1DOF Sensor and Display system of Haptic and Temperature SensationHiroaki Yano∗

University of TsukubaItsuro Hayashi†

University of TsukubaHiroo Iwata‡

University of Tsukuba

ABSTRACT

This paper describes development of a haptic sensor and displaysystem that is sensing hardness and temperature of a real object si-multaneously and displaying them as a virtual object. The sensorsystem consists of a force sensor, a linear-encoder, and a thermis-tor. And the display system is composed of a DC motor, a rotary-encoder, and a planer end effecter which mounts a peltier device.Evaluation of this system was performed through a measurementand display experiment.

Index Terms: H.5.1 [INFORMATION INTERFACES ANDPRESENTATION]: Multimedia Information Systems—Artificial,augmented, and virtual realities; H.5.2 [INFORMATION INTER-FACES AND PRESENTATION]: User Interfaces—Haptic I/O;

1 INTRODUCTION

By the latest rapid growth of the performance of network technol-ogy and computer, a huge quantity of digital data can be exchangedbetween remote users. Information of visual and auditory sensationsuch as pictures or video is mainly exchanged now. In addition, bythe above technical progress, the haptic sensation will be exchangedbetween remote users. For example, in a remote shopping applica-tion, a friend goes to a shop and remote users can see live video andtalk with him/her. In addition, he/she scans haptic information of aproduct with a haptic scanner and then send the information to theremote users. The remote users can not only see the live video butalso feel haptic information with a haptic interface. In such situa-tion, force feedback is useful for feeling the shape and hardness ofan object. Also, temperature information is useful to feel the ma-terial of the object. By using a haptic server, remote users can feelthe haptic information of the object in real time or at any time.

Many temperature displays had been developed and some ofthem combined with tactile interface [4]. However, there is no dis-play combined with proprioceptive display and temperature display.It is quite natural for users to use a rich haptic interface such as 6DOF (Degree Of Freedom) force feedback interface and a tactile in-terface. However, we can acquire much information by using sim-ple 1 DOF interface like a communication with Morse code. Fur-thermore, the 1DOF interface can be manufactured with low cost.

In this study, we developed a 1 DOF haptic interface that candisplay proprioceptive sensation and temperature simultaneously toa user. Also, we developed data acquisition system of hardness andtemperature, of a remote object simultaneously.

2 SYSTEM CONFIGURATION

This system consists of a haptic sensor system, a display systemand their control PC (DELL DIMENSION 8250) (Figure 1).

∗e-mail: yano@iit.tsukuba.ac.jp†e-mail:hayashi@vrlab.esys.tsukuba.ac.jp‡e-mail:iwata@kz.tsukuba.ac.jp

Figure 1: Basic configuration of this system.

Figure 2: Basic configuration of the haptic sensor system.

2.1 Haptic sensor systemThe sensor system composes of a hardness sensor and a temperaturesensor (Figure 2).

As hardness parameters of an object, there are Young’s modulus,Poisson ratio and Brinell hardness, Shore hardness, etc. Amongthese, Young’s modulus can be considered the most fundamentalparameter in case of use with a haptic interface. However, the shapeof target object is required to measure Young’s modulus. Alterna-tively, spring constant of Hooke’s law is easy to measure and usein haptic interface. In this study, we implemented an equipment formeasuring the spring constant of a real object. Although there areseveral methods to measure a hardness such as a method by usinghigh frequency vibrator [1], considering easy to fabrication at lowcost, we use two sensors, a displacement sensor and force sensor.By calculating a value of the force over the displacement from anobject’s surface, we can get the spring constant. A prototype hard-ness sensor is shown in Figure 2. It has a base plate and a rodwhich are made from aluminum. The rod connects with the plateby a spring coil and it can be put in a hole on the plate. In addi-tion, a linear encoder (LIC-0308, made by Murata ManufacturingCompany, Ltd.) connects the base plate and the rod. Consider-ing hardness of real objects at dairy life, a force sensor (FlexiForceA201-25 maximum measuring load 110 N, made by NITTA Cor-poration, ) is attached to the underside of the rod. In an initial state,the underside of the rod and the underside of the plate are the same

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Symposium on Haptic Interfaces for Virtual Environments and Teleoperator Systems 200813-14 March, Reno, Nevada, USA978-1-4244-2005-6/08/$25.00 ©2008 IEEE

Figure 3: Basic configuration of the display system.

height. When a user puts the underside of the sensor to an object,the plate contacts the object surface. And the object caves in ac-cording to displacement between the rod and the plate. The springconstant of the object can be calculated with the displacement andthe force measured by the encoder and the force sensor. The res-olution of the encoder is 0.125 micro meter. The resolution of theforce sensor is 9.8 mN.

Temperature can be measured by using an infrared camera, athermoelectric couple or a platinum resistance temperature detec-tor. However, since our sensor attaches to a target object, it is dif-ficult to use a camera system. Also to avoid deformation causedby temperature sensor’s shape, it has to be thin, light and flexible.Considering above, we use thermistor as a temperature sensor. Aprototype temperature sensor consists of a thermistor (JT Thermis-tor 103JT, made by Ishizuka Electronics Corporation) and its drivercircuit. The thermistor is attached on the underside of the baseplate of hardness sensor near the rod. Since the thermistor has 1mm height, it might cause force sensor error if it attached on theunderside of the rod. The sensor has resolution of 0.02 [deg C].

Spring constants and temperatures of a sponge, a forearm and abean-paste bun were measured by using the sensor system. As a re-sult, spring constant were 0.4, 1.0 and 0.2 N/mm and temperatureswere 23, 32 and 45 deg C respectively.

2.2 haptic Display systemWe developed a 1 DOF haptic display system, which can displayhardness and temperature, of a virutal object simultaneously. Thedisplay system consists of a hardness display and a temperature dis-play (Figure 3).

The prototype hardness display consists of a linkage which ro-tates about a horizontal axis, and its controller. Since we don’t pushso strongly when we touch a virtual object, we assumed that de-formation of an object was small. The pushing operation, whichwill be a linear motion, can be approximated by the linkage. Fur-thermore the configuration of the linkage is easy to implement withlow cost. The linkage is 0.06 m length and is attached to a gearedDC servo motor (RE25 made by Maxon motor) with an optical shaftencoder. A user can feel a reaction force of 18.3N at the maximum.The resolution of the encoder is 0.09 [deg]. The reaction force iscalculated by the Hooke’s law.

As a temperature display, there are a resistance heating elementand a heat pump system. However, they become large and it is dif-ficult to heat user’s finger or to cool it with the same equipment .Then a peltier device (T151-40-031S made by S.T.S) is used in thisstudy. It is attached on top of the linkage of the hardness display.A user can touch it directly and feel a temperature and a reactionforce simultaneously by using the display system. The peltier de-vice is controlled at open loop control. It can present a temperaturefrom room air temperature to 90 [deg C]. In this study since a hugecooling mechanism is required for decreasing the temperature, thetarget temperature is set above the room air temperature.

Figure 4: Average preference rate about hardness.

3 EVALUATION WITH PAIRED COMPARISON METHODFor texture perception, factors, such as surface roughness, heattransfer property, and modulus of elasticity are used [3]. By us-ing the prototype system, an experiment which investigates whethertemperature has influence with hardness perception was conducted.Evaluation is based on the Scheffe’s paired comparison method. Inthis experiment, 3 hard nesses (0.4, 1.0 and 0.2 kg/cm) and 3 tem-peratures (23, 32 and 45 deg C) were provided. These values werecaptured from a sponge, a forearm and a bean-paste bun by usingthe sensor system. By combining these values, a total of 9 condi-tions were provided. Two of the 9 conditions were chosen as teststimulus. Subjects answered which stimulus was harder with thevalues from -3 (soft) to 3 (hard). The subjects wore an eye maskand a headphone which played white noise of -20 dB , to shut outvisual and auditory cues. To reset haptic sensation at the subject’sfingertip, Over 10 seconds refresh period was prepared before eachtrial. During the period, the subjects put his/her fingertip on analuminum plate with the room air temperature. 6 male subjects(whose ages were from 19 to 24) conducted 72 trials respectively.The result is shown in Figure 4. The horizontal axis means aver-age preference ratio of each condition. As a result, all subjects candistinguish 3 hardnesses, not affected by temperature. There is nosignificant difference between each temperature at same hardnessin this condition. The system operation capability was confirmedthrough this experiment.

4 CONCLUSIONIn this paper, a haptic sensation and temperature sensation captureand display system was developed. Through an evaluation test, thesystem operation capability was confirmed.

When we recognize the material of an object, we use skin tem-perature change after contact as a key [2]. We plan to improve thecontrol algorithm of our temperature display to present more real-istic sensation.

REFERENCES[1] http://www.microphotonics.com/sonohard.html.[2] S. Ino and et.al. A tactile display for presenting quality of materials

by changing the temperature of skin surface. In Proc. of IEEE Inter-national Workshop on Robot and Human Communication, pages 220–224, 1993.

[3] H. Shirado and T. Maeno. Modeling of texture perception mechanismfor tactile display and sensor. In Proc. of World HAPTICS 2005, pages629–630, 2005.

[4] Yang and et.al. Development of quantitative tactile display device toprovide both pin-array-type tactile feedback and thermal feedback. InProc. of World HAPTICS 2007, pages 578–579, 2007.

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