Optical sensor
By introducing a control loop into the optical sensor, using the transmission power and temperature as the actual variables, and combining the control pulse width and pulse amplitude as the control variables, the problem that the optical sensor cannot reproduce short optical pulses under temperature changes is solved, and high detection sensitivity and anti-interference ability are achieved.
Patent Information
- Application Number
- CN202411450976.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-10-17
- Filing Date
- 2024-10-17
- Publication Date
- 2025-04-18
AI Technical Summary
Existing optical sensors cannot reproduce the generation of short optical pulses under temperature changes, resulting in a decrease in detection accuracy and sensitivity, and are sensitive to external interference.
By introducing a control loop into the optical sensor, using the transmission power and temperature as the actual variables, and combining the control pulse width and pulse amplitude as the control variables, stable control of the optical pulse parameters is achieved.
High detection sensitivity and stability under temperature changes and external interference conditions are achieved, ensuring the reproducibility and anti-interference ability of light pulses.
Smart Images
Figure CN119846601A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to an optical sensor. Background Art
[0002] Such optical sensors are typically used to capture objects within a detection area.
[0003] Such optical sensors usually include at least one transmitter that emits a light beam and at least one receiver that receives the light beam as sensor components. The transmitter and the receiver are advantageously integrated in one housing. The light beam emitted by the transmitter is reflected by the object back to the receiver. In addition, the optical sensor includes an evaluation unit in which an object detection signal is generated as a function of the reception signal of the receiver.
[0004] Such an optical sensor can be designed in particular as a distance sensor, in which the distance measurement is performed using a pulse transit time method.
[0005] To this end, the transmitter emits a light beam in the form of light pulses. The transmitter is formed by a laser diode that emits laser light. In order to determine the distance to an object, the light transit time of the light pulse from the transmitter to the object and back to the receiver is determined.
[0006] In order to achieve high measurement accuracy, it is desirable for the transmitter to emit very short light pulses. The pulse width, ie the duration of the light pulse, should preferably be in the range of a few hundred picoseconds.
[0007] With such short light pulses, a particularly steep rising edge of the light pulse is obtained. This is advantageous for low black / white errors in object detection. Depending on the degree of reflection of the object, not only different amplitudes of the light pulse but also different signal forms of the light pulse are obtained for the reflected light pulse, which can lead to distortions in the distance measurement. These error sources are reduced by using light pulses that are as short as possible.
[0008] Another aspect of such laser-based optical sensors is the issue of eye safety. Standard regulations regarding eye safety define the maximum intensity and exposure time of laser light to the human eye.
[0009] It is also advantageous here if the emitter of the optical sensor emits light pulses that are as short as possible. The shorter the pulse amplitude of the light pulse, the higher the intensity of the light pulse, i.e. the pulse amplitude, without violating standard requirements regarding eye safety. The higher the pulse amplitude of the light pulse, the higher the detection sensitivity of the object detection.
[0010] In order to generate short light pulses, it is known to use laser diodes as transmitters which are equipped with laser drivers which generate short control pulses.
[0011] A significant disadvantage is that these components for generating light pulses are not temperature-stable, so that the generation of short light pulses cannot be reproduced using optical sensors exposed to varying temperature influences. Summary of the invention
[0012] The object of the present invention is to provide an optical sensor of the above-mentioned type which is insensitive to external influences and has a high detection sensitivity.
[0013] The features of claim 1 are intended to provide a solution to this object. Advantageous embodiments and suitable further developments of the invention are described in the dependent claims.
[0014] The invention relates to an optical sensor having a transmitter for emitting light pulses, a receiver for receiving the light pulses, and an evaluation unit in which an object detection signal is generated as a function of a received signal of the receiver. The evaluation unit has a control loop by means of which the pulse width and / or pulse amplitude of the light pulses emitted by the transmitter are controlled. The transmission power of the transmitter forms the actual variable of the control loop, wherein the control pulse width and / or the control current for the transmitter form the control variable of the control loop.
[0015] With the optical sensor according to the invention, a high detection sensitivity can be achieved reproducibly during object detection and the sensor is insensitive to external influences.
[0016] This is achieved by the transmitter emitting a light pulse whose parameters are specified and stabilized by a control loop.
[0017] These parameters include the pulse width, ie the pulse duration of the light pulse, and its pulse amplitude.
[0018] In the simplest case, only the pulse width of the light pulse can be controlled, so that a light pulse with a defined pulse width can be achieved by the control.
[0019] Advantageously, the pulse width is in the picosecond range, in particular approximately one hundred picoseconds.
[0020] The controlled and therefore stable generation of light pulses with defined pulse width ensures a high detection sensitivity.
[0021] In principle, it is also possible to adjust only the pulse amplitude.
[0022] It is particularly advantageous if both the pulse width and the pulse amplitude of the light pulse are controlled by the control loop, so that the transmitter generates light pulses with a defined pulse width and pulse amplitude.
[0023] The control variables of the control loop are the control pulse width and the control current for the transmitter, which are advantageously generated by means of a suitable control circuit.
[0024] According to the invention, the transmission power of the transmitter forms the actual variable of the control loop, wherein the actual variable is continuously captured by suitable measuring means.
[0025] The transmitted power is a real variable which can be easily, quickly and accurately captured using metrological means. This represents a considerable advantage over direct metrological recording of pulse width and pulse amplitude as real variables, since capturing these would involve considerable technical effort, which in turn would lead to undesirably high manufacturing costs for the optical sensor.
[0026] Thus, the transmitted power can be used as the actual variable, and the dependence of the pulse width and pulse amplitude of the generated light pulses on the transmitted power is known in the optical sensor, i.e. stored in the form of a characteristic curve or the like. A temperature-dependent characteristic curve can also be stored in the optical sensor in order to take temperature influences into account when generating the light pulses.
[0027] It is particularly advantageous if the transmission power is measured during precalibration of a nominal light pulse of the transmitter and is stored in the evaluation unit as a reference variable for the control loop.
[0028] The reference variable represents the nominal value to which the transmit power is to be adjusted.
[0029] Pre-calibration can be performed using an optical detector with a large bandwidth and a sampling oscilloscope to signal the light pulse of the emitter. The light pulse is set by the control pulse width and the control current of the emitter, which form the control variable. Once set, the emission power of the emitter is determined and stored in the evaluation unit of the optical sensor as a reference variable (i.e. nominal value) for the control loop.
[0030] According to an advantageous embodiment, the temperature prevailing in the optical sensor forms a further actual variable.
[0031] For this purpose, a temperature sensor is advantageously provided, by means of which the temperature inside the optical sensor is determined.
[0032] By considering the temperature in the optical sensor as an actual variable, the temperature influence can be captured in the control process for specifying the pulse width and / or pulse amplitude, thereby ensuring a temperature-stable control of these parameters.
[0033] Alternatively or additionally, the temperature dependency of the control variable can be stored in a table in the evaluation unit.
[0034] The temperature dependence of the control variable can be determined during the calibration or learning process. This also facilitates temperature-stable control of the pulse width and / or pulse amplitude or the light pulses generated by the transmitter.
[0035] According to an advantageous further development, disturbance variables are taken into account in the control loop.
[0036] Disturbance variables are external influencing variables, such as contamination of optical sensors or external light influences.
[0037] By taking the disturbance variables into account in the control loop, an increased interference immunity of the optical sensor is achieved.
[0038] According to an advantageous embodiment, the emitter is a laser diode.
[0039] In particular, the emitters are VCSEL (Vertical Cavity Surface Emitting Laser) diodes.
[0040] The actual variable of the control loop of the optical sensor is therefore the laser power, in particular the average laser power of the laser diode.
[0041] It is particularly advantageous if the laser diode has a monitor diode, with which the emission power is determined.
[0042] Alternatively, a separate, ie external, diode may be provided for measuring the emission power, ie the laser power.
[0043] Where the emitter is in the form of a laser diode, the control circuit is advantageously a laser driver.
[0044] According to an advantageous embodiment, the optical sensor is designed as a distance sensor, with which the distance to an object is determined. In principle, the determined distance value can be output directly as an object detection signal. Alternatively, a threshold value evaluation of the determined distance value can also be performed, so that a switching signal can be output as an object detection signal, whose switching state indicates whether the object is within a certain distance range.
[0045] The distance measurement is advantageously performed using a pulse transit time method.
[0046] According to another advantageous embodiment, fluorescence measurements, ie capturing fluorescent objects, are performed using optical sensors.
[0047] The light pulses emitted by the transmitter have a specific wavelength. The reflection of the light pulses on the fluorescent object changes the wavelength. The receiver of the optical sensor is designed to capture the light pulses with the changed wavelength.
[0048] Typical applications include capturing fluorescent markings on objects, where the fluorescent markings can be detected by optical sensors. In particular, objects can be marked in a tamper-proof manner. It is also possible to distinguish between fluorescent and non-fluorescent objects.
[0049] In general, optical sensors can be formed as safety sensors, which can be used in safety-related applications. For this purpose, the optical sensors have a fail-safe design. This can be achieved by a redundant design of the evaluation unit, for example in the form of two computer units that monitor each other cyclically. BRIEF DESCRIPTION OF THE DRAWINGS
[0050] The invention is explained below based on the accompanying drawings. The accompanying drawings show:
[0051] Figure 1 : Example of an embodiment of an optical sensor according to the present invention.
[0052] Figure 2 :Used according to Figure 1 Laser driver for optical sensors.
[0053] Figure 3 :Used according to Figure 1 The control loop of the optical sensor.
[0054] Figure 4 : Time curves of the optical sensor light pulse at different temperatures. DETAILED DESCRIPTION
[0055] Figure 1 A highly schematic embodiment example of an optical sensor 1 according to the invention is shown.
[0056] The optical sensor 1 has a housing 2 in which all components of the optical sensor are integrated. The optical sensor 1 has a transmitter 4 that emits a light beam 3 and a receiver 5 that receives the light beam 3. For beam forming of the light beam 3, a transmitting optical system (not shown) can be arranged downstream of the transmitter 4. For focusing the light beam 3 onto the receiver 5, a receiving optical system (also not shown) can be arranged upstream of the receiver 5.
[0057] A transparent front screen 6 is integrated into the housing 2 to guide the light beam 3 out of and into the housing 2 .
[0058] Furthermore, the optical sensor 1 has an evaluation unit 7 for evaluating the received signal of the receiver 5 . Based on the evaluation, an object detection signal is generated in the evaluation unit 7 , which is output via an output 8 .
[0059] In the simplest case, the evaluation unit 7 is formed by a computer unit, such as a microprocessor. If the optical sensor 1 is a safety sensor, the evaluation unit 7 has a redundant design, for example in the form of two computer units which cyclically monitor each other.
[0060] Finally, a control circuit 9 connected to the evaluation unit 7 is provided, said control circuit 9 being used to control the transmitter 4 .
[0061] For object detection, a light beam 3 emitted by a transmitter 4 is guided through a front screen 6 into a detection area. From an object 10 present there, the light beam 3 is guided back to a receiver 5.
[0062] The transmitter 4 of the optical sensor emits a light beam 3 in the form of light pulses. The transmitter 4 is formed by a laser diode, in particular a VCSEL diode. The receiver 5 can be formed by a photodiode, in particular an avalanche photodiode.
[0063] The optical sensor 1 can be designed, for example, for detecting fluorescent objects 10. In the present case, the optical sensor 1 is a distance sensor. The distance measurement is performed using the pulse transit time method. To determine the distance, the light transit time of a light pulse from the sensor to the object 10 and back to the receiver 5 is evaluated. The determined distance value can be output directly as an object detection signal. Alternatively, a threshold value evaluation in the evaluation unit 7 determines whether an object 10 is present in the distance range, whereby a binary switching signal is generated as an object detection signal.
[0064] Figure 1 The optical sensor 1 shown emits a light beam 3 in a fixed, specified spatial direction.
[0065] The optical sensor 1 can also be designed generally as a scanner, in particular as an area distance sensor. The light beam 3 is thereby guided periodically in a flat detection area. For this purpose, a deflection unit can be arranged downstream of the transmitter 4. Alternatively, the transmitter 4 and the receiver 5 can be part of a rotary measuring head.
[0066] The emitter 4 of the optical sensor is designed as a laser diode, and the control circuit 9 is designed in the form of a laser driver. Figure 2 It is schematically shown in FIG.
[0067] The laser driver has a controlled current source 11 at a potential V and a switching device 12 switchable to ground potential GND, so that a variable controlled pulse width can be generated for the light pulse to be generated, such as Figure 2 As shown schematically in FIG.
[0068] According to the invention, the evaluation unit 7 of the optical sensor has a control circuit 13 (in Figure 3 ), using the control circuit 13 to generate stable, in particular temperature-stable short light pulses in the picosecond range.
[0069] In a manner known per se, the control circuit 13 has a controller 14 , an actuator 15 and a controlled system 16 .
[0070] According to the invention, the emission power, i.e. the average laser power of the laser diode forming the transmitter 4, is continuously captured by the sensor device 17 as an actual variable of the control loop 13. In the present case, the sensor device 17 is formed by the monitoring diode of the laser diode. In general, a separate diode can also be used for this purpose.
[0071] The actual value determined by the sensor device 17 is compared in a comparator 18 with a reference variable provided via an input line 19 , ie, a nominal value for control.
[0072] Advantageously, the transmission power is measured in a precalibration for a nominal light pulse of the transmitter 4 and is stored in the evaluation unit 7 as a reference variable for the control loop 13 .
[0073] A further advantage is that the temperature prevailing in the evaluation unit 7 can form a further actual variable.
[0074] A temperature sensor is provided, by means of which the temperature inside the optical sensor is determined.
[0075] The comparator 18 provides a control deviation as an output variable, which is fed to the controller 14. A control variable is generated in the controller 14 and fed to the actuator 15.
[0076] The control variable for the controlled system 16 is generated in the actuator 15. In this example, the control variable is a control pulse width and / or a control current for a laser driver, wherein the emitter 4 emits controlled and stable light pulses. Here, during control, the pulse width and / or the pulse amplitude can be controlled.
[0077] The temperature dependencies of the control variables are advantageously stored in a table in the evaluation unit 7 .
[0078] This allows the temperature dependence to be systematically captured during control, ensuring temperature-stable generation of light pulses.
[0079] In order to achieve increased immunity to interference when generating the light pulses, the interference variables captured by the metering device are fed to the controlled system 16 via a line 20 .
[0080] Figure 4 The results of the control according to the present invention are shown. Here, the time curve of the light pulse emitted by the emitter 4 of the optical sensor using the control system according to the present invention is plotted. The curve of the light pulse changing with time from -40°C to 70°C is plotted. Figure 4 It can be seen from the graph that high temperature stability of the light pulses is achieved by the control according to the present invention.
[0081] Reference numerals list
[0082] 1 Optical sensor
[0083] 2 Shell
[0084] 3 beams
[0085] 4 Transmitters
[0086] 5 Receiver
[0087] 6Front screen
[0088] 7 Evaluation Units
[0089] 8 output terminals
[0090] 9. Control Circuit
[0091] 10 Objects
[0092] 11 Power Supply
[0093] 12 Switching device
[0094] 13 Control loop
[0095] 14 Controller
[0096] 15 Actuator
[0097] 16 Controlled Systems
[0098] 17 Sensor device
[0099] 18 Comparator
[0100] 19 Input lines
[0101] 20 lines
[0102] GND Ground potential
[0103] V potential
Claims
1. An optical sensor (1) comprising a transmitter (4) for emitting light pulses, a receiver (5) for receiving light pulses, and an evaluation unit (7), in which an object detection signal is generated based on a received signal of the receiver (5), characterized in that: The evaluation unit (7) has a control loop (13), by means of which the pulse width and / or pulse amplitude of the light pulses emitted by the transmitter (4) are controlled, wherein the emission power of the transmitter (4) forms the actual variable of the control loop (13), and wherein the control pulse width and / or the control current for the transmitter (4) forms the control variable of the control loop (13).
2. The optical sensor (1) according to claim 1, characterized in that The transmission power is measured during precalibration of a nominal light pulse for the transmitter (4) and is stored in the evaluation unit (7) as a reference variable for the control loop (13).
3. The optical sensor (1) according to claim 1 or 2, characterized in that The temperature therein forms another practical variable.
4. The optical sensor (1) according to any one of claims 1 to 3, characterized in that: The temperature dependency of the control variable is stored in a table in the evaluation unit (7).
5. The optical sensor (1) according to claim 3 or 4, characterized in that A temperature sensor is provided, by means of which the temperature in the interior of the optical sensor is determined.
6. The optical sensor (1) according to any one of claims 1 to 5, characterized in that: The transmitter (4) is equipped with a control circuit (9) in which the control variable is generated.
7. The optical sensor (1) according to any one of claims 1 to 6, characterized in that: The emitter (4) is a laser diode.
8. The optical sensor (1) according to claim 7, characterized in that The emitter (4) is a vertical cavity surface emitting laser (VCSEL) diode.
9. The optical sensor (1) according to claim 7 or 8, characterized in that: The laser diode has a monitoring diode, and the emission power is determined by using the monitoring diode; or an external monitoring diode is provided, and the emission power of the laser diode is determined by using the external monitoring diode.
10. The optical sensor (1) according to any one of claims 7 to 9, characterized in that: The control circuit (9) is a laser driver.
11. The optical sensor (1) according to any one of claims 1 to 10, characterized in that: The optical sensor (1) is a distance sensor.
12. The optical sensor (1) according to any one of claims 1 to 10, characterized in that: A fluorescent object (10) is captured using the optical sensor (1).
13. The optical sensor (1) according to any one of claims 1 to 12, characterized in that: Disturbance variables are taken into account in the control loop (13).
14. The optical sensor (1) according to any one of claims 1 to 13, characterized in that: The pulse width of the light pulses is in the picosecond range.