Initial situation

Technologies and methods for the presentation of virtual reality are increasing in numerous fields of application. Apart from seeing and hearing, feeling also plays an important role for immersing into artificial worlds. In this context the feeling of objects with a different and locally varying stiffness has strong significance.

A physician can detect pathologic changes of organs, such as tumors, by using the diagnosis of palpation (feeling). By external detection of the consistency of tissue inside the body – comparable to ultrasonic diagnostics – and its virtual presentation outside the body, the applicability of palpation as a soft method of diagnosis would be extended. The separated detection, storage and virtual presentation of the consistency of tissue can also be used for remote diagnosis in telemedicine, assessment of tissue changes as well as learning palpation.

Additionally, it is also attractive to present simple haptic impressions by suitable technologies. This concerns the perception of forces on moving objects in a virtual world (force feedback) as well as the use of operation tools like push-button switches or rotating knobs. For this purpose, it can be necessary to equip push, impact or snap in points with flexible response. Presently only few matured and expensive technologies exist for the generation of such functions.

Guide to solution

Electrorheological fluids (ERF) offer various possibilities for the realization of actuator elements with diverse functions. The consistency of such materials can be changed quickly and reversibly by a strong electric field. On applying the voltage, the ERF becomes gelleous within some milliseconds and returns to its liquid state right after switching off the voltage.

By using this electrorheological effect, resistance forces are generated which can be felt by the user. The forces can be regulated according to the present situation with a convenient software. Since such devices are mechatronic systems, much attention has to be paid to the tuning of the properties of the fluid and the mechanical as well as electric components.

The Fraunhofer ISC develops electrorheological fluids for haptic applications. In feasibility studies haptic actuator elements ranging up to functional prototypes have been built; for instance a joystick with force feedback which moves a cursor on a computer screen. If the cursor enters a special region, the user perceives an increased resistance against the motion, i.e. the motion is conveyed not only optically but also haptically according to the principle “you feel what you see”. Such a system could also give support to people with poor eye-sight working with computers (“you feel what you cannot see”).

Compared to single actuator elements for the operation of devices, the haptic presentation of object surfaces requires much more effort. For this purpose the arrangement of a large number of actuatoric elements in an array is necessary in order to reach the required local resolution and to convey the user with an impression approaching reality when he feels the virtual object. A haptic actuator array was developed in a joint project with various partners funded by the BMBF (German Ministry for Education and Research). It consists of numerous cells with a size of about two millimeters, the perceivable stiffness of them is generated by an ERF.

While the Fraunhofer ISC developed an ERF with the required properties, the Institute of Microtechnology Mainz (IMM) produced the tactile cells with microtechnological production methods. The individual electric supply of the electrorheological tactile actuators was realized by the Fachhochschule Regensburg. With the method of ultrasonic elastography a sensor system determines consistency data of real objects which afterwards can be displayed on the actuator system. The sensor system was developed at the Ruhr University Bochum. With this composite system in the joint project an innovative technology platform was created from which new products can arise in future.

Application perspectives

Haptic sensor actuator systems are considered to be especially interesting for medical technology. Representing other applications, the palpation of organs should be mentioned in comparing diagnosis, in telemedicine as well as in simulations in training. Furthermore, promising perspectives arise for the entertainment industry. Graphic and acoustic presentations may be extended by haptic elements in electronic games or multimedia presentations.

Such haptic systems can also be used in information and communication technology as well as in electronic commerce. Thus, information can be transferred haptically via touch panels which is of great importance for operating devices (man-machine-interface) or for blind and poor-sighted people who work with computers. In future electronic commerce one could also transfer the haptic impression of products via the internet. Further perspectives of application for the haptic sensor actuator system arise in telerobotics.