Virtual reality is a fast-growing field of research that is applied
applied in various domains, such as gaming, medicine or in the automotive industry.
The large potential of force feedback devices for interacting in virtual reality has been illustrated in multiple research prototypes.
Yet, these devices are still rarely in use, especially in the automotive industry.
Therefore it remains unclear how to move these research into practice and how a suitable device would look like.
We contributed a participatory design study on the use of force feedback devices in the automotive industry.
We did a requirement analysis with 13 automotive VR engineers.
We showed them different feedback devices and asked about their pros and cons
in order to understand their problems of current existing devices and to define requirements.
We showed them propeller based feedback devices, electrical muscle stimulation, string based devices such as wi-eality and INCA 6D,
the Virtuose 6D, force feedback gloves and an exo-skeleton.
Based on the results, we defined 13 requirements, such as a flexibility in usage, a fast setup, high comfort or provide feedback on multiple body parts.
We checked which current force feedback devices meet of our defined requirements.
We saw the most potential in the wireality and inca 6D devices because of their low latency and high forces.
However, we wanted to optimize their flexibility in usage, price and mobility.
Our resulting prototype is STRIVE, a string-based force feedback device.
STRIVE is very mobile because of its weight and size, has low production costs and can cover a workspace up to 2 meters.
One STRIVE can provide a force feedback in one degrees of freedom in pushing direction, so you can use multiple to increase the degree of freedom.
Thereby, the users can decide their own tradeoff between degrees of freedom and comfort.
Here we attached one strive to the user’s backpack.
We can also place STRIVES on static objects such as tables, chairs or rigs.
Here we mounted a third strive on the controller and connected it to the user’s foot.
A STRIVE is able to stop the string extraction with the same technique that is used in Wireality [15],
which demonstrated strong arresting forces (180 N) with low latency (30ms) and a small, robust, and cheap design.
It has a reel with a mainspring for the string traction that is attached on a ratchet gear and a ratchet pawl that is connected to a solenoid.
If the solenoid is activated, it pushes the ratchet pawl inside the ratchet gear and the reel is blocked.
To communicate with the Virtual reality application, it has a bluetooth module and an arduino nano.
To provide flexible use cases, we designed different mounting modules to position strive on different objects or body parts,
such as the velcro strip for chairs, backpacks or hmds,
the screw module for aluminum profiles or walls,
the pants module to quickly attach it to pants,
and the controller module for the htc vive controller.
In order that the system knows when to activate which STRIVE, it needs only a few information.
It needs the solenoid position 𝑝𝑠𝑜𝑙 of the STRIVEs, the collision position pcol
and its normal which is determined by unity’s default colliders.
Now the system calculates the angle alpha, which is the angle between the collision normal and the vector between the collision and the solenoid position.
The smaller 𝛼, the better the collision can be simulated. Therefore, we do not activate the solenoids if alpha is higher than 90 degrees.
Using STRIVE, it is important to have a suitable string material that allows for a smooth friction and is thin and robust.
We had the hypothesis that strings that can be kinked, like nylon-coated braided steel strings, do have some force peaks when a kink passes the opening.
Therefore, we decided to do a small study on three different string materials, a fishing wire, nylon and a nylon-steel string.
Results show that there was an obvious force increase at the kinks. We measured a mean force increase of 0.9 N
0.9 N with the nylon steel and 0.4 N with the nylon string. Fishing wires instead, cannot be kinked.
These forces can already perceived as wrong collisions, therefore we recommend to use fishing wires for the STRIVES.
Additional, we measured how deep a user can penetrate virtual objects caused of the latency of STRIVE.
For this reason, we collided against a virtual wall multiple times with different velocities and measured the penetration distance.
Results show that the distance increases linearly.
There are some peaks in the low speed area.
We assume that these peaks occur due to the mounting module and the velcro strip, which are too elastic.
However, we estimate the mean working speed in vr under 20 cm / s, so the penetration distance is under 1 cm.
We evaluated STRIVE in five use cases with 16 VR experts of the automotive industries.
In the first use case we used two Strives and connected them to the controller.
With Strive the user feels the collision on the car components.
Therefore, he can feel the distances to objects in a more realistic way and can make a more reliable statement
statement whether the specific components are comfortable to reach.
In this use case, the user have to evaluate the ergonomic behavior of the assembly task.
Here, three STRIVEs that are connected to the user's head mounted display.
The ergonomic movement is depending on the head position.
The lower the user has to bend, the non-ergomical the task.
In this use case, we connected two controllers with a STRIVE to simulate forces on cable routing.
STRIVE stops the user's movement when he reaches the cable length .
Therefore, the cables behave in a more realistic way.
The user has to route cables on a car component.
Here, we use four STRIVEs to provide force feedback in a bi-manual assembly task.
Because of the large size of the component, it can not fully be seen in the user's field of view.
Without haptic feedback, the user can just visually check where a collision occurs.
In this use case, the user has to check whether he can reach a screw that he cannot see.
Four STRIVEs are connected to a 3D-printed screwdriver in order to simulate collision on the screwdrivers tip.
Here, the users have to evaluate the free moving space of the screwdriver.
The same use case is also important regarding the ergonomic movement of the user, because the working space is very limited.
Therefore, we connected two STRIVEs to the user's head mounted display and one to the elbow.
Each participant performed each use case twice, first without haptic feedback and then with strive.
After each use case, we interviewed the participant.
To measure the haptic experience, we orientated our questions on Defining Haptic Experience,
which guides design and research of haptic systems.
We asked about utility, restriction, consistency, saliency, harmony, realism and immersion.
Additionally, we asked them to rate each answer on a 7-point Likert scale where 7 means very positive and 1 means very negative.
The results were very positive.
The mean utility ranking is 5.1, and were very high at the headcollision and screwdriver use case.
The experts reported a mental relief, because they do not have to visually search for collisions.
Other experts explained us that STRIVE gave them more trust and confidence in their task results.
We were surprised by the positive feedback of the question about restriction.
The mean ranking is 5.1, where 7 means no restriction and 1 means high restriction.
The participants sometimes collided with the strings of strive,
however, they were not that irritated and restricted as we expected and some experts said they just have to get used to it.
The worst ranked question results was about realism with an average score of 4.5.
Some of the experts had problems with the virtual representation we used,
which did not match to the feedback they perceived. Other experts criticized the accuracy or the missing weight simulation.
Overall, the study results show a high potential in STRIVE and 14 of 16 experts would use STRIVE in their work.
They liked the flexibility and simplicity of strive. However, the experts mentioned some limitations.
Some experts were annoyed by the sound, that the solenoids create when they are activated.
Other experts criticized the accuracy of strive or the complexity when using many strives.
In the future, we would like to conduct a user study with a focus on setup.
With the experts mentioning that quick and easy setup is one of the most important requirements,
we would like to explore the setup process further to understand how we can bring STRIVE into their daily work.
Another technical future work is to make STRIVE more stable so that users can lean against virtual objects with their entire body weight.
Thank you for your attention.