The computer industry is currently striving to make computers and computer application programs more "user-friendly." Many user-friendly computer application programs permit users to input commands via a graphical user interface, e.g., a screen displaying various options in graphical format. Software programs using the WINDOWS.TM. environment, manufactured by Microsoft Corporation, often take advantage of the user-friendly interface permitted under this environment, by allowing users to enter commands by moving a cursor or pointer on the computer screen to select various options or move through windows.
In today's computers, cursor movement is often controlled using input devices such as mice or trackballs. These input devices also allow selection of options and navigation through windows and menus, however, are unsuitable for applications requiring high resolution computer input such as drawing, inking, gesturing, recognition and absolute positioning. Another drawback of mice and trackballs are that they are attached to the computer by a cord. At times, this cord can be annoying or a hindrance.
Pen and tablet and other similar digitizing computer input devices permit high resolution input. However, these input devices are not readily suited for cursor control, selection of options and navigation through windows and applications. Another drawback of pen and tablet input devices are that they require a special digitizing tablet upon which to move the pen. This tablet is often bulky and unsuitable in some working environments.
U.S. Pat. No. 5,166,668 describes a wireless computer input system using a battery-powered pen-type input device having a light emitting element at its tip. Light generated by a light-emitting diode in a pen is received by an input unit. The input unit detects and calculates the pen's position and outputs the position coordinates to a computer. The pen must be moved within a small area proximate to the input unit. The input unit has two sets of optical elements each having: a lens, an optical detector, and an optical filter. The optical detector is described as a two-division photodiode which detects a ratio of light impinging on both halves of the detector.
The system described in the above patent relies on two-division photodiodes. Two-division photodiodes require both halves to be tuned to provide equal outputs in response to an equal amount of impinging light, i.e., the two divisions must be identical. Such photodiodes are expensive to produce and may suffer from less than optimal resolution. The incident light spot must be large enough to impinge on both halves of the photodiode, and with enough energy, to produce ample current at the output terminals. Therefore, the photodiode output is dependent on the amount of incident light received. This often requires the light emitting element to produce a large amount of light, quickly draining the pen's battery during frequent use.
U.S. Pat. No. 5,045,843 describes another computer input system using a moveable, wireless remote unit and a stationary input unit, both transmitting signals between each other. The remote unit contains a light emitting element, a light detector, a switch, a power supply, and a controller. The stationary input unit contains a light emitting element, a photo detector, an amplifier, and a processor.
One problem with the system described in this patent is that the light detector and associated circuitry are included in a large and cumbersome wireless remote unit. The light detector is placed at the end of a long tube, forming a camera-type receiver. The receiver, and the system as a whole, would be expensive to manufacture because of the many and costly components necessary to operate the invention. Another problem is that the remote unit must be moved in a large area, and would be unsuitable for small, detailed and accurate movements on a small work surface. The remote unit is used primarily to move a cursor on a television screen at a substantial distance (several feet) from the television. Consequently, this system cannot be used for inking, gesturing, or character recognition, because these functions require precision recognition of a user's small hand movements.