Imagine being able to point into the sky and fly. Or perhaps walk through space and connect molecules together. These are some of the dreams that have come with the invention of virtual reality. With the introduction of computers, numerous applications have been enhanced or created. The newest technology that is being tapped is that of artificial reality, or “virtual reality” (VR). When Morton Heilig first got a patent for his “Sensorama Simulator” in 1962, he had no idea that 30 years later people would still be trying to simulate reality and that they would be doing it so effectively.
Jaron Lanier first coined the phrase “virtual reality” round 1989, and it has stuck ever since. Unfortunately, this catchy name has caused people to dream up incredible uses for this technology including using it as a sort of drug. This became evident when, among other people, Timothy Leary became interested in VR. This has also worried some of the researchers who are trying to create very real applications for medical, space, physical, chemical, and entertainment uses among other things.
In order to create this alternate reality, however, you need to find ways to create the illusion of reality with a piece of machinery known as the computer. This is done with several omputer-user interfaces used to simulate the senses. Among these, are stereoscopic glasses to make the simulated world look real, a 3D auditory display to give depth to sound, sensor lined gloves to simulate tactile feedback, and head-trackers to follow the orientation of the head. Since the technology is fairly young, these interfaces have not been perfected, making for a somewhat cartoonish simulated reality.
Stereoscopic vision is probably the most important feature of VR because in real life, people rely mainly on vision to get places and do things. The eyes are approximately 6. 5 centimeters apart, and allow ou to have a full-colour, three-dimensional view of the world. Stereoscopy, in itself, is not a very new idea, but the new twist is trying to generate completely new images in real- time. In 1933, Sir Charles Wheatstone invented the first stereoscope with the same basic principle being used in today’s head-mounted displays.
Presenting different views to each eye gives the illusion of three dimensions. The glasses that are used today work by using what is called an “electronic shutter”. The lenses of the glasses interleave the left-eye and right-eye views every thirtieth of a second. The shutters electively block and admit views of the screen in sync with the interleaving, allowing the proper views to go into each eye. The problem with this method though is that you have to wear special glasses. Most VR researchers use complicated headsets, but it is possible to create stereoscopic three-dimensional images without them.
One such way is through the use of lenticular lenses. These lenses, known since Herman Ives experimented with them in 1930, allow one to take two images, cut them into thin vertical slices and interleave them in precise order (also called multiplexing) and put cylinder shaped lenses in front of them so that hen you look into them directly, the images correspond with each eye. This illusion of depth is based on what is called binocular parallax. Another problem that is solved is that which occurs when one turns their head.
Nearby objects appear to move more than distant objects. This is called motion parallax. Lenticular screens can show users the proper stereo images when moving their heads well when a head- motion sensor is used to adjust the effect. Sound is another important part of daily life, and thus must be simulated well in order to create artificial reality. Many scientists including Dr. Elizabeth Wenzel, a esearcher at NASA, are convinced the 3D audio will be useful for scientific visualization and space applications in the ways the 3D video is somewhat limited.
She has come up with an interesting use for virtual sound that would allow an astronaut to hear the state of their oxygen, or have an acoustical beacon that directs one to a trouble spot on a satellite. The “Convolvotron” is one such device that simulates the location of up to four audio channels with a sort of imaginary sphere surrounding the listener. This device takes into account that each person has specialized auditory signal processing, and personalizes what each erson hears.
Using a position sensor from Polhemus, another VR research company, it is possible to move the position of sound by simply moving a small cube around in your hand. The key to the Convolvotron is something called the “Head- Related Transfer Function (HRTF)”, which is a set of mathematically modelable responses that our ears impose on the signals they get from the air. In order to develop the HRTF, researchers had to sit people in an anechoic room surrounded with 144 different speakers to measure the effects of hearing precise sounds from every direction by using tiny microphone probes laced near the eardrums of the listener.
The way in which those microphones distorted the sound from all directions was a specific model of the way that person’s ears impose a complex signal on incoming sound waves in order to encode it in their spatial environment. The map of the results is then converted to numbers and a computer performs about 300 million operations per second (MIPS) to create a numerical model based on the HRTF which makes it possible to reconfigure any sound source so that it appears to be coming from any number of different points within the acoustic sphere.
This portion of a VR system can really nhance the visual and tactile responses. Imagine hearing the sound of footsteps behind you in a dark alley late at night. That is how important 3D sound really is. The third important sense that we use in everyday life is that of touch. There is no way of avoiding the feeling of touch, and thus this is one of the technologies that is being researched upon most feverishly. The two main types of feedback that are being researched are that of force- reflection feedback and tactile feedback.
Force feedback devices exert a force against the user when they try to push something in a virtual world that is ‘heavy’. Tactile feedback is the sensation of feeling an object such as the texture of sandpaper. Both are equally important in the development of VR. Currently, the most successful development in force- reflective feedback is that of the Argonne Remote Manipulator (ARM). It consists of a group of articulated joints, encoiled by long bunches of electrical cables. The ARM allows for six degrees of movement (position and orientation) to give a true feel of movement.
Suspended from the ceiling and connected by a wire to the computer, this machine grants a user the power to reach out and manipulate 3D objects that are not real. As is the case at the University of North Carolina, it is possible to “dock molecules” using VR. Simulating molecular forces and translating them into physical forces allows the ARM to push back at the user if he tries to dock the molecules incorrectly. Tactile feedback is just as important as force feedback in allowing the user to “feel” computer-generated objects. There are several methods for providing tactile feedback.
Some of these include inflating air bladders in a glove, arrays of tiny pins moved by shape memory wires, and even fingertip piezoelectric vibrotactile actuators. The latter ethod uses tiny crystals that vibrate when an electric current stimulates them. This design has not really taken off however, but the other two methods are being more actively researched. According to a report called “Tactile Sensing in Humans and Robots,” distortions inside the skins cause mechanosensitive nerve terminals to respond with electrical impulses. Each impulse is approximately 50 to 100mV in magnitude and 1 ms in duration.
However, the frequency of the impulses (up to a maximum of 500/s) depends on the intensity of the combination of the stresses in the area near the receptor which is responsive. In ther words, the sensors which affect pressure in the skin are all basically the same, but can convey a message over and over to give the feeling of pressure. Therefore, in order to have any kind of tactile response system, there must be a frequency of about 500 Hz in order to simulate the tactile accuracy of the human. Right now however, the gloves being used are used as input devices.
One such device is that called the DataGlove. This well-fitting glove has bundles of optic fibers attached at the knuckles and joints. Light is passed through these optic fibers at one end of the glove. When a finger is bent, the fibers also bend, and the mount of light that is allowed through the fiber can be converted to determine the location at which the user is. The type of glove that is wanted is one that can be used as an input and output device. Jim Hennequin has worked on an “Air Muscle” that inflates and deflates parts of a glove to allow the feeling of various kinds of pressure.
Unfortunately at this time, the feel it creates is somewhat crude. The company TiNi is exploring the possibility of using “shape memory alloys” to create tactile response devices. TiNi uses an alloy called nitinol as the basis for a small grid of what look like ballpoint-pen tips. Nitinol can take the shape of whatever it is cast in, and can be reshaped. Then when it is electrically stimulated, the alloy it can return to its original cast shape. The hope is that in the future some of these techniques will be used to form a complete body suit that can simulate tactile sensation.
Being able to determine where in the virtual world means you need to have orientation and position trackers to follow the movements of the head and other parts of the body that are interfacing with the computer. Many companies have developed successful methods of allowing six degrees of freedom including Polhemus Research, and Shooting Star Technology. Six degrees of freedom refers to a combination cartesian coordinate system and an orientation system with rotation angles called roll, pitch and yaw.
The ADL-1 from Shooting Star is a sophisticated and inexpensive (relative to other trackers) 6D tracking system which is mounted on the head, and converts position and orientation information into a readable form for the computer. The machine calculates head/object position by the use of a lightweight, multiply-jointed arm. Sensors mounted on this arm measure the angles of the joints. The computer-based control unit ses these angles to compute position-orientation information so that the user can manipulate a virtual world. The joint angle transducers use conductive plastic potentiometers and ball bearings so that this machine is heavy duty.
Time-lag is eliminated by the direct-reading transducers and high speed microprocessor, allowing for a maximum update rate of approximately 300 measurements/second. Another system developed by Ascension Technology does basically the same thing as the ADL-1, but the sensor is in the form of a small cube which can fit in the users hand or in a computer mouse specially developed to encase it. The Ascension Bird is the first system that generates and senses DC magnetic fields. The Ascension Bird first measures the earth’s magnetic field and then the steady magnetic field generated by the transmitter.
The earth’s field is then subtracted from the total, which allows one to yield true position and orientation measurements. The existing electromagnetic systems transmit a rapidly varying AC field. As this field varies, eddy currents are induced in nearby metals which causes the metals to become electromagnets which distort the measurements. The Ascension Bird uses a steady DC magnetic filed which does ot create an eddy current. The update rate of the Bird is 100 measurements/second. However, the Bird has a small lag of about 1/60th of a second which is noticeable.
Researchers have also thought about supporting the other senses such as taste and smell, but have decided that it is unfeasible to do. Smell would be possible, and would enhance reality, but there is a certain problem with the fact that there is only a limited spectrum of smells that could be simulated. Taste is basically a disgusting premise from most standpoints. It might be useful for entertainment purposes, but has almost no urpose for researchers or developers. For one thing, people would have to put some kind of receptors in their mouths and it would be very unsanitary.
Thus, the main senses that are relied on in a virtual reality are sight, touch, and hearing. Applications of Virtual Reality Virtual Reality has promise for nearly every industry ranging from architecture and design to movies and entertainment, but the real industry to gain from this technology is science, in general. The money that can be saved examining the feasibility of experiments in an artificial world before they are done could be great, and the money saved on nergy used to operate such things as wind tunnels quite large.
The best example of how VR can help science is that of the “molecular docking” experiments being done in Chapel Hill, North Carolina. Scientists at the University of North Carolina have developed a system that simulated the bonding of molecules. But instead of using complicated formulas to determine bonding energy, or illegible stick drawings, the potential chemist can don a high-tech head-mounted display, attach themselves to an artificial arm from the ceiling and actually push the molecules together to determine whether or not they can be connected.
