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FEELEX

Fig1.FEELEX1

The FEELEX is a combination of an object-oriented-type force display and real-world graphics. A user of a real-world graphics system, such as the DigitalDesk or the Luminous Room space, interacts with rigid objects. On the other hand, the FEELEX system presents deformable objects, just like living creatures. This function provides a new interaction style compared to the object-oriented-type force display and real-world graphics.
In 1995, we started to develop a preliminary implementation of the FEELEX. A rubber screen was put on top of five linear actuators. An image was projected onto the screen and was deformed by the motion of the linear actuators. The basic function of the FEELEX was confirmed by this prototype. We developed further prototypes using down-sized actuators that improved the resolution of the haptic surface.
We developed the FEELEX 1 in 1997. It was designed to enable double-handed interaction using the whole of the palms. Therefore, the optimum size of the screen was determined to be 24cm X 24cm. The screen is connected to a linear actuator array that deforms its shape. Each linear actuator is composed of a screw mechanism driven by a DC motor. The screw mechanism converts the rotation of an axis of the motor to the linear motion of a rod. The motor must generate both motion and a reaction force on the screen. The diameter of the smallest motor that can drive the screen is 4cm. Therefore, a 6X6 linear actuator array can be set under the screen. The deformable screen is made of a rubber plate and a white nylon cloth. The thickness of the rubber is 3mm. Fig.1 shows an overall view of the device.
The screw mechanism of the linear actuator has a self-lock function that maintains its position while the motor power is off. We learned of the difficulty involved in representing a hard virtual wall from our experiences with the tool-handling-type force display. Considerable motor power is required to generate the reaction force from the virtual wall, which often leads to uncomfortable vibrations. The screw mechanism is free from this problem. A soft wall can be represented by the computer-controlled motion of the linear actuators based on the data from the force sensors. A force sensor is set at the top of each linear actuator. Two strain gauges are used as a force sensor. The strain gauge detects small displacements of the top end of the linear actuator caused by the force applied by the user. The position of the top end of the linear actuator is measured by an optical encoder connected to the axis of the DC motor. The maximum stroke of the linear actuator is 80mm, and the maximum speed is 100mm/s.

Introductory movie of FEELEX1 for SIGGRAGH '98 (as Haptic Screen)

Fig2.FEELEX2

The FEELEX 2 is designed to improve the resolution of the haptic surface. In order to determine the resolution of the linear actuators, we considered the situation where a medical doctor palpates a patient. Considering the above condition, the distance is set to be 8mm. The size of the screen is 50mm X 50mm, which allows the user to touch the surface using three fingers.
In order to realize 8mm resolution, a piston-crank mechanism is employed for the linear actuator. The size of the motor is much larger than 8mm, so the motor should be placed at a position offset from the rod. The piston-crank mechanism can easily achieve this offset position. Figure 4 illustrates the mechanical configuration of the linear actuator. A servo-motor from a radio-controlled car is selected as the actuator. The rotation of the axis of the servo-motor is converted to the linear motion of the rod by a crank-shaft and a linkage. The stroke of the rod is 18mm, and the maximum speed is 250mm/s. The maximum torque of the servo-motor is 3.2Kg-cm, which applies a 1.1Kgf force at the top of each rod.
This force is sufficient for palpation using the fingers. The flexible screen is supported by twenty-three rods, and the servo-motors are set remotely from the rods. Fig.2 shows an overall view of the FEELEX 2. The twenty-three separate sets of piston-crank mechanisms can be seen in the picture.

The diameter of each rod is 6mm. We cannot put a strain gauge on the top of the rod because of its small size, so we therefore measure the electric current going to each servo-motor to sense the force. The servo-motor generates a force to maintain the position of the crank-shaft. When the user applies a force to the rod, the electric current on the motor increases to balance the force. We measured the relationship between the applied force and the electric current. The applied force at the top of the rods is calculated using data from the electric current sensor. The resolution of the force sensing capability is 40gf.

Introductory movie of FEELEX2 for SIGGRAGH 2001

Related paper

  • Hiroo Iwata, Hiroaki Yano, Fumitaka Nakaizumi, Ryo Kawamura : Project FEELEX: Adding Haptic Surface to Graphics,Proceeding of SIGGRAPH2001(2001) pdf >>