Computer graphics processing and selective visual display system – Display peripheral interface input device – Cursor mark position control device
Reexamination Certificate
1996-05-14
2001-07-10
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Cursor mark position control device
C345S156000, C463S038000
Reexamination Certificate
active
06259433
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention relates to a one or multiple axis joystick that uses incremental optical encoding and the principle of mechanical advantage to obtain a digital output of enhanced resolution that is a reliable measure of absolute shaft position and which can be read by a computer without interface circuitry.
2. Description of Prior Art
There is much prior art related to the use of joysticks as man-to-machine input devices. A variety of joysticks have been used to input commands to video game controllers or to control the motion of a cursor on a video screen. Examples include U.S. Pat. No. 4,488,017 (Lee) and U.S. Pat. No. 4,501,939 (Hyltin et al). Devices of this type employ electrical contacts or switches which are actuated by motion of the joystick shaft. Most of these joysticks are able to sense the motion of the shaft in one of four or eight different radial directions but do not sense how far the shaft has moved in the chosen direction. The output signal is digital in the sense that each contact or switch actuated by shaft motion is either open or closed. However, the digital resolution is exceedingly low (one binary bit of information for each of the eight detectable directions of shaft motion). Also, the electrical contacts in mechanically operated switches are subject to wear, corrosion, contamination, pitting, and contact bounce. Joysticks of this type lack the resolution and reliability needed for control of powered wheelchairs, fork lifts, machine tools, earth-moving machines, robotic devices, etc.
Efforts have been made to improve the resolution of digital joysticks that utilize mechanically actuated electrical contacts by increasing the number of contacts. One example is described in related U.S. Pat. Nos. 4,142,180; 4,148,014; 4,161,726; and 4,306,232 (Burson). Four-bit resolution along each of two orthogonal axes is obtained with eight sets of contacts. Other examples of multi-contact joysticks are described in U.S. Pat. No. 3,770,915 (Bennett et al) and U.S. Pat. No. 5,225,831 (Osborn). In each case of this type, the resolution achievable increases with the number of contacts employed but the joystick becomes mechanically complex if high resolution is needed. Note that the mechanical precision required doubles with each additional bit of resolution. Furthermore, the reliability of the joystick decreases and the cost increases as the number of contacts is raised to improve resolution.
Optoelectronic devices (typically pairs of light emitting diodes and phototransistors) have been used to improve the reliability of digital joysticks. U.S. Pat. No. 5,117,102 (Mitchell) describes such a joystick. It is intended as a direct replacement for the simpler joysticks employing mechanically actuated electrical contacts. As such, its resolution is limited to one binary bit in each of eight detectable directions. Another example of a digital joystick employing optical switches is disclosed in U.S. Pat. No. 4,856,785 (Lantz et al.). This device is intended as a direct replacement for the joysticks of the preceding paragraph that use multiple mechanically actuated electrical contacts for improved resolution. This patent describes a system employing six optical switches that provide slightly less than three bits of resolution along each of a pair of orthogonal axes. As with its mechanical counterparts, this approach can achieve higher resolution with more optical switches at the expense of rapidly escalating complexity and cost. Another disadvantage of this prior art device (Lantz et al.) is that it includes, along with some other prior art devices, an inherent source of non-linearity due to its conversion of shaft rotation to rectilinear motion of plates transporting the encoded medium. This problem will be discussed in detail later since the present invention removes it.
In an effort to achieve the very high resolution of joysticks employing resistive potentiometers while overcoming their well known reliability problems, non-contact analog joysticks have been developed. Some use inductive techniques while others exploit optoelectronic devices. U.S. Pat. No. 4,685,678 (Frederiksen) and U.S. Pat. No. 4,855,704 (Betz) disclose joysticks in which motion of the shaft alters the inductance of a coil which is part of an oscillator circuit. Then, a property of the oscillator (frequency, amplitude, or phase) is processed electronically to obtain an indication of shaft position. Variable transformer coupling between an excitation coil, moved by the joystick shaft, and fixed sensor coils is employed in U.S. Pat. No. 4,434,412 to obtain an analog signal indicative of shaft position. These approaches are more reliable than resistive potentiometers but are inherently non-linear (i.e., unlike resistive potentiometers which are normally fabricated to be very linear, the analog output signal from these inductive devices does not vary linearly with joystick shaft position). Electronic compensation of this inherent non-linearity is feasible but adds to cost and complexity. Furthermore, the analog signal must be processed through interface circuitry, typically including an analog-to-digital converter, before it can be used in a modern control system, almost all of which use digital microprocessors or microcomputers.
The analog joysticks employing optoelectronic devices suffer from the same drawbacks as the inductive devices just described. That is, the analog output signals tend to vary in a non-linear manner with changes of shaft position and the signal must be processed through interface circuitry before it can be utilized in a digital control system. Examples of this type of joystick are disclosed in U.S. Pat. No. 4,533,827 (Fincher); U.S. Pat. No. 4,607,159 (Goodson et al); U.S. Pat. No. 4,686,361 (Bard); and U.S. Pat. No. 4,731,530 (Mikan).
Historically, analog computers gave way to digital computers. Analog measuring instruments have been largely supplanted by digital instruments. Today, digital television is on the brink of replacing analog television. The reasons are numerous and some of them apply to joysticks. They include better immunity to noise, elimination of drift, improved repeatability of output readings (for a given joystick shaft position) from one reading to the next and one device to the next, greater accuracy, higher reliability, ease of transmission of the results, and lower cost. It seems probable that analog joysticks will go the way of analog computers and be displaced by digital devices like that of the present invention.
Many of the disadvantages of the preceding approaches to joystick implementation can be overcome by the use of digital optical encoding. Digital optical encoders are well developed, reliable, can be made very linear, and can interface directly with microprocessors or microcomputers without extra circuitry. There are two basic types of digital optical encoders, absolute and incremental. Both types can be very linear because the linearity is accurately built into the encoding disc or strip by photographic means. Absolute encoders use one track of an optically encoded disc or strip plus a light emitter-detector pair for each binary bit of resolution desired. Thus, the output of such an encoder is a binary word with all bits read in parallel to obtain an absolute indication of the position of the encoded disc or strip at that instant. Like the digital devices described earlier employing multiple switch contacts, the precision required on the optically encoded disc or strip doubles with each additional bit of resolution. Also, the demands placed upon the emitter-detector pairs escalate geometrically as the number of bits is increased. Hence, the complexity, size, and cost rise rapidly as the resolution increases and absolute encoders generally have not been exploited for joystick applications. Note, however, that the device described earlier as disclosed in U.S. Pat. No. 4,856,785 (Lantz et al.) can be viewed as a joystick employing absolute optical encoding but with relatively low resolution. Absolute digital optical encode
Lewis David L.
Renner , Otto, Boisselle & Sklar, LLP
Shalwala Bipin
LandOfFree
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