Study on Telexistence LXXIV
Haptic Layer Design and Integration for Virtual Telesar
MHD Yamen SARAIJI, Charith Lasantha FERNANDO, Masahiro FURUKAWA, Kouta
MINAMIZAWA and Susumu TACHI
Keio University, {yamen, charith, m.furukawa, kouta, tachi}@tachilab.org
In this paper, we present haptic sensor design as a part of virtual telexistence platform, which aims to aid the designer
to select the proper sensors as a haptic sensor for robot hand. Profiling curve defines the relation between sensor’s
measurements from the simulated environment and its output providing to the display. By providing various profilingcurves, we can have variations of the same sensor but with different characteristics for various applications. By
assuming that the simulated environment provides a representation to the real physical environment, the sensor can beassumed as a candidate for physical utilizing. Here we provide an implementation for a pressure sensor as an exampleof the approach.
Key Words: Virtual Reality, haptic sensing, telexistence

1. Introduction
On telexistence, haptic feedback plays an important role inmaintaining the feeling of surface textures as well as thefeeling of being actually existed in the remote environment.
Actually we’ve already achieved to have haptic experienceswith textures of clothes [1].
The sensors, which are embedded on the tip of robot’s
fingers, palms, fore arms, or etc., are required to be designed
to fit some conditions; measurable range, dynamics
following capability and so on when the sensor contacts withobjects. It is still difficult to design proper sensor as well as
to select a proper one, to position it and etc., because
physical prototyping of the sensor obviously requires us to
use the physical avatar robot to experience and evaluate theprototype. This is the reason why the simulator is necessary.
However, it often uses an ideal physical model not referring
property of physical sensors in order to calculate reactive
forces in real-time [2] [3].
Thus, we propose a virtual prototyping method fortelexistence, which reflects the actual sensor properties. It
seems significant to provide real-time experience during
evaluation in addition not only to choice a sensor based on aspecification, but also to change the its position easily.
Therefore, in this study, we provide a model of physicalsensor as a virtual one, implement a graphical user interface
for editing the sensor profile and implement it as a part ofvirtual telexistence platform with physical haptic display[3].

2.

Concept

2.1 System Architecture
As we reported before, Virtual Telesar [4] is designed
modular based platform to provide an interactive visualexperience to the operator as shown in in Fig. 1.
Virtual Telesar architecture contains physics simulation
layer, to simulate a dynamics of avatar robot, which reflects
user’s behavior through a master cockpit. Addition to thearchitecture, we add a haptic layer, which provides contact
positions and forces affecting sensor’s surface as well as
control the haptic display [3].

Fig. 1 Virtual Haptic interaction as in physical environment(L) Real Robot Interaction (R) Simulated Interaction

Basically, the focused haptic sensors we would integratewith this platform are: contact force feedback sensor, thermalsensor, and tactile sensor. Although there are several
considerations to consider as a tactile sensor, in this paper,
we focus on the pressure type sensor because it is consider asa proper sensor for receiving static force or dynamic forcechanging slowly. In contrast, texture sampling requires aproperty of high frequency response, for example, whenstroking the rough surface defined in a virtual world. To
evaluate the possibility of haptic layer design, we focus on
the former one; force sensor receives static force.
2.2 Haptic Layer Design
This layer consists of the sensor appearance, profile, anddriving ability of the haptic display to experience the force tothe operator. The layer is independent from the core part ofthe simulator called Virtual Telesar.
The virtual sensor behaves as a transducer from contact
force obtained between virtual sensor and the object into themeasured value. The sensors can be defined by its
transformation function. The function relates the inputs of thesensor (observed values) and converts those captured values
into output value set.
By defining different transformation functions for eachtype of sensor, we can create multiple sensors simulating thebehavior of different physical sensors. This method also isavailable for simulating a custom sensor. By using various
sensor behaviors, we can either design custom sensors for theaim of experience, or we experience simulated sensors.

3.

Sensor Model

3.1 Physical Sensor
Depending on the properties of the sensor, output signal

can be linear or nonlinear. For most physical sensors, byplotting their characteristic chart we can notice the nonlinear
behavior.
For example, a plot for force sensor INASTOMER SF-R-3
φ77.2mm shown in Fig. 2, which shows how it responses
better to low forces than high forces (this is a measuredgraph, not an official one). On the other hands, other sensors,
such as LMA-A-5N with a linear response curve, havedifferent characteristics and behavior towards the acting
forces. Depending on the response curve, the application areaand proper purpose might be different.

achieve that. In this test we used a haptic display [3] toprovide the measured forces into the finger. First wemeasured the display’s response curve when the sensor wasusing a linear modulation function: G(Fs)= Fs . In order todesign proper modulation curve for the sensor, we studied
the display behavior towards its input.
To create the modulation curve, a GUI tool allows thedesigner to create such curve as in Fig. 4. The designed
modulation curve is saved later as a separate profiling file tobe assigned to the sensor.

Fig. 4 Modulation curve design user interface
Fig. 2 INASTOMER sensor response curve

Thus, it is essential in the virtual environment to be able todefine such curves for the sensors in order to estimate for thephysical sensors. Or to provide proper output to the haptic
display which would be reflected on the user experience.
Also, in order to decide the suitable characteristics curvefor virtual sensor, it is important to understand the response
curve for the haptic display.
3.2 Sensor Behavior
In the physical sensor case, it works by capturing theapplied forces over the contact surface. As same as this, inorder to obtain the amount of force affecting the sensor, wecalculate the incorporated sum of the forces, which areaffecting on the axis of the sensor using Eq. (1):(1)Where M represents number of contact points, Fk is force
value. Nk represents force normal k on sensor’s surface, Ns issensor’s axis and Fs is the result force. The inner productbetween normal in the previous formula acts as a weight tothe force, measuring the force exerting the sensor’s axis asshown in Fig. 3.

The maximum force we could generate before thesaturation of the display was ~110g; this is due to display’slimit. The modulation and converting the response to belinear helped to fix the experience when interacting with thevirtual objects.
Using this method it would be possible to change theprofile for the sensor at run time. The user of the system thencan select the target profile depending on his application.
Those profiles can be either to achieve an ideal sensor or tosimulate the behavior of real sensors as in Fig. 2.

4. Conclusion
We proposed the haptic layer design to find the proper
sensor with subjective experience. The layer behaves as apart of virtual telexistence platform and it contains the visualsensor with actual sensor profile curve. It also controls thehaptic display to let the operator experience the static force.
By using such method we can define various curves to gain
different sensations when contacting the virtual objects.
As a next step, we proceed by implementing other types of
haptic sensors using this approach of design to become partof the platform.

Acknowledgement
This work was supported by JSPS Grant-in-Aid for
Scientific Research A (23240017).
References[1][2]

Fig. 3 Illustration of the applied force on sensor’s surface

3.3 Profiling Curve
The modulation curve can be defined as a function G(Fs) inwhich is exerted on the force signal calculated in Eq. (1).
Depending on how we want the sensor to respond to theforce, and most of the time that would depend on the type ofthe display we are using, we can define a suitable function to[3][4]Fernando, C.L.; Furukawa, M.; Kurogi, T.; Kamuro, S.; Sato, K.;
Minamizawa, K.; Tachi, S., "Design of TELESAR V for transferring
bodily consciousness in telexistence," IROS, 2012, pp.5112-5118.
Thomas H. Massie, Kenneth J. Salisbury. PHANToM haptic
interface: a device for probing virtual objects American Society ofMechanical Engineers, Dynamic Systems and Control Division(Publication) DSC, Vol. 55-1, pp. 295-299.
Minamizawa, K., Fukamachi, S., Kajimoto, H., Kawakami, N., Tachi,
S,. Gravity grabber: wearable haptic display to present virtual masssensation, ACM SIGGRAPH 2007 emerging technologies (2007),Article 8, 1 page.
Saraiji, M.Y., Fernando, C.L., Furukawa, M., Minamizawa, K., Tachi,
S., Virtual Telesar - designing and implementation of a modular based
immersive virtual telexistence platform, SICE-SI, 2012