Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2002-09-11
2003-11-25
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S23700G, C250S231140, C341S011000
Reexamination Certificate
active
06653620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a process for evaluating the signal of an optoelectronic position or angular position measuring device with an encoder disk that can move relative to a transceiver comprising a light source and a sensor array having a number of optoelectronic transducers and that has at least one digital code track, with this process including the assignment of certain sensor array transducers to the at least one code track. The invention also concerns a preferred use of such a process.
2. Background Art
Position and angular position measuring devices are frequently used for automatic positioning and measurement in machine tools and in coordinate measuring instruments. For example, rotation angle sensors are used in the area of motor vehicles to determine the absolute angular position of the steering wheel and therefore they are also called steering angle sensors. Such optoelectronic steering angle sensors essentially include a rotor and a stator. The rotor is an encoder disk coupled to the rotational motion of the steering wheel and the stator is a transceiver. The encoder disk includes a light source, for example an LED system, located on one side of the encoder disk. A receiving device, which is usually a line sensor with numerous adjacent transducers, is on the other side of the encoder disk. From time to time the coding used by the encoder disk is a digital code which includes several parallel code tracks and is built in the manner of a Gray code, for example.
A value indicative of the steering angle is needed in motor vehicles so that this value can be supplied, for example, to a vehicle movement dynamics control system. In addition to the mentioned steering angle values, such a vehicle movement dynamics control system receives other measurement data, such as the wheel speed or the rotation of the motor vehicle about its vertical axis. The absolute steering angle and the steering speed are needed so that these values, along with the other captured data, can be evaluated by the vehicle movement dynamics control system and converted to control actuators such as the brakes and/or the engine management system.
Previously known position and angular position measuring devices evaluate the signal amplitudes of the transducers assigned to each code track by comparing the signal amplitude with a specified signal threshold. If the signal threshold is exceeded, the signal amplitude of the transducers assigned to this code track is evaluated as being exposed by the coding of the code track. If the signal amplitude is smaller than the specified signal threshold, an evaluation is made that the coding of this code track is not causing exposure of the transducers assigned to this code track.
Assignment of certain transducers to a code track is used in the previously known process to compensate for play of the encoder disk in its movement relative to the transceiver. For this purpose, the coding has at least one reference track assigned to it. Because the distance from the code tracks to the reference track is the same over the length of the code tracks, it can be determined which code track is exposing which transducer(s) by determining the position of the reference track on the sensor array.
Although the previously known process can achieve sufficiently precise results when the conditions which have an influence on signal detection remain constant, such position and angular position measuring devices can provide incorrect measurement results if, for example, environmental influences should change the idealized measurement parameters specified during the design of the position or angular position measuring device. When such an angular position measuring device is used as a motor vehicle steering angle sensor exact angle detection should be ensured under the most diverse influences.
For example, such a measuring system can be affected by stray light, or by the encoder disk being covered with condensation, ice, dust, etc., and the signal threshold is often exceeded in the examples mentioned not only when there is an actual direct exposure by the coding of a code track, but also due to stray light exposing the transducer elements assigned to such a code track. In a corresponding manner, it is also possible for the signal threshold not to be exceeded despite being exposed by the coding of a code track, for example, when there is dust. In these cases the angle value read from a steering angle sensor is faulty. Accordingly, the subsequent evaluations and analyses based on this value are also faulty.
SUMMARY OF THE INVENTION
Therefore, starting from this prior art that has been discussed, the invention is based on the task of further developing a process of the type mentioned above in such a way that it is able to avoid as much as possible the disadvantages described above.
In accordance with the invention this task is solved by evaluating the signal amplitudes of the transducers assigned to a code track and a non-code track. The relative difference in brightness is determined between the code track signal (which is relatively brighter when there is an exposure) and a non-track signal (which is relatively darker). A determination is then made on the basis of the difference in brightness about whether or not the transducers assigned to the code track are exposed by the coding of the code track.
In contrast to the known prior art, the process according to the invention involves evaluating the signal amplitude assigned to the one code track not in comparison with a specified fixed absolute signal threshold, but rather by determining the relative difference in brightness between the code track signal (which is relatively brighter when there is an exposure) and a non-track signal (which is relatively darker compared with it). Thus, in principle, the evaluation is independent of a signal threshold that takes into account only the absolute signal amplitude. The evaluation of signal amplitudes is much more sensitive this way, so that the decision threshold can be established at a substantially lower level.
This method makes it possible to compensate for environmental influences by relative evaluation. If there should be a reduction, which might also possibly be only local, in the luminosity exposing the sensor array transducers—which would mean that the signal would no longer be recognized using the prior art, for example—there still remains a detectable contrast between a code track or code track section exposing certain of the sensor array transducers and the non-track sections not exposed by these code tracks, so that the desired evaluation can be carried out without limitations. The signals of a code track are then evaluated as a function of the difference in brightness that is found between the code track signal (which is relatively brighter when there is an exposure) and a non-track signal (which is relatively darker) by determining whether or not the transducers assigned to the at least one code track are exposed by the coding.
The difference in brightness between the signals of a code track and a non-code track can be determined, for example, by considering the difference in these signal amplitudes, with a specified difference in brightness serving as a signal threshold. However, the relative difference in brightness of the two signal amplitudes can also be determined by dividing one by the other, with a specified ratio then serving as a signal threshold.
A relatively darker non-code track can be provided by a dark track which remains the same over the possible amount of movement of the encoder disk and which may be located next to the digital coding. However, it is also possible if several parallel code tracks are used to use the intermediate spaces between the code tracks, which are present anyway, as so-called intermediate tracks, in order to evaluate the sensor array transducers assigned to these intermediate tracks as non-track signals.
However, under especially unfavorable, low-contrast measurement conditions it can happen that
Bläsing Frank
Schirp Christian
Allen Stephone B.
Brooks & Kushman P.C.
Leopold Kostal GmbH & Co. KG
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