MoTiS Parameters for Multi-Robot Expressive Motion

MoTiS Expressive Motion Parameters

(Mo)tion, (Ti)me and (S)pace: A hierarchical framework for multi-robot expressive motion that allows people of varying programming experience to generate and design expressive multi-robot motion

What key aspects of group and individual motion are needed to generate a wide range of expressive and social motions?

How are variations on each of these parameters perceived?

(Mo)tion, (Ti)me, and (S)pace

MoTiS is a hierarchical framework for multi-robot expressive motion consisting of six features: (1) relative direction, (2) coherence, (3) relative speed, (4) relative start time, (5) proximity, and (6) geometry. This framework seeks to extend and coalesce prior concepts from single and multi-robot expressive motion, as well as introduce novel parameters.

Relative Motion

Relative motion refers to how the group or individual agents move relative to something else, and they are features that span both time and space. The two parameters under relative motion are relative direction and coherence, both of which extend prior concepts from single and multi-robot expressive motion.

Relative direction being used to signal the human can enter

Relative direction being used to block an entryway and signal the human is not welcome.

Relative Direction

Relative direction refers to the direction individual robots, or the robot group, move relative to something else, for example the robot group moves away from a human.

Direction is also a key part of functional tasks. For example, to deliver a package a robot will have to move towards the package recipient.

Design Recommendations for Relative Direction:

Moving towards is interpreted as...
- Functionally blocking the human when moving relative to an entryway or person approaching
- Aggressive and threatening when robot speeds are slow and moving relative to a person
- Friendly and welcoming when robot speeds are fast and moving relative to a person

Moving away is interpreted as...
- Allowing a human to enter a space when moving relative to an entryway or a person approaching
- Fear or dislike when moving relative to a person
- Friendly and welcoming when moving relative to an entryway

Coherence

Coherence refers to the degree to which the individual robots in the group are doing the same thing. The idea of group coherence has been used in multiple works on generating multi-robot expressive motion, which has specifically looked at general temporal and spatial synchronicity in multi-robot groups.

The coherence parameter in this work is extended beyond temporal and spatial synchronicity. In this work, coherence can apply to many different aspects of the group motion, for example directional coherence or speed coherence.

Design Recommendations for Coherence:

Coherent motion can lead to strong communicatory signals
- However it is sometimes perceived more negatively than incoherent motion, especially when moving towards a person
Subgroup size affects communication strength, ie larger subgroups have stronger communication within a group
Incoherent motion can lead to more nuanced stories of the subgroup motivations than coherent motion

Relative Spacing

Relative spacing refers to how the agents are spaced as a group, or what shape they are creating as a whole. The two parameters under relative spacing are geometry and proximity.

Threatening triangle

Fun line

Geometry

Geometry refers to the shape the robot group is making as a whole, and has been shown to be an effective tool in creating expressive and communicative group motion. The concept of shape in an expressive context has also been studied, and different shapes have been shown to elicit different emotional responses in humans . Geometry also closely maps to the Laban concepts of Shape and Space, which are used in dance and choreography, both of which are forms of expressive motion.

Proximity

Proximity is the relative distance between two things. The proximity parameter is inspired by work in proxemics that explore the social spacings between humans, and the prior work in social robotics that has used proxemics in social navigation.

We extend proximity to also include the proxemics between the robot group as a whole and humans, rather than individual agents within the group.

https://teachernvc.weebly.com/proxemics.html

Relative Time

Relative timing refers to the timing of movements of individual agents relative to something else. The two parameters under relative timing are relative start time and relative speed.

Relative Speed

We extend the concept of speed to include the "relative'' term, which means speed is not only referring to the speed of the multi-robot group as an absolute, but also as relative to something. For example, the multi-robot group can move down a sidewalk faster than the average pace of the pedestrians, rather than just moving "fast.''

Here, speed is specifically not defined as velocity, since velocity is comprised of both direction and speed.

Relative Start Time

Relative start time is when one robot in the group, or the whole robot group, starts moving relative to something else.

Similar concepts to start time, such as delays and arrival time, have been previously studied in single robot expressive motion.

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Publications:

Bacula, Alexandra, and Heather Knight. "MoTiS Parameters for Expressive Multi-Robot Systems: Relative Motion, Timing, and Spacing." International Journal of Social Robotics. Nov, 2022.
Bacula, Alexandra, Heather Knight. "Incoherent Robot Groups: How Divergent Motions within a Robot Group Predict Functional and Social Interpretations." Proceedings of the 8th International Conference on Movement and Computing, pp. 1-6. June, 2022.
Berger, Jaden, Alexandra Bacula, Heather Knight. “Exploring Communicatory Gestures for Simple Multi-Robot Systems,” Proceedings of the 13th International Conference on Social Robotics, Singapore, November, 2021.

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