Optoelectronical position detection

Details Optoelectronical position detection Optoelectronical position detection

1999-07-13

2001-06-05

Gutierrez, Diego (Department: 2859)

Geometrical instruments

Distance measuring

Scale reading position sensor

C250S231140, C033S0010PT

Reexamination Certificate

active

06240652

ABSTRACT:

TECHNICAL FIELD
The present invention relates to optoelectronic position detection devices for detecting the position of a movable body and, more particularly, to an optoelectronic position detection device for detecting the displacement between a movable body relative to a fixed body.
BACKGROUND ART
Optoelectronic position detecting devices detect the absolute position and movement of specific machine parts with respect to each other. For example, optoelectronic position detecting devices detect robot movements. Optoelectronic position detecting devices are used in the automotive industry, for example, for detecting steering angles. The steering angle and the steering angle lock in motor vehicles is required by a driving dynamics control system. In addition to the steering angle values, the driving dynamics control system obtains further measurement data such as wheel rotational speed and the rotation of the motor vehicle about its vertical axis. The driving dynamics control system evaluates the absolute steering angle lock and the steering speed with other detected data for generating control signals. The control signals control actuators such as brakes and are used for engine management.
DE 40 22 837 A1 discloses an optoelectronic steering angle sensor. The steering angle sensor includes a light source and a line sensor arranged in parallel and spaced apart from each other to form a gap. A round encoder disc engages into the gap and is non-rotatable connected to the steering spindle. A code transmitter is formed as a light slit disc having a code trace. The code trace is a spiral which increases in size from the inside outwards. A CCD-sensor line is the line sensor. Because of the exposure of the image points of the line sensor in the case of a specific steering lock, it is possible to obtain information regarding the steering angle lock.
Steering angle sensor systems are installed in the region of the steering spindle of the motor vehicle. The installation space available in this region for installing steering angle sensor systems is limited. The available installation space is particularly limited in the axial direction of the steering spindle. The steering angle sensor of DE 40 22 837 A1 does not satisfy the demands of the minimum installation space. A line-source-LED is located as the light source on one side of the encoder disc on a plate and the sensor line is located on another plate on the other side of the encoder disc. The installation space is determined by the structure of the electronic components on the two plates and the width of the gap provided between these two electronic elements. The gap must be sufficiently large to ensure that the encoder disc can be rotated therein with a sufficient degree of axial play.
DE 36 41 288 C1 discloses an optoelectronic position detecting device requiring a smaller installation space than the required installation space of the device disclosed in DE 40 22 837 A1. The light source and the sensors of this device are located on the same side of the encoder disc. The encoder disc is essentially impervious to light on its side pointing towards the light source and the sensor elements. An annular light coupling window is exposed only in the region of the rotational center of the encoder disc. Accordingly, windows are provided in the light-impervious layer. The windows decouple the light from the encoder disc.
DE 36 41 288 C1 discloses another embodiment of the optoelectronic position detection device in which light is coupled from the side over the peripheral surface of the encoder disc. However, the problem associated with such an arrangement is that the encoder disc can only have a single trace.
DE 86 21 057 U1 discloses an optoelectronic angle measuring device requiring a small amount of installation space. The required amount of installation space is small because the encoder disc includes an annular recess into which a fixed light source protrudes. The light emitted by the light source is coupled by the annular recess into the encoder disc. The light is then reflected on a curved, metallized peripheral surface towards the planar base surface of the encoder disc such that the coding provided on this side of the encoder disc is exposed to light. However, this optoelectronic position detecting device has the problem that it is not possible to expose a plurality of code traces to a sufficient quantity of light.
DISCLOSURE OF INVENTION
Accordingly, it is an object of the present invention to provide an optoelectronic position detecting device requiring minimal installation space while enabling a plurality of code traces to be exposed to light simultaneously.
In carrying out the above object and other objects, the present invention provides an optoelectronic position detecting device for determining the absolute position of a movable body that is rotatable with respect to a fixed body. The device includes a light source for providing light. A transmitter disc is coupled to the movable body to move in correspondence therewith. The transmitter disc has a scanning code trace on one surface and a reference code trace on the opposite surface. The scanning code trace spirally extends around the one surface of the transmitter disc and the reference code trace circularly extends around the opposite surface of the transmitter disc. The transmitter disc has a peripheral connecting the opposing surfaces for receiving light from the light source. The scanning code trace and the reference code trace have respective reflective surfaces for reflecting respective light beams from the light received from the light source. A photosensitive line sensor is fixed with respect to the transmitter disc for receiving the respective reflected light beams from the scanning code trace and the reference code trace. The photosensitive line sensor generates output signals in response to the respective reflected light beams from the scanning code trace and the reference code trace. The output signals are indicative of the position of the movable body with respect to the fixed body as the movable body rotates.
The optoelectronic position detecting device enjoys the advantage of the light source not lying directly opposite to the line sensor. Consequently, the required installation space is minimal because the light beams for forming the light traces of the scanning trace and the reference trace are laterally transmitted into the transmitter element. The reflection surfaces of the transmitter element then reflect the light beams towards the photosensitive surface of the line sensor. The respective reflection surfaces represent the two code traces, the scanning trace and the reference trace. To enable this process, the transmitter element is formed as a transparent light-guiding body.
Furthermore, in addition to the minimal required installation space, the optoelectronic position detecting device enjoys the advantage that it is unnecessary to make adjustments between the light source and the line sensor. Also, the light source and the line sensor can be attached to the same printed circuit board.
The reflection surfaces representing the code traces take the form of notches extending into the surface of the transmitter element. Because the notches engage into the surface of the transmitter element at different depths, adjacent code traces on the surface of a line sensor can be represented. The encoder disc has a sufficient thickness such that the desired number of notches having different depths can be provided. The notches, i.e., reflection surfaces, are disposed at an angle with respect to the plane of the transmitter element such that the reflected light beams expose the surface of the line sensor. In so doing, the notch representing the scanning trace is in one surface of the transmitter element and the notch representing the reference trace is in the other surface of the transmitter element.
In a preferred embodiment, the lateral edge of the transmitter element, into which the light beams are coupled, is curved spherically outwards to act as a lens. The has th

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