t. typical robot arm lengths) to force a robot manipulating the door to move its base during the manipulation.
In the end, the capability of correctly operating doors with vertical-axis hinges is a necessity for any robot designed to effectively operate in human environments (and especially homes). However, this “door manipulation” functionality requires that the robot is capable of:
- Estimating the direction where the door opens (e.g., by trying each way and using force feedback to determine if resisting torque is compatible with a door opening that way);
- Correctly controlling the motion of the door in presence of variable resisting torque;
- Operating the locking handle (if present) in order to unlock the door.
Platforms allowed. Any robot platform with a movable base, an arm, and end effector capable of gripping a door handle (though different -though arguably less generally useful- configurations are applicable).
Setting. When the episode starts, the robot is in front of a wall at least 4 m long, facing such wall. In the center of the wall is a closed door. If the handle of the door is of the locking type, the door is also locked by it. The door has the typical look (frame, panels, handle) of one of the inner doors of an apartment. No other doors are present within 15 m from the robot.
Procedure. The robot must identify the door and approach it, remaining on the same side of the wall where it is at the start of the episode. When it reaches the door, the robot is required to identify the handle and use it to unlock the door (if the handle is a locking one), then open it completely. Complete opening is reached when the door orientation wrt its original orientation is within a specified tolerance from 90°.
The robot is considered as having completed the opening when two conditions occur at the same time:
- The end effector is no more in contact with the handle;
- The door is stationary.
The robot can only interact with the door using the handle. If the handle is a locking one, the robot must correctly operate it to unlock the door before the door can be moved.
If the door is of the bi-directional type, the opening direction of the door (away from the robot or towards the robot) is not known in advance, otherwise it is known to the robot. The only other information known to the robot at the start of the episode is that the door rotates around a vertical axis coincident with the side which is farther from the handle. In order to operate the door, the robot must autonomously ascertain:
- On what side of the door is the handle/are the hinges;
- If the door handle is a locking one (rotating) or not (fixed);
- (for bi-directional doors) What is the opening direction of the door (this can be done by trying both: only one will work).
While the door is moving, the robot must control its movement even in the presence of torque applied to the door by the door torque actuators (if present). The only predefined rules about the way this torque is related to the door opening angle are:
- The relation does not change over time;
- Torque is zero when the opening angle is 0° or 90° (or, possibly, within an angular range from each of these values which is unknown to the robot).
Please note that (as it happens with real doors) the relation between torque and angle may change according to the direction in which the door is rotating. Also, the torque applied to the door by its torque actuators (if present) is generally nonzero for angles (sufficiently) different from 0° and 90°: therefore the door moves on its own when not controlled by the robot, except at the extremes of its range.
DH interaction. None.
Main functionality(ies). The main functionality tested is Manipulation.
Auxiliary functionalities. Mobility/Navigation.
- Correctly opening the door.
- Correctly passing through the open door.
- Correctly pushing down the door handle.
- Damaging the door or the door handle.
- Stumbling on the door while crossing it.
- Being unable to open the door.
- Being unable to grasp the door handle.