Data processing: measuring – calibrating – or testing – Measurement system – Orientation or position
Reexamination Certificate
2002-06-05
2003-09-02
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Orientation or position
C702S033000, C702S036000, C702S041000, C702S094000, C702S113000, C702S115000
Reexamination Certificate
active
06615156
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This application relates generally to absolute position detectors, and in particular to an absolute position detector that interprets, rather than avoids, abnormal sensory states.
BACKGROUND OF THE INVENTION
In simple systems, an absolute position detector (APD) is generally used to determine the position of a moving component along a path of travel. The APD typically accomplishes this via detection of the current position of a marker affixed to or associated with the component. In more sophisticated systems, the APD is further used to determine the positional state of an assembly of interrelated moving components, such as gears, via resolution of the combined current position of a series of markers on the interrelated moving components.
APDs are commonly used in connection with an assembly of multiple rotating gears, such as may be found, for example, in valve actuator mechanisms. In a valve actuator, an APD generally detects the positional state of a series of interrelated circular gears, the positional state representative of the degree of openness of the valve. In such cases the APD monitors the paths of circular travel of markers on the interrelated gears.
Such circular travel is by no means the only type of motion monitored by APDs, however. APDs may be used to monitor position, for example, on other shaped closed loop paths, such as elliptical or irregular closed loop paths. Alternatively, APDs may be used to measure position on straight or curved paths that are not on a closed loop. Travel along such open paths may or may not be reciprocating. For example, APDs can be used to measure the state of a torque sensor in a valve actuator via monitoring of the current position of a member traveling along a pendulum-like path.
It is also well understood that absolute position detection is a dynamic operation. Successive samples of a current positional state may be resolved into a stream that forms a dynamic control tool.
The advent of computerized control has increased the need for APDs that generate high speed streams of samples that indicate current positional states in digital format. The speed and capacity of modern computers allow positional samples to be processed at a high speed. There is a particular need for APDs that generate samples at that speed. The faster the stream of samples that is processed, the finer the resolution of monitoring and control of the positional state.
For this reason, APDs relying on mechanical systems, such as cams to activate a switch or a potentiometer, are fast becoming obsolete. These devices have always suffered from backlash because of the mechanical load on the components. Wear and tear on the mechanical parts has always tended to shorten operational life. On top of these inherent drawbacks, such mechanical APDs tend not to be robust enough to be able to be operated at high speeds.
The prior art has addressed the problems of mechanical APDs by teaching use of non-contact APDs, such as those described in U.S. Pat. No. 5,640,007. This patent describes an optical encoder in which a plurality of encoder wheels each contain a series of openings that pass by a light emitting device as the gears are turned. As light is shined through these openings and detected, the openings through which light is transmitted encodes the position of the wheels, and this code is compared to a defined code sequence to determine the position of a rotatable shaft functionally connected to the position detector.
Certain types of detectors have also utilized magnetic fields to encode the position of a device and to determine the position of a rotatable shaft. A magnetic sensor apparatus is described in U.S. Pat. No. 4,728,950. The device described in the '950 patent addresses the problem of automation of reading decimal gears, such as the type normally used in utility meters, in which each higher order digit is displaced in a 10 to 1 ratio relative to the lower digit. The devices described teach use of Hall Effect sensor devices to detect the magnetic field of a magnet attached to each digit gear. In the devices described, each gear has a permanent magnet attached thereto, and an array of 10 Hall Effect sensor devices are placed in a circular array with respect to each gear, so that the magnets pass over the sensor devices in succession as the gears turn. The resulting coded output of the sensor devices is read in a linear fashion, such that the reading of the position of the higher gears are dependent on the readings of the lower gears.
Both of the '007 and '950 inventions rely exclusively on normal state recognition, and indeed go to great lengths to avoid abnormal states. This reliance on normal state recognition is typical of prior art APDs. The term “normal state” refers to an environment in which preselected individual sensors, and often single individual sensors, are associated with a corresponding number of discrete absolute positions available to a source. Whenever the source occupies one of those positions and activates solely the designated sensor or group of sensors for that position, the APD is in a “normal state.” In contrast, whenever the source is between those positions in its path of travel, or otherwise activates more than one designated sensor or group of sensors at the same time, the APD is in an “abnormal state.”
Returning to the '007 and '950 patents, these inventions are characteristic of the traditional prior art approach using exclusively normal state position detection. A key feature of these prior art inventions is to ensure that stray or unfocused emissions from the source are not recorded in error by the wrong sensor, i.e. a sensor other than the one designed to be indicative of the current absolute position. In the case of the '007 patent, reflective surfaces are used to focus light through the apertures and onto the light sensing devices. In the case of the '950 patent, a three-pole magnet is used to focus the magnetic field onto single Hall Effect devices in predefined normal states.
Sole reliance on normal state detection imputes a number of drawbacks and inherent limitations on APDs. First, the resolution of the APD is limited to the number of discrete sensors deployed. The APD can measure no finer a resolution than the predefined number of normal states monitored for. Further, structural or space limitations may dictate that less than an optimal number of sensors can be deployed on a particular moving component.
Second, while stray and erroneous sensory readings can perhaps be minimized, they can never truly be eradicated. This is especially true for a safe, low-cost sensory medium such as magnetic flux, which exists in more of a field than a directed beam. This is further especially true in high speed environments where the transitions between successive normal states become harder to identify. Thus, APDs relying solely on normal state detection necessarily include a lot of structure minimizing the effect of the inevitable. This structure adds to the cost and complexity of the APD, while possibly detracting from overall robustness.
This prior art tendency towards “extra structure to minimize the inevitable” is highlighted in U.S. Pat. No. 4,737,710. A complex combination of Hall Effect device placements, stray flux shielding, and signal adaptation circuitry is disclosed to purify detection of normal states in high speed service. It is nonetheless a fact that APDs such as illustrated in the '710 patent exist in an abnormal state most of the time. Except when a source is momentarily directly in communication with a single sensor, the APD is effectively between sensors, and thus by definition in an abnormal state. Sole reliance on normal state detection may therefore not always be the most optimal approach.
It will therefore be appreciated that an APD that interprets detection of abnormal states, rather than avoiding them, would be highly advantageous. The disadvantages of sole reliance on normal state detection as described above would be obviated. Further, s
Elliott Lynn H.
Lowery Jason R.
Scalf Gerald W.
EIM Company, Inc.
Hoff Marc S.
Tsai Carol S W
Vinson & Elkins L.L.P.
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