Abstract:
The optical distance detecting or measuring device comprises a light source with an emitting optic for projecting a light beam according to the axis of the emitting optic onto a target to be measured and a first detector defining the receiving axis contained in the same reference plane as the emitting axis. The device comprises at least a second detector that is aligned with the first detector on an axis contained in a plane that is inclined at an angle α with respect to the reference plane, said angle being comprised between 10° and 170°. Alternatively, two emitters may be arranged in an inclined plane and one receiver in the reference plane. This arrangement allows a significant improvement of the performance of such a device.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention refers to an optical distance detecting or measuring device, comprising a light source with an emitting optic for projecting a light beam according to the axis of the emitting optic onto a target to be measured and a first detector defining the receiving axis contained in the same reference plane as the emitting axis.  
         BACKGROUND OF THE INVENTION  
         [0002]    Prior art devices including optical reflection sensors with background suppression or distance measuring devices generally make use of the triangulation principle described by FIG. 1. Beyond a maximum distance, the operation of the sensor is impaired due to the fact that the angular sensitivity decreases with the distance. When attempting to increase this distance, the result is an enlargement of the dead zone which excludes an operation in the proximity of the sensor.  
           [0003]    In order to adapt this limited measuring range to varying situations, certain manufacturers use an adjustable mirror that allows the best adaptation of the measuring range. Such a solution is e.g. described in U.S. Pat. No. 3,759,614.  
           [0004]    Other solutions are known as well: Different references such as GB-A-2 069 286 and DE-A-196 19 308 suggest a pulsed emission and an analysis of two receiver channels. DE-A-24 55 733 alternatingly uses two lighting optics located in the same plane. DE-C-40 04 530, DE-C-40 40 225, DE-C-41 40 614 as well as DE-C-198 08 215 suggest that a plurality of alternatingly emitting light sources are provided in the same optical channel. The receiver channel is formed by multiple detectors or by a position-sensitive detector, e.g. PSD, the electronic circuit being capable of processing the signals corresponding to each one of the light sources to obtain information concerning the distance to the target. A sophisticated treatment of this information allows a slight extension of the range of the measuring system.  
           [0005]    However, the inherent limitations of the principle of triangulation between elements that are situated in the same plane as defined by the optical axes of the emitting and receiving systems do not allow a substantial improvement of the performance with respect to distance, linearity, and the dead zone. Thus, in the case of a measuring sensor or of a background suppression triangulation sensor, a calculation of the ratio between the maximum detection distance and the minimum distance of the measuring range yields a quality number that is rarely greater than 5. On the other hand, such detectors are very often sensitive to the amount of light reflected by the target, which depends on the texture and the color of the latter.  
           [0006]    On the background of this prior art, a first object of the present invention consists in substantially improving the results of measurements by triangulation without the need for complex analyzing circuits. This is accomplished by an optical distance detecting or measuring device wherein said device comprises at least a second detector that is aligned with the first detector on an axis contained in a plane that is inclined at an angle with respect to the reference plane, said angle being comprised between 10° and 170°.  
           [0007]    A second object is to allow the realization of efficient measuring or background suppression sensors having small dimensions. This is accomplished by an optical distance detecting or measuring device, comprising a light source and receivers, wherein the light source emits light pulses of different intensities that are intended alternatingly for each one of said receivers, the emitted intensities being regulated in such a manner as to produce signals having identical amplitudes or corresponding to a predetermined function on the receivers, and an optical distance detecting or measuring device, comprising a sensor with a single lens including distinct emitting and receiving sectors, each sector being provided with a prism for focusing the light beams on the emitting and the receiving elements, respectively. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The invention will be explained in more detail hereinafter with reference to the accompanying drawings.  
         [0009]    [0009]FIG. 1 schematically shows the known measuring principle by triangulation;  
         [0010]    [0010]FIG. 2 describes the disposition of the measuring elements of the invention;  
         [0011]    [0011]FIG. 3 illustrates the values measured in function of the distance;  
         [0012]    FIGS.  3 A- 3 C are sectional views according to C-C, C 1 -C 1 , and C 2 -C 2  in FIG. 3;  
         [0013]    [0013]FIG. 4 shows the performance of the invention;  
         [0014]    [0014]FIG. 5 schematically describes a simple embodiment of a device of the invention;  
         [0015]    [0015]FIG. 6 shows the realization of a compact sensor;  
         [0016]    [0016]FIG. 6A shows a sectional view according to line F-F of the sensor of FIG. 6; and  
         [0017]    [0017]FIG. 7 describes a variant of the embodiment of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    In FIG. 1, illustrating the known measuring principle by triangulation, shows light source  21  and emitting optic  22  which project the beam onto target C that is to be measured, thereby defining optical emitting axis e. The light resulting from the diffusing reflection of target C is focused on receiver  23  by lens  24 . These two elements define the reference axis r of the receiving system. The axes of emitting optic e and of receiving optic r define a plane in which all elements of this triangulation measuring system are situated. Thus, an additional receiver  25  is disposed near the reference receiver. It determines a new receiving axis r 1 , also comprised in the same plane, which extends the measuring range to C 1 .  
         [0019]    The detecting system is thus formed of an assembly of two or more detectors, and the same detecting function can also be realized by a position-sensitive detector such as PSD. The electronic circuit processing the signals delivered by the detectors will determine the position of the luminous impact and deduce the information of the measured distance from that position.  
         [0020]    The performance of such an arrangement depends on the number of detectors and on the space therebetween, as well as on their position with respect to the emitting optic. With regard to basis X, which is defined as the distance between the emitting optic and the receiving optic, it appears that the measuring range M is limited and the dead zone Z is large. Linearity is affected by the sensitivity of the detectors to angular variations of the incident beam, which decreases as the distance from the target increases.  
         [0021]    The present invention provides a different arrangement of the detectors. The novel arrangement is shown in FIG. 2, illustrating light source  1  and the lens of emitting channel  2 , which define the optical axis Oe of the emitting system. Reference detector  3  and lens  4  define the reference axis Or of the receiving system. These two axes of the emitter and the receiving system determine reference plane A. Plane C represents the target that is to be detected or whose distance is to be measured.  
         [0022]    It will be shown that when an additional detector  5 , defining a new receiving axis Or 1 , is situated in a plane B that is inclined at an angle α with respect to reference plane A, the intensities measured by the detectors allow to obtain a highly linear information in function of the distance in a large measuring range. The optimum value of inclination a is 90°, but any other inclination α between 10° and 170° is advantageous. In the text, reference will be made to 90°, while it is understood that the angle α may be different.  
         [0023]    [0023]FIG. 3 schematically shows the envelopes of the beams in the suggested arrangement. Envelope E of the idealized emitting beam is shown in the case of a large distance focusing of source  1  and of lens  2 . After lens  2 , the envelope is cylindrical. The envelopes of receiving beams R and R 1  are also illustrated in a cylindrical form. Emitting source  1  and reference receiver  3  are situated in the principal plane and aligned on axis a while the two receivers  3  and  5  are aligned on an axis b that is perpendicular to axis a.  
         [0024]    [0024]FIGS. 3A to  3 C show the intersections of the three beams for three positions of the target and allow to determine the ratios between the luminous intensities measured by the two receivers by means of an area calculation.  
         [0025]    If the ratio between the intensity of principal receiving beam i and that of secondary beam il is calculated and this ratio is represented in function of the distance d measured between the detector and the target, the diagram of FIG. 4 is obtained. It appears that the variation of this ratio il/i is linear in a large portion of the measuring range. A calculus of the ratio between the maximum distance and the dead zone, as defined earlier in the description, yields a quality number of up to 10. The diagram of FIG. 4 shows clearly that the first object of the present invention is attained, namely the improvement of the measuring results by triangulation, i.e. a large measuring range, a very small dead zone, and a high linearity are obtained.  
         [0026]    In order to obtain these results, it is important that the envelope curves of the beams are as cylindrical as possible. This must be the case over a distance corresponding to the measuring range. To this effect, the real rather than the punctual dimensions of the source and of the detectors must be taken into account. The distances between these components and the lenses must be adapted to the focal distances in such a manner that the beams are as close to the cylindrical shape as possible.  
         [0027]    A device realized according to this principle, comprising an emitter LED and two receiving photodiodes, is suggested and schematically described by FIG. 5 as an example of a simple embodiment. The light pulses are emitted by LED  1  alternatingly for each one of photodiodes  3  and  5 . In this exemplary embodiment, the photodiodes are aligned on an axis that is perpendicular to the plane defined by the emitting axis and the reference receiving axis. The alternating emitting intensities E 3  and E 5  are regulated such that the respective amplitudes of the signals R 3  and R 5  measured by each one of the receivers are identical or correspond to a predetermined function. The information concerning the distance results from the ratio of the intensities E 3  and E 5  of the emitted light. This procedure offers the additional advantage of a very low sensitivity of this device to the color of the target.  
         [0028]    The described principle, according to which the alternating emitting intensities E 3  and E 5  are regulated such that the respective amplitude of the signals R 3  and R 5  measured by each one of the receivers are identical or correspond to a predetermined function, applies both to an optical device where the photodiodes are situated in the same plane as the emitter diode or in an inclined plane.  
         [0029]    However, the advantage of this principle combined with the advantage of the inclined plane results in a particularly advantageous device.  
         [0030]    An example of a compact sensor that is adapted for realizing a device according to FIG. 5 is described by FIG. 6. Sensor  10  comprises a small enclosure D including bridge apparatus of the present invention will now be described while referring to FIG. 1.  
         [0031]    According to the present invention, the bridge apparatus comprises: a wireless LAN device driver unit  31 , for exchanging wireless LAN communication data; a LAN device driver unit  32 , for exchanging wire LAN communication data; a bridging unit  21 , for establishing a bridge for connecting the wireless LAN device driver unit  31  and the LAN device driver unit  32 ; and a QoS middleware unit  1 , positioned between the bridging unit  21  and the wireless LAN device driver unit  31 . The QoS middleware unit  1  includes: a header comparator  111 , for relaying to the wireless LAN device driver unit  31  a frame transmission request received from the bridging unit  21 ; a transmission FIFO unit  51 , including a plurality of FIFO queues for which predetermined priorities are provided; and a synthesization unit  112 , for synthesizing transmission data obtained from the transmission FIFO unit  51 .  
         [0032]    The header comparator  111  extracts priorities using preregistered data in a cache table  53  and session data extracted from header data, queues transmission requests (transmission events) in the transmission FIFO unit  51  in accordance with the priorities and, consonant with a predetermined priority order, selects and relays a specific frame having a high priority. That is, when the header comparator  111  adds a transmission request (transmission event) for a high priority frame to an FIFO queue in the transmission FIFO unit  51 , in the queue, the priority for the transmission request to be issued to the wireless LAN device driver unit  31  is increased. to the system described in FIG. 2. This system comprises two or several emitting sources  1  and  7  aligned in a plane B that is inclined at an angle α, preferably at 90°, with respect to plane A which is defined by the reference emitting axis Oe and the receiving axis Or extending between receiver  3  and optic  4  for focusing the diffuse light on the receiver.