Hi, I am XXX from National Taiwan University.
I am going to share our work, ElastiLinks.
Force Feedback between VR Controllers with Dynamic Points of Application of Force.
Handheld controllers are the common devices in VR.
Force feedback is commonly used to enhance realism.
Force feedback is not only on but also between controllers,
like playing a shooting game using a bow and a slingshot.
However, to achieve realistic force feedback,
not only realistic force types,
but also proper points of application of force are essential.
A point of application of force,
or also called a PAF,
is where the resultant force is applied to.
As we can see the red points in the figure.
Ｗhen pulling a bow,
users perceive resistive force without torque
since the positions of the PAF and the hand are almost the same.
However, when pulling a slingshot,
users perceive torque of resistive force
since the PAF is above the hand on the controller.
Therefore, a dynamic PAF on each controller is required
for proper PAFs between controllers.
Previous works majorly focus on various force feedback on a controller
instead of between controllers.
For force feedback between controllers,
Haptic Links proposed three mechanical brakes on their three links, respectively,
to render variable shapes and stiffness feedback.
However, the PAFs are fixed.
Some methods leverage the property of dynamic PAFs
by moving weights to generate weight- and shape-changing illusions in VR.
However, how force feedback with dynamic PAFs between controllers affects users’ VR experience
still waits to be explored.
ElastiLinks consist of two controllers, tracks, connectors, and force links.
Each controller rotates a track and moves a connector,
where the links connect to the controller, on the track.
Therefore, the connector becomes a dynamic PAF
and is able to provide different torque to the controller and the hand.
The force feedback between the controllers is generated by force links.
Furthermore, ElastiLinks provide two common types of force feedback, resistive force and impact,
based on our previous works ElasticVR and ElastImpact,
on the two links, respectively, between the controllers.
With the two types of force feedback and two dynamic PAFs,
ElastiLinks achieve realistic and versatile force feedback between controllers in VR.
Here we can see how ElastiLinks work.
The connectors with rotation and offset movement achieve dynamic PAFs.
The offset is perpendicular to the rotation plane.
Then, we performed three user studies to evaluate our device, ElastiLinks.
We first conducted a perception study to understand
users’ resistive force and impact level distinguishability between controllers,
which is for a proper PAF study design.
Two VR scenes were built for two force feedback, respectively.
By adjusting the width of the elastic band between the controllers
and the size of the ball hitting the controller in VR,
the participants needed to match the visual feedback
and the perceived force feedback best.
The wider that the elastic band is, the stronger is the resistive force.
The larger that the ball is, the stronger is the impact.
The results show that 3 levels are distinguishable for both force feedback.
We then performed another perception study to observe
users’ distinguishability of PAF rotation and offset differences for resistive force and impact, respectively,
which also proves the necessity of requiring dynamic PAFs.
This study design was similar to the previously conducted force perception study.
The participants adjusted the PAF position
instead of the force levels in the visual feedback in this study.
For rotation, we observed that
two PAFs with the same rotation angle from the initial position but in the opposite
was easily confused.
Therefore, we computed the absolute values of the rotation data
to remove the direction from the consideration for further analysis.
The results show that the participants could distinguish the rotation of the PAF stimuli
but not the torque direction.
For offset, 3 offset stimuli are distinguishable for both feedback.
Here are the results of the study.
Interestingly, we observe that
resistive force with a longer application time than impact has better PAF distinguishability.
Finally, we performed a VR experience study with 3 applications,
to observe how dynamic PAFs affect users in VR
and verify whether the force feedback with dynamic PAFs from ElastiLinks enhances the VR experience.
Different PAFs and force levels for resistive force and impact were provided in
survival shooter game with bimanual interaction,
fighting game with one controller grounded on body,
and fishing game with one controller grounded in environment.
In first application, survival shooter game,
the weapons were provided are two bows, two slingshots, rifle and launcher.
Participants used these weapons to prevent zombies from approaching.
The force feedback of bows and slingshots are resistive force.
For the rifle and launcher, the feedback are impact.
In second application, fighting game,
we explored how ElastiLinks used for the interaction, grounded on body.
One controller was fixed on the arm, and the other was held by the dominant hand.
The weapons were provided are knife, knife with reverse grip, knuckle and claw.
Participants needed to attack approaching mummies by these weapons.
All force feedback in this application are impact.
In final application, fishing game,
we anchored one controller on a desk
to show how ElastiLinks were used for interaction, grounded in the environment.
The participants held the other controller as a fishing rod in VR.
The grounded controller rotated the track back and forth between -45 degrees and 45 degrees
to simulate the fish moving against the participants.
Three feedback methods were compared in this study
including vibration, fixed PAFs, and ElastiLinks.
Vibration from the Vive controllers was regarded as the baseline for the comparisons.
Fixed PAFs method was implemented by ElastiLinks devices
with multilevel resistive force and impact but with fixed PAF.
The results show that ElastiLinks have better realism, enjoyment and distinguishability.
In conclusion,
this paper provides force feedback between controllers with dynamic PAF,
explores user's resistive and impact force level perception between controllers,
explores user's distinguishability of offset and rotation differences of PAF,
and proves that force feedback with dynamic PAF from ElastiLinks enhances VR realism.
Thank you for your attention.