Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1998-12-02
2001-07-31
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S231180
Reexamination Certificate
active
06268601
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to position determining devices and more particularly to an apparatus for determining the absolute position of a rotating shaft.
It is a common problem to want to know the position of a device whose position is being controlled by an actuator or some other means. For example, in the controls industry, devices such as valves, each having a valve stem or valve shaft which is rotatable by an actuator, are typically used to control the flow of liquids or various gasses associated with the industrial process. In these applications, it is a common need to know the precise absolute position of the controlled shaft or stem. This information allows for an improved understanding of the process and, subsequently, a more accurate control of the process by a process control system.
A number of prior solutions are known for measuring or determining this aforementioned position. One method is the use of linear variable differential transformers which can provide accurate positional information. However, they require a mechanical linkage to translate the positional information to a sensor and, additionally, consume a relatively high amount of power in their operation.
Slidewire, potentiometers, or other rotary transducers again require a mechanical link to the controlled device and also have the disadvantage of a sliding electrical contact which can cause long-term unreliability as well as having a potential for producing arcing and/or sparking, precluding the use of these devices in volatile environments.
Hall effect transducers, as they are currently used, generally require a mechanical linkage and are generally susceptible to ambient magnetic fields, electrostatic discharge, and other Electro-Magnetic Interference (EMI).
A more efficient form of solution is taught by my U. S. Pat. No. 5,828,060, which issued on Oct. 27, 1998 and is assigned to the same assignee as the present application.
Additionally, all of the aforementioned devices and methods require the use of extensive electronic circuitry to convert the predominately analog positional information to the digital signals normally required by modern computer-controlled industrial process control systems.
Therefore, it is the object of the present invention to provide a reliable position-determining apparatus that does not require a mechanical linkage between the apparatus and a rotatable shaft.
It is a further object of the present invention to provide a position-determining apparatus that has long-term reliability, is immune to EMI, and is cost effective.
It is a further object of the invention to provide a position-determining apparatus that exhibits the benefits of a greatly reduced parts count when interfacing the resultant positional signals to a computer-controlled industrial process control system.
SUMMARY OF THE INVENTION
The apparatus of the present invention contemplates the use of a light detecting device, and a rotatable disk having a single opening through the disk, where the rotatable disk is positionable between the light detecting device and a source of light energy. The center axis of the rotatable disk is aligned along the longitudinal axis of the shaft or valve stem of a suitable rotating device whose position is to be measured.
The rotatable disk includes an extended isosceles triangle having two curvilinear sides located on the disk in circumferential relationship to the shaft to be measured. The light detecting device responds to the magnitude of the distance between the two long sides of the triangle which increase in width longitudinally as the disk mounted upon the shaft is rotated.
The apparatus of the present invention includes a source of light energy which provides a constant source of light. The light detecting device is positionable in a first position adjacent the rotatable shaft and along a rotational center line of the disk where the aforementioned opening is located. The light detecting device is positioned opposite the light source on the opposite side of the disk arranged to produce a detection signal responsive to the detection of light energy.
The disk opening allows light from the light source to fall on the light detecting device, as the disk is rotated in a clockwise direction. The amount of light energy passed by the opening provides a form of modulation to the light detecting device. As the disk is rotated, the opening allows light to fall on the light detecting device, which produces the detection signal. As the disk is further rotated, the light detecting device receives more light. Upon further continued clockwise rotation of the disk, the opening allows more and more light from the light source to fall on the light detecting device, producing a detection signal of increased magnitude.
The signals are read by a shaft position-determining scheme whereby the signals are used to calculate the position of the shaft based on the amount of light measured by the light detecting device.
Thus, there is provided an apparatus for determining the position of a rotatable shaft and which offers long-term reliability, is immune to EMI, and is cost effective in its operation. The present invention requires sensed analog positional information to be translated into digital information, which is typically required by modern computer-controlled industrial process control systems.
It is noted that the present apparatus is a non-contact feedback mechanism with an assumed long-life expectancy and is immune to ambient magnetic fields while inherently self-correcting for drift in the analog parts due to temperature changes or aging of components.
As noted previously, the light source and the light detector are both positionable adjacent to the rotating disk. This positioning occurs by virtue of their being attached to a solenoid mechanism which is controllable from a central point to place the light source and the detector adjacent to the disk or withdraw both elements from their position adjacent to the disk until such time as measurement is required. Control of the solenoid would normally be under the control of the computer to which the read out of the light detecting device is applied as taught by the present invention.
REFERENCES:
patent: 4781742 (1988-11-01), Hill et al.
patent: 4911449 (1990-03-01), Dickinson et al.
patent: 5650613 (1997-07-01), Lewis
patent: 6043483 (2000-03-01), Schreiber
Black Robert J.
Honeywell International , Inc.
Lee John R.
Miologos Anthony
Pyo Kevin
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