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In this paper, we have designed a technique to operate the computer without using a mouse. This may make the tasks easy for the paralyzed users and no need to strain their hands while keeping it in one position. We met with a lot of challenges and problems in the design of this project but we somehow were successful in finding the solutions for these problems. Finally, in this paper we deal with the market analysis statistics explaining what is the condition of the paralytic people and how this little tool may help in the life of million people.
Index words -- challenges, paralyzed
It is with the advance in MEMS technology that has imparted considerable cost and performance advantages to the consumer devices and applications. HCI as the name suggests, is related to humans and computers and the way both interact with each other. It is the Art and Science of making computer applications more usable for humans rather than making humans adapted to computers. The human-computer interface can be described as the point of communication between the human user and the computer. The flow of information between the human and computer is defined as the loop of interaction. HCI technology will be apt for applications where there is a requirement for quicker response times and improved accuracy of human intention
2. Existing System
Till date the system that came in the forefront for human computer interface had a major drawback in the mouse navigation in the graphics user interface based operating system. The existing system enables the user to move the mouse only in the positive and negative x-axis (horizontal), which restricts the movement of mouse in vertical direction.
The other system which has hit the market is Eye-Controlled computer user interface. This system uses the movement of the eye for locating the object on the screen and eye blink to select them. The drawback of this system is that the operation is slow and it will become very tedious and fatiguing when used for very long periods. It also has certain health hazards as it uses IR light to detect eye gaze.
The latest of all is the Head-controlled computer user interface. This system uses the movement of head for cursor movement and eye blink detector for selection. The downside of this system which we want to rectify is the sensitivity.
3. Proposed System:
As detection of eye motion proved more challenging, we decided to build an accelerometer based tilt detector to determine head motion. In this project, we are trying to use the head movement in order to move the cursor on the computer. This method requires tilt sensor to be placed in the head set to determine the head position. The system uses accelerometer to detect the users head tilt and an eye-blink sensor in order to select the document.
Our proposed system mainly aids the paralyzed people and so we have incorporated all the functionalities in order to make it intuitive. In the present system, along with the intentional gestures, the false gestures are also executed and thus creating lot of problems. We have built a system in order to detect even the false gestures so that high accuracy is maintained without wrong output. Another main challenge is the sensitivity factor of the accelerometer when used in the head . We have introduced the g-select lines to minimize the deviation produced.
4. Principle of Operation:
In this design, we have an interface system that would allow the users to interact with the computer with almost full functional capabilities. There is another sensor called eye-blink sensor which we will be using. This sensor detects each twitch of muscle surrounding our eyes which is done by piezo-electric transducer that produces a pulse. Here we have to differentiate between the intentional blink and normal blink. It is found that intentional blink has more intensity than the normal one. The keyboard function is implemented by allowing scrolling the letter with head tilt and eye-blink as selection mechanism. In the eye-blink sensor, the muscular vibrations around the eye are detected by the piezo electric crystal. Each blink of the eye is detected when a muscle twitch occurs near the eye. We decided to use eye blinking as we wanted the device to be functional for both non-vocal and ventilated users. Mainly the inputs from both the sensors are given to the microcontroller and depending on the two inputs; the microcontroller sends information about the X, Y, Z coordinates. After transmission, the information is passed on to the computer via RF transmission. Thus the movement of the cursor and the document selection can be seen through the computer. This is the main principle of our project. The small block diagram of the setup is roughly shown in the figure.
In our project, we have two sensors in order to give the position of the cursor information to the microcontroller. Both the signal output coming from sensors will be analog which will be converted to digital via ADC in the microcontroller.
5. Hardware Tools
- Mems accelerometer sensor
- Eye blink sensor
- RF Module
- Serial communication
6. Eye Blink Sensor
This switch is activated when the user blinks their eye. It allows individuals to operate electronic equipment like communication aids and environmental controls hands-free. Each blink of the eye is detected when a muscle twitch occurs near the eye. The eye blink switch can be set up to operate on either eye and may be worn over normal glasses. The sensitivity of the switch can be tuned to the user's needs and involuntary blinks are ignored. The sensor is connected to a hand-held control unit with a rechargeable battery.
6.1 Piezo Electric Transducers:
A transducer can be defined as a device that converts energy from one form to another. Piezoelectric material is that material which is commonly used as a basic component of transducers. Piezoelectric devices are very much reliable and inexpensive means of converting electrical energy into physical motion. It exhibits a high tolerance to environmental factors such as electromagnetic fields and humidity. A piezoelectric element is a crystal when mechanical force is applied between its faces, delivers a voltage and it deforms mechanically when voltage is applied between its faces. Because of these characteristics a piezoelectric element is capable of acting both as a transmitting and a sensing element. Piezoelectricity is a phenomenon in which positive and negative electric charges appear on opposite sides of some non-conducting crystals when subjected to mechanical pressure. The converse piezoelectric effect, electrostriction, is the property of some non-conductors, or dielectrics, that deform slightly under the application of an electric field. Piezoelectricity exists due to some atomic lattice structures have as a necessary cell a cubic or rhomboid atomic cage, and this cage holds a semi-mobile ion which has many stable quantum position states inside itself. Piezoelectric transducers have been traditionally used to convert electric signals into sound waves or other mechanical vibrations, or to convert mechanical vibrations into electric signals. A piezoelectric transducer includes a vibrating piece which has on both its surfaces electrodes for providing an electric field to the vibrating piece. The piezoelectric transducer converts the electric signals into mechanical vibrations or vice versa by using the morphological change of a crystal which occurs on voltage application, or conversely by monitoring the voltage generated by a pressure applied on a crystal .
The Piezoelectric effect uses the fact that force applied to certain materials causes stresses that generate this electric charge. In the case of piezo switches, the force could be compressive pressure that causes the (typically disc-shaped) piezo element to bend. Thus piezo switches produce a single, brief "on" pulse.
6.2 Piezoelectric Based Blink Detection:
We decided to use blinking as we wanted the device to be functional for non-vocal or ventilated users. Whenever we blink our eye, a muscle twitch occurs at the areas surrounding our eyes. This muscle twitch can be considered to be a mechanical disturbance that can be detected by the piezoelectric transducer, which produces a pulse. The pulse was used to indicate blink.
7. Three-Axis Accelerometer:
Accelerometer is the device used to measure the acceleration. Acceleration can be defined as the rate of change of velocity with respect to time. Single- and multi-axis models are available to detect magnitude and direction of the acceleration as a vector quantity, and can be used to sense orientation, vibration and shock. Micromachined accelerometers are more and more present in portable electronic devices and video game controllers which can be used to detect the orientation of the device or provide for game input. It is a vector of both magnitude and direction. As we require both in order to locate the cursor we go for the three axis accelerometer.
A micromechanical, dithered device which comprises of a substrate, a movable mass which is connected to the substrate by a suspension, a position sensor, a dither signal generator, a dither force transducer connected between the movable mass and the substrate, the input of the dither force transducer being connected to the output of the dither signal generator and a calculator taking as inputs at least the position sensor output and the dither signal generator output. In one physical form of the invention, the dithered device includes an electrostatic force transducer which is used for applying feedback. In this device, dither force may be directly applied to the mechanical proof-mass utilizing electrostatic structures similar to electrostatic structures can be used for feedback. The electrostatic dithering structures provide good matching between dither electrodes and the feedback which enables the use of simple logic for subtraction of the dither signal from the accelerometer output .
7.1 General principle of accelerometer:
Accelerometers with capacitive sensing elements typically use the proof mass as one plate of the capacitor and the base as the other. When the sensor is accelerated, the proof mass tends to moves and the voltage across the capacitor changes; this change in voltage corresponds to the applied acceleration. These types of sensors may be operated open-loop or closed-loop.
The 3 axis accelerometer consists of two surface micromachined capacitive sensing cells which is called a g-cell and a signal conditioning ASIC contained in a single integrated circuit package. The elements that are used for sensing are sealed air tight at the wafer level using a bulk micromachined cap wafer. The g-cell is a mechanical structure formed from polysilicon based semiconductor material using the process of masking and etching. It can be modeled as a set of beams attached to a movable central mass that move between the other two fixed beams. When the system is subjected to acceleration the movable beams is deflected from their rest position. When this beam, which is attached to the central mass moves, the distance between itself and other two fixed beam varies. That is, the distance between one beam increases and other decreases by the same amount. This change in distance is the measure of acceleration.
Two back-to back capacitor forms the g-cell beams. As the center beam moves with acceleration, the distance between the beams changes and as a result each capacitor's value will change. This is the basic principle for the capacitive type 3-axis accelerometer. The ASIC uses a technique based on switched capacitor to measure the values of the g-cell capacitors and find the required acceleration data from the difference between the two capacitors. Single pole switched capacitor filters are present onboard in the 3 axis accelerometer. Since the filter is realized using switched capacitor techniques, we need not require any external passive components such as resistors and capacitors to set the cut-off frequency.
The g-cell is a mechanical structure obtained from semiconductor materials (polysilicon) using semiconductor method (masking and etching). It can be represented as a set of beams attached to a movable central mass that move in between fixed beams. The movable beams can be deflected from their rest position by subjecting the system to an acceleration. The g-Select feature allows for the choice among 8 sensitivities present in the device. Depending upon the logic inputs given on pins 1 and 2 and 3, the device internal gain will be changed allowing it to function with a 1.5g, 2g, 4g, 6g, 8g.
This feature helps in reducing the sensitivity problem that is faced. Fine adjustments of the sensitivity are possible by using three select lines. For example- gselect 1 ,gselect2, and gselect3 can be left unconnected for applications requiring only 1.5g.
A surface micro-machined accelerometer can be made using a silicon-on-insulator (SOI) wafer structure. Both the acceleration (or deceleration) sensor and associated signal conditioning circuitry are monolithically fabricated on the same substrate. The sensing member is the top silicon layer of the SOI wafer, corresponding to the movable, common electrode of a differential capacitor pair. Standard SOI processing techniques are those techniques which are used to fabricate the components of the signal conditioning circuitry. It does not suffer from the stress related warping common with polysilicon members as the top silicon layer is single crystal silicon. Furthermore, the method described is compatible with bipolar, BiCMOS, or CMOS process flows, it may be used to fabricate faster and lower noise level signal conditioning circuitry than can be obtained using current techniques for making monolithic accelerometers.
7.2 Sleep mode:
Another important block in the 3-axis accelerometer is the sleep mode. When Sleep Mode is active, the device outputs are turned off, providing considerable reduction of operating current. A low input signal on pin 12(Sleep Mode) will place the device in this mode and reduce the current to 3uA typ. For lower power consumption, it is recommended to set g-Select1 and g-Select2 and gselect3to 1.5g mode. By placing a high input signal on pin 12, the device will resume to normal mode of operation.
- Selectable Sensitivity (1.5g/2g/4g/6g)
- Low Current Consumption: 500 microampere
- Sleep Mode: 3 microampere
- Low Voltage Operation: 2.2 V - 3.6 V
- High Sensitivity (800 mV/g @ 1.5g)
- Robust Design, High Shocks Survivability
- Low Cost
8.1 Theory of Finite Element Analysis:
Finite Element Analysis (FEA) is a computer-based numerical technique for calculating the strength and behavior of engineering structures. It can be used to calculate deflection, stress, vibration, buckling behavior and many other phenomena. It can be used to analyze either small or large-scale deflection under loading or applied displacement. It can analyze elastic deformation, or "permanently bent out of shape" plastic deformation. A two dimensional, static, sequential coupled analysis will be performed where the device is built by ANSYS modeler. The structure contains proof mass which is suspended between fixed rigid electrodes to provide differential capacitance measurements. ANSYS is used for finite element analysis (FEA) modeling and simulation In our project, we have done FEA analysis for the accelerometer model as shown in the figure:
Capacitive micro accelerometers have the combined advantages of high sensitivity, good dc response and noise performance, low-drift,low-temperature sensitivity and low-power dissipation. In our capacitive sensing accelerometer, the acceleration force (in terms of g) deflects the proof mass. Micro fabricated cantilever beams are widely used in MEMS capacitive-type sensors as the sensing element. The design models are modeled in ANSYS and split into the required number of segments in order to obtain element Continuity. Upper and the lower plates are made up of electrodes while the middle one is the mass and we have used aluminium electrodes. In-between medium is filled up with air.
The five areas maintain their individuality (they are not "added").After Glue, they become connected at their intersection. The ouput of the geometry will look like as shown in the figure:
The next step in the simulation process is Meshing. Mesh generation is one of the most critical aspects of ansys simulation. Too many cells may result in long solver runs and too few many result in inaccurate results. ANSYS Meshing allows the user to find the balance and get the right mesh for their simulation in the most automated way possible. ANSYS Meshing technology has been built on the strengths of class leading meshing tools that use to be independent prior to acquisitions by ANSYS. The strongest aspects of these separate tools have been brought together in a single environment to produce some of the most powerful meshing to date.
8.3 Temperature plot:
In the next step of our simulation, we have to apply loads to both the lower and the upper plates. First we have to apply temperature boundary condition in the upper plate and then to the lower plate. In our design, we had given 0 in the upper plate and 30 in the lower plate.
The various colours found in the above diagram corresponds to different temperature scale. Note that the electrical connection pads are the same color, reflecting the constant temperature boundary condition.
8.4 Voltage Plot:
Similar to the temperature loads applied, we have to apply voltages to both the upper and lower plates. We had applied 0 and 30V in these plates respectively.
Here also the various voltages are distributed among the geometry as shown in figure.
MEMS (MicroElectroMechanical Systems) accelerometers has the ability to sense linear motion (X and Y axis) and angular movement (Z axis), on a single chip, at a cost approaching $1 per axis, is opening the door for the rapid growth of tri-axis reports EmTech Research, a division of Small Times Media.
MEMS gyroscopes and accelerometers market increased by 55% from 2005 to 2006 to reach USD 232 M last year. An average 35% CAGR for 2006-2011 periods is expected. The market dynamic mainly comes from accelerometers: about 65% of the total inertial sales by 2011. Consumer applications will progressively take a 40% share of the total inertial MEMS activity by 2011 (including automotive, medical, industrial, aeronautic and defence sectors).
MEMS accelerometers and gyroscopes are emerging at a very fast pace in consumer electronics products. MEMS gyroscopes were widely integrated into camcorders since 1998 to provide optical stabilization features. MEMS accelerometers entered consumer applications in 2003, in large volume, as a protection feature for Hard Disk Drives.
In 2006, Nintendo Wii's motion sensing remote control gave for the first time, public visibility to inertial MEMS. The new attractive Human Machine Interface from game controls such as the Wii, is even expected to penetrate the cell phone market .
9 Challenges Faced:
We were facing lot of challenges regarding the accelerometer sensitivity and false gesture recognition. But we somehow made some alterations in the mechanism to get the required output. Regarding the sensitivity, there were generally two g-select lines inorder to adjust the sensitivity. In our design , we included the third g-select line inorder to give wider option for the sensitivity to be adjusted. So totally there are 8 combinations of sensitivity values that can be adjusted .
Human Computer Interface provides scope in advancement for the paralyzed person in computer field. Proper utilization and testing will stretch applications for the usage of all people. Mass production can also be achieved using MEMS accelerometer and also provide a strong base for future technology and very good transformation as well.
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