07-11-2012, 05:10 PM
Electrooculography (EOG)
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INTRODUCTION
Background
There are several techniques used to aid the disabled peoples based on the communication between the human and machine such as mouse, keyboard. In addition to other systems depend on voice recognition or visual information and techniques that based on eye movement detection are also used for same object ,where all these techniques can be applied to the disabled persons according to the degree of disability, according to [1][2].
In eye movement characteristics such as saccades, fixations, and blinks, as well as deliberate movement patterns detected in EOG signals, have already been used for hands-free operation of static human-computer and human-robot interfaces, also the EOG-based interfaces have been developed for assistive robots or as a control for an electric wheelchair these systems are intended to be used by physically disabled people who have extremely limited peripheral mobility but still retain eye-motor coordination so it will be very helpful for them. According to many studies that showed the EOG is a measurement technique that is inexpensive, easy to use, reliable, and relatively unobtrusive when compared to head-worn cameras used in video-based mobile robots. All this systems allow their users to travel more efficiently and with greater ease [3].
Electrooculography (EOG) is a new technology of placing electrodes on user’s forehead around the eyes to record eye movements. This technology is based on the principle of recording the polarization potential or corneal-retinal potential (CRP), which is the resting potential between the cornea and the retina. This potential is commonly known as electrooculogram. (EOG) is a verysmall electrical potential that can be detected using electrodes. The EOG ranges from 0.05 to 3.5mV in humans and is linearly proportional to eye displacement. Compared with the electroencephalography (EEG), EOG signals have the characteristics as follows: the amplitude is relatively the same (15-200uV), the relationship between EOG and eye movements is linear, and the waveform is easy to detect.
According to [4] the cornea of the eye is electrically positive relative to the back of the eye (retina). Since this potential was not affected by the presence or absence of light, it was thought of as a resting potential. In fact, it is not constant but slowly varying and is the basis for the electrooculogram (EOG). So in our approach is to use EOG as a source of information on a person’s activity in order to control DC motor. Figure 1.1 shows the anatomy of the eye.
The process of measuring the eye signal start from a single dipole oriented from the cornea to the retina,where such corneoretinal potentials are well established. As well as eye movements produce a moving (rotating) dipole source and, accordingly, signals that are a measure of the movement can be obtained. The measurement of horizontal eye movements can be done by fix a pair of electrodes at the outside of the left and right eye. When the eye at rest the electrodes are effectively at the same potential and no voltage is recorded. While rotate the eye to the right results in a difference of potential, with the electrode in the direction of movement, becoming positive relative to the second electrode. The opposite effect results from a rotation to the left, as illustrated. The calibration of the signal may be achieved by having the patient look consecutively at two different fixation points located a known angle apart and recording the concomitant EOGs. Typical achievable accuracy is ±2°, and maximum rotation is ±70° however, linearity becomes progressively worse for angles beyond 30° as shown in figure(1.2). Typical signal magnitudes range from 5-20 µV/° according to [4]. In addition the EOG signal range is from 0.05 to 3.5 mv in human with frequency range from DC to 100 HZ, it's behavior is linear for gaze angle range of ± 30 degree.
In figure 1.3 ,the diagram top figure shows the three types of eye movements and the bottom figure shows the original EOG waveform. Positive or negative pulses will be generated when the eyes rolling upward or downward. The amplitude of pulse will be increased with the increment of rolling angle, and the width of the positive (negative) pulse is proportional to the duration of the eyeball rolling process. When the eyes are stationary or when the eyes are looking straight ahead, there is no considerable change in potential and the amplitude of signal obtained is approximately zero. When the eyes are made to move upwards, then there results an action potential, Similarly a downward movement of the eyes will give a similar voltage with opposite polarities to that obtained due to the upward movement.
State of problem
Using the eye signal (EOG signal) to control on DC motor where it will turn on by moving the eyes as example to right and turn off by reverse movement. Where this technique may be it will be helpful to disable people via give them a method to control on many necessary devices by only eye movement like control on wheelchair.
Objective
The objective of this work is to use the signals (information) which obtained by measuring a biological signal resulting from the movement of the human eye to create a control signal to drive the DC motor.