Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-04-05
2001-08-14
Lee, John R. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S231140
Reexamination Certificate
active
06274864
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention pertains to an optical scanning device, in particular, for steering angle sensors. Scanning devices of this type contain a code carrier with toothed segments distributed over its length or periphery. These segments are irradiated by a radiation transmitter arranged in front of the toothed segments, and the radiation which passes through the intermediate spaces between the segments is measured with a receiver arranged behind the toothed segments.
It is frequently desired that the output signal of the receiver have a certain ratio between pulses and interpulse periods, e.g., a ratio of 1:1. This can only be achieved by utilizing a pulse shaper. A pulse shaper converts the output signals of a receiving photodiode into square-wave signals at the output of the receiver. In order to achieve a certain ratio between the pulses and the interpulse periods at the output, the transmission voltage can be changed such that the radiation level is reduced and a chronological shift of the response threshold of the converter is attained on the reception side. Another option consists of changing the response threshold on the reception side such that the beginning and the end of the respective output pulses can be controlled. However, both of the aforementioned measures are expensive and require a complicated control arrangement.
SUMMARY OF THE INVENTION
The invention is based on a scanning device and aims to achieve a predetermined scanning ratio on the output side with simple means. The invention, in principle, consists of selecting a relatively high value for the transmission current such that the phototransistor operates near the saturation point. Due to this measure, the transmission side of the scanning device is less sensitive to current or voltage fluctuations and radiation originating from the environment. Due to the increased transmission current, the scanning ratio on the output side is changed while the response threshold of the receiver remains the same. If it is not intended to change the response threshold, which is designed for the highest possible sensitivity, the invention proposes to change the length ratio between the teeth and the gaps between the teeth on the code carrier in a suitable fashion. This means that, if the ratio between pulses and interpulse periods is increased on the output side by increasing the transmission current, the length of the teeth is increased on the input side and the length of the gaps between the teeth is correspondingly decreased. For example, if excessively short (positive) output pulses are obtained with a predetermined tooth length on the code carrier by utilizing an inverting circuit, the length of the teeth is correspondingly increased and the gaps between the teeth are decreased in order to increase the ratio between the output pulses (i.e., excessively long negative pulses) and the corresponding interpulse periods.
According to one additional development of the invention, a favorable ratio between pulses and interpulse periods is 1:1.
When measuring rotational angles by means of the scanning device, a particular simple design of the code carrier is defined by a toothed disk on the periphery of which permeable and impermeable regions are circularly distributed. In this case, the teeth may be circularly arranged on the edge of the disk such that they extend perpendicular to the disk.
With respect to the transmitter and the receiver, it is proposed to provide the transmitter with a phototransistor and the receiver with a photodiode.
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ITT Manufacturing Enterprises Inc.
Lee John R.
Lewis J. Gordon
Pyo Kevin
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