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Human-robot handovers

102 Chapter 3. Toward seamless Human-Robot Handovers

was presented able to grasp unknown arbitrary objects for interactive manipulation tasks. In [98] Sisbot et al. developed a navigation planner that creates safe, legi-ble, and socially acceptable paths. Takayama et al. [99] explored how personal space (proxemics) varies when approaching and being approched by a robot based on the human’s experience with robots and where the robot looks during the approach. In [100] Mumm et al. studied how proxemics varies with a robot’s likeability and eye gaze. Mainprice et al. [101] created a trajectory and motion planner that can vary the amount of human motion required to handover, allowing the robot to choose the best handover location based on context.

Reaching: In [47] Glasauer et al. investigated how a robot can convey the intent to handover and signal its readiness using human-like reaching gestures.

Transfer: A physical aspect of the handover is transferring control of the object.

Nagata et al. [59] presented a grasping system based on force and torque feedback that senses when the humans has a stable grasp on the object, after which the robot can release the object. In [102] Sadigh et al. presented a robotic grasping controller inspired by human grasping to grasp an object with minimal normal forces while ensuring that the object does not slip.

Common Ground: During the handover, the actors use their common ground to de-cide how to communicate with each other, plan tasks, and coordinate actions. Hoff-man et al. [103] created a measure of fluency for huHoff-man-robot interactions and also found that anticipatory agents are more efficient than pure reactive agents. This work highlights that robots should be able to accurately predict for human actions.

What - Joint Commitment: Before handing over, the actors must have a joint com-mitmentto handover, establishing that they are both willing and able to perform the handover. One capability that facilitates entering a joint commitment and maintaining the commitment is the recognition of engagement. Rich et al. [104] observed engage-ment in human interactions, used these observations to derive four types of events that contribute to the perceived engagement, and created a computational pipeline that robots can use to detect these events and determine human engagement.

When: The handover process requires the actors to coordinate when the handover will occur. From the study in [76], we know that eye gaze is very important when

3.3. Human-robot handovers 103

signaling when to handover in human-human handovers. Mutlu et al.[105] examined the effectiveness of gaze cues performed by robots that are designed with abstracted human-like features. In [106] Cakmak et al. confirm that arm extension is an impor-tant signal to communicate readiness to handover. They also suggest that having a distinct carrying posture prior to extending the robot arm, is critical for people to un-derstand when they can grab an object from the robot. Grip positions may matter less in terms of signaling its readiness to hand over an item, though it may make it more convenient for people take an object out of robots’ hands.

Where: The handover process requires the actors to coordinate where the handover will occur. In [60] Edsinger et al. found that during a handover humans will pose an object in the robot’s stationary hand regardless of the robot’s hand pose, demonstrat-ing that humans adapt to the robot’s hand pose. Pandey et al. [61] investigated how a robot can predict where the human will handover and then proactively move to this location. Sisbot et al. [63] developed a manipulation planning framework that chooses handover locations based the human’s safety, accessibility, field of view, posture, and preferences. In [11] Cakmak et al. suggest that robot should choose the best handover configuration taking into consideration the human’s preferences, i.e. choose the best object location, object pose, and arm configuration.

3.3.2 Human-robot handover phases addressed in this thesis

The two systems described in the previous chapter implement various aspects of human-robot handovers and the user studies conducted evaluate their performance.

These aspects are all parts of the physical process of handing over, specifically how to present and negotiate the physical handover, but they also are used to coordinate when and where the handover should occur.

The system described in section 2.2 was used to explore how to perceive human readiness and how to negotiate when and where to hand over. This issue has been already addressed in [61] in cases where the robot suggests the hand over location. In my study, I focused on cases where the human suggests the hand over location while the robot complies, such as in the mechanic example where the robot is the assistant.

The system developed is able to infer the human readiness by detecting reaching

104 Chapter 3. Toward seamless Human-Robot Handovers

gestures of the human, to negotiate the where by tracking the position of the object that the human is holding, and to convey the robot readiness to start the transfer by reaching out and softly touching the object. These skills have been achieved using an accurate perception system and a reactive controller to move the robot arm which, during a user study, has proved to be suitable for this kind of interaction. Since the robot actively negotiates where to handover up to the contact with the object, it needs to behave in a way which is accepted by the human and that makes the human feel comfortable and safe. In the user study described in section 2.2 I found out that in order to obtain such a suitable behavior the following four factors are crucial during the interaction when negotiating the where and when of the handover:

Forcefulness: The robot must be able to apply the proper force to the object in the final part of the reaching and during the transfer of the object.

Aggressiveness: The robot must tune its velocity. It is important that the robot does not move too fast when close to the human. Its velocity should be directly propor-tional to the distance from the object.

Predictability: Predictability makes humans more comfortable around the robot because they can plan into the future and know that it won’t do anything strange.

Timing: Human-human handover are fast. Robots should be as fast as humans to obtain a seamless interaction.

The system described in section 2.3 was exploited to study where the robot should hand over an object when delivering it to a human, how it should present the object and how the robot can detect the human readiness to start the transfer of the object.

In addition, the system has been used to study how the joint commitment can be obtained (through verbal interaction) in cases where the robot does not have enough information to infer a handover based on human cues and the context does not contain information about which object has to be delivered. User studies showed that in order to obtain a seamless interaction the robot should include the following considerations in its behavior:

• the robot should perceive the human and his/her position and configuration in order to propose the object in front of him when it is possible.