Dr. Zadeh can be contacted by:
Phone: (810) 762-9500, Ext. 5914
Fax : (810) 762-9830
Office: AB 2-703-P
Email : email@example.com
Electrical & Computer Engineering Dept.
Kettering University, 1700 Third Avenue West,
Flint, Michigan 48504
Design of haptic displays is one of the main challenges in creating virtual reality systems that have the sense of touch. The haptic interface design depends critically on the capabilities of human perception. Human factors studies are required to quantify our force thresholds and investigate the effects of factors on our force perception. Knowledge about these human factors can be incorporated in haptic applications such as the design of haptic interfaces, development of haptic data compression techniques, and improvement of computer-aided design (CAD) systems. Listed below are my primary research work:
- Perception-based haptic compression techniques
- Adaptation of kinesthetic sense to forces in a virtual environment (VE)
- Factors affecting the just noticeable difference (JND) of force perception
- Studying the effect of sub-threshold forces on human performance in VEs
- Modelling haptic devices using a rule-based expert system
- Haptic Display of deformable objects
Perception-based haptic compression techniques
Since realistic haptic environments require significant data transfer, compression techniques play a significant role in transmission of multi-media information. Researchers have investigated efficient lossy compression techniques for image compression (jpeg) to facilitate the storage and transmission of images. Most lossy visual compression techniques rely on the lack of sensitivity in humans to pick up detailed information in certain scenarios. Similarly, limitations in the sensitivity of human touch could be exploited to create haptic models with the minimum amount of haptic data necessary to reproduce the correct feel to the user under a given set of conditions. These compression techniques store the haptic data only when the force exceeds a certain threshold of the force perception.
In this research, the absolute force thresholds (AFT) of the human haptic system are detected for three different ranges of velocity of the user's hand motion through psychophysical experiments. The AFT is the smallest amount of force necessary to produce a sensation. The detected AFTs can be used in a psychophysically motivated lossy haptic (force) compression technique in cases where the human user or the object is in relative motion. This study implies that, when a user's hand is in motion, fewer haptic details are required to be stored, calculated or transmitted.
Adaptation of kinesthetic sense to forces in a virtual environment (VE)
Realistic haptic rendering is one of the most challenging issues in the field of virtual reality. The kinesthetic sense of the human haptic system is mostly used to feel a virtual surface using haptic devices. Of course the intent is for the user to experience the same sensations in the virtual realm as they would in the real world. Therefore, we need to know the capabilities of the human haptic system. With this in mind, limitations in the sensitivity of human kinesthetic sense could be exploited to create haptic models with much less detail. For example, a compression technique stores the haptic data only when the force exceeds a certain threshold of the force perception. If the threshold is higher, the haptic data can be more efficiently compressed. The force threshold increases when the sensory system adapts to forces.
In this study, the existence of adaptation to force feedbacks in a virtual environment (VE) is invesigated. Psychophysical experiments are conducted to study how adaptation is influenced by changes in the force intensity and direction. The results indicate that the users definitely adapt to forces in a VE. However, the force direction and force increment/decrement do not affect adaptation. This limitation can be incorporated in the haptic compression technique when users are in touch with the haptic device for an extended period of time. If the force threshold is higher due to adaptation, the haptic data can be more efficiently compressed.
Factors affecting the just noticeable difference (JND) of force perception
The capabilities of the human haptic system play an important role in designing haptic displays. Thus, quantitative human studies are required to ascertain the impact of human factors on the design of haptic devices. The focus of this study is on the quantitative measures of human force thresholds that affect the design specifications of force feedback haptic interfaces. Most researchers in this field have measured the Just Noticeable Difference (JND) of the human haptic system with the user in static interaction with a stationary rigid object. However, we are interested in detecting the limitations of the haptic perception in the haptic rendering of virtual environments where the user's hand is in motion. Our study focuses on the determination of force thresholds in a virtual environment using a PHANToM haptic device, instead of dealing with real textured surfaces via a real probe.
First, two experiments are conducted to study the potential effects of the direction of force application on the force JNDs with respect to changes in the increment/decrement of forces. The results indicate that the force JNDs depend on the force direction and the force increment/decrement, and these two variables must be incorporated in the design of haptic displays.
Second, four experiments are conducted to measure the JND of the human haptic system using methodologies from psychophysics. The effects of three factors on the force JND are also studied, including the base force intensity, the user's hand velocity, and the force increment/decrement. The experiments are conducted for two different ranges of base force intensity, the velocity of the user's hand motion and the force increment/decrement. This study shows that, when a user's hand is moving, not only the force JND of the human haptic system depends on the force increment/decrement, the JND also depends on the user's hand velocity. The results also indicate that the base force intensity has a major effect on the force threshold of the human haptic system. Measured human factors such as the just noticeable difference (JND) of force perception that affect the design specifications of force feedback haptic interfaces when the human user or the object is in relative motion.
Studying the effect of sub-threshold forces on human performance in VEs
In virtual reality applications, a user usually grasps an input device to explore inside of a virtual environment. A virtual probe or a tool tip usually represents the user's hand in the virtual environment. The user can see the tool tip through a computer or a head-mounted display. Thus, users can only maintain their movement and accuracy using visual cues. However, in a haptic-enabled virtual environment, users can explore and manipulate virtual objects using the sense of touch. Haptic-enabled virtual environments are widely used in a variety of applications such as computer-aided design (CAD), computer-aided assembly, computer-assisted surgery and so on. In most of these applications, human performance efficiency in virtual environments is critical to carry out a task.
The main goal of this research is to study the effect of sub-threshold forces on human performance in a haptic-enabled virtual reality system. A multi-modal task similar to Fitts is used to study the effects of the sub-threshold forces on user performance. Each user's movement is manipulated using controlled forces such that the user is not aware of the forces. Subjects can see the position of the haptic probe in a virtual environment where they are manipulated using sub-threshold forces. The multi-modal task is used to measure the accuracy of subjects in two experiments. During the experiments, the effects of force intensity and the relative direction of applied forces to the direction of user's hand motion in the presence of visual cues are investigated. A performance index is also introduced that can be used to evaluate human performance in the application of sub-threshold forces. A psychophysical method is utilized to ensure that the applied forces on the user's hand are below the force threshold of the human haptic system. Results indicate that user performance is affected by both the intensity and direction of sub-threshold forces even when the users could control their actions through visual feedbacks. The results can be incorporated in an active manipulation technique to maintain the accuracy of user's movement in a haptic-enabled environment without the user being aware of the forces.
Modelling haptic devices using a rule-based expert system
A methodology is proposed that generates a model which employs qualitative reasoning to encapsulate nonlinear effects that are often approximated as linear processes. Fuzzy set theory is utilized to implement rule-based expert systems based on constant parameters from a) experimental data and b) expert knowledge. The parameters are tuned for multiple operating regions to model the nonlinear damping behaviour of the PHANToM haptic device.
Haptic Display of Deformable Objects
Stable and robust point-based haptic rendering interaction and sliding with and on various types of deformable elastic objects, ranging from low-stiffness (soft) to high-stiffness (rigid), is one of the main technical challenges in the field of virtual environments and force feedback haptic displays. The methods proposed in this work offer a high-fidelity 3D force reflecting haptic model to guarantee a stable interaction and sliding of deformable objects. Consequently, one is able to maintain a continuous force feedback field over the surface of polygonal-based deformable bodies with different normal stiffnesses in each polygonal mesh. Listed below are the steps to develop a haptic display that can simulate deformable objects using the PHANToM haptic device:
- Developed and simulated a nonlinear model for PHANToMTM device using the MATLABTM, Simulink and Maple, including kinematics and dynamics of the device
- Obtained an experimental linear model of the haptic device by utilizing model-based system identification techniques
- Estimated and validated the device friction (damping) factors by comparing experimental and model data
- Obtained a model of the system with (a) the known friction parameters, (b) the combined nonlinear kinematics and force/torque transformations and (c) the nonlinear device model
- Linearized the nonlinear model for the purpose of control design and utilized two different position/force feedback linear control strategies
- Investigated the robustness and performance of the control strategies for different modeling configurations with respect to the changes in the applied force and stiffness of a deformable object