Method Of Determining And/Or Evaluating A Differential Optical Signal

Abstract

The invention relates to a method for determining and/or evaluating a differential, optical signal. According to the invention, at least two first light sources (S1, S2) which are sequentially clocked in terms of light and emitted in a phased manner are provided, in addition to at least one receiver (E) which is used to receive at least the alternating light portion arising from the first light sources (S1, S2). The light-intensity radiating through at least one light source (S1, S2) in the measuring arrangement is controlled in such a manner that the clock-synchronous alternating light portion, which occurs between different phases, is zero in the receiver (E). By determining the reception signal in the receiver (E) in relation to the phase position in order to regulate the radiated light intensity and by producing an adjustable variable (R) directly or by adding current in the receiver, it is possible to simplify digital implementation of the method with as little sensitivity loss as possible.

Description

BRIEF DESCRIPTION OF THE FIGURES

The invention is illustrated in detail in the following on the basis of the accompanying drawings, in which:

FIG. 1 shows a block diagram of a method for establishing an optical signal which is independent of extraneous light according to the prior art,

FIG. 2 shows signal characteristics in a control circuit according to FIG. 1,

FIGS. 3, 4 show different embodiments for a receiver,

FIGS. 5, 6 show block diagrams for digital control of a method of this kind,

FIG. 7 shows a block diagram for regulation with a separate compensation light source.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is now described in detail by way of example with reference to the accompanying drawings. However the embodiments are only examples, which are not intended to limit the inventive concept to a specific arrangement.

The figures show a method for determining and/or evaluating a differential optical signal with at least two first light sources S1, S2 which emit light in a sequentially clocked, phased manner. At least one receiver E is provided to receive the signal thus emitted, this receiver receiving the clock-synchronous alternating light component coming from the first light sources S1, S2. The light intensity which is irradiated in the measuring arrangement through at least one light source S1, S2, which may also be a compensation light source K, is then regulated such that the clock-synchronous alternating light component, which occurs between the different phases, becomes zero at the receiver E. This was illustrated in detail at the outset in the introductory part of the description.

Taking this as a starting point, the principle which is pursued is now illustrated in general in the following before discussing the more precise implementations according to FIGS. 5 to 7.

In order to regulate the irradiated light intensity, instead of assessing and evaluating the incoming signal with regard to its amplitude, as in the case of an analogue evaluation, the incoming signal at the receiver E is determined in terms of phase position and a correcting variable is thus produced. This correcting variable R may either be transmitted as a light signal through a corresponding current to at least one of the first light sources S1, S2, although it is also possible to feed the entirety through a current signal to the receiver through current addition. The additional light source, which can regulate the light intensity, may in this respect be one of the first light sources S1, S2. However it may alternatively also be an additional light source K which is associated with the receiver, with the regulation taking place through this additional light source K such that it changes its phase as a result of this additional light source K being controlled by means of at least one EXOR gate 21 or at least one EXNOR gate.

The integral value of the phase position, that is, e.g. +1 or −1 corresponding to 0° or 180°, is integrated by means of a counter Z in order to produce the correcting variable R. The digitized incoming signal is used as a directional signal for the receiver E. The incoming signal is fed to a flipflop 11, with the clock of the flipflop being derived from the transmitting clock such that the signal of one of the first light sources S1 is reproduced in-phase and the signal of the other of the first light sources S2 is reproduced inverted as the control signal for the counting direction of the counter Z (FIG. 5). It is alternatively also possible to use the digitized incoming signal as a clock signal for the counter Z, while the counting direction is predetermined by the clock of a clock generator 12 which determines the clock of the first light source S1, S2 (FIG. 6). The incoming signal has a phase displacement of preferably 90° with respect to the clock of the clock generator 12 in the latter case. The incoming signal is preferably temporarily stored as a counter clock in the time range of the edge of the clock pulse.

In order for the counter Z to run up faster, the counter reading of the counter Z may, if required, be predetermined or is optionally predeterminable in software terms. In order to utilize the resolution of the controller as fully as possible, the correcting variable R may additionally comprise a predetermined or predeterminable, fixed component. This is particularly the case if only a specific control range is always used in a specific application. Significantly increased resolution is thus obtained for the control range which then remains and which is determined by the variable component of the correcting variable. This variable component of the correcting variable is added to the fixed component through current addition, e.g. at the light source S1, S2, K. The correcting variable R may additionally be added to the weaker light source(s) S1, S2, K in a clocked fashion through current addition.

The invention is now illustrated in further detail on the basis of embodiments and with reference to the figures. According to FIG. 2, the receiver signal corresponds to the clock of the transmitter S1 or of the transmitter S2. There is in addition an additional phase displacement d which is caused by the transfer function of the LED drivers, the receiver and, in a small proportion, by the light propagation time. The signal characteristics are represented in FIG. 2. Represented from top to bottom are the outgoing signals of the transmitter S1 and of the transmitter S2 as well as the associated incoming signals E(S1) and E(S2), in the case of which either the transmitter S1 or the transmitter S2 predominates, according to phase.

A common feature of the two implementations presented in the following is that the incoming signal is amplified to a limiting condition, so that a square-wave signal is obtained. This square-wave signal can be obtained according to FIG. 3 by means of a comparator 14 from the high-pass-filtered incoming signal, or, according to FIG. 4, through a first limiting amplification by means of a transimpedance amplifier 13 and an amplitude limiter 15, this being converted to the required digital level in a subsequent stage. This second implementation has the advantage of preventing the saturation effects in amplifiers or the differing switching times for the leading and trailing edge in comparators.

The implementation may take place according to FIG. 5 such that the digitized incoming signal is fed to the data line of a D flipflop 16. The clock for the flipflop is derived from the transmitting clock of the clock generator 12—if necessary by means of a time-delay circuit 19—such that, for example, the clock signal of the transmitter S1 is reproduced in-phase and that of the transmitter S2 in inverted fashion. These values, thus stored, serve as a control signal for the counting direction of the counter Z. The counter reading is converted into the transmission amplitude of, for example, the transmitter S2 by means of a D/A converter 17, 18. According to the two regulating possibilities initially mentioned, the transmitting power of the transmitter S1 is, if necessary, controlled by the inverted counter reading or the inverted D/A converter result. In the corrected state the counter Z always fluctuates periodically up and down by one counting step at the predetermined clock. The receiver E therefore controls the direction of the counter Z. Features of this implementation are:

• • One counting step per cycle
  • The receiver E need only regenerate the phase
  • The receiver E may be designed with extremely high amplification
  • Clock-synchronous operation of the counter Z
  • A circuit for generating a sampling pulse

In the alternative implementation according to FIG. 6 the digitized incoming signal has a phase displacement of typically 90° with respect to the clock. This may be achieved, for example, by a bandpass filter in the receiver E. This incoming signal serves as a clock for the counter Z, while the counting direction is predetermined by the clock. In order to prevent inadmissible edge overlaps, the incoming signal serving as the counter clock is temporarily stored shortly before and after each edge of the clock pulse serving as the counting direction. In other respects the D/A converters 17, 18 are used as in FIG. 5. Features of this implementation are:

• • One counting step per cycle, if there is a change of direction per each half-cycle
  • The receiver needs only to regenerate the phase, phase displacement is necessary
  • The receiver may be designed with extremely high amplification
  • An asynchronous clock of the counter
  • A circuit for blocking the incoming signal in the case of an edge change of the clock pulse is necessary

As in the case of the implementation according to FIG. 6, the counter reading is changed over to the transmitter drivers.

A method for the phase-correct compensation of a differential optical signal is known from the earlier German patent application 103 00 223.5. Here it is essential for the sole regulated transmitter, in most cases an additional light source K as compensator, to undergo a change in phase. The disclosed content of this application is hereby also made the subject matter of the present invention. However, in so far as this is of importance for this invention, the content of that application is illustrated in the following. In principle, when a light source emits light, a clock-synchronous electrical signal is generated in a photodiode which receives this light, e.g. following reflection from an object. Therefore, if, for example, the light-emitting diode emits light at a clock frequency of 40 kHz, the photodiode will generate a corresponding signal at the same frequency and almost the same phase. If, in the case of two light-emitting diodes operated in clocked fashion, the alternating light component which is relevant here is considered with regard to the transmitting phase of 0°, this alternating light component may be positive and negative, i.e. have a phase of 0° or 180°, as one light-emitting diode radiates at a phase of 0° and the other at a phase of 180°. In this respect 0° is identified with a positive sign and 180° with a negative sign. If an additional light source K, which operates independently of the light sources emitting the light, is now turned on, this light can irradiate out-of-phase in terms of amplitude and sign. In other words, the additional light source K can therefore take over the compensation for the most part or even alone through additional light irradiation. The clock-synchronous incoming signal is thereby influenced in terms of its amplitude by the light output of the additional light source K, even in the case of complex measuring arrangements with position, direction and distance detection, such that the incoming signal becomes zero.

This is achieved according to the present invention according to FIG. 7 in that the counter reading is not delivered directly, but rather via the EXOR gate 21 or optionally an EXNOR gate, to the D/A converter 22. An EXOR gate 21 with two inputs can be conceived as a controllable inverter. If a logic zero level is applied to one input (control input), the output of the gate follows the second input (data input). If, on the other hand, a logic 1 is applied to the control input, the output of the gate corresponds to the inverted data input. A gate of this kind is connected to each output of the counter Z, and all control inputs are connected to the inverted most significant bit (MSB) of the counter. There is therefore a functional connection at the gate outputs with respect to the counter reading of those shown in FIG. 7. The MSB also acts as a control signal on an EXOR gate 23, through which the clock is routed to the modulator 24 of the light source K as compensation LED. The transmitters S1 and S2 are not regulated in the embodiment of FIG. 7.

The counter Z may overflow. As a result, when the control circuit is unable to adjust on account of unfavorable optical damping conditions, the control circuit oscillates, so that the counter Z counts permanently and the intensity of one or both LEDS(s) changes cyclically. In order to prevent this, overflow is prevented by suitable wiring. For this purpose the counter Z is blocked for the counting direction concerned upon reaching the maximum or minimum counter reading. This blocking process is implemented, for example, by coupling the transmission output to the ENABLE input of the counter Z. The exact design depends on how the counter is implemented.

In the presented implementations the counter reading changes by one step per clock pulse. A larger counting step may also be initiated through a suitable logic circuit which detects that the last counting steps go in the same direction. This corresponds to a D component in the controller.

In order to accelerate a transient oscillation of the controller, the counter Z may also be able to set it to a predetermined counter reading.

If the change in the optical transmission only takes place in a narrow range, it is possible to enlarge this range. For this purpose the correcting variable is formed from two parts, namely a fixed setting in the form of an offset and a variable component which is controlled by the controller. In the case of compensation as proposed in the earlier German patent application 103 00 223.5 illustrated above, it is therefore possible to dispense with the actual compensation LED and add the regulated component to the respective in-phase transmitter through current addition.

It is understood that this description can undergo a wide variety of modifications, changes and adaptations taking place in the range of equivalents to the appended claims.

List of Reference Characters

10 controller

11 flipflop

12 clock generator

13 transimpedance amplifier

14 comparator

15 amplitude limiter

16 flipflop

17, 18, 22 digital-analogue converter

19 time-delay circuit

21, 23 EXOR gate

24 modulator

d phase displacement

E receiver

E(S1), E(S2) incoming signals of S1, S2

K additional light source

R correcting variable

S1, S2 first light source

Z counter

Claims

1. Method for determining and/or evaluating a differential, optical signal with at least two light sources which emit light in a sequentially clocked, phased manner, and with at least one receiver for receiving at least a clock-synchronous alternating light component coming from the light sources, wherein a light intensity which is irradiated into the measuring arrangement by at least one light source is regulated such that the clock-synchronous alternating light component, which occurs between different phases, becomes zero at the at least one receiver (E), wherein in order to regulate the irradiated light intensity, a incoming signal at the at least one receiver (E) is determined in terms of phase position and a correcting variable (R)fo controlling the irriadiated light intensity is thus produced.

2. Method according to claim 1, wherein in order for the clock-synchronous alternating light component, which occurs between the different phases, to become zero at the at least one receiver, an additional light source is used or one of the first light sources (S1,S2) is used as additional light source.

3. Method according to claim 2, wherein the additional light source, which is associated with the at least one receiver, is regulated by the regulation such that it changes its phase as a result of this additional light source being controlled by means of at least one EXOR gate or at least one EXNOR gate.

4. Method according to claim 1, wherein the correcting variable is added to a current signal of the receiver through current addition.

5. Method according to claim 1, wherein a value of the phase position is integrated by means of a counter in order to produce the correcting variable.

6. Method according to claim 5, wherein a counter reading of the counter is, predetermined or predictable.

7. Method according to claim 5 wherein the value of the phase position is evaluated at 0° or 180°.

8. Method according to claim 7, wherein the incoming signal is fed to a flipflop, wherein the clock of the flipflop is derived from the transmitting clock such that the signal of one of the first light sources (S1) is reproduced in-phase and the signal of the other of the first light sources (S2) is reproduced inverted as the control signal for the counting direction of the counter (Z).

9. Method according to any one of claims 1-6, characterized in that the digitized incoming signal is used as a clock signal for the counter (Z), while the counting direction is predetermined by the clock of a clock generator (12) which determines the clock of the first light sources (S1, S2).

10. Method according to claim 9, characterized in that the incoming signal has a phase displacement of preferably 90° with respect to the clock of the clock generator (12).

11. Method according to claim 9 or 10, characterized in that the incoming signal is temporarily stored as a counter clock in the time range of the edge of the clock pulse.

12. Method according to any one of the preceding claims, characterized in that the counter reading of the counter (Z) is, if required, predetermined or predeterminable.

13. Method according to any one of the preceding claims, characterized in that the correcting variable (R) comprises a predetermined or predeterminable, fixed component.

14. Method according to claim 13, in so far as it relates to any one of claims 1-3 and 5-12, characterized in that a variable component of the correcting variable (R) is added to the fixed component through current addition at the light source (S1, S2, K).

15. Method according to any one of claims 1-3, 5-14, characterized in that the correcting variable (R) is added to the weaker light source(s) (S1, S2, K) in a clocked fashion.